MARINE BIOLOGICAL LABORATORY. Received ..... Accession No. ....... 3. A 3. ..... X... Given by. Place, . *** No book or pamphlet is to be removed from the Lab- oratory without the permission of the Trustees. I ru a 3" i-q CD D m D A TEXT-BOOK OF GENERAL LICHENOLOGY, WITH DESCRIPTIONS AND FIGURES OF THE GENERA OCCURRING IN THE NORTHEASTERN UNITED STATES. BY ALBERT SCHNEIDER, M.S., M. D., Felloiv in Botany, Columbia University, 1894-1896. BINGHAMTON, N. Y. WILLARD N. CLUTE & COMPANY. 1897. COPYRIGHT, 1897. BY WILLARD N. CLUTE cV: CO. PRESS OF Tm: NKW ERA PRINTING COMI-ANY LANCASTER. PA. Vll PREFACE. This work is primarily intended as a text-book for the use of students in colleges and universities, but will also be found useful to the specialist. Although the title designates it as a text-book of general lichenology, the discussion of the Basidiolichenes and more or less problematical Gasterolichenes has been omitted, since these orders are not represented in the northeastern United States. The systematic arrangement of the families and genera here pro- posed is by no means perfect, yet it is hoped that some progress has been made toward establishing a natural system. The fact that most arrangements heretofore proposed had little scientific basis is due to the lack of knowledge of the morphology and physiology of these plants. Even now our methods of physiological investigation are too imperfect to allow us to obtain any satisfactory data in regard to the life-history of the individual lichen. Until our methods of investigation are more perfect, all systems of classification must of necessity be more or less artificial and subject to changes. In lichenology the conception of genus and species is vague and uncertain. This is the chief reason why every lichenographer has introduced or sought to introduce a new system, and as a result we have about as many systems as there are authors. Within compara- tively recent years various investigators have studied lichens from a scientific point of view, especially from the standpoint of morphol- ogy. Of these morphologists may be mentioned Hedlund, Lindau, Minks, Reinke, Schwendener, Zahlbruckne and Zukal. Among those who have studied lichens from a physiological standpoint Bon- nier and Jumelle deserve special mention. The arrangement of families and genera here adopted is based upon morphological data and is in accordance with the results of recent investigations. In agreement with Reinke, lichens are treated as a distinct class, coequal in systematic importance with the fungi and algae. The present conception of the class Lichenes is, however, essentially differ- Vlll ent from that of the older authors, such as Tuckerman and others, being in a great measure the outcome of recent investigations in symbiosis. For this reason it was thought advisable to include a chapter on the more common phenomena of symbiosis, which, it is hoped, will enable the student to obtain a better knowledge of the true nature of lichens. Part II. treats of the special morphology of the families and genera of lichens occurring in the northeastern United States. The drawings (with the exception of Plate 5) were made by Mr. F. Emil, under the author's supervision. Duly considering the diffi- culties usually encountered in making drawings of this kind it is be- lieved that they give a fairly accurate presentation of the histological characters of the genera occurring in the territory. It is hoped that this work will act as an incentive toward leading others to the more scientific methods of studying this interesting group of plants. With Reinke, I wish to emphasize the necessity for studying more carefully the polyphyletic origin and relationship of the various lichen groups. This will, no doubt, lead to a more accurate delimitation of the families, and incidentally also to a more accurate knowledge of the phylogeny of other plants. COLUMBIA UNIVERSITY, May 31, 1897. Ill TABLE OF CONTENTS. PREFACE . . GLOSSARY. . LITERATURE vn ix xi PART I. THE HISTORY, GENERAL MORPHOLOGY AND PHYSIOLOGY OF LICHENS. CHAPTER I. THE HISTORY OF LICHENOLOGY. INTRODUCTION l I. PERIOD: From Theophrastus (371-286 B. C.) to Tournefort (1694) II. PERIOD: From Tournefort ( 1694) to Micheli (1729) . . . 6 III. PERIOD: From Micheli (1729) to Weber ( 1779) .... 7 IV. PERIOD: From Weber ( 1779) to Wallroth and Meyer (1825) . . n V. PERIOD: From Wallroth and Meyer (1825) to Schwendener ( 1868) . . . 17 VI. PERIOD: From Schwendener ( 1868) to Reinke (1894) ... . . 24 VII. PERIOD: From Reinke ( 1894) to the close of 1896 28 CHAPTER II. SYMBIOSIS. INTRODUCTION 31 3- Antagonistic Symbiosis of I. ANTAGONISTIC SYMBIOSIS (Para- Lichens with Mosses .... 34 sitism) 3 1 H. NUTRICISM 35 1. Antagonistic Symbiosis of III. MUTUALISTIC SYMBIOSIS.. ... 36 Fungi with Lichens ... 32 i. Mutualism 36 2. Antagonistic Symbiosis of 2. Individualism 37 Lichens with Lichens (Syn- 3. Contingent Mutualism ... 39 trophy) -33 . '" CHAPTER III. THE GENERAL MORPHOLOGY AND PHYSIOLOGY OF LICHENS. INTRODUCTION 40 7. The Cilia 61 I. ORGANS OF ASSIMILATION 40 II. REPRODUCTIVE AND PROPAGA- 1. TheThallus. . . . . 40 TIVE ORGANS. . . 62 (a) Tegmentary Layer (Dermis). t . The Apothecia 62 (6) The Upper Cortical Layer. (a) T he Epithecium. (c) The Algal Layer (Gonidial Layer). ^^ The Thecium. (d) The Medullary Layer. (c) The Hypotheciiim. (e) The Lower Cortical Layer. < d) The Upper Algal Layer. 2. Tj'pes of Thalli 47 (e) The Medullary Layer. (a) The Crustaceous Type. (f) The Lower Algal Layer. (b) The Foliose Type. (g) The Cortical Layer. (c) The Fruticose Type. ,. Types of Apothecia 66 3. Breathing Pores 52 (a) The Fungal Type. 4. The Cyphellae .... 52 (b) The Thalline Type. 5. The Cephalodia 55 3- The Soredia . (a) Ectotrophic Cephalodia. 4. The Thecial Algae ( Hymenial (*) Endotrophic Cephalodia. Gonidia) 68 6. The Rhizoids. . ... 59 IV CHAPTER IV. THE GROWTH, MECHANICS AND CHEMISTRY OF LICHENS. INTRODUCTION II. GROWTH OF THE APOTHECIA . . 75 I. THE GROWTH OF THE THALLUS. 71 III. THE DEVELOPMENT AND STRUC- 1. The Protothallus (Hypothal- TURE OF THE SPORES ... 77 lus, Promycelium) . . . 71 IV. GROWTH OF THE ALGAE . . . 78 2. Development of the Thallus. 72 V. THE SPERMAGONIA . So (a) Horizontal Growth. VI. MECHANICAL ADAPTATIONS . . . Si (6) Vertical Growth. VII. THE CHEMISTRY OF Li CHENS 84 (c) Intercalary Growth. CHAPTER V. REPRODUCTION AND PROPAGATION OF LICHENS. I. THE SPORES 87 II. THE SOREDIA AS PROPAGATIVE 1. The Ejection and Distribu- ORGANS 92 tion of Spores ... . . 87 III. VEGETATIVE PROPAGATION ... 93 2. The Germination of Spores 89 IV. LIFE-PERIOD OF LICHENS . 94 3. Spores as Organs of Repro- duction 90 CHAPTER VI. THE POLYPHYLOGENY OF LlCHENS. INTRODUCTION 96 2. Chroolepus ( Trentopohlia ) I. THE FUNGAL TYPES 97 umbrina 100 1. The Pezizaceae 98 3. Pleurococcus vulgaris . . . 100 2. The Patellariaceae 98 4. Dactylcococus infusionum . 100 3. The Phacidiaceae .... 98 5. Nostoc commune 100 4. The Stictidaceae 99 6. Rivularia nitida 101 5. The Sphaeriaceae .... 99 7- Polycoccus punctiformis . . 101 II. THE ALGAL TYPES 99 8. Gloeocapsa polydermatica . 101 i. Cystococcus humicola ... 99 9- Sirosiphon pulvinatus . . . 101 PART II. THE CLASIFICATION AND SPECIAL MORPHOLOGY OF LICHENS. CHAPTER I. A SYSTEM OF CLASSIFICATION. I. INTRODUCTORY CONSIDERATIONS. 102 II. CHEMICAL REACTIONS . . . . 106 CHAPTER II. DESCRIPTIONS OF THE FAMILIES AND GENERA. INTRODUCTION. 108 3. Calicium . . .114 GENERAL DESCRIPTION OF THE 4. Cyphelium . . .115 PLATES . . no 5. Acolium 115 KEY TO THE FAMILIES 109 6. Sphaerophorus ... .117 I. CALICIACEAE no II. CLADONIACEAE 118 1. Mycocalicium 112 i. Baeomyces 120 2. Coniocybe 112 2. Pilophoron 122 3. Stereocaulon 124 4. Cladonia 125 5. Thamnolia 127 III. LECIDEACEAE 128 1. Biatorella 130 2. Biatorina 131 3. Biatora 132 4. Bilimbia 133 5. Baciuia 134 6. Lecidea 135 7. Celidiopsis .... . . 135 8. Buelliopsis . . .... 136 9. Buellia .... .... 136 10. Calillaria 137 IT. Megalospora 137 12. Lopadium 138 13. Gjalecta 139 14. Psora 140 15. Gyrophora 141 16. Umbilicaria 143 IV. GRAPHIDACEAE 144 1. Hazslinskya . . 145 2. Opegrapha . 146 3. Graphis ... 146 4. Xylographa 147 5. Arthonia . . . 148 6. Mycoporum 149 7. Arthothelium 150 V. PHYSCIACEAE 151 1. Rinodina 152 2. Placodium 154 3. Pyxine . . 155 4. Physcia 156 5. Theloschistes 158 VI. PARMELIACEAE 159 1. Urceolaria 161 2. Haernatotnma 162 3. Lecanora 164 4. Acarospora 165 5. Speerschneidera 166 6. Parmelia 167 7. Cetraria 169 8. Evernia 170 9. Ramalina 172 10. Alectoria 173 11. Bryopogon 175; 12. Usnea 176 VII. VERRUCARIACEAE 177 1. Trypethelium . .' 179 2. Pyrenula 180 3. Conotrema . 181 4. Thelotrema . 182 5. Gyrostomum . . 184 6. Verrucaria . . ... 185 7. Pertusaria 186 8. Dermatocarpon 188 9. Endocarpon 189 VIII. COLLEMACEAE 191 1. Collema 193 2. Leptogium 194 3. Mallotium 195 4. Hydrothyria 196 IX. PANNARIACEAE 197 1. Ephebe . . ... 199 2. Lecothecium . .... 200 3. Lichina. 201 4. Omphalaria 203 5. Polychidium 204 6. Psoroma 205 7. Heppia 206 8. Pannaria 207 9. Peltigera 209 10. Solorina 210 11. Nephromium 212 12. Stictina 213 13. Sticta .... 215 CHAPTER III. LEPRARIACEAE Pseudolichenes . . . 217 1. Lepra 217 2. Amphiloma 218 THE CONTINENTAL RANGE OF THE GENERA OCCURRING IN THE NORTHEASTERN UNITED STATES -219 GENERAL INDEX 223 IX GLOSSARY. Antagonistic symbiosis, a form of symbiosis in which one of the sym- bionts is benefited at the expense of the other; usually known as parasitism. Apothecium (Apothecia), the spore-bearing structure of lichens, in- cluding epithecium, thecium, hypothecium and exciple. Areolate, a term referring to a crustaceous thallus which is marked off into minute, usually polygonal areas. Breathing pores, intercellular canals in the cortical layers leading from the interior of the thallus to the exterior. Cephalodium (Cephalodia), usually a globular, flattened or irregular outgrowth from the upper or lower surface of the thallus, induced by for- eign algae and bearing them. Contingent symbiosis, a form of symbiosis which is not constant in its occurrence. (Incipient symbiosis. Raumparasitismus. ) Cortex, see Cortical. Cortical layers, pseudo-parenchymatous tissue (upper and lower) of the thallus of the higher lichens. Crustaceous thallus, a firmly adherent thallus of lichens devoid of distinctly cortical layers. Cuticle, see Epidermis. Cyphella (Cyphellae), a pit or depression in the under surface of the thallus of most Stictei ( Sticta and Stictina). They are neoformations anal- ogous to lenticels. Endospore, the inner coat of the spore-wall. Epidermis, the thin horizontal scaly layer on the upper surface of the higher foliose lichens. Epilithic. a term applied to the parts of lichens occurring on and above the surfaces of rocks. Epiphloeodal, occurring on the surface of the bark. Epispore, see Exospore. Epithecium, the upper colored structureless coating of the thecium. Exciple or Excipulum, the outer covering of the apothecium; when formed by the thallus and bearing algae it is known as thalloid exciple ; when formed by the perithecium and not bearing algae it is known as proper exciple. Exospore, the outer coat of the spore-wall. Fibril or Cilium, a slender filament, consisting of united hyphae, usually occurring on the margin of the thallus. Foliose thallus, an expanded entire or lobed thallus, having one or two cortical layers, usually attached by rhizoids. Also known as foli- aceous or frondose thallus. Fruticose thallus. a thallns consisting of rounded or flattened, vertical or ascending branches. Also called fruticulose thallus. Gonidium (Gonidia), a term applied to the symbiotic algae of lichens. Granule (adj. Granulose), a minute thalloid elevation firmly adherent to the substratum, usually bearing an indistinct upper cortical layer. Hymenium, see Thecium. Hypolithic, occurring below the surfaces of rocks. Hypophloeodal, referring to that portion of the thallus or other struc- ture of lichens occurring beneath the surface of the bark. Hypothecium, the dense hypal tissue immediately below the thecium. Individualism, a form of symbiotic relationship existing between two or more organisms in which the resulting organic structure is wholly differ- ent from any of the symbionts and in which at least one of the symbionts cannot exist independently. Isidium (Isidia), a small cylindric simple or branched thalloid out- growth from the surface of the thallus. Medulla, the loose hyphal network in the interior of the thallus. Mutualism, a form of symbiosis in which the symbionts are mutually beneficial. Mycorhiza, a term applied to the symbiotic association of fungi and roots of higher plants (especially CupnUfcrae} . Divided into endotrophic and ectotrophic mycorhiza according to whether the fungi occur within the parenchyma-cells of the root or upon their exterior. Mycodomatiae, term applied to the group of symbiotic organisms (rhizobia^) which have the power of inducing tubercular neo-formations in the roots of plants. Nutricism, a form of symbiosis in which only one of the symbionts is especially benefited. Paraphysis (Paraphyses), a slender simple or more rarely branched, sterile filament among the spore-sacs. Perithecium, the hyphal tissue of the so-called Pyrenolichenes ( Vcr- rncariaceae) enclosing the thecium. Phyllocladium (Phyllocladia), a small highly assimilative branch of fruticose thalli. (This term is often applied to all secondary thalli.) Podetium (Podetia), the elongated alga-bearing apothecial stalk of lichens developed from the primary thallus. (Usually applied to the ver- tical thallus of a Cladonia.} Primary thallus, a term referring to the thallus from which the podetia develop. Pycnidium (Pycnidia), the structure upon the thallus of lichens con- taining the so-called stylospores. (Perhaps closely related to the sperma- gonium.) XI Rhizoids, special hyphal elongations from the under surface of the thal- his which enter the substratum. Secondary thalli, thalloid outgrowths from the thallus and podetia of lichens. Sometimes also applied to the podetia of Cladonia. Seta (Setae), see Fibril. Soredium (Soredia), a minute spherical body consisting of algae en- closed by a hyphal network and having the power of developing into a new lichen. Spermagonium (Spermagonia), the structure upon the thallus con- taining the so-called sterigmata and spermatia. Spermatium (Spermatia), a spore-like body formed in the sperma- gonium. (Considered by Stahl and others as the male reproductive organ of lichens.) Spore=sac, the closed sac-like structure in which the spores are formed. Squamule, a small entire thalloid lobe. Usually forming the transition to the typical foliose thallus. Sterigmata, the filaments of the spermagonium bearing the spermatia. Stipe, an apothecial stalk free from algae ( Caliciaccae and Baeomyces). Symbiosis, a contiguous association 'of two or more organisms ac- companied by an interchange of assimilated food-substances. Thallus (Thalli), the vegetative and assimulative portion of lichens, bearing the apothecia and soredia. Theca (Thecae), see Spore=sac. Thecium (Thecia), the layer consisting of thecae and paraphyses. Umbilicus, the single root-like attachment of certain lichen-thalli ( Um- bilicaria, GvropJiora), Verrucose, see Warty. Warty, referring to a thallus bearing numerous thalloid elevations larger than the granules. LITERATURE. The references here given are to the principal works on the mor- phology, physiology and chemistry of lichens issued since the year 1850, and terminating with the year 1896. 1. BABIKOFF, M. Du developpement des cephalodies sur le thallus clu lichen Peltigera aphthosa Hoff. Bull. 1' Acad. Imp. Sc. St. Petersb. 24 : 54 8 -559- l8 7 8 - 2. BACHMANN, E. Ueber nichtkrystallisirte Flechtenfarbstoffe. Jahrb. wiss. Bot. 21 : i -60. 1890. 3. BACHMANN, E. Der Thallus der Kalkflechten. Ber. deutsch. hot. Ges. 10 : 30-37. 1892. Xll 4. BARANETZKY, J. Beitrag zur Kenntniss des selbststiindigen Lebens cler Flechtengonidien. Jahrb. wiss. Bot. 7: 1-17. 1869. 5. BAYRHOFFER, J. D. W. Einiges iiber Lichenen und deren Befruch- tung. Bern. 1851. 5a. BAYRIIOFFER, J. D. W. Entwickelungund Befruchtung der Clado- niaceen. Frankfurt am Main. 1860. 6. BEYERINCK, M. W. Culturversuche mit Zoochloreilen, Lichen- gonidien und anderen niederen Algen. Bot. Zeitung, 41 : 765-768, 781 785. 1890. 7. BONNIER, G. Culture des lichens a 1'air libre et dans un milieu prive des germes. Bull. Soc. Bot. France, 33: 546-548. 1886. S. BONNIER, G. Recherches exprimentales sur la synthese des lichens dans un milieu prive des germes. Comptes rendus, 103: 942-944. 1886. 9. BONNIER, G. La constitution des lichens. Journal de Botanique, I : 1-5. 1887. 10. BONNIER, G. Recherches sur la synthese des lichens. Annales des sc. nat. (VII) 9: 1-34. 1889. 11. BONNIER, G. Germination des lichens sur les protonemes des mousses. Rev. gen. bot. I : >6^-i69. 1889. 12. BONNIER ET MANGIN. .Sur les echanges gazeux entre les lichens et 1'atinosphere. Bull. Soc. Bot. France, 31: 118119. 1884. 13: BORNET, E. Recherches sur la structure de V Ephebe pubescens Fr. Ann. sc. nat. (Ill) 18 : 155-171. 1852. 14. BORNET, E. Description de trois lichens nouveaux. Mem. de la soc. de Sc. nat. de Cherbourg, 4: 231. 1856. 15. BORNET, E. Recherches sur les gonidies des lichens. Ann. sc. nat. (V) 19: 314-320. 1874. 16. BORNET, E. Deuxieme note sur les gonidies des lichens. Ann. sc. nat. (V) 19: 316. 1874. 17. CROMBIE, REV. J. M. See KREMPELIIUBER. 18. CURTISS, C. C. A contribution to the history of the formation of the lichen-thallus. Journal of the Xew York Microscopical Society, 10 : 3. 1894. 19. DANGEARD, P. A. Recherches sur la structure des lichens. Le Botaniste, 4 : 18-20. 1894. 20. DARBISHIRE, Kritische Bernerkungen iiber das " Microgonidium." Hedwigia, 34 : 181-190. 1895. 21. DEBARY, A. Morphologic und Physiologic der Pilxe, Flechten und Myxomyceten. Leipzig, 1866. 22. DEBARY, A. Ueber die Keimung einiger grosssporiger Flechten. Jahrb. wiss. Bot. 5: 201-216. 1866-1867. 23. FAMINTZIN UND BARANETZKY. Beitrag zur Entwickelungsge- Xlll schichte dcr Gonidicn uiul Zoosporenbildung bei P/n'sr/a parictiua D. N. Bot. Zeitung. 25: 181190. 1867. (Preliminary report.) 24. FAMINTZIN UNO BARANETZKY. Zur Entwickelungsgeschichte der Gonidicn und Zoosporenbildung der Flechten. Memoires de 1'acacl. de St. Petersbourg, n : 1-9. 1868. 25. FORSSELL, K. B. J. Studier ofver cephalodierne. Bihang till k. Svenska vet. Akad. Handlinger, 8: i. 1883. Separatabdruck, Stock- hoi 111,1883. 26. FORSSELL, K. B. J. Beitriige zur Kenntniss der Anatomic mid Systematik der Glocolichenen. Nova Acta Reg. Soc. Sc. Ups. 1885. 27. FORSSELL, K. B. J. Ueber den Polymorphisms der Algen (Flechtengonidien) aus Anlass von Herrn Zukal's Flechtenstudien mid seinem Epilog dazu. Flora, 69: 49-64. 1886. 28. FRANK, A. B. Ueber die biologische Verhiiltnisse des Thallus einiger Krnstenflechten. Cohn's Beitriige. Breslau. 1876. 29. FRIES, T. M. Beitrag xur Kenntniss der sogenannten Cephalo- dien dei den Flechten. Flora, 49 : 17-25. 1866. 30. FUISTING. Beitriige zur Entwickelungsgeschichte der Lichenen. Bot. Zeitung, 26: 641-647, 657-665, 673-684. 1868. 31. FUNFSTUCK, M. Tliallusbildung an den Apothecien von I\>ltidca aphthosa (L.) Ach. Ber. deutsch. bot. Ges. 2: 447-452. 1884. 32. FUNFSTUCK, M. Die Fettabscheidungen der Kalkflechten. Bei- triige ziir Wissenschaftlichen Botanik, i : 157-220. 1895. 33. GIBELLI, G. Sugli organi reproduttori del genere \ 'crrncaria Milano, 1865. 34. GIBELLI, G. Ueber die Reproductionsorgane der Gattung }'ernt- caria (iibersetzt von A. v. Krempelhuber). Flora, 49: 65-75, 87-92, 101- 106. 1866. 35. GIBELLI, G. Sulla genesi degli apotecii delle Verrucariaceae. Nuovo giornale botanico Italiano, 2: 194206. 1870. 36. HEDLUND, J. T. Kritische Bemerkungen iiber die Flechtengat- tungen Lecarwra Ach., Lccidca Ach. und Mzcarea Fr. vStockholm. 1892. 37. HULTII, J. M. Ueber Reservestoffbehiilter bei Flechten. Bot. Centralblatt, 45 : 209-210,269-270. 1891. 38. ITZIGSOHN, H. Die Antheridien und Spermatozoen der Flechtc-n. Bot. Zeitung, 8: 393, 913. 1850. 40. ITZIGSOIIN, H. Wic verhalt sich Collcnia xu ^Vostoc und xu den Nostochineen ? Bot. Zeitung, 12: 521-527. 1854. 41. ITZIGSOHN, H. Die Gloeocapsen- und Chroococcus-Diamorphose. Bot. Zeitung, 12: 641-651. 1854. 42. ITZIGSOHX H. Kultur der Glaucogonidicn von I\'Itiifcra caitiua. Bot. Zeitung, 26: 185-196. 1868. XIV 43- JUMELLE, H. L'assimilation chez les lichens. Comptes rendus, 112: 888-893. 1891. 44. JUMELLE, H. Recherches physiologiques sur les lichens. Rev. gen. Bot. 4: 49-64, 103-121, 159-175, 220-231, 259-272, 305-320. 1892. 45. KNY, L. Ueber die Entwickelung cles Thallus von Lichina pyg- maea Ag. und deren Beziehung zu Rrcnlaria m'tidaAg. Soc. Mun. Nov. 21, 1874. 46. ROBERT, R. Ueber Giftstoffe der Flechten. Sitzungsberichte der Dorpater Naturforscher-Gesellschaft, 157-166. 1892. (Beihefte Bot. Centralblatt, 1893). 47. KORBER, G. W. Zur Abwehr der Schwendener-Bornet'schen Flechtentheorie. Breslau. 1874. 48. KRABBE, G. Entwickelungsgeschichte und Morphologic der Poly- morphen Flechtengattung Cladonia. Ein Beitrag zur Kenntniss der As- comyceten. Leipzig. 1891. 49. KRABBE, G. Entwickelung, Sprossung und Theilung einiger Flechtenapothecien. Bot. Zeitung, 40: 65-83, 89-99, 105-116, 221-242. 1882. 50. KREMPELHUBER, A. Rev. J. M. Crombie, "On the Lichen- gonidia Question," Popular Science Review, July, 1874. Flora, 57 : 17-21, 33-45 > 49-59- lS 74- 51 . LAGERHEIM, G. Ueber eine durch die Einwirkung von Pilzhyphen enstandene Varieta't von Stichococcus baciUaris Nag. Flora, 71 : 61-63. 1888. 52. LINDAU, G. Ueber die Anlage und Entwickelung einiger Flechten- apothecien. Flora, 71 : 451-489. iSSS. 53. LINDAU, G. Die Beziehung der Flechten zu den Pilzen. Iled- wigia, 34: 195-204. 1895. 54. LINDAU, G. Lichenologische Untersuchungen. Heft I. Ueber Wachsthum und Anheftungsweise der Rindenflechten. Dresden. 1895. 55. LINDSAY, W. L. On the spermagones and pycnides of lichens. Proceedings of the Royal Society of Edinburgh, 4: 174-182. March, 1859- 56. LINDSAY, W. L. Memoir on the spermagones and pycnides of filamentous, fruticulose and foliaceous lichens. Transactions of the Royal Society of Edinburgh, 22 : 101-303. 1859. 57. LINDSAY, W. L. On the polymorphism in the fructification of lichens. Quarterly Journal of Microscopical Science, Jan., 1868. 58. LOTSY, J. P. Beitrage zur Biologic der Flechtenflora des Hain- berges bei Gottingen. Inaugural Dissertation. Gottingen. 1890. 59. LUTZ, K. G. Ueber die sogenannten Netzbildungen bei Ramalina rcticitlata Krplhbr. Ber. deutsch. bot. Ges. 12: 207-214. 1894. XV 60. MAGIN, A. Organization des lichens. Bull. Soc. Bot. Lyon, 7 : 42, 43. 1889. 61. MARTELLI, U. Un caso di dissociazione naturalc nei licheni. Nuovo Giornale Botanico Italiano, 22: 4^0451. 1890. 62. MAULE, C. Zur Entwickelungsgeschichte von.Tricothecium inicro- carpon Arn. Ber. deutsch. hot. Ges. 8: 113-117. 1890. 63. MAULE, C. Uebcr die Fruchtanlagen bei Phvscia pul-ccrnlenta (Schaer.) Nyl. Ber. deutsch. hot. Ges. 9: 209-213. 1891. 64. MINKS, A. Das Microgonidium. Ein Beitrag zur Kenntniss des wahren Wesens der Flechten. Basel, Genf, Lyon. 1879. 65. MINKS, A. Beitriige zur Kenntniss des Baues und Lebens der Flechten. I. Verhandlungen der k. k. zoologisch-bot. Ges. Wien, 26 : 477-600. 1877. 66. MINKS, A. Was ist Myriangium? Eine morphologisch-licheno- graphische Studie. Ber. deutsch bot. Ges. 8: 243-250. 1890. 67. MINKS, A. Beitriige zur Kenntniss des Baues und Lebens der Flechten. II. Yerhandl. der k. k. zoologisch-bot. Ges. Wien, 42: 377-508. 1892. 68. MOI.LER, A. Ueber die Cultur flechtenbildender Ascomyceten ohne Algen. Inaug. Dissert. Bot. Institut d. k. Akad. Minister. 1887. 69. MULLER, J. Ein Wort zur Gonidienfrage. Flora, 57 : 27-29. 1874. 70. NEUBNER, E. Beitriige zur Kenntniss der Calicieen. Flora, 41: 291-301, 307-317. 1883. 71. NEUBNER, E. Untersuchungen iiber den Thallus und die Frucht- anfiinge der Calicieen. Ein Beitrag zur Kenntniss der krustig-staubarti- gen Flechten. Wissenschaftlishe Beitriige zu dem IV. Jahresbericht d. k. (.Tym. zu Plauen, 8: 12. 1893. 72. NYLANDER, W. De Cephalodiis in Peltidca vcnosa. Flora, 8 : 216. 1866. 73. Oersted, A. S. Spore-planterne. Copenhagen. 1867. 74. REES. Enstehung der Flechte Collcma glmicescens, Monatsber. d. Berliner Akad. 523 533. Oct. 26, 1871. 75. REINKE, J. Abhandlungen iiber Flechten. Jahrb. wiss. Bot. 1894-1896. I. Das Podetium von Cladonia. 26: 49^-523. II. Die Stellung der Flechten im Pflanzensystem. 26: 524542. III. 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Flora, 74: 92107. 1891. no. ZUKAL, H. Morpholbgische and biologische Untersuchungen iiber die Flechten. Sitzungsberichte der Kaiserlichen Akademie der Wis- senschaften Wien, Math.- Naturwigsench. Cl. 104: 1303-1395. 1895. PART I. THE HISTORY, GENERAL MORPHOLOGY AND PHYSIOLOGY OF LICHENS. CHAPTER I. THE HISTORY OF LICHENOLOGY I N T R O D U C T I O N. The lichens were more generally neglectegl by the early botanists than any other group of plants. The causes for this are not far to seek. These plants possess no qualities to make them conspicuous ; they are not, as a rule, striking in color, size or form, nor do they pos- sess very marked useful or harmful properties. Until the advent of scientific botany, herbalists devoted their attention chiefly to the higher plants, which were endowed with real or imaginary medicinal properties, or which served some other use in the household. Later, when lichens began to receive some attention from the lead- ing botanical systematists, they were for a long time subject to great abuse because of careless study. They were taken up as a side study for the information of the few who took a momentary interest in them. Some of the most fantastic and varied opinions were held with regard to their origin, nature and position in the vegetable king- dom. For these reasons and others, which will become apparent later, it was thought not only interesting but highly important that the student of lichenology should have an insight into the changes which this special science has undergone. It is hoped that the stu- dent may better realize therefrom how much work must yet be accom- plished before our knowledge in regard to these plants can attain any degree of perfection. The historical review here presented is, in the main, a condensed retrospect of Krempelhuber's Geschichte der Lichenologie. The limitations of the first four periods correspond to those of Krempel- huber ; the others are materially changed, and the review has been completed to the beginning of 1897. Other works treating of the history of these plants, notably Lindsay's British Lichens have also been made use of. Each period is marked by some special evolutionary progress in lichenology. It must not be supposed, however, that these periods are in reality clearly and distinctly separated. One period gradu- ally merges into the other, which makes the distinction more or less accidental or arbitrary. There are no doubt minds that tower above ml their contemporaries and whose works are to a certain degree epoch- making ; on closer examination it is found, however, that they have built upon the foundation laid by workers that have gone before. Only a few of the more important investigators in lichenology are mentioned. It would be impracticable as well as unnecessary to refer to all the authors who have written on the subject. The publications issued number thousands ; to collect and digest these would be the work of many years. The references cited as footnotes are pri- marily of historic interest. The more important references to works having real scientific value are given on pp. xi-xvii. In order to avoid repetition these are referred to by number, where they are mentioned in the historical review, or in the text proper. It is thought most appropriate and convenient to divide the his- tory of lichenology into seven periods, as follows : I. Period: From Theophrastus (371-286 B. C.) to Tourne- fort (1694). II. Period: From Tournefort (1694) to Micheli (1729). III. Period: From Micheli (1729) to Weber (1779). IV. Period : From Weber (1779) to Wallroth and Meyer (1825). V. Period: From Wallroth and Meyer (1825) to Schwen- dener (1868). VI. Period: From Schwendener (1868) to Reinke (1894). VII. Period: Beginning with Reinke (1894). I. PERIOD. FROM THEOPHRASTUS (371-286 B. C.) TO TOURNEFORT (1694). The earliest references to lichens are all more or less unre- liable. There is little doubt that lichens were known, but they were looked upon as mosses, algae or fungi, and classified with these 3 under such comprehensive terms as muscus, bryum, sphagnum. The term lichen (hiyyv) was doubtless used to designate various liverworts, especially species of Marchantia. Only after a much later period was this term employed exclusively in application to lichens. Historians are uncertain as to what plant or plants Dios- corides and Plinius intended to designate by the term lichen ; it was in all probability a species of Marchantia or other liverwort. The first somewhat authentic references to lichens are to be found in the writings of Theophrastus, 1 a pupil and follower of Aristotle. It is generally conceded that this eminent naturalist de- scribed several plants which were doubtless lichens. The very im- perfect descriptions are supposed to refer to Usnca barbata and Ro- cclla tinctoria. No further record seems to have been made of lichens until the first century of our era when Dioscorides and Plinius again mention the lichens supposed to have been described by Theophrastus. There is little doubt that these authors referred to Rocella tinctoria as a "marine fungus growing upon rocks, pos- sessing coloring properties." Usnca no dovibt attracted attention be- cause of its remarkable development. During the dark ages few observations were made on lichens, in fact all scientific progress came to a standstill. Only plants of evident or imaginary medicinal or economic uses were studied. It is remarkable that a period of over seventeen centuries elapsed during which nothing was added to the knowledge of lichens. Ruellius,' 1 Dorstenius 3 and Gesner, 4 the first commentators on the writings of Theophrastus, Dioscorides and Plinius did little more than to reiterate what had been known of the two lichens above mentioned. We may safely state that up to time of Fuchsius 5 scarcely anything was known of lichens. There can be little doubt that various lichens came to the notice of botanists and herbalists of the time, but they were not thought of sufficient importance for special study. Then followed a number of botanists who incidentally observed and described a few lichens with which they came in contact during ] A Latin translation byj. Bodaeus. Theophrasti Eresii de Ilistoria Plantarum Libri Decem. 156. Amstelodami. 1644. 2 Ruellius,J. De Natura Stirpium Libri III. Paris. 1536. 3 Dorstenius. Botanicon continens Herbarum aliorumque Simplicium quorums usus in Medicinis est, etc. Frankfurt. 1540. 4 Gesner, K. Historia Plantarum. Basel. 1541. 5 Fuchsius, L. De Stirpium Historia Commentarii. Basel. 1549- their collecting trips. We shall mention only a few of these botanists, especially those who were active in the various provinces of Germany and Austria, as well as in other countries of continental Europe. They were Mathiolus, 1 Caesalpinus, 2 Camerarius, 3 C. Bauhin, 4 Clusius 5 and J. Bauhin. 6 These and various other authors discovered and de- scribed in all about twenty-eight kinds of lichens : mostly species belonging to the genera Usnea, Sticta, Cetraria and Cladonia. The descriptions and attempts at illustration were indeed very defective, so that later authors were often at a loss to know what species was really meant. Up to this epoch lichens had been given no definite position in the vegetable kingdom. They were variously classified with algae, fungi, liverworts and mosses. About this time also we find the first record of observations made on the development and reproduction of Lichens. Porta 7 gave some very crude explanations of the origin and growth of Lichens. Malpighi 8 was the first author to demon- strate the presence of soredia. He also observed that these struc- tures were propagative organs and for that reason considered them as true seeds. One of the most active lichenologists of this period was the Scotch botanist Morison." He described fifty-six species in all, of which ten were new ; he also gave fairly good illustrations of about twenty-one species. This observer paid little attention, how- ever, to the development of these plants, as is evident from his belief that lichens were excrementitious matter produced by the earth, rocks and trees. This brief retrospect gives some idea of how little was known of lichens at the close of this period. Only such forms as were re- markable for their size, color or use in medicine received any at- tention. The use of Rocella tinctoria in the processes of dyeing 1 Mathiolus, P. A. Commentarii in libros VI Dioscorides de Materia Medica. Venice. 1565 and 1583. 2 Caesalpinus, A. De Plantis Libri XVI. Florence. 1583. 3 Camerarius, J. De Plantis Epitome Utilissima, P. A. Mathioli Senensis. Frank- fort-on-the-Main. 1^86. 4 Bauhin, C. Phytopinax sen Enumeratio Plantarum Nostro Saeculo Descrip- tarum. Basel. 1596. 5 Clusius, C. Historia Plantarum Rariorum cum Appendice et Auctoria et Fig. urisii35. Antwerp. 1601. 6 Bauhin, J. Historia Generalis Plantarum Novae et Absolutae Prodromus. 1619. 7 Porta, J. B. Phytognomonica VIII Libris Contenta. Frankfort. 1591- s Malpighi, M. Opera Omnia. London. 1686. 9 Morison, R. Historia Plantarum Universalis Oxoniensis. 1680. 1699, 1715- was doubtless known before the time of Pliny. It is generally sup- posed that the blue and purple of the Old Testament (Ezekiel, XXVII. 