Full text of "Lichens"
Cambridge Botanical Handbooks
Edited by A. C. SEWARD and A. G. TANSLEY
LICHENS
CAMBRIDGE UNIVERSITY PRESS
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LICHENS
BY
ANNIE LORRAIN SMITH, F.L.S.
ACTING ASSISTANT, BOTANICAL DEPARTMENT, BRITISH MUSEUM
CAMBRIDGE:
AT THE UNIVERSITY PRESS
1921
r r t\ ~J i
JuUl 1
IN «RBAT MfTAUE.
I O
PREFACE
THE publication of this volume has been delayed owing to war con-
ditions, but the delay is the less to be regretted in that it has allowed
the inclusion of recent work on the subject. Much of the subject-matter
is of common knowledge to lichenologists, but in the co-ordination and
arrangement of the facts the original papers are cited throughout. The
method has somewhat burdened the pages with citations, but it is hoped
that, as a book of reference, its value has been enhanced thereby. The
Glossary includes terms used in lichenology, or those with a special licheno-
logical meaning. The Bibliography refers only to works consulted in the
preparation of this volume. To save space, etc., the titles of books and papers
quoted in the text are generally translated and curtailed: full citations-will
be found in the Bibliography. Subject-matter has been omitted from the
index : references of importance will be found in the Table of Contents or
in the Glossary.
I would record my thanks to those who have generously helped me
during the preparation of the volume : to Lady Muriel Percy for taking
notes of spore production, and to Dr Cavers for the loan of reprints. Prof.
Potter and Dr Somerville Hastings placed at my disposal their photographs
of the living plants. Free use has been made of published text-figures
which are duly acknowledged.
I have throughout had the inestimable advantage of being able to consult
freely the library and herbarium of the British Museum, and have thus been
able to verify references to plants as well as to literature. A special debt
of gratitude is due to my colleagues Mr Gepp and Mr Ramsbottom for
their unfailing assistance and advice.
A. L. S.
LONDON,
February ) 1920
CONTENTS
PAGE
GLOSSARY xix
ERRATA xxii
INTRODUCTION xxiii
CHAPTER I
HISTORY OF LICHENOLOGY
A. INTRODUCTORY i
B. PERIOD I. PREVIOUS TO 1694 2
C. PERIOD II. 1694—1729 5
D. PERIOD III. 1729 — 1780 6
E. PERIOD IV. 1780—1803 ...... 9
F. PERIOD V. 1803—1846 ...... 10
G. PERIOD VI. 1846—1867 . '. ^15
H. PERIOD VII. 1867 AND AFTER '18
CHAPTER II
CONSTITUENTS OF THE LICHEN THALLUS
I. LICHEN GONIDIA
i. GONIDIA IN RELATION TO THE THALLUS
A. HISTORICAL ACCOUNT OF LICHEN GONIDIA . . 21
B. GONIDIA CONTRASTED WITH ALGAE 22
C. CULTUREEXPERIMENTSWITHTHELlCHENTHALLUS 24
D. THEORIES AS TO THE ORIGIN OF GONIDIA . . 25
E. MICROGONIDIA 26
F. COMPOSITE NATURE OF THALLUS .... 27
G. SYNTHETIC CULTURES 27
H. HYMENIAL GONIDIA 30
I. NATURE OF ASSOCIATION BETWEEN ALGA AND
FUNGUS 31
a. Consortium and symbiosis
b. Different forms of association
J. RECENT VIEWS ON SYMBIOSIS AND PARASITISM . 36
2. PHYSIOLOGY OF THE SYMBIONTS
A. NUTRITION OF LICHEN ALGAE 39
a. Character of algal cells
b. Supply of nitrogen
c. Effect on the alga
d. Supply of carbon
e. Nutrition within the symbiotic plant
/ Affinities of lichen gonidia
B. NUTRITION OF LICHEN FUNGI 44
C. SYMBIOSIS OF OTHER PLANTS . . . . . 45
viii CONTENTS
II. LICHEN HYPHAE
PAGE
A. ORIGIN OF HYPHAE . 46
B. DEVELOPMENT OF LICHENOID HYPHAE . . . 47
C. CULTURE OF HYPHAE WITHOUT GONIDIA . . 49
D. CONTINUITY OF PROTOPLASM IN HYPHAL CKLLS . 51
III. LICHEN ALGAE
A. TYPES OF ALGAE 51
a. Myxophyceae associated with Phycolichens
b. Chlorophyceae associated with Archilichens
B. CHANGES INDUCED IN THE ALGA .... 60
a. Myxophyceae
b. Chlorophyceae
C. CONSTANCY OF ALGAL CONSTITUENTS ... 63
D. DISPLACEMENT OF ALGAE WITHIN THE THALLUS . 64
a. Normal displacement
b. Local displacement
E. NON-GONIDIAL ORGANISMS ASSOCIATED WITH
LICHEN HYPHAE . . ... . . . 65
F. PARASITISM OF ALGAE ON LICHENS . . • , . 65
CHAPTER III
MORPHOLOGY
I. GENERAL ACCOUNT OF LICHEN STRUCTURE
ORIGIN OF LICHEN STRUCTURES
A. FORMS OF CELL-STRUCTURE . . • '••.'••• . 67
B. TYPES OF THALLUS . . . \ ,. . • . 68
a. Endogenous thallus
b. Exogenous thallus
II. STRATOSE THALLUS
i. CRUSTACEOUS LICHENS
A. GENERAL STRUCTURE . ... .. - -..', . 70
B. SAXICOLOUS LICHENS . . . - .. > „ . ;0
a. Epilithic lichens
aa. Hypothallus or protothallus
bb. Formation of crustaceous tissues
cc. Formation of areolae
b. Endolithic lichens
c. Chemical nature of the substratum
C. CORTICOLOUS LICHENS
a. Epiphloeodal lichens
b. Hypophloeodal lichens
CONTENTS ix
2. SQUAMULOSE LICHENS
I'AGE
A. DEVELOPMENT OF THE SQUAMULE .... 79
B. TISSUES OF SQUAMULOSE THALLUS . . . . 81
3. FOLIOSE LICHENS
A. DEVELOPMENT OF FOLIOSE THALLUS ... 82
B. CORTICAL TISSUES 82
a. Types of cortical structure
b. Origin of variation in cortical structure
c. Loss and renewal of cortex
d. Cortical hairs
C. GONIDIAL TISSUES . . . . . . . 87
D. MEDULLA AND LOWER CORTEX .... 88
a. Medulla
b. Lower cortex
c. Hypothallic structures
E. STRUCTURES FOR PROTECTION AND ATTACHMENT . 91
a. Cilia
b. Rhizinae
c. Haptera
F. STRENGTHENING TISSUES OF STRATOSE LICHENS . 95
a. Produced by development of cortex
b. Produced by development of veins or nerves
III. RADIATE THALLUS
1. CHARACTERS OF RADIATE THALLUS
2. INTERMEDIATE TYPES OF THALLUS
3. FRUTICOSE AND FILAMENTOUS THALLUS
A. GENERAL STRUCTURE OF THALLUS 101
Cortical Structures
a. The fastigiate cortex
b. The fibrous cortex
B. SPECIAL STRENGTHENING STRUCTURES . . .103
a. Sclerotic strands
/'. Chondroid axis
C. SURVEY OF MECHANICAL TISSUES .... 105
D. RETICULATE FRONDS 106
E. ROOTING BASE IN FRUTICOSE LICHENS . . . 108
IV. STRATOSE-RADIATE THALLUS
i. STRATOSE OR PRIMARY THALLUS
A. GENERAL CHARACTERISTICS HI
B. TISSUES OF PRIMARY THALLUS 112
a. Cortical tissue
b. Gonidial tissue
c. Medullary tissue
d. Soredia
x • CONTENTS
2. RADIATE OR SECONDARY THALLUS
PAGE
A. ORIGIN OF THE PODETIUM . . • . .114
B STRUCTURE OF THE PODETIUM . . . .114
a. General structure
b. Gonidial tissue
c. Cortical tissue
d. Sored ia
C. DEVELOPMENT OF THE SCYPHUS . . . .117
a. From abortive apothecia
b. From polytomous branching
c. From arrested growth
d. Gonidia of the scyphus
e. Species without scyphi
D. BRANCHING OF THE PODETIUM . . . . 119
E. PERFORATIONS AND RETICULATION OF THE PODE-
TIUM 120
F. ROOTING STRUCTURES OF CLADONIAE . . .121
G. HAPTERA 122
H. MORPHOLOGY OF THE PODETIUM . . . .122
I. PILOPHORUS AND STEREOCAULON . . . .125
V. STRUCTURES PECULIAR TO LICHENS
i. AERATION STRUCTURES
A. CYPHELLAE AND PSEUDOCYPHELLAE . . .126
a. Historical
b. Development of cyphellae
c. Pseudocyphellae
d. Occurrence and distribution
B. BREATHING-PORES 129
a. Definite breathing-pores
b. Other openings in the thallus
C. GENERAL AERATION OF THE THALLUS . . .132
2. CEPHALODIA
A. HISTORICAL AND DESCRIPTIVE 133
B. CLASSIFICATION 135
I. CEPHALODIA VERA
II. PSEUDOCEPHALODIA
C. ALGAE THAT FORM CEPHALODIA . . . .136
D. DEVELOPMENT OF CEPHALODIA . . . 137
a. Ectotrophic
b. Endotrophic
c. Pseudocephalodia
E. AUTOSYMBIOTIC CEPHALODIA 140
CONTENTS xi
3. SOREDIA
PAGE
A. STRUCTURE AND ORIGIN OF SOREDIA . . .141
a. Scattered soredia
b. Isidial soredia
c. Soredia as buds
B. SORALIA 144
<7. Form and occurrence of soralia
b. Position of soraliferous lobes
c. Deep-seated soralia
C. DISPERSAL AND GERMINATION OF SOREDIA . . 147
D. EVOLUTION OF SOREDIA 148
4. ISIDIA
A. FORM AND STRUCTURE OF ISIDIA . . . -149
B. ORIGIN AND FUNCTION OF ISIDIA . . . . 151
VI. HYMENOLICHENS
A. AFFINITY WITH OTHER PLANTS . . . . 152
B. STRUCTURE OF THALLUS 153
C. SPORIFEROUS TISSUES 154
CHAPTER IV
REPRODUCTION
I. REPRODUCTION BY ASCOSPORES
A. HISTORICAL SURVEY 155
B FORMS OF REPRODUCTIVE ORGANS . . . .156
a. Apothecia
b. Perithecia
C. DEVELOPMENT OF REPRODUCTIVE ORGANS . . 159
i. DISCOLICHENS
a. Carpogonia of gelatinous lichens
b. Carpogonia of non-gelatinous lichens
c. General summary
d. Hypothecium and paraphyses
e. Variations in apothecial development
aa. Parmeliae
bb. Pertusariae
cc. Graphideae
dd. Cladoniae
xii CONTENTS
2. PYRENOLICHENS
• PAGE
a. Development of the perithecium
b. Formation of carpogonia
D. APOGAMOUS REPRODUCTION 174
E. DISCUSSION OF LICHEN REPRODUCTION . . . 177
a. The Trichogyne
b. The Ascogonium
F. FINAL STAGES OF APOTHECIAL DEVELOPMENT . 181
a. Open or closed apothecia
b. Emergence of ascocarp
G. LICHEN ASCI AND SPORES 184
a. Historical
b. Development of the ascus
c. Development of the spores
d. Spore germination
e. Multinucleate spores
/ Polaribilocular spores
II. SECONDARY SPORES
A. REPRODUCTION BY OIDIA 189
B. REPRODUCTION BY CONIDIA 190
a. Rare instances of conidial formation
b. Comparison with Hyphomycetes
C. CAMPYLIDIUM AND ORTHIDIUM .... 191
III. SPERMOGONIA OR PYCNIDIA
A. HISTORICAL ACCOUNT OF SPERMOGONIA. . . 192
B. SPERMOGONIA AS MALE ORGANS .... 193
C. OCCURRENCE AND DISTRIBUTION .... 193
a. Relation to thallus and apothecia
b. Form and size
c. Colour
D. STRUCTURE 196
a. Origin and growth
b. Form and types of spermatiophores
c. Periphyses and sterile filaments
E. SPERMATIA OR PYCNIDIOSPORES .... 201
a. Origin and form
b. Size and structure
c. Germination
d. Variation in pycnidia
F. PYCNIDIA WITH MACROSPORES 204
CONTENTS xiif
PAGE
G. GENERAL SURVEY ..... . 205
a. Sexual or asexual
b. Comparison with fungi
' c. Influence of symbiosis
d. Value in diagnosis
CHAPTER V
PHYSIOLOGY
I. CELLS AND CELL PRODUCTS
A. CELL-MEMBRANES 209
a. Chitin
b. Lichenin and allied carbohydrates
c. Cellulose
B. CONTENTS AND PRODUCTS OF THE FUNGAL CELLS. 213
a. Cell-substances
b. Calcium oxalate
c. Importance of calcium oxalate
C. OIL-CELLS 215
a. Oil-cells of endolithic lichens
b. Oil-cells of epilithic lichens
c. Significance of oil-formation
D. LICHEN-ACIDS 221
a. Historical
b. Occurrence and examination of acids
c. Character of acids
d. Causes of variation in quantity and quality
e. Distribution of acids
E. CHEMICAL GROUPING OF ACIDS 225
I. ACIDS OF THE FAT SERIES
II. ACIDS OF THE BENZOLE SERIES
SUBSERIES I. ORCINE DERIVATIVES
SUBSERIES II. ANTHRACENE DERIVATIVES
F. CHEMICAL REAGENTS AS TESTS FOR LICHENS . 228
G. CHEMICAL REACTIONS IN NATURE .... 229
II. GENERAL NUTRITION
A. ABSORPTION OF WATER 229
a. Gelatinous lichens
b. Crustaceous lichens
c. Foliose lichens
d. Fruticose lichens
B. STORAGE OF WATER 232
b
xiv CONTENTS
PAGE
C. SUPPLY OF INORGANIC FOOD . . . .... . 232
a. In foliose and fruticose lichens
b. In crustaceous lichens
D. SUPPLY OF ORGANIC FOOD . ... - '. . . 235
a. From the substratum
b. From other lichens
c. From other vegetation
III. ASSIMILATION AND RESPIRATION
A. INFLUENCE OF TEMPERATURE ., „.. . . . 238
a. High temperature
b. Low temperature
B. INFLUENCE OF MOISTURE . . . . . . 239
a. On vital functions
b. On general development
IV. ILLUMINATION OF LICHENS
A. EFFECT OF LIGHT ON THE THALLUS . . . 240
a. Sun lichens
b. Colour-changes due to light
c. Shade lichens
d. Varying shade conditions
B. EFFECT OF LIGHT ON REPRODUCTIVE ORGANS . 244
a. Position and orientation of fruits with regard to light
b. Influence of light on colour of fruits
V. COLOUR OF LICHENS
A. ORIGIN OF LICHEN-COLOURING » . V.' . 245
a. Colour given by the algal constituent
A Colour due to lichen-acids
c. Colour due to amorphous substances
d. Enumeration of amorphous pigments
e. Colour due to infiltration
CHAPTER VI
BIONOMICS
A. GROWTH AND DURATION OF LICHENS . . .252
B. SEASON OF FRUIT FORMATION. . .255
C. DISPERSAL AND INCREASE 256
a. Dispersal of crustaceous lichens
b. Dispersal of foliose lichens
i. Dispersal of fruticose lichens
D. ERRATIC LICHENS . . . ... . . , 258
CONTENTS xv
PAGE
E. PARASITISM 260
a. General statement
b. Antagonistic symbiosis
c. Parasymbiosis
d. Parasymbiosis of fungi
e. Fungi parasitic on lichens
/ Mycetozoa parasitic on lichens
F. DISEASES OF LICHENS 268
a. Caused by parasitism
b. Caused by crowding
c. Caused by adverse conditions
G. HARMFUL EFFECT OF LICHENS .... 269
H. GALL-FORMATION 270
CHAPTER VII
PHYLOGENY
I. GENERAL STATEMENT
A. ORIGIN OF LICHENS . 272
B. ALGAL ANCESTORS ....... 273
C. FUNGAL ANCESTORS 273
a. Basidiolichens
b. Ascolichens
II. THE REPRODUCTIVE ORGANS
A. THEORIES OF DESCENT IN ASCOLICHENS . . 273
B. RELATION OF LICHENS TO FUNGI .... 275
a. Pyrenocarpineae
b. Coniocarpineae
c. Graphidineae
d. Cyclocarpineae
III. THE THALLUS
A. GENERAL OUTLINE OF DEVELOPMENT OF THALLUS 281
a. Preliminary considerations
b. Course of evolution in Hymenolichens
c. Course of evolution in Ascolichens
B. COMPARATIVE ANTIQUITY OF ALGAL SYMBIONTS . 282
C. EVOLUTION OF PHYCOLICHENS 283
a. Gioeolichens
b. Ephebaceae and Collemaceae
c. Pyremdiaceae
d. Heppiaceae and Pannariaceae
e. Peltigeraceae and Stictaceae
xvi CONTENTS
PAGE
D. EVOLUTION OF ARCHILICHENS . . . . 287
a. Thallus of Pyrenocarpineae
b. Thallus of Coniocarpineae
c. Thallus of Graphidineae
d. Thallus of Cyclocarpineae
AA. LECIDEALES
aa. COENOGONIACEAE
bb. LECIDEACEAE AND GYROPHORACEAE
cc. CI.ADONIACEAE
i. Origin of Cladonia
i. Evolution of the primary thnllus
3. Evolution of the secondary thallus
4. Course of podetial development
5. Variation in Cladonia
6. Causes of variation,
7. Podetial development and spore-dissemination
8. Pilophorus, Stereocaulon and Argopsis
BB. LECANORALES
aa. COURSE OF DEVELOPMENT
bb. LECANORACEAE
cc, PARMELIACEAE
dd. USNEACEAE
ee. PHYSCIACEAE
CHAPTER VIII
SYSTEMATIC
I. CLASSIFICATION
A. WORK OF SUCCESSIVE SYSTEMATISTS . . . 304
a. Dillenius and Linnaeus
b. Acharius
c. Schaerer
d. Massalongo and Koerber
e. Nylander
/ M tiller- Argau
g. Reinke
h. Zahlbruckner
B. FAMILIES AND GENERA OF ASCOLICHENS . . 311
C HYMENOLICHENS 342
II. NUMBER AND DISTRIBUTION
i. ESTIMATES OF NUMBER
2. GEOGRAPHICAL DISTRIBUTION
A. GENERAL SURVEY 343
B. LICHENS OF POLAR REGIONS 345
C. LICHENS OF THE TEMPERATE ZONES . . .348
D. LICHENS OF TROPICAL REGIONS .... 352
III. FOSSIL LICHENS
CONTENTS xvii
CHAPTER IX
ECOLOGY
PAGE
A. GENERAL INTRODUCTION .* 356
B. EXTERNAL INFLUENCES . . . " . . . 357
a. Temperature
b. Humidity
c. Wind
d. Human Agency
C. LICHEN COMMUNITIES 362
1. ARBOREAL 363
a. Epiphyllous
b. Corticolous
c. Lignicolous
2. TERRICOLOUS 367
a. On calcareous soil
b. On siliceous soil
c. On bricks
d. On humus
e. On peaty soil
/ On mosses
g. On fungi
3. SAXICOLOUS 371
a. Characters of mineral substrata
b. Colonization on rocks
c. Calcicolous
d. Silicicolous
4. OMNICOLOUS LICHENS 376
5. LOCALIZED COMMUNITIES 378
a. Maritime lichens
b. Sand-dune lichens
c. Mountain lichens
d. Tundra lichens
e. Desert lichens
f. Aquatic lichens
D. LICHENS AS PIONEERS . .... 392
a. Soil-formers
b. Outposts of vegetation
CHAPTER X
ECONOMIC AND TECHNICAL
A. LICHENS AS FOOD 395
a. Food for insects
b. Insect mimicry of lichens
c. Food for the higher animals
d. Food for man
CONTENTS
B. LICHENS AS MEDICINE ...... 4°5
a. Ancient remedies
b. Doctrine of "signatures"
c. Cure for hydrophobia
d. Popular remedies
C. LICHENS AS POISONS ..... . . 410
D. LICHENS USED IN TANNING, BREWING AND DISTIL-
LING ....... . . .411
E. DYEING PROPERTIES OF LICHENS . . . .411
a. Lichens as dye-plants
b. The orchil lichen, Roccella
c. Purple dyes : orchil, cudbear and litmus
d. Other orchil lichens
e. Preparation of orchil
f. Brown and yellow dyes
g. Collecting of dye-lichens
h. Lichen colours and spectrum characters
F. LICHENS IN PERFUMERY ...... 418
a. Lichens as perfumes
b. Lichens as hair-powder
G. SOME MINOR USES OF LICHENS .... 420
APPENDIX ....... .-• . 421
ADDENDUM ...... , 422
BIBLIOGRAPHY . . . ... ... 423
INDEX . . . . . . ... 448
GLOSSARY
Acrogenous, borne at the tips of hyphae; see spermatium, 312.
Allelositismus, Norman's term to describ* the thallus of Moriolaceae (mutualism), 313.
Amorphous cortex, formed of indistinct hyphae with thickened walls ; cf. decomposed
cortex.
Amphithecium, thalline margin of the apothecium, 157.
Antagonistic symbiosis, hurtful parasitism of one lichen on another, 261 et seq.
Apothecium, open or disc-shaped fructification, 11, 156 et passim. Veiled apothecium,
169. Closed or open at first, 182.
Archilichens, lichens in which the gonidia are bright green (Chlorophyceae), 52, 55
et passim.
Ardella, the small spot-like apothecium of Arthoniaceae, 158.
Areola (areolate), small space marked out by lines or chinks on the surface of the thallus,
73 et passim.
Arthrosterigma, septate tissue-like sterigma (spermatiophore), 197.
Ascogonium, the cell or cells that produce ascogenous hyphae, 180 et seq.
Ascolichens, lichens in which the fungus is an Ascomycete, 159, 173 et passim.
Ascus, enlarged cell in which a definite number of spores (usually 8) are developed ; cf.
theca, 157, 184.
Ascyphous, podetia without scyphi, i \qetpassim.
Biatorine, apothecia that are soft or waxy, and often brightly coloured, as in Biatora, 158.
Blasteniospore, see polarilocular spore.
Byssoid, slender, thread-like, as in the old genus Byssus..
Campylidium, supposed new type of fructification in lichens, 191.
Capitulum, the globose apical apothecium of Coniocarpineae ; cf. mazaedium, 319.
Carpogonium, primordial stage of fructification, 160, 164 et passim.
Cephalodium, irregular outgrowth from the thallus enclosing mostly blue-green algae ; or
intruded packet of algae within the thallus, 1 1, 133 et passim.
Chrondroid, hard and tough like cartilage, a term applied to strengthening strands of
hyphae, 104, 1 14.
Chroolepoid, like the genus Chroolepis (Trentepohlia).
Chrysogonidia, yellow algal cells ( Trentepohlia).
Cilium, hair-like outgrowth from surface or margin of thallus, or margin of apothecium, 91.
Consortium (consortism), mutual association of fungus and alga (Reinke); also termed
"mutualism," 31, 313.
Corticolous, living on the bark of trees, 363.
Crustaceous, crust-like closely adhering thallus, 70-79.
Cyphella, minute cup-like depression on the under surface of the thallus (Sticta, etc.),
i.i, 126.
Decomposed, term applied to cortex formed of gelatinous indistinct hyphae (amorphous),
73-8i et passim, 357.
Determinate, thallus with a definite outline, 72.
Dimidiate, term applied to the perithecium, when the outer wall covers only the upper
portion, 159.
xx GLOSSARY
Discoid, disc-like, an open rounded apothecium, 1 56.
Discolichens, in which the fructification is an apothecium, 160 et seq.
Dual hypothesis, the theory of two organisms present in the lichen thallus, 27 et seq.
Effigurate, having a distinct form or figure; cf. placodioid, 80, 201
Endobasidial, Steiner's term for sporophore with a secondary sporiferous branch, 200.
Endogenous, produced internally, as spores in an ascus, 179; see also under thallus.
Endolithic, embedded in the rock, 75.
Endosaprophytism, term used by Elenkin for destruction of the algal contents by enzymes
of the fungus, 36.
Entire, term applied to the perithecium when completely surrounded by an outer wall, 159.
Epilithic, growing on the rock surface, 70.
Epiphloeodal, thallus growing on the surface of the bark, 77.
Epiphyllous, growing on leaves, 363.
Epithecium, upper layer of thecium (hymenium), 158.
Erratic lichens, unattached and drifting, 259.
Exobasidial, Steiner's term for sporophore without a secondary sporiferous branch, 200.
Exogenous, produced externally, as spores on tips of hyphae ; see also under thallus.
Fastigiate cortex, formed of clustered parallel hyphal branches vertical to long axis of
thallus, 82.
Fat-cells, specialized hyphal cells containing fat or oil, 75, 215 et passim.
Fibrous cortex, formed of hyphae parallel with long axis of thallus, 82.
Filamentous, slender thallus with radiate structure, 101 et seq.
Foliose, lichens with a leafy form and stratose in structure, 82-97.
Foveolae, Foveolate, pitted, 373.
Fruticose, upright or pendulous thallus, with radiate structure, 101 et seq.
Fulcrum, term used by Steiner for sporophore, 200.
Gloeolichens, lichens in which the gonidia are Gloeocapsa or Chroococcus, 284, 373, 389.
Gonidium, the algal constituent of the lichen thallus, 20-45 et passim.
Gonimium, blue-green algal cell (Myxophyceae), constituent of the lichen thallus, 52.
Goniocysts, nests of gonidia in Moriolaceae, 313.
Gyrose, curved backward and forward, furrowed fruit of Gyrophora, 184.
Hapteron, aerial organ of attachment, 94, 122.
Haustorium, outgrowth or branch of a hypha serving as an organ of suction, 32.
Helotism, state of servitude, term used to denote the relation of alga to fungus in
lichen organization, 38, 40.
Heteromerous, fungal and algal constituents of the thallus in definite strata, 13, 68, 305
et passim.
Hold-fast, rooting organ of thallus, 109, 122 et passim.
Homobium, interdependent association of fungus and alga, 31
Homoiomerous, fungal and algal constituents more or less mixed in the thallus, 1 3, 68,
305 et passim.
Hymenial gonidia, algal cells in the hymenium, 30, 314, 315, 327.
Hymenium, apothecial tissue consisting of asci and paraphyses ; cf. thecium, 157.
HymenolichenSj, lichens of which the fungal constituent is a Hymenomycete, 152-154, 342.
Hypophloeodal, thallus growing within the bark, 78, 364.
Hypothallus, first growth of hyphae (proto- or pro-thallus) persisting as hyphal growth at
base or margin of the thallus, 70, 257 et passim.
Hypothecium, layer below the thecium (hymenium), 157.
GLOSSARY xxi
Intricate cortex, composed of hyphae densely interwoven but not coalescent, 83.
Isidium, coral-like outgrowth on the lichen thallus, 149-151.
Lecanorine, apothecium with a thalline margin as in Lecanora, 158.
Lecideine, apothecium usually dark-coloured or carbonaceous and without a thalline
margin, 158.
Leprose, mealy or scurfy, like the old form genera, Lepra, Lepraria, 191.
Lichen-acids, organic acids peculiar to lichens, 221 et seq.
Lignicolous, living on wood or trees, 366.
Lirella, long narrow apothecium of Graphideae, 158.
Mazaedium, fructification of Coniocarpineae, the spores lying as a powdery mass in the
capitulum, 176.
Medulla, the loose hyphal layer in the interior of the thallus, 88 et passim.
Meristematic, term applied by Wainio to growing hyphae, 48.
Microgonidia, term applied by Minks to minute greenish bodies in lichen hyphae, 26.
Multi-septate, term applied to spores with numerous transverse septa, 316 et seq.
Murali-divided, Muriform, term applied to spores divided like the masonry of a wall, 187.
Oidium, reproductive cell formed by the breaking up of the hyphae, 189.
Oil-cell, hyphal cell containing fat globules, 215.
Orculiform, see polarilocular.
Orthidium, supposed new type of fructification in lichens, 192.
Palisade-cells, the terminal cells of the hyphae forming the fastigiate cortex, 82, 83.
Panniform, having a felted or matted appearance, 260.
Paraphysis, sterile filament in the hymenium, 157.
Parasymbiosis, associated harmless but not mutually useful growth of two organisms, 263.
Parathecium, hyphal layer round the apothecium, 157.
Peltate, term applied to orbicular and horizontal apothecia in the form of a shield, 336.
Perithecium, roundish fructification usually with an apical opening (ostiole) containing
ascospores, 158 et passim.
Pervious, referring to scyphi with an opening at the base (Perviae\ 118.
Phycolichens, lichens in which the gonidia are blue-green (Myxophyceae), 52 et passim.
Placodioid, thallus with a squamulose determinate outline, generally orbicular ; cf.
effigurate, 80.
Placodiomorph, see polarilocular.
Plectenchyma (Plectenchymatous), pseudoparenchyma of fungi and lichens, 66 et passim.
Pleurogenous, borne laterally on hyphal cells ; see spermatium, 312.
Pluri -septate, term applied to spores with several transverse septa, 321 et seq.
Podetium, stalk-like secondary thallus of Cladoniaceae, 1 14, 293 et seq.
Polarilocular, Polaribilocular, two-celled spores with thick median wall traversed by a
connecting tube, 188, 340-341.
Poly torn ous, arising of several branches of the podetium from one level, 118.
Proper margin, the hyphal margin surrounding the apothecium, 157.
Prothallus, Protothallus, first stages of hyphal growth ; cf. hypothallus, 71.
Pycnidiospores, stylospores borne in pycnidia, 198 et passim.
Pycnidium, roundish fructification, usually with an opening at the apex, containing
sporophores and stylospores ; cf. spermogonium, 192 et seq.
Pyrenolichens, in which the fructification is a closed perithecium, 173 et passim.
Radiate thallus, the tissues radiate from a centre, 98 et seq.
xxii GLOSSARY
Rhagadiose, deeply chinked, 74 ; cf. rimose.
Rhizina, attaching "rootlet," 92-94.
Rimose, Rimulose, cleft or chinked into areolae, 73.
Rimose-diffract, widely cracked or chinked, 74.
Scutellate, shaped like a -platter, 156.
Scyphus, cup-like dilatation of the podetium, in, 117.
Signature, a term in ancient medicine to signify the resemblance of a plant to any part
of the human body, 406, 409.
Soralium, group of soredia surrounded by a definite margin, 144.
Soredium, minute separable particle arising from the gonidial tissue of the thallus, and
consisting of algae and hyphae, 141.
Spermatium, spore-like body borne in the spermogonium, regarded as a non-motile male
cell or as a pycnidiospore, 201.
Spermogonium, roundish closed receptacle containing spermatia, 192.
Sphaeroid-cell, swollen hyphal cell, containing fat globules, 215.
Squamule, a small thalline lobe or scale, 74 et passim.
Sterigma, Nylander's term for the spermatiophore, 197.
Stratose thallus, where the tissues are in horizontal layers, 70.
Stratum, a layer of tissue in the thallus, 70.
Symbiont, one of two dissimilar organisms living together, 32.
Symbiosis, a living together of dissimilar organisms, also termed commensalism, 31, 32
et seq.
Tegulicolous, living on tiles, 369.
Terebrator, boring apparatus, term used by Lindau for the lichen " trichogyne," 179.
Thalline margin, an apothecial margin formed of and usually coloured like the thallus ;
cf. amphithecium.
Thallus, vegetative body or soma of the lichen plant, 11,421. Endogenous thallus in which
the alga predominates, 68. Exogenous thallus in which the fungus predominates, 69.
Theca, enlarged cell containing spores ; cf. ascus.
Thecium, layer of tissue in the apothecium consisting of asci and paraphyses ; cf.
hymenium, 157.
Trichogyne, prolongation of the egg-cell in Florideae which acts as a receptive tube ;
septate hypha in lichens arising from the ascogonium, 160, 177-181, 273.
Woronin's hypha, a coiled hypha occurring in the centre of the fruit primordium, 1 59, 163.
ERRATA
p. 24. For Baranetsky razaTB
p. 277. For Ascolium read Acolium.
p. 318. For Lepolichen coccophora read coccophorus.
INTRODUCTION
LICHENS are, with few exceptions, perennial aerial plants of somewhat
lowly organization. In the form of spreading encrustations, horizontal leafy
expansions, of upright strap-shaped fronds or of pendulous filaments, they
take possession of the tree-trunks, palings, walls, rocks or even soil that
afford them a suitable and stable foot-hold. The vegetative body, or thallus,
which may be extremely long-lived, is of varying colour, white, yellow,
brown, grey or black. The great majority of lichens are Ascolichens and
reproduction is by ascospores produced in open or closed fruits (apothecia
or perithecia) which often differ in colour from the thallus. There are a few
Hymenolichens which form basidiospores. Vegetative reproduction by
soredia is frequent.
Lichens abound everywhere, from the sea-shore to the tops of high
mountains, where indeed the covering of perpetual snow is the only barrier
to their advance ; but owing to their slow growth and long duration, they
are more seriously affected than are the higher plants by chemical or other
atmospheric impurities and they are killed out by the smoke of large towns:
only a few species are able to persist in somewhat depauperate form in or
near the great centres of population or of industry.
The distinguishing feature of lichens is their composite nature: they
consist of two distinct and dissimilar organisms, a fungus and an alga, which,
in the lichen thallus, are associated in some kind of symbiotic union, each
symbiont contributing in varying degree to the common support : it is
a more or less unique and not unsuccessful venture in plant-life. The
algae — Chlorophyceae or Myxophyceae — that become lichen symbionts or
"gonidia" are of simple structure, and, in a free condition, are generally to
be found in or near localities that are also the customary habitats of lichens.
The fungus is the predominant partner in the alliance as it forms the fruiting
bodies. It belongs to the Ascomycetes1, except in a few tropical lichens
(Hymenolichens), in which the fungus is a Basidiomycete. These two
types of plants (algae and fungi) belonging severally to many different
genera and species have developed in their associated life this new lichen
organism, different from themselves as well as from all other plants, not
only morphologically but physiologically. Thus there has arisen a distinct
class, with families, genera and species, which through all their varying forms
retain the characteristics peculiar to lichens.
1 E. Acton (1909) has described a primitive lichen Rotrydina vnlgaris, in which there is no
fruiting stage, and in which the fungus seems to show affinity with a Hyphomycete.
xxiv INTRODUCTION
In the absence of any " visible " seed, there was much speculation in
early days as to the genesis of all the lower plants and many opinions
were hazarded as to their origin. Luyken1, for instance, thought that lichens
were compounded of air and moisture. Hornschuch2 traced their origin to
a vegetable infusorium, Monas Lens, which became transformed to green
matter and was further developed by the continued action of light and air,
not only to lichens, but to algae and mosses, the type of plant finally evolved
being determined by the varying atmospheric influences along with the
chemical nature of the substratum. An account3 is published of Nees von
Esenbeck, on a botanical excursion, pointing out to his students the green
substance, Lepraria botryoides, which covered the lower reaches of walls and
rocks, while higher up it assumed the grey lichen hue. This afforded him
sufficient proof that the green matter in that dry situation changed to
lichens, just as in water it changed to algae. An adverse criticism by
Dillenius4 on a description of a lichen fructification is not inappropriate to
those early theorists : " Ex quo apparet, quantum videre possint homines,
si imaginatione polleant."
A constant subject of speculation and of controversy was the origin of
the green cells, so dissimilar to the general texture of the thallus. It was
thought finally to have been established beyond dispute that they were
formed directly from the colourless hyphae and, as a corollary, Protococcus
and other algal cells living in the open were considered to be escaped
gonidia or, as Wallroth5 termed them, " unfortunate brood-cells," his view
being that they were the reproductive organs of the lichen plant that had
failed to develop.
It was a step forward in the right direction when lichens were regarded
as transformed algae, among others by Agardh6, who believed that he had
followed the change from Nostoc lichenoides to the lichen Collema limosum.
Thenceforward their double resemblance, on the one hand to algae, on the
other to fungi, was acknowledged, and influenced strongly the trend of study
and investigation.
The announcement7 by Schwendener8 of the dual hypothesis solved the
problem for most students, though the relation between the two symbionts
is still a subject of controversy. The explanation given by Schwendener,
and still held by some9, that lichens were merely fungi parasitic on algae,
was indeed a very inadequate conception of the lichen plant, and it was hotly
contested by various lichenologists. Lauder Lindsay10 dismissed the theory
as " merely the most recent instance of German transcendentalism applied
1 Luyken 1809. 2 Hornschuch 1819. 3 Raab 1819. 4 Dillenius 1741, p. 200.
8 Wallroth 1825. 6 Agardh 1820. 7 See p. 27. 8 Schwendener 1867.
9 Fink 1913. 10 Lindsay 1876.
INTRODUCTION xxv
to the Lichens." Earlier still, Nylander1, in. a paper dealing with cephalodia
and their peculiar gonidia, had denounced it : " Locum sic suum dignum
occupat algolichenomachia inter historias ridiculas, quae hodie haud paucae
circa lichenes, majore imaginatione quam scientia, enarrantur." He never
changed his attitude and Crombie2, wholly agreeing with his estimate of
these " absurd tales," translates a much later pronouncement by him3 :
"All these allegations belong to inept Schwendenerism and scarcely deserve
even to be reviewed or castigated so puerile are they — the offspring of in-
experience and of a light imagination. No true science there." Crombie4
himself in a first paper on this subject declared that " the new theory would
necessitate their degradation from the position they have so long held as an
independent class." He scornfully rejected the whole subject as "a Romance
of Lichenology, or the unnatural union between a captive Algal damsel and
a tyrant Fungal master." The nearest approach to any concession on the
algal question occurs in a translation by Crombie5 of one of Nylander's
papers. It is stated there that a saxicolous alga (Gongrosira Kiitz.) had
been found bearing the apothecia of Lecidea herbidula n. sp. Nylander adds :
"This algological genus is one which readily passes into lichens." At a later
date, Crombie6 was even more comprehensively contemptuous and wrote:
" whether viewed anatomically or biologically, analytically or synthetically,
it is instead of being true science, only the Romance of Lichenology." These
views were shared by many continental lichenologists and were indeed, as
already stated, justified to a considerable extent: it was impossible to regard
such a large and distinctive class of plants as merely fungi parasitic on the
lower algae.
Controversy about lichens never dies down, and that view of their para-
sitic nature has been freshly promulgated among others by the American
lichenologist Bruce Fink7. The genetic origin of the gonidia has also been
restated by Elfving8: the various theories and views are discussed fully in
the chapter on the lichen plant.
Much of the interest in lichens has centred round their symbiotic growth.
No theory of simple parasitism can explain the association of the two
plants: if one of the symbionts is withdrawn — either fungus or alga — the
lichen as such ceases to exist. Together they form a healthy unit capable
of development and change : a basis for progress along new lines. Permanent
characters have been formed which are transmitted just as in other units of
organic life.
A new view of the association has been advanced by F. and Mme Moreau9.
They hold that the most characteristic lichen structures — more particularly
1 Nylander 1869. 2 Crombie 1891. 3 Nylander 1891. 4 Crombie 1874.
8 Crombie 1877. 6 Crombie 1885. 7 Fink 1913. 8 Elfving 1913.
9 Moreau 1918.
xxvi INTRODUCTION
the cortex— have been induced by the action of the alga on the fungus.
The larger part of the thallus might therefore be regarded as equivalent to
a gall: "it is a cecidium, an algal cecidium, a generalized biomorphogenesis."
The morphological characters of lichens are of exceptional interest, con-
ditioned as they are by the interaction of the two symbionts, and new
structures have been evolved by the fungus which provides the general
tissue system. Lichens are plants of physiological symbiotic origin, and that
aspect of their life-history has been steadily kept in view in this work. There
are many new requirements which have had to be met by the lichen hyphae,
and the differences between them and the true fungal hyphae have been
considered, as these are manifested in the internal economy of the com-
pound plant, and in its reaction to external influences such as light, heat,
moisture, etc.
The pioneers of botanical science were of necessity occupied almost
exclusively with collecting and describing plants. As the number of known
lichens gradually accumulated, affinities were recognized and more or less
successful efforts were made to tabulate them in classes, orders, etc. It was
a marvellous power of observation that enabled the early workers to arrange
the first schemes of classification. Increasing knowledge aided by improved
microscopes has necessitated changes, but the old fundamental "genus"
Lichen is practically equivalent to the Class Lichenes.
The study of lichens has been a slow and gradual process, with a con-
tinual conflict of opinion as to the meaning of these puzzling plants — their
structure, reproduction, manner of subsistence and classification as well as
their relation to other plants.. It has been found desirable to treat these
different subjects from a historical aspect, as only thus can a true under-
standing be gained, or a true judgment formed as to the present condition
of the science. It is the story of the evolution of lichenology as well as of
lichens that has yielded so much of interest and importance.
The lichenologist may claim several advantages in. the study of his
subject : the abundant material almost everywhere to hand in country
districts, the ease with which the plants are preserved, and, not least, the
interest excited by the changes and variations induced by growth conditions ;
there are a whole series of problems and puzzles barely touched on as yet
that are waiting to be solved.
In field work, it is important to note accurately and carefully the nature
of the substratum as well as the locality. Crustaceous species should be
gathered if possible along with part of the wood or rock to which they are
attached ; if they are scraped off, the pieces may be reassembled on gummed
paper, but that is less satisfactory. The larger forms are more easily secured;
INTRODUCTION xxvii
they should be damped and then pressed before being laid away : the process
flattens them, but it saves them from the risk of being crushed and broken,
as when dry they are somewhat brittle. Moistening with water will largely
restore their original form. All parts of the lichen, both thallus and fruit,
can be examined with ease at any time as they do not sensibly alter in the
herbarium, though they lose to some extent their colouring : the blue-grey
forms, for instance, often become a uniform dingy brownish-grey.
Microscopic examination in the determination of species is necessary in
many instances, but that disability — if it ranks as such — is shared by other
cryptogams, and may possibly be considered an inducement rather than a
deterrent to the study of lichens. For temporary examination of microscopic
preparations, the normal condition is best observed by mounting them in
water. If the plants are old and dry, the addition of a drop or two of potash
— or ammonia — solution is often helpful in clearing the membranes of the
cells and in restoring the shrivelled spores and paraphyses to their natural
forms and dimensions.
If serial microtome sections are desired, more elaborate methods are
required. For this purpose Peirce1 has recommended that " when dealing
with plants that are dry but still alive, the material should be thoroughly
wetted and kept moist for two days, then killed and fixed in a saturated
solution of corrosive sublimate in thirty-five per cent, alcohol." The solu-
tion should be used hot : the usual methods of dehydrating and embedding
in paraffin are then employed with extra precautions on account of the
extremely brittle nature of lichens.
Another method that also gave good results has been proposed by
French2 : " first the lichen is put into 95 per cent, alcohol for 24 hours, then
into thin celloidin and thick celloidin 2/\. hours each. After this the specimens
are embedded in thick celloidin which is hardened in 70 per cent, alcohol
for 24. hours and then cut." French advises staining with borax carmine :
it colours the fungal part pale carmine and the algal cells a greenish-red
shade.
Modern research methods of work are generally described in full in the
publications that are discussed in the following chapters. The student is
referred to these original papers for information as to fixing, embedding,
staining, etc.
Great use has been made of reagents in determining lichen species.
They are extremely helpful and often give the clinching decision when
morphological characters are obscure, especially if the plant has been much
altered by the environment. It must be borne in mind, however, that a
1 Peirce 1898. * French 1898.
xxviii INTRODUCTION
species is a morphological rather than a physiological unit, and it is not the
structures but the cell-products that are affected by reagents. Those most
commonly in use are saturated solutions of potash and of bleaching-powder
(calcium hypochlorite). The former is cited in text-books as KOH or simply
as K, the latter as CaCl or C. The C solution deteriorates quickly and
must, therefore, be frequently renewed to produce the required reaction,
i.e. some change of colour. These two reagents are used singly or, if con-
jointly, K followed by C. The significance of the colour changes has been
considered in the discussion on lichen-acids.
Iodine is generally cited in connection with its staining effect on the
hymenium of the fruit; the blue colour produced is, however, more general
than was at one time supposed and is not peculiar to lichens ; the asci of
many fungi react similarly though to a less extent. The medullary hyphae
in certain species also stain blue with iodine.
CHAPTER I
HISTORY OF LICHENOLOGY
A. INTRODUCTORY
THE term "lichen" is a word of Greek origin used by Theophrastus in his
History of Plants to signify a superficial growth on the bark of olive-trees.
The name was given in the early days of botanical study not to lichens, as
we understand them, but to hepatics of the Marchantia type. Lichens
themselves were generally described along with various other somewhat
similar plants as "Muscus" (Moss) by the older writers, and more definitely
as "Musco-fungus" by Morison1. In a botanical work published in 170x3 by
Tournefort'- all the members of the vegetable kingdom then known were
for the first time classified in genera, and the genus Lichen was reserved for
the plants that have been so designated since that time, though Dillenius3
in his works preferred the adjectival name Lichenoides.
A painstaking historical account of lichens up to the beginning of
modern lichenology has been written by Krempelhuber4, a German licheno-
logist. He has grouped the data compiled by him into a series of Periods,
each one marked by some great advance in knowledge of the subject,
though, as we shall see, the advance from period to period has been con-
tinuous and gradual. While following generally on the lines laid down by
Krempelhuber, it will be possible to cite only the more prominent writers
and it will be of much interest to British readers to note especially the work
of our own botanists.
Krempelhuber's periods are as follows:
I. From the earliest times to the end of the seventeenth century.
II. Dating from the arrangement of plants into classes called genera
by Tournefort in 1694 to 1729.
III. From Micheli's division of lichens into different orders in 1729
to 1780.
IV. The definite and reasoned establishment of lichen genera based
on the structure of thallus and fruit by Weber in 1780 to 1803.
V. The arrangement of all known lichens under their respective
genera by Acharius in 1803 to 1846.
VI. The recognition of spore characters in classification by De
Notaris in 1846 to 1867.
1 Morison 1699. 2 Tournefort 1694 and 1700. 3 Dillenius 1/41. 4 Krempelhuber 1867-1872.
S. L. « I
2 HISTORY OF LICHENOLOGY
A seventh period which includes modern lichenology, and which dates
after the publication of Krempelhuber's History, was ushered in by
Schwendener's announcement in 1867 of the hypothesis as to the dual
nature of the lichen thallus. Schwendener's theory gave a new impulse to
the study of lichens and strongly influenced all succeeding investigations.
B. PERIOD I. PREVIOUS TO 1694
Our examination of lichen literature takes us back to Theophrastus,
the disciple of Plato and Aristotle, who lived from 371 to 2848.0., and who
wrote a History of Plants, one of the earliest known treatises on Botany.
Among the plants described by Theophrastus, there are evidently two
lichens, one of which is either an Usnea or an Alectoria, and the other
certainly Roccella tinctoria, the last-named an important economic plant
likely to be well known for its valuable dyeing properties. The same or
somewhat similar lichens are also probably alluded to by the Greek phy-
sician Dioscorides, in his work on Materia Medica, A.D. 68. About the
same time Pliny the elder, who was a soldier and traveller as well as a
voluminous writer, mentions them in his Natural History which was
completed in 77 A.D.
During the centuries that followed, there was little study of Natural
History, and, in any case, lichens were then and for a long time after
considered to be of too little economic value to receive much attention.
In the sixteenth century there was a great awakening of scientific
interest all over Europe, and, after the printing-press had come into
general use, a number of books bearing on Botany were published. It will
be necessary to chronicle only those that made distinct contributions to the
knowledge of lichens.
The study of plants was at first entirely from a medical standpoint
and one of the first works, and the first book on Natural History, printed
in England, was the Crete Herball1. It was translated from a French work,
Hortus sanitatis, and published by Peter Treveris in Southwark. One of
the herbs recommended for various ailments is "Muscus arborum," the
tree-moss (Usnea}. A somewhat crude figure accompanies the text.
Ruel2 of Soissons in France, Dorstenius3, Camerarius4 and Tabernae-
montanus5 in Germany followed with works on medical or economic botany
and they described, in addition to the tree-moss, several species of reputed
value in the art of healing now known as Sticta (Lobaria) pulmonaria,
Lobaria laetevirens, Cladonia pyxidata, Evernia prunastri and Cetraria
islandica. Meanwhile L'Obel6, a Fleming, who spent the latter part of his
life in England and is said to have had charge of a physic garden at
1 Crete Herball 1526. » Ruel I536 8 Dorstenius 1MO
4 Camerarius 1586. 5 Tabernaemontanus 1590. 6 L'Obel 1576.
PERIOD I. PREVIOUS TO 1694 3
Hackney, was appointed botanist to James I. He published at Antwerp
a large series of engravings of plants, and added a species of Ramalina to
the growing list of recognized lichens. Dodoens1, also a Fleming, records
not only the Usnea of trees, but a smaller and more slender black form
which is easily identifiable as Alectoria jubata. He also figures Lichen
pulmonaria and gives the recipe for its use.
The best-known botanical book published at that time, however, is the
Herball of John Gerard2 of London, Master in Chirurgerie, who had a
garden in Holborn. He recommends as medicinally valuable not only
Usnea, but also Cladonia pyxidata, for which he coined the name "cuppe-
or chalice-moss." About the same time Schwenckfeld3 recorded, among
plants discovered by him in Silesia, lichens now familiar as Alectoria
jubata, Cladonia rangiferina and a species of Peltigera,
Among the more important botanical writers of the seventeenth century
may be cited Colonna4 and Bauhin5. The former, an Italian, contributes,
in his Ecphrasis, descriptions and figures of three additional species easily
recognized as Physcia ciliaris, Xanthoria parietina and Ramalina calicaris.
Kaspar Bauhin, a professor in Basle, who was one of the most advanced of
the older botanists, was the first to use a binomial nomenclature for some
of his plants. He gives a list in his Pinax of the lichens with which he was
acquainted, one of them, Cladonia fimbriata, being a new plant.
John Parkinson's6 Herball is well known to English students; he adds
one new species for England, Lobaria pulmonaria, already recorded on the
Continent. Parkinson was an apothecary in London and held the office of
the King's Herbarist; his garden was situated in Long Acre. How's7
Phytographia is notable as being the first account of British plants compiled
without reference to their healing properties. Five of the plants described
by him are lichen species: "Lichen arborum sive pulmonaria" (Lobaria
pulmonaria}, "Lichen petraeus tinctorius" (Roccella}, "Muscus arboreus"
(Usnea}, "Corallina montana" (Cladonia rangiferina} and "Muscus pixoides"
(Cladonia}. Several other British species were added by Merrett8, who records
in his Pinax, "Muscus arboreus umbilicatus" (Physcia dliaris}, "Muscus
aureus tenuissimus" ( Teloschistes flavicans), "Muscus caule rigido" (Alec-
toria) and "Lichen petraeus purpureus" (Parmelia omphalodes}, the last-
named, a rock lichen, being used, he tells us, for dyeing in Lancashire.
Merret or Merrett was librarian to the Royal College of Physicians.
His Pinax was undertaken to replace How's Phytographia published
sixteen years previously and then already out of print. Merrett's work
was issued in 1666, but the first impression was destroyed in the great fire
of London and most of the copies now extant are dated 1667. He arranged
1 Dodoens 1583. 2 Gerard 1597. 3 Schwenckfeld 1600. 4 Colonna 1606.
5 Bauhin 1623, pp. 360-2. * Parkinson 1640. 7 How 1650. 8 Merrett 1666.
4 HISTORY OF LICHENOLOGY
the species of plants in alphabetical order, but as the work was not critical
it fell into disuse, being superseded by John Ray's Catalogus and Synopsis.
To Robert Plot1 we owe the earliest record of Cladonia cocci/era which had
hitherto escaped notice; it was described and figured as a new and rare
plant in the Natural History of Staffordshire^. Plot was the first Gustos
of Ashmole's Museum in Oxford and he was also the first to prepare
a County Natural History.
The greatest advance during this first period was made by Robert
Morison2, a Scotsman from Aberdeen. He studied medicine at Angers in
France, superintended the Duke of Orleans' garden at Blois, and finally,
after his return to this country in 1669, became Keeper of the botanic
garden at Oxford. In the third volume of his great work2 on Oxford
plants, which was not issued till after his death, the lichens are put in
a separate group — "Musco-fungus" — and classified with some other plants
under "Plantae Heteroclitae." The publication of the volume projects into
the next historical period.
Long before this date John Ray had begun to study and publish books
on Botany. His Catalogue of English Plants* is considered to have com-
menced a new era in the study of the science. The Catalogue was followed
by the History of Plants*, and later by a Synopsis of British Plants5, and in
all of these books lichens find a place. Two editions of the Synopsis
appeared during Ray's lifetime, and to the second there is added an
Appendix contributed by Samuel Doody which is entirely devoted to
Cryptogamic plants, including not a few lichens — still called "Mosses" —
discovered for the first time. Doody, himself an apothecary, took charge
of the garden of the Apothecaries' Society at Chelsea, but his chief interest
was Cryptogamic Botany, a branch of the subject but little regarded before
his day. Pulteney wrote of him as the "Dillenius of his time."
Among Doody's associates were the Rev. Adam Buddie, James Petiver
and William Sherard. Buddie was primarily a collector and his herbarium
is incorporated in the Sloane Herbarium at the British Museum. It contains
lichens from all parts of the world, many of them contributed by Doody,
Sherard and Petiver. Only a few of them bear British localities : several are
from Hampstead where Buddie had a church.
The Society of Apothecaries had been founded in 1617 and the mem-
bers acquired land on the river-front at Chelsea, which was extended later
and made into a Physick Garden. James Petiver6 was one of the first
Demonstrators of Plants to the Society in connection with the 'garden, and
one of his duties was to conduct the annual herborizing tours of the
apprentices in search of plants. He thus collected a large herbarium on
the annual excursions, as well as on shorter visits to the more immediate
1 Plot 1686. * Morison 1699. 3 Ray 1670. 4 Ray 1686. 5 Ray 1690. 6 Petiver 1695.
PERIOD I. PREVIOUS TO 1694 5
neighbourhood of London. He wrote many tracts on Natural History
subjects, and in these some lichens are included. He was one of the best
known of Ray's correspondents, and owing to his connection with the
Physic Garden received plants from naturalists in foreign countries.
Sherard, another of Doody's friends, had studied abroad under Tournefort
and was full of enthusiasm for Natural Science. It was he who brought
Dillenius to England and finally nominated him for the position of the first
Sherardian Professor of Botany at Oxford. Another well-known contem-
porary botanist was Leonard Plukenet1 who had a botanical garden at Old
Palace Yard, Westminster. He wrote several botanical works in which
lichens are included.
Morison is the only one of all the botanists of the time who recognized
lichens as a group distinct from mosses, algae or liverworts, and even he
had very vague ideas as to their development. Malpighi2 had noted the
presence of soredia on the thallus of some species, and , regarded them as
seeds. Porta3, a Neapolitan, has been quoted by Krempelhuber as probably
the first to discover and place on record the direct growth of lichen fronds
from green matter on the trunks of trees.
C. PERIOD II. 1694-1729
The second Period is ushered in with the publication of a French work,
Les Elemens de Botatiique by Tournefort4, who was one of the greatest
botanists of the time. His object was — "to facilitate the knowledge of plants
and to disentangle a science which had been neglected because it was found
to be full of confusion and obscurity." Up to this date all plants were
classified or listed as individual species. It was Tournefort who first
arranged them in groups which he designated "genera" and he gave a
careful diagnosis of each genus.
Les Elemens was successful enough to warrant the publication a few
years later of a larger Latin edition entitled Institutiones5 and thus fitted for
a wider circulation. Under the genus Lichen, he included plants "lacking
flowers but with a true cup-shaped shallow fruit, with very minute pollen or
seed which appeared to be subrotund under the microscope." Not only the
description but the figures prove that he was dealing with ascospores and
not merely soredia, though under Lichen along with true members of the
"genus" he has placed a Marchantia, the moss Splachnum and a fern. A few
lichens were placed by him in another genus Coralloides.
Tournefort's system was of great service in promoting the study of
Botany: his method of classification was at once adopted by the German
writer Rupp6 who published a Flora of plants from Jena. Among these
1 Plukenet 1691-1696. 2 Malpighi 1686. 3 Porta 1688.
4 Tournefort 1694. 5 Tournefort 1700. 6 Rupp 1718.
6 HISTORY OF LICHENOLOGY
plants are included twenty-five species of lichens, several of which he
considered new discoveries, no fewer than five being some form of Lichen
gelatinosus (Collema}. Buxbaum1, in his enumeration of plants from Halle,
finds place for forty-nine lichen species, with, in addition, eleven species of
Coralloides; and Vaillant2 in listing the plants that grew in the neighbour-
hood of Paris gives thirty-three species for the genus Lichen of which a
large number are figured, among them species of Ramalina, Parmelia,
Cladonia, etc.
In England, however, Dillenius3, who at this time brought out a third
edition of Ray's Synopsis and some years later his own Historia Muscorum,
still described most of his lichens as "Lichenoides" or "Coralloides" ; and no
other work of note was published in our country until after the Linnaean
system of classification and of nomenclature was introduced.
D. PERIOD III. 1729-1780
Lichens were henceforth regarded as a distinct genus or section of
plants. Micheli4, an Italian botanist, Keeper of the Grand Duke's Gardens
in Florence, realized the desirability of still further delimitation, and he
broke up Tournefort's large comprehensive genera into numerical Orders.
In the genus Lichen, he found occasion for 38 of these Orders, determined
mainly by the character of the thallus, and the position on it of apothecia
and soredia. He enumerates the species, many of them new discoveries,
though not all of them recognizable now. His great work on Plants is
enriched by a series of beautiful figures. It was published in 1729 and
marks the beginning of a new Period — a new outlook on botanical science.
Micheli regarded the apothecia of lichens as "floral receptacles," and the
soredia as the seed, because he had himself followed the development of
lichen fronds from soredia.
The next writer of distinction is the afore-mentioned Dillen or
Dillenius. He was a native of Darmstadt and began his scientific career
in the University of Giessen. His first published work5 was an account of
plants that were to be found near Giessen in the different months of the
year. Mosses and lichens he has assigned to December and January.
Sherard induced him to come to England in 1721, and at first engaged his
services in arranging the large collections of plants which he, Sherard, had •
brought from Smyrna or acquired from other sources.
Three years after his arrival Dillenius had prepared the third edition of
Ray's Synopsis for the press, but without putting his name on the title-page6.
Sherard explained, in a letter to Dr Richardson of Bierly in Yorkshire, that
"our people can't agree about an editor, they are unwilling a foreigner should
1 Buxbaum 1721. 2 Vaillant 1727. » Dillenius 1724 and 1741.
4 Micheli 1729. 5 Dillenius 1719. s See Druce and yines IQ_
PERIOD III. 1729-1780 7
put his name to it." Dillenius, who was quite aware of the prejudice against
aliens, himself writes also to Dr Richardson : "there being some apprehension
(me being a foreigner) of making natives uneasy if I should publicate it in
my name." Lichens were already engaging his attention, and descriptions
of 91 species were added to Ray's work. So well did this edition meet the
requirements of the age, that the Synopsis remained the text-book of
British Botany until the publication of Hudson's Flora Anglica in 1762.