7) refers to the dye made from this lichen. It is certain that it had formed for a long period an important article of com- merce. After the fall of the Roman Empire the knowledge of the use of this dye seems to have been lost. In the year 1300, Federigo, a Florentine of German parentage, accidentally rediscovered the meth- od of preparing and using it ; he is said to have achieved such suc- cess in his commercial transactions with this substance that in time he became the head of a distinguished family, the Oricellarii, who were later known as Rucellarii and Rucellai. From these names are derived orseille, the name of the coloring substance, and Rocella, the genus of lichens from which orseille is prepared. For more than a century Italy supplied the market with orseille derived mainly from lichens collected on the islands of the Mediterranean. After the discovery of the Canary islands in 1402 much of the orseille was derived from those islands, and later from the Cape Verde islands. Later orseille was collected from other islands and coun_ tries. It was also found that other genera besides Rocella furnished excellent dyes ; for example, Lecanora, Pcrtitsaria, Umbilicaria. Like other practically inert plants, lichens were supposed to have medicinal properties. Sticta -pnlinonaria was strongly recommended in diseases of the lungs. Dorstenius was the first to give a more exact description and illustration of this lichen. He also described the medicinal preparations made therefrom, and their special thera- peutic properties. Because lichens were supposed to have a strong retaining power for various odors and scents they were much used in the preparation of certain perfumes. Some of the fruticose lichens were especially recommended for this purpose. They formed the basis of the renowned Cyprian hair powder (Puh'is Cypt'tus), which was supposed to remove dandruff and to promote the growth of hair. Because of the astringent and bitter principles in some species of lichens they were used in tanning and brewing. The beer of a cer- tain Siberian monastery which was noted for its peculiar bitterness owed this to Sticta pnlmonaria. Lichens also found a temporary use in the manufacture of paper, pasteboard and parchment. The "miraculously' 1 ' supplied manna of the Israelites in the wilderness is supposed to have been a species of Lecanora {Lecanora cscnlcnta). This lichen occurs very plentifully in Algeria and Tar- tary, as well as in mountainous districts of other countries. The plant seems to grow and spread rapidly and, being loosely attached, the wind readily carries it down the mountain-sides into the valleys, where the ignorant inhabitants suppose it to have " rained from heaven." Travelers in the above countries have reported several noteworthy and extensive " rains of manna." The Kirghiz Tar- tars eat this lichen, under the name of " earth-bread." Various other lichens were also used as articles of diet ; among them Cetraria Island/en takes perhaps first rank, as it contains a high percentage of lichen-starch (lichenin). However, from the fact that nearly all lichens contain a bitter principle which is very disagree- able to the taste, they were extensively eaten only in arid countries and in times of famine. II. PERIOD. FROM TOURXEFORT (1694) TO MICIIELI (1729). As already stated, the lichens were given no definite position in the vegetable kingdom in the previous period. Under the collective name " muscus " or " musco-fungi " (Morison), they were variously classed as algae, fungi, liverworts and mosses. The fact which separates this period from the preceding is that lichens were now being looked upon as a distinct class of plants. Tournefort 1 was doubtless the first to separate these plants from others and to ar- range them as a distinct class under the comprehensive designation "lichens." This in itself was indicative of considerable prog- ress. A group of plants must be given some definite position in the vegetable world before it can receive more careful study. Tourne- fort was one of the few investigators of his time who believed in lay- ing a foundation before beginning to build. He did not concern himself so much with species-making as with a general study of lichens. In all his works he does not describe more than forty-four species and varieties, although fifty-six species and varieties were al- ready known. This noted botanist, who was by no means especially interested in lichens, devoted his limited attentions to them taken collectively, and this led him to arrange them as a separate class. 1 Tournefort, J. P. de. Elements de Botanique. Paris. 1^94. Institutiones Rei Ilerbariae. Paris. 1/19. His illustrations also lead us to believe that he had more or less cor- rect conceptions of the spores and apothecia. It is much to be re- gretted that Tournefort did not explain his illustrations more fully ; to make matters worse later commentators have variously misinter- / preted his explanations. When we consider the imperfection of the magnifying lenses at that time we can not help admiring the excel- lent work done by this French savant. Plukenet 1 and Petiver' 2 described several new species. They also added some comparatively accurate illustrations. Vaillant 3 likewise added a number of good illustrations, besides describing several new species. New species were also described by Ray, 4 Morton 5 and others. There were other botanists of various countries who described species of lichens already known and added here and there a few new ones. During this period some seventy new species were de- scribed, which made in all about one hundred and twenty. Nothing was known concerning the physiology of these plants and very little of the minute anatomy. When we consider that the / V scientific world was already familiar with the names of R. Hook, N. Grew, A. Loewenhoek, J. B. Triumfetti, and with the excellent work done with the simple microscope, we feel convinced that lichens must have been subject to a special neglect, leaving out of consideration the really excellent work of Tournefort. Petiver' 5 is supposed to have given the first description of a lichen from America (Sticta damaccornts] . III. PERIOD. FROM MICHELI (1729) TO WEBER (1789). Micheli, 7 an Italian botanist, was the first to call attention to the inadequacy of grouping all lichens generically under the designation 1 Plukenet, L. Phytographia. London. 1691. Almagestum Botanicum. Lon- don. 1696. Amaltheum Botanicum. London. 1705. 2 Petiver, J. Gazophjllaceii Naturae etArtis Decas I. -X. 1703-1719. Musci Cen- turia X. London. 1695-1703. 3 Vaillant, S. Botanicon Parisiense. Leide and Amsterdam. 1727. 4 Raj, J. Sjnops. Meth. Stirp. Brit. London. 1690. 1696. 1724. 5 Morton, J. Natural History of Northamptonshire. London. 1712. 6 Petiver, J. Pterigraphia Americana. London. 1712. "Micheli, P. A. Nova Plantarum Genera Juxta Tournefortii Methodum Disposita. Florence. 1729. 8 Lichen. This generic term became unsatisfactory in proportion as the number of known forms increased. There were, no doubt, botan- ists before Micheli who recognized this defect in lichen classification, but this author was the first to point it out to the botanical world. Micheli went, perhaps, to the opposite extreme and made too many sub- divisions. He divided lichens into thirty-eight orders, basing this division upon the external appearance and consistency of the thallus, the position of the apothecia (receptacula flontm], and the soredia (semina). Nineteen of these orders, representing one hundred species, were illustrated. This step in advance was, however, more apparent than real, be- cause of the fact that but little progress had been made in studying the morphology of these plants. It cannot be denied, however, that Micheli made good use of the simple microscope in the study of lichens. The next prominent lichenologist was J. J. Dillen, 1 who made a considerable change in the system of Micheli. He grouped the lichens with mosses and subdivided them into three classes. These classes were again subdivided into orders, series and divisions, ac- cording to the structure of the thallus, and the structure and position of the apothecia. After Micheli and Dillen other botanists did not hesitate to propose other arrangements, none of which were, perhaps, equal in value to those of the two eminent workers mentioned. These attempts were, however, indirectly productive of good results, because, in order to establish new systems, it was found necessary to make more care- ful observations in regard to the gross, as well as to the minute anat- omy of the thallus and apothecia. Hill, 2 who classed lichens with mosses, divided all the known species into six genera Collcma, Usnea, Platysma, Cladonia, Pyxidinm and Placodiimi whose limitations have been retained in part up to modern times. Adanson 3 classed lichens with fungi and separated them into nine genera. Linne's 4 system of lichens was in a certain sense retrogressive, since he grouped all these plants under the generic term Lichen (see Tournefort). This group was, 1 Dillenius, J. |. Historia Miiscorum. London. 1763. 2 Hill, J. A. History of Plants. London. 1751. 3 Adanson, M. Families des Plants. Paris. 1763. 4 Linne, C. Species Plantarum. Holmiae. 1753. however, again subdivided into seven divisions, to which two more were added at a later period. Linne's system is of special impor- tance, because it shows the first attempt at a natural arrangement. Beginning with Graphis, which he probably supposed to be the lowest form, he gives an ascending series terminating with Us-uca, which is certainly a highly developed lichen. Nearly all authors of this period, subsequent to 1753, adopted Linne's system of classification. The most remarkable characteristic of this period was the re- newed uncertainty as to the position of lichens in the vegetable king- dom. Some authors classed them as fungi, others as algae, again as mosses. This doubt as to their true position continued to agi- tate the minds of botanists, and it has not been definitely removed at the present writing. It would be impossible to review all the works on botany issued during this period which incidentally treat of lichens. As yet no specialists in the study of lichens had arisen ; in fact, all the crypto- gams were very much neglected. The study* of higher plants of economic and of real or imaginary medicinal value absorbed the at- tention of botanists. The great systematists, in particular, took no interest in the lower forms of plant life. Linne designated lichens as " rustici pauperrimi," which may well be rendered "poor trash' of vegetation. In his " Species Plantarum " only eighty-six species are mentioned, although 170 were known at the time. Progress in the study of the anatomy and physiology of lichens was especially slow and unsatisfactory although these divisions of botany were already known. Many botanists seemed possessed with the idea that there must be an analogy between flowering plants and lichens ; hence efforts were made to find the male and female repro- ductive organs, fruit and seed. Wild and fantastic conjectures were made as to what structures in lichens should be compared to special organs in higher plants. Naturally, opinions differed very greatly. Micheli looked upon the soredia as " pollen dust, "the apothecia were supposed to be the floral receptacles ( ' reccptacula floruni), the spores the true " flowers." As already mentioned, this author also explained the asexual propagation of lichens by means of the soredia. Dillen, whose work was likewise of considerable importance, believed that the soredia constituted the pollen. His opinions in regard to the apothecia varied. At one time he supposed them to be the recepta- 10 cles for the seed, again the seed itself, or young plants, or even buds which served the purpose of reproduction. Gleditsch, Scopoli and Linne believed that the apothecia were the male reproductive organs, while the soredia were the female re- productive organs. Necker 1 held the opposite opinion. Haller 2 ac- cepted the theory of Micheli with regard to the functions of the apothecia and soredia. It scarcely need be stated that these various and varied opinions were based upon purely hypothetical assump- tions and not upon direct observations. In the pages devoted to the previous periods mention has been made of some of the uses to which lichens had been put in medicine and in the arts. In this period further efforts were made to widen their range of supposed usefulness. From the fact that scarcely any- thing was known of their anatomy and chemical composition, it is evident that many erroneous opinions must have been entertained in regard to their usefulness. Mead 3 recommended Pcltigcra canina as a cure for hydrophobia. Dried and finely powdered thalli of P. canina, mixed with finely powdered red pepper, formed the noted " pulvis antilyssus " (anti-hydrophobia powder) of the London Pharmacopoeia (1721 to 1788). In the history of the Royal Society it is recorded that several mad dogs, belonging to the Duke of York, were saved by this powder. The following is Dr. Mead's treat- ment in the case of hydrophobia. "The patient is bled and ordered to take a dose of powder in warm milk for four consecutive mornings ; thereafter he must take a cold bath every morning for a month, and for two weeks subsequently three times a week." Usnea barbata was a favorite remedy for whooping cough ; it was also recommended as an anodyne. (Dioscorides states that it was employed in certain diseases.) From its appearance it was sup- posed to promote the growth of hair. The yellow Xanthoria parietina was recommended in jaundice. The tonic and astringent properties of Cetraria Islandica were highly lauded by Ebeling. 4 Physicians and apothecaries of Iceland and Denmark recommended it in haemoptysis and phthisis. As an article of diet it had been long in use, not only for man, but also for domestic animals. " Ice- land scurvy " was said to have been prevented by consuming a suffi- cient quantity of this lichen. 1 Necker, N. J. Physiologia Muscorum. Mannheim. 1774. 2 Haller, A. Historia Stirpium Indigenarum. Helvetiae Bernae. 1768. 3 Mead, R. Poisons, 5th ed. 1818. 4 Ebeling. Du Quassia et Cetraria Islandica. Glasgow. 1779. II IV. PERIOD. FROM WEBER (1779) TO WALLROTH AND MEYER (1825). In the previous periods lichens were classified mainly according to the differences in the form and structure of the thallus. In this period an attempt was made to classify them according to the " fruit- ing," that is, according to the form and structure of the apothecia. The first beginnings of this new departure, of course, commenced in the previous period, as we have already noted. Weber, 1 however, made the first intelligent effort to classify lichens upon this new basis. This author had formerly grouped all lichens in one order under lt Cryptogamta;" he now arranged them under eight genera, Verrucaria, Tnbcrcularia, Sphacroccphahini, Placodium, Lichen, Collema, Cladonia and Usnea ; of these, the first four were based upon the characters of the apothecia alone ; the others upon the characters of the thallus, as well as those of the apothecia. The majority of Weber's contemporaries adopted this new method of classification, with the result that entirely new systems were formed and new genera established. The following were some of the most active systematists: Willdenow, 2 who discovered the genus Pel ti- ger a ; Schreber, 3 who proposed the genera P/iyscia, Cornicularia, Sticta and Stereocanlon ; Humboldt, 4 who founded the genus Ope- grapha. To Persoon 5 are credited the genera Caliciiun^ Sphacro- phorus, Baconivccs and Placodiitm. Although the majority of lichenologists followed in the footsteps of Weber, there were a con- siderable number who could not disengage themselves from the Lin- naean influence. Of these we will mention only Hagen 6 and Joly- clerk. 7 The Swedish lichenologist Acharius 8 began his study of lichens ''Weber, G. H. Wigger's Primitiae Florae Holsatiae. Kiel. 1780. Also, Spici- legium Florae Goettingensis. Gothae. 1778. 2 \Vildenow, C. L. Flora Berolinensis Prodromus. Berolini. 1787. 3 Schreber, D. J. C. See Linne's Genera Plantarum, Sth ed., Vol. I. Frankfort- on-the-Main. 1791- 4 Humboldt, A. von. Florae Freibergensis. Berolini. 1793. 5 Persoon, C. H. Einige Bemerkungen iiber Flechten. Usteri neue Annalen der Botanik, I : 1-32. 1794. 6 Hagen, C. G. Tentamen Historiae Lichenum. Regiomont. 1782. ' Joh'clerk, N. Cryptogamie complete, ou description des plantes, dont les etami- nes sont pen apparantes. Paris. 1799. 8 Acharius, E. Nov. Act. Reg. Sc. Holmiae, 15 : 237-259. 1794. Nov. Act. Reg. Sc. Stockholmiae, 16 : 1795. 12 about 1793, and his great work was issued about seventeen years later (1810) . This author divided lichens into three families according to the structure of the thallus : I. Lichcnes crnstacei; II. Lichenes foliacci; III. Lichcnes caulescentes. Each of these families was again divided into several tribes (twenty-eight in all) according to the structure and position of the apothecia. He changed this system very materially at a later period. It would be impossible to mention all lichenologists (including collectors) of greater or less note. However we may state that they made valuable collections at home and abroad and that their main desire was to determine old or new species. Little or nothing was done to ascertain the life-history of any of these interesting plants. Lamarck 1 described one hundred and fifty-seven species besides a number of doubtful forms. Jolyclerk mentioned and described three hundred and sixty-five species, which was a fairly complete list of all the lichens published at that time. It is, of course, impossible to know whether this was the actual number of species discovered on account of the numerous collections which were not published. There is also little doubt that many species published were duplicates. The most active collectors were at work in Germany, France, Austria, England and Switzerland. In 1802 it was admitted on good au- thority that in all about five hundred species of lichens were known. In regard to the reproduction of lichens the controversy of the previous period continued : the question was still under discussion as to what lichen structures should be considered as the male and female organs. As in the previous period, these discussions and conclusions were mainly based upon hypothetical assumptions. Hoffmann - agreed with Micheli that the soredia were the true seeds of lichens, but further believed that it was not improbable that the scutellae (apothecia) also contained seed; lichens were thus sup- posed to have a double means of reproduction. The true pollen (fertilizing substance) was supposed to be hidden in the lichen, and that fertilization took place internally during the early development of the plant. 3 Gartner "* perhaps came nearest the truth in regard 1 Lamarck, M. de. Encyclopedic Methodique. Botanique, 3 : 470-508. Paris. 1789. 2 Hoffmann, G. F. Commentatio de Vario Lichenum usu. Erlangen. 1786. 3 Hoffmann's general illustrated works on lichens are : i. Enumeratio Lichenum. Erlangen. 1784. 2. Descriptio et Adumbratio Plantarum. Classes Cryptogamica Linnaei quae Lichenes dicuntur. Leipzig. 1790-1801. 4 Gartner, J. De Fructibus et Seminibus Plantarum. 1788-1805. to the function of the soredia. He believed them to be lateral branches or buds (propagincs} and divided them into pulverulent (pnlrcntlcntac}, filamentous (scobiformes) and leaf-like (bracteo- /atnc}. From this it is evident that his conception of soredia was much more comprehensive than that of the present day, as this au- thor, no doubt, included the so-called isidioid outgrowths as well as the secondary thalloid branches. He stated that t\\epropagincs took their origin from the surface of the thallus and had the power of de- veloping into new lichens without any preliminary changes. Schreb- er looked upon the soredia as gemmae rather than male reproduc- tive organs, thus agreeing with Gartner within certain limitations. Relhan ' and others believed the apothecia were the female sexual organs and the soredia the male sexual organs. One of the most important works of the period was that of Hedwig. 2 He discovered the spermagonia, and not only gave very good descriptions of these organs, but of the apothecia, the spores and soredia as well. His descriptions were greatly strengthened by good illustrations. His conclusions were essentially as follows : The spermagonia which are the male reproductive organs develop first ; subsequently the apothecia and soredia are developed upon them. He believed the apothecia with the spores to be the female reproductive organs, while the soredia constituted the fertilizing elements or the true pollen. As far as his conception of spermagonia and apothecia are concerned, we see that Hedwig anticipated the opinions held by some lichenolo- gists of to-day. His theory with regard to the function of the sore- dia was, however, further from the truth than those of his predeces- sors. We must also mention the rather unique experiments of De Can- dolle 3 illustrating the method in which lichens were supposed to take up their food-supply. This noted author employed a cochineal solu- tion to observe the manner and rapidity with which various lichens absorbed this substance. As the result, he grouped lichens as to the manner in which he supposed them 'to absorb their food-supply, i. Those which take their nourishment through the exterior. 2. Those 'Relhan, R. Flora Cantabrigiensis. Cantabria. 1785. Supplement I. 1786. Supplement II. 1788. 2 Hedwig, J. Theoria Generationis et Fructificationis Plantarum Crvptogamariim Linnaei. 1784. 3 De Candolle, A. P. Premier essai sur la nutrition des Lichens. Journal de Physique, de Chimie et d'llistoire naturelle, 47: 107. 1798. which take their nourishment through a central canal. 3. Those which absorb through the exterior, but which also possess a central canal. As a whole, his explanations are very imperfect, which accounts, perhaps, for the fact that his treatise is at present almost entirelv neglected. Georgi 1 made some valuable chemical examinations of lichens and demonstrated the presence of oils, resins, gums, alkaline salts, silica, and other substances. Acharius 2 seems to have been in great doubt as to the origin and structure of lichens. For a time he even questioned whether they were plants ; that they, perhaps, belonged to the polyps. It was this doubt which led him to make more careful investigations concerning these plants. He made an especially careful study of the structure of the apothecia upon which his system 3 of classification is based. Though this system was doubtless an improvement on previous ones, it was subjected to severe criticism by Weber and other writers- This led Acharius 4 to improve and enlarge his former work. The illustrations of the structure of the apothecia and thalli are fairly good, but they indicate that he must have used poor microscopes. He gives only a few very crude illustrations of spores. One can readily understand that this system must, of necessity, be very defi- cient because no use w r as made of the spore-characters. Sprengel 5 made an attempt to classify lichens according to the structure of the apothecia ; it proved to be very unsatisfactory ; it is evident at least, that this author had no definite ideas in regard to the " seed" and "fruit" of these plants. In a later work 6 Sprengel adopts the essentials of the system of Acharius and introduces Ger- man diagnoses of species. Of the numerous lichenographers of this period there are ye three who deserve special mention, namely, Fries, Eschweiler and Fee. Fries 7 devoted his attention to the purely systematic con- 1 Georgi. Chemische Untersuchungen einiger Flechten. Act. Acad. Scien. Petropol. pars. alt. 1779. 2 Acharius, E. Anmiirkinger rorande Lafarterne. Kongl. Vet. Acad. Nya Handl. 17: 1796. Prod. Lich. Suec. XVII. 1798. 3 Acharius, E. Methodus Lichenum. 1803. 4 Acharius, E. Lichenographia Universalis. Gdttingen. 1810. "'Sprengel, K. Einleitung in das Studium der crvptogamischen Gewachse. Halle. 1804. English translation. London. 1807. 6 Sprengel, K. Anleitung zur Kenntniss der Gewachse. 2d Ed. Halle. 1817. 7 Fries, E. Conspectus Lichenum. K. Vetensk. Acad. Handl. 323-324. 1821. sideration of lichens, without adding anything important to their morphology. His system of classification is not especially com- mendable, although it was for a time generally accepted. He divided lichens into two great divisions, the Lichenes gymnocarpi and Lichenes angiocarpi. The generic distinctions were based upon the form and structure of the apothecia and thallus. Of much greater value are the works of Eschweiler. 1 This author, whose early death was a great loss to lichenology as well as to botany in general, made a careful study of the apothecia and spores of lichens. He was the first to call attention to the different forms of spores, al- though his attempts at utilizing these spore-characters in his system of classification met with little success. Fee 2 in 1824 divided lichens into eighteen orders and sixty-six genera, seventeen of the latter being new. The characters of the thallus were utilized in the determination of the orders. His system was not favorably re- ceived. Fries and Fee will again be mentioned in the following period. In America the work of collecting and naming lichens was also begun with great zeal, although the important work was not done until later periods. Many of the workers of this period devoted themselves to mere catalogueing. Mich an x 3 published a short list of lichens (mostly new) collected in Carolina and Canada. Miihlen- berg" 1 published a list of Pennsylvania lichens. Eaton 5 published a list of North American lichens, likewise Torrey 6 and Halsey. 7 In this period also appeared a number of monographs on lichens. The most noteworthy were those of Acharius who elucidated the genera Arthonia, Thelotrcma, Pyrcnnla, Trypctheliiuii, Caliciiiin. Glyphis and Chiodecton. Floerke issued monographs on Cladonia and crustaceous lichens. Schaerer wrote a valuable treatise on the Systema Orbis Vegetabilis. Part I. 1825. Lichenographia Europaea reformata. Lund. 1831. 1 Eschweiler, Fr. G. Systema Lichenum. Nurenberg. 1824. 2 Fee, A. L. A. Essai sur les cryptogames ecarees exotiques officinales. Paris 1824. 3 Michaux, A. Flora Boreali-Americana. 1803. 4 Miihlenberg, H. Catalogue of the Plants of North America. Lancaster, 1813. Second Edition, Philadelphia, 1818. 5 Eaton, A. Manual of Botany for North America. Albanv. 1818. 6 Torrey, J. A Catalogue of Plants growing spontaneously within 30 miles of New York City. Albany. 1819. 7 Halsey, A. Synoptical view of the Lichens growing: in the vicinity of the City of New York. Ann. Lye. Nat. His. N. Y. i : 3-21. 1824. i6 Gyrophorae of Switzerland. The more important monographs, however, were not issued until the following period. During this period little or no progress was made in the knowl- edge of the anatomy and physiology of lichens. Although the com- pound microscope had been introduced, little use was made of it. This can readily be accounted for by the fact that the first compound microscopes were very imperfect and also because, being an innova- tion, they were regarded with distrust. Eminent opticians of the tjme boldly declared that the compound microscope could never excel the most perfect simple microscopes. Strange opinions were entertained in regard to the origin of lichens. The belief in spontaneous generation and spontaneous transformation was general. It will be instructive as well as amus- ing to enter more carefully into some of the opinions entertained. Hornschuch 1 occupied himself with the problems of "generation' and "evolution." His opinions as far as they applied to lichens were as follows : " Algae, lichens and mosses may develop without seed from decomposing water. The decomposition of water induced by warmth and sunlight gives rise to the common ancestral type of the above vegetable forms. This ancestral type is a vegetable infusorium known as Monas lens (green substance of Priestley) which, when acted upon by light and air, undergoes an evolutionary transforma- tion into alga, lichen and moss. Lichens are in reality mosses which have been checked in their evolution and might well be designated vegetable monstrosities. The apothecia (of lichens) are not the fruit, but rather the beginnings of a corolla, analogous to the flower of mosses (Moosroschen) . The observations of Micheli in regard to the development of lichens from soredia are to be discredited since the discovery of the spontaneous generation of lichens." Sprengel 2 otherwise an accurate observer, believed that Lccidea immcrsa and Monilia viridis were evolved from chaotic masses due to the action of some force inherent in nature. The noted algologist Agardh 3 states that he observed the transformation of JVostoc muscontm, var. lichcn- oidcs into CoUcma liinosuni. Nees von Esenbeck 4 was wont to lead 1 Hornschuch, Dr. Einige Beobachtungen iiber das Entstehen der Algen, Flech- ten und Laubmoose. Flora, z : 140-144. 1819. 2 Sprengel, G. Ueber Bau und Natur der Gewachse. Halle. 1812. 3 Agardh, C. A. Dissertatio de Metamorphosi Algarum. Lund. 1820. Flora, 16: 17-41. (Beilage.) 1823. 4 Esenbeck, Nees von. Handbuch der Botanik. 1820. his pupils to an old castle in order to demonstrate ad ocn/os how the green substance of Priestley, 1 when occurring on rocks, will develop into lichens. These few citations will suffice to show that the science of botany was in its infancy. Better work was being done in the chemical study of lichens. Here the investigations were limited to such lichens as had been found useful in the arts and in medicine. Most of the results ob- tained were published in the various chemical and pharmaceutical journals of the time. Those specially interested will find the refer- ences in various works on lichens. The investigations in regard to the medicinal uses of lichens were not so extensive as in the previous period. During the wars of 1809 1815 fevers of all sorts were prevalent in military hospitals. Quinine, which was the popular remedy in all cases of fever, became very scarce because of the enormous quantities consumed and because of the commercial blockade of Europe. The Austrian government, therefore, offered a prize of five hundred ducats for the discovery of a cheap available substitute for quinine. Sanders, 2 who secured this prize in part, proposed Parmelia -parietina as a substitute for quinine. It was soon found that the medicinal properties of this lichen were very unsatisfactory and the remedy was abandoned by physicians. V. PERIOD. FROM WALLROTH AND MEYER (1825) TO SCHWEXDENER (1868). This period marks the awakening of scientific lichenology as well as of scientific botany in general. It also marks the discovery of the " gonidia," which were destined to revolutionize the study and con- ception of lichenology. Likewise the spore-characters were begin- ning to be considered in the various systems of classification. We may well be astounded when we recollect that from Dioscorides to Wallroth, a period of two thousand years or more, the advance made in the exact knowledge of the anatomy of lichens was practically zero. The mere collection and arbitrary arrangement of plants do not give us any insight into their true nature. 'Wiegmann, A. F. Erzeugung mehrerer Gewiichse a us der Priestley'schen griinen Materie. Flora, 4 : 8-15. 1821. 2 Sanders, G. C. H. Die Wandflechte (Parmelia parietina) ein Arzneimittel. Sonderhausen. 1815. i8 The first investigators who entered into a scientific study of lichens were Wallroth 1 and Meyer. 2 It is remarkable that the more important works of these authors should appear in the same year. Their ob- ject was not to collect and classify, but, rather, to study and compare the material already at hand. Of the two investigators it is gener- ally conceded that Wallroth had the clearer insight into the nature of lichens, though in many respects he was not so careful an investigator as Meyer. The student of lichenology will however find, to his sorrow, that Wallroth's style is very involved. Each sentence contains a long series of parenthetical clauses which makes it very difficult to follow him. His terminology is also new and requires a special studv. In spite of all these objectionable features, the work is cer- tainly epoch-making. Wallroth was the first author to give us some knowledge of the vegetative propagative cells (Brutzellen == gonidia) . He dwelt at considerable length on the "metamorphoses" of the thallus as well as on its general morphology. He demonstrated that some lichens were " homoemerous " and some " heteromerous" (these two terms are about all that have been retained of Wallroth's termin- ology). He made a careful study of the soredia and found that they consisted of gonidia enclosed by a delicate network (hyphae), and held the opinion that the gonidia, hence also the soredia, could develop into new plants. Under unfavorable circumstances the gonidium or soredium will not develop into a lichen, but simply form a green coat- ing over the substratum. Though many of the conclusions were er- roneous, it must be borne in mind that this was the first attempt at a scientific study of lichens. It is also much to be regretted that this author did not make use of the compound microscope ; in some in- stances there is no evidence that he used even the simple lens. Meyer's studies were perhaps more comprehensive than those of Wallroth. He entered into a careful consideration of the structure and metamorphosis of the thallus and apothecia, the gonidia and spores, the relation of lichens to the substratum, the growth and nu- trition of lichens, etc. Meyer believed in the spontaneous genera- tion (generatio originaria} of lichens which was stoutly denied by Wallroth. Wallroth believed that the gonidia and spores were the only reproductive organs of lichens. 