William Sherard died in 1728. He left his books and plates to the
University of Oxford with a sum of money to endow a Professorship of
Botany. In his will he had nominated Dr Dillenius for the post. The great
German botanist was accordingly appointed and became the first Sherardian
Professor of Botany, though he did not remove to Oxford till 1734. The
following years were devoted by him to the preparation of Historia Mus-
corum, which was finally published in 1741. It includes an account of the
then known liverworts, mosses and lichens. The latter — still considered by
Dillenius as belonging to mosses — were grouped under three genera, Usnea,
Coralloides and Lichenoides. The descriptions and figures are excellent, and
his notes on occasional lichen characteristics and on localities are full of
interest. His lichen herbarium, which still exists at Oxford, mounted with
the utmost care and neatness, has been critically examined by Nylander and
Crombie1 and many of the species identified.
Dillenius was ignorant of, or rejected, Micheli's method of classification,
adopting instead the form of the thallus as a guide to relationship. He also
differed from him in his views as to propagation, regarding the soredia as
the pollen of the lichen, and the apothecia as the seed-vessels, or even in
certain .cases as young plants.
Shortly after the publication of Dillenius' Historia, appeared Haller's2
Systematic and Descriptive list of plants indigenous to Switzerland. The
lichens are described as without visible leaves or stamens but with "corpus-
cula" instead of flowers and leaves. He arranged his lichen species, 160 in
all, under seven different Orders: I. "Lichenes Corniculati and Pyxidati";
2. "L. Coralloidei"; 3. "L. Fruticosi"; 4. "L. Pulmonarii"; 5. "L. Crustacei"
(with flower-shields); 6. "L. Scutellis" (with shields but with little or no
thallus); and 7. "L. Crustacei" (without shields).
This period extends till near the end of the eighteenth century, and
thus includes within its scope the foundation of the binomial system of
naming plants established by Linnaeus3. The renowned Swedish botanist
rather scorned lichens as "rustici pauperrimi," happily translated by
Schneider4 as the "poor trash of vegetation," but he named and listed about
80 species. He divided his solitary genus Lichen into sections: i. "Leprosi
tuberculati"; 2. "Leprosi scutellati"; 3. "Imbricati"; 4. "Foliacei";
1 Crombie 1880. - Haller 1742. 3 Linnaeus 1753. 4 Schneider 1897.
8 HISTORY OF LICHENOLOGY
5. "Coriacei"; 6. "Scyphiferi"; 7. "Filamentosi." By this ordered sequence
Linnaeus showed his appreciation of development, beginning, as he does,
with the leprose crustaceous thallus and continuing up to the most highly
organized filamentous forms. He and his followers still included the genus
Lichen among Algae.
A voluminous History of Plants had been published in 1751 by
Sir John Hill1, the first superintendent to be appointed to the Royal
Gardens, Kew. In the History lichens are included under the Class
"Mosses," and are divided into several vaguely limited ''genera"— Usriea,
tree mosses, consisting of filaments only; Platysma, flat branched tree
mosses, such as lungwort; Cladonia, the orchil and coralline mosses, such as
Cladoniafurcata ; Pyxidium, the cup-mosses; and Placodium, the crustaceous,
friable or gelatinous forms. A number of plants are somewhat obscurely
described under each genus. Not only were these new Lichen genera sug-
gested by him, but among his plants are such binomials as Usnea compressa,
Platysmacorniculatum, Cladoniafurcata and Cladonia tophacea ; other lichens
are trinomial or are indicated, in the way then customary, by a whole sen-
tence. Hill's studies embraced a wide variety of subjects; he had flashes of
insight, but not enough concentration to make an effective application of
his ideas. In his Flora Britannica*, which was compiled after the publication
of Linnaeus's Species Plantarum, he abandoned his own arrangement in
favour of the one introduced by Linnaeus and accepted again the single
genus Lichen.
Sir William Watson3, a London apothecary and physician of scientific
repute at this period, proposed a rearrangement and some alteration of
Linnaeus's sections. He had failed to grasp the principle of development,
but he gives a good general account of the various groups. Watson was the
progenitor of those who decry the makers and multipliers of species. So in
regard to Micheli, who had increased the number to "298," he writes: "it is to
be regretted, that so indefatigable an author, one whose genius particularly
led him to scrutinize the minuter subjects of the science, should have been
so solicitous to increase the number of species under all his genera: an error
this, which tends to great confusion and embarassment and must retard the
progress and real improvement of the botanic science." Linnaeus however
in redressing the balance earned his full approbation: "He has so far
retrenched the genus (Lichen} that in his general enumeration of plants he
recounts only 80 species belonging to it."
Linnaeus's binomial system was almost at once adopted by the whole
botanical world and the discovery and tabulation of lichens as well as of
other plants proceeded apace. Scopoli's4 Flora Carniolica, for instance,
published in 1760, still adhered to the old descriptive method of nomen-
1 Hill i75i. Hill'sgenus Collema is Nostoc, etc. 2 Hill 1760. 8 Watson 1759. 4 Scopoli 1760.
PERIOD III. 1729-1780 t 9
clature, but a second edition, issued twelve years later, is based on the new
system : it includes 54 lichen species.
About this time Adanson1 proposed a new classification of plants,
dividing them into families, and these again into sections and genera. He
transferred the lichens to the Family "Fungi," and one of his sections
contains a number of lichen genera, the names of these being culled from
previous workers, Dillenius, Hill, etc. A few new ones are added by himself,
and one of them, Graphis, still ranks as a good genus.
In England, Hudson2, who was an apothecary and became sub-librarian
of the British Museum, followed Linnaeus both in the first and later editions
of the Flora Anglica. He records 102 lichen species. Withering3 wras also
engaged, about this time, in compiling his Arrangement of Plants. He
translated Linnaeus's term "Algae" into the English word "Thongs," the
lichens being designated as "Cupthongs." In later editions, he simply
classifies lichens as such. Lightfoot4, whose descriptive and economic notes
are full of interest, records 103 lichens in the Flora Scotica, and Dickson5
shortly after published a number of species from Scotland, some of them
hitherto undescribed. Dickson was a nurseryman who settled in London,
and his avocations kept him in touch with plant-lovers and with travellers
in many lands.
E. PERIOD IV. 1780-1803
The inevitable next advance was made by Weber6 who at the time was
a Professor at Kiel. In a first work dealing with lichens he had followed
Linnaeus; then he published a new method of classification in which the
lichens are considered as an independent Order of Cryptogamia, and that
Order, called "Aspidoferae," he subdivided into genera. His ideas had been
partly anticipated by Hill and by Adanson, but the work of Weber indicates
a more correct view of the nature of lichens. He established eight fairly
well-marked genera, viz. Verrucaria, Tubercularia, Sphaerocephalum and
Placodium,vf\\ic\\ were based on fruit-characters, the thallus being crustaceous
and rather insignificant, and a second group Lichen, Collema, Cladonia and
Usnea, in which the thallus ranked first in importance. Though Weber's
scheme was published in 1780, it did not at first secure much attention.
The great authority of Linnaeus dominated so strongly the botany of the
period that for a long time no change was welcomed or even tolerated.
In our own country Relhan at Cambridge and Sibthorp7 at Oxford
were making extensive studies of plants. The latter was content to follow
Linnaeus in -his treatment of lichens. Relhan8 also grouped his lichens
under one genus though, in a second edition of his Flora, he broke away
from the Linnaean tradition and adopted the classification of Acharius.
1 Adanson 1763. 2 Hudson 1762 and 1778. 3 Withering 1776. * Lightfoot 1777.
5 Dickson 1785. 6 Weber 1780. 7 Sibthorp 1794. 8 Relhan 1785 and 1820.
I0 HISTORY OF LICHENOLOGY
Extensive contributions to the knowledge of English plants generally
were made by Sir James Edward Smith1 who, in 1788, founded the Linnean
Society of London of which he was President until his death in 1828. He
began his great work, English Botany, in 1790 with James Sowerby as
artist. Smith's and Sowerby 's part of the work came to an end in 1814;
but a supplement was begun in 1831 by Hooker who had the assistance of
Sowerby's sons in preparing the drawings. Nearly all the lichens recorded
by Smith are published simply as Lichen, and his Botany thus belongs to
the period under discussion, though in time it stretches far beyond.
Continental lichenologists had been more receptive to new ideas, and
other genera were gradually added to Weber's list, notably by Hoffmann2
and Persoon3.
For a long time little was known of the lichens of other than European
countries. Buxbaum4 in the East, Petiver5 and Hans Sloarie6 in the West
made the first exotic records. The latter notes how frequently lichens grew
on the imported Jesuit's bark, and he quaintly suggests in regard to some
of these species that they may be identical with the "hyssop that springeth
out of the wall." It was not however till towards the end of the eighteenth
century that much attention was given to foreign lichens, when Swartz7 in
the West Indies and Desfontaines8 in N. Africa collected and recorded
a fair number. Swartz describes about twenty species collected on his
journey through the West Indian Islands (1783-87).
Interest was also growing in other aspects of lichenology. Georgi9, a
Russian Professor, was the first to make a chemical analysis of lichens. He
experimented on some of the larger forms and extracted and examined the
mucilaginous contents of Ramalina farinacea, Platystna glaucum, Lobaria
pulmonaria, etc., which he collected from birch and pine trees. About this
time also the French scientists Willomet10, Amoreux and Hoffmann jointly
published theses setting forth the economic value of such lichens as were
used in the arts, as food, or as medicine.
F. PERIOD V. 1803-1846
The fine constructive work of Acharius appropriately begins a new era
in the history of lichenology. Previous writers had indeed included lichens
in their survey of plants, but always as a somewhat side issue. Acharius
made them a subject of special study, and by his scientific system of classifi-
cation raised them to the rank of the other great classes of plants.
Acharius was a country doctor at Wadstena on Lake Malar in Sweden,
as he himself calls it, " the country of lichens." He was attracted to the
1 Smith 1790. 3 Hoffmann 1798. 8 Persoon 1794. 4 Buxbaum 1728.
5 Petiver 1712. 6 Sloane 1796 and 1807. 7 Swartz 1788 and 1791. s Desfontaines 1798-1800.
9 Georgi 1797. 10 Willomet, etc. 1787.
PERIOD V. 1803-1846 ii
study of them by their singular mode of growth and organization, both of
thallus and reproductive organs, for which reason he finally judged that
lichens should be considered as a distinct Order of Cryptogamia.
In his first tentative work1 he had followed his great compatriot
Linnaeus, classifying all the species known to him under the one genus
Lichen, though he had progressed so far as to divide the unwieldy Genus
into Families and these again into Tribes, these latter having each a tribal
designation such as Verrucaria, Opegrapha, etc. He established in all twenty-
eight tribes which, at a later stage, he transformed into genera after the
example of Weber.
Acharius, from the beginning of his work, had allowed great importance
to the structure of the apothecia as a diagnostic character though scarcely
recognizing them as true fruits. He gave expression to his more mature
views first in the Methodus Lichenum*, then subsequently in the larger
Lichenographia Universalia*. In the latter work there are forty-one genera
arranged under different divisions; the species are given short and succinct
descriptions, with habitat, locality and synonymy. No material alteration
was made in the Synopsis Lichenum*, a more condensed work which he pub-
lished a few years later.
The Cryptogamia are divided by Acharius into six " Families," one of
which, " Lichenes," is distinguished, he finds, by two methods of propagation :
by propagula (soredia) and by spores produced in apothecia. He divides
the family into classes characterized solely by fruit characters, and these
again into orders, genera and species, of which diagnoses are given. With
fuller knowledge many changes and rearrangements have been found
necessary in the application and extension of the system, but that in no way
detracts from the value of the work as a whole.
•' In addition to founding a scientific classification, Acharius invented
a^lerminology for the structures peculiar to lichens. We owe to him the
names and descriptions of " thallus," " podetium," " apothecium," " peri-
thecium," "soredium," "cyphella" and "cephalodium," the last word how-
ever with a different meaning from the one now given to it. He proposed
several others, some of which are redundant or have fallen into disuse, but
many of his terms as we see have stood thotest of time and have been
found of service in allied branches of botany. J\
Lichens were studied with great zest by the men of that day. Hue5
recalls a rather startling incident in this connection: Wahlberg, it is said,
had informed Dufour that he had sent a large collection of lichens from
Spain to Acharius who was so excited on receiving them, that he fell ill
and died in a few days (Aug. Hth, 1819). Dufour, however, had added the
comment that the illness and death might after all be merely a coincidence.
1 Acharius 1798. 2 Acharius 1803. 3 Acharius 1810. 4 Acharius 1814. ° Hue 1908.
12 HISTORY OF LICHENOLOGY
Among contemporary botanists, we find that De Candolle1 in the volume
he contributed to Lamarck's French Flora, quotes only from the earlier work
of Acharius. He had probably not then seen the Methodus, as he uses none
of the new terms ; the lichens of the volume are arranged under genera
which are based more or less on the position of the apothecia on the thallus.
Florke2, the next writer of consequence, frankly accepts the terminology
and the new view of classification, though differing on some minor points.
Two lists of lichens, neither of particular note, were published at this
time in our country: one by Hugh Davies3 for Wales, which adheres to the
Linnaean system, and the other by Forster4 of lichens round Tonbridge.
Though Forster adopts the genera of Acharius, he includes lichens among
algae. A more important publication was S. F. Gray's5 Natural Arrange-
ment of British Plants. Gray, who was a druggist in Walsall and afterwards
a lecturer on botany in London, was only nominally6 the author, as it was
mainly the work of his son John Edward Gray7, sometime Keeper of Zoology
in the British Museum. Gray was the first to apply the principles of the
Natural System of classification to British plants, but the work was opposed
by British botanists of his day. The years following the French Revolution
and the Napoleonic wars were full of bitter feeling and of prejudice, and
anything emanating, as did the Natural System, from France was rejected
as unworthy of consideration.
In the Natural Arrangement, Gray followed Acharius in his treatment
of lichens ; but whereas Acharius, though here and there confusing fungus
species with lichens, had been clear-sighted enough to avoid all intermixture
of fungus genera, with the exception of one only, the sterile genus Rhizo-
morpha, Gray had allowed the interpolation of several, such as Hysterium,
Xylaria, Hypoxylon, etc. He had also raised many of Acharius's subgenera
and divisions to the rank of genera, thus largely increasing their number.
This oversplitting of well-defined genera has somewhat weakened Gray's
work and he has not received from later writers the attention he deserves.
The lichens of Hooker's8 Flora Scotica, which is synchronous with Gray's
work, number 195 species, an increase of about 90 for Scotland since the
publication of Lightfoot's Flora more than 40 years before. Hooker also
followed Acharius in his classification of lichens both in the Flora Scotica
and in the Supplement to English Botany*, which was undertaken by the
younger Sowerbys and himself. To that work Borrer (1781-1862), a keen
lichenologist, supplied many new and rare lichens collected mostly in Sussex.
It is a matter of regret that Greville should have so entirely ignored
lichens in his great work on Scottish Cryptogams™. The two species of
1 De Candolle 1805. 2 Florke 18x5-1819. » Davies 1813. * Forster :8i6. 5 S. F. Gray 1821.
6 Carrington 1870. 7 See List of the Books, etc. by John Edward Gray, p. 3 1872
8 Hooker 1821. » Hooker 1831. " Greville 1823-1827.
PERIOD V. 1803-1846 13
Lichina are the only ones he figured, and these he took to be algae. He1 was
well acquainted with lichens, for in the Flora Edinensis he lists 128 species
for the Edinburgh district, arranging the genera under "Lichenes" with the
exception of Opegrapha and Verrucaria which are placed with the fungus
genus Poronia in " Hypoxyla." Though he cites the publications of Acharius,
he does not employ his scientific terms, possibly because he was writing his
diagnoses in English. Two other British works of this time still remain to
be chronicled : Hooker's2 contributions to Smith's English Flora and
Taylor's3 work on lichens in Mackay's Flora Hibernica. Through these the
knowledge of the subject was very largely extended in our country.
The classification of lichens and their place in the vegetable kingdom
were now firmly established on the lines laid down by Acharius. Fries4 in
his important work Lichenographia Europaea more or less followed his dis-
tinguished countryman. The uncertainty as to the position and relationship
of lichens had rendered the task of systematic arrangement one of peculiar
difficulty and had unduly absorbed attention ; but now that a satisfactory
order had been established in the chaos of forms, the way was clear for other
aspects of the study. Several writers expressed their views by suggesting
somewhat different methods of classification, others wrote monographs of
separate groups, or genera. Fee5 published an Essay on the Cryptogams
(mostly lichens) that grew on officinal exotic barks; Florke8 took up the
difficult genus Cladonia\ Wallroth7 also wrote on Cladonia\ Delise8 on Sticta,
and Chevalier9 published a long and elaborate account of Graphideae.
Wallroth and Meyer at this time published, simultaneously, important
studies on the general morphology and physiology of lichens. Wallroth10
had contemplated an even larger work on the Natural History of Lichens,
but only two of the volumes reached publication. In the first of these he
devoted much attention to the " gonidia " or " brood-cells " and established
the distinction between the heteromerous and homoiomerous distribution of
green cells within the thallus; he also describes with great detail the "mor-
phosis" and "metamorphosis" of the vegetative body. In the second volume
he discusses their physiology — the contents and products of the thallus,
colouring, nutrition, season of development, etc. — and finally the pathology
of these organisms. He made no great use of the compound microscope,
and his studies were confined to phenomena that could be observed with a
single lens.
Meyer's11 work contains a still more exact study of the anatomy and
physiology of lichens; he also devotes many passages to an account of their
metamorphoses, pointing out that species alter so much in varying conditions,
that the same one at different stages may be placed even in different genera;
1 Greville 1824. - Hooker 1833. 3 Taylor 1836. 4 Fries 1831. 5 Fee 1874. 6 Florke 1828.
7 Wallroth 1829. 8 Delise 1822. » Chevalier 1824. 10 Wallroth 1825. " Meyer 1825.
I4 HISTORY OF LICHENOLOGY
he however carries his theory of metamorphosis too far and unites together
widely separated plants. Meyer was the first to describe the growth of the
lichen from spores, though his description is somewhat confused. Possibly
the honour of havingfirst observed their germination should be given to a later
botanist, Holle1. The works of both Wallroth and Meyer enjoyed a great
and well-merited reputation : they were standard books of consultation for
many years. Koerber2, who devoted a long treatise to the study of gonidia,
confirmed Wallroth's theories: he considered at that time that the gonidia
in the soredial condition were organs of propagation.
Mention should be made here of the many able and keen collectors who,
in the latter half of the eighteenth century and the beginning of the nine-
teenth, did so much to further the knowledge of lichens in the British Isles.
Among the earliest of these naturalists are Richard Pulteney (1730-1801),
whose collection of plants, now in the herbarium of the British Museum, in-
cludes many lichens, and Hugh Davies (1739-1821), a clergyman whose
Welsh plants also form part of the Museum collection. The Rev. John
Harriman (1760-1831) sent many rare plants from Egglestone in Durham
to the editors of English Botany and among them were not a few lichens.
Edward Forster (1765-1849) lived in Essex and collected in that county,
more especially in and near Epping Forest, and another East country
botanist, Dawson Turner (17/5-1858), though chiefly known as an algologist,
gave considerable attention to lichens. In Scotland the two most active
workers were Charles Lyell (1767-1849), of Kinnordy in Forfarshire, and
George Don (1798-1 856), also a Forfar man. Don was a gardener and became
eventually a foreman at the Chelsea Physic Garden. Sir Thomas Gage of
Hengrave Hall (1781-1823) botanized chiefly in his own county of Suffolk ;
but most of his lichens were collected in South Ireland and are incorporated in
the herbarium of the British Museum. Miss Hutchins also collected in Ireland
and sent her plants for inclusion in English Botany. But in later years, the
principal lichenologist connected with that great undertaking was W. Borrer,
who spent his life in Sussex : he not only supplied a large number of specimens
to the authors, but he himself discovered and described many new lichens.
American lichenologists were also extremely active all through this
period. The comparatively few lichens of Michaux's3 Flora grouped under
" Lichenaceae " were collected in such widely separated regions as Carolina
and Canada. A few years later Miihlenberg4 included no fewer than 184
species in his Catalogue of North American Plants. Torrey6 and Halsey6
botanized over a limited area near New York, and the latter, who devoted
himself more especially to lichens, succeeded in recording 176 different forms,
old and new. These two botanists were both indebted for help in their work
1 Holle 1849. 2 Koerber 1839. 3 Michaux 1803.
4 Muhlenberg 1813. 5 Torrey 1819. * Halsey 1824.
PERIOD V. 1803-1846 15
to Schweinitz, a Moravian brother, who moved from one country to another,
working and publishing, now in America and now in Europe. His name is
however chiefly associated with fungi. Later American lichenology is
nobly represented by Tuckerman1 who issued his first work on lichens in
1839, and who continued for many years to devote himself to the subject.
He followed at first the classification and nomenclature that had been
adopted by Fee, but as time went on he associated himself with all that was
best and most enlightened in the growing science.
Travellers and explorers in those days of high adventure were constantly
sending their specimens to European botanists for examination and deter-
mination, and the knowledge of exotic lichens as of other classes of plants
grew with opportunity. Among the principal home workers in foreign
material, at this time, may be cited Fee2 who described a very large series
on officinal barks {Cinchona, etc.) so largely coming into use as medicines;
he also took charge of the lichens in Martius's3 Flora of Brazil. Montagne4
named large collections, notably those of Leprieur collected in Guiana, and
Hooker5 and Walker Arnott determined the plants collected during Captain
Beechey's voyage, which included lichens from many different regions.
G. PERIOD VI. 1846-1867
The last work of importance, in which microscopic characters were
ignored, was the Enumeratio critica Lichenum Europaeum by Schaerer6, a
veteran lichenologist, who rather sadly realized at the end the limitations
of that work, as he asks the reader to accept it " such as it is." Many years
previously, Eschweiler7 in his Systema and Fee8 in his account of Cryptogams
on Officinal Bark, had given particular attention to the internal structure as
well as to the outward form of the lichen fructification. Fe"e, more especially,
had described and figured a large number of spores; but neither writer had
done more than suggest their value as a guide in the determination of genera
and species.
It was an Italian botanist, Giuseppe de Notaris9, a Professor in Florence,
who took up the work where Fee had left it. His comparative studies of both
vegetative and reproductive organs convinced him of the great importance
of spore characters in classification, the spore being, as he rightly decided,
the highest and ultimate product of the lichen plant. In his microscopic
examination of the various recognized genera, he found that while, in some
genera, the spores conformed to one distinct type, in others their diversities
in form, septation or colour gave a decisive reason for the establishment of
new genera, while minor differences in size, etc. of the spores proved to be of
great value in distinguishing species. The spore standard thus marks a new
1 Tuckerman 1839. 2 Fee 1824. s Martius 1833. 4 Montagne 1851. 5 Hooker 1841.
6 Schaerer 1850. ~ Eschweiler 1824. 8 Fee 1824. 9 De Notaris 1846.
16 HISTORY OF LICHENOLOGY
departure in lichenology. De Notaris published the results of his researches
in a fragment of a projected larger work that was never completed. Though
his views were overlooked for a time, they were at length fully recognized
and further elaborated by Massalongo1 in Italy, by Norman2 in Norway, by
Koerber3 in Germany and by Mudd4 in our own country. Massalongo had
drawn up the scheme of a great Scolia Lichenographica, but like de Notaris,
he was only able to publish a part. After twelve years of ill-health, in which
he struggled to continue his work, he died at the early age of 36.
Lindsay5, Mudd and Leighton6 were at this time devoting great attention
to British lichens. Lauder Lindsay's Popular History of British Lichens,
with its coloured plates and its descriptive and economic account of these
plants has enabled many to acquire a wide knowledge of the group. Mudd's
Manual, a more complete and extremely valuable contribution to the subject,
followed entirely on the lines of Massalongo's work. From his large
experience in the examination of lichens he came to the conclusion that :
" Of all organs furnished by a given group of plants, none offer so many
real, constant and physiological characters as the spores of lichens, for the
formation of a simple and natural classification."
Meanwhile, a contemporary writer, William Nylander, was rising into
fame. He was born at Uleaborg in Finland7 in 1822 and became interested
in lichens very early in his career. His first post was the professorship of
botany at Helsingfors; but in 1863 he gave up his chair and removed to
Paris where he remained, except for short absences, until his death. One
of his excursions brought him to London in 1857 to examine Hooker's
herbarium. He devoted his whole life to the study of lichens, and from
1852, the date of his first lichen publication, which is an account of the lichens
of Helsingfors, to the end of his life he poured out a constant succession of
books or papers, most of them in Latin. One of his earliest works was an
Essay on Classification91 which he elaborated later, but which in its main
features he never altered. He relied, in his system, on the structure and form
of thallus, gonidia and fructifications, more especially on those of the
spermogonia (pycnidia), but he rejected ascospore characters except so far as
they were of use in the diagnosis of species. He failed by being too isolated
and by his unwillingness to recognize results obtained by other workers.
In 1866 he had discovered the staining reactions of potash and hypochlorite
of lime on certain thalli, and though these are at times unreliable owing to
growth conditions, etc., they have generally been of real service. Nylander,
however, never admitted any criticism of his methods; his opinions once
stated were never revised. He rejected absolutely the theory of the dual
nature of lichens propounded by Schwendener without seriously examining
1 Massalongo 1852. » Norman 1852. - 3 Koerber 1855. 4 Mudd 1861.
5 Lindsay 1856. « Leighton 1851, etc. 7 See Hue 1899. 8 Nylander 1854 and 1855.
PERIOD VI. 1846-1867 17
the question, and regarded as personal enemies those who dared to differ
from him. The last years of his life were passed in complete solitude. He
died in March 1899.
Owing to the very inadequate powers of magnification at the service of
scientific workers, the study of lichens as of other plants was for long restricted
to the collecting, examining and classifying of specimens according to their
macroscopic characters; the microscopic details observed were isolated and
unreliable except to some extent for spore characters. Special interest is
therefore attached to the various schemes of classification, as each new one
proposed reflects to a large extent the condition of scientific knowledge of
the time, and generally marks an advance. It was the improvement of the
microscope from a scientific toy to an instrument of research that opened
up new fields of observation and gave a new impetus to the study of a group
of plants that had proved a puzzle from the earliest times.
Tulasne was one of the pioneers in microscopic botany. He made
a methodical study of a large series of lichens1 and traced their develop-
ment, so far as he was able, from the spore onwards. He gave special attention
to the form and function of spermogonia and spermatia, and his work is
enriched by beautiful figures of microscopic detail. Lauder Lindsay2 also
published an elaborate treatise on spermogonia, on their occurrence in the
lichen kingdom and on their form and structure. The paper embodies the
results of wide microscopic research and is a mine of information regarding
these bodies.
Much interesting work was contributed at this time by Itzigsohn3,
Speerschneider 4, Sachs5, Thwaites6, and others. They devoted their researches
to some particular aspect of lichen development and their several contribu-
tions are discussed elsewhere in this work.
Schwendener7 followed with a systematic study of the minute anatomy
of many of the larger lichen genera. His work is extremely important in
itself and still more so as it gradually revealed to him the composite
character of the thallus.
Several important monographs date from this period : Leighton8 reviewed
all the British " Angiocarpous " lichens with special reference to their
" sporidia " though without treating these as of generic value. He followed
up this monograph by two others, on the Graphideae9 and the Umbili-
carieae™, and Mudd11 published a careful study of the British Cladoniae.
On the Continent Th. Fries12 issued a revision of Stereocaulon and Pilo-
pkoron and other writers contributed work on smaller groups.
1 Tulasne 1852. 2 Lauder Lindsay 1859. 3 Itzigsohn 1854-1855. 4 Speerschneider 1853.
5 Sachs 1855. fi Thwaites 1849. 7 Schwendener 1863-1868. 8 Leighton 1851.
9 Leighton 1854. 10 Leighton 1856. " Mudd 1865. 12 Th. Fries 1858.
I8 HISTORY OF LICHENOLOGY
H. PERIOD VII. 1867 AND AFTER
Modern lichenology begins with the enunciation of Schwendener's1 theory
of the composite nature of the lichen plant. The puzzling resemblance of
certain forms to algae, of others to fungi, had excited the interest of botanists
from a very early date, and the similarity between the green cells in the
thallus, and certain lower forms of algae had been again and again pointed
out. Increasing observation concerning the life-histories of these algae and
of the gonidia had eventually piled up so great a number of proofs of their
identity that Schwendener's announcement must have seemed to many an
inevitable conclusion, though no one before had hazarded the astounding
statement that two organisms of independent origin were combined in the
lichen.
f The dual hypothesis, as it was termed, was not however universally
accepted. It was indeed bitterly and scornfully rejected by some of the
most prominent lichenologists of the time, including Nylander2, J. Miiller
and Crombie3. Schwendener held that the lichen was a fungus parasitic
on an alga, and his opponents judged, indeed quite rightly, that such a view
was wholly inadequate to explain the biology of lichens. It was not till a
later datgjhat the truer conception of the "consortium" or "symbiosis" was
proposed. ^T he researches undertaken to prove or disprove the new theories
cojne under review in Chapter II.
( Stahl's work on the development of the carpogonium in lichens gave a
rte^direction to study, and notable work has beeadone during the last forty
years in that as in other branches of lichenology./
Exploration of old and new fields furnished the lichen-flora of the world
with many new plants which have been described by various systematists —
by Nylander, Babington, Arnold, Mujler, Th. Fries, Stizenberger, Leighton,
Crombie and many others, and their contributions arc scattered through
contemporary scientific journals. The number of recorded species is now
somewhere about 40,00x3, though, in all probability, many of these will be
found to be growth forms. Still, at the lowest computation, the number of
different species is very large.
Systematic literature has been enriched by a series of important mono-
graphs, too numerous to mention here. While treating definite groups, they
have helped to elucidate some of the peculiar biological problems of the
symbiotic growth.
Morphology, since Schwendener's time, has been well represented by
Zukal, Reinke, Lindau, Funfstiick, Darbishire, Hue, and by an increasing
number of modern writers whose work is duly acknowledged under each
1 Schwendener 1867. n- Nylander 1874. :i Croml.ie 1885.
PERIOD VII. 1867 AND AFTER 19
subject of study. Hesse and Zopf, and more recently Lettau, have been
engaged in the examination of those unique products, the lichen acids, while
other workers have investigated lichen derivatives such as fats. Ecology of
lichens has also been receiving increased attention. Problems of physiology,
symbiosis, etc., are not yet considered to be solved and are being attacked
from various sides.
British lichenologists since 1867 have been mainly engaged on field
work, with the exception of Lauder Lindsay who published after that date
a second great paper on the spermogonia of crustaceous lichens. Leighton
in his Lichen Flora and Crombie in numerous publications gave the lead in
systematic work, and with them were associated a band of indefatigable
collectors. Among these may be recalled Alexander Croall (1809-85), a
parish schoolmaster in Scotland whose Plants of Braemar include many of
the rarer mountain lichens. Henry Buchanan Holl (1820-86), a surgeon in
London, collected in the Scottish Highlands as well as in England and
Wales. William Joshua (1828-98) worked mostly in the Western counties
of Somerset and Gloucestershire. Charles Du Bois Larbalestier, who died in
191 1, was a keen observer and collector during many years; he discovered
a number of new species in his native Jersey, in Cambridgeshire and also in
Connemara; his plants were generally sent to Nylander to be determined
and described. He issued two sets of lichens, one of Channel Island plants,
the other of more general British distribution, and he had begun the issue
of Cambridgeshire lichens. Isaac Carroll (1828-80), an Irish botanist, issued
a first fascicle of Lichenes Hibernici containing 40 numbers. More recently
Lett1 has reported 80 species and varieties from the Mourn e Mountains in
Ireland. Other more extensive sets were issued by Mudd and by Leighton,
and later by Crombie and by Johnson. All these have been of great service
to the study of lichenology in our country. Other collectors of note are
Curnow (Cornwall), Martindale (Westmoreland), and E. M. Holmes whose
valuable herbarium has been secured by University College, Nottingham.
The publication of the volume dealing with Lichenes in Engier and
Prantl's Pflanzenfamilien has proved a boon to all who are interested in the
study of lichens. Fiinfstuck2 prepared the introduction, an admirable
presentation of the morphological and physiological aspects of the subject,
while Zahlbruckner3, with equal success, took charge of the section dealing
with classification.
1 Lett 1890. - Fiinfstiick 1898. :t Zahlbruckner 1903-1907.
CHAPTER II
CONSTITUENTS OF THE LICHEN THALLUS
I. LICHEN GONIDIA
THE thallus or vegetative body of lichens differs from that of other green
plants in the sharp distinction both of form and colour between the assimi-
lative cells and the colourless tissues, and in the relative positions these
occupy within the thallus: in the greater number of lichen species the green
chlorophyll cells are confined to a narrow zone or band some way beneath
and parallel with the surface (Fig. i); in a minority of genera they are dis-
tributed through the entire thallus (Fig. 2); but in all cases the tissues
Fig. i. Physcia aipolia Nyl. Vertical
section of thallus. a, cortex; b, algal
layer; c, medulla; d, lower cortex,
x 100 (partly diagrammatic).
Fig. i. Collema ntgrescens Ach. Vertical
section of thallus. «, chains of the
alga Nostoc ; b, fungal filaments, x 600.
remain distinct. The green zone can be easily demonstrated in any of the
larger lichens by scaling off the outer surface cells, or by making a vertical
section through the thallus. The colourless cells penetrate to some extent
among the green cells; they also form the whole of the cortical and
medullary tissues.
These two different elements we now know to consist of two distinct
organisms, a fungus and an alga. The green algal cells were at one time
considered to be reproductive bodies, and were called "gonidia," a term still
in use though its significance has changed.
LICHEN GONIDIA 21
i. GONIDIA IN RELATION TO THE THALLUS
A. HISTORICAL ACCOUNT OF LICHEN GONIDIA
There have been few subjects of botanical investigation that have
roused so much speculation and such prolonged controversy as the question
of these constituents of the lichen plant. The green cells and the colourless
filaments which together form the vegetative structure are so markedly
dissimilar, that constant attempts have been made to explain the problem
of their origin and function, and thereby to establish satisfactorily the
relationship of lichens to other members of the Plant Kingdom.
In gelatinous lichens, represented by Collema, of which several species
are common in damp places and grow on trees or walls or on the ground,
the chains of green cells interspersed through the thallus have long been
recognized as comparable with the filaments of Nostoc, a blue-green
gelatinous alga, conspicuous in wet weather in the same localities as those
inhabited by Collema. So among early systematists, we find Ventenat1
classifying the few lichens with which he was acquainted under algae and
hazarding the statement that a gelatinous lichen such as Collema was only
a Nostoc changed in form. Some years later Cassini2 in an account of Nostoc
expressed a somewhat similar view, though with a difference: he suggested
that Nostoc was but a monstrous form of Collema, his argument being that,
as the latter bore the fruit, it was the normal and perfect condition of
the plant. A few years later Agardh3 claimed to have observed the meta-
morphosis of Nostoc up to the fertile stage of a lichen, Collema limosum.
But long before this date, Scopoli4 had demonstrated a green colouring
substance in non-gelatinous lichens by rubbing a crustaceous or leprose
thallus between the fingers; and Persoon5 made use of this green colour
characteristic of lichen crusts to differentiate these plants from fungi.
Sprengel6 went a step further in exactly describing the green tissue as
forming a definite layer below the upper cortex of foliaceous lichens.
The first clear description and delimitation of the different elements
composing the lichen thallus was, however, given by Wallroth7. He drew
attention to the great similarity between the colourless filaments of the
lichen and the hyphae of fungi. The green globose cells in the chlorophylla-
ceous lichens he interpreted as brood-cells or gonidia, regarding them as
organs of reproduction collected into a "stratum gonimon." To the same
author we owe the terms "homoiomerous" and "heteromerous," which he
coined to describe the arrangement of these green cells in the tissue of the
thallus. In the former case the gonidia are distributed equally through the
structure; in the latter they are confined to a distinct zone.
1 Ventenat 1794, p. 36. 2 Cassini 1817, p. 395. 3 Agardh 1820. 4 Scopoli 1/60, p. 79.
5 Persoon 1794, p. 17. 6 Sprengel 1804, p. 325. 7 Wallroth 1825, I.
22 CONSTITUENTS OF THE LICHEN THALLUS
Wallroth's terminology and his views of the. function of the gonidia were
accepted as the true explanation for many years, the opinion that they were
solely reproductive bodies being entirely in accordance with the well-known
part played by soredia in the propagation of lichens — and soredia always
include one or more green cells.
B. GONIDIA CONTRASTED WITH ALGAE
In describing the gonidia of the Graphideae Wallroth1 had pointed out
their affinity with the filaments of Chroolepus ( Trentepohlid) umbrina. He
considered these and other green algae when growing 10986 on the trunks of
trees to be but "unfortunate brood-cells" which had become free and, though
capable of growth and increase, were unable to form again a lichen plant.
Further observations on gonidia were made by E. Fries2: he found that
the green cells escaped from the lichen matrix and produced new individuals;
and also that the whole thallus in moist localities might become dissolved
into the alga known as Protococcus viridis\ but, he continues, "though these
Protococcus cells multiplied exceedingly, they never could rise again to the
perfect lichen." Kiitzing3, in a later account of Protococcus viridis, also
recognized its affinity with lichens; he stated that he could testify from
observation that, according to the amount of moisture present, it would
develop, either in excessive moisture to a filamentous alga, or in drier con-
ditions "to lichens such as Lecanora subfusca or Xanthoria parietina."
A British botanist, G. H. K. Thwaites4, at one time -superintendent of
the botanical garden at Peradeniya in Ceylon, published a notable paper
on lichen gonidia in which he pointed out
that as in Collema the green constituents
of the thallus resembled the chains of Nostoc,
so in the non-gelatinous lichens, the green
globose cells were comparable or identical with
Pleurococctis, and Thwaites further observed that
they increased by division within the lichen
thallus. He insisted too that in no instance were
gonidia reproductive organs : they were essen-
tial component parts of the vegetative body and
necessary to the life of the plant. In a further
paper on Chroolepus cbeneus Ag., a plant con-
Fig. 3. Coenogomum ebeneum A. L. . . . . ,
Sm. Tip ofiichen filament, the alga sisting of slender dark-coloured felted fila-
overgrown by dark fungal hyphae ments, he described these filaments as being
composed of a central strand which closely
resembled the alga Chroolepus, and of a surrounding sheath of dark-coloured
1 Wallroth 1825, 1, p. 303. * Fries 1831, pp. Ivi and Ivii.
3 Kutzing 1843. 4 Thwaites 1849, pp. 219 and 241.
LICHEN GONIDIA
cells (Fig. 3): "occasionally," he writes, "the internal filament protrudes
beyond the investing sheath, and may then be seen to consist of oblong
cells containing the peculiar reddish oily-looking endochrome of Chroolepus?
Thwaites placed this puzzling plant in a new genus, Cystocolens, at the same
time pointing out its affinity with the lichen genus Coenogoninm. The
plant is now known as Coenogonium ebeneum. Thwaites was on the
threshold of the discovery as to the true nature of the relationship between
the central filament and the investing sheath, but he failed to take the next
forward step.
Very shortly after, Von Flotow1 published his views on some other
lichen gonidia. He had come to the conclusion that the various species of
the alga, Gloeocapsa, so frequently found in damp places, among mosses and
lichens, were merely growth stages of the gonidia of Ephebe pubescens, and
bore the same relation to Ephebe as did Lepra viridis (Protococcus) to Par-
melia. The gonidium of Ephebe is the gelatinous
filamentous blue-green alga Stigonema (Fig. 4),
and the separate cells are not unlike those of
Gloeocapsa. Flotow had also demonstrated that the
same type of gonidium was enclosed in the cepha-
lodia of Stereocaulon. Sachs2, tob, gave evidence as
to the close connection between Nostoc and Col-
lema. He had observed numerous small clumps of
the alga growing in proximity to equally abundant
thalli of Collema, with every stage of development
represented from one to the other. He found cases
where the gelatinous coils of Nostoc chains were
penetrated by fine colourless filaments "as if in-
vaded by a parasitic fungus." Later these threads were seen to be attached
to some cell of the Nostoc trichome. Sachs concluded, however, from very
careful examination at the time, that the colourless filaments were produced
by the green cells. As growth proceeded, the coloured Nostoc chains became
massed towards the upper surface, while the colourless filaments tended to
occupy the lower part of the thallus. He calculated that during the summer
season the metamorphosis from Nostoc to a fertile Collema thallus took from
three to four months. He judged that in favourable conditions the change
would inevitably take place, though if there should be too great moisture no
Collema would be formed. His study of Cladonia was less successful as he
mistook some colonies of Gloeocapsa for a growth condition of Cladonia
gonidia, an error corrected later by Itzigsohn3.
But before this date Itzigsohn4 had published a paper setting forth his
views on thallus formation, which marked a distinct advance. He did not
1 Flotow 185^. - Sachs 1855. 3 Itzigsohn 1855. 4 Itzigsohn 1854.
Fig. 4. Ephebe pubescens Nyl.
Tip of lichen filament >: 600.
24 CONSTITUENTS OF THE LICHEN THALLUS
hazard any theory as to the origin of gonidia, but he had observed spermatia
growing, much as did the cells of Oscillaria: by increase in length, and, by
subsequent branching, filaments were formed which surrounded the green
cells; these latter had meanwhile multiplied by repeated division till finally
a complete thallus was built up, the filamentous tissue being derived from
the spermatia, while the green layer came from the original gonidium. In
contrasting the development with that of Collema, he represents Nostoc as
a sterile product of a lichen and, like the gonidia of other lichens, only able
to form a lichen thallus when it encounters the fructifying spermatia.
Braxton Hicks1, a London doctor, some time later, made experiments
with Chroococcus algae which grew in plenty on the bark of trees, and
followed their development into a lichen thallus. He further claimed to
have observed a C/ilorococcus, which was associated with a Cladonia, divide
and form a Palmella stage.
C. CULTURE EXPERIMENTS WITH THE LICHEN THALLUS
It had been repeatedly stated that the gonidia might become independent
of the thallus, but absolute proof was wanting until Speerschneider2, who
had turned his attention to the subject, made direct culture experiments
and was able to follow the liberation of the green cells. He took a thinnish
section of the thallus of Hagenia (Pkyscia) ciliaris, and, by keeping it moist,
he was able to observe that the gonidial cells increased by division; the
moist condition at the same time caused the colourless filaments to die
away. This method of investigation was to lead to further results. It was
resorted to by Famintzin and Baranetsky3 who made cultures of gonidia
extracted from three different lichens, Physcia (Xanthorid) parietina,
Evernia furfur acea and Cladonia sp. They were able to observe the growth
and division of the green cells and, in addition, the formation of zoospores.
They recognized the development as entirely identical with that of the
unicellular green alga, Cystococcus humicola Naeg. Baranetsky4 continued
the experiments and made cultures of the blue-green gonidia of Peltigera
canina and of Collema pulposum. In both instances he succeeded in isolating
them from the thallus and in growing them in moist air as separate
organisms. He adds that "many forms reckoned as algae, may be con-
sidered as vegetating lichen gonidia such as Cystococcus, Polycoccus, Nostoc,
etc." Meanwhile Itzigsohn5 had further demonstrated by similar culture
experiments that the gonidia of Peltigera canina corresponded with the
algae known as Gloeocapsa monococca Kiitz., and as Polycoccus punctiformis
Kiitz.
1 Hicks 1860 and 1861. 2 Speerschneider 1853. =» Famintzin and Baranetsky 1867.
4 Baranetsky 1869. 5 Itzigsohn 1867.
LICHEN GONIDIA 25
D. .THEORIES AS TO THE ORIGIN OF GONIDIA
Though the relationship between the gonidia within the thallus and free-
living algal organisms seemed to be proved beyond dispute, the manner in
which gonidia first originated had not yet been discovered. Bayrhoffer1
attacked this problem in a study of foliose and other lichens. According
to his observations, certain colourless cells or filaments, belonging to the
"gonimic" layer, grew in a downward direction and formed at their tips a
faintly yellowish-green cell ; it gradually enlarged and was at length thrown
off as a free globose gonidium, which represented the female cell. Other
filaments from the "lower fibrous layer" of the thallus at the same time grew
upwards and from them were given off somewhat similar gonidia which
functioned as male cells. His observations and deductions, were fanciful,
but it must be remembered that the attachment between hypha and alga
in lichens is in many cases so close as to appear genetic, and also it often
happens that as the gonidium multiplies it becomes free from the hypha.
In his Meuioire sur les Lichens, Tulasne2 described the colourless
filaments as being fungal in appearance. The green cells he recognized as
organs of nutrition, and once and again in his paper he states that they
arose directly by a sort of budding process from the medullary or cortical-
filaments, either laterally or at the apex. This apparently reasonable view
of their origin was confirmed by other writers on the subject: by Speer-
schneider3 in his account of the anatomy of Usnea barbata, by de Bary4,
and by Schwendener5 in their earlier writings. But even while de Bary
accepted the hyphal origin of the gonidia, he noted6 that, accompanying
Opegrapha atra and other Graphideae, on the bark were to be found free
Chroolepus cells similar to the gonidia in the lichen thallus. He added that
gonidia of certain other lichens in no way differed from Protococcus cells;
and as for the gelatinous lichens he declared that "either they were the
perfect fruiting form of Nostocaceae and Chroococcaceae — hitherto looked
on as algae — or that these same Nostocaceae and Chroococcaceae are algbe
which take the form of Col/etna, Ephebe, etc., when attacked by an ascomy-
cetous fungus."
All these investigators, and other lichenologists such as Nylander7, still
regarded the free-living organisms identified by them as similar to the green
cells of the thallus, as only lichen gonidia escaped from the matrix and
vegetating in an independent condition.
The old controversy has in recent years been unexpectedly reopened by
Elfving8 who has sought again to prove the genetic origin of the green cells.
His method has been to examine a large series of lichens by making
sections of the growing areas, and he claims to have observed in every case
1 Bayrhoffer 1851. 2 Tulasne 1852. ;! Speerschneider 1854. 4 de Bary 1866, p. 242.
* Schwendener 1860, p. 125. 6 deBary 1866, p. 291. ~ Nylander 1870. 8 Elfving 1903 and 1913.
26 CONSTITUENTS OF THE LICHEN THALLUS
the hyphal origin of the gonidia: not only of Cystococcus but also of Trente-
potdia, Stigonema and Nostoc. In the case of Cystococcus, the gonidium, he
says, arises by the swelling of the terminal cell of the hypha to a globose
form, and by the gradual transformation of the contents to a chlrophyll-
green colour, with power of assimilation. In the case of filamentous gonidia
such as Trentepohlia, the hyphal cells destined to become gonidia are
intercalary. In Peltigera the cells of the meristematic plectenchyma become
transformed to blue-green Nostoc cells.
A study was also made by him of the formation of cephalodia1, the
gonidia of which differ from those of the " host" thallus. In Peltigera aphtkosa
he claims to have traced the development of these bodies to the branching
and mingling of the external hairs which, in the end, form a ball of inter-
woven hyphae. The central cells of the ball are then gradually differentiated
into Nostoc cells, which increase to form the familiar chains. Elfving allows
that the gonidia mainly increase by division within the thallus, and that they
also may escape and live as free organisms. His views are unsupported by
direct culture experiments which are the real proof of the composite nature
of the thallus.
E. MlCROGONlDIA
Another attempt to establish a genetic origin for lichen gonidia was made
by Minks2. He had found in his examination of Leptogium myochroum that
the protoplasmic contents of the hyphae broke up into a regular series of
globular corpuscles which had a greenish appearance. These minute bodies,
called by him microgonidia, were, he states, at first few in number, but
gradually they increased and were eventually set free by the mucilaginous
degeneration of the cell wall. As free thalline gonidia, they increased in
size and rapidly multiplied by division. Minks was at first enthusiastically
supported by Miiller3 who had found from his own observations that micro-
goiiidia might be present in any of the lichen hyphae and in any part of
thf thallus, even in the germinating tube of the lichen spore, and was in that
case most easily seen when the spores germinated within the ascus. He
argued that as spores originated within the ascus, so microgonidia were
developed within the hyphae. Minks's theories were however not generally
accepted and were at last wholly discredited by Zukal4 who was able to
prove that the greenish bodies were contracted portions of protoplasm in
hyphae that suffered from a lowered supply of moisture, the green colour
not being due to any colouring substance, but to light effect on the pro-
teins— an outcome of special conditions in the vegetative life of the plant.
Darbishire5 criticized Minks's whole work with great care and he has arrived
at the conclusion that the microgonidium may be dismissed as a totally
mistaken conception.
1 See p. .33. - Minks 1878 and 1879. 3 Muller 1878 and 1884. 4 Zukal 1884. 5 Darbishire 1895!.
LICHEN GONIDIA 27
F. COMPOSITE NATURE OF THALLUS
Schwendener1 meanwhile was engaged on his study of lichen anatomy.
Though at first he adhered to the then accepted view of the genetic con-
nection between hyphae and gonidia, his continued examination of the
vegetative development led him to publish a short paper2 in which he
announced his opinion that the various blue-green and green gonidia were
really algae and that the complete lichen in all cases represented a fungus
living parasitically on an alga: in Ephebe, for example, the alga was a form
of Stigonema, in the Collemaceae it was a species of Nostoc. In those lichens
enclosing bright green cells, the gonidia were identical with Cystococcus
humicola, while in Graphideae the brightly coloured filamentous cells were
those of Chroolepus (Trentepohlia). This statement he repeated in an
appendix to the larger work on lichens3 and again in the following year4
when he described more fully the different gonidial algae and the changes
produced in their structure and habit by the action of the parasite: "though
eventually the alga is destroyed," he writes, "it is at first excited to more
vigorous growth by contact with the fungus, and in the course of generations
may become changed beyond recognition both in size and form." In support
of his theory of the composite constitution of the thallus, Schwendener
pointed out the wide distribution and frequent occurrence in nature of the
algae that become transformed to lichen gonidia. He claimed as further
proof of the presence of two distinct organisms that, while the colourless
filaments react in the same way as fungi on the application of iodine, the
gonidia take the stain of algal membranes.
G. SYNTHETIC CULTURES
Schwendener's "dual hypothesis," as it was termed, excited great interest
and no little controversy, the reasons for and against being debated with
considerable heat. Rees5 was the first who attempted to put the matte*. to
the proof by making synthetic cultures. For this purpose he took spores
from the apothecium of a Collema and sowed them on pure cultures of Nostoc,
and as a result obtained the formation of a lichen thallus, though he did not
succeed in producing any fructification. He observed further that the
hyphal filaments from the germinating spore died off when no Nostoc was
forthcoming.
Bornet6 followed with his record of successful cultures. He selected for
experiment the spores of PJiyscia (Xanthoria) parietina and was able to
show that hyphae produced from the germinating spore adhered to the free-
1 Schwendener 1860, etc. 2 Schwendener 1867. 3 Schwendener 1868, p. 195.
4 Schwendener 1869. 5 Rees 1871. 6 Bornet 1872.
CONSTITUENTS OF THE LICHEN THALLUS
growing cells of Protococcus1 viridis and formed the early stages of a lichen
thallus. Woronin2 contributed his observations on the gonidia of Parmelia
(Physcid) pulverulenta which he isolated from the thallus and cultivated in
pure water. He confirmed the occurrence of cell division in the gonidia and
also the formation of zoospores, these again forming new colonies of algae
identical in all respects with the thalline gonidia. He was able to see the
germinating tube from a lichen spore attach itself to a gonidium, though he
failed in his attempts to induce further growth. In our own country Archer3
welcomed the new views on lichens, and attempted cultures but with very
little success. Further synthetic cultures were made by Bornet4, Treub5 and
Borzi6 with a series of lichen spores. They also were able to observe the
first stages of the thallus. Borzi observed spores of Physcia (Xanthorid)
parietina scattered among Protococcus cells on the branch of a tree. The
spores had germinated and the first branching hyphae had already begun to
encircle the algae.
Additional evidence in favour of the theory of the independent origin of
the colourless filaments and the green cells was furnished by Stahl's7 re-
search on hymenial gonidia in Endocarpon (Fig. 5). By making synthetic
„ Endocarpon pusillum
edw. Asci and spores,
with hymenial gonidia x
320 (after Stahl).
Fig. 6. Endocarpon pusillum Hedw. Spore
germinating in contact with hymenial
gonidia x 320 (after Stahl).
1 The authors quoted have been followed in their designation of the various green algae that form
lichen gonidia. It is however now recognized ( Wille 1913) that either Protococcus viridis Ag. , Chlorella
or other Protococcaceae may form the universal green coating on trees, etc., and be incorporated as
lichen gonidia. Pleurococcus vulgaris Naeg. and Pleurococcus Naegeli Chod. are synonyms of Proto-
coccus virtdis. In that alga there is no pyrenoid, and no zoospores are formed.
The genus Cystococcus, according to Chodat ( 1913), is characterized by the presence of a pyrenoid
and by reproduction with zoospores and is identical with Pleurococcus z^fcawMenegh. (non Naeg.),
though Wille regards Meneghini's species as of mixed content. Paulson and Hastings (1920) now
find that Chodat's pyrenoid is the nucleus of the cell.
» Woronin ,87a. » Archer ,873, ,874, 1875. « Bornet r873 and 1874.
'Treub ,873. 'Borzi ,875. 7 Stahl lg
LICHEN GONIDIA
29
cultures of the mature spores with these bodies, he was able to observe not
only the germination of the spores and the attachment of the filaments to
the gonidia (Fig. 6), but also the gradual building up of a complete lichen
thallus to the formation of perithecia and spores.
Some years later Bonnier1 made an interesting series of synthetic cultures
between the spores of lichens germinated in carefully sterilized conditions,
and algae taken from the open (Figs. 7 and 8). Separate control cultures of
Fig. 7. Germination of spore of Physcia parietitia De Not. in
contact with Protococcus viridis Ag. x 950 (after Hornet).
Fig. 8. Physcia parietitia De Not. Vertical section of thallus
obtained by synthetic culture x 130 (after Bonnier).
spores and algae were carried on at the same time, with the result that in
one case lichen hyphae alone, in the other algae were produced. The various
lichen spores with which he experimented were sown in association with the
following algae:
(i) PROTOCOCCUS.
Pure synthetic cultures of Physcia ( Xanthoria) parietina were begun in
August 1884 on fragments of bark. In October 1886 the thallus was several
centimetres in diameter, and some of the lobes were fruited.
Physcia stellaris was also grown on bark; in one case both thallus and
apothecia were developed.
1 Bonnier 1886 and 1889.
3o CONSTITUENTS OF THE LICHEN THALLUS
Parmelia acetabulum, another corticolous species, formed only a minute
thallus about 5 mm. in diameter, but entirely identical with normally growing
specimens.
(2) PLEUROCOCCUS.
Lecanora (Rinodina) sophodes, sown on rock in 1883, reached in 1886 a
diameter of 13 mm. with fully developed apothecia.
Lecanora ferruginea and L. subfusca after three years' culture formed
sterile thalli only.
Lecanora coilocarpa in four years, and L. caesio-rufa in three years formed
very small thalli without fructification.
(3) TRENTEPOHLIA (Chroolepus).
Opegrapha vulgata in two years had developed thallus and apothecia.
The control culture of the spores formed, as in nature, a considerable felt of
mycelium in the interstices of the bark, but no pycnidia or apothecia.
Graphis elegans. Only the beginning of a differentiated thallus was
obtained with this species.
Verrucaria muralis (?)T gave in less than a year a completely developed
thallus.
Bonnier also attempted cultures with species of Collema and Ephebe, but
was unsuccessful in inducing the formation of a lichen plant.
H. HYMENIAL GONIDIA
Reference has already been made to the minute green cells which were
originally described by Nylander- as occurring in the perithecia of a few
Fyrenolichens as free gonidia, i.e. unentangled with lichen hyphae. Fuisting3
found them in the perithecium of Polyblastia (Staurothele) catalepta at a very
early stage of its development when the perithecial tissues were newly
differentiated from those of the surrounding thallus. The gonidia enclosed
in the perithecium differed in no wise from those of the thallus: they had
become mechanically enclosed in the new tissue; and while those in the
outer compact layers died off, those in the centre of the structure, where a
hollow space arises, were subject to very active division, becoming smaller
in the process and finally filling the cavity. Winter's4 researches on similar
lichens confirmed Fuisting's conclusions: he described them as similar to
the thalline gonidia but- lighter in colour and of smaller size, measuring
frequently only 2-3 ^ in diameter, though this size increased to about 7 yu,
when cultivated outside the perithecium.
Stahl5 sufficiently demonstrated the importance of these gonidia in
1 Bonnier was probably experimenting with an Arthopyrenia. Verrucaria species combine with
Protococcus or according to Chodat with Coccobotrys gen. nov.
2 Nylander [858. * Fuisting 1868, p. 674. * Winter 1876, p. 264. 5 Stahl 1877.
LICHEN GONIDIA 31
supplying the germinating spores with the necessary algae. They come to
lie in vertical rows between the asci and, owing to pressure, assume an
elongate form1 (Figs. 5 and 6). They have been seen in very few lichens, in
Endocarpon and Staurothele, both rather small genera of Pyrenolichens,and,so
far as is known, in two Discolichens, Lecidea pkylliscocarpa and L.phyllocaris,
the latter recorded from Brazil by Wainio2, and, on account of the inclusion
of gonidia in the hymenium, placed by him in a section, Gonothecium,
I. NATURE OF ASSOCIATION BETWEEN ALGA AND FUNGUS
a. CONSORTIUM AND SYMBIOSIS. These cultures had established con-
vincingly the composite nature of the lichen thallus, and Schwendener's
opinion, that the relationship between the two organisms was some
varying degree of parasitism, was at first unhesitatingly accepted by most
botanists. Reinke3 was the first to point out the insufficiency of this view
to explain the long continued healthy life of both constituents, a condition
so different from all known instances of the disturbing or fatal parasitism of
one individual on another. He recognized in the association a state of
mutual growth and interdependence, that had resulted in the production
of an entirely new type of plant, and he suggested Consortium as a truer
description of the connection between the fungus and the alga. This term
had originally been coined by his friend Grisebach in a paper3 describing
the presence of actively growing Nostoc algae in healthy Gunnera stems;
and Reinke compared that apparently harmless association with the similar
phenomenon in the lichen thallus. The comparison was emphasized by him
in a later paper4 on the same subject, in which he ascribes to each "consort"
its function in the composite plant, and declares that if such a mutual life
of Alga and Ascomycete is to be regarded as one of parasitism, it must be
considered as reciprocal parasitism; and he insists that "much more
appropriate for this form of organic life is the conception and title of Con-
sortium" In a special work on lichens, Reinke5 further elaborated his theory
of the physiological activity and mutual service of the two organisms forming
the consortium.