1 Wallroth, F. W. Naturgeschichte der Flechten. Frankfurt-am-Main. I. 1825. II. 1827. 2 Meyer, G. F. W. Die Entvvickelung, Metamorphose und Fortpflanzung der Flechten, etc. Gottingen. 1825. We shall refer briefly to some of the other morphologists of this period. Mohl 1 made a careful study of the spores of crypto- gams, including those of lichens. Korber" studied the gonidia and in the main verified the conclusions of Wallroth. He also made observations in regard to the reproduction and growth 3 of lichens. Korber's system of lichens * has no commendable features, his diagnoses being usually based upon macroscopic examinations. His orders, genera and species correspond to those of Massalongo. One thousand and fifty-one species of lichens are described as oc- curing in Germany and Switzerland. Two hundred and seventy- two species are described as new ; from this it may safely be con- cluded that many species are only imaginary. The modern lichen- ologist will find it impossible to recognize many of the species from his descriptions. In passing it may be stated that this criticism will apply to the greater number of systematic works issued during this period as well as in the previous periods. The results of Mas- salongo's 5 studies were of considerable importance. This author concluded that the spore-characters, as well as the form and structure of the apothecia and thallus, should be considered in the establish- ment of the genera. It is, however, generally conceded that many of his species and some of his genera were poorly founded. Fries 6 also recognized the importance of spore-characters in generic dis- tinctions and in addition considered the form of the spermatia and sterigmata of importance in classification. It was, however, left to Stitzenberger (91) to point out the real value and significance of the spore-characters in the classification of lichens. He believed that in general it was necessary to consider the number of septa in the spores as well as their direction. Lichens with spores differing in the number of septa are not to be included in the same genus. He believed that the spores were equal in importance to the flowers and 'Mohl, H. Einige Bemerkungen iiber die Entwickelung und den Ban der Sporen der cryptogamischen Gewachse. Flora, 16 : 32-46,49-63,65-73. 1833. 2 K6rber, G. W. De Gonidiis Lichenum. Berlin. 1839. 3 K6rber, G. W. Bemerkungen iiber individuelle Fortpflanzung der Flechten. Flora, 24: 6-14. 17-32. 1841. 4 Korber, G. W. Syste'ma Lichenum Germaniae. Breslau. 1855. Parerga Lichenologica. Breslau. 1865. 5 Massalongo, A. Recerche sulP anatomia dei Licheni crostosi. Verona. 1852. Memoiree Lichenografiche. Verona. 1853. Monografia dei Licheni blasteniospori. Venice. 1853. 6 Fries, Th. M. Genera Heterolichenum Europaea recognita. Upsala. 1861. 2O fruit in higher plants ; the spermatia were not looked upon as being of any special significance in the classification of lichens. The English lichenologist, Mudd, 1 emphasized the importance of the spore-characters and likewise considered the spermagonia as being of only secondary importance. At this time the arrangements proposed by Massalongo and by Korber received general recognition. Now, however, appeared an investigator, an able systematist, who, in a certain sense, revolution- ized the classification of lichens. Nearly all previous lichenologists arranged them beginning with the highest forms and working toward the lowest. Nylander, 2 however, had an entirely different conception of how these plants should be arranged. He believed that they presented a double affinity ; on the one hand they showed a close resemblance to fungi, on the other hand to algae. In his system he arranged lichens beginning with those forms most nearly resembling the algae, thence proceeding to the highest forms as Sticta, Parmclia and allied groups. From these highest forms he proceeded to the forms most nearly resembling the fungi. From this it would seem that he had the first somewhat definite conception of the true nature of lichens. The most remarkable thing in his sys- tem is the contempt with which he treated the spore-characters in the limitation of genera and tribes, restricting them to specific distinc- tions. He believed that the form, structure and composition of the thallus, apotheciaand spermagonia must form the generic characters. Chemical reactions of the thecium, especially with iodine, were con- sidered of much importance. Nylander also considered the color and structure of the gonidia. He published a list of all the known lichens, which included 1,348 species, 298 of which were described as new. 3 We have mentioned the leading systematists of the period. We shall now hastily review the works of the leading morphologists of this time. It must not, however, be forgotten that many of the sys- tematists also devoted some attention to the morphology of lichens, but only in so far as it was necessary to enable them to arrange the plants according to some preconceived system. No advanced work was done by them ; this was left to the investigators who believed 1 Mudd, W. A Manual of British Lichens. Darlington. 1861. 2 Nylander, W. Syn. Meth. Lichenum. Paris. 1858. 3 Nylander, W. Enumeration generale des Lichens avec 1'indication sommaire de leur distribution geographique. Cherbourg. 1858. 21 that a thorough study of the life-history, morphology and physiology of plants was necessary before they could be properly classified. Ttzigsohn will be the first to receive our attention. His opinions varied in regard to the spermagonia (38). He was inclined to be- lieve that they were parasitic fungi, abnormal spore-organs, apo- thecia or even parasitic lichens. Later (41) he expressed it as his opinion that the spermagonia were the antheridia of lichens analo- gous to those of mosses, and the spermatia, the spermatozoa. Still later (42) he states as the result of the study of Pannelia -parietina that the gonidia "of lichens which are reproduced from gonidia," are the female organs and the spermatia the male organs, and that fer- tilization of the gonidia takes place outside of the thallus. Plcnro- coccus, UlothriX) and other algae were supposed to be unfertilized gonidia enabled to lead an independent existence. Of much more value were the investigations of Tulasne. He gave the first somewhat exact description of the morphology of many lichens (97 ) . Especially valuable are the accompanying illustrations of sections of the thallus, apothecia and spermagonia. This author proposed the term spermagonium for the small structures upon the thallus, and spermatia for the minute rod-like bodies within the sper- magonium. He was also the first to demonstrate that the spermatia are formed on sterigmata, and that they do not have autonomous movement. As to the function of the spermagonia he believed that they were peculiar reproductive organs, physiologically closely re- lated to the apothecia. He was also the first to call attention to the " pycnids " and the " stylospores. ' Lindsay likewise did some excellent work in the morphology of lichens. In his prize essay he presents a communication in regard to the morphology of spermagonia and pycnidia. As to their function he is inclined to the belief that they are analogous to male repro- ductive organs. Lindsay has also given us a very interesting and popular history of British lichens. 1 This excellent little work con- tains good illustrations showing the morphology of the thallus, apothecia and spermagonia ; it gives the history of lichenology, the uses of lichens and diagnoses of the more prominent forms. Schwendener, whom we shall mention more particularly in the next period, now began his interesting studies of lichens (79). He made a careful research on the morphology of the majority of known 1 Lindsay, W. L. A popular History of British Lichens. London. 1856. 22 lichens, doubtless the most comprehensive study of the subject ever undertaken up to this time. Especially valuable are his observa- tions in regard to the growth of lichens. His careful study of the anatomy of these plants contributed very valuable aid to the future classification of lichens. It is, however, especially interesting to note that at this time (1858-1863) he was convinced that the gonidia developed from the hyphae, as branches develop from the side of a stem. In this he agreed with Bayrhoffer (5, 5a) and Speerschneider (84). In the next period we shall find that he changed his opinions as far as gonidia were concerned. Not much can be said in favor of the illustrations accompanying Schwendeners communications. Another important work of the period was that of de Bary. 1 In the work cited, this author gave a clear and concise description of the minute structure of lichens. In many respects it resembled the work of Schwendener ; in fact, a number of the illustrations were taken from his work. De Bary gave a very comprehensive description of the morphological and anatomical relations of the crustaceous lichens. We cannot enter into a full discussion of de Bary's work ; one opinion expressed by this author should, however, be referred to in particular, since it has bearing upon the conclusions arrived at in the next period. De Bary believed that some of the gelatinous lichens (JSphebc, etc.) were either perfect or mature states of plants whose immature states are recognized as forms of Nostoc, Chroococ- cus, etc. ; or that these organisms are true algae, attacked by certain ascomycetes, whose hyphae penetrate the algae and form the lichen-thallus. From this we see that De Bary was the first author to hint at the true nature of lichens. He also issued a very valu- able communication in regard to the development of certain lichen- spores (22). Considerable progress was also made in the chemical study of lichens. Various substances peculiar to lichens were discovered, such as cetrarin, variolin, orcin, erythrin, picroerythrin, evernin, physodm, besides various acids, as cetraric acid, evernic acid, and fatty acids. The alkaloids and acids discovered proved so varied and variable that Schunk - came to the conclusion that one J De Barv, A. Morphologic und Physiologic der Pilze, Flechten und Myxomyceten. Leipzig. 1866. 2 Schunk, E. Einige Bermerkungen liber die von Stenhouse in der Rocella tinc- toria and Evernia prunastri entdeckten Substanzen. Erdmann's Journal f ur practische Chemie, 46 : 18-30. 1849. 23 and the same lichen would yield different chemical compounds de- pending upon a difference of .locality and substratum. French and Scandinavian chemists employed lichens (especially Cladonia rangifcrina] in the manufacture of alcohol. These chemical investigations were primarily conducted with a view to improve the dye industry dependent upon the various color- ing substances derived from lichens. France, more than any other country, improved upon the methods of extracting the dye, as well as of applying it. Orseille was especially recommended in dyeing woolen and silken goods. Innumerable methods for extracting the dye as well as for improving its durability were employed. Some of these methods were patented. Lichens also found a wider use as an article of diet. Cetraria Islandica, because of its high percentage of lichen-starch (lichenin), was especially recommended as already mentioned. The inhabit- ants of Iceland, Norway and Sweden mixed this lichen with various cereals and mashed potatoes, from which an " uncommonly palata- ble and healthful bread was prepared." Sir John Franklin and his companions made use of this lichen during their Arctic voyages. Its use to prevent the peculiar disease known as " Iceland scurvy' continued. In general, however, it may be stated that lichens were used as an article of diet onlv in the case of a famine or in those / countries where the cereals are not abundant, principally because all lichens contain a bitter principle, which is very disagreeable to the taste and difficult to remove and which has a deleterious effect upon the digestive tract, producing a form of intestinal inflammation. As to the use of lichens in medicine it was found that they were not reliable, and other drugs soon supplanted them. They were, however, recommended as an article of diet for convalescents, espe- cially "Iceland moss" (Cetraria Islandica"). The peasantry of various countries still believe in the healing properties of various lichens. We have already mentioned Peltigcra canina. In Sweden Pcltigera aphthosa was boiled in milk and given to children afflicted with " thrush." Decoctions of various lichens (especially Parmelias and Cladoniai] were employed in intermittent fevers. The purga- tive properties of most lichens (particularly the Umbilicarias) are well known ; various species of Gyrophora and Umbilicaria were the cause of severe illness among members of the Franklin expedi- tion. 2 4 VI. PERIOD. FROM SCHWENDENER (i86S) TO REINKE (1894). This is by far the most important period in the entire history of lichenology. It is marked by the recognition of the true nature of lichens and their classification as modified fungi. Since most of the literature of this period is readily accessible I shall not review it at length and shall limit myself to a very brief outline of the work done during this period, mentioning only a few of the leading in- vestigators. The most important work of the period was the discovery of the dual nature of lichens. That is, a lichen consists of a fungal and an algal portion associated in an intimate organic union. Al- though Schwendener is generally credited with having made known this discovery, it must not be forgotten that the preparatory work was done in the preceding period ; also that Schwendener did not at first believe in the dual nature of lichens. Not until the year 1868 (79) did he express the opinion that the gonidia of various lichens corresponded to certain low forms of algae. His conclu- sions of that time may be summarized as follows : 1 . There is no direct proof of any genetic relation between the gonidia and the hyphal elements. 2. The cell-walls of the gonidia have a different chemical be- havior from the membranes of the hyphae ; the former react similarly to those of algae, the latter similarly to those of fungi. 3. As to structure and development the various forms of gonidia correspond to different forms of algae. The resemblance is so close that in many cases a given isolated gonidium cannot be distinguished from the corresponding alga. The algal types are as follows : (a) The majority of heteromerous lichens (Usnca, Bryopogon, Evernia, Ph\sica, Anaptychia, Imbn'caria, Parmelia, etc.), con- tain species of the algal genus Cystococcns Naeg. ( C. humicohi and related forms). (b) Some other heteromerous lichens contain species of Pleuro- coccus Menegh. (P. vulgar is and related forms). (c) In Rocclla we find the algal genus Exococcus Naeg. (d) Omphalaria and other lichens with blue-green gonidia con- tain various representatives of the Chroococcaceae as Gloeocapsa^ Chroococcns, and perhaps other related forms. 2 5 (e) The Collemaceae are associated with Nostoc. (f) Ephcbe and related genera with Stigonema. (Ephebella JfegetscJtzveilert with Scytonema.) (g) Hormogonium and Cystocolcns are associated with an alga belonging to the Confervaceae. (h) GraphiS) Opcgrapha and related forms are associated with Ckroolepus. 4. The development of the spore never proceeds further than the protothalloid stage, perhaps because of the absence of the requisite algae. 5. There is a great similarity between the lichens and the pyreno- mycetous fungi. Schwendener issued a communication on the algal types of lichens in the following year (81). It is accompanied by colored plates illustrating most of the lichen-algae. Famintzin and Baranetzky (23, 24) demonstrated experimentally that the gonidiaof heteromerous lichens, such as P/iyscia, Evernia, Cladonia and Pcttigera, as well as some of the gelatinous lichens, as CoUenta, are capable of devel- oping apart from the thallus, even producing zoospores like the uni- cellular algae. In spite of this fact these investigators concluded that the gonidia were not algae, and further expressed the opinion that perhaps many of the unicellular algae were simply free lichen- gonidia. Woronin (103) demonstrated that the gonidia of Parmclia piil- -verulenta never produce hyphal filaments, but always develop into new gonidia ; or, what is the same thing, the free gonidium which is neither more nor less than a species of Cystococcns develops into new colonies of algae. He thus opposes the view held by Baranetzky and Famintzin and favors the theory of Schwendener. Rees (74) demonstrated that the hyphae developed from the spores of CoUcma g/auccsccns will not mature unless associated with Nostoc lichenoides ; in the absence of such an association the young hyphae soon perish. A few years later Bornet (15, 16) isolated and determined specifically the algae which enter into the composition of a large number of lichens. He also described the method by which the hyphae envelop the algae, as well as the mutual benefit derived from the intimate asso- ciation of algae and fungi. Similar observations were made by Treub (94). These and other experiments demonstrated beyond a doubt the 26 dual nature of lichens. They also demonstrated that this association was not like that of ordinary parasitism, but rather formed a union for mutual benefit, thus enabling these plants to exist where neither of the components could exist alone. This association was known as consortism (Reinke), or symbiosis (de Bary). There were also a large number of investigators engaged in the study of the morphology as well as the physiology of particular groups of lichens as well as of lichens in general. We will mention a few of these. Stahl (89, 90) made a special study of the spermagonia. His conclusions were that in Collcnia the spermatia are the male reproduc- tive organs. The female reproductive organ known as the carpogone after being fertilized by the spermatia develops into the apothecium. It is interesting to note that this form of sexual reproduction was ob- served only in CoJlcma. Recently Sturgis has apparently verified Stahl's results (93). Further investigations are necessary to estab- lish Stahl's theory. A number of investigators have demonstrated that the spermatia will develop a hyphal network, even developing new spermagonia. This would seem to prove that spermatia are true spores instead of sexual organs. The most important work in re- gard to the physiology of lichens was done by Jumelle (44). This author gave us the first reliable results of observations made on the exchanges of gases in fruticose and foliose as well as in crustaceous lichens. He found that the exchange of O for CO 2 is independent of the substratum and dependent upon sunlight and moisture, and also that this gaseous exchange varies greatly in different lichens. An excess of moisture reduces carbon-assimilation. Respiration in some lichens still goes on at very low temperatures, - - 10 to - - 40 C. Lichens can also resist much higher temperatures than phanerogams. For instance, respiration was still active when the lichen was exposed for one day to a temperature of 45 C., three hours at 50 C. and one-half hour at 60 C. Among the systematists we will mention Tuckerman, 1 who con- sidered Korber's system the most useful and adopted it in his classifica- tion of the North American lichens ; his diagnoses are carefully given, accompanied by spore-measurements. With Nylander he considered the spermagonia of great importance in classification. A number of new species were described. He also issued a work Tuckerman, E. Synopsis of North American Lichens. Parti. 1882. Part II. 1888. 27 on the genera of lichens and t;teir relationships, 1 which is, however, unsatisfactory, because the author did not seem to have any clear con- ception of genera. Leighton's manual of English lichens " has no commendable features : the spore measurements are quoted ; his diagnostic terminology is a peculiar mixture of English and Latin. Korber's and Nylander's methods of classification were referred to in the previous period. Hue published a list of exotic lichens, 3 from which it is safe to estimate that nearly five thousand species and varieties were known at the time. Of this number some are no doubt duplicates. It must be remembered also that a host of varieties, sub-varieties and forms were described. It is at present impossible to state the actual number of authentic species. Schwendener and his followers uniformly agreed to classify li- chens as fungi. To this the systematists objected very strongly. Naturally, they also objected to Schwendener's theory as to the true nature of lichens. In fact, all through this period we find the mor- phologists and physiologists pitted against the systematists ; the former earnestly endeavoring to get at the life-history of the various lichens, the latter refusing to recognize the discoveries made by the former and continuing the work of arbitrary classification. The work of Jatta 4 deserves special mention. He precedes the descrip- tions of the lichens of southern Italy by a discussion of the anatomy and biology of lichens, and adds a number of colored plates illus- trating the principal morphological characters. It is not complete, but it is a work contributing much to the scientific evolution of li- chenology. The use of lichens in the arts, in medicine and in the household was still continued. Great improvements were made in the method of using the various lichens in the dye industries. For further par- ticulars the student is referred to three little works on the uses of lichens by Magnin 5 , Henneguy 6 and Porcher 7 . As far as the medi- cinal uses of lichens are concerned we find that the allopathic school 1 Tuckerman, E. Genera Lichenum. Amherst. 1872. 2 Leighton. W. A. The Lichen-flora of Great Britain, Ireland and the Channel Is- lands. Shrewsbury. 1879. 3 Hue, A. M. Lichenes Exotici. Paris. 1892. *Jatta, A. Monographia Lichenum Italiae meridionalis. Trano. 1889. 5 Magnin, Dr. A. Les Lichens utiles. Lyon. 1877. 6 Henneguy, Dr. F. Les Lichens utiles. Paris. 1883. 7 Porcher, F. P. The Medicinal, Poisonous and Dietetic Properties of the Cryp- togamic Plants of the United States. New York. 1854. 28 has practically abandoned them as being too unreliable in their effects- In Bartholow's Materia Medica (1884) we find that only Cctraria Islandicais recommended to be given as a stomachic tonic, " but only to be prescribed when the more efficient remedies are not well borne." The homeopathic school of medicine still recommends certain lich- ens in a few diseases, for example, Sticta pulmonaria in lung troubles. Other lichens are given in whooping-cough, etc. VII. PERIOD. FROM REINKE (1894) TO THE CLOSE OF 1896. I may be justly criticised for recognizing this as a period, since Reinke's propositions have not been generally accepted as correct. It can not, however, be denied that his conclusions are based upon sound argument and should, therefore, mark the beginning of the period in which lichens are recognized as a distinct class of plants ; such recognition being based upon physiological considerations. In his article on " Die Stellung der Flechten im Pflanzensysteme " (75, III) Reinke endeavors to demonstrate that lichens are autonomous struc- tures. He recognizes and admits all the facts established by Schwendener and his followers, but maintains that lichens are physi- ologically as well as morphologically sufficiently distinct from both fungi and algae to be recognized as a distinct class. Although the lichen-algae may be cultivated artifically this does not indicate that lichens should be considered as fungi parasitically associated with algae. The fact remains that when either of the symbionts is re- moved the lichen no longer exists ; its autonomy is destroyed. The difference between the school of Schwendener and that of Reinke is principally a difference of opinion as to what constitutes autonomy. Tubeuf (96) states that in mutualism we have a union of fungus and alga which produces an individual wholly different from either of the components and entirely distinct as to form, requirements and condi- tions of life. This intimate nutritive association of two or more originally distinct organisms, which is typically met with in lichens, Tubeuf designates as individualism. According to this definition lichens should, doubtless, be treated as a distinct class. It will be remembered that Tuckerman and others of the previ- 2 9 ous period maintained that lichens formed a distinct class of plants. But Tuckerman and Reinke had entirely different conceptions as to the nature of lichens. The former did not believe in their dual nature and, therefore, could not form any true idea as to the relation they bear to other groups of plants, the fungi and algae in particular. For that reason we are justified in stating that Reinke was the first to indicate the true position of lichens in the vegetable kingdom. Lindau (53) is opposed to Reinke's views and strenuously up- holds the theory of Schwendener. As has already been indicated, the future must decide which theory will prevail. Reinke also pointed out the polyphyletic origin of lichens (75, III, IV). The various groups (usually generic) of lichens are derived from different fungal ancestors. Usually several fungal an- cestors have become associated with the same algal type, or the same fungal type may have become adapted to different algal types. Reinke has proposed a system based upon this polyphyletic relation- ship, which, when more perfected, will form the first approximately natural system of classification for lichens. As this author states, to study the exact phylogenetic relation of lichens to fungi and algae, is one of the important works of the future. Fimfstiick (32) has investigated the fatty secretions found within crustaceous rock lichens. His conclusions are briefly summarized / as follows : Calcivorous crustaceous lichens vary greatly as to the depth to which they penetrate the substratum ; the endolithic forms have a deficient algal layer as compared with the epilithic forms ; the fatty deposition increases with the increase of the gonidial layer, but has no genetic relation to it ; the fatty substance is de- posited in the hyphae lying within the substratum ; fat is deposited only in lichens growing upon a substratum bearing carbonates ; the formation of the fatty substance is very likely initiated by the de- composition of the carbonates. Lindau (54) has also issued the first of a series of communications on the morphology and physiology of lichens. Part i treats of the growth and mode of adhesion of crustaceous bark lichens. He con- cludes fhat the hyphae never penetrate the intact cells of the sub- stratum. He has also considered the question whether lichens have or have not an injurious effect upon trees (54)- He comes to the conclusion that they have no injurious effect upon trees growing under normal conditions. Only when the trees are growing in poor 30 soil, or when too closely crowded, can a profuse development of lichens have an injurious effect. Of the systematists of this period we will mention only Crombie. ' In his classification of British lichens this writer has adopted Ny- lander's system. He does not recognize Schwendener's theory and divides the lichen-algae into gonidia, gonimia and gonidimia. His diagnostic terminology is that peculiar mixture and combination of English and Latin so much employed by English systematists of this as well as of the preceding period. We shall conclude this historical. review with a brief reference to fossil lichens ; so far there is no reliable record of any such remains. There is, however, little doubt that lichens existed during former geologic ages. No records are left for the same reason that we have few authentic records of fossil algae and fungi, that is, lichens are not sufficiently resisting to become fossilized. Excavations of pre- historic cave dwellings (Germany) have revealed the presence of lichens (Cladonia rangiferina} among the bones of various animals and the stone implements, which would indicate that man of that early period had already made some economic uses of them. 1 Crombie, British Lichens, I., 1895. CHAPTER II. SYMBIOSIS. INTRODUCTION. Since Schwendener's epoch-making researches, which have fully established the dual nature of lichens, other investigators have made valuable discoveries in regard to the nutritive interdependence of different organisms. The student will readily comprehend the im- portant bearing this subject has upon the study of lichens. A gen- eral consideration of the subject of symbiosis will enable us to have a more definite opinion in regard to the life-history of the individual lichen. The study of the symbiotic relationship (consortism of Reinke, symbiosis of De Bary) of different organisms is of comparatively recent origin. As generally admitted, the phenomenon of sym- biosis was first explained by De Bary in the year 1879 l . By symbi- osis this author understood a form of nutritive commensalism or con- sortism of different organisms which proved mutually beneficial. It was, therefore, placed in opposition to parasitism, which is a form of cpmmensalism in which one of the organisms is benefited at the ex- pense of the other. Within recent years the term symbiosis has been* used to designate all forms of commensalism, whether parasitic, in- different or mutually beneficial. It is in this broader sense that the term is here used. We shall now briefly consider the gradation from antagonistic symbiosis (parasitism) to the most highly developed mutualistic sym- biosis (individualism) as we find it in lichens. I. ANTAGONISTIC SYMBIOSIS. (PARASITISM.) It is assumed that the student is sufficiently familiar with the an- tagonistic symbiosis of fungi with higher plants as well as with ani- 1 The phenomenon of symbiosis had, however, been previously explained by Reinke. lie used the term " consortism " to distinguish this relationship from true parasitism. His views are explained in the following publications : Reinke, J. Gottinger Nachrichten, p. 100. 1872. Reinke, J. Morphologische Abhandlungen. Leipzig. 1873. Reinke and Grisebach, A. S. Oersted's System der Pilze, Lichenen und Algen. 1873. 31 3 2 mals to require no further elucidation of the subject here. Another and but little known phase of this subject is the antagonistic symbi- osis of fungi with lichens, and of lichens with lichens, and with mosses. We shall now consider these relations somewhat more in detail. I. ANTAGONISTIC SYMBIOSIS OF FUNGI WITH LICHENS. There are no natural reasons why this form of symbiosis should not be of frequent occurrence, although no special study has been made of the subject. It is also very likely that many so-called para- sitic lichens are in reality parasitic fungi. A number of herbarium specimens described as parasitic lichens proved, on closer study, to be fungi ; in no case could a thallus be detected. It was also evident that these parasitic fungi (Ascomycetes) had an injurious effect upon the algae of the lichen-thallus, as they were nearly all destroyed in the immediate vicinity of the fungus. As far as it has been possible to observe, these parasitic fungi usually occur on the .upper surface of the lichen-thallus, quite rarely on the lower surface, as in Endo- carpon miniatum. It is a comparatively difficult matter to study the organic union of the symbionts, since the hyphal threads of both are very similar. This difficulty we do not encounter where fungi are parasitic upon higher plants. I have repeatedly made careful sec- tions through host and parasite and employed various staining meth- ods, but did not succeed in demonstrating definitely that the hyphal network of the supposed parasite was or was not continuous with that of the host. By crushing methods, assisted by various alkaline sol- vents, one can readily separate the two symbionts, but this is not in- contestible evidence that they were not organically united. This difficulty of investigation also applies to the so-called pycnidia and spermagonia. But since we are certain that there are ascomycetous fungi parasitic upon lichens, so, likewise, in regard to sper- magonia and pycnidia it is reasonable to assume that they are parasitic fungi, especially since it has not been conclusively demon- strated that they are male reproductive organs. It is also reasonable to assume that the parasitic fungi of lichens are morphologically and physiologically different from the same forms of parasitic fungi of higher plants, a variation induced by a marked difference in the sub- strata. Even leaving out of consideration the spermagonia, which we shall discuss more in detail in another chapter, parasitic fungi are 33 * quite common upon lichens. Although most of the fungi parasitic upon lichens belong to the Ascomycetes, there are also a few from other groups. Not unfrequently some species of Mucor entirely de- stroys the lichen-thallus ; it is, however, quite probable that this oc- curs only when the vitality of the lichen is very much reduced and the plant exposed to a high degree of moisture. The method of infection is much the same as in higher plants. A spore of the parasite falls upon the surface of the thallus, where it develops a mycelium which destroys the hyphal tissue of the host, or, at least, very materially retards growth, so that in time the parasite is more or less completely enclosed by the upper layers of the lichen- thallus. The line of demarcation between host and parasite is some- times abrupt and distinct, owing to a difference in color, but, as already indicated, it is very difficult to demonstrate the relation of the hyphae of the parasite to those of the host. It is very desirable that this form of symbiosis should be investigated more carefully. Some ex- periments solving the problem of the true physiological relationship of fungal parasites to lichen-hosts would be especially interesting. Physarum mucoroidcs, a Myxomycete, occurs quite constantly upon Pertusarta communis and Sticta globifera ; other Myxomycetes oc- cur less constantly. 