Frank H suggested the term Homobium as appropriate, but it' is faulty
inasmuch as it expresses a relationship of complete interdependence, and
it has been proved that the fungus partly, and the alga entirely, have the
power of free growth.
A wider currency was given to this view of a mutually advantageous
growth by de Bary 7. He followed Reinke in refusing to accept as satisfactory
the theory of simple parasitism, and adduced the evident healthy life of the
algal cells — the alleged victims of the fungus— as incompatible with the
1 See p. 62. 2 Wainio 1890, 2, p. 29. :! Reinke 1872, p. 108.
4 Reinke 187.^. 5 Reinke 1873'-, p. 98. 6 Frank 1876. 7 de Bary 1879.
32 CONSTITUENTS OF THE LICHEN THALLUS
parasitic condition. He proposed the happily descriptive designation of a
Symbiosis or conjoint life which was mostly though not always, nor in equal
degree, beneficial to each of the partners or symbionts.
b. DIFFERENT FORMS OF ASSOCIATION. The type of association be-
tween the two symbionts varies in different lichens. Bornet1, in describing
the development of the thallus in certain members of the Collemaceae,
found that though as a rule the two elements of the thallus, as in some
species of Collema itself, persisted intact side by side, there was in other
members of the genus an occasional parasitism: short branches from the
main hyphae applied themselves by their tips to some cell of the Nostoc
chain (Fig. 9). The cell thus seized upon began to increase in size, and the
Fig. 9. Pkysma chalazanum Arn. Cells of Nostoc chains penetrated
and enlarged by hyphae x 950 (after Bomet).
plasma became granular and gathered at the side furthest away from the
point of attachment. Finally the contents were used up, and nothing was
left but an empty membrane adhering to the fungus hypha. In another
species the hypha penetrated the cell. These instances of parasitism are
most readily seen towards the edge of the thallus where growth is more
active; towards the centre the attached cells have become absorbed, and
only the shortened broken chains attest their disappearance. The other
cells of the chains remain uninjured.
In Synalissa, a small shrubby gelatinous genus, the hypha, as described
by Bornet and by Hedlund2, pierces the outer wall of the gelatinous alga
(Gloeocapsd) and swells inside to a somewhat globose haustorium which
rests in a depression of the plasma (Fig. 10). The alga, though evidently
Bornet 1873.
2 Hedlund 1892.
LICHEN GONIDIA
undamaged, is excited to a division which takes place on a plane that passes
through the haustorium; the two daughter-cells then separate, and in so
doing free themselves from the hypha.
Hedlund followed the process of association between the two organisms
in the lichens Micarea (Biatorina) prasina and
M. denigrata {Biatorina synothea), crustaceous
species which inhabit trunks of trees or palings.
In these the alga, one of the Chlorophyceae, has
assumed the character of a Gloeocapsa but on
cultivation it was found to belong to the genus
Gloeocystis. The cells are globose and rather
small ; they increase by the division of the con-
tents into two or at most four portions which
become rounded off and covered with a mem-
brane before they become free from the mother-
cell. The lichen hypha, on contact with any one
of the green cells, bores through the outer membrane and swells within to a
haustorium, as in the gonidia of Synalissa.
Penetrating haustoria were demonstrated by Peirce1 in his study of the
gonidia of Ramalina reticulata. In the first stage the tip of a hypha had
pierced the outer wall of the alga, causing the protoplasm to contract away
from the point of contact (Fig. 11). More advanced stages showed the
extension of the haustorium into the centre of the cell, and, finally, the
Fig. 10. Synalissa symphorea Nyl.
Algae (Gloeocapsa) with hyphae
from the internal thallus x 480
(after Hornet).
Fig. 1 1 . Gonidia from Ramalina reticulata
Nyl. A,gonidium pierced and cell con-
tents shrinking x 560 ; B, older stage,
the contents of gonidium exhausted x 900
(after Peirce).
Fig. 12. Pertusaria globultfera Nyl. Fungus
and gonidia from gonidial zone x 500
(after Darbishire).
complete disappearance of the contents. In many cases it was found that
penetration equally with clasping of the alga by the filament sets up an
irritation which induces cell-division, and the alga, as in Synalissa, thus
becomes free from the fungus. Hue2 has recorded instances of penetration
in an Antarctic species, Physcia puncticulata. It is easy, he says, to see the tips
of the hyphae pierce the sheath of the gonidium and penetrate to the nucleus.
1 Peirce 1899. z Hue 1915.
S.L 3
34 CONSTITUENTS OF THE LICHEN THALLUS
Lindau1 has described the association between fungus and alga in
Pertusaria and other crustaceous forms as one of contact only (Fig. 12).
He found that the cell-membrane of the two adhering organisms was un-
broken. Occasionally the algal cell showed a slight indentation, but was
otherwise unchanged. The hyphal branch was somewhat swollen at the tip
where it 'touched the alga, and the wall was slightly thinner. The attach-
ment between the two cells was so close, however, that pressure on the cover-
glass failed to separate them.
Generally the hypha simply surrounds the gonidium with clasping
branches. Many algae also lie free in the gonidial zone, and Peirce2 claims
that these are larger, more deeply coloured and in every way healthier
looking than those in the grasp of the fungus. He ignores, however, the case
of the soredial algae which though very closely invested by the fungus are
yet entirely healthy, since on their future increase depends in many cases
the reproduction of new individual lichens.
In a recent study of a crustaceous sandstone lichen, " Caloplaca pyracea"
Claassen3 has sought to prove a case of pure parasitism. The rock was at first
covered with the green cells of Cystococcus sp. Later there appeared greyish-
white patches on the green, representing the invasion of the lichen fungus.
These patches increased centrifugally, leaving in time a bare patch in the
centre of growth which was again colonized by the green alga. The lichen
fruited abundantly, but wherever it encroached the green cells were more
or less destroyed. The true explanation seems to be that the green cells
were absorbed into the lichen thallus, though enough of them persisted to
start new colonies on any bare piece of the stone. In the same way large
patches of Trentepohlia aurea have been observed to be gradually invaded
by the dark coloured hyphae of Coenogonium ebeneum. In time the whole of
the alga is absorbed and nothing is to be seen but the dark felted lichen.
The free alga as such disappears, but it is hardly correct to describe the
process as one of destruction.
This algal genus Trentepohlia (Chroolepus) forms the gonidia of the
Graphideae, Roccelleae, etc. It is a filamentous aerial alga which increases
by apical growth. In the Graphideae, many of which grow on trees beneath
the outer bark (hypophloeodal), the association between the two symbionts
may be of the simplest character, but was considered by Frank4 to be of an
advanced type. According to his observations and to those of Lindau5, the
fungal hyphae penetrate first between the cells of the periderm. The alga,
frequently Trentepohlia nmbrina, tends to grow down into any cracks of the
surface. It goes more deeply in when preceded by the hyphae. In some
species both organisms maintain their independent growth, though each
shows increased vigour when it conies into contact with the other. In some
1 Lindau 1895'. * Peirce I899
LICHEN GONIDIA 35
instances the cells of the alga are clasped by the fungus which causes the
disintegration of the filament. The cells lose their bright yellow or reddish
colour and are changed in appearance to greenish lichen gonidia; but no
penetration by haustoria has ever been observed in Trentepohlia.
Bachmann's1 study of a similar gonidium in a calcicolous species of
Opegrapha confirms Frank's results. The algae had pierced not only between
the looser lime granules but also through a crystal of calcium carbonate, and
occupied nests scooped out in the rock by means of acid formed and excreted
by their filaments. When association took place with the fungus, the algal
cells were more restricted to a gonidial zone; but some of the cells, having
been pushed aside by the hyphae, had started new centres of gonidia. On
contact with the hyphae there was a tendency to bud out in a yeast-like
growth.
In the thallus of the Roccelleae, the algal filament, also a Trentepohlia, is
broken up into separate cells, but in the Coenogoniaceae, whether the
gonidium be a Cladophora as in Racodium,or a Trentepohlia as in Coenogonium,
the filaments remain intact and are invested more or less closely by the
hyphae.
A somewhat different type of association takes place between alga and
fungus in Strigula complanata, an epiphyllous lichen more or less common
in tropical regions. Cunningham2, who found it near Calcutta, described the
algal constituent and placed it in a new genus, Mycoidea (Cephaleuros). It
forms small plate-like expansions on the surface of the leaf, and also pene-
trates below the cuticle, burrowing between that and the epidermal cells;
occasionally, as observed by Cunningham, rhizoid-like growths pierce deeper
into the tissue — into and below the epidermal layer. Very frequently, in the
wet season, a fungus takes possession of
the alga and slender colourless hyphae
creep along its surface by the side of the
cell rows, sending out branches which
grow downwards. Marshall Ward3 de-
scribed the same lichen from Ceylon. He
states that the alga may be attacked at
any stage, and if it is in a very young con-
dition it is killed by the fungus; at a F»g- '3- Outer edge of Phycopeltis expansa
. . Term., the alga attacked by hyphae and
more advanced period of growth it COn- passing into separate gonidia x 500 (after
tinues to develop as an integral part of Vaughan Jennings),
the lichen thallus, but with more frequently divided and smaller cells.
Vaughan Jennings4 observed Strigula complanata in New Zealand associated
with a closely allied chroolepoid alga Phycopeltis expansa. He also noted the
growth of the fungus over the alga breaking up the plates of tissue and
1 Bachmann 1913. 2 Cunningham 1879. 3 Ward 1884. 4 Jennings 1895.
3—2
36 CONSTITUENTS OF THE LICHEN THALLUS
separating the cells which, from yellow, change to a green colour and
become rounded off (Fig. 13). The mature lichen, a white thallus dotted
with black fruits, contrasts strikingly with the yellow membranous alga.
Lichen formation usually begins near the edge of the leaf and the margin of
the thallus itself is marked by a green zone showing where the fungus has
recently come into contact with the alga.
More recently Hans Fitting1 has described " Mycoidea parasitica" as it
occurs on evergreen leaves in Java. The alga, a species of Cephaleuros,
though at first an epiphyte, becomes partially parasitic at maturity. It pene-
trates below the cuticle to the outer epidermal cells and may even reach
the tissue below. When it is joined by the lichen fungus, both constituents
grow together to form the lichen. Fitting adds that the leaf is evidently but
little injured. In this lichen the alga in the grip of the fungus loses its
independence and may be killed off: it is an instance of something like
intermittent parasitism.
J. RECENT VIEWS ON SYMBIOSIS AND PARASITISM
No hyphal penetration of the bright-green algal cell by means of
haustoria had been observed by the earlier workers, Bornet2, Bonnier3 and
others, though they followed Schwendener4 in regarding the relationship as
one of host and parasite. Lindau, also, after long study accepted parasitism
as the only adequate explanation of the associated growth, though he never
found the fungus actually preying on the alga.
In recent years interest in the subject has been revived by the researches
of Elenkin5, a Russian botanist who claims to have established a case for
parasitism or rather "endosaprophytism." He has demonstrated by means
of staining reagents the presence in the thallus of large numbers of dead
algal cells. A few empty membranes are to be found in the cortex and in
the gonidial zone, but the larger proportion occur below the gonidial zone
and partly in the medulla. He describes the lower layer as a "necral" or
"hyponecral" zone, and he considers that the hyphae draw their nourishment
chiefly from dead algal material. The fungus must therefore be regarded in
this case as a saprophyte rather than a parasite. The algae, he considers,
may have perished from want of sufficient light and air or they may have
been destroyed by an enzyme produced by the fungus. The latter he thinks
is the more probable, as dead cells are frequently present among the living
algae of the gonidial zone. To the action of the enzyme he also attributes
the angular deformed appearance of many gonidia and the paler colour and
gradual disintegration of their contents which are finally used up as endo-
saprophytic nourishment by the fungus. Dead algal cells were more easily
1 Fitting 1910. 2 Bornet 1873. 3 Bonnier i8892. 4 Schwendener 1867.
5 Elenkin 1903! and 1904!, 19042.
LICHEN GONIDIA 37
seen, he tells us, in crustaceous lichens associated with " Pleurococcus" or
" Cystococcus" \ they were much less frequent in the larger foliose or fruticose
lichens. Dead cells of Trentepohlia were also difficult to find.
In a second paper Elenkin records one clear instance of a haustorium
entering an algal cell, and says he found some evidence of hyphal branches
penetrating otherwise uninjured gonidia, round holes being visible in their
outer wall, but he holds that it is the cell-wall of the alga that is mainly
dissolved by the ferment and then used as food by the hyphae.
No allowance has been made by Elenkin for the normal wasting common
to all organic beings: the lichen fungus is continually being renewed,
especially in the cortical structures, and the alga must also be subject to
change. He1 claims, nevertheless, that his observations have proved that the
one symbiont is always preying on the other, either as a parasite or as a
saprophyte. He has likened the conception of symbiosis to that of a balance
between two organisms, "a moveable equilibrium of the symbionts." If, he
says, we could conceive a state where the conditions of life would be equally
favourable for both partners there would be true mutualism, but in practice
one only is favoured and gains the upper hand, using its advantage to prey
on the other. Unless the balance is redressed, the complete destruction of
the weaker is certain, and is followed in time by the death of the stronger.
The fungus being the dominant partner, the balance, he considers, is tipped
in its favour.
Elenkin's conclusions are not borne out by the long continued and healthy
life of the lichen. There is no record of either symbiont having succumbed
to the other, and the alga, when set free, is unchanged and able to resume its
normal development. Without the alga the fungus cannot form the ascigerous
fruit. Is that because as a parasite within the lichen it has degenerated past
recovery, or has it become so adapted to symbiosis that in saprophytic con-
ditions it fails to develop ?
Another Russian lichenologist, U. N. Danilov2, records results which
would seem to support the theory of parasitism. He found that from the
clasping hyphae minute haustoria were produced, which penetrate the algal
cell-wall, and branch when within the outer membrane, thus forming a
delicate network over the plasma; secondary haustoria arising from this
network protrude into the interior and rob the cell-contents. He observed
gonidia filled with well-developed hyphae and these, after having exhausted
one cell, travel onwards to others. Some gonidia under the influence of the
fungus had become deformed and were finally killed. As a proof of this
latter statement he adduces the presence in the thallus of some gonidia
containing shrivelled protoplasm, of others entirely empty. He considers, as
further evidence in favour of parasitism, the finding of empty membranes as
1 Elenkin I9o62. 2 Danilov 1910.
5G01.1
38 CONSTITUENTS OF THE LICHEN THALLUS
well as of colourless gonidia filled with the hyphal network. This description
hardly tallies with the usual healthy appearance of the gonidial zone in the
normal thallus, and it has been suggested that where the fungus filled the
algal cell, it was as a saprophyte preying on dead material.
The gradual perishing of algal cells in time by natural decay and their
subsequent absorption by the fungus is undisputed. It is open to question
whether the varying results recorded by these workers have any further
significance.
These observations of Elenkin and Danilov have been proved to be
erroneous by Paulson and Somerville Hastings1. They examined the thalli
of several lichens (Xanthoria parietina, Cladonia sp., etc.) collected in early
spring when vegetative growth in these plants was found to be at its highest
activity. They found an abundant increase of gonidia within the thallus,
which they regarded as sporulation of the algae, and the most careful methods
of staining failed to reveal any case of penetration of the gonidia by the
hyphae.
Nienburg2 has published some recent observations on the association of
the symbionts. In the wide cortex of a Pertusaria he found not only the
densely compact hyphae, but also isolated gonidia. In front of these latter
there was a small hollow cavity and, behind, parallel hyphae rich in contents.
These gonidia had originated from the normal gonidial zone. They were
moved upward by special hyphae called by Nienburg "push-hyphae." After
their transportation, the algae at once divide and the products of division
pass to a resting stage and become the centre of a new thalline growth. A
somewhat similar process was noted towards the apex of Evernia furfur acea.
Radial hyphae pushed up the cortex, leaving a hollow space over the gonidial
zone. Into the space isolated algae were thrust by "push-hyphae." In this
lichen he also observed the penetration of the algal cell by haustoria of the
fungus. He considers that the alga reaps advantage but also suffers harm,
and he proposes the term helotism to express the relationship.
An instructive case of the true parasitism of a fungus on an alga has been
described by Zukal3 in the case of Endomyces scytonemata which he calls
a "half-lichen." The mature fungus formed small swellings on the filaments
of the Scytonema and, when examined, the hyphae were seen to have attacked
the alga, penetrating the outer gelatinous sheath and then using up the
contents of the green cells. It is only after the alga has been destroyed and
absorbed, that asci are formed by the fungus. Zukal contrasts the develop-
ment of this fungus with the symbiotic growth of the two constituents in
EpJiebe where both grow together for an indefinite time.
Mere associated growth however even between a fungus and an alga
does not constitute a lichen. An instance of such growth is described by
1 Paulson and Hastings 1920. 2 Nienburg 1917. 3 Zukaj l89I>
LICHEN GONIDIA 39
Sutherland ] in an account of marine microfungi. One of these, a species of
Mycosphaerella, was found on Pelvetia canaliculata, and Sutherland claims
that as no apparent injury was done to the alga, it was a case of
symbiosis and that there was formed a new type of lichen. The mycelium,
always intercellular, pervaded the whole host-plant, and the fungal fruits
were invariably formed on the algal receptacles close to the oogonia. Their
position there is, of course, due to the greater food supply at that region.
Both fungus and alga fruited freely. A closer analogy could have been found
by the writer in the smut fungus which grows with the host-cereal until
fruiting time; or with the mycorrhiza of Calluna which also pervades every
part of the host-plant without causing any injury. In the true lichen, the
alga, though constituting an important part of the vegetative body, takes no
part in reproduction, except by division and increase of the vegetative cells
within the thallus. The fruiting bodies are always of a modified fungal
nature.
2. PHYSIOLOGY OF THE SYMBIONTS
The occurrence of isolated cases of parasitisVn — the fungus preying on
the alga — in any case leaves the general problem unsolved. The whole
question turns on the physiological activity and requirements of the two
component elements of the thallus. From what sources do they each
procure the materials essential to them as living organisms? It is chiefly
a question of nutrition.
A. NUTRITION OF ALGAE
a. CHARACTER OF ALGAL CELLS. Gonidia are chlorophyll-containing
bodies and assimilate carbon-dioxide from the atmosphere by photo-
synthesis as do the chlorophyll cells of other plants. They also require
water and mineral salts which, in a free condition, they absorb from their
immediate surroundings, but which, in the lichen thallus, they must obtain
from the fungal hyphae. If the nutriment supplied to them in their inclosed
position be greater or even equal to what the cells could procure as free-
living algae, then they undoubtedly gain rather than lose by their asso-
ciation with the fungus, and are not to be considered merely as victims of
parasitism.
b. SUPPLY OF NITROGEN. Important contributions on the subject of
algal nutrition have been made by Beyerinck2 and Artari3. The former
conducted a series of culture experiments with green algae, including the
gonidia of Physcia (Xanthoria) parietina. He successfully isolated the
lichen gonidia and, at first, attempted to grow them on gelatine with an
infusion of the Elm bark from which he had taken the lichen. Growth was
1 Sutherland 1915. 2 Beyerinck 1890. 3 Artari 1902.
40 CONSTITUENTS OF THE LICHEN THALLUS
very slow and very feeble until he added to the culture- medium a solution
of malt-extract which contains peptones and sugar. Very soon he obtained
an active development of the gonidia, and they multiplied rapidly by
division1 as in the lichen thallus. This proved to him conclusively the great
advantage to the algae of an abundant supply of nitrogen.
Artari in his work has demonstrated that there are two different physio-
logical races of green algae: (i) those that absorb peptones— which he
designates peptone-algae— and (2) those that do not so absorb peptones.
He tested the cells of Cystococcus humicola taken from the thallus of Physcia
parietina, and found that they belonged to the peptone group and were
therefore dependent on a sufficiency of nitrogenous material to attain their
normal vigorous growth. It was also discovered by Artari that the one
race can be made by cultivation to pass over to the other: that ordinary
algae can be educated to live on peptones, and peptone-algae to do without.
We learn further from Beyerinck's researches that Ascomycetes, the
group of fungi from which the hyphae of most lichens are derived, are
what he terms ammonia^sugar fungi; that is to say, the hyphae can
abstract nitrogen from ammonia salts and, with the addition of sugar, can
form peptones. The lichen peptone-algae are thus evidently, by their
contact with such fungi, in a favourable position for securing the nitro-
genous food supply most suited to their requirements. In their deep-seated
layers, they are to a large extent deprived of light, but it has been proved
by Artari2 in a series of culture experiments extending over a long period,
that the gonidia of Xanthoria parietina remain green in the dark under
very varied conditions of nutriment, though the colour is distinctly fainter.
Recently Treboux3 has revised the work done by Artari and Beyerinck
in reference to Cystococcus humicola. He denies that two physiological races
are represented in this alga, the lichen gonidia, in regard to the nitrogen
that they absorb, behaving exactly as do the free-living forms of the species.
He finds that the gonidium is not a peptone-carbohydrate organism in the
sense that it requires nitrogen in the form of peptones, inorganic ammonia
salts being a more acceptable food supply. Treboux concludes that his
results favour the view that the gonidia are in an unfavourable situation for
receiving the kind of nitrogenous compound most advantageous to them,
that .they are therefore in a sense "victims" of parasitism, though he
qualifies the condition as being a lichen-parasitism or helotism. This view
does not accord with Chodat's4 results: in his cultures of gonidia he
observed that with glycocoll or peptone, which are nearly equivalent, they
developed four times better than with potassium nitrate as their nitrogenous
food, and he concluded that they assimilated nitrogen better from bodies
allied to peptides.
1 See p. 56. 2 Artari 1902. 3 Treboux 1912. 4 Chodat 1913.
LICHEN. GONIDIA 41
c. EFFECT OF SYMBIOSIS ON THE ALGA. Treboux's observations how-
ever convinced him that the alga leads but a meagre existence within the
thallus. Cell-division — the expression of active vitality — was, he held, of rare
occurrence in the slowly growing lichen-plant, and zoospore formation in
entire abeyance. He contrasts this sluggish increase1 with the rapid multi-
plication of the free-living algal cells which cover whole tree-trunks with
their descendants in a comparatively short time. These latter cells, he
finds, are indeed rather smaller, being generally the products of recent
division, but mixed with them are numbers of larger resting cells, com-
parable in size with the lichen gonidia. He states further, that the gonidia
are less brightly green and, as he judges, less healthy, though in soredial
formation or in the open they at once regain both colour and power of
division. Treboux had entirely failed to observe the sporulation which is so
abundant at certain seasons.
Their quick recovery seems also a strong argument in favour of the
absolutely normal condition of metabolism within the gonidial cell; and
the paler appearance of the chlorophyll is doubtless associated with the
acquisition of carbohydrates from other' sources than by photosynthesis.
There is a wide difference between any degree of unfavourable life-conditions
and parasitism however slight, even though the balance of gain is on the
side of the fungus. It is not too fanciful to conclude that the demand for
nitrogen on the part of the alga has influenced its peculiar association with
the fungus. In the thallus of hypophloeodal lichens it has been proved
indeed that the alga Trentepohlia with apical growth is an active agent in
the symbiotic union. Cystococctis and other green algal cells are stationary,
but they are doubtless equally ready for — as many of them are equally
benefited by — the association. Keeble2 has pointed out in the case of
Convoluta roscoffensis that nitrogen-hunger induces the green algae to
combine forces with an animal organism, though the benefit to them is only
temporary and though they are finally sacrificed. The lichen gonidia, on
the contrary, persist for a long time, probably far beyond their normal
period of existence as free algae.
Examples of algal association with other plants might be cited here: of
Nostoc in the roots of Cycas and in the cells of Anthoceros, and of Anabczna
in the leaf-cells of Azolla, but in these instances it is generally held that
the alga secures only shelter. It was by comparing the lichen-association
with the harmless invasion of Gunnera cells by Nostoc that Reinke3 arrived
at his conception of "consortism."
d. SUPPLY OF CARBON. Carbon, the essential constituent of all organic
life, is partly drawn from the carbon-dioxide of the air, and assimilated by
1 See Paulson and Hastings 1920. 2 Keeble 1910. 3 Reinke 1872.
42 CONSTITUENTS OF THE LICHEN THALLUS
the green cells; it is also partly contributed by the fungus as a product of
its metabolism. A proof of this is afforded by Dufrenoy1: he found a
Parmelia growing closely round pine needles and even sending suckers into
the stomata. He covered the lichen with a black cloth and after seven weeks
found that the gonidia had remained very green. That growth had not
been checked was evidenced by an unusual development of soredia and
of spermogonia. Dufrenoy describes the condition as a parasitism of the
algae on the fungus which in turn was drawing nourishment from the
pine needles.
Artari2 has proved that lichen gonidia can obtain carbohydrates from
the substratum as well as by photosynthesis. He cultivated the gonidia of
Xanthoria parietina and Placodium murorum on media which contained
organic substances as well as mineral salts, while depriving them of atmo-
spheric carbon-dioxide and in some cases of light also. The gonidia not
only grew well but, even in the dark, they remained normally green, a
phenomenon coinciding with Etard and Bouilhac's3 experience in growing
Nostoc in the dark: with suitable culture media the alga retained its colour.
Nostoc also grows in the dark in the rhizome of Gunnera. Radais'4 experi-
ments with Chlorella vulgaris confirmed these results. On certain organic
media growth and cell-division were as rapid in the dark as in the light,
and chlorophyll was formed. The colour was at first yellowish and the full
green arrived slowly, especially on sugar media, but in ten days it was
uniform and normal.
When making further experiments with the alga, Siichococcus badllaris,
Artari5 found that it also grew well on an organic medium and that grape
sugar was the most valuable carbonaceous food supply. Chodat6 also found
that sugar or glucose was a desirable ingredient of culture media.
Treboux7, in his work on organic acids, has also proved by experimental
cultures with a large series of algae, including the gonidia of Peltigera, that
these green plants in the absence of light and in pure cultures would grow
and form carbohydrates if the culture medium contained a small percentage
of organic acids. The acids he employed were combined with potassium
and were thus rendered neutral or slightly alkaline; acetate of potash
proved to be the most advantageous compound of any that was tested.
Amino-acids and ammonia salts were added to provide the necessary
nitrogen. Oxalic acid and other organic acids of varying composition are
peculiarly abundant in lichen tissues and may be a source of carbon supply.
Marshall Ward8 has found calcium carbonate crystals in the lower air-
containing tissues of Strigula complanata.
Treboux finally concluded from his researches that just as fungi can
1 Dufrenoy 19 i 8. 2 Artari 1899. » Etard and Bouilhac 1898. 4 Radais 1900.
6 Artari 1901. « Chodat 1913. ? Treboux 1905. 8 Marshall Ward 1884.
LICHEN GONIDIA 43
extract carbohydrates from many sources, so algae can secure their carbon
supply in a variety of ways. He affirms that the metabolic activity of the
alga in these cultural conditions is entirely normal, and the various cell-
contents are formed as in the light. Whether, in this case, starch is formed
directly from the acids or through a series of combinations has not been
determined. Uhlir1, with electric lighting, made successful cultures of
Nostoc isolated from Collemaceae on silicic acid, proving thereby that these
gonidia do not require a rich nutriment. A certain definite humidity was
however essential, and bacteria were never eliminated as they are associated
with the gelatinous membranes of Nostocaceae.
e. NUTRITION WITHIN THE SYMBIOTIC PLANT. Culture experiments
bearing more directly on the nutrition of lichens as a whole were carried
out by F. Tobler2. He proved that the gonidia had undoubtedly drawn on
the calcium oxalate secreted by the hyphae for their supply of carbon. In
a culture medium of poplar-bark gelatine he grew hyphae of Xantkoria
parietina, and noted an abundant deposit of oxalate crystals on their cell-
walls. A piece of the lichen thallus including both symbionts and grown on
a similar medium formed no crystals, and microscopic examination showed
that crystals were likewise absent from the hyphae of the thallus that had
grown normally on the tree, the inference being that the gonidia used them up
as quickly as they were deposited. It must be remembered in this connection,
however, that Zopf 3 has stated that where lichen acids are freely formed
as, for instance, in Xanthoria parietina, there is always less formation and
deposit of calcium oxalate crystals, which may partly account for their
absence in the normal thallus so rich in parietin.
Tobler next introduced lichen gonidia into a culture medium in which
the isolated hyphal constituent of a thallus had been previously cultivated,
and placed the culture in the dark. In these circumstances he found that
the gonidia were able to thrive but formed no colour: they were obtaining
their carbohydrates, he decided, not from photosynthesis, but from the
excretory products such as calcium oxalate that had been deposited in the
culture medium by the lichen hyphae. We may conclude with more or less
certainty that the loss of carbohydrates, due to the partial deprivation of
light and air suffered by the alga owing to its position in the lichen thallus,
is more than compensated by a physiological symbiosis with the fungus4.
It has indeed been proved that in the absence of free carbon-dioxide, algae
may utilize the half-bound CO2 of carbonates, chiefly those of calcium and
magnesium, dissolved in water.
/ AFFINITIES OF LICHEN GONIDIA. Chodat5 has, in recent years,
made cultures of lichen gonidia with a view to discovering their relation to
1 Uhlir 1915. 2 Tobler 1911. 3 Zopf 1907. * Chambers 1912. 5 Chodat 1913
44 CONSTITUENTS OF THE LICHEN THALLUS
free-living algae and to testing at the same time their source of carbon
supply. He has come to the conclusion that lichen gonidia are probably in
no instance the normal Protococcus viridis: they differ from that alga in the
possession of a pyrenoid and in their reproduction by zoospores when free.