2. ANTAGONISTIC SYMBIOSIS OF LICHENS WITH LICHENS. (SYNTROPHY.) That different species of lichens should occur in symbiotic associa- tion is not surprising when we consider the fact of their close prox- imity in nature ; there is a continual struggle for space. Very frequently we find foliose or fruticose lichens spreading over and crowding out the crustaceous forms. We also find that one form of crustaceous lichen will encroach upon another form and gradually cause it to disappear This is readily understood in the case where one lichen is of more rapid growth than another. As Minks has shown in his communication on the syntrophy of lichens (65, 67), one species of crustaceous lichen may form the lower thalloid portion, while a second parasitic species may develop the apothecia. Not only one, but several, different species may form successive layers upon the lower- most host-species. It frequently happens, doubtless, that the host- lichens are sooner or later entirely destroyed, in which case we can find only the parasitic form growing upon the fragmentary remnants 34 * of the host or hosts. Minks is also inclined to believe that the so- called " protothallus " is simply the remnant of a host-lichen. Al- though it is questionable whether syntrophy is of as frequent occur- rence as Minks supposes, there is no doubt that it does occur, not only among the lower lichens, but among the higher forms as well. I have found a species of Lecanora growing upon a Cotlema-thallus. There are many undecided problems connected with this form of symbiosis. No one has as yet been able to observe the complete course of development of this form of parasitism ; that it is parasitism is quite certain. I have not adopted the term syntrophy proposed by Minks, since it indicates nothing which is not already implied by the term parasitism or antagonistic symbiosis. 3. ANTAGONISTIC SYMBIOSIS OF LICHENS WITH MOSSES. According to Bonnier (n) certain lichens, Lccidca vernalis in particular, live parasitically upon the protonema of mosses. This author has made numerous culture experiments to verify his obser- vations. He placed moss and lichen spores upon sterilized substrata, where their development could be readily observed. It was found that the hyphal filaments formed a mycelium about the protonema, even entering the cells, where they formed a dense network, causing the protonemal cell to become considerably enlarged. It is evi- dently a form of antagonistic symbiosis, because the protonema is killed in a short time. Bonnier has observed this antagonistic sym- biosis of lichens in different genera of mosses. Lichens also occur parasitically upon the leaves and other parts of mosses, as well as upon higher plants. Practically nothing is known of the life-his- tory of lichens parasitic upon higher chlorophyll-bearing plants, although they are numerous and have been known for a long time. They are mostly low forms of lichens and occur principally in tropi- cal regions. Many of the occurrences of supposed antagonistic symbiosis require further study. There is little doubt that many of the injurious effects supposed to be due to antagonistic symbiosis of lichens is, in reality, caused by mechanical interference. For in- stance, a lichen spreading over a moss, which is of frequent occur- rence, cuts off sunlight as well as air, thus having an injurious effect in an indirect way. It is generally admitted by the leading investi- gators that the lower forms of lichens, in particular, take very little 35 nourishment from the substratum (host-plant), at least not sufficient to produce any injurious effects. (For further particulars see n.) II. NUTRICISM. This establishes a connecting link between antagonistic symbiosis and mutualistic symbiosis. Tubeuf defines it as that form of symbio- sis in which one symbiont nourishes the second symbiont without re- ceiving any food supply in return ; that it is, so to speak, a one-sided symbiosis. Tubeuf recognizes two forms of nutricism. In the first the saprophytic fungus living in contact with the growing root-tips of higher plants supplies soluble organic food substances, the fun- gus acting in the manner of a transfer agent. In the second the fun- gus lives within the root-cells of the host-plant. The author ad- mits that the fungus is at first nourished by the host, but that it finally dies and is absorbed. The second form is undoubtedly mutualistic symbiosis, as will be explained in the ,next chapter. I will there- fore, limit myself to a discussion of the first case ; it must be re- membered that it is very frequently difficult to decide what is merely nutricism and what is mutualistic symbiosis. The most common form of nutricism is met with in the occurrence known as mycorhiza (fungus-root). This is the association of a fungus and the root of some higher plant. It is frequently met with among the Cupuliferae growing in humus-bearing soil. The hyphal fungus forms a network about the young root-tip of the growing tree ; its function is to supply the tree with organic food substances taken from the soil ; in a certain sense it supplants the function of the hair-cells which are wanting in the mycorhiza. The fungus does not receive any marked benefit from this association, but it has been conclusively proven, experimentally, that the tree is very materially benefited. The hyphae of the fungus always remain on the outside of the root and this form is, therefore, known as ectotrophic mycorhiza. In the endotrophic mycorhiza of Orchids the fungus enters the parenchyma cells of the root where the hyphae develop a mycelial network ; too little is known concerning this phenomenon to give any correct explanation of it ; it is at present impossible to state whether it is a case of antagonistic symbiosis, nutricism or mutualistic symbiosis. In regard to the ectotrophic mycorhiza we are certain that it is not a form of antagonistic symbiosis. In Cycas rcvolnta we find a form of symbiosis which is un- 36 doubtedly nutricism, but it differs from that above described in that the host-plant acts as the transfer agent. It is found that in the majority of cultivated Cycas species there are numerous tubercular outgrowths from the roots which usually contain a species of Nostoc between the cells of a specialized parenchyma. This is evidently not a form of parasitism, as is shown by the fact that the cycads bear- ing the greater number of tubercles are in no wise injuriously af- fected. Neither has it been proved that the host receives any ma- terial benefit from this association. There is, however, no doubt that the J^ostoc is dependent upon the host for its food supply. For the time being it may be looked upon as nutricism. There are numerous other forms of symbiosis which come under the head of nutricism, but sufficient has been given to explain the subject and to prepare the way to a better understanding of mutual- istic symbiosis. III. MUTUALISTIC SYMBIOSIS. In mutualistic symbiosis host and parasite form a biological union resulting in mutual benefit. On closer examination two forms may be recognized. In one the symbionts (there may be two or more) are not wholly dependent upon each other for their existence; that is, the symbionts are all capable of leading an independent exist- ence. In the second form at least one of the symbionts is absolutely dependent upon the symbiotic association. The former Tubeuf designates as.mutuatism, the latter as individualism. I. MUTUALISM. This form of symbiosis is of comparatively recent discovery. Frank, more than any other investigator, has given this subject his at- tention, especially its occurrence among the leguminous plants. In the Leguminosae we find the constant occurrence of certain bacteria (rhizobia) within the root-parenchyma causing the development of tubercles. It is, doubtless, a form of mutualism, although Tubeuf considers it a case of nutricism. The bacteria which infect the root- cells and cause the development of the tubercles are dependent upon the host for their food supply. They are even excessively supplied with nourishment, as is indicated by their enormous development. The host in return receives the nitrogenous compounds formed by the bacteria in the process of binding the free nitrogen of the air. It 37 is true that the benefit received by the host is far greater than that received by the infecting bacteria, but it is nevertheless mutual. It has been demonstrated experimentally that the host may thrive with- out the symbiotic bacteria and that the bacteria occur normally in the soil and that they will readily develop in artificial culture media. This shows conclusively that the symbionts are not absolutely de- pendant upon each other. Host and parasite, however, thrive much better when in symbiotic association, especially in poor soil. 2. INDIVIDUALISM. In individualism is reached the acme of mutualistic association. As already explained, the conditions of this occurrence require that one of the symbionts be absolutely dependent upon the mutual relationship. The phenomenon is typically met with in lichens. In these plants we find the nutritive interdependence so marked that a new individual is formed, which in its morphology and physiology is wholly different from any of the symbionts. From the historical re- view of the Schwendenerian period we learned that in lichens we have an association of a fungus with an alga or algae. It has been demonstrated experimentally that while the algal portion is capable of existing independently, the fungal portion can not do so, that is, the symbionts are not mutually dependent. Individualism will have reached its highest development when all the members of the symbi- otic relationship are incapable of existing independently. There is no doubt that in time this will be the case in our present lichens. Since the fungus has lost its power of independent existence as a re- sult of the symbiotic association it is reasonable to assume that the alga likewise is undergoing a change indicative of a more highly developed dependence upon this association. It seems quite evident that it is more difficult to cultivate the lichen-algae than the corre- sponding free forms. We shall now very briefly explain the difference between individ- ! The student is advised to consult the following works giving a condensed review of the phenomenon of mutualism as it occurs in the Leguminosae : Frank, A. B. Lehrbuch der Botanik, i : pp. 255-275. Leipzig. 1892. Atkinson, G. F. Contribution to the biology of the organisms causing leguminous tubercles. Bot. Gaz. 18 : 157, 226, 257. 1893. Schneider, A. Observations on some American Rhizobia. Bull. Torr. Bot. Club, 19 : 205-218. 1892. 38 ualism, as met with among lichens, and mutualism. These explana- tory statements will be more fully discussed in other chapters. In their development lichens stand alone. They occur in places where neither alga nor fungus could exist independently. Jumelle has proven experimentally that they can resist much greater ex- tremes of heat and cold than other chlorophyll-bearing plants. Every observer of nature is familiar with their wide distribution and wonder- ful power of adaptability. They are of slow growth and are en- dowed with an exceedingly long life period. The symbionts unite to form a microcosm w r hich not only performs the life functions originally inherent in both, but also additional life functions which it has acquired during its phylogeny as a lichen. The fungal symbiont, considered by itself, still retains at least a part of its ancestral func- tion of saprophyte : it has acquired in addition the habits of an obligative symbiont upon the enclosed alga. The algal symbiont, whose function is that of assimilating CO , must be looked upon as a facultative symbiont, since it can exist and mature independently. As already stated, the fungal symbiont is incapable of maturing into an independent fungus ; it is absolutely dependent upon the mutualistic association. Considering the lichen as a unit we find that the fungal portion supplies the symbiotic algae with water containing soluble food substances taken from the substratum ; in return the algae supply the fungi with products of assimilation (carbon compounds). The question bearing directly upon the discussion of individ- ualism is whether lichens shall be considered as autonomous struc- tures or not ; that is, shall we consider lichens as modified fungi in agreement with Schwendener and his followers, or shall we consider them as a distinct class in agreement with Reinke ? From the very nature of individualism it is evident that the resulting structure is a morphological unit in the full sense of the word. That is, a lichen is neither fungus nor alga, but a new individual which should be given a definite position in the vegetable kingdom. It is an inde- pendent individual because we find that on separating the symbionts the individual is destroyed, as has already been indicated. There is, perhaps, no doubt that in the lowest forms of lichens the fungal symbiont may develop to maturity without its algal symbiont, but this is not the case in the higher forms. These probable exceptions to the rule do not disprove that lichens are autonomous, nor do they warrant the method of classification adopted by Schwendener. 39 3- CONTINGENT MUTUALISM. Contingent mutualism is a term designating a form of symbiosis which is quite frequently met with among lichens and elsewhere but which has received little attention. Besides the constant symbiotic algae of lichens enclosed by the tissues of the thallus there occur algae which are always found on the outside of the thallus or which, at least, never penetrate the lichen tissue very deeply. Sometimes these algae occur on the upper surface of the thallus, sometimes on the lower surface, sometimes in or among the apothecia. They may be present in one plant, while in another lichen of the same species none may be found. That is, this form of symbiosis is not constant in its occurrence ; hence, it is designated as contingent. It has not been ascertained experimentally whether it is in reality a mutual- istic, indifferent or antagonistic symbiosis. It certainly does not seem to be antagonistic, because in lichens bearing a large number of these accidental algae we do not find the least indication of any harmful influence ; the lichens thus affected seem, indeed, to be un- commonly thrifty, which suggests an additional or secondary mutu- alism. The fact that this association does not result in any notice- able structural adaptation would seem to be evidence that the elective affinity between the symbionts is only slight. That there is some elective affinity is evident from the fact that one and the same species of algae usually occurs on representatives of certain lichen genera. For example, Sirosi-phon -pulvinatus and a species of Nostoc occur on Umbilicaria and Gyrophora ; Pleurococcus vulgar is on Parmelia and Physcia; Pleurococcus -punctiformis on young Cladonia and Baeo- myces. The three algae mentioned are the principal forms which enter into contingent nutritive association with lichens. Under this form of symbiosis I do not include the occurrence of algae upon dead or decaying lichen-thalli, which is of frequent oc- currence and is not a case of symbiosis. Nor do I include the un- mistakably mutualistic symbiosis met with in the so-called " pseudo- lichenes," as Lepra viridis and Amphiloma. CHAPTER III. THE GENERAL MORPHOLOGY AND PHYSIOLOGY OF LICHENS. INTRODUCTION. By way of introduction to this branch of our subject it is highly important to call attention to the interrelation of morphology and physiology, which is of special significance in the study of the lower groups of plants, fungi, lichens, and algae in particular. The in- vestigator soon finds that morphological conformations of plants and plant organs coincide with certain functions and, vice versa, certain functions coincide with definite morphological characters of plants and parts of plants. It is true that there are a number of scientists who believe that morphology and physiology should be kept separate for didactic purposes ; they even go farther and subdivide these main divisions and endeavor to teach each subdivision as a distinct subject. The anatomical-physiological tendency, which received such a strong impetus through the influence of Schwendener and his pupils, is slowly gaining a footing in England and America. Heretofore it has been customary to devote almost exclusive attention to the mor- phology of plants ; the physiological significance of morphology has been neglected. In order to avoid any erroneous conclusions as to the meaning of the terms morphology and physiology an outline of their limitations as employed throughout this book is given. Morphology treats of macroscopical (gross anatomy, morphology in the narrower sense) as well as microscopical structure (minute anatomy or histology). Physiology treats of the life phenomena of cells, tissues, organs and individuals. Vegetable pathology (teratology, abnormal physiology ) and the corresponding pathological morphology are subordinated to physiology and morphology respectively. I. ORGANS OF ASSIMILATION. I. THE THALLUS. The thallus is the alga-bearing assimilative portion of lichens. This comprehensive definition would also include the thalloid ex- 40 4 1 ciple, which contains algae, and is, therefore, assimilative. The term is, however, usually limited to the alga-bearing portion, ex- clusive of apothecia. On account of the perfect mutualistic adapta- tion of the lichen symbionts we find some very marked structural characters to meet the requirements of different cases. In the lower forms of lichens this structural adaptation is not so readily recogniz- able, but in the higher forms the physiological and mechanical adapta- tions are, in fact, more marked than they are in the higher plants. We will now take up the discussion of a typical foliose thallus because in it the morphological differentiations are most highly developed. After having a thorough understanding of the highest type of thallus there will be little difficulty in understanding the lower forms. The following are the tissues met with in a vertical section of the thallus of Sticta. (a) Tegitincntary Layer. (Dennis.) (b) Upper Cortical Layer. (c) Algal Layer. (Gonidial Layer.} (d) Medullary Layer. (e) Lower Cortical Layer. These layers will be described in this order ; the rhizoids, cy- phellae, breathing pores, cephalodia and other accessories of the thallus will be treated independently. (a) The Tegnii/entary Layer. (Dennis.} This is the uppermost layer of the thallus and is usually rudimen- tary or wanting, except in the higher lichens, especially Sticta and Stictina. It consists of several layers of flattened hyphal cells extending at right angles to the underlying cortical cells. The cells are rather irregular in form ; their walls are usually more gelatinous than those of the cortical layer. The walls of the more internal cells are frequently slightly colored, due to a deposit of lichenic acid. The outermost cell-walls are, however, perfectly colorless and gelatinized. Sometimes the outermost cells develop hair-like pro- longations whose function is not definitely known. In PeUigera apkthosa, for example, they doubtless serve to retain the soredia, which subsequently develop into cephalodia. They, perhaps, also serve to retain moisture. The dermis contains intercellular canals which are continuous with the canals of the cortical layer below. The outermost cells are continually removed by abrasion, while new 4 2 ones are formed from the cortical layer. The change from cortical to tegumentary cells consists in a retardation of growth in a vertical direction and a stretching combined with growth in a horizontal direction. As a result of these combined influences the cells become much flattened. The primary function of the dermis is, doubtless, to prevent the sudden and excessive evaporation of moisture. It also provides a mechanical protection to the underlying tissues. (/>>) The Upper Cortical Layer. This layer, in different degrees of perfection, is present in all warty, squamose, foliose and fruticose thalli. It is usually desig- nated as a semicortical or semiparenchymatous tissue. Structurally it certainly resembles very closely the parenchymatous tissue of higher plants. The cells are somewhat elongated in a vertical di- rection and lie in actual contact ; in outline they are quite irregular ; the walls are usually considerably thickened, especially at the angles ; the lumen is in part filled with air. The cells of this layer are directly continuous below with the hyphal cells of the algal layer and above with those of the dermis. There is a continual regeneration or development of new cortical cells proceeding upward from the algal layer, while the upper cortical are converted into dermal. The cortical layer varies greatly in thickness in different species as well as in different portions of the same thallus. From the fact that the thallus performs the function of assimilation as well as that of me- chanical support, it is evident that the structures destined to perform these functions must be suitably adapted and arranged with reference to each other. The upper cortical layer, whose function is primarily mechanical, is variously modified so as to adapt it to the requirements of the underlying assimilating tissue. This is very beautifully shown in Solorina saccata : in this species the lower outline of the upper cortical layer is serrate, that is, the cortical layer is alternately thicker and thin- ner ; this gives great mechanical support and at the same time favors the grouping of the algae near the surface for exposure to the influence of sunlight, and to permit the exchange of gases. We find this layer thickest in those lichens having no lower cortical layer, very likely because the exchange of gas can readily take place downward. There are, however, other provisions to permit 43 the ready exchange of gases ; as, for example, the breathing pores and the cyphellae. The breathing pores are the intercellular canals met with in the upper and lower cortical layers, which are continuous with those of the dermis ; they are especially numerous in the thinner portions of the layers. The breathing pores, and especially the cyphellae, will be more fully discussed in another chapter. The primary function of this layer is usually mechanical. Two other functions almost equal in importance are those of protecting the underlying tissues, especially the algae, and preventing the sud- den and excessive evaporation of moisture. That the primary func- tion is purely mechanical in most cases, is evident from its structural adaptations in form and position to meet mechanical requirements. In some lichens it is likewise evident that the primary function is not mechanical, since we find special mechanical tissues distinct from the cortical layer, as, for example, in the podetia of Cladonia and in some species of Gvrop/wra, as well as in many of the fruticose thalli. In these cases the prime function is evidently to protect the under- lying algae. (c) The Algal Layer. (Gonidial Layer.} This is by far the most important structure of the thallus. It con- tains the symbiotic algae whose special function is that of assimila- tion. The layer consists of hyphal filaments continuous with the cells of the cortical and medullary layers, and the algal cells which are in more or less intimate union with the terminal branches of the hyphae ; it varies considerably in thickness ; in the same species it is thickest in the young growing plant ; in the older portions of the thallus the algae are less numerous. As already indicated, the as- similating algal layer makes suitable concessions as to position to the mechanical tissue. As a rule, the algae are most numerous where the cortical layer is thinnest. The subject of greatest interest is the relation of the algae to the hy- phae. It will be remembered from the historical review that Schwen- dener, in 1863, and others at one time, believed that the algae (gonidia) develop from terminal branches of the hyphal filaments. From this it is evident that they recognized the close organic union. It is, however, also evident that this association is not very intimate in many forms of lichens, for instance in the Collemaceae, in which the algal symbiont is represented by the genus Nostoc. We find the 44 closest union in lichens whose algal symbiont is represented by Cys- i toccocus Jmmicola Nag ; this alga occurs in far the greater number of species. The forms of union between hyphae and algae are separated into three kinds: i, Simple contact; 2, Extracellular haustoria ; 3, Intracellular haustoria. 1. In this form of association the hyphae and algae are simply contiguous. The hyphae seem to undergo no change in form or development. This is especially the case in those lichens in which Nostoc or Ri'cnlaria occurs (so-called gelatinous lichens) . In Lichina for instance, the chains of Rivnhiria lie parallel and in contact with the hyphal filaments. I have been unable to detect any influence that the algae may have upon the direction of growth in the hyphae. The same may be said of the Collemaceae. It is, never- theless, evident from the life histories of the individuals of the groups mentioned, that the symbiotic relationship is very highly developed. From observation it also becomes evident that this contact-association prevails in lichens bearing algae which are -naturally enclosed by a gelatinous coat ; what influence this coat has on the symbiotic asso- ciation has not been explained. (PI. i . f. 2.) 2. In the majority of lichens the algae are enclosed by numerous short terminal branches of the hyphal filament. Whenever a hyphal filament comes in contact with an alga the contact surface is retarded in growth, and, as a result, the filament begins to curve about the alga. The presence of the alga also causes the development of short hyphal branches which wind about the alga in the manner just men- tioned. These branches are not only short, but they are usually much thinner and their walls more delicate than the normal branches ; they are also much more frequently septate. As the term extracel- lular haustoria indicates, these enveloping terminal filaments never penetrate the algal cell. The interchange of food substances takes place by osmotic action through the hyphal and algal cell-walls. The haustoria differ greatly in the degree of development. In some instances they are few in number and very loosely united with the algae ; when most completely developed they form a network or covering closely united with the alga, so that it is almost impossible to separate the symbionts. (PL i . f. j, 4.) 3. This is, doubtless, the highest form of symbiotic association oc- curring in lichens. Here we find that the haustoria of the hyphal 45 filament penetrate the alga; this penetration varies greatly in de- gree; the tip of the haustorium may pass through the algal cell- wall, forming a somewhat expanded filament between the wall and cell-plasm. In its highest development the haustorium, after entering the algal cell, develops a much-branched network which encloses but does not penetrate the cell-plasm. This haustorial network is made up of delicate gelatinized hyphal branches. Intracellular haustoria are comparatively rare ; I have observed them most fre- quently in young growing species of Cladonia, Parmdia and Stereocaulon. The question as to the manner in which the haus- toria gain entrance into the interior of the alga requires further study ; also the question of the biologic significance of this form of union. Can the liberated algal cell with its haustoria develop into a new lichen? It consists of both symbionts, all that is required for the formation of a new thallus ; it may, however, be that the haustorium when separated from the parent filament can no longer continue to grow. Algae which have intracellular haustoria have also, as a rule, extracellular haustoria. The plasmic contents of the algal cell are in time entirely absorbed by the haustorium, so that nothing re- mains but the algal wall enclosing the hyphal network. (PL i. f.5,6-} (d) The Medullary Layer. In the majority of lichens this layer is much thicker than any of the others ; it usually consists almost entirely of hyphae ; rarely we find distributed through it small groups of algae. The hyphal fila- ments consist of branching much elongated cells and are morpho- logically closely allied to ordinary fungal hyphae. The cell-walls do not become gelatinized like those of the cortical and dermal layers, and, like all' lichen tissues, do not stain readily. Occasionally we find a coloring matter deposited within or upon the cell-walls ; as a rule, however, they are colorless. In the middle portion of the layer the hyphae extend^in a direction parallel to the main axis of growth ; above and below they extend vertically to the cortical layers with which they are continuous. Structurally the medullary layer forms a marked contrast to the cortical layers. It consists of a network of very loosely interwoven hyphae with large air spaces. In this respect it is analogous to the spongy tissue of the foliage leaves of higher plants. t)ccasion- 46 ally we find groups of tissue elements distributed through this layer whose primary function is mechanical. This is, however, rare ; mechanical tissues as a rule occurring outside of the medullary layer. In some lichens, especially the so-called Lichenes gelatinosi (Collemaceae;, there is no distinct medullary layer ; that is the algal and medullary layers are, so to speak, intermingled. There is no medullary tissue proper in the crustaceous lichens, since none is nec- essary at least as far as the requirements of aeration are concerned. Structurally this layer is adapted to perform two functions. The hyphae conduct food substances such as water, mineral salts, carbon compounds, nitrogen, hydrogen, to and from the algae. They form the paths of exchange between the products of assimilation formed by the algae and the soluble food substances taken up by the fungal portion. Much work is, however, yet to be done in the physiological study of these functions. According to Zukal (no) the medullary hyphae also serve as storage tissues, accumulating for future use various carbo-hydrates (lichenin, isolichenin), gelatine, fats and fatty oils. Lichenin is stored in the cell-walls, causing them to become considerably thick- ened. The excess may or may not become reabsorbed in the future life processes of "the plant. Fat is stored within the cells and varies considerably in amount but never occurs in large quantities ; it seems probable that the fat is stored at one point to be again utilized at some other point in the same plant. Fat also frequently occurs in the spores, where it doubtless plays an important part in the processes of germination. The sphaeroid-cells occurring in the calcivorous crus- taceous lichens are special fat-storing structures. It is as yet a dis- puted question whether this fat is waste product or whether it is really utilized in further metabolic processes. ( authors have placed R. oreina in the genus Dimelaena, which is supposed to be characterized by "immersed apothecia." A care- ful comparative study of the representatives of the genus Rinodina soon demonstrates that the apothecia are more or less immersed in the thallus in all of its lower species. Referring to the key (p. 10) it will be seen that this is the first family in which the thalloid exciple becomes apparent; it is unmis- takable in Thcloschistes, Physcia and Pyxine, but in Rinodina and Placodium it is sometimes not very apparent, especially in those forms in which the apothecia are mostly immersed. In nearly all cases a close examination with a lens will reveal the thalloid outer covering of the apothecium which usually extends slightly above the margin of the dark disk. The generic characters are sufficiently marked, so that it will not be necessary to give any lengthy description of the family characters. 12 152 The apothecia are disk-like, rarely immersed in the thallus ; the disk is usually flattened or concave, sometimes convex, especially in Pla- c odium ; the apothecia usually vary from small to medium. A yel- low color predominates in the thallus and apothecia of the genera Placodiuni and Theloschistes due to a deposition of crystals of some lichen acid in and upon the hyphal cell-walls. Rinodina is also more or less impregnated with this coloring material. The algal symbiont is Cystococcus humicola Nag. The fungal symbionts are doubtless derived from one, or, at most, a few ances- tral forms of the Patellariaceae (plate 5). KEY TO THE GENERA. Thallus crustaceous, areolate, margin often foliose and lobed. Spores brown ; thallus not bright yellow. i. Rinodina. Spores colorless ; thallus yellow to orange. 2. Placodiitm. Thallus foliose, grey, not yellow. Hypothecium dark. 3. Pvxine. Hypothecium colorless. 4. Phvscia. Thallus foliose to fruticose, yellow. 5. Theloschistes. i. RINODINA Ach. ; Gray's Brit. PI. p. 448. 1821. This genus doubtless forms the lowest group of the Physciaceae ; it is distinguished from Placodhim by the uniformly dark-colored spores and the absence of any orange coloration in the thallus ; the thallus is grey or greenish in most species ; in R. orctiia, however, it is a pale or dirty lemon or sulphur color, and in R. chrysomelaena there is a marked yellowish tinge. The thallus is usually recognized as typically crustaceous. There is, however, a tendency toward the foliose type, especially near the margin, where lobation is sometimes quite distinct ( R. oreina.} Sometimes there is a warty structure as in R. chrysomelaena. Usu- ally the surface is crustaceous and more or less distinctly areolate ; it is always closely adnate and attached to the substratum by means of numerous black rhizoids. The black hypothallus of authors is not sufficiently understood ; in many cases it seems to be the remnant of some lichen (usually a related species) over which the Rinodina has spread. (Syntrophy of Minks. See parasitic lichens.) Different species of the Phvsciaceae are frequently in close prox- imity, especially among the Rinodinas and Placodiums ; there seems to be an inherent tendency to form symbiotic associations. 153 The apothecia are either immersed in the thallus or sessile ; the immersed forms can not be said to have thalloid exciples ; but the sessile apothecia are enclosed by a layer of the thallus and should therefore be looked upon as having true thalloid exciples. Usually the apothecia are quite small with flattened disks ; in the sessile forms the thalloid margin extends somewhat above the dark disk ; in the immersed apothecia the outline of the disk is quite irregular, reminding one strongly of some species of Buellia (R, or etna). The hypothecium is colorless and not cortical in structure ; the outer layer of the thalloid exciple is cortical or semicortical, resembling the cortical tissue of Physcia. The spores in the majority of species are dark and typically two-celled as explained in the discussion of the family characters. There are, however, exceptions ; in R. oreina the connecting plasmic bridge is usually wanting ; and it is probable that this species should be classed with the Buellias or separately as Dimelacna oreina as its spore characters, as well as apothecial characters, strongly point to its exclusion from Rinodina. It is not probable that BueUia is as closely related to Rinodina as Reinke and others seem to think ; further study will perhaps demonstrate that discoid sessile apothecia with dark two-celled spores (two cells united by a plasmic bridge) will fully characterize Rinodina and that the forms with distinctly immersed apothecia and two-celled spore, the cells of which are not united by a plasmic thread, should be excluded. The algae of R. oreina are also different from those of the other species which I have examined, being bright green slightly tinged with blue, rather irregular in form, at least more so than in Cystococcus humicola proper ; they resemble more nearly Plcurococcus vulgaris. The algae in the remaining undoubted representatives of Rinodina are Cystococcus humicola. They vary in size in the different species, while their general form remains constant. Ectotrophic haustoria are numerous and are closely adherent to the algae ; endotrophic haustoria seem to be comparatively rare. There are also multisporous forms of Ri-n odin a (pi. 34, f. 7. ), which according to some authors are included in a distinct genus (Maronea). The Rinodinas are quite common throughout the territory and occur upon rocks and bark, less commonly upon soil and moss. PLATE 34. RlNODINA SOPHODES (Ach.) N\l. 1. Natural size. 2. A small portion magnified. 3. Section of apothecium. a, thecium ; b and c, the two layers of the hypothecium ; d, uppei' algal layer; e, medullary layer; f, lower algal layer; g, cortical layer. 4. Section of thallus. 5. Paraphyses and spore-sac. 6. Spores. 7. Paraphyses and spore-sac of If. constans. 8. Spores of R. constans. 2. PLACODIUM Ach. Lich. Suec. 100. 1798. This genus, which in many of its characters resembles Rinodina^ is characterized by the orange color of the apothecial disk ; this rarely changing from a rusty red to dark ( P. ferrugineum ) . The thallus is usually yellow or orange, rarely grey to dark. The spores are colorless, with terminal plasmic masses, otherwise they are char- acteristic of the family ; they are rarely simple. The thallus varies from almost typically crustaceous (P. citrinum) to typically foliose (P. mtirorunt) ; in general, it may be said that it is more highly differentiated than in Rinodina ; as in Rinodina lobation first shows itself near the margin, the inner portion of the thallus becoming areolate ; usually both upper and lower cortical layers are present. In P. elcgans and other species the mutual adaptation of mechanical and physiological functions are beautifully illustrated (see plate 35) ; the upper cortical layer is not uniformly thick ; at certain areas the tissue is very thin, which allows the algae to approach near the upper surface of the thallus for the purpose of assimilation ; the thickened areas supply the nec- essary mechanical support. The rhizoids are more specialized than in Rinodina\ the hyphal cells are thicker and more rigid. In the lower representatives of the genus the thallus is closely adherent to the substratum, but in its higher forms, as P. elegans, P. murorum and a few others, the thallus-lobes are more or less ascend- ing, approaching in this character the higher groups. The yellow color is due to the deposition of crystals of chryso- phanic acid upon the hyphal cells, especially in the upper portion of the thallus as well as in the thecium ; on account of this bitter acid, various lichens of this family were used as a substitute for quinine ; it is present in nearly all lichens in larger or smaller quantities. The apothecia are of medium size, typically discoid, and sessile upon the upper surface of the thallus ; the thalloid exciple is well developed. The distribution of the Placodiums is much as in Rinodina. They seem to be somewhat more specially adapted to substrata of rock but also occur upon bark, dead trees, and old boards. Like the Rino- dinas they seem to be able to resist a high degree of dry ness. The species seem to be fairly well defined thojLigh they are sometimes confused with those of Theloschistes. PLATE 35. PLACODIUM ELEGANS (Link) D.C. 1. Portion of thallus natural size. 2. Portion of a thallus-lobe magnified. 3. Section of apothecium. 4. Section of thallus. 5. Different forms of paraphyses, and spore-sac. 6. Spores. 3. PYXINE Fr. PI. Homon. 267. 1825. The spore characters undoubtedly indicate that this genus belongs to the Physciaceae. A contrasting and negative character is found in the black hypothecium ; this is so marked that there is a strong tendency to exclude the genus from the family. All the structural characters of the thallus, as well as the apothecia and spores, point to a close relationship to the Rinodinas. Pyxinc is evidently also closely related to Physcia ; and it seems probable that it and Physcia represent two different branches which proceeded from the Rino- dinas. Placodinm may likewise have been derived from one of the Rinodinas. The thallus of Pyxinc as represented by the only two species, P. -picta and P. sorcdiata, is large, consisting of frequently branch- ing lobes. In P.focta the lobes are agglutinate and thin, and they lie flat upon the substratum ; the upper surface is light grey to greenish ; the lower surface is dark or black, especially in P. picta; black rhi- zoids are quite numerous. The apothecial and spore characters are taken from P. picta, P. sorediata being, to my knowledge, always sterile. They are in most respects similar to those of the higher forms of JRtnodma; the paraphyses are shorter and the spores are comparatively few in number * the dark hypothecium is semi-cortical in structure ; the hyphae everywhere contain large deposits of crys- tals of lichen-acid. In the thallus of P. picta the upper cortical tissue is deficient ; the lower is wholly wanting, its place being taken by a network of hyphae with dark-colored cell-walls. The thallus of P. sorediata is more highly developed than that of P. -picta; it bears numerous soredia upon the upper surface of the thallus, as well as along the margin. Apothecia never occur ; propagation in this species being entirely dependent upon the soredia. P. ptcta seems to be southern in its range, w r hile P. sorediata is more northern ; both occur upon bark and rotten logs. PLATE 36. PYXINE PICTA (Sw.) Tuck. 1. Portion of thallus, natural size. 2. Section of apothecium. 3. Section of thallus. 4. Paraphyses and spore-sac. 5. Spores. 6. Algae. 4. PHYSCIA Schreb. Gen. 2: 768. 1791. The thallus of Physcia presents all gradations from nearly crus- taceous (P. adglutinata), through foliose (P. stellaris and the ma- jority of species) to fruticose (P. ciliaris, P. leucomela} . The gen- eral characters of P. adghitinata indicate the close relationship of Physcia to Rinodina, from which genus it is doubtless phylogenetic- ally derived. In the majority of the representatives of this genus the thallus is typically foliose with the various tissue-layers well differentiated. The cortical tissue, however, differs considerably from that of Parmelia and the majority of foliose lichens, con- sisting of rather short, much interwoven, closely united hyphal branches, and the walls of the hvphal cells are considerably thick- ened and gelatinized ; intercellular spaces are rare and the cell-lu- mina are much reduced. Rhizoids are numerous and well developed. The color of the thallus in most species of Physcia is grey, tinged with green above, but having a different color beneath, visually lighter, rarely dark to black ; much of the dark colora- tion of the lower surface is due to the black rhizoids. Growth of the thallus is usually radial ; sometimes it becomes eccentrically ra- dial, clue to local influences. Branching is usually distinctly dichoto- mous and very frequent ; in the forms with a fruticose tendency the lobes become linear, with the margin lined with long simple or branched cilia (P. ciliaris, P. leiicomcla}. Some of the species are quite constantly sterile, in which cases they usually bear numerous soredia upon the upper surface of the thallus as well as along the margin of its lobes. As compared with Parmclia, the apothecia are of medium size, sessile, typically discoid with a highly developed thalloid exciple ; the thalloid margin usually extends above the disk ; in some forms the excipular margin becomes crenate or rugose, in others it remains smooth. In the fruticose forms the margin of the thalloid exciple bears thalloid fringes of considerable size. The disk is dark in color ; the spores are in most respects similar to those of Rinodina ; the color and size is, however, more variable. Some species are said to have four-celled to eight-celled spores, but none of them have come to my notice ; it is probable that these are not Physcias. In their distribution the Physcias, especially the higher forms, have a southern range. They occur most frequently upon tree-trunks, less commonly upon rocks. Like nearly all the Physciaceae, this group is adapted to a comparatively dry substratum, but for their growth they require a moist atmosphere, at least an atmosphere in which the average percentage of moisture is high ; this accounts for the large development of the highly hygroscopic tissue in the thallus (the cor- tical tissue), which readily absorbs the atmospheric moisture and re- tains it for the use of the plant. The algae (Cystococcus humicola} are intimately enclosed by haustorial branches. Endotrophic haustoria seem to be common in some species, especially in younger and more actively growing plants. Another characteristic of many of the Physcias is the presence of numerous spermagonia, which develop upon the younger por- tion of the thallus, where they appear as minute black dots. I have found it impossible to employ them in the determination of species, but it is, however, noteworthy that they occur more frequently upon some species than upon others. 158 PLATE 37. PHYSCIA SPECIOSA Fr. 1. Natural size. 2. Section of apothecium. a, thecium ; b, c, the two layers of the hypothecium ; d, upper algal layer ; e, medullary layer ; f , lower algal layer ; g, cortical layer. 3. Section of thallus. a, colored layer; b, cortical layer; c, algal layer; d, medullary layer ; e, lower cortical layer. 4. Paraphyses and spore-sac with spores. ^. Spores. 6. Colorless spores of another species. 7. Algae. 5. THELOSCHISTES Norm. ; Tuck. Gen. Lich. 18. 1872. The question whether Theloschistes or Physcia is the higher seems to me undecided. As previously indicated the fruticose forms repre- sent the climax of structural development ; the fruticose tendency is more marked in this genus, for which reason I consider it the higher, but the plausible objection that the development of Theloschistes as a whole is lower than Physcia can, however, be raised. The representatives of this genus are recognized by the presence of a yellow or even orange coloration in the thallus and apothecia, and the fruticose tendency of the thallus. T. parietinus is, however, distinctly foliose, although the lobes have a tendency to ascend or to turn upward at the margin. The extreme fruticose development is reached in T. flavicans, in which species the thallus-branches are very long, linear, somewhat rounded, showing a marked tendency toward a radial structure. In the majority of species the thallus-lobes are distinctly flattened (centric structure) and comparatively short. In some species the thallus is very short, the lobes are flat and sparingly branched toward the top {T. poly carpus}. The thallus is attached to the substratum by clusters of root-like rhizoids. In the foliose forms the bunches of rhizoids occur toward the middle portion of the thallus ; cilia also occur on the margin of the lobes and apothecia. The yellow color of the thallus is due to a deposit of crystals of chrysophanic acid, as m Placodiiuu, which occurs most plentifully on the upper surface of the younger portions, gradually fading into grey or brown with age. The lower surface is usually pale yellow or grey, likewise showing a shading in color similar to the upper. Black coloration is wanting ; the rhizoids are usually grey. '59 The apothecia are of medium size and are quite common on most species, especially so in T. polycarpus, but they are rare or wanting in T. jl&vicans . The formation of soredia is less common than in Physcia. In the higher fruticose forms the apothecia are usually terminal, a character which also manifests itself in the fruti- cose Physcias. In the lower fruticose forms and the foliose forms the apothecia may be terminal, on the margin or upon the surface. The disk is yellow or orange in color ; the margin of the cup is frequently lined with cilia. In other respects the apothecia resemble those of Physcia and Placodiitni. The spores closely resemble those of Placodinm, which seems to be strong evidence that this group is phylogenetically derived from that genus. In their distribution the Theloschistes are still more southern than the Physcias, and they also have a western range. They occur upon the bark and smaller branches of trees, rarely upon decaying wood, old boards, rocks, etc., frequently in association with species of Physcia. PLATE 38. THELOSCHISTES CHRYSOPHTHALMUS (L.) Norm. 1. Natural size. 2. Terminal portion of thallus magnified. 3. Section of apothecium. 4. Longitudinal section of thallus. 5. Paraphyses and spore-sac with spores. 6. Spores. Family 6. PARMELIACEAE. The limitations and position of this family are dependent upon four essential characters, i. The presence of the thalloid exciple sepa- rates it from the Caliciaceae, Cladoniaceae and Lecidiaceae. 2. The non-union of the spore-plasms excludes it from the Physciaceae. 3. The presence of the discoid apothecium separates it from the Verrucariaceae. 4. The absence of cyanophyceous algae separates it from the Collemaceae and Pannariaceae. It has more nearly the general characters of the Lecideaceae than any other family, those of the apothecia being very much alike. In this group the fruticose thallus reaches its highest develop- i6o ment (Usnea~). The radial structure predominates in Cetraria, and in the genera above it. The question may therefore arise as to- whether the fruticose or the foliose lichen-thallus presents the highest lichen-type. The answer to this question depends upon whether we consider the mechanical or the physiological function as of prime importance. In the study of Alectoria, Bryopogon, Usnea, in fact of all typically fruticose thalli ( Sphaerophorus, podetia of Cladonia) we find that the mechanical adaptation is highly spec- ialized ; the physiological adaptations are, however, not corre- spondingly developed. In living organisms the physiological func- tion takes precedence over the mechanical function, which suggests the reason why the Collemaceae and Pannariaceae are here placed higher than the Parmeliaceae. Some of the general characters of the family are the following : The apothecia are discoid with thalloid exciple ; but in Urceolaria and Pcrtusaria they are more or less immersed in the thallus and can therefore not be said to have a true thalloid exciple ; the thallus is usually greenish in color, though there are marked exceptions, as in Alectoria and Bryopogon ; and most of the Evernias are tinged with yellow ; the spores are quite variable as to the number of septa but quite constant as to size and absence of color ; they are medium in size but vary greatly in form. Urceolaria is the only genus with multilocular dark spores. The evidence of the spore-characters is in favor of the theory that the spores degenerate as the lichen be- comes more highly specialized ; this is also well illustrated in the genus Parmelia. The higher forms are quite constantly sterile or with very few apothecia, while the lower are constantly apothecium- bearing ; it is evident in this genus that the occurrence of the soredia increases with the decrease of the apothecia. The symbiotic algae are typically Cystococcus hiimicola Nag. They seem to reach their maximum size in the fruticose forms as Evernia, Alectoria and Bryopogon ; their maximum increase in num- ber is reached in Parmelia and other foliose forms and in the cen- tric thallus-lobes of Cetraria. The fungal portion of the Parmeliaceae indicates a polyphyletic derivation from the Patellariaceae ; but which groups of the Patellar- iaceae represent the ancestral forms from which the various lichen genera were derived is not definitely known. The spermagonia are quite numerous in some of the genera, particularly in Parmelia and Cetraria, usually occurring near the margin or younger portion of the thallus ; they frequently occur near the base of apothecia, but I have not found such occurrence to be constant. Sometimes the sper- magonia are wholly or almost wholly wanting. i . -7 3- 4- Urceolaria. Hacmatomma . Lecanora. Acarospora, 5. Speerschneidera* 6. Parmelia. KEY TO THE GENERA. Thallus crustaceous, areolate, to thickly warty, and minutely foliose. Spores multiiocular, dark. Spores 4-6-septate, acicular, colorless. Spores simple, colorless. Spores very minute, numerous. Thallus foliose, lobed or branching. Spores two-celled, colorless. Spore simple, colorless. Thallus fruticose. Lobes of thallus distinctly flattened. Spores simple, colorless. Thallus-lobes much flattened ; structure centric. 7. Cetraria. Thallus-lobes less flattened ; structure radial. 8. Evernia. Spores two-celled, colorless. 9. Ramalina. Lobes of thallus cylindrical, filamentous, radial in structure. Central hyphal bundle wanting. Spore-sacs with 24 spores; exosporium thick. 10. Alectoria. Spore-sacs with S spores ; exosporium normal. 11. Bryopogon. Central hyphal bundle present. 12. Usnea. i. URCEOLARIA Ach. Lich. Univ. 74. 1810. There is some hesitation about placing this group with the Parme- liaceae because of the immersed apothecia. At first it may seem that the prevailing characters point toward the Verrucariaceae,but on closer examination it is, however, found that the apothecia are not globose and that the paraphyses are not gelatinous. The thallus is crustaceous, usually quite thick, areolate, the areoles becoming distinctly convex, or warty in some species ; there is a semicortical upper layer, followed by the algal layer ; the medullary layer is well developed and forms the greater thickness of the thallus ; there is no evidence of lower cortical tissue. The rhizoidal hyphae l62 are numerous and differ little from the medullary hyphae or not at all. The prevailing color of the upper surface is gray, the medullary layer is white, as is also the lower surface. The algae, which are doubtless Cystococcus humicola, often occur in clusters of from four to as many as twelve, enclosed by a common membrane, but solitary forms are also common, in which respect they differ from the majority of Cystococci occurring in lichens. The apothecia are quite small and occur immersed in the thallus ; there is usually one in each areole ; rarely two or three, the disk is markedly concave, the excipular margin never extending above the surface of the thallus; sometimes the excipular margin is con- stricted, thus forming a more or less complete perithecium, which is dark, and the hypothecium is also more or less dark colored, but never distinctly black. The paraphyses are rather long and slender and somewhat granular. The spore-sacs are cylindrical, with the spores usually in a single row. The spores remain colorless until they are fully formed ; in fact the immature colorless spores are larger that the mature dark colored ones. The cause of this secondary reduction in size is not ex- / plained ; it may be a degenerative process, since the oldest and darkest spores are more or less structureless. Most of the representatives of the genus are northern in their dis- tribution. The majority occur upon rocks ; a few upon the soil. PLATE 39. URCEOLARIA SCRUPOSA (L.) Nyl. 1. Natural size. 2. Apothecium and portion of thallus magnified. 3. Section of apothecium. 4. Section of thallus. 5. Paraphyses and spore-sac. 6. Spores, a, colorless immature spore; b, mature spore. 7. Algae. 2. HAEMATOMMA Mass. Mem. Lich. 32. 1853. This group is usually combined with Lecanora ; but it has, however, strongly marked spore-characters, which have led me to maintain the genus. There is no doubt that it is closely related to Lecanora^ but it is rather difficult to decide whether it is phylogenetic- 1 63 ally higher or lower. The thallus seems to be somewhat more highly developed in Haemdtomma^ while the thalloid exciple is considerably higher in its development in Lecanora. This, however, only applies to the Hacmatommas and Lecanoras of the territory, some of the European Lecanoras having well-developed foliose thalli and are, therefore, undoubtedly much above the highest Hacmatommas. The apothecial, as well as the spore characters, point to close rela- tionship with Lecanora and Parmclia. The thallus is usually regarded as crustaceous. A more or less well-developed upper cortical layer is present in most species ; in the lower forms it is scarcely noticeable, consisting of agglutinate hyphae intermingled with the remnants of dead algae. The algae are quite large, considerably larger than the normal or the majority of other lichen Cystococci. Endotrophic haustoria are quite numerous. The medullary layer is well developed, consisting of much branched hyphae, terminating below in the numerous rhizoidal threads. In H. ventosa the thallus is very thick, warty and areo- late ; in the other species, it is comparatively thin. Soredia are nu- merous in most species, but they do not occur in clusters, being rather evenly scattered over the entire upper surface of the thallus. The color of the thallus is grey, tinged with green, or sometimes yel- lowish. \ The apothecia are medium to sometimes quite large, sessile, or partially adnate to the upper surface of the thallus ; they are usually disk-shaped, sometimes irregular in outline, or several disks agglutinate {H. ventosa) ; the disk may be flattened, somewhat con- cave or convex ; the thalloid exciple rarely extends beyond the disk; the outer layer of the thalloid exciple is semicortical, consisting of short hyphal branches placed vertically to the surface and parallel to each other ; this layer is considerably thicker than the upper cortical layer of the thallus, with which it is continuous. The excipular algae are few in number and occur only near the cor- tical layer. The hypothecium is colorless and not cortical, nor is it possible to distinguish more than one layer. The paraphyses are quite slender, sometimes branching ; the epithecium and the upper ends of the paraphyses are usually reddish brown in color. The spores are long, acicular, pointed at one end, indistinctly 4-6-septate,. curved, undulate or spiral, colorless ; they are so characteristic that it is almost impossible to confound them with any others ; they resemble most nearly those of Bacidia. 164 The species occur upon rocks, tree-trunks, earth, logs, etc. As to their distribution they seem to be most common in northern latitudes and in mountainous districts. PLATE 40. HAEMATOMMA VENTOSA (L.) Stein. 1 . Natural size. 2. Section of apothecium. 3. Section of thallus. a, upper cortical layer; b, algal layer; c, medullary layer. 4. Paraphyses and spore-sac. 5. Spores. 6. Algae. 3. LECANORA Ach. Lich. Univ., 344. 1810. The thjallus varies from distinctly crustaceous to markedly foliose ; in the majority of species occurring in the territory it is crustaceous, varying from thin, to quite thick and, as in L, tartarea, closely re- sembling the thallus of Haematomma ventosa. In the higher crustace- ous forms and the foliose forms the upper cortical layer is well devel- oped. ( In the foliose forms (Z. rubina) there is also a well developed lower cortical layer ; the foliose forms also show a decided fruticose tendency as is seen from the ascending lobes and decidedly centric structure (two algal layers). The medullary layer is well developed in the higher crustaceous and foliose forms. The lower surface of the typically foliose thalli bear few or no rhizoids ; they are attached by an umbilicus, as in Umbilicaria and Gyrophora. Apothecia are usually quite numerous, medium to large, disk-like, sessile with the thalloid exciple extending somewhat above the disk. The margin of the exciple may be entire or rugose and more or less folded. The thecium varies in color from brown to nearly black. The paraphyses are simple, and rather thick. The hypothecium is colorless. The spores are simple, colorless, elliptical ; their form as well as size is somewhat variable ; in one species (L, Sambuci) they are numerous, there being 12-32 in each spore-sac. The algae are in all cases Cystococcus humicola. In the older portions of the foliose Lecanoras the algae begin to disappear so that none can ever be found near the umbilicus ; they seem to be- come quite large, though not very numerous ; there is no explanation advanced for this increase in size ; it is perhaps due to excessive nutrition ; otherwise they seem normal. The majority of the representatives of this genus occur in the temperate and north temperate zones, most frequently upon rocks and trees. PL ATE 41. LECANORA HAGEXI Ach. 1 . Natural size. 2. Magnified. 3. Section of apothecium. 4. Section of thallus. t;. Paraphyses and spore-sac. 6. Spores. 7. Algae. 4. ACAROSPORA Mass. Mem. Lich. 27. 1853. Several authors have combined this genus with Lecanora, though 110 logical reason can be assigned for such a procedure, it having few, if any characters in common with that genus. The thallus is almost wholly wanting in the lower forms ; in the higher forms (A. chlorop/iana] it becomes almost distinctly foliose, and lobed, particularly near the margin. In many respects the thal- lus, as well as apothecia, resemble those of Haematomma. The fol- lowing are the structural characters of the thallus : In most forms, even the lower, there is a decided tendency toward a cortical structure ; there is a well defined upper layer of cortical cells extending verti- cally, which varies in thickness and also somewhat in structure ; in all species the outermost cell-layers of the cortical tissue, above and below, are lined with acid crystals to which the characteristic color of the thallus is due, this color being dark in the lower forms and dis- tinctly yellow in the higher. Upon these color-differences sub-genera might be based, but it is, however, not probable that there are sufficient differences to separate them as genera. The hyphal tissue in the algal layer is also more or less cortical. The algae are Plcurococcns vulgaris and tend to arrange themselves in vertical rows parallel to the hyphal cells. In the higher species there is a distinct lower cortical layer which resembles the upper cortical layer, though it is thinner ; in the lower forms the semicortical medullary tissue gradually merges into the rigid rhizoidal hyphae. The apothecia are quite variable in size and form, and in all 1 66 species are more or less immersed in the thallus. A distinct thalloid exciple exists only in the higher forms. The disk varies from orbicu- lar to irregularly lobate and somewhat folded or crenate ; it is usually flattened, more rarely convex, or its margin slightly raised. The epithecium and upper ends of the simple paraphyses are of the same color as the thallus, that is either dark or yellow. The spore-sacs are long-cylindrical and contain numerous (several hundred, or more) minute, colorless spores. The Acarosporas are quite generally distributed, the majority perhaps occurring in the temperate zones ; they grow mostly upon rocks and sandy soil. PLATE 42. AcAROSPORA. 1. Natural size. 2. Single apothecium and fragment of thallus magnified. 3. Section of apothecium. 4. vSection of thallus. 5. Paraphyses and spore-sac. 6. Spores. 7. Algae, a, as they occur in the thallus; b, normal forms occurring upon the thallus. 5. SPEERSCHNEIDERA Trev. ; Tuck. Gen. Lich. 17. 1872. This is a somewhat doubtful and little-known genus, so far repre- sented by only one species, S. cuploca. This lichen has certain characters which indicate that it is closely allied to Parmelia, but some authors are inclined to consider it more closely related to Physcia. Many of its characters point to such a double relationship, but, owing to the incongruity of the spore characters, it cannot be included in the Physciaceae. The thallus is foliose, with a slight fruticose tendency. It is uniformly and frequently dichotomously branched ; the lobes are narrow, linear and of uniform width throughout. The appearance of the thallus is so characteristic that it cannot readily be mistaken ; its color is light grey above and below ; the lobes are more or less curved upward, so that they only come in contact with the substra- tum at certain areas, at which the rhizoids occur. Upon microscopical examination of the thallus it is found that the upper and lower cortical layers are enormously developed, while the 167 medullary layer is much reduced. This is no doubt for the purpose of supplying the necessary mechanical support to the slender branches. The algae (Cystococcus humtcola) are quite numerous and rather small. The air enters the thallus at the sides, where the cor- tical tissue is very thin and is traversed by breathing canals. The apothecia are of medium size, sessile upon the upper surface of the thallus near the middle, hence the older portions ; the thalloid exciple scarcely reaches above the flattened disk ; the epithecium is light brown and the hypothecium colorless, very thick, cortical in structure, and is divided into two layers ; in the upper the cells are elongated at right angles to the surface of the disk ; in the lower, which is by far the thicker, the cells are elongated vertically to this surface. The paraphyses are simple and colorless. The spores are rather small, elliptical, colorless and distinctly two-celled ; the two cells are not, however, united by a plasmic thread, which excludes the genus from the Physciaceae. 5. euploca seems to be southern and western in its distribution, and is certainly very rare in the eastern United States. It occurs upon rocks. The specimens which came to my notice were associated with a species of Collcina. PLATE 43. SPEERSCHNEIDERA EUPLOCA (Tuck.) Trev. 1. Thallus natural size, a, apothecia. 2. Portion of thallus magnified. 3. Section of apothecium. 4. Section of thallus. c;. Paraphysis and spore-sac. 6. Spores. . Alae. 6. PARMELIA Ach. Lich. Univ. 89. 