Careful cultures were made of different Cladonia gonidia which were
morphologically indistinguishable, and which varied in size from 10 to 16/4
in diameter, though smaller ones were always present. He recognized them
to be species of Cystococcus: they have a pyrenoid1 in the centre and a
disc-like chromatophore more or less starred at the edge. These gonidia
grew well on agar, still better on agar-glucose, but best of all with an
addition of peptone to the culture. There was invariably at first a slight
difference in form and colour in the mass between the gonidia of one
species and those of another, but as growth continued they became alike.
In testing for carbon supply, he found that gonidia grew slowly without
sugar (glucose), and that, as sources of carbon, organic acids could not
entirely replace glucose though, in the dark, the gonidia used them to some
extent; the colony supplied with potassium nitrate, and grown in the dark,
had reached a diameter of only 2 mm. in three months. With glucose, it
measured 5 mm. in three weeks, while in three months it formed large
culture patches.
A further experiment was made to test their absorption of peptones by
artificial cultures carried out both in the light and the dark. The gonidia
grew poorly in all combinations of organic nitrogen compounds. When
combined with glucose, growth was at once more vigorous though only half
as much in the dark as in the light, the difference in this respect being
especially noticeable in the gonidia from Cladonia pyxidata. He concludes
that as gonidia in these cultures are saprophytic, so in the lichen thallus
also they are probably more or less saprophytic, obtaining not only their
nitrogen in organic form but also, when possible, their carbon material as
glucose or galactose from the hyphal symbiont which in turn is saprophytic
on humus, etc.
B. NUTRITION OF FUNGI
Fungi being without chlorophyll are always indebted to other organisms
for their supply of carbohydrates. There has never therefore been any
question as to the advantage accruing to the hyphal constituent in the
composite thallus. The gonidia, as various workers have proved, have also
a marked preference for organized nourishment, and, in addition, they obtain
carbon by photosynthesis. Chodat2 considers that probably they are thus
able to assimilate carbon-dioxide in excess, a distinct advantage to the
hyphae. In some instances the living gonidium is invaded and the contents
1 See note Paulson and Hastings, p. 28. 2 Chodat 1913.
LICHEN GONIDIA 45
used up by the fungus and any dead gonidia are likewise utilized for food
supply. It is also taken for granted that the fungus takes advantage of the
presence of humus whether in the substratum or in aerial dust. In such
slow growing organisms, there is not any large demand for nourishment on
the part of the hyphae: for many lichens it seems to be mere subsistence
with a minimum of growth from year to year.
C. SYMBIOSIS OF OTHER PLANTS
The conception of an advantageous symbiosis of fungi with other plants
has become familiar to us in Orchids and in the mycorhizal formation on
the roots of trees, shrubs, etc. Fungal hyphae are also frequent inhabitants
of the rhizoids of hepatics though, according to Gargeaune1, the benefit to
the hepatic host-plant is doubtful.
An association of fungus and green plant of great interest and bearing
directly on the question of mutual advantage has been described by
Servettaz2. In his study of mosses, he was able to confirm Bonnier's3
account of lichen hyphae growing over such plants as Vaticheria and
the protonema of mosses, which is undoubtedly hurtful; but he also found
an association of a moss with one of the lower fungi, Streptothrix or
Oospora, which was distinctly advantageous. In separate cultivation the
fungus developed compact masses and grew well in peptone agar broth.
Cultures of the moss, Phascum cuspidatum, were also made from the
spores on a glucose medium. The specimens in association with the fungus
were fully grown in two months, while the control cultures, without any
admixture of the fungus, had not developed beyond the protonema stage.
Servettaz draws attention to the proved fact that, in certain instances,
plants benefit when provided with substances similar to their own decay
products, and he considers that the fungus, in addition to its normal gaseous
products, has elaborated such substances, as acid products, from the glucose
medium to the great advantage of the moss plant.
A symbiotic association of Nostoc with another alga, described by
Wettstein4, is also of interest. The blue-green cells were lodged in the
pyriform outgrowths of the siphoneous alga, Botrydium pyriforme Kiitz.,
which the author of the paper places in a new genus, Geosiphon. The
sheltering Nostoc symbioticum fills all of the host left vacant by the plasma,
and when the season of decay sets in, it forms resting spores which migrate
into the rhizoids of the host, so that both plants regenerate together.
Wettstein has compared this symbiotic association with that of lichens,
and finds the analogy all the more striking in that the membrane of his new
alga had become chitinous, which he thinks may be due to organic nutrition.
1 Gargeaune 1911. 2 Servettaz 1913. 3 See p. 65. 4 Wettstein 1915.
46 CONSTITUENTS OF THE LICHEN THALLUS
II. LICHEN HYPHAE
A. ORIGIN OF HYPHAE
Lichen hyphae form the ground tissue of the thallus apart from the
gonidia or algal cells. They are septate branched filaments of single cell
rows and are colourless or may be tinged by pigments or lichen acids to
some shade of yellow, brown or black. They are of fungal nature, and are
produced by the mature lichen spore.
The germination of the spore was probably first observed by Meyer1.
His account of the actual process is somewhat vague, and he misinterpreted
the subsequent development into thallus and fruit entirely for want of the
necessary magnification; but that he did succeed in germinating the spores
is unquestionable. He cultivated them on a smooth surface and they grew
into a "dendritic formation" — a true hypothallus. Many years later the
development of hyphae from lichen spores was observed by Holle2 who saw
and figured the process unmistakably in Borrera (Physcici) ciliaris.
A series of spore cultures was undertaken by Tulasne3 with the twofold
object of discovering the exact origin of hyphae and gonidia and of their
relationship to each other. The results of his classical experiment with the
spores of Verrucaria muralis — as interpreted by him — were accepted by the
lichenologists of that time as conclusive evidence of the genetic origin of the
gonidia within the thallus.
The spores- of the lichen in large numbers had been sown by Tulasne
in early spring on the smooth polished surface of a piece of limestone, and
Fig. 14. Germinating spores of Verrucaria nmralis Ach. after two
months' culture x ca. 500 (after Tulasne).
were covered with a watch-glass to protect them from dust, etc. At
irregular intervals they were moistened with water, and from time to time
1 Meyer 1825. * Ho,,e ^ , ^^ ^.^
LICHEN HYPHAE . 47
a few spores were abstracted from the culture and examined microscopically.
Tulasne observed that the spore did not increase or change in volume in the
process of germination, but that gradually the contents passed out into the
growing hyphae, till finally a thin membrane only was left and still persisted
after two months (Fig. 14). For a considerable time there was no septation ;
at length cross-divisions were formed, at first close to the spore, and then
later in the branches. The hyphae meanwhile increased in dimension, the
cells becoming rounder and somewhat wider, though always more slender
than the spore which had given rise to them. In time a felted tissue was
formed with here and there certain cells, filled with green colouring matter,
similar to the gonidia of the lichen and thus the early stages at least of a
new thallus were observed. The green cells, we now know, must have gained
entrance to the culture from the air, or they may have been introduced with
the water.
B. DEVELOPMENT OF LICHENOID HYPHAE
Lichen hyphae are usually thick-walled, thus differing from those of fungi
generally, in which the membranes, as a rule, remain comparatively thin.
This character was adduced by the so-called "autonomous" school as a proof
of the fundamental distinction between the hyphal elements of the two
groups of plants. It can, however, easily be observed that, in the early
stages of germination, the lichen hyphae, as they issue from the spore, are
thin-walled and exactly comparable with those of fungi. Growth is apical,
and septation and branching arise exactly as in fungi, and, in certain circum-
stances, anastomosis takes place between converging filaments. But if algae
are present in the -culture the peculiar lichen characteristics very soon
appear.
Bonnier1, who made a large series of synthetic cultures, distinguishes
three types of growth in lichenoid hyphae (Fig. 15):
1. Clasping filaments, repeatedly branched, which attach and surround
the algae.
2. Filaments with rather short swollen cells which ultimately form the
hyphal tissues of cortex and medulla.
3. Searching filaments which elongate towards the periphery and go to
the encounter of new algae.
In five days after germination of the spores, the clasping hyphae had
laid hold of the algae which meanwhile had increased by division; the
swollen cells had begun to branch out and ten days later a differentiation
of tissue was already apparent. The searching filaments had increased in
number and length, and anastomosis between them had taken place when
1 Bonnier i88q2.
48 CONSTITUENTS OF THE LICHEN THALLUS
no further algae were encountered. The cell-walls of the swollen hyphae
and their branches had begun to thicken and to become united to form a kind
of cellular tissue or "paraplectenchyma1." At a later date, about a month
Fig. 15. Synthetic culture of Physcia parietina spores and Protococcus
viridis five days after germination, s, lichen-spore ; a, septate fila-
ments ; b, clasping filaments; c, searching filaments, x 500 (after
Bonnier).
after the sowing of the spores, there was a definite cellular cortex formed
over the thallus. The hyphal cells are uninucleate, though in the medulla
they may be i-2-nucleate.
The hyphae in close contact with the gonidia remain thin- walled, and
have been termed by Wainio2 "meristematic." They furnish the growing
elements of the lichen either apical or intercalary. In most genera the organs
of fructification take rise from them, or in their immediate neighbourhood,
and isidia and soredia also originate from these gonidial hyphae.
As the filaments pass from the gonidial zone to other layers, the cell-
walls become thicker with a consequent reduction of the cell-lumen, very
noticeable in the pith, but carried to its furthest extent in the "decomposed"
cortex where the cells in the degenerate tissue often become reduced to dis-
connected streaks indicating the cell-lumen, and the outer cortical layer is
merely a continuous mass of mucilage.
All lichen -tissues arise from the branching and septation of the hyphae,
the septa always forming at right angles to the long axis of the filaments.
There is no instance of longitudinal cell-division except in the spores of
certain genera (Collema, Urceolaria, Polyblastia, etc.). The branching of the
hypha is dichotomous or lateral, and very irregular. Frequent septation and
coherent growth result in the formation of plectenchyma.
1 Term coined by Lindau (1899) to describe the pseudo-cellular tissue of lichens and fungi now
referred to as "plectenchyma." 2 Wainio 1897.
LICHEN HYPHAE 49
C. CULTURE OF HYPHAE WITHOUT GONIDIA
Artificial cultures had demonstrated the germination of lichen spores,
with the formation of hyphae, and from synthetic cultures of fungus and
alga complete lichen plants had been produced. To Moller1 we owe the first
cultures of a thalline body from the fungus alone, both from spermatia and
from ascospores. The germination of the spermatia has a direct bearing
on their function as spores or as sexual organs and is described in a
later chapter.
The ascospores of Lecanora sitbfusca were caught in a drop of water on
a slide as they were ejaculated from the ascus, and, on the following day, a
very fine germinating tube was seen to have pierced the exospore. The
hypha became slightly thicker, and branching began on the third day. If
in water alone the culture soon died off, but in a nutrient solution growth
slowly continued. The hyphae branched out in all directions from the spore
as a centre and formed an orbicular expansion which in fourteen days had
reached a size of 'I mm. in diameter. After three weeks' growth it was large
enough to be visible without a lens ; the mycelial threads were more crowded,
and certain terminal hyphae had branched upwards in an aerial tuft, this
development taking place from the centre outwards. Moller marked this
stage as the transition from a mere protothallus to a thallus formation. In
three months a diameter of i'5-2 mm. was reached; a transverse section
gave a thickness of "86 mm. and from the under side loose hyphae branched
downwards and attached the thallus, when it had been transferred to a solid
substratum such as cork. Above these rhizoidal hyphae, a stratum of rather
loose mycelium represented the medulla, and, surmounting that, a cortical
layer in which the hyphae were very closely compacted. Delicate terminal
branches rose into the air over the whole surface, very similar in character
to hypothallic hyphae at the margin of the thallus.
Lecanora subfusca has a rather small simple spore; it emitted germinating
tubes from each end, and a septum across the middle of the spore appeared
after germination had taken place. Another experiment was with a much
larger muriform spore measuring 80^, in length and 20 //, in thickness. On
germination about 20 tubes were formed, some of them rising into the air at
once, the others encircling the spore, so that the thallus took form imme-
diately; growth in this case also was centrifugal. In three months a diameter
of 6 mm. was reached with a thickness of I to 2 mm. and showing a differen-
tiation into medulla and cortex. The hyphae did not increase in width, but
frequently globose or ovate swellings arose in or at the ends, a character which
recurs in the natural growth of hyphae both of lichens and of Ascomycetes.
These swellings depend on the nutrition.
1 Moller 1887.
50 CONSTITUENTS OF THE LICHEN THALLUS
Pertusaria communis possesses a very large simple spore, but it is multi-
nucleate and germinates with about 100 tubes which reach their ultimate
width of 3 to 4 /x before they emerge from the exospore. The hyphae
encircle the spore, and an opaque thalline growth is quickly formed from
which rise terminal hyphal branches. In ten weeks the differentiation into
medulla and cortex was reached, and in five months the hyphal thallus
measured 4 mm. in diameter and i to 2 mm. in thickness.
Moller instituted a comparison between the thalli he obtained from the
spores and those from the spermatia of another crustaceous lichen, Buellia
punctiformis (B. myriocarpa). After germination had taken place the hyphae
from the spermatia grew at first more quickly than those from the ascospores,
but as soon as thallus formation began the latter caught up and, in eight
weeks, both thalli were of equal size.
Another comparative culture with the spermatia and ascospores of
Opegrapha subsiderella gave similar results: the spores of that species are
elongate-fusiform and 6- to 8-septate; germination took place from the end
cells in two to three days after sowing. The germinating hyphae corre-
sponded exactly with those from the spermatia and growth was equally slow
in both. The middle cells of the spores may also produce germinating tubes,
but never more than about five were observed from any one spore. A
browning of the cortical layer was especially apparent in the hyphal culture
from another lichen, Graphis scripta: a clear brown colour gradually changing
to black appeared about the same period in all the cultures.
The hyphae from the spores of Arthonia developed quickest of all: the
hyphae were very slender, bt»t in three to four months the growth had reached
a diameter of 8 mm. In this plant there was the usual outgrowth of delicate
hyphae from the surface; no definite cortical layer appeared, but only a very
narrow line of more closely interwoven somewhat darker hyphae. Frequently,
from the surface of the original thallus, excrescences arose which were the
beginnings of further thalli.
Tobler1 experimenting with Xanthoria parietina gained very similar
results. The spores were grown in malt extract for ten days, then transferred
to gelatine. In three to five weeks there was formed an orbicular mycelial
felt about 3 mm. in diameter and 2 mm. thick. The mycelium was frequently
brownish even in healthy cultures, but the aerial hyphae which, at first, rose
above the surface were always colourless. After these latter disappeared a
distinct brownish tinge of the thallus was visible. In seven months it had
increased in size to 15 mm. in length, 7 mm. in width and 3 mm. thick with
a differentiation into three layers: a lower rather dense tissue representing
the pith, above that a layer of loose hyphae where the gonidial zone would
1 Tobler 1909.
LICHEN HYPHAE 51
normally find place, and above that a second compact tissue, or outer cortex,
from which arose the aerial hyphae. The culture could not be prolonged
more than eight months.
D. CONTINUITY OF PROTOPLASM IN HYPHAL CELLS
Wahrlich1 demonstrated that continuity of protoplasm was as constant
between the cells of fungi as it has been proved to be between the cells of
the higher plants. His researches included the hyphae of the lichens, Cla-
donia fimbriata and Physcia (Xanthoria) parietina.
Baur2 and Darbishire3 found independently that an open connection
existed between the cells of the carpogonial structures in the lichens they
examined. The subject as regards the thalline hyphae was again taken up
by Kienitz-Gerloff4 who obtained his best results in the hypothecial tissue
of Peltigera canina and P. polydactyla. Most of the cross septa showed one
central protoplasmic strand traversing the wall from cell to cell, but in some
instances there were as many as four to six pits in the walls. The thickening
of the cell-walls is uneven and projects variously into, the cavity of the cell.
Meyer's5 work was equally conclusive: all the cells of an individual hypha,
he found, are in protoplasmic connection ; and in plectenchymatous tissue
the side walls are frequently perforated. Cell-fusions due to anastomosis are
frequent in lichen hyphae, and the wall at or near the point of fusion is also
traversed by a thread of protoplasm, though such connections are regarded
as adventitious. Fusions with plasma connections are numerous in the
matted hairs on the upper surface of Peltigera canina and they also occur
between the hyphae forming the rhizoids of that lichen. The work of Salter6
may also be noted. He claimed that his researches tended to show complete
anatomical union between all the tissues of the lichen plant, not only between
the hyphae of the various tissues but also between hyphae and gonidia.
III. LICHEN ALGAE
A. TYPES OF ALGAE
The algal constituents of the lichen thallus belong to the two classes,
Myxophyceae, generally termed blue-green algae, and Chlorophyceae which
are coloured bright-green or yellow-green. Most of them are land forms,
and, in a free condition, they inhabit moist or shady situations, tree-trunks,
walls, etc. They multiply by division or by sporulation within the thallus;
zoospores are never formed except in open cultivation. The determination
of the genera and species to which the lichen algae severally belong is often
uncertain, but their distribution within the lichen kingdom is as follows:
1 Wahrlich 1893. 2 Baur 1898. 3 Darbishire 1899.
4 Kienitz-Gerloff 1902. 5 Meyer 1902. 6 Salter 1902.
4—2
CONSTITUENTS OF THE LICHEN THALLUS
a. MYXOPHYCEAE ASSOCIATED WITH PHYCOLICHENS. The blue-green
algae are characterized by the colour of their pigments which persists
in the gonidial condition giving various tints to the component lichens, and
by the gelatinous sheath in which most of them are enclosed. This sheath,
both in the lichen gonidia1 and in free-living forms, imbibes and retains
moisture to a remarkable extent and the thallus containing blue-green algae
profits by its power of storing moisture. Myxophyceae form the gonidia
of the gelatinous lichens as well as of some other non-gelatinous genera.
Several families are represented2:
Fam. CHROOCOCCACEAE. This family includes unicellular algae with
thick gelatinous sheaths. They increase normally by division, and colonies
arise by the cohesion of the cells. Several genera form gonidia:
1. CHROOCOCCUS Naeg. Solitary or forming small colonies of 2-4-8
cells (Fig. 1 6) generally surrounded by firm gelatinous colourless sheaths in
definite layers (lamellate). Chroococcus is considered by some lichenologists
to form the gonidium of Cora, a genus of Hymenolichens.
2. MlCROCYSTis Kiitz. Globose or subglobose cells forming large
colonies surrounded by a common gelatinous layer (gonidia of Coris-
cium).
3. GLOEOCAPSA Kiitz. (including Xanthocapsd). Globose cells with a
wm
WB
Fig. 17. Gloeocapsa magma
Kiitz. x 450 (after West).
Fig. 16. Examples of Chroococcus. A, Ch. gigantens
West ; B, Ch. turgidus Naeg. ; C and D, Ch. schizo-
dermaticus West x 450 (after West).
lamellate gelatinous wall, forming colonies enclosed in a common sheath
(Fig. 17); the inner integument is often coloured red or orange. These
1 Nylander (1866) gave the term "gonimia" to the blue-green algae of the Phycolichens, retaining
the term " gonidia " for the bright-green algae of the Archilichens : the distinction is not now main-
tained.
2 For further details see also the chapter on Classification.
LICHEN ALGAE
53
Gloeocapsa
two genera form the gonidia in the family Pyrenopsidaceae.
polydermatica Kiitz. has been identified as a lichen gonidium.
Fam. NOSTOCACEAE. Filamentous algae unbranched and without base
or apex.
NOSTOC Vauch. Composed of flexuous trichomes, with intercalary
heterocysts (colourless'cells) (Fig. 1 8). Dense gelatinous colonies of definite
Fig. 18. Examples of Nostoc. N. Linckia Born. A, nat. size ; B, small portion x 340 ;
C, N. coerulescens Lyngbye, nat. size (after West).
Fig. 19. Example of Scytnnema alga. 5. mirabile Thur. C, apex of a branch ; D, organ
of attachment at base of filament." x 440 (after West).
form are built up by cohesion. In some lichens the trichomes retain their
chain-like appearance, in others they are more or less broken up and massed
together, with disappearance of the gelatinous sheath (as in Peltigera);
colour mostly dark blue-green.
Nostoc occurs in a few or all of the genera of Pyrenidiaceae, Collemaceae,
Pannariaceae, Peltigeraceae and Stictaceae, and N. sphaericum Vauch
54
CONSTITUENTS OF THE LICHEN THALLUS
(N. lichenoides Kutz.) has been determined as the lichen gonidium. When
the chains are broken up it has been wrongly classified as another alga,
Poly coccus punctiformis.
Fam. SCYTONEMACEAE. Trichomes of single-cell rows, differentiated into
base and apex. Pseudo-branching arises at right angles to the main filament.
SCYTONEMA Ag. Pseudo-branches piercing the sheath and passing out
as twin filaments (Fig. 19); colour, golden-brown. This alga occurs in
genera of Pyrenidiaceae, Ephebaceae, Pannariaceae, Heppiaceae, in Petractis
a genus of Gyalectaceae, and in Dictyonema one of the Hymenolichens.
Fam. STIGONEMACEAE. Trichomes of several-cell rows with base and
apex ; colour, golden-brown.
STIGONEMA Ag. Stouter than Scytonema, with transverse and vertical
division of the cells, and generally copious branching (Fig. 20). This alga
occurs only in a few genera of Ephebaceae. S.panniforme Kirchn. (Siro-
siphon pulvinatus Breb.) has been determined as forming the gonidium.
Fam. RIVULARIACEAE. Trichomes with a heterocyst at the base and
tapering upwards, enclosed in mucilage (Fig. 21).
Fig. 20. Stigonema sp. x 200 (after
Comere).
• -*•«*-*• 1 »
Fig. 21. Examples of Rivularia ; A, B, £,R.Bia-
sokttiana Menegh. ; D and E, R. minutula
Born, and Fl. A and D nat. size; B, C and E
x48o (after West).
LICHEN ALGAE
55
RlVULARiA Thuret. In tufts fixed at the base and forming roundish
gelatinous colonies; colour, blue-green. The gonidium of Lichinaceae has
been identified as R. nitida Ag.
Algae belonging to one or other of these genera of Myxophyceae also
combine with the hyphae of Archilichens to form cephalodia1 and Krem-
pelhuber2 has recorded and figured a blue-green alga, probably Gloeocapsa,
in Baeomyces paeminosus from the South Sea Islands. They also form the
gonidia in a few species and genera of such families as Stictaceae and
Peltigeraceae.
b. CHLOROPHYCEAE ASSOCIATED WITH ARCHILICHENS. The lichens of
this group are by far the most numerous both in genera and species, though
fewer algal families are represented.
Fam. PROTOCOCCACEAE. Consisting of globular single cells, aggregated
in loose colonies, dividing variously.
i. PROTOCOCCUS VIRIDIS Ag. (Pleurococcus vulgaris Menegh., Cystococ-
cushumicola Naeg.). Cells dividing
into 2, 4 or 8 daughter-cells and
not separating readily; in exces-
sive moisture forming short fila-
ments. The cells contain parietal
chloroplasts, and, according to
Chodat3, are without a pyrenoid
(Fig. 22). This alga, and allied
species, forms the familiar green
coating of tree-trunks, walls etc.,
and, in lichenological literature,
are quoted as the gonidia of most
of the crustaceous foliose and fru-
ticose lichens. Chodat3, who has
recently made comparative artificial cultures of algae, throws doubt on the
identity of many such gonidia. He lays great emphasis on the presence or
absence of a pyrenoid in algal cells. West, on the contrary, considers the
pyrenoid as an inconstant character. Chodat insists that the gonidia that
contain pyrenoids belong to another genus, Cystococcus Chod. (iwn Naeg.),
a pyrenoid-containing alga, which, in addition to multiplying by division
of the cells, also forms spores and zoospores when cultivated. He further
records the results of his cultures of gonidia, and finds that those taken
from closely related lichens, such as different species of Cladonia, though
they are alike morphologically, yet show constant variations in the culture
colonies. These, he holds, are sufficient to indicate difference of race if not
Fig. 22. Pleurococcus vulgaris Menegh. (Protococ-
cus viridis Ag. ). chl. chloroplast ; p. protoderma
stage; /<?, palmelloid stage; py, pyrenoid. x 520
(after West).
See p. 133.
2 Krempelhuber 1873.
Chodat 1913.
CONSTITUENTS OF THE LICHEN THALLUS
Fig. 23. Cystococcus Cladoniae
pyxidatae Chod. from cul-
ture x 800 (after Chodat).
of species and he designates the algae, according to the lichen in which
they occur, as Cystococcus Cladoniae pyxidatae, C. Cladoniae Jimbriatae, etc.
Meanwhile Paulson and Somerville Hastings1 by their careful research
on the growing thallus have thrown considerable light on the identity of the
Protococcaceous lichen gonidium. They selected such well-known lichens
as Xanthoria parietina, Cladonia spp. and others, which they collected
during the spring months, February to April, the period of most active
growth. Many of the gonidia, they found, were in a stage of reproduction,
that showed a simultaneous rounding off of the
gonidium contents into globose bodies varying in
number up to 32. Chodat had figured this method
of "sporulation" in his cultures of the lichen goni-
dium both in Chlorella Beij. and in Cystococcus Chod.
(Fig. 23). It has now been abundantly proved that
this form of increase is of frequent occurrence in the
thallus itself. Chlorella has been suggested as .prob-
ably the alga forming these gonidia and recently
West has signified his acquiescence in this view2.
2. CHLORELLA Beij. Occurring frequently on damp ground, bark of
trees, etc., dividing into numerous daughter-
cells, probably reduced zoogonidia (Fig. 23).
Chodat distinguishes between Cystococcus
and Chlorella in that Cystococcus may form
zoospores (though rarely), Chlorella only
aplanospores. He found three gonidial species,
Chlorella lichina in Cladonia rangiferina, Ch.
viscosa and Ch. Cladoniae in other Cladonia
spp.
3. COCCOBOTRYS Chod. The cells of this
new algal genus are smaller than those of
Cystococcus ox Protococcus and have no pyrenoid.
They were isolated by Chodat from the thallus
of Verrucaria nigrescens (Fig. 24), and, as
they have thick membranes, they adhere in
a continuous layer or thallus. Chodat also
claims to have isolated a species of Cocco-
botrys from Dermatocarpon miniatum, a foliose
Pyrenolichen.
4. COCCOMYXA Schmidle. Cells ellipsoid, also without a pyrenoid.
Two species were obtained by Chodat from the thallus of Solorinae and
are recorded as Coccomyxa Solorinae croceae and C. Solorinae saccatae.
'ig. 23 A. A, C, Chlorella vulgaris
Beyer. B and C, stages in division
x about 800 (after Chodat) ; E,
Chi. faginea Wille x 520 (after
Gerneck); F — I Chi. miniata ; F,
vegetable cell ; G— I, formation
and escape of gonidia x 1000
(after Chodat).
1 Paulson and Hastings 1920.
2 Paulson in litt.
LICHEN ALGAE
57
Coccomyxa subellipsoidea is given1 as the gonidium of the primitive
lichen Botrydina vulgaris (Fig. 25). The cells are surrounded by a common
gelatinous sheath.
Fig. 24. Coccobotrys Verrucariae Chod.
from culture x 800 (after Chodat).
Fig. 25. Coccomyxa subellipsoidea Acton.
Actively dividing cells, the dark portions
indicating the chloroplasts x 1000 (after
Acton).
5. DiPLOSPHAERA Bial.2 D. Chodati was taken from the thallus of
Lecanora tartarea and successfully cultivated. It resembles Protococcus^ but
has smaller cells and grows more rapidly ; it is evidently closely allied to
that genus, if not merely a form of it.
6. IJROCOCCUS Kiitz. Cells more or less globose, rather large, and
coloured with a red-brown pigment, with the cell-wall thick and lamellate,
forming elongate strands of cells (Fig. 26). Recorded by Hue3 in the
cephalodium of Lepolichen coccopkora, a Chilian lichen.
Fam. TETRASPORACEAE. Cells in groups of 2 or 4 surrounded by a
gelatinous sheath.
i . PALMELLA Lyngb. Cells globose, oblong or ellipsoid, grouped without
order in a formless mucilage (Fig. 27). Among lichens associated with
Palmella are the Epigloeaceae and Chrysothricaceae.
Fig. 26. Urococcus sp. Group of cells
much magnified (after Hassall).
Fig. 27. Palmella sp. x 400 (after Comere).
2. GLOEOCYSTIS Naeg. Cells oblong or globose with a lamellate
sheath forming small colonies ; colour, red-brown
(Fig. 28). This alga along with Urococcus was
found by Hue in the cephalodia of Lepolichen
coccophora, but whereas Gloeocystis frequently occu-
pies the cephalodium alone, Urococcus is always
accompanied by Scytonema, the normal gonidium
of the cephalodium.
Fig. 28. Gloeocystis sp. x 400
(after Comere).
1 Acton 1909.
- Bialosuknia 1909.
Hue 1905.
58 CONSTITUENTS OF THE LICHEN THALLUS
Fig. 30. Example of Cladophora. Cl. glomerata Klitz
A.nat. s,ze; B, x 85 (after West).
iff. 29- A, Trentepohlia umbrina Born ;
K, /. aurea Mart, x 300 (after Kiitz.).
LICHEN ALGAE 59
Fam. TRENTEPOHLIACEAE. Filamentous and branched, the filaments
short and creeping or long and forming tufts and felts or cushions; colour,
brownish-yellow or reddish-orange.
TRENTEPOHLIA Born. Branching alternate; cells filled with red or
orange oil ; no pyrenoids (Fig. 29). A large number of lichens are associated
with this genus : Pyrenulaceae, Arthoniaceae, Graphidaceae, Roccellaceae,
Thelotremaceae, Gyalectaceae and Coenogoniaceae, etc., in whole or in part.