1810. It is highly probable that this group is phylogenetically derived from Lccaiiora, as there is certainly a close similarity between the higher Lecanoras and lower Parmclias. The thallus in this genus is foliose and shows a distinct dorsi- ventral structure. There is no indication of any fruticose tendency. In the majority of representatives dichotomous branching of the '3 i68 thallus is very marked (ex. P. centrifuga)^ in others (P. pcrlata, P. rudecta, P. latissiina) the lobes are very large and the dichoto- mous branching is not distinct, even approaching the entire form. Branching of the thallus is, however, characteristic of the genus, in this respect approaching the characters of the thallus in Phvscia^ but in general it is larger and shows higher specializations. The prevailing colors of the upper surface are greenish grey and greenish brown ; the lower surface is brown to black, usually bearing black rhizoids ; cilia sometimes occur along the margin. Soredia are also numerous on the upper surface of the thallus as well as along the margin. Sometimes numerous isidioid branches form nearest the middle of old thalli (especially in P. Borreri}, finally nothing remaining but a broken-down thallus bearing them in large numbers ; there is no doubt that these outgrowths serve as vegetative propagative organs, similar to the soredia. Both upper and lower cortical layers are present and are far more characteristically cortical than in any of the genera heretofore de- scribed. The cells are considerably shortened, with firm walls and rather large lumina. The algal layer is clearly defined. The medullary layer consists of a loose network of hyphae especially adapted to act as an aerating tissue. In some species (P. physodes} there is a highly specialized aerating tissue, consisting of an air- space just above the lower cortical layer. The apothecia vary from medium to very large ; they are sessile upon the upper surface of the thallus ; in general it may be stated that they are comparatively rare, especially in those forms with numerous soredia. The enormous development of the thalloid ex- ciple would make it seem probable that the prime significance of this structure is to aid in assimilation rather than in reproduction by spore formation ; each apothecium is in reality a secondary thal- lus having a combined radial and centric structure ; the epithe- cium is usually brown in color; the paraphyses are simple, very rarely branching, rather rigid with slight coloration at the upper ends ; the hypothecium is colorless and consists of two, usually more or less distinct layers, much as in S-peer Schneider a. The spores are simple, colorless, elliptical and quite constant in size and form ; they very frequently contain two oil-globules which to casual observance presents the appearance of a two-celled spore ; the spore-wall is perfectly colorless, quite thin and somewhat gelatinous. 169 Most of the representatives of this genus are fairly well charac- terized ; some critical study is, however, necessary to settle disputes in regard to many of the supposed " varieties " and " forms/' They are almost cosmopolitan in their distribution. The major- ity of species perhaps occur in the north temperate zone and live upon rocks and trees ; some species show a preference for the rougher barks, while others seem to have no choice. PLATE 44. PARMELIA PERLATA (L.) Ach. 1. Plant natural size. a, apothecia; b, lobe of thallus; c, soredial patches. 2. Section of apothecium. a, thecium ; b and c, the two layers of the hypothecium ; d, upper algal layer; e, colonies of algae scattered through the medullary layer; f, lower algal layer; g, lower cortical layer. 3. Section of thallus. 4. Paraphyses and spore-sac. 5. Spores. 6. Algae and haustoria. 7. CETRARIA Ach. Meth. Lich., 35. 1803. It is highly probable that this genus is phylogenetically derived from Parmelia, or it may bear the same relation to Lecanora that Thcloschistes does to Placodium ; that is, it may be looked upon as a fruticose branch derived from Lecanora or from Parmelia. The thallus-lobes are in all cases distinctly flattened. In the majority of species a centric structure is evident. In some cases the thallus lies quite flat and has a dorsiventral (bifacial) structure (C. juniper ina). The upper and lower cortical tissues are well devel- oped in both the centric and dorsiventral thalli ; in the former there are, however, two algal layers, while in the latter there is only one. Rhizoids are few or wanting, even in the horizontal thalli ; cilia are, however, frequently present (C. Islandica}. Many of the Cetrarias also contain a high per cent, of acid crystals (cetraric acid) deposited in and upon the hyphal cell-walls. The color of the thallus is quite variable; it may be brown (C. Islandica}, yellow or yellowish ( C. juniper ina^) , or almost coal-black ( C. Fahlunensis) . The apothecia are medium to large, sessile upon the upper sur- 170 face of the thallus, but in the majority of species are few or wanting. The disk is quite thin, margin somewhat torn or crenate, with a brown shining epithecium. The colorless hypothecium is divided into two well-marked more or less cortical layers. The paraphyses and spore-sacs are very short; the spores small, otherwise as in Par- melia ; the thecium of Cetraria resembles in all respects a reduced thecium of Parmelia. Soredia are not of such frequent and plentiful occurrence as in the preceding genus, which gives the thallus a somewhat smoother aspect. The thallus is also more brittle than in Parmelia, due to the greater development of the cortical layers, with a corresponding reduction of the medullary tissue. Most of the Cetrarias are northern ; they occur upon trees, soil and rocks of the higher altitudes and latitudes ; their distribution east and west seems to be about uniform. Most of the European forms occur in North America, but a few American species do not oc- cur in Europe. PLATE 45. CETRARIA JUNIPERINA (L.) Ach 1. Portion of the thallus natural size. 2. Section of apothecium. 3. Section of thallus. 4. Paraphyses and spore- sac. 5. Spores. 6. Algae. 8. EVERNIA Ach. Lich. Univ. 84. 1810. This genus has very likely been derived from Cetraria, We have here a markedly higher differentiation of the fruticose type ; the lobes have become much narrowed and in the majority of species are somewhat cylindrical and as a natural consequence show a radial arrangement of the tissue-elements. Branching of the thallus is often dichotomous with an acropetal decrease in the size of the lobes (.Zf. vnlpina and others). In the forms with a foliose tendency the lobes are more uniform in size (E. furfitracea) . The thallus never has that smooth shining appearance so common in Cetraria \ the outer surface appears as though covered with a very fine powder, due to the presence of a considerable de- posit of acid crystals (vulpinic acid) in and upon the cells of the outer semicortical layer. Soredia and isidioid branches are also frequently present, particularly in E. vulpina and E. fnrfuracca. The general structure of the thallus is as follows : The outer- most protective covering consists of an irregular network of hyphal cells which usually extend in a direction vertical to the outer surface ; the cell-walls are much gelatinized and lined with the above men- tioned deposit of acid crystals ; next follows the algal layer, which consists of Cystococcus hnniicola surrounded by the haustorial branches ; the algae, while few in number, are comparatively large, no doubt due to hypernutrition ; still more internally is found the medullary layer, usually associated with the special mechanical tis- sue ; the central area is either hollow, or filled with a loose hyphal tissue, the cells of which are more or less interwoven ; the mechan- ical tissue consists of hyphal bundles, the cells of which extend par- allel with the longitudinal axis of the thallus ; these bundles occur at regular intervals, forming a broken ring as seen in cross section ; sometimes this ring becomes more or less continuous, approaching in structure the hollow cylinder ; the mechanical tissue is especially adapted to resist both longitudinal (pulling) and lateral tensions. In some species this special mechanical tissue is wanting, the nec- essary mechanical tissue being supplied by the external cortical layer, while the entire interior is filled by the loose medullary tissue. The color of the thallus varies from greenish grey (E. furftir- acea) to brilliant yellow {E. vnlpina). Various fungal parasites are not uncommon upon the thallus of E. vnlpina and other species besides the spermagonia. The apothecia are usually terminal, or nearly so, large, the disk flattened with a more or less irregular outline; the margin (excipu- lar) often bears small thalloid branches ; the thecium is brown to dark brown. The paraphyses and spore-sacs are much as in Cetra- ria, likewise the spores. The hypothecium is colorless and usually consists of two distinct layers. The Evernias are typically western, most of them being limited to the Rocky mountains and Pacific coast region, where they occur upon trees and rocks. Only the sterile form of E. viilpina occurs in our territory. 172 PLATE 46. EVERNIA VULPIXA (L.) Ach. 1. Portion of thallus natural size. 2. Section of apothecium. a, thecium ; b and c, layers of the hypothecium ; d, algal layer; e r medullary tissue; e, mechanical tissue (hyphae) ; f, algal layer; g, protecting and mechanical tissue. 3. Radial transverse segment of thallus. a, outer covering corresponding to 2 g ; b, algal layer; c, medullary tissue; d, mechanical bundle cut transversely. 4. Paraphyses and spore-sac. 5. Spores. 9. RAMALINA Ach. Lich. Univ., 122. 1810. The phyletic relationship of this group is as yet undetermined. According to the spore-characters it is not derived from the Lccan- oras or Parmelias ; some authors regard it as closely related to ffo- cclla but it is morphologically quite different. The position of the genus is also somewhat uncertain. Micro- scopically considered, some of the forms (R. lincaris) are closely related to Usnca, and hence higher in position than Evcrnia. Its mechanical adaptations seem to indicate a lower position. The thallus, although fruticose in all the species, always remains flattened. In this genus we have the centric structure well charac- terized, with a radial tendency in some of the forms. The tissue- layers are quite constant throughout the genus and are essentially as follows : An outer layer, quite well developed, consisting of closely agglutinate hyphae extending parallel to the long axis of the thallus ; sometimes this tissue is interwoven with hyphae which extend for the most part radially horizontal ; this layer constitutes the protec- tive and mechanical tissue, differing quite materially from the outer layer in Evernia^ not only structurally, but also in the absence of the numerous acid crystals, which accounts for the comparative smooth- ness of the outer surface of the Rainalina thallus ; next follows the algal layer, in which the algae ( Cystococcus) occur in colonies, con- siderably larger than in Evcruia, otherwise much the same. The entire interior is occupied by a medullary tissue, consisting of loosely interwoven hyphae. It should, however, be remarked that occasion- ally there are a few scattered mechanical hyphae nearer the algal layer, which always extend in a longitudinal direction and which perhaps indicate the beginnings of mechanical bundles, similar to those in Evcrnia. The apothecia are small to medium and occur upon the upper sur- face of the thallus, along the margin or sometimes terminal ; th.e disk is flattened, convex or concave ; the excipular margin is entire, with- out cilia or thalloid fringes ; the hypothecium is colorless, consisting of much interwoven hyphae ; the two layers are rather indistinct. The paraphyses and spore-sacs are somewhat longer than in Ever- n ia and Cetraria. The thecium is usually light-brown or almost of the same color with the thallus. The spores are quite small, colorless, two-celled, elliptical, some- times somewhat curved. The representatives of this genus are southern and western in their distribution, occurring upon trees, rocks and sandy soil. Some of the tree forms attain an enormous size (/?. rcticulata^ R. linearis). Only comparatively few of the species occur in the territory, and of these R. calicaris is most frequent. PLATE 47. RAMALINA CALICARIS (L.) Fr. 1. Natural size. 2. Portion of thallus with apothecia. 3. Section of apothecium. 4. Longitudinal section of thallus. 5. Paraphyses and spore-sac. 6. Spores. 7. Algae. 10. ALECTORIA Ach. Lich. Univ. 120. 1810. This genus differs from the foregoing in its cylindrical radially built thallus, and its large spores with thick walls. The thallus is in all cases typically fruticose, never showing any foliose tendency. Branching is frequent and more or less distinctly dichotomous, with a gradual decrease in the size of the branches in an acropetal direction. At the points of branching the thallus is somewhat flattened for the purpose of supplying mechanical sup- port. In this group the mechanical (and protective) tissue is highly developed and specially adapted to resist lateral tensions, that is the mechanical tissue is arranged on the plan of a hollow cylinder, with a secondary adaptation to resist longitudinal tensions. The structure is comparatively simple and is essentially as follows : The outer mechanical tissue consists of a continuous layer of closely ag- glutinate hyphae extending in a longitudinal direction ; occasional branches are irregularly interwoven between these ; the cells of the hyphae situated toward the outer surface tend to become cortical in structure, and are often more or less colored, even becoming entirely black ; deposits of acid crystals are very plentiful through- out the entire hyphal structure ; this mechanical layer is quite thick, forming by far the greatest bulk of the substance ; the hyphal walls are very thick, gelatinous and become brittle when dry ; the algal layer which follows next is very deficient, consisting of rather minute, sparingly scattered clusters of algae suspended in a very loose and deficient medullary tissue. The interior is not hollow, though the hyphal tissue is sparingly developed. In A. sarmentosa the entire thallus bears oval soredial patches which apparantly serve a two-fold purpose, that of supplying a means of vegetative propagation and of admitting air into the in- terior. The color of the thallus varies from light to black. This varia- tion may be observed in the same plant at different periods of its de- velopment (A. sarmentosa}. The apothecia are few, of medium size, sessile upon the sides of the thallus. The hypothecium is colorless and consists of two dis- tinct layers of semicortical tissue ; sometimes a third intermediary layer is noticeable, forming a sort of transition layer between the upper and lower layers. The spore-sacs and simple paraphyses are of medium size and length. The spores are simple, rather large, usually two in each spore- sac. The spore-wall is divided into two distinct layers (exosporium and endosporium) which are of considerable thickness. The size and thickness of the wall at once distinguish these spores from those of related groups. They are usually described as colorless, but they become distinctly brown (smoky-brown) with age ; they do, however, remain colorless for a considerable time. The Alcctorias are confined to the arctic and subarctic zones, and to mountainous districts. Only a few species have so far been reported from our territory. They occur upon trees and rocks. PLATE 48. ALECTORIA SARMENTOSA Ach. 1. Portion of thallus natural size. 2. Section of apothecium. a, thecium ; b, c, d, three layers of the hypothecium ; cl, algal and medullary layer; f, protective layer. 3. Transverse radial section "of thallus. a, outer layer of longitudinal hyphiv ; b, algal layer: c, medullary tissue. 4. Paraphysis and spore-sac. <^. Spores. ii. BRYOPOGON Link. Handb. 3:164. 1833. This group is very closely related to Alcctoria in the structural arrangements of the thallus. The essential differences are found in the spore-characters. The thallus is in all cases typically fruticose and radial in struc- ture ; the outer mechanical and protective layer resembles that of Alcctoria in structure, but differs in being considerably thinner and in the meagre deposit of acid crystals. The cell-walls of the outer- most hyphae become dark to black in color ; the algae are distrib- iited as in Alectoria. The central medullary tissue of loosely inter- woven hyphae is traversed by a few mechanical bundles consisting of several agglutinate hyphae extending longitudinally ; these give additional support to resist longitudinal (pulling) tensions, which is highly essential, since the thalli in most species are very long and slender. The thalli are also somewhat flattened at the points of branching ; .soredia are common in some species; the prevailing color of the thallus is black, the long slender forms closely resembling coarse black hair ; branching is dichotomous and usually less frequent than in Alcctoria. The apothecia are very few and sessile upon the sides of the thal- lus. The spore-sacs and paraphyses are quite short, the hypothe- cium colorless and separable into two layers ; the disk is entire, somewhat irregular in outline ; the epithecium is of a lighter color than the thallus ; the spores are very small, colorless, simple, eight in each spore-sac. Owing to the fact that forms of Alectoria and Bry- -ofog'on are very frequently sterile, one is apt to confuse the genera ; 176 the structural differences of the thallus may therefore be of signifi- cance in separating them. The representatives of this genus are also mostly northern, oc- curring upon trees, rocks and fences. Most of the American species occur north and west of our territory. PLATE 49. BRYOPOGON FREMOXTII (Tuck.) 1. Portion of thallus natural size. 2. Portion of branch with apothecium magnified. 3. Section of apthecium. 4. Radial transverse section of thallus. a, outer protective and mechanical tissue of longitudinal hyphae ; b r medullarv tissue; c, mechanical bundles of longitudinal hyphae. 5. Paraphysis and spore-sac. 6. Spores. 12. USNEA Adans. F.\m. PL 2: 7. 1763. The Usncas are at once recognized by the well developed central mechanical bundle of hyphae ; they represent the acme of develop- ment in the fruticose thalli, both as to size and functional as well a& morphological specialization. The fruticose thallus is frequently branched, cylindrical, without being flattened at the points of branching. The branches usually form an angle approaching 90. A section reveals the following structures which are quite constant in all the representatives of the genus. An outer semicortical tissue, whose exact structure is rather difficult to make out, owing to the fact that cell-walls are quite indis- tinct ; it consists of agglutinate, somewhat cortical hyphal cells, which for the most part extend vertical to the surf ace ; it is practically impossible to determine the exact outline of the individual cells, and the difficulty is increased by the presence of acid crystals deposited upon the cell-walls, particularly toward the outer surface. This layer is followed by the algal layer, which consists of groups of algae, held together by the haustorial branches ; as in Alcctoria and Bryo- pogon the algae are comparatively few in number. The third layer constitutes the medullary tissue which consists of a loose network of */ hyphae. In the middle occurs the mechanical bundle of elongated hyphae, which is sometimes separated from the medullary layer by 177 a thin covering of much-branched rather small-celled hyphae, a tissue comparable to the endoderm or root-sheath of higher plants. The prevailing color of the thallus is light green to grayish green, sometimes changing to a reddish brown. In a few species, es- pecially U. barbata,\ho. main branches are covered by minute second- ary thalli which never bear apothecia ; these are for the purpose of increasing the assimilating surface and are functionally comparable to the leaves of higher plants. Soredia sometimes occur. As a rule the apothecia are few ; sometimes, however, individuals occur on which they are numerous ( U. barbatd} ; they are large and usually terminal. The disk is much flattened and thin, the margin bearing numerous small thalloid branches and sometimes somewhat torn ; the epithecium is of about the same color as the thallus ; thecium and hypothecium are colorless. The spores are simple, colorless, without any special characters. The Usncas are somewhat northern in their distribution ; U. bar- bata seems to be quite cosmopolitan ; they occur most frequently upon trees. PLATE 50. USNEA BARBATA (L.) Fr. 1. Small portion of thallus natural size. 2. Section of apothecium. 3. Radial longitudinal section of thallus. 4. Paraphyses and spore-sac. 5. Spores. Family 7. VERRUCARIACEAE. This family is quite definitely limited by its apothecial characters* The apothecium is more or less spherical and disk closed. In the lower forms ( Trypethelium, Pyrenula] the apothecia are partly or almost entirely hvpophloeodal. In the higher forms (Derma tocar- pon, Endocarpoii) the apothecia are immersed in the thallus. In the intermediate forms (Conotrema, Thclotrcnia, I'cn-itcariu} they are sessile upon the substratum and partially enclosed by the rudi- mentary thallus. In the non-foliose forms the thallus is mostly hv- pophloeodal. The paraphyses have a tendency to become gelatin- ized, especially in the higher forms ( Vcrnicaria^ Dcrniatocarpou, Endocarpon^). In the lower forms the paraphyses are long, slender and very soft or partially gelatinized. Older lichenologists have 1 7 8 even stated that some of the groups are devoid of paraphyses, which is, however, not the case, as closer examination will clearly show. Frequently the cell-walls of the paraphyses are so much gelatinized that their outline is not distinguishable ; in such cases it is usually possible to trace the direction of the cells by the granular plasmic contents. The great differences in the spore characters indicate a polyphy- letic origin. The fungal ancestors are doubtless to b'e found in the Pyrenomycetous groups Sphaeriaceae and Massariaceae. Two forms of algae predominate in this family. Chroolepns umbrina occurs in the genera from Trypethelmm to Vcrrucaria. Exceptionally Cystococcus humicola occurs in certain species, whether constantly or not I am at present unable to state. Pleurococcus vul- garis Menegh. occurs in Vei'ntcan'a, Dcnnatocarpon and Endocar- ^pon, where it seems to have become greatly modified in size and form (see Thecial Algae) ; it may, however, be possible that the alga is not Pleurococcus vulgaris, though the culture experiments of Stahl and others seem to prove that such is the case. It is also evident that many intermediate forms of this family are wanting, as, for instance, the connecting links between Verrucaria and Dermatocarpon and between Dermatocarpon and Endocarpon. In the former the intermediate forms between rudimentary crustaceous thallus and typical foliose thallus are wanting ; the difference be- tween the thallus of Dermatocarpon and that of Endocarpon is princi- pally that of size ; yet it seems evident that there must have been intermediate forms. KEY TO THE GENERA. Thallus crustaceous, often hypophloeodal. Spores 6-8 celled, colorless. i. Trypethelium. Spores 4-celled, brown. 2. Pyramid. Spores many-celled. 3. Conotrcma. Spores multilocular, colorless. Exosporium normal. 4. Thelotrema. Exosporium thick, gelatinous. 5. Gyrostomnm. Spores simple, colorless. Spores medium size. 6. T cmtcana. Spores very large. 7- Pertusaria. Thallus foliose. Spores multilocular, colorless. 8. Dermatocarpon. Spores simple, colorless. 9- Endocarpon. 179 i. TRYPETHELIUM Spreng. Kennt. d. Gewachse, 3: 350. 1804. This group takes the same position in the family that Mycocali- cinm does in the Caliciaceae. Some of the representatives are very doubtful lichens. In all of the species occurring in the territory the thallus is very rudimentary and entirely hypophloeodal. Careful sectioning and searching is necessary to detect any algae {Chroo- lepus umbrina), which occur in small clusters distributed about the base of the apothecia. The thallus can not be said to have any structure. There is simply a meagre hyphal network, continuous with the hyphae of the apothecium, which encloses the algae ; the filaments are slender, much branched and much contorted. Tucker- man and others describe the structure and macroscopic appearance of the thallus, which plainly shows that these authors had in mind the secondary color-changes in the substratum (bark), and not the thallus. The network of hyphae holding the algae occurs in the intercellular spaces of the bark. Neither of the symbionts ever penetrate the intact cork cells. The chemical changes causing the modifications in color of the bark have not been satisfactorily explained, but they are doubtless clue to acids secreted by the lichen. The apothecia are likewise entirely hypophloeodal. They occur in clusters of five to forty or even more. Each apothecium is, how- ever, entirely free from the neighboring ones and may be con- sidered as an individual belonging to the colony ; the outlines of these colonies are very irregular. The apothecium is globular in form and simple in structure. The dark to black hypothecium and proper exciple (perithecium) at first entirely enclose the thecium consisting of long, simple, slender, soft, more or less gelatinous paraphyses and the spore-sacs. As the apothecia grow they push up the superimposed layer of bark, producing a warty appearance of the surface. At maturity the excipular opening (ostiole) widens more and more ; finally a small pore-like opening is also formed in the layer of cork which allows the spores to escape. The paraphyses are highly hygroscopic and there is little doubt that they play an rrn- portant part in forcing up the layer of bark as well as in ejecting the spores. The covering of bark performs the function of the cor- tical layers in the higher lichens, that is, it forms a mechanical protection for the rudimentary thallus and the young growing apo- thecia. The corky covering immediately above the apothecia is of a dark rusty color, which gradually fades into the brownish or greenish color of the area over the thallus. i So The spores are normally colorless and eight-celled; in form they are spindle-shaped ; the plasmic portions are somewhat dia- mond-shaped, two obtuse angles closely approaching each other near a transverse septum. Much confusion exists in the limitation of this genus, some au- thors uniting Trypet he/in in and Pyrcnula in one, but it seems more consistent to keep them separate, since the spore-characters are very marked in both genera ; only a very few species occur in the terri- tory ; many of the forms described as TrypcthcJium belong to Pyren- u la. This genus is essentially southern ; the species occur upon trees, forming patches of considerable extent ; they are evidently closely related to some of the Sphaeriaceae ; the immediate fungal ancestors require further study. PLATE 5 1 . TRYPETHELIUM VIRENS Tuck. 1. Plants natural size, a, apothecial colony. 2. Semidiagramatic section through apothecia and substratum (mag- nified) a, apothecium developing below the substratum ; b, mature apothecium. 3. Section of apothecium. 4. Algae and hyphae of the very rudimentary thallus. =;. Paraphyses and spore-sac. 6. Spores. 2. PYRENULA Ach. Lich. Univ. 64. 1810. This genus closely resembles Trypethelium. The thallus and apothecia are hypophloeodal, the latter opening by a pore at ma- turity. In by far the greater number of species the thallus is quite as rudimentary as in the preceding genus, but in the higher forms the algal colonies ( Chroolepus) are quite apparent. The fungal ances- tors are evidently derived from the Sphaeriaceae. In fact, there is little doubt that many herbarium specimens catalogued as species of Pyrcnula are really fungi ; careful study of the specimen is neces- sarv to demonstrate the absence or presence of a thallus. In the majority of the representatives of the genus the apothecia are quite uniformly scattered ; in some they form colonies, as in Trypethelium. The superimposed corky layers of the substratum un- dergo a change in color, usually becoming grey, brown or dark brown, especially over the apothecia ; as in Trypethelmm, the thallus never becomes visible to the naked eye. The hypothecium and ex- ciple are quite constantly dark in color, consisting of a network of hyphae with dark cell-walls. The paraphyses are colorless, shorter than in Trvpcthclium, slender, with a decided tendency to become gelatinous or granular. The spore-sacs are quite slender and cylin- drical. The spores are usually more or less colored and constantly four- celled, otherwise resembling those of the preceding genus ; some forms seem to have spores devoid of color ; it may be, however, that these represent immature conditions. It should also be remark- ed that the young, undeveloped spores of TrypcthcUum are four to six-celled and also that all the younger spores of Pyrenula are co- lorless. The representatives of this genus are southern in their distribu- tion, though quite a number occur in our territory; they live upon the smoother barks where they form colonies of considerable size. In their habit they do not seem to differ materially from the closely related fungi (Sphaeriaceae). The symbiotic relationship is as yet in a rudimentary stage ; it would be interesting to determine if any of the Pyremilas can develop apothecia without the symbiotic algae. PLATE 52. PYRENULA NITIDA Ach. 1. Plants natural size, a, apothecia. 2. Single apothecium enlarged. 3. Section of apothecium. 4. Algae and hypae 5. Paraphyses and spore-sac. 6. Spores. 3. COXOTREMA Tuck. Syn. Lich. 186. 1848. The present position of the genus is very doubtful ; it has no characters which will give it a definite position in any of the nine families. Its apothecial characters place it nearest the Verrucaria- ceae ; the algae are, however, foreign to this family, for instead of Chroohpus they are Cystococcns. Exceptions of this kind occur elsewhere and therefore need not be considered of special impor- 182 tance. Some authors consider this group very closely related to Urceolaria ; the apothecial characters are, however, essentially different. The thallus is mostly epiphloeodal, particularly the older portion, crustaceous, thin, somewhat areolate ; the algae (Cystococcus humi- cola) very rarely occur below the surface of the substratum ; the thallus is attached to the substratum by comparatively long sparingly branched hyphae, which are easily torn loose by heavy winds and rains ; thus it happens that a considerable portion of the thallus is removed, bringing into greater prominence the more firmly attached globose apothecia. The apothecia are comparatively large, with a dark perithecium (hypothecium and proper exciple). The pore is quite large and be- gins to form early in the development of the apothecium. The apo- thecium is partly hypophloeodal ; very early in its development it breaks through the thin layer of superimposed cork-tissue. The paraphyses are comparatively long, slender, and sparingly branched near the apex ; they also show a decided tendency to be- come granular. The spore-sacs are quite large, cylindrical, each containing eight long colorless spores. It is impossible to confuse these spores with any others ; their extreme length, cylindrical form and numerous transverse septa are striking. Only one species has so far been reported, which seems to occur throughout the territory upon trees with comparatively smooth bark, such as Bctula and Acer. PLATE 53. COXOTREMA URCEOLATUM Tuck. 1. Natural size, a, apothecia. 2. Apothecium and fragment of thallus magnified. 3. Section of apothecium. 4. Section of thallus. 5. Paraphyses and spore-sac. 6. Spores, a, exosporium ; b, cell-lumina. 4. THELOTREMA Ach. Lich. Univ. 62. 1810. This is another group whose position in the system is not defi- nitely determined. Many of the characters met with in Conotrema also present themselves here. As in the former genus the thallus is quite rudimentary and partly hypophloeodal ; the algae, which are Chroolcpns iinibrina, are rather sparingly scattered about the apothecium and still less sparingly over the substratum or just beneath its surface. The hyphae are slender and much branched with very indistinct septa, penetrating deeply into the substratum. A hyphal branch enters into the inte- rior of a cork cell through the small pores and destroys parts of the cell-wall. The necessary mechanical protection to the thallus is supplied by the superficial cork layers of the substratum which are, however, broken here and there, thus allowing the thallus to spread over the surface. The hyphae are intimately united with the algae, but I have not been able to find any evidence that they pene- trate the algal cell-wall. The apothecia are very striking in appearance. They resemble in all respects a miniature volcanic crater {T. Icpadinnni) ; this character alone will enable one to recognize the genus ; they are usually very numerous, quite uniformly scattered over the thallus, and begin their development below the surface of the substratum, somewhat more superficially than in Pyrenula and Trypethelinm. The superimposed corky tissue is forced upward by the hygroscopic paraphyses. At an early period the spores begin to form, and at maturity are of considerable size. The exciple early in the history of the apothecial development separates from the rigid cone formed by the corky cells and the hyphae, and at maturity the hypothecial disk alone remains attached to the substratum ; the inflexibility of the cone and the alternate loss and gain of water of the thecium causes the separation of the greater portion of the perithecium. In the dry state the excipular fringe is plainly visible within the hollow of the cone ; on the absorption of moisture the excipular margin is forced against the sides of the cone, which projects above the disk and the excipular margin. The paraphyses are long, simple, slen- der and highly hygroscopic. The absence of color throughout the entire plant is noteworthy. The spores are large, multilocular, colorless, long spindle-shap- ed, with a rather thick gelatinous outer wall, which is more or less rugose, particularly in T. Icpadinnni. The above generic description is taken from T. lepadinnm, which is, perhaps, the only species occurring in the territory. The representatives of this genus have a decidedly southern range and grow upon the bark of various trees. 