Two species have been determined, T. umbrina Born., the gonidium of the
Graphidaceae, and T. aurea which is associated with the only European
Coenogonium, C. ebeneum (Fig. 3). Deckenbach1 claimed that he had proved
by cultures that T. umbrina was a growth stage of T. aurea.
Fam. CLADOPHORACEAE. Filamentous, variously and copiously branched,
the cells rather large and multinucleate.
CLADOPHORA Klitz. Filaments branching, of one-cell rows, attached
at the base ; colour, bright or dark green ; mostly aquatic and marine
(Fig. 30). Only one lichen, Racodium rupestre, a member of the Coeno-
goniaceae, is associated with Cladophora. It is a British lichen, and is always
sterile.
Fam. MYCOIDEACEAE. Epiphytic algae consisting of thin discs which
are composed of radiating filaments.
1. MYCOIDEA Cunningh. (Cephaleuros Kunze). In Mycoidea parasitica
the filaments of the disc are partly
erect and partly decumbent, reddish
to green (Fig. 31). It forms the goni-
dium of the parasitic lichen, Strigula
complanata, which was studied by
Marshall Ward in Ceylon2. Zahl-
bruckner gives Phyllactidium as an
alternative gonidium of Strigula- Fig. 31. Mycoidea parasitica Cunningh. much
magnified (after Marshall Ward).
CG3.C.
2. PHYCOPELTIS Millard. Disc a stratum one-cell thick, bearing seta,
adnate to the lower surface of the leaf, yellow-green in colour. Phycopeltis
(Fig. 32) has been identified as the gonidium of Strigula complanata in
New Zealand and of Mazosia (Chiodectonaceae), a leaf lichen from tropical
America.
1 Deckenbach 1893.
2 In a comparative study of leaf algae from Ceylon and Barbadoes, N. Thomas (1913) came to the
conclusion that Marshall Ward's alga in its early stages is the same as Phyllactidium ti'opicum
Moebius ; and that the Barbadoes alga with which she was working represented the older stages, it
being then subcuticular in habit, forming rhizoids, barren and sterile aerial hairs and subcuticular
zoosporangia.
6o
CONSTITUENTS OF THE LICHEN THALLUS
There is some confusion as to the genera of algae that form the gonidia
of these epiphyllous lichens. Phyllactidium
given by Zahlbruckner as the gonidium of
all the Strigulaceae (except Strigula in
part) is classified by de Toni1 as probably
synonymous with Phycopeltis Millard, and
as differing from Mycoidea parasitica in the
mode of growth.
Fam. PRASIOLACEAE. Thallus filamen-
Fig. 3,. Phycopeltis expansa Jenn. tous, often expanded into broad sheets by
much magnified (after Vaughan the fusion of the filaments in one plane.
Jennings).
PRASIOLA Ag. Thallus filamentous, of one- to many-cell rows, or
widely expanded (Fig. 33). The gonidium of Mastoidiaceae (Pyreno-
carpeae).
Fig. 33. Prasiola parietina Wille x 500 (after West).
B. CHANGES INDUCED IN THE ALGA
a. MYXOPHYCEAE. Though, as a general rule, the alga is less affected
by its altered life-conditions than the fungus, yet in many instances it
becomes considerably modified in appearance. In species of the genus
Pyrenopsis — small gelatinous lichens — the alga is a Gloeocapsa very similar to
G. magma. In the open it forms small colonies of blue-green cells surrounded
by a gelatinous sheath which is coloured red with gloeocapsin. As a
gonidium lying towards or on the outside of the granules composing the
thallus, the red sheath of the cells is practically unchanged, so that the
resemblance to Gloeocapsa is unmistakable. In the inner parts of the thallus,
the colonies are somewhat broken up by the hyphae and the sheaths are not
1 De Toni 1889.
LICHEN ALGAE 61
only less evident but much more faintly coloured. In Synalissa, a minute
shrubby lichen which has the same algal constituent, the tissue of the thallus
is more highly evolved, and in it the red colour can barely be seen and
then only towards the outside; at the centre it disappears entirely. The
long chaplets of Nostoc cells persist almost unchanged in the thallus of the
Collemaceae, but in heteromerous genera such as Pannaria and Peltigera
they are broken up, or they are coiled together and packed into restricted
areas or zones. The altered alga has been frequently described as Polycoccus
punctiformis. A similar modification occurs in many cephalodia, so that the
true affinity of the alga, in most instances, can only be ascertained after free
cultivation.
Bornet1 has described in Coccocarpia molybdaea the change that the alga
Scytonema undergoes as the thallus develops : in very young fronds the
filaments of Scytonema are unchanged and are merely enclosed between
layers of hyphae. At a later stage, with increase of the thallus in thickness,
the algal filaments are broken up, their covering sheath disappears, and the
cells become rounded and isolated. Petractis (Gyalecta) exanthematica has
also a Scytonema as gonidium, and equally exact observations have been
made by Funfstiick2 on the way it is transformed by symbiosis: with the
exception of a very thin superficial' layer, the thallus is immersed in the
rock and is permeated by the alga to its lowest limits, 3 to 4 mm. below the
surface, Petractis being a homoiomerous lichen. The Scytonema trichomes
embedded in the rock become narrower, and the sheath, which in the
epilithic part of the thallus is 4/4 wide, disappears almost entirely. The
green colour of the cells fades and septation is less frequent and less regular.
The filaments in that condition are very like oil-hyphae and can only be
distinguished as algal by staining reagents such as alkanna. They never
seem to be in contact with the fungal elements : there is no visible appearance
of parasitism nor even of consortism.
b. CHLOROPHYCEAE. As a rule the green-celled gonidium such as
Protococcus is not changed in form though the colour may be less vivid, but
in certain lichens there do occur modifications in its appearance. In Micarea
(Biatorina) prasina, Hedlund3 noted that the gonidium was a minute alga
possessing a gelatinous sheath similar to that of a Gloeocapsa. He isolated
the alga, made artificial cultures and found that, in the altered conditions,
it gradually increased in size, threw off the gelatinous sheath and developed
into normal Protococcus cells, measuring 7 to IO/LI in diameter. The gelatinous
sheath was thus proved to be merely a biological variation, probably of
value to the lichen owing to its capacity to imbibe and retain moisture.
Zukal4 also made cultures of this alga, but wrongly concluded it was a
Gloeocystis,
1 Bornet 1873. 2 Fiinfstiick 1899. 3 Hedlund 1892. 4 Zukal 1895, p. 19.
62 CONSTITUENTS OF THE LICHEN THALLUS
Moebius1 has described the transformation from algae to lichen gonidia
in a species epiphytic on Orchids in Porto Rico. He had observed that most
of the leaves were inhabited by a membranaceous alga, Phyllactidium, and
that constantly associated with it were small scraps of a lichen thallus con-
taining isolated globose gonidia. The cells of the alga, under the influence
of the invading fungus, were, in this case, formed into isolated round bodies
which divided into four, each daughter-cell becoming surrounded by a
membrane and being capable, in turn, of further division.
Frank2 followed the change from a free alga to a gonidium in Chroolepus
(Trentepohlia) umbrinum, as shown in the hypophloeodal thalli of the
Graphideae. The alga itself is frequent on beech bark, where it forms wide-
spreading brownish-red incrustations consisting of short chains occasionally
branched. The individual cells have thick laminated membranes and vary
in width from 2Oyu, to 37/1. The free alga constantly tends to penetrate below
the cortical layers of the tree on which it grows, and the immersed cells
become not only longer and of a thinner texture, but the characteristic red
colour so entirely disappears, that the growing penetrating apical cell may
be light green or almost colourless. As a lichen gonidium the alga under-
goes even more drastic changes : the red oily granules gradually vanish and
the cells become chlorophyll-green or, if any retain a bright colour, they are
orange or yellow. The branching of the chains is more regular, the cells
more elongate and narrower; usually they are about 13 to 21/1, long and S/j,
wide, or even less. Deeper down in the periderm, the chains become dis-
integrated into separate units. Another notable alteration takes place in
the cell-membrane which becomes thin and delicate. It has, however, been
observed that if these algal cells reach the surface, owing to peeling of the
bark, etc., they resume the appearance of a normal Trentepohlia.
In certain cases where two kinds of algae were supposed to be present
in some lichens, it has been proved that one species only is represented, the
difference in their form being caused by mechanical pressure of the sur-
rounding hyphae, as in Endocarpon and Staurothele where the hymenial
gonidia are cylindrical in form and much smaller than those of the thallus.
They were on this account classified by Stahl8 under a separate algal genus,
Stichococcus, but they are now known to be growth forms of Protococcus, the
alga that is normally present in the thallus. Similar variations were found
by Neubner4 in the gonidia of the Caliciaceae, but, by culture experiments
with the gonidia apart from the hyphae, he succeeded in demonstrating
transition forms in all stages between the " Pleurococcus" cells and those of
" Stichococcus" though the characters acquired by the latter are transmitted
to following generations. The transformation from spherical to cylindrical
i Moebius 1888. 2 Frank 1876, p. 158. 3 Stahl 1877. * Neubner 1893.
LICHEN ALGAE 63
algal cells had been also noted by Krabbe1 in the young podetia of some
species of Cladonia, the change in form being due to the continued pressure
in one direction of the parallel hyphae.
Isolated algal cells have been observed within the cortex of various
lichens. They are carried thither by the hyphae from the gonidial zone in
the process of cortical formation, but they soon die off as in that position
they are deprived of a sufficiency of air and of moisture. Forssell2 found
Xanthocapsa cells embedded in the hymenium of Omphalaria Heppii. They
were similar to those of the thallus, but they were not associated with hyphae
and had undergone less change than the thalline algae.
C. CONSTANCY OF ALGAL CONSTITUENTS
Lichen hyphae of one family or genus, as a rule, combine with the same
species of alga, and the continuity of genera and species is maintained.
There are, however, related lichens that differ chiefly or only in the characters
of the gonidia. Among such closely allied genera or sections of genera may
be cited Sticta with bright-green algae and the section Stictina with blue-
gr-een; Peltidea similarly related to Peltigera and Nephroma to Nephromium.
In the genus S0/orina,some of the species possess bright-green, others blue-
green algae, while in one, 5. crocea*, there is an upper layer of small bright-
green gonidia that project in irregular pyramids into the upper cortex ;
while below these there stretches a more or less interrupted band of blue-
green Nostoc cells. The two layers are usually separated by strands of
hyphae, but occasionally they come into close contact, and the hyphal
filaments pass from one zone to the other. In this genus cephalodia con-
taining blue-green Nostoc are characteristic of all the "bright-green" species.
Harmand4 has recorded the presence of two different types of gonidia in
Lecanora atra f. subgrumosa\ one of them, the normal Protococcus alga of the
species, the other, pale-blue-green cells of Nostoc affinity.
Forssell5 states that in Lecanora (Psoroma) hypnorum, the normal bright-
green gonidia of some of the squamules may be replaced by Nostoc. In that
case they are regarded as cephalodia, though in structure they exactly
resemble the squamules of Pannaria pezizoides, and Forssell considers that
there is sufficient evidence of the identity of the hyphal constituent in these
two lichens, the alga alone being different.
It may be that in Archilichens with a marked capacity to form a second
symbiotic union with blue-green algae, a tendency to revert to a primitive
condition is evident — a condition which has persisted wholly in Peltigera
with its Nostoc zone, but is manifested only by cephalodia formation in the
1 Krabbe 1891. 2 Forssell 1885. 3 Hue 1910. * Harmand 1913, p. 1050.
5 Forssell 1886.
64 CONSTITUENTS OF THE LICHEN THALLUS
Peltidea section of the genus. In this connection, however, we must bear in
mind Forssell's view that it is the Archilichens that are the more primitive1.
The alien blue-green algae with their gelatinous sheaths are adapted to
the absorption and retention of moisture, and, in this way, they doubtless
render important service to the lichens that harbour them in cephalodia.
D. DISPLACEMENT OF ALGAE WITHIN THE THALLUS
a. NORMAL DISPLACEMENT. Lindau2 has contrasted the advancing
apical growth of the creeping alga Trentepohlia with the stationary condition
of the unicellular species that multiply by repeated division or by sporulation,
and thus form more or less dense zones and groups of gonidia in most
lichens. The fungus in the latter case pushes its way among the algae and
breaks up the compact masses by a shoving movement, thus letting in light
and air. The growing hypha usually applies itself closely round an algal
cell, and secondary branches arise which in time encircle it in a network of
short cells. In the thallus of Variolaria* the hyphae from the lower tissues,
termed push-hyphae by Nienburg4, push their way into the algal groups and
filaments composed of short cells come to lie closely round the individual
gonidia. Continued growth is centrifugal, and the algae are carried outward
with the extension of the hyphae (Fig. 12). Cell-division is more active at the
periphery, that being the area of vigorous growth, and the algal cells are, in
consequence, generally smaller in that region than those further back, the
latter having entered more or less into a resting condition, or, as is more
probable, these smaller cells are aplanospores not fully mature.
b. LOCAL DISPLACEMENT. Specimens of Parmelia physodes were found
several times by Bitter, the grey-green surface of which was marbled with
whitish lines, caused by the absence of gonidia under these lighter-coloured
areas. The thallus was otherwise healthy as was manifested by the freely
fruiting condition : no explanation of the phenomenon was forthcoming.
Bitter compared the condition with the appearance of lighter areas on the
thallus of Parmelia obscurata.
Something of the same nature was observed on the thallus of a Peltigera
collected by F. T. Brooks near Cambridge. The marking took the form of
a series of concentric circles, starting from several centres. The darker lines
were found on examination to contain the normal blue-green algal zone,
while the colour had faded from the lighter parts. The cause of the difference
in colouration was not apparent.
1 See Chap. VII. 2 Lindau 1895. 3 Darbishire 1897. 4 Nienburg 1917.
LICHEN ALGAE
E. NON-GONIDIAL ORGANISMS ASSOCIATED WITH LlCHEN HYPHAE
Bonnier1 made a series of cultures with lichen spores and green cells
other than those that form lichen gonidia. In one instance he substituted
Protococcus botryoides for the normal gonidia of Parmelia (Xanthoria)
parietina\ in another of his cultures he replaced Protococcus viridis by the
filamentous alga Trentepolilia abietina. In both cases the hyphae attached
themselves to the green cells and a certain stage
of thallus formation was reached, though growth
ceased fairly early. Another experiment made
with the large filaments of Vaucheria sessilis met
with the same amount of success (Fig. 34). The
germinating hyphae attached themselves to the
alga and grew all round it, but there was no ad-
vance to tissue formation.
Cultures were also made with the protonema
of mosses. Either spores of mosses and lichens
were germinated together, or lichen spores were
sown in close proximity to fully formed proto-
nemata. The developing hyphae seized on the
moss cells and formed a network of branching
anastomosing filaments along the whole length of
the protonema without, however, penetrating the
cells. If suitable algae were encountered, proper
thallus formation commenced, and Bonnier con-
siders that the hyphae receive stimulus and
nourishment from the protonema sufficient to
tide them over a considerable period, perhaps until the algal symbiont is
met. An interesting variation was noted in connection with the cultures of
Mnium hornum*. If the protonema were of the usual vigorous type, the
whole length was encased by the hyphal network; but if it were delicate and
slender, the protoplasm collected in the cell that was touched by hyphae
and formed a sort of swollen thick-walled bud (Fig. 35). This new body
persisted when the rest of the filament and the hyphae had disappeared,
and, in favourable conditions, grew again to form a moss plant.
g. 34. Germinating hyphae of
Lecanora subfusca Ach. , grow-
ing over the alga Vaucheria
sessilis DC., much magnified
(after Bonnier).
F. PARASITISM OF ALGAE ON LICHENS
A curious instance of undoubted parasitism by an alga, not as in
Strigula on one of the higher plants, but on a lichen thallus, is recorded
by Forssell3. A group of Protococcns-\ti<& cells established on the thallus
Bonnier 1888 and 1889*.
3 Forssell 1884, p. 34.
66
CONSTITUENTS OF THE LICHEN THALLUS
of Peltigera had found their way into the tissue, the underlying cortical
cells having degenerated. The blue-green cells of the normal gonidial layer
Fig. 35. Pure culture of protonema of Mnium hornum L. with spores and hyphae of
Lecidea vernalis Ach. a,a,a, buds forming x 150 (after Bonnier).
had died off before their advance but no zone was formed by the invading
algae; they simply withdrew nourishment and gave seemingly no return.
The phenomenon is somewhat isolated and accidental but illustrates the
capacity of the alga to absorb food supply from lichen hyphae.
An instance of epiphytic growth has also been recorded by Zahlbruckner1.
He found an alga, Trentepohlia abietina, covering the thallus of a Brazilian
lichen, Parmelia isidiophora, and growing so profusely as to obscure the
isidiose character towards the centre of the thallus. There was no genetic
connection of the alga with the lichen as the former was not that of the
lichen gonidium. Lichen thalli are indeed very frequently the habitat of
green algae, though their occurrence may be and probably is accidental,
* Zahlbruckner 1902.
CHAPTER III
MORPHOLOGY
GENERAL ACCOUNT OF LICHEN STRUCTURE
I. ORIGIN OF LICHEN STRUCTURES
THE two organisms, fungus and alga, that enter into the composition of the
lichen plant are each characterized by the simplicity of their original structure
in which there is little or no differentiation into tissues. The gonidia-forming
algae are many of them unicellular, and increase mainly by division or by
sporulation into daughter-cells which become rounded off and repeat the life
of the mother-cell ; others, belonging to different genera, are filaments,
mostly of single cell-rows, with apical growth. The hyphal elements of the
lichen are derived from fungi in which the vegetative body is composed of
branching filaments, a character which persists in the lichen thallus.
The union of the two symbionts has stimulated both, but more especially
the fungus, to new developments of vegetative form, in which the fungus, as
the predominant partner, provides the framework of the lichen plant-body.
Varied structures have been evolved in order to secure life conditions favour-
able to both constituents, though more especially to the alga ; and as the
close association of the assimilating and growing tissues is maintained, the
thallus thus formed is capable of indefinite increase.
A. FORMS OF CELL-STRUCTURE
There is no true parenchyma or cellular structure in the lichen thallus
such as forms the ground tissue of the higher
plants. The fungal hyphae are persistently fila-
mentous and either simple or branched. By
frequent and regular cell-division — always at right
angles to the long axis — and by coherent growth,
a pseudoparenchyma may however be built up
which functions either as a protective or strength-
Lindau1 proposed the name "plectenchyma" >^^^PSK?S3^3^-
for the tangled weft of hyphae that is the prin-
J r Fig. 36. Vertical section of
cipal tissue system in fungi as well as lichens. young stage of stratose thai-
The more elaborated pseudoparenchyma he desig- & ^JjSjgSS
nates as "paraplectenchyma," while the term cortex ; 6, medullary hyphae ;
, , „ , i r i /- 1 c< gonidial zone, x 500 (after
prosoplectenchyma he reserved for the fibrous Schwendener).
1 Lindau 1899.
5—2
68 MORPHOLOGY
or chondroid strands of compact filaments that occur frequently in the
thallus of the larger fruticose lichens, and are of service in strengthening
the fronds. The term plectenchyma is now generally used for pseudo-
parenchyma.
B. TYPES OF THALLUS
Three factors, according to Reinke1, have been of influence in determining
the thalline development. The first, and most important, is the necessity to
provide for the work of photosynthesis on the part of the alga. There is
also the building up of a tissue that should serve as a storage of reserve
material, essential in a plant the existence of which is prolonged far beyond
the natural duration of either of the component organisms; and, finally,
there is the need of protecting the long-lived plant as a whole though more
particularly the alga.
Wallroth was the first to make a comparative study of the different
lichen thalli. He distinguished those lichens in which the green cells and
the colourless filaments are interspersed equally through the entire thallus
as "homoiomerous" (Fig. 2), and those in which there are distinct layers of
cortex, gonidia, and medulla, as "heteromerous" (Fig. i), terms which,
though now considered of less importance in classification, still persist
and are of service in describing the position of the alga with regard to the
general structure. A less evident definition of the different types of thallus
has been proposed by Zukal2 who divides them into "endogenous" and
"exogenous."
a. ENDOGENOUS THALLUS. The term has been applied to a compara-
tively small number of homoiomerous lichens in which the alga predominates
in the development, and determines the form of the thallus. These algae,
members of the Myxophyceae, are extremely gelatinous, and the hyphae
grow alongside or within the gelatinous sheath. In the simpler forms the
vegetative structure is of the most primitive type: the alga retains its
original character almost unchanged, and the ascomycetous fungus grows
along with and beside it (Fig. 4). Such are the minutely tufted thalli of
Thermutis and Spilonema and the longer strands of Epkebe, in which the
associated Scytonema or Stigonema, filamentous blue-green algae, though
excited to excessive growth, scarcely lose their normal appearance, making
it difficult at times to recognize the lichenoid character unless the fruits also
are present.
Equally primitive in most cases is the structure of the thallus associated
with Gloeocapsa. The resulting lichens, Pyrenopsis, Psorotichia, etc. are
simply gelatinous crusts of the alga with a more or less scanty intermingling
of fungal hyphae.
1 Reinke 1895. 2 Zukal l895> p. gfo.
ORIGIN OF LICHEN STRUCTURES 69
In the Collemaceae, the gonidial cells of which are species of Nostoc
(Fig. 2), there appears a more developed thallus; but in general, symbiosis
in Collema has wrought the minimum of change in the habit of the alga,
hence the indecision of the earlier botanists as to the identification and
classification of Nostoc and Collema. Though in many of the species of the
genus Collema no definite tissue is formed, yet, under the influence of
symbiosis, the plants become moulded into variously shaped lobes which
are specifically constant. In some species there is an advance towards
more elaboration of form in the protective tissues of the apothecia, a layer
of thin-walled plectenchyma being occasionally formed beneath or around
the fruit as in Collema granuliferum.
In all these lichens, it is only the thallus that can be considered as
primitive: the fruit is a more or less open apothecium — more rarely a peri-
thecium — with a fully developed hymenium. Frequently it is provided with
a protective thalline margin.
b. EXOGENOUS THALLUS. In this group, composed almost exclusively
of heteromerous lichens, Zukal includes all those in which the fungus takes
the lead in thalline development. He counts as such Leptogium, a genus
closely allied to Collema but with more membranous lobes, in which the
short terminal cells of the hyphae have united to form a continuous cortex.
A higher development, therefore, becomes at once apparent, though in some
genera, as in Coenogonium, the alga still predominates, while the simplest
forms may be merely a scanty weft of filaments associated with groups of
algal cells. Such a thallus is characteristic of the Ectolechiaceae, and some
Gyalectaceae, etc., which have, indeed, been described by Zahlbruckner1
as homoiomerous though their gonidia belong to the non-gelatinous
Chlorophyceae.
Heteromerous lichens have been arranged by Hue2 according to their
general structure in three great series :
1. Stratosae. Crustaceous, squamulose and foliose lichens with a
dorsiventral thallus.
2. Radiatae. Fruticose, shrubby or filamentous lichens with a strap-
shaped or cylindrical thallus of radiate structure.
3. Stratosae- Radiatae. Primary dorsiventral thallus, either crustaceous
or squamulose, with a secondary upright thallus of radiate structure called
the podetium (Cladoniaceae).
1 Zahlbruckner 1907. 2 Hue 1899.
;o MORPHOLOGY
II. STRATOSE THALLUS
i. CRUSTACEOUS LICHENS
A. GENERAL STRUCTURE
In the series "Stratosae," the plant is dorsiventral, the tissues forming
the thallus being arranged more or less regularly in strata one above the
other (Fig. 37). On the upper surface there is a hyphal layer constituting
I
Fig. 37. Vertical section of crustaceous lichen (Lecanora subfusca
var. chlarona Hue) on bark, a, lichen cortex; b, gonidia;
c, cells of the periderm. x 100.
a cortex, either rudimentary or highly elaborated ; beneath the cortex is .
situated the gonidial zone composed of algae and hyphae in close asso-
ciation ; and deeper down the medulla, generally a loose tissue of branching
hyphae. The lower cortex which abuts on the medulla may be as fully
developed as the upper or it may be absent.
The growing tissue is chiefly marginal ; the hyphae on the outer edge
remain "meristematic"1 and provide for horizontal as well as vertical ex-
tension; and there is also continual increase of the algal cells. There is in
addition a certain amount of intercalary growth due to the activity of the
gonidial tissue, both algal and fungal, providing for the renewal of the
cortex, and even interposing new tissue.
B. SAXICOLOUS LICHENS
a. EPILITHIC LICHENS, The crustaceous lichens forming this group
spread over the rock surfaces. The support must be stable to allow the
necessary time for the slowly developing organism, and therefore rocks that
are friable or subject to continual weathering are bare of lichens.
aa. Hypothallus or Prothallus. The first stage of growth in the lichen
thallus can be most easily traced in epilithic crustaceous species, especially
in those that inhabit a smooth rock surface. The spore, on germination,
produces a delicate branching septate mycelium which radiates on all sides,
as was so well observed and recorded by Tulasne2 in Verrucaria muralis
(Fig. 14). Zukal3 has called this first beginning the prothallus. In time the
1 Wainio has adopted this term for growing hyphae 1897, p. 33.
2 Tulasne 1852. 3 Zukal lg
STRATOSE THALLUS
cell-walls of the filaments become much thicker and though, in some species,
they remain colourless, in others they become dark-coloured, all except the
extreme tips, owing to the presence of lichen pigments — a provision, Zukal1
considers, to protect them against the ravages of insects, etc. The pro-
thallic filaments adhere - closely to the substratum and the branching
becomes gradually more dendroid in form, though sometimes hyphae are
united into strands, or even form a kind of plectenchymatous tissue. This
purely hyphal stage may persist for long
periods without much change. In time
there may be a fortuitous encounter with
the algae (Fig. 38 A) which become the
gonidia of the plant. Either these have
been already established on the substra-
tum as free-growing organisms, or, as
accidentally conveyed, they alight on the
prothallus. The contact between alga
and hypha excites both to active growth
and to cell-division; and the rapidly
multiplying gonidia are as speedily sur-
rounded by the vigorously growing hyphal
filaments.
Schwendener2 has thus described the
origin and further development of pro-
thallus and gonidia: on the dark-coloured
proto- or prothallus, he noted small nestling groups of green cells which
he, at that time, regarded as direct outgrowths from the lichen hyphae.
These gonidial cells, increasing by division, multiplied gradually and
gathered into a connected zone. He also observed that the hyphae in
contact with the gonidia became more thin-walled and produced many new
branches. Some of these newly formed branches grow upwards and form
the cortex, others grow downwards and build up the medulla or pith; the
filaments at the circumference continue to advance and may start new
centres of gonidial activity (Fig. 386). In many species, however, this
prothallus or, as it is usually termed at this stage, the hypothallus, be-
comes very soon overgrown and obscured by the vigorous increase of the
first formed symbiotic tissue and can barely be seen as a white or dark line
bordering the thallus (Fig. 39). Schwendener3 has stated that probably
only lichens that develop from the spore are distinguished by a proto-
thallus, and that those arising from soredia do not form these first creeping
filaments.
Fig. 38 A. Hypothallus of Rhizocarpon
confervoides DC., from the extreme edge,
with loose gonidia x 600.
Zukal 1895.
2 Schwendener 1866.
3 Schwendener 1863.
72 MORPHOLOGY
bb. Formation of crustaceous tissues. Some crustaceous lichens have
a persistently scanty furfuraceous crust, the vegetative development never
advancing much beyond the first rather loose association of gonidia and
Fig. 38 B. Young thallus of Rhizocarpon confervoides DC., with various
centres of gonidial growth on the hypothallus x 30.
Fig. 39. Lecanora parella Ach. Determinate thallus with white bordering
hypothallus, reduced (M. P., Photo.).
STRATOSE THALLUS 73
hyphae ; but in those in which a distinct crust or granules are formed, three
different strata of tissue are discernible:
1st. An upper cortical tissue of interlaced hyphae with frequent septa-
tion and with swollen gelatinous walls, closely compacted and with the
lumen of the cells almost obliterated, not unfrequently a layer of mucilage
serving as an outer cuticle. This type of cortex has been called by Hue1
"decomposed." It is subject to constant surface weathering, thin layers
being continually peeled off, but it is as continually being renewed endo-
genously by the upward growth of hyphae from the active gonidial zone.
Exceptions to this type of cortex in crustaceous lichens are found in some
Pertusariae where a secondary plectenchymatous cortex is formed, and in
Dirina where it is fastigiate2 as in Roccella.
2nd. The gonidial zone — a somewhat irregular layer of algae and
hyphae below the cortex— which varies in thickness according to the species.
3rd. The medullary tissue of somewhat loosely intermingled branching
hyphae, with generally rather swollen walls and narrow lumen. It rests
directly on the substratum and follows every inequality and crack so
closely, even where it does not penetrate, that the thallus cannot be
detached without breaking it away.
In Verrucaria mucosa, a smooth brown maritime lichen found on rocks
between tide-levels, the thallus is composed of tightly packed vertical rows
of hyphae, slender, rather thin-walled, and divided into short cells. The
gonidia are chiefly massed towards the upper surface, but they also occur in
vertical rows in the medulla. One or two of the upper cells are brown and
form an even cortex. The same formation occurs in some other sea-washed
species; the arrangement of the tissue elements recalls that of crustaceous
Florideae such as Hildenbrandtia, Cruoria, etc.
cc. Formation of areolae. An "areolate" thallus is seamed and scored
by cracks of varying width and depth which divide it
into minute compartments. These cracks or fissures or
chinks originate in two ways depending on the presence
or absence of hypothallic hyphae. Where the hypothallus
is active, new areolae arise when the filaments encounter
new groups of algae. More vigorous growth starts at once
and proceeds on all sides from these algal centres, until
Fig. 40. Young
similarly formed areolae are met, a more or less pro- thallus of Rhizo-
nounced fissure marking the limits of each. This primary S^rfc^^'kh
areolation, termed rimose or rimulose, is well seen in the primary and sub-
thin smooth thallus of Rhizocarpon geographicum (Fig. 40);
but the first-formed areolae are also very frequently slightly x 5-
1 Hue 1906. 2 See p. 83.
74 MORPHOLOGY
marked by subsequent cracks due to unequal growth. The areolation caused
by primary growth conditions tends to become gradually less obvious or to
disappear altogether.