184 PLATE 54. THELOTREMA LEPADINUM Ach. 1. Natural size. 2. Two apothecia and fragment of thallus magnified, a, raised por- tion of thallus and substratum ; b, excipular fringe. 3. Section of apothecium. 4. Section of thallus. 5. Paraphyses and spore-sac. 6. Spores. 5. GYROSTOMUM Fr. PL Homon. 268. 1825. This genus is represented by one species (6r. scyphulifernni^), very simple in its structure, with well-marked and apparently con- stant characters. As in the preceding, the thallus and apothecia begin to de- velop below the surface of the substratum. The thallus, especially the algae, remain almost entirely hypophloeodal ; only a few algae ( Chroolepus nmbrina) exist, about which the slender hyphae form a close network ; there is no distinction into layers. The alga- bearing hyphal network extends between the separated cell-layers of the superficial cork, never penetrating the intact cells of the sub- stratum. The apothecia are quite small and semi-globose ; they begin their development below the surface of the substratum but soon break through, and about this time the apical pore begins to form ; it increases considerably in size, so that at maturity the apothecia are more or less urn-shaped. The hypothecium (perithecium) is black, likewise the epithecium. The paraphyses are simple and consider- ably gelatinized. The spores are multilocular, colorless, with a thick gelatinous exosporium. This lichen is of southern range, occurring upon various trees. PLATE 55. GYROSTOMUM SCYPHULIFERUM (Ach.) Fr. 1 . Natural size. 2. Portion magnified. 3. Section of apothecium. 4. Section of thallus. 5. Paraphyses and spore-sac. 6. Spores, a, young spores; b, later stage; c, mature spores. 7. Algae. 6. VERRUCARIA Wig. Prim. Fl. Hoi. 85. 1780. The representatives of this genus are unquestionably lichens ; the thallus, though crustaceous, is usually well developed ; there is, however, great confusion among authors as to tire limitations of the genus ; some include species with simple, two-celled, and many- celled to multilocular spores, both colorless and colored ; such variabil- ity in spore-characters associated with imperfect descriptions of the thallus (algae in particular) has caused a great difficulty in attempt- ing to determine supposed species of Verrucaria. In order to avoid this I have included under Verrucaria all lichens having the following characteristics. The thallus is crustaceous but shows a high degree of differenti- ation, as is indicated by the hvphal structure and its relation to the algae ; the hyphal tissue is semicortical in structure, consisting of closely united short cells, much like those of Acarospora ; the algae are Pleurocaccus vulgaris and have much the position and general arrangement in the thallus that they do in Endocarpon, to which genus Verrucaria is phylogenetically related. All the species examined contained Pleurococcus, though according to some au- thors Chroolepus umbrina is supposed to be typical of the genus. The apothecia are very small, almost entirely immersed in the thallus and substratum ; the perithecium (hypothecium and excipular margin) is quite dark in color due to a deposition of lichenic acid within and upon the hyphal cell-walls ; the paraphyses are compara- tively short and almost entirely gelatinized, so much so that some authors have cited the absence of paraphyses as a generic character ; close examination will demonstrate that this is not the case ; the spore-sacs are also much gelatinized and contain eight colorless sim- ple spores ; the spore-wall is thin ; the plasmic contents are granular and mixed with oil globules ; the whole presents the appearance of degenerative products. It is probable that these degenerative pro- cesses began with the fungal ancestor and not since lichen evolution ; it is, however, very likely that the symbiotic associations hasten the retrogressive changes as far as the apothecia and spores are con- cerned, since these are probably of little value in the processes of reproduction. The process of gelatinization begins quite early in the development of the apothecia and reaches its climax at an early period ; as a rule spores are few in number, while the apothecia oc- cur quite plentifully. i86 The Verrucarias as above limited seem to be quite cosmopolitan ; their _usual habitat is rock. The majority of so-called tree Verru- carias belong to other genera. PLATE 56. VERRUCARIA RUPESTRIS Schrad. 1. Natural size. 2. Apothecium and portion of thallus magnified. 3. Section of apothecium. 4. Section of thallus. 5. Galatinous paraphyses and spore-sac. 6. Spores, a, simple forms ; b, septate forms. 7. Hyphae and algae (Plcnrococciis vulgaris.} 7. PERTUSARIA DC. Fl. Franc. 2: 319. 1895. This group is usually placed near Urceolaria among the Parme- line lichens. There is, however, no reason why it should be given such a position ; the apothecial characters indicate the true relationship which is doubtless with the Verrucariaceae, close to Trypethclium and Pyrcmila. It is affirmed that some Pertusarias have apothecia resembling those of Lecanora, thus indicating a re- lationship to the Parmeliaceae ; such a resemblance seems to exist in the higher European forms of this genus. In all the species which came to my notice from our territory the apothecia are globose and immersed either in the substratum or in the thallus. The close relationship to TrypctheJium is very apparent from a critical study of P. pustuJata which is one of the lowest representatives of the genus ; in this species the thallus and apothecia are almost entirely hypophloeodal, the latter occurring in clusters forming warty ele- vations of the bark ; the apothecia open by very minute, almost imperceptible pores. In the majority of Pertusarias, however, the thallus inclusive of apothecia is epilithic or epiphloeodal. To these the following general description applies. The thallus is essentially crustaceous in its general appearance ; there is, however, a fairly well developed upper cortical layer ; the medullary tissue is also well developed ; no lower cortical layer is present, the entire thallus being closely adnate to the substratum by means of the numerous rhizoidal hyphae ; the upper surface is almost smooth, warty to papillose ; the thallus is quite variable in thickness and in the higher European forms the thallus becomes i8 7 more or less lobate. The color varies from light grey to greenish grey. The algae (Cystococcus hnmicola} are normal in appearance and do not seem to occur very plentifully. The apothecia are minute, globose and emersed in the warty elevations where they occur in colonies of five or six. Usually there is no perceptible pore-opening. In the higher forms the part of the thallus above the disk becomes more or less sunken, which to casual observance may give the appearance of an apothecial disk. In the majority of species the apothecium remains globose, being almost entirely enclosed by the usually colorless perithecium. The paraphyses are long, slender and more or less branched ; they are quite gelatinous and perfectly colorless. The spores are mostly very large, simple, colorless and usually one to three in each enormously developed spore-sac. The spore-wall is very thick, and in some species {P. comiunnis) the inner membrane is reticulately thickened. During germination hyphae begin to form at the thin areas. The plasmic contents are granular, sometimes bearing oil globules. The Pertusarias are also characterized by the numerous soralia which form upon the upper surface of the thallus, often in rounded masses, almost white in color, which may on casual observation be taken for apothecia ; these have been made the subject of special study by Darbishire. 1 Most of the representatives are cosmopolitan, occurring either upon rock or bark, but some also occur on mosses. PLATES 57 and 58. PERTUSARIA COMMUNIS DC. 1. Natural size. 2. Semidiagramatic section of apothecium. a, cortical layer; b, algal layer; d, apical pore through which the spores escape; c, medullary tissue ; e, thecium. 3. Section of apothecium. 4. Section of thallus. 5. Paraphyses and spore-sac, a, young spore-sac; b, later stage; c, mature spore-sac with three spores; d, spore-sac with apical seg- ment removed to allow the escape of the spores. 6. Mature spore, a, exosporium ; b, endosporium with reticular thick- enings as seen in optical section ; c, oil globules. 1 Die deutschen Pertusariaceen mit besonderer Beriicksichtigung ihrer Soredien- bildung. Engler's hot. Jahrb. 22 : 593-679. 1897. i88 8. DERMATOCARPON Eschw. Syst. Lich. 21. 1824. This genus, considered from a morphological standpoint, forms the connecting link between Verrucaria and Endocarpon. Phyloget- ically it does not seem to be derived from Verrucaria, as is indicated by a marked difference in the spore-characters. It is more than likely that these two genera are represented by two different fungal ancestors derived from some generic groups of the Sphaeriaceae. The description of this genus is based upon the characters occur- ring in the only well-known representative, namely, Dermatocarpon pusilhim, usually included in Endocarpon. In D. pusilhim the thallus, though very minute, is typically foli- ose. There is present an upper cortical layer, an algal layer, a medullary layer, but no true lower cortical layer, its place being taken by a layer consisting of a more dense network of hyphal tissue whose cell-walls are dark colored. The thallus, consisting of a single entire lobe, is held to the substratum by numerous rhizoids. As a rule, the thalli occur in clusters of five to twenty or more ; more rarely they occur isolated over the substratum. The algae (Pleuro- coccus vulgar is} are quite numerous and are arranged in a manner typical of this alga when occurring in the lichen-symbiosis, that is, they occur in vertical more or less irregular rows, closely sur- rounded by the semi-cortical hyphal tissue. The apothecia are very small, usually one on each thallus. They are immersed in the thallus opening by an irregular pore in its super- imposed tissues (algal layer and upper cortical layer). The hypothe- cium is dark and shows a tendency to become cortical. The para- physes are almost entirely gelatinized, as are also the spore-sacs. The genus is at once recognized by its spore-characters. In Verrucaria and the related group, Endocarpon, the spores are sim- ple, colorless and eight in each spore-sac, while in Dermatocarpon as represented by D. pusilhim there are from one to three colorless more or less ovoid multilocular spores. It may, however, be possible that there are species of Dermatocarpon with eight spores in each spore-sac. Further careful revision of Verrucaria, Staurothele, Dermatocarpon and Endocarpon will reveal whether this be so or not and also whether all species of Dermatocarpon have foliose thalli. Another character constantly met with in D. pusilhim is the pres- ence of thecial algae, which are ejected with the spores to which they adhere (see discussion of Thecial Algae). 189 D. pusiUnni is rather difficult to find because of its minuteness. It seems to be southern in its range and rather rare, occurring upon limestone. PLATE 59. DERMATOCARPOX PUSILLUM (Hedw.) 1. Natural size. 2. Four apothecium-bearing areoles of the thallus, magnified. 3. Section of the apothecium. 4. Section of the thallus. a, upper cortical layer ; b, algal layer ; c, medullary tissue ; d, dark colored lower limiting layer ; e, rhizoidal hyphae. ^. Paraphyses and spore-sac. 6. Spores with adhering algae (thecial algae) . 7. Algae of the thallus. 8. Thecial algae. 9. ENDOCARPON Hedwig, Stirp. Crypt. 2: 56. 1789. All the characters of this genus indicate its close relationship to Verrucaria, It seems still more closely related to Dcrmatocarpon, with the exception of the spore-characters, which are widely differ- ent, as already indicated ; the high development of the thallus in this genus determines the relatively high position of the family to which it belongs ; yet it may be questioned whether the Verrucariaceae should be placed higher than the Parmeliaceae. According to Reinke they take even a higher position than is here accorded them. The representatives of the genus are distinguished from the spe- cies of Verrucaria by the presence of a foliose thallus. In the lower Endocarpons {E. hepaticnuf) the thallus-lobes are quite small and closely adherent to the substratum, reminding one much of the thallus of Dermatocarpon pnsillnm ; in the intermediate forms {E. jluviatilc) the thallus-lobes are much larger and more or less ascend- ing, while in the highest forms (E. miniatwii), the lobes are very large and attached by an umbilicus, in fact closely resembling the thallus of some Umbilicaria or Gyrophora ; in consistency the thallus is rigid, being comparatively thick ; its color is quite variable ; grey and brown seem to be the predominating colors ; the lower surface being usually darker than the upper ; the dark lower surface of E. miniatum usually bears numerous wart- like elevations which upon examination prove to be the apothe- 190 cia of some parasitic fungus ; these apothecia take their origin just above the lower cortical layer ; as growth proceeds the cortical layer is pushed outward and finally ruptures, allowing the rather large black apothecia to protrude ; the spores of the parasite are ob- long, elliptical, colorless, two to four-celled. Most works on lichens refer to the apothecia as " warty outgrowths on the lower surface of the thallus." Further critical study is necessary to find the true morphological and physiological relationship of parasite to host ; in- cidentally it may be mentioned that careful sectioning does not reveal the structural union between host and parasite ; also that the same parasite seems to occur constantly, so that the question might arise which are the true apothecia of Endocarpon miniatum^ or whether both forms of apothecia belong to parasitic fungi. As already mentioned, the thallus is quite thick ; the upper and lower cortical layers are well developed ; the algae (Pleurococcus vulgaris} are situated in a semicortical tissue just below the upper cortical layer; the algal cells, which are larger and more irregular in shape than those in Dermatocarpon or Verrucaria, seem to occur within the hyphal cells. No haustoria occur, since none are needed. The products of assimilation pass through the algal and fungal cell- walls by direct osmosis. The medullary hyphae are much branched and comparatively short-celled, forming a rather close mesh-work. The apothecia are very numerous, small, and wholly immersed in the thallus ; they open by minute pores through which the spores escape. The paraphyses, spore-sacs and spores are in all respects similar to those of Verrucaria. The representatives of the genus seem to be more or less cosmopolitan, but E. miniatum is by far the most common in the territory ; they occur upon the soil, rocks and the bark of trees. PLATE 60. ENDOCARPON MINIATUM (L.) Schaer. 1. Thallus natural size. 2. Section of apothecium. 3. Section of thallus. 4. Spore-sac with spores. 5. Spores. 6. Algae enclosed by hyphal cells. Family S. COLLEMACEAE. This is without doubt the most clearly defined and natural lichen- family, its representatives being at once recognized by the presence of the alga Nostoc (except in the genus Hydrothyria) . The generic groups doubtless form a continuous series, having no close relation- ship to generic groups of any other family. According to the spore- characters they are perhaps most closely related to Psoroma and Pan- intn'a of the Pannariaceae. All of the members of the family are foliose, from the lowest to the highest ; the algae are numerous and usually quite uniformly distributed throughout the entire thickness of the thallus. For this O reason they were formerly designated as homoimerous lichens. The highly gelatinous condition of the thallus is due to the gelatinous covering of the algae and not to special gelatinization of the hyphal cell-walls. A Cortical layer is present in the forms above Collema, but none exists in that genus and it should therefore be compared with crustaceous lichens, at least when considered from the stand- point of comparative morphology. The principal reason why it differs essentially from the usual crustaceous lichens is due to the presence of the algal gelatine which gives the thallus a smooth ap- pearance and does not permit the formation of areoles. In some Collemas the thallus-lobes are very small and irregular in form. In all Collemaceae the thallus is considerably folded and rugose, prin- cipally due to inequalities in growth and to the interrelation of hyphae and algae. An area of the thallus bearing comparatively more algae than another area of the same thallus will expand more upon the absorption of moisture and cause the two areas to become disturbed relative to each other due to the force exerted. Subse- quent processes of growth cause these inequalities to become fixed. (Retardation and acceleration of growth due to pressure.) In general it may be stated that the morphology of the family in- dicates a comparatively low stage of development, but their physio- logical adaptation is highly developed if we consider them from the standpoint of their origin. The algal symbiont, which was ori- ginally a form of Nostoc closely related to N. commune, has under- gone great changes by way of adapting itself to new environments \ from being dependent upon a constant high degree of moisture it be- came enabled to exist and thrive upon tree-trunks, rocks, etc. ; it also became much reduced in thickness, forming a thin, evenly I 9 2 spreading layer upon the substratum ; its greatest adaptations are perhaps in relation to new habitats. Although the Collemaceae may perhaps not be able to resist such extremes of dryness and tempera- ture as most lichens, yet from the original habits of the predomina- ting symbiont (JVbs/oc) it is evident that the adaptive changes were even greater than in the majority of lichens. The changes are, of course, primarily due to the interaction of both symbionts since the establishment of the lichen phylogeny. The fungal symbiont is doubtless derived from some group of the Patellariaceae. Whether the family has been developed from one or from several fungal ancestors is questionable. From the study of the genera it seems that two ancestors are, perhaps, represented, one for Collema, Leptogimn and Mallotium, and one for Hydrothyria. In this family, also, the spores are retrogressive in their development, as is indicated by the absence of coloration and a tendency toward sim- pler forms, which is shown by the existence of non-septate and thin- walled spores. Soredia are comparatively few, due, no doubt, to the difficulty of enclosing the algal gelatine by the hyphae. Haustoria proper can not be said to exist in the family. The hyphae lie in con- tact with the algae and pass through the gelatinous substance, which position is sufficient to enable the hyphae to absorb the assimilated food-substances of the algae. As to the algal symbiont, it presents the general appearance of N. commune \ the threads are of about the same length ; the heterocysts are, perhaps, somewhat fewer in number ; several observers have cultivated it in various media, free from its fungal symbiont. The al- gal symbiont of Hydrothyria is Rivularia. As already stated, the members of the Collemaceae are foliose ; the color of the thallus and apothecia varies from greyish blue to dark blue. They are attached to the substratum by the gelatine and rhizoids, also by a central attachment, (umbilicus) as in Umbrticaria, and are quite common throughout the territory. KEY TO THE GENERA. Cortical layers wanting. i. Collema. Cortical layers present. Venation wanting. Long rhizoids not present. 2. Leptogimn. Long rhizoids present. 3. Mallotium. Venation on lower surface of thallus 4. Hydrothyria. i. COLLEMA Wigg. Prod. Fl. Hoist. 89. 1780. This genus is most typical of the family, and is readily distin- guished from the following ones by the absence of a cortical tissue. It is a large genus and further careful study may make a subdivision into two or more genera convenient ; the spore-characters seem to make such a division possible. The general characters not already mentioned in the description of the family are as follows : The thallus consists of numerous minute lobes in the lower forms, while in the higher the thallus-lobes are large and comparatively few ; its color varies from dark blue to nearly black ; in general the lower surface is somewhat lighter. The resemblance of this thallus to the thalli of other lichens is only apparent ; for instance, the thallus of Parmclia is also large and lobed, but the histological structure is wholly different, as a comparison will clearly show. The thallus of CoUemci is perhaps more nearly homoimerous than that of any other lichens, yet it is found that the algae (JVostoc) are more numerous near the upper surface. It is evident that the distri- bution of the algae in the thallus can be of little importance in clas- sification. Of still less consequence is the gelatinous nature of li- chens ; the algae which give the gelatinous consistency to the thallus are, however, of prime importance. Older lichenologists who intro- duced the separation into gelatinous and nongelatinous lichens did not recognize the nature of the algae and their relation to the thallus ; for that reason such distinctions are no longer of any value in classifi- cation. The apothecia are comparatively small or medium ; in some species they are very numerous, in others very few. A thalloid exciple is present which usually extends somewhat above the margin of the thecial disk. The general contour of the apothecium reminds one strongly of the apothecia of Parmclia and other related genera. The color of the disk is usually brown to very dark ; in form it may be slightly convex, flattened or concave ; the margin of the thalloid ex- ciple is frequently crenate. The colorless hypothecium consists of numerous short-celled hyphae. The cells are somewhat rounded and thin-walled ; the paraphytes are quite slender and unbranched. The spore-characters of this group are quite variable ; as a rule the spores are colorless, though they may become somewhat colored in some species ; they vary from simple (comparatively few) to multi- 1 94 loculaiv; the wall and septa are quite thin and translucent or trans- parent. In general the spores present degenerative characters, indicated by the thin wall, absence of color, and the apparent ten- dency toward simple nonseptate forms. Frequently the septa be- come indistinct. In the retrogressive transition-forms from multi- locular to transversely septate we find septa formed diagonally to the normal direction (longitudinal and transverse), which are very in- constant in their occurrence. As already stated elsewhere, the alga of Collcma has been culti- vated in artificial media. It would be interesting to demonstrate whether or not the Nostoc of any Collcma is capable of existing without its fungal symbiont and of leading the life of an indepen- dent Nostoc without the aid of culture media ; also, whether the fun- gal symbiont is capable of leading an independent existence. CoUemas are propagated vegetatively either by means of soredia or from portions of the thallus. The *thallus is also endowed with continuous marginal growth. Each lobe is capable of forming the center of a new individual ; it may or may not sever its connection with the mother plant. The species occur upon bark, mosses, rarely upon rocks, on soil, seldom partially or wholly submerged in water ; they are plentiful in the northern and north-temperate zones, both east and west. PLATE 61. COLLEMA PULPOSUM Ach. 1. Thallus natural size. 2. Lobe of thallus with apothecia, magnified. 3. Section of apothecium. 4. Section of thallus. 5. Paraphysis and spore-sac. 6. Spores. 7. Algae. 2. LEPTOGIUM Ach. ; S. F. Gray, Brit. PI. I : 400. 1821. In all its essential characters this genus closely resembles Collcma^ from which it is no doubt phylogenetically derived. As compared with Collcma, the thallus-lobes are larger and somewhat more rigid ; the rhizoids are comparatively few and slender. The essential dif- ference becomes apparent upon the examination of vertical sections ;. in Leptogium both the upper and lower cortical tissue is developed, though it is usually one cell-layer in thickness ; it is very charac- teristic, closely resembling in appearance the epidermal layer of a leaf ; in certain areas it consists of more than one cell-layer. As in Collema the algae are more numerous near the upper surface of the thallus. The structural differences are more marked in the apothecium ; the cortical layer of the thalloid exciple is well developed ; the hypo- theeium is quite thick and cortical in structure. The spores have the same general characters as in Collema ; they differ in that they are usually more pointed at the ends ; they lie parallel to each other diagonally across the spore-sac, which is also true of Collema spores as far as I have been able to observe. The algal characters are the same as in Collema. The habitat of the species and their distribution is the same as in that genus. PLATE 62. LEPTOGIUM TREMELLOIDES Fr. 1 . Thallus natural size. 2. Portion of thallus-lobe with apothecia, magnified. 3. Section of apothecium. 4. Section of thallus. 5. Paraphysis and spore-sac. 6- Spores. 7. Algae. 3. MALLOTIUM Ach. ; S. F. Gray, Brit. PI. 1:399. 1821. Vegetatively this group represents highly evolved forms ; it presents a much higher development than Leptogtum, as is indi- cated by an increase in the size of the thallus ; the cortical layers are also more developed. The algae (Nostoc) indicate a marked ten- dency to accumulate near the upper surface of the thallus. The es- sential character which distinguishes this genus from Lcptoginm is the presence of numerous long, comparatively rigid, gray rhizoids which extend in clusters from the lower surface of the thallus ; they partly serve as organs of adhesion and as special organs for absorb- ing moisture from the substratum and from the air ; incidentally they may also serve as organs of protection by keeping off crawling insects. The bitter lichenic acid which occurs abundantly in these 196 rhizoids also hinders the attacks of snails which feed upon lichens (Zukal). As a rule the few representatives which occur in the territory are sterile, while the soredia are very numerous ; soredioid or isidioid branches are sometimes common on the upper surface of the thallus {M. saturninum) ; in all probability propagation proceeds from so- redia. The apothecia present the general characteristics of those of Leptogium ; the hypothecium is, however, not cortical ; as far as I have been able to observe, it consists of two layers of hyphae the lower of which extends parallel to the surface of the disk. The habitat and distribution is the same as in Collema. PLATE 63. MALLOTIUM SATURNINUM (Dcks.). 1 . Thallus natural size. 2. Section of apothecium. 3. Section of thallus, with long rhizoids. 4. Paraphyses and spore-sac. 5. Spores. 4. HYDROTHYRIA Russ. Proc. Essex Inst. I : 188. 1856. The general macroscopic characters indicate such a close rela- tionship to the foregoing genera of the Collemaceae that one is sur- prised at the actual histological and physiological differences. In- stead of Nostoc we find that Rivularia is the symbiotic alga, but it may be possible that the original symbiont was Nostoc. The changes in the fungal portion, due to the symbiotic association, may have adapted it to become associated with Rivnlaria rather than Nostoc ; a similar condition of affairs is met with in Stictina and Sticta. The general morphological characters of the thallus very closely resemble those of Leptogium and Mallotium. The corti- cal layers are less clearly marked, in fact, the entire hyphal tissue is semicortical ; the outer cortical tissue proper contains no algae ; its cells are thin-walled and quite irregular in size, and it usually con- sists of more than one layer of cells. The lobes of the thallus are quite large and, in color, thickness and consistency, remind one of Leptogium ; the lower surface is, however, distinctly marked with veins extending from the central point of attachment toward the per- iphery ; in appearance these strongly resemble the venation of a leaf 1 97 and they consist structurally of bundles of hyphae extending longi- tudinally with the long axis of the thallus-lobes just above the lower cortical layer. These are, doubtless, primarily a mechanical tissue adapted to resist longitudinal (pulling) tensions. The apothecia are comparatively few, scarcely medium in size, and closely resemble those of Leptogium. The spores are more elongated and are not multilocular. It seems probable that this is a further degenerative change in the Collemaceous spores. It may, however, be probable that Hydrothyria is represented by a different fungal ancestor than the preceding genera. Another marked peculiarity of Hydrothyria is its habitat. Nor- mally it occurs upon rocks in the bottom of clear running water, in which position it matures its spores. Further observations in re- gard to its life-history are necessary. Its distribution is perhaps much as the preceding genera. Only one species has so far been reported (H. venosa Russ.) It is highly probable that Hydrothyria is closely related to Pso- roma and Heppia. For the time being its present position seems to be most nearly in accordance with our knowledge of the subject. It is also interesting to note that spermagonia have never been observed on Hydrothyria, and this seems to be additional evidence that these structures can not be the male reproductive organs, since apothecia are formed without them ; they could not occur as para- sitic fungi on account of the submerged habit of the plant. PLATE 64. HYDROTHYRIA VENOSA Russ. 1. Thallus natural size. 2. Lobe of thallus showing venation on lower surface. 3. Section of apothecium. 4. Section of thallus; d, vein cut transversely. 5. Paraphysis and spore-sac. 6. Spores. 7. Algae. Family 9. PANNARIACEAE. The limitations of this family are at present uncertain ; cer- tain genera are included which no doubt belong to some other family ; , in particular, is out of place ; Solorina, Peltigera and Ne- 198 Chromium are usually classed under a distinct family-group {Pel ti- ger ei) ; they have, however, so many characters in common with Pannaria and Physina on the one hand and Stictina and Sticta on the other that it seems perfectly justifiable to include them in the family ; it is also very difficult to decide upon what characters to base further subdivisions. Upon careful consideration it becomes evident that the characters of the apothecia, of the thallus, or of the algae taken separately will not suffice to establish the family or fam- lies. For instance, Pannaria, Psoroma, Hcppia and Physina are closely related according to their spore-characters and the general features of the thallus and apothecium, but differ widely as to the al- gal symbionts. Lichina and Physma are closely related by their algae, but differ widely as to the general conformations of the thallus. Stictina and Sticta are unquestionably closely related, in fact they are quite frequently combined in one genus, yet the algal symbionts are constantly different ; from these varying characters it is evident that careful comparative study is necessary to find the true relation- ships of the genera belonging to the family ; it is also evident that constant family characters are not to be found or are at least very few; the algal characters are, perhaps, most reliable; with several exceptions the symbiotic algae belong to the Cyanophyceae, charac- terized by a blue-green color ; in the first five genera the thallus is fruticose (excepting Lecothecium) ; in the remaining genera the thallus is typically foliose and shows some high structural adapta- tions ; the apothecial characters differ considerably and likewise show structural adaptations indicating a higher specialization ; since these specializations are quite variable they will be discussed in the generic descriptions in so far as they have not already been described. The question may be raised why the fruticose types are considered lower in this family and higher in the Parmeliaceae. The fruticose types of the Pannariaceae are small and present a low organization as lichens, while just the reverse is true of the fruticose types of the Parmeliaceae. To solve the relationship of the fruticose to foliose thalli and their relative position in the scale of development as lichens it is necessary to consider the morphology of the algal as well as fungal ancestral forms in so far as that is possible. As already in- dicated, the morphology of the ancestral forms of the symbionts has a marked influence upon the development of the lichen. This is well illustrated in Ephcbe and Lichina \ both are fruticose lichens, though widely different in their general histology ; in the former the algal symbiont forms the general structure, in the latter the fungal symbi- ont gives form to the thallus. KEY TO THE GENERA. Symbiotic algae SirosipJion i . Symbiotic algae not SirosipJion. Thallus crustaceous, dark. 2. Thallus fruticose, minute. Cortical tissue wanting ; spores simple. Algae Rivularia. 