Secondary areolation is due to unequal intercalary growth of the
otherwise continuous thallus1. A more active increase of any minute portions
provokes a tension or straining of the cortex between the swollen areas
and the surrounding more sluggish tissues ; the surface layers give
way and chinks arise, a condition described by older lichenologists as
"rimose-diffract" or sometimes as "rhagadiose." The thallus is generally
thicker, more broken and granular in the older central parts of the lichen.
Towards the circumference, where the tissue is thinner and growth more
equal, the chinks are less evident. Sometimes the more vigorously growing
areolae may extend over those immediately adjoining, in which case the
covered portions become brown and their gonidia gradually disappear.
Strongly marked intersecting lines, similar to those round the margin
of the thallus, are formed when hypothalli that have themselves started
from different centres touch each other. A large continuous patch of
crustaceous thallus may thus be composed of many individuals (Fig. 41).
Fig. 41. Rhizocarpon geographicum DC. on boulder, reduced (M.P., Photo.}.
b. ENDOLITHIC LICHENS. In many species, only the lower hyphae
penetrate the substratum either of rock or soil. In a few, more especially
those growing on limestone, the greater part or even the whole of the vege-
tative thallus and sometimes also the fruits are, to some extent, immersed
1 Malinowski 1911.
STRATOSE THALLUS 75
in the rock. It has now been demonstrated that a number of lichens,
formerly described as athalline, possess a considerable vegetative body
which cannot be examined until the limestone in which they are embedded
is dissolved by acids. One such species, Petractis (Gyalecta) exanthematica,
studied by Steiner1 and later by Funfstuck 2, is associated with the blue-
green filamentous alga, Scytonema, and is homoiomerous in structure, the
alga growing through and permeating the whole of the embedded thallus.
A partly homoiomerous thallus, associated with Trentepohlia, has been
described by Bachmann3. He found the bright-yellow filaments of the
alga covering the surface of a calcareous rock. By reason of their apical
growth, they pierced the rock and dissolved a way for themselves, not only
among the loose particles, but right through a clear calcium crystal reaching
generally to a depth of about 200 /u, though isolated threads had gone 350/1*
below the surface. Near the outside the tendency was for the algae to
become stouter and to increase by intercalary growth and by budded yeast-
like outgrowths; lower down they were somewhat smaller. The hyphae
that became united with the algae were unusually slender and were charac-
terized by frequent anastomoses. They closely surrounded the gonidia
and also filled the loose spaces of the limestone with their fine thread-like
strands. Though oil was undoubtedly present in the lower hyphae there
were no swollen nor sphaeroid cells4. Some interesting experiments with
moisture proved that the part of the rock permeated with the lichen
absorbed much more water and retained it longer than the part that was
lichen-free.
Generally the embedded tissues follow the same order as in other
crustaceous lichens : an upper layer of cortical hyphae, next a gonidial
zone, and beneath that an interlaced tissue of medullary or rhizoidal hyphae
which often form fat-cells4. Friedrich5 has given measurements of the
immersed thallus of Lecanora (Biatorella) simplex: under a cortical layer of
hyphae there was a gonidial zone 600-700/4 thick, while the lower hyphae
reached a depth of 1 2 mm. ; he has also recorded an instance of a thallus
reaching a depth of 30 mm.
On siliceous rocks such as granite, rhizoidal hyphae penetrate the rock
chiefly between the thin separable flakes of mica. Bachmann6 has recog-
nized in these conditions three distinct series of cell-formations: (i) slender
long-celled sparsely branched hyphae which form a network by frequent
anastomoses; (2) further down, though only occasionally, hyphae with
short thick-walled bead-like cells; and (3) beneath these, but only in or
near mica crystals, spherical cells containing oil or some albuminous
substance.
1 Steiner r88i. 2 Funfstuck 1899. 3 Bachmann 1913.
4 See p. 215. 5 Friedrich 1906. ' Bachmann 1907.
;6 MORPHOLOGY
c. CHEMICAL NATURE OF THE SUBSTRATUM. Lichens growing on
calcareous rocks or soils are more or less endolithic, those on siliceous
rocks are largely epilithic, but Bachmann1 found that the mica crystals in
granite were penetrated, much in the same way as limestone, by the lichen
hyphae. These travel through the mica in all directions, though they tend
to follow the line of cleavage, thus taking the direction of least cohesion.
He found that oil-hyphae were formed, and also certain peculiar bristle-like
terminal branches; in other cases there were thin layers of plectenchyma, and
gonidia were also present. If however felspar or quartz crystals, no matter
how thin, blocked the way, further growth was arrested, the hyphae being
unable to pierce through or even to leave any trace on the quartz2. On
granite containing no mica constituents the hyphae can only follow the
cracks between the different impenetrable crystals.
Stahlecker3 has confirmed Bachmann's observations, but he considers
that the difference in habit and structure between the endolithic and
epilithic series of lichens is due rather to the chemical than to the physical
nature of the substratum. Thus in a rock of mixed composition such as
granite, the more basic constituents are preferred by the hyphae, and are
the first to be surrounded: mica, when present, is at once penetrated;
particles of hornblende, which contain 40 to 50 per cent, only of silicic
acid, are laid hold of by the filaments of the lichen before the felspar, of
which the acid content is about 60 per cent.; quartz grains which are pure
silica are attacked last of all. though in the course of time they also become
corroded.
The character of the substratum also affects to a great extent the
comparative development of the different thalline layers: the hyphal tissues
in silicicolous lichens are much thinner than in lichens on limestone, and
the gonidial zone is correspondingly wider. In a species of Staurothele on
granite, Stahlecker3 estimated the gonidial zone to be about 600/1, thick,
while the lower medullary hyphae, partly burrowing into the rock, measured
about 6 mm. Other measurements at different parts of the thallus gave a
rhizoidal depth of 3 mm., while on a more finely granular substratum, with
a gonidial zone of 350 p, the rhizoidal hyphae measured only i£mm. On
calcareous rocks, on the contrary, with a gonidial zone that is certainly no
larger, the hyphal elements penetrate the rock to varying depths down to
1 5 mm. or even more.
Lang4 has recorded equally interesting measurements for Sarcogyne
(Biatorelld) latericola: on slaty rock which contained no mixture of lime,
the gonidial zone had a thickness of 80 //,, a considerable proportion of the
very thin thallus. Funfstiick5 has indeed suggested that this lichen on acid
1 Bachmann 1904. 2 Bachmann 1904. 3 Stahlecker 1906.
4 Lang 1903. B Funfstiick 1899.
STRATQSE THALLUS 77
rocks is only a starved condition of Sarcogyne (Biatorella) simplex, which on
calcareous rocks, though with a broader gonidial zone, has, as noted above,
a correspondingly much larger hyphal tissue.
Stahlecker's theory is that the hyphae require more energy to grow in
the acid conditions that prevail in siliceous rocks, and therefore they make
larger demands on the algal symbionts. It follows that the latter must be
stimulated to more abundant growth than in circumstances favourable to
the fungus, such as are found in basic (calcareous) rocks; he concludes that
on the acid (siliceous) rocks, the epilithic or superficial condition is not only
a physical but a biological necessity, to enable the algae to grow and
multiply in a zone well exposed to light with full opportunity for active
photosynthesis and healthy increase.
C. CORTICOLOUS LICHENS
The crustaceous lichens occurring on bark or on dead wood, like those
on rocks, are either partly or wholly immersed in the substratum (hypo-
phloeodal), or they grow on the surface (epiphloeodal); but even those with
a superficial crust are anchored by the lower hyphae which enter any crack
or crevice of wood or bark and so securely attach the thallus, that it can
only be removed by cutting away the underlying substance.
a. EPIPHLOEODAL LICHENS. These lichens originate in the same way
as the corresponding epilithic series from soredia or from germinating
spores, and follow the same stages of growth; first a hypothallus with
subsequent colonization of gonidia, the formation of granules, areolae, etc.
The small compartments are formed as primary or secondary areolae; the
larger spaces are marked out by the encounter of hypothalli starting from
different centres.
The thickness of the thallus varies considerably according to the species.
In some Pertusariae with a stoutish irregular crust there is a narrow
amorphous cortical layer of almost obliterated cells, a thin gonidial zone
about 35/4 in width and a massive rather dense medulla of colourless
hyphae. Darbishire1 has described and figured in Varicellaria microsticta,
one of the Pertusariaceae, single hyphae that extend like beams across the
wide medulla and connect the two cortices. In some Lecanorae and Lecideae
there is, on the contrary, an extremely thin thallus consisting of groups of
algae and loose fungal filaments, which grow over and between the dead
cork cells of the outer bark. On palings, there is often a fairly substantial
granular crust present, with a gonidial zone up to about So/* thick, while
the underlying or medullary hyphae burrow among the dead wood fibres.
1 Darbishire 1897.
78 MORPHOLOGY
b. HYPOPHLOEODAL LICHENS. These immersed lichens are compar-
able with the endolithic species of the rock formations, as their thallus is
almost entirely developed under the outer bark of the tree. They are recog-
nizable, even in the absence of any fructification, by the somewhat shining
brownish, white or olive-green patches that indicate the underlying lichen.
This type of thallus occurs in widely separated families and genera, Lecidea,
Lecanora, etc., but it is most constant in Graphideae and in those Pyreno-
lichens of which the algal symbiont belongs to the genus Trentepohlia,
The development of these lichens is of peculiar interest as it has been
proved that though both symbionts are embedded in the corky tissues, the
hyphae arrive there first, and, at some later stage, are followed by the
gonidia. There is therefore no question of the alga being a "captured
slave" or "unwilling mate."
Frank1 made a thorough study of several subcortical forms. He found
that \nArthonia radiata, the first outwardly visible indication of the presence
of the lichen on ash bark was a greenish spot quite distinct from the
normal dull-grey colour of the periderm. Usually the spots are round in
outline, but they tend to become ellipsoid in a horizontal direction, being
influenced by the growth in thickness of the tree. At this early stage only
hyphae are present; Bornet2 as well as Frank described the outer periderm
cells as penetrated and crammed with the colourless slender filaments.
Lindau3, in a more recent work, disputes that statement: he found that the
hyphae invariably grew between the dead cork cells, splitting them up and
disintegrating the bark, but never piercing the membranes. The purely
prothallic condition, as a weft of closely entangled hyphae, may last, Frank
considers, for a long period in an almost quiescent condition — possibly for
several years — before the gonidia arrive.
It is always difficult to observe the entrance of the gonidia but they
seem to spread first under the second or third layers of the periderm. With
care it is possible to trace a filament of Trentepohlia from the surface down-
wards, and to see that the foremost cell is really the growing and advancing
apex of the creeping alga. Both symbionts show increased vigour when
they encounter each other: the thallus at once develops in extent and in
depth, and, ultimately, reproductive bodies are formed. In some species the
apothecia or perithecia alone emerge above the bark, in others the outer
peridermal cells are thrown off, and the thallus thus becomes superficial to
some extent as a white scurfy or furfuraceous crust.
The change from a hypophloeodal to a partly epiphloeodal condition
depends largely on the nature of the bark. Frank1 found that Lecanora
pallida remained for a long time immersed when growing on the thick
rugged bark of oak trunks. When well lighted, or on trees w'ith a thin
1 Frank 1876. 2 Bornet 1873, p. 81. 3 Lindau 1895.
STRATOSE^THALLUS 79
periderm, such as the ash, the lichen emerges much earlier and becomes
superficial.
Black (or occasionally white) lines intersect the thallus and mark, as in
saxicolous lichens (Fig. 41), the boundary lines between different indi-
viduals or different species. The pioneer hyphae of certain lichens very
frequently become dark-coloured, and Bitter1 has suggested as the reason
for this that in damp weather the hypothallic growth is exceptionally
vigorous. When dry weather supervenes, with high winds or strong sun-
shine, the outlying hyphae, unprotected by the thallus, become dark-
coloured. On the return of more normal conditions the blackened tips are
thrown off. Bitter further states that species of Graphideae do not form a
permanent black limiting line when they grow in an isolated position: it is
only when their advance is checked by some other thallus that the dark per-
sistent edge appears, a characteristic also to be seen in the crust of other
lichens. The dark boundary is always more marked in sunny exposed
situations: in the shade, the line is reduced to a mere thread.
Bitter's restriction of black boundary lines to cases of encountering
thalli only, would exclude the comparison one is tempted to make between
the advancing hyphae of lichens and those of many woody fungi where the
extreme edge of the white invaded woody tissue is marked by a dark line.
In the latter case however it is the cells of the host that are stained black
by the fungus pigment.
2. SQUAMULOSE LICHENS
A. DEVELOPMENT OF THE SQUAMULE
The crustaceous thallus is more or less firmly adherent to, or confused
with, the substratum. Further advance to a new type of thallus is made
when certain hyphal cells of soredium or granule take the lead in an
ascending direction both upwards and outwards. As growth becomes
definitely apical or one-sided, the structure rises free from the substratum,
and small lobules or leaflet-like squamules are formed. Each squamule
in this type of thallus is distinct in origin and not merely the branch of
a larger whole.
In a few lichens the advance from the crustaceous to the squamulose
structure is very slight. The granules seem but to have been flattened out
at one side, and raised into minute rounded projections such as those that
compose the thallus of Lecanora badia generally described as "subsquamu-
lose." The squamulose formation is more pronounced in Lecidea ostreata,
and in some species of Pannaria ; and the whole thallus may finally consist
of small separate lobes as in Lecidea lurida, Lecanora crassa, L. saxicola,
1 Bitter 1899.
8o
MORPHOLOGY
species of Dermatocarpon and the primary thallus of the Cladoniae. Most of
these squamules are of a firm texture and more or less round in outline; in
some species of Cladonia, etc., they are variously crenate, or cut into pinnate-
like leaflets. Squamulose lichens grow mostly on rocks or soil, occasionally on
dead wood, and are generally attached by single rhizoidal hyphae, either
produced at all points of the under surface, or from the base only, growth
in the latter case being one-sided. In a few instances, as in Heppia Guepint,
there is a central hold-fast.
A frequent type of squamulose thallus is that termed "placodioid," or
"effigurate," in which the squamulose character is chiefly apparent at the
circumference. The thallus is more or less orbicular in
outline ; the centre may be squamulose or granular and
cracked into areolae ; the outer edge is composed of
radiating lobules closely appressed to the substratum
(Fig. 42).
All lichens with this type of thallus were at one time
included in the genus Placodium, now restricted by some
lichenologists to squamulose or crustaceous species with
polarilocular spores. Many of them rival Xanthoria parietina in their
brilliant yellow colouring.
Fig. 42. Placodium
murorum DC.
Part of placodioid
thallus with apo-
thecia x i.
Fl'g- 43- Lecania candicans A. Zahlbr., with placodioid thallus,
reduced (S. H., Photo.}.
There are also greyish-white effigurate lichens such as Lecanora saxicola,
Lecania candicans (Fig. 43) and Buellia canescens, well-known British
species.
STRATOSE THALLUS 81
B. TISSUES OF SQUAMULOSE THALLUS
The anatomical structure of the squamules is in general somewhat
similar to that of the crustaceous thallus: an upper cortex, a gonidial zone,
and below that a medullary layer of loose hyphae with sometimes a lower
cortex.
1. The upper cortex, as in crustaceous lichens, is generally of the
"decomposed"1 or amorphous type: interlaced hyphae with thick gelatinous
walls. A more highly developed form is apparent in Parmeliella and
Pannaria where the upper cortex is formed of plectenchyma, while in the
squamules of Heppia the whole structure is built up of plectenchyma, with
the exception of a narrow band of loose hyphae in the central pith.
2. The gonidia are Myxophyceae or Chlorophyceae ; the squamules in
some instances may be homoiomerous as in Lepidocollema, but generally
they belong to the heteromerous series, with the gonidia in a circumscribed
zone, and either continuous or in groups. Friedrich2 held that, as in crus-
taceous lichens the development of the gonidial as compared with the other
tissues depended on the substratum. The squamules of Pannaria micro-
phylla on sandstone were lOOyu- thick, and the gonidial layer occupied 80 or
90 /A of the whole3. With that may be compared Placodium Garovagli on
lime-containing rock: the gonidial layer measured only 50 //. across, the
pith hyphae 280 p and the rhizoidal hyphae that penetrated the rock 500 //..
3. The medullary layer, as a rule, is of closely compacted hyphae which
give solidity to the squamules; in those of Heppia it is almost entirely
formed of plectenchyma.
4. The lower cortex is frequently little developed or absent, especially
when the squamules are closely applied to the support as in some species
of Dennatocarpon. In some of the squamulose Lecanorae (L. crassa and
L. saxicoUi) the lowest hyphae are somewhat more closely interwoven;
they become brown in colour, and the lichen is attached to the substratum
by rhizoid-like branches. In Lecanora lentigera there is a layer of parallel
hyphae along the under surface. Further development is reached when
a plectenchyma of thick-walled cells is formed both above and below, as in
Psoroma hypnorum, though on the under surface the continuity is often
broken. The squamules of Cladoniae are described under the radiate-stratose
series.
1 See p. 83. - Friedrich 1906. 3 See p. 76.
82 MORPHOLOGY
3. FOLIOSE LICHENS
A. DEVELOPMENT OF FOLIOSE THALLUS
The larger leafy lichens are occasionally monophyllous and attached at
a central point as in Umbilicaria, but mostly they are broken up into lobes
which are either imbricate and crowded, or represent the dividing and
branching of the expanding thallus at the circumference. They are hori-
zontal spreading structures, with marginal and apical growth. The several
tissues of the squamule are repeated in the foliose thallus, but further pro-
vision is made to meet the requirements of the larger organism. There is the
greater development of cortical tissue, especially on the lower surface, and
the more abundant formation of rhizoidal organs to attach the large flat
fronds to the support. There are also various adaptations to secure the aera-
tion of the internal tissues1.
B. CORTICAL TISSUES
Schwendener2 was the first who, with the improved microscope, made
a systematic study of the minute structure of lichens. He examined typical
species in genera of widely different groups and described their anatomy in
detail. The most variable and perhaps the most important of the tissues
of lichens is the cortex, which is most fully developed in the larger thalli, and
as the same type of cortical structures recurs in lichens widely different in
affinity as well as in form, it seems well to group together here the ascertained
facts about these covering layers.
a. TYPES OF CORTICAL STRUCTURE. Zukal3, and more recently
Hue4, have made independent studies in the comparative morphology of
the thallus and have given particular attention to the different varieties
of cortex. They each find that the variations come under a definite series
of types. Zukal recognized five of these :
1. Pseudoparenchymatous (plectenchyma): by frequent septation of
regularly arranged hyphae and by coalescence a kind of continuous cell-
structure is formed.
2. Palisade cells: the outer elongate ends of the hyphae lie close
together in a direction at right angles to the surface of the thallus and form
a coherent row of parallel cells.
3. Fibrous: the cortical hyphae lie in strands of fine filaments parallel
with the surface of the thallus.
4. Intricate: hyphae confusedly interwoven and becoming dark in
colour form the lower cortex of some foliose lichens.
1 See p. 126. 2 Schwendener 1860, 1863 and 1868. 3 Zukal 1895, p. 1305. 4 Hue 1906.
STRATOSE THALLUS
These four types, Zukal finds, are practically without interstices in the
:issue and form a perfect protection against excessive transpiration. He adds
^et another form:
5. A cortex formed of hyphae with dark-coloured swollen cells,
,vhich is not a protection against transpiration. It occurs among lower crus-
:aceous forms.
Hue has summed up the different varieties under four types, but as he
las omitted the "fibrous" cortex, we arrive again at five different kinds of
:ortical formation, though they do not exactly correspond to those of
£ukal. A definite name is given to each type:
i. Intricate : an intricate dense layer of gelatinous-walled hyphae,
Dranching in all directions, but not coalescent (Fig. 44). This rather unusual
:ype of cortex occurs in Sphaerophorus and Stereocanlon, both of which
lave an upright rigid thallus (fruticose).
f
Fig. 44. Sphaerophorus coralloides Pers. Trans-
verse section of cortex and gonidial layer
near the growing point of a frond x 600.
Fig. 45. Roccella fudformis'DC. Trans-
verse section of cortex near the
growing point of a frond x 600.
2. Fastigiate : the hyphae bend outwards or upwards to form the
:ortex. A primary filament can be distinguished with abundant branches,
all tending in the same direction; anastomosis may take place between the
hyphae. The end branches are densely packed, though there are occasional
interstices (Fig. 45). Such a cortex occurs in Thamnolia\ in several genera
af Roccellaceae — Roccellographa^ Roccellina, Reinkella, Pentagenella, Combea,
Schizopelte and Roccella — and also in the crustaceous genus Dirina. The
fastigiate cortex corresponds with Zukal's palisade cells.
3. Decomposed: in this, the most frequent type of cortex, the hyphae
that travel up from the gonidial layer become irregularly branched and
frequently septate. The cell-walls of the terminal branches become swollen
into a gelatinous mass, the transformation being brought about by a change
6—2
84
MORPHOLOGY
in the molecular constituents of the cell-walls which permits the imbibitior
and storage of water. The tissue, owing to the enormous increase of the
wall, is so closely pressed together that the individua
hyphae become indistinct; the cell-lumen finall}
disappears altogether, or, at most, is only to be
detected in section as a narrow disconnected dart
streak. The decomposed cortex is characteristic
of many lichens, crustaceous (Fig. 46) and squamu-
lose, as well as of such highly developed genera as
Usnea, Letharia, Ramalina, Cetraria, Evernia anc
certain Parmeliae.
Zukal took no note of the decomposed cortex
but the omission is intentional and is due to his
regarding the structure of the youngest stages of the
thallus near the growing point as the most typical and as giving the besi
indication as to the true arrangement of hyphae in the cortex. He thu5
describes palisade tissue as the characteristic cortex of Evernia, since the
formation near the growing point of the fronds is somewhat palisade-like
and he finds fibrous cortex at the tips of Usnea filaments. In both these
instances Hue has described the cortex as decomposed because he takes
account only of the fully formed thallus in which the tissues have reached
a permanent condition.
4. Plectenchymatous: the last of Hue's types corresponds with the
first described by Zukal.^It is the result of the lateral coherence and frequent
septation of the hyphae into short almost square or rounded cells (Fig. 47)
The simplest type of such a cortex can be studied in Leptogiumt a genus oi
Fig. 46. Lecanora glaucoma
va.r.corrugata'Ny\. Vertical
section of cortex x 500 (after
Hue).
Fig. 47. Peltigera canina DC. Vertical section
of cortex and gonidial zone x 600.
STRATOSE THALLUS 85
gelatinous lichens in which the tips of the hyphae are cut off at the surface
by one or more septa. The resulting cells are wider than the hyphae and
they cohere together to form, in some species, disconnected patches of cells;
in others, a continuous cortical covering one or more cells thick, while in
the margin of the apothecium they form a deep cellular layer. The cellular
type of cortex is found also, as already stated, in some crustaceous Pertu-
sariae, and in a few squamulose genera or species. It forms the uppermost
layer of the Peltigera thallus and both cortices of many of the larger foliose
lichens such as Sticta, Parmelia, etc.
5. The "fibrous" cortex must be added to this series, as was pointed
out by Heber Howe1 who gave the less appropriate designation of "simple"
to the type. It consists of long rather sparingly branched slender hyphae
that grow in a direction parallel with the surface of the thallus (Fig. 48).
It is characteristic of several fruticose and foliose lichens with more or less
upright growth, such as we find in several of the Physciae, and in the allied
genus TeloschisteS) in Alectoria, several genera of Roccellaceae, in Usnea
longissima and in Parmelia pubescens, etc. Zukal would have included all
the Usneae as the tips are fibrous.
Fig. 48. Physcia ciliaris DC. Vertical section of thallus. a, cortex;
b, gonidial zone; c, medulla, x 100.
More than one type of cortex, as already stated, may appear in a genus;
a striking instance of variability occurs in Solorina where, as Hue2 has
pointed out, the cortex of .S". octospora is fastigiate, that of all the other
species being plectenchymatous. Cortical development is a specific rather
than a generic characteristic.
b. ORIGIN OF VARIATION IN CORTICAL STRUCTURE. The immediate
causes making for differentiation in cortical development are: the prevailing
direction of growth of the hyphae as they rise from the gonidial zone; the
amount of branching and the crowding of the filaments ; the frequency of
septation ; and the thickening or degeneration of the cell-walls which may
1 Heber Howe 1912. Hue 1911.
86 MORPHOLOGY
become almost or entirely mucilaginous. In the plectenchymatous cortex,
the walls may remain quite thin and the cells small as in Xanthoria parie-
tina, or the walls may be much thickened as in both cortices of Sticta.
As a result of stretching the cell may increase enormously in size: in some
instances where the internal hyphae are about 3 ft to 4 /A in width, the
cortical cells formed from these hyphae may have a cell cavity 15 /j, to 16/1,
in diameter.
c. Loss AND RENEWAL OF CORTEX. Very frequently the cortex is
covered over by a layer of homogeneous mucilage which forms an outer
cuticle. It arises from the continual degeneration of the outer cell-walls
and it is liable to friction and removal by atmospheric agency as was
first described by Schwendener1 in the weather-beaten cortex of Umbi-
licaria pustulata. He had noted the irregular jagged outline of the cross
section of the thallus, and he then suggested, as the probable reason, the
decay of the outer rind with the constant renewal of it by the hyphae from
the underlying gonidial zone, though he was unable definitely to prove his
theory. The peeling of the dead outer layer (with its replacement by new
tissue) has however been observed many times since his day. It has been
described by Darbishire2 in Pertusaria: in that genus there is at first a
primary cortex formed of hyphae that grow in a radial direction, parallel
to the surface of the thallus. The walls of these hyphae become gradually
more and jmore mucilaginous till the cells are obliterated. Meanwhile
short-celled filaments grow up in serried ranks from the gonidial layer and
finally push off the dead "fibrous" cortex. The new tissue takes on a
plectenchymatous character, and the outer cells in time become decomposed
and provide a mucilaginous cuticle which in turn is also subject to wasting.
The same process of peeling was noted by Rosendahl3 in some species of
brown Parmeliae, where the dead tissues were thrown off in shreds, though
only in isolated patches. But whether in patches or as a continuous sheath,
there is constant degeneration, with continual renewal of the dead material
from the internal tissues.
The cortex is the most highly developed of all the lichen structures and
is of immense importance to the plant as may be judged from the various
adaptations to different needs4. The cortical cell-walls are frequently
impregnated with some dark-coloured substance which, in exposed situa-
tions, must counteract the influence of too direct sunlight and be of
service in sheltering the gonidia. Lichen acids — sometimes very brightly
coloured — and oxalic acid are deposited in the cortical tissues in great
abundance and aid in retaining moisture; but the two chief functions to
1 Schwendener 1863, p. 180. a Darbishire 1897. * Rosendahl 1907.
4 See p. 96.
STRATOSE THALLUS 87
which the cortex is specially adapted are the checking of transpiration and
the strengthening of the thallus against external strains.
d. CORTICAL HAIRS OR TRICHOMES. Though somewhat rare, cortical
hairs are present on the upper surface of several foliose lichens. They take
rise, in all the instances noted, as a prolongation of one of the cell-rows
forming a plectenchymatous cortex.
In Peltidea (Peltigerd) apJithosa they are especially evident near the
growing edges of the thallus; and they take part in the development of
the superficial cephalodia1 which are a constant feature of the lichen. They
tend to disappear with age and leave the central older parts of the thallus
smooth and shining. In several other species of Peltigera (P. canina, etc.)
they are present and persist during the life of the cortex. In these lichens
the cells of the cortical tissue are thin-walled, all except the outer layer,
the membranes of which are much thicker. The hairs rising from them are
also thick-walled and septate. Generally they branch in all directions and
anastomose with neighbouring hairs so that a confused felted tangle is
formed; they vary in size but are, as a rule, about double the width of the
medullary hyphae as are the cortical cells from which they rise. They disap-
pear from the thallus, frequently in patches, probably by weathering, but
over large surfaces, and especially where any inequality affords a shelter,
they persist as a soft down.
Hairs are also present on the upper surface of some Parmeliae. Rosen-
dahl2 has described and figured them in P. glabra and P. verniculifera —
short pointed unbranched hyphae, two or more septate and with thickened
walls. They are most easily seen near the edge of the thallus, though they
persist more or less over the surface; they also grow on the margins of the
apothecia. In P. verruculifera they arise from the soredia; in P. glabra
a few isolated hairs are present on the under surface.
In Nephromium tomentosum there is a scanty formation of hairs on the
upper surface. They are abundant on the lower surface, and function as
attaching organs. A thick tomentum of hairs is similarly present on the
lower surface of many of the Stictaceae either as an almost unbroken
covering or in scattered patches. In several species of Leptoginm they grow
out from the lower cortical cells and attach the thin horizontal fronds ; and
very occasionally they are present in Collema.
C. GONIDIAL TISSUES
With the exception of some species of Collema and Leptogium lichens
included under the term foliose, are heteromerous in structure, and the algae
that form the gonidial zone are situated below the upper cortex and, there-
1 See p. 133. 2 Rosendahl