3. Algae Gloeocapsa. 4. Cortical tissue present ; spores two-celled, col- Ephebe. Lecothecium. Lichina. Omphalaria. 5 . PolycJi idiu m , 6. 7- 8. orless. Thallus foliose. Spores simple, colorless. Algae bright green ( Cystococcas}. Algae blue-green (Scytonema}. Algae blue-green (Polycoccus}. Spores not simple. Lower cortical layer wanting. Spores 4 6-cellecl, colorless, acicular. 9. Spores 2 -celled, brown. 10. Lower cortical layer present. Spores 4-celled, elliptical, colorless, n. Nephromium. Spores 2-4-celled, colorless, acicular. Algae blue-gi een . 12. Algae bright green. 13. Psoroma, Hep pi a. Pannaria. Peltigera . Solorina. Stictina. Sticta. i. EPHEBE Fr. PI. Homon. 256. 1825. This genus, which is represented by two species, only one of which has came to my notice, stands without a parallel in the history of lichen-development. Its general structure and appearance is de- termined by the algal symbiont, which is SirosipJion pidvinatus ; it is therefore very small, dark in color and branching. The thallus consists of the alga mentioned, through the interior of which the hyphae extend. The hyphae, which are so few in number as not to materially modify the appearance and form of the alga, extend in a longitudinal direction between the algal cells, usually terminating at a short distance behind the apex ; it may happen that some of the 200 algal branches remain without hyphae. It must also be remembered that careful examination with the aid of a good microscope is abso- lutely necessary to determine whether the plant under consideration is Sh-ostp/wi^ puh'inatus or Ephcbc pnbescens. The hyphae are fur- thermore quite slender and devoid of any special characteristics of color and form. The difficulty is further increased by the fact that apothecia are very rare. So far I have been unable to detect any apothecia in the numerous specimens of E. pnbescens examined. Sperm agonia are, however, very frequently present ; these appear as minute glis- tening pustules on the sides of the thallus, finally opening on the ex- terior by a minute pore. This group of lichens is evidently low in the scale of development because there are practically no changes in structure or function as the result of the symbiotic association. The lichen occurs in the same position as the alga and, as already indicated, has practically under- gone no change in form. The apothecia are said to occur within the algal tissue in the older branches ; these apothecia-bearing branches are recognized by a knot- ted swollen appearance, and they remain covered by the algal tissue until maturity, when an opening is formed to allow the escape of spores. The Ephcbcs occur upon rock and soil in wet places or where there is running or dripping water ; their distribution seems to be through the temperate and tropical zones. PLATE 70. EPHEBE PUBESCENS Fr. 1. Natural size. 2. Branch of thallus magnified; a, apothecia ; b, spermagonia. 3. Section of thallus-branch and a spermagonium. 4. Section through a younger portion of a thallus-branch ; c, formation of a new branch. 5. Spore-sac with spores (after Crombie). 6. Spores (after Crombie). 7. Sterigmata. 8. Spermatia. 2. LECOTHECIUM Trev. ; Kbr. Syst. Lich. Ger., 398. 1855. The position of this genus is rather difficult to determine. The 2OI representatives which came to my notice have been included under Pannaria as P. microphylla, P. nigra and others. The algae and spore-characters at once indicate that these species can not be includ- ed in Pannaria nor are the genera even closely related. The thallus is crustaceous as to its macroscopical appearance. On making sections it is, however, found that a well-marked upper cortical layer is quite constantly present, which is dark in color, due to a deposit of coloring substance in the cell-walls. The algal layer is also well developed and consists of the alga Rivularia nitida with its usual gelatinous covering through which the hyphal cells extend. Haustoria proper are not present ; the medullary tissue consists of rather short-celled, somewhat frequently branching hyphae which are continuous below with the dark rhizoidal hyphae. As indicated, the color of the thallus is dark ; this is true of all the species which came to my notice ; close examination with a hand lens will reveal the fact that the higher forms tend to become foliose, the thallus consisting of very minute scaly lobules, dark above as well as beneath ; these lobules are cortical above and below. The apothecia are of medium size, sessile or partially immersed in the thallus ; the disk is flattened, the epithecium brown to dark ; the hypothecium is usually of a brown coloration, sometimes blue-black ; the spores are few, variable in size and form, due to the fact that but few attain maturity. When mature they are oblong, colorless and four-celled ; it may, however, be possible that they become colored, though none such came to my notice. It need scarcely be stated that a true thalloid exciple is not present. The few representatives so far as known in this country occur in the north temperate zone and the arctic regions ; they seem to live normally upon rock or coarse sandy soil. PLATE 15, fig. 10. LECOTHECIUM NIGRUM (Huds.) Paraphyses and spore-sac with two-celled immature spores. 3. LICHINA Ag. Syn. Alg. Scancl. xii. 1817. This interesting group of lichens has been erroneously placed by various authors, owing to the fact that the histology was not suffi- ciently known. On account of the dark minute much-branched thallus it has been placed near Ephcbc ; again, because of the more or less 2O2 globose terminal apothecia it has been thought to be a near relative to Sphacro-phorus. Both conjectures are wide of the mark. The thallus is minute, dark in color, dichotomously branched and very rigid when dry. The greater bulk of the structure consists of the hvphae which extend longitudinally in the central portion of the thallus-branches, but describe a trajectory outward near the sides. The arrangement of the tissues is typically radial. There is no cortical tissue ; the hyphal projections and branches nearest the outer surface undergo a change whereby they serve as a protective cov- ering, more especially intended to prevent excessive evapora- tion of moisture. Next to this incipient tegument lies the algal layer ; the algae, which are Rivularia nitida, occur in chains lying parallel with the curved or diagonally inclined hyphae ; it was impos- sible to observe whether they extend beyond the surface or not, al- though this is affirmed by some authors. The hyphae do not form haustoria about the algae ; they simply extend through the gelatin- ous covering or lie in contact with them. There are no algae in the central hyphal portion of the thallus, nor do they extend quite to the apex. The apothecia are small, globose and terminal, appearing as small nodular enlargements on the ends of the branches. At first the apothecium is entirely enclosed by the terminal portion of the thal- lus, but finally an apical pore is formed which may increase to a con- siderable size. The epithecium is dark, of about the same color as the thallus. The paraphyses are long and slender, the spore-sacs cylindrical, with eight colorless simple elliptical spores in one row. The hypothecium is colorless and consists of a hyphal network. Only a few species are known, which grow upon rocks in moist places ; they seems to occur in the temperate and tropical zones as well as in the far north. PLATE 66. LlCHINA CONFINIS (Mliell.) Ag. 1. Natural size. 2. Terminal portion of thallus with apothecia, magnified. 3. Section of apothecium. 4. Section of thallus. 5. Paraphyses and spore-sac. 6. Spores. 7. Algae. 203 4. OMPHALARIA Dur. et Mont., Orb. Diet. 7: 351. 1849. Considerable uncertainty exists as to the limitations of this genus, caused by the variability of the apothecial and spore-characters, and to a lesser degree by the changes in the algal symbiont. In this group the thallus has a decided fruitcose tendency. The lobes become broad and irregularly branched in the higher forms, closely resembling, in external appearances, some of the lower Colle- mas. In the lower forms the thallus is small, sparingly branched, with short nearly cylindrical lobes ; these, with their terminal, nearly J J / globose apothecia, closely resemble Lichina, from which this group is probably phylogenetically derived. There is no cortical tissue, not even in the highest forms ; the outer thin conglomerate layer consists of shriveled hyphae and dead algal cells, similar to that in Lichina ; this is followed by the algal layer, which consists of hyphal branches, much interwoven and for the most part extending vertically to the outer surface ; the individ- ual algal cells closely resemble those of Lichina, so that superficial examination is apt to lead to mistaken conclusions. In Ri-cnJaria the entire algal chain is enclosed by the gelatinous layer. In the algae of Omphalarta each cell is enclosed by a gelatinous layer. From this it is evident that the algae are not Rivularia nit i da, but some species of Gloeocapsa, perhaps G. polydermatica, though much larger than the form occurring in Baeomyces roseus (hypernutri- tion). Sometimes it also happens that Nostoc occurs in the same thallus with Gloeocapsa. The central portion of the thallus, especially in lower forms, is occupied by the hyphal bundle, which is, however, not sharply demarcated from the algal layer. The hyphal branches extend longitudinally, giving off numerous lateral branches. The color of the thallus is very dark, in fact of about the same color (and con- sistency) as that of the CoUcmas. The apothecia are rarely numerous, terminal, globose, often wholly wanting ; at the beginning soon becoming more or less cup- shaped. They resemble very closely the apothecia of Lichina. Sometimes the hypothecium as well as the greater portion of the thecium is dark in color; again these structures appear colorless. The thecium and upper ends of the paraphyses are always dark in color. The spores also seem to be variable ; in the ma- jority of species they seem to be simple, colorless, and elliptical ; 204 again they appear larger, colorless, three to five-septate with thin septa and spore- wall. It is likely that further studies of the group will separate it into several genera ; at present I have retained them in the one genus, since only a few representatives occur in the terri- tory. Even if all the undoubted and doubtful Omphalarias are grouped together they do not form a large genus. The difficulty of studying the group is increased since the higher Omphalarias are frequently or quite constantly sterile. The species occur in the temperate and arctic zones ; they grow upon rocks in much the same localities as the Lichinas. PLATE 67. OMPHALARIA UMBETLA Tuck. 1. Natural size. 2. Terminal portion of thallus with apothecia, magnified. 3. Section of apothecium. 4. Longitudinal radial section of the thallus. 5. Spore-sac and paraphyses. 6. Spores. 7. Algae and haustoria. 8. Chain of Nostoc. 5. POLYCHIDIUM Ach. ; S. F. Gray, Brit. PI. I : 401. 1821. This interesting genus is represented by only one species, P. muscicolum, quite generally included under Leptogium, from which it is, however, essentially different ; the casual observer is at once struck by its resemblance to Ephebe pubescens ; its histology is, how- ever, quite unlike. The thallus is minute, typically fruticose, consisting of cylindri- cal branches of a dark color, in fact almost identical with Ephebe as far as external appearances are concerned ; usually, however, the lobes are shorter. Upon examining carefully prepared sections the following struc- ture is revealed : there is an outer tissue consisting of one layer, which is typically cortical, very closely resembling the epidermal layer of a leaf in higher plants ; the entire interior is occupied by a hyphal tissue and the algae ; the algae {Rivularia nit i da) are most numer- ous toward the outer surface ; the central tissue is, however, never totally devoid of algae ; since the thallus is typically fruticose the 205 structure is, of course, radial, and, as in Omphalarta, the algae seem to have undergone considerable change from the normal type. The apothecia are usually few in number, small, disk-like, ses- sile upon the basal portion of the thallus, never terminal. The hy- pothecium is colorless, well developed and typically cortical ; the thecium is colorless, the paraphyses rather thick, simple, colorless ; the epithecium is light brown ; the spores are comparatively large, oblong, elliptical or spindle-shaped, sometimes slightly curved, color- less, two-celled. It is evident that in its histology Polychidium is almost without a parallel. The algae and fruticose structure exclude it from Lepto- gium ; the structure and position of the apothecia exclude it from Lichina and Omphalaria ; its resemblance to Ephcbe is only appar- ent ; it is withal a difficult genus to classify, its present position being only tentative. As far as known, P, nuiscicohim is rather northern in its dis- tribution, occurring upon rocks and moss in moist places ; it has been frequently collected in the mountainous districts of Vermont. PLATE 68. POLYCHIDIUM MUSCICOLUM (Sw.) Stein. 1. Plant magnified. 2. Section through apothecium and thallus. 3. Paraphyses and spore-sac. 4. Spores. 5. Algal chain enclosed by the gelatinous covering. 6. PSOROMA Ach. ; Michx. Fl. Bor. Am. 2: 321. 1803. This group differs from the preceding in its algal characters ; here the algae are Cystococcus Jmmicola instead of Poly coccus punc- tiformis. There is no doubt that Psoroma is phylogenetically de- rived from Pannaria \ both genera are represented by the same fun- gal ancestors, as is indicated by the spores, and the apothecial char- acters. The reason why a given species of Pannaria should substi- tute Cystococcus for Polycoccus is not known ; theoretically the con- dition of affairs was perhaps as follows : the gradual changes wrought in the ancestral forms of Pannaria brunnea finally adapted it to enter into a more suitable symbiotic association with Cystococcus .hnmicola, and as a result Psoroma hypnorum came into existence ; 206 both lichens now continued to exist side by side, undergoing modifi- cations due to the change of environment. The reason for assuming that in Psoroma hypnorum we have a more suitable symbiotic re- lationship is the fact that this lichen has reached a somewhat higher perfection than Pannaria brunnea (compare plates 69 and 71). It may, however, be possible that the hyphae of one and the same lichen may enter into a symbiotic association with either Cystococcus or Polycoccus. Careful experimentation would decide whether this is possible ; some such experiments are highly important, as they would throw light on the permanency or variability of the algal sym- biont. Only two species of Psoroma have so far come to my notice from the territory ; both have been taken from Pannaria ; they are P. hyp- norum and P. stellata; they occur upon moss or upon the soil, and seem to be somewhat northern in their distribution. PLATE 69. PSOROMA HYPNORUM (Kbr.) Hoffm. 1. Natural size. 2. Section of apothecium. 3. Section of thallus. 4. Paraphyses and spore-sac. 5. Spores. 7. HEPPIA Naeg. ; Mass. Geneac. Lich. 8. 1854. This is a well characterized genus represented by only a few species ; or it may be that there is in reality only one species. H. Des-preuxii) which is the only species so far reported from America,, is, in all respects, identical with the European H. urceolata and H. adglutinata. The following generical characters are, therefore, based upon the study of H. Dcspreuxii. The thallus is of medium size, typically foliose, but closely ad- nate to the substratum by means of numerous rhizoids ; it is dis- tinctly lobate at the margin ; the structure of the thallus is peculiar, being almost entirely cortical throughout, the cells extending verti- cally ; there is a thin layer above and below in which the cells are not elongated vertically, and these layers seem to be identical with the cortical layers of other foliose lichens ; there is no medullary tis- sue proper. Almost the entire space between the thin cortical layers 207 is occupied by the alga-bearing tissue ; the alga in this case is a species of Scytonema ; its branching, and relative position of the cells are difficult to observe even in the most careful sectioning ; they seem to have undergone considerable modification in structure since their association as lichens, and for this reason it is also difficult to de- termine the species. In the thallus the algal chains extend vertically parallel with the hyphal cells ; at certain points they approach very near the upper surface. The color of the thallus is brown above as well as below, becoming quite dark with age. The apothecia are comparatively large, situated in depressions of the thallus. The apothecium itself is disk-like, but not raised above the general surface of the thallus ; there is, therefore, no noticeable line of demarcation between the thallus and apothecium ; one passes into the other without any structural differences observable by the nak- ed eye. The hypothecium is colorless and cortical in structure. The thecium is brown, much as in Psoroma, The paraphyses and spore- sacs are rather long and colorless ; the spores are colorless, simple, thin-walled with somewhat granular contents and quite variable in size and form. H. Dcspreiixii seems to be southern in its distribution, though it extends well into the territory. It occurs upon the soil, somtimes upon coarse sand. PLATE 70. HEPPIA DESPREUXII (Mont.) Tuck. 1. Thallus natural size; a, apothecia. 2. Section of apothecium. 3. Section of thallus. 4. Paraphyses and spore-sac. 5. Spores. 6. Algae and hyphae. 8. PANNARIA Delis. ; Kbr. Syst. Lich. Ger. 105. 1855. This is another much confused genus, the confusion primarily caused by failure to distinguish or recognize the proper algae. The thallus is quite distinctly foliose in the majority of species, though the lobules are usually small. In the lower species the thallus presents a crustaceous appearance, but upon careful examina- tion it is found, however, that both upper and lower cortical layers 208 are present. The crustaceous appearance is frequently emphasized by the presence of numerous soredia or isidioid outgrowths from the upper surface. The upper cortical layer is well developed, the cells rather large, irregular in form and position. The algal layer is also well developed, the algae being in all cases colonies of Poly coccus punctifonm's of a bright blue-green color and enclosed by a common gelatinous cover- ing. The medullary layer consists of rather thick rigid branching hyphae, quite frequently becoming somewhat cortical throughout. The lower cortical layer is thinner than the upper and bears numer- ous long simple usually black rhizoids. The upper surface of the thallus is usually a reddish brown ; the lower surface is lighter in color. The apothecia are rather small, disk-like, sessile upon the thallus, the disk flattened with the thalloid exciple slightly raised. They are numerous in the lower forms, few or wanting in the higher species (P. lepidota) . The epithecium is reddish brown ; thecium and hy- pothecium colorless, though the latter may be more or less tinged with brown ; the spore-sacs are cylindrical with eight colorless simple spores with pointed ends ; the exosporium is gelatinous and usually of an irregular outline. I have excluded P. lanuglnosa from the genus (see Pseudo- lichenes) ; also P. inolybdea, which does not possess a single char- acter in common with the Pannarias proper. There are, no doubt, other so-called Pannarias which should also be excluded. As here limited, the genus seems to be southern, extending, how- ever, well into the north temperate zone, even into the arctic ; the species occur upon moss, soil, rocks and trees. P. brunnea and a few other species are frequently found spreading over Polychidium muscicolum when this lichen occurs on moss. Both lichens seem to thrive well, which makes it probable that we have here a form of mutualism. PLATE 71. PANNARIA LURIDA (Mont.). 1. Natural size; a, apothecia. 2. Section of apothecium. 3. Section of thallus. 4. Paraphysis and spore-sac. 209 5- Spores; a, gelatinous exosporium. 6. Algae ; a, impoverished chain from the upper portion of thnllus; b, normal free chain; c and d, colonies of algae enclosed by the common cov- ering or membrane. 9. PELTIGERA Willd. Fl. Berol. 347. 1787. Although the representatives of this genus are distinctly foliose, yet they have characters not occurring in the great majority of foli- ose lichens heretofore discussed. One of these characteristic fea- tures is the total absence of the lower cortical layer ; there is not even any indication of a line of demarcation between the medullary layer and the rhizoidal structure. The thallus itself is large, com- paratively thick and rigid, but not brittle, as in Collema; it is typic- ally dorsiventral in structure and lies flat upon the substratum, to which it is rather loosely attached ; it is simple, with marginal lobes upon which the apothecia are borne ; the color above is blue-green which changes to brown ; the lower surface is light brown. The structural features are clearly defined ; the upper cortical layer is well developed ; its surface is roughened by numerous short hyphae which are structurally and functionally comparable to certain trichomes of higher plants ; they also serve to retain the sore- dia of Peltigera and other lichens ( St ictinas) where these develop into warty structures {P. aphthosa}. These trichomatic hyphal cells dif- fer from the hyphae of the medullary layer in the greater thickness of their walls and the shortness of the cells. The cells of the cortical layer are closely united, the lumina large, the walls firm and non- gelatinous. The algal layer is well developed, indicating a high assimilative function; the algae are Poly coccus -punctiformis ; the colonies are small and the chains scarcely discernible ; the individual cells are considerably larger than the normal. The medullary layer consists of a rather loose network of hyphae as in the majority of lichens ; it usually contains a large quantity of air ; below the medullary layer is another hyphal layer in which the majority of the hyphae extend horizontally in the direction of growth ; the cells of this layer are larger and walls thicker than in the medul- lary layer ; it contains but little air, and it no doubt forms a me- chanical as well as a protective tissue. An additional mechanical support is furnished by the numerous hyphal bundles occurring 210 in association with the layer just described ; these consist of parallel hyphae extending in the direction of growth and are comparable to the "veins" in the lower surface of the thallus of Hydrothyria zr- nosa. The apothecia are large, orbicular and occur on the margin of the thallus-lobes. Thev are immersed in the thallus so that the */ large flat disk is scarcely raised above the surface. This is a mark- ed contrast to the apothecia of the Parmelias and the majority of fo- liose lichens, reminding one somewhat of the apothecia of Heppia. The epithecium "and upper ends of the paraphyses are brown; the hypothecium is colorless and non-cortical in structure, nor is it separ- able into layers. The paraphyses are colorless and simple. The spore-sacs are of medium size, cylindrical, with the upper portion of the cell-wall considerably gelatinized ; at the upper end occurs a projecting cone of firm lichen cellulose to which the ends of the spores adhere. The spores are acicular, colorless and three to five-septate, us- ually slightly curved. The range of the species is northern, though some of them ex- tend far south. A large per cent, of the known species occur in the territory, particularly in the mountainous regions ; they grow most commonly upon moss, but also upon soil, rocks and trees. PLATE 72. PELTIGERA CANINA (L.) Hoffin. 1. Plant natural size. 2. Section of apothecium. 3. Section of thallus. 4. Paraphysis and spore-sac. 5. Spores. 10. SOLORINA Ach. Lich. Univ. 27. 1810. This group, which is represented by only a few species, is very interesting from several standpoints. It resembles the preceding genus in the total absence of a lower cortical layer and in its apothe- cial characters, but in other respects it is markedly different. As a rule the thallus is considerably smaller than in Pcltigcra, but is, however, thicker, and shows higher structural differentiations, as we shall presently see ; it is loosely attached to the substratum 211 by means of long rhizoids ; the margin is lobed but not so dis- tinctly as in Pcltigcra. The color of the upper surface is brown ; the lower surface is a light brown (S. saccata), or nearly brick-red (,5". crocca). The upper cortical layer is smooth above, that is, no trichomatic hyphae are present. This layer is not of uniform thickness ; at certain elongated areas the algae extend almost to the surface, and at these areas the cortical tissue is deficient and the intercellular breathing pores are very numerous. In a vertical section the lower outline of the cortical layer presents a serrate appearance. The al- gal layer is well developed and is peculiar in that two species of al- gae are quite constantly present. The predominating species which occurs nearest the cortical layer is Dactylococcus infnsionum ; these algae are most numerous at the above mentioned thin areas. The second species, which is far less abundant, and which occurs just be- low the former, is, perhaps, a species of Polycoccus related to the one found in Pcltigcra ; it occurs in groups distributed through the medulla and never intermingles with the other form. It is also noticable that in those areas where Polycoccus is quite plentiful, D. infusionuni is deficient. It seems probable that this group of lichens is now in a transition stage ; that is, it may be assumed theoretically that the original alga was Polycoccus and that the phylogenetic modifications in the fun- gal symbiont are gradually adapting it to enter into a more suit- able symbiotic relationship with D. infusionuni : or it may be pos- sible that the lichen originally entered into a symbiotic association with two species of algae. The medullary layer very closely resembles that of Pelttgera; the lower hyphal layer is more highly developed ; the hyphal bundles are more numerous and well developed. The reddish color of the lower surface of the thallus is due to a deposit of acid crystals upon the cell-walls of the lower non-cortical limiting layer and the hyphal bundles. The general characters of the apothecia resemble those of Pclti- gera ; as a rule they are, however, not marginal but occur toward the middle of the thallus or its lobe ; In S. saccata they occur in depressions of the thallus, much as in Ifeppia. The epithecium is dark brown, but in all other respects the apothecial characters closely resemble those of Peltigera. The spore-characters are, however, 212 essentially different ; in Solorina the spores are elliptical, two-celled, and brown in color. Owing to these marked differences in the spores we can not assume that Solorina is derived from Peltigera or vice versa. The species are essentially northern in their habitat ; they occur upon moss, rock and soil. PLATE 73. SOLORIXA CROCEA (L.) Ach. 1. Portion of thallus, natural size. 2. Section of apothecium. 3. Section of thallus. 4. Spore-sac and paraphyses. 5. Spores. 6. Algae {Dactylococcus infusionum) . 7. Algae (Poly coccus). ii. NEPHROMIUM Ach. Lich. Univ. 101. 1810. The representatives of this genus are at once recognized by the fact that the apothecia occur on the lower surface of the thallus. The general appearance of the thallus reminds one of Solorina and Peltigera ; it is, however, somewhat more lobulate and more rolled in and folded ; the upper surface is sometimes rugose ; in thickness and consistency it closely resembles that of Peltigera. Upon microscopical examination we find a well developed upper cortical layer without trichomatic hyphae ; the algal layer is well de- fined ; in by far the majority of species the alga is Poly coccus -puncti- formis, thus indicating a relationship to Peltigera. Authors, how- ever, disagree as to the symbiotic alga ; some give Dactylococcns in- fusioninn. I find this alga only in N. arcticum, which should, there- fore, be excluded from Ncphromium and classified under the genus Nephroma; for the time being I have, however, refrained from reestablishing this genus. If, after a careful study of these groups, it is found that these algal differences apply to a number of species, it will no doubt be advisable to separate them. The medullary layer is well developed and closely similar to that of Peltigera there is a distinct lower cortical layer, from the lower surface of which the rhizoids extend. As a rule the lower cortical layer is much thinner than the upper part but essentially the same in structure. 213 The apothecia are borne on the margin of the lower surface of the lobes ; they are quite large, orbicular or transversely oval ; there is a line of demarcation between thallus and apothecium which consists of a slight ridge of semi-cortical tissue gradually merging into the lower cortical tissue and the thecium. Although the apothecia are developed on the lower surface of the thallus, the disk is turned up- ward 100 or more by a folding back of the lobe of the thallus ; this movement is slowly brought about by a more rapid development of the lower cortical tissue in the immediate vicinity of the apothecium. The general characters of epithecium, thecium and hypothecium are the same as in Pcltigcra. The spores are spindle-shaped, almost acicular in some species, tinged with a brown coloration and two to six-celled. The range and habitat of the Ncphromiums seems to be about the same as that of the Pcltigcras. PLATE 74. NEPHROMIUM LAEVIGATUM Ach. 1. Natural size; a, apothecia on upturned lobes of thallus. 2. Section of apothecium. 3. Section of thallus. 4. Paraphyses and spore-sac. 5. Spores. 6. Spores of Nephroma arcticum. 7. Algae (Dactylococcus infusionum) of N. arcticum. 8. Algae {Poly coccus punct if ormis) enclosed by hyphae. 9. Free cells of 8 at a, colony at b. 12. STICTINA Nyl. Flora, 43 : 65-66. 1860. Many authors combine this genus with Sticta, since the general structural characters are the same in both genera, but the constant algal differences make it more consistent to keep them separate. It is in all respects a condition similar to that of Psoroma and Panna- ria ; that is, Stictina represents the oldest type from which Sticta branched off by a process of special algal adaptation. The thallus is quite large, typically foliose, of medium thickness, not brittle ; lobation is usually quite distinct ; there is no marked tendency in the lobes to ascend ; they lie quite flat upon the sub- stratum to which they are rather loosely attached by means of long 2I 4 rhizoids ; the color of the upper surface is usually dark brown tinged with bluish-green ; frequently the margin is lined with yellowish so- redia ; the lower surface is either lighter or darker than the upper. The upper cortical layer is well developed and of quite uniform thickness ; the cells are rather small, the cell-walls are comparatively thick ; the uppermost layers are colored a dark brown, evidently a protection against excessive illumination ; the algae are Dactylococ- cus infusionum and in their arrangement in the thallus strongly re- mind one of Peltigera ; the medullary layer consists of the usual network of hyphae ; it presents a yellowish appearance owing to a deposit of yellow acid crystals upon the hyphae. It is this deposit of acid crystals which gives the yellowish color to the soredia and the cyphellae ; the lower cortical layer is much thinner than the upper and bears numerous long, usually colored, rhizoids below ; the lower portion of this layer is also colored ; this layer is also broken here and there by the cyphellae, both forms of which are represented. Stictinas occur only sterile within the territory. The descriptions of apothecia and spores are based upon the examination of South American specimens. Even in southern specimens apothecia are few ; they are rather small, disk-like, sessile upon the upper surface of the thallus. It is worthy of note that the thalloid exciple is very deficient for a lichen in which the thallus is evidently so highly organized. In most of the older apothecia the algae have entirely disappeared ; the excipular margin rarely extends above the surface of the disk ; otherwise it presents the distinctive tissues of the thalloid exciple ; that is cortical layer and medullary layer. In the younger apothecia the algal layer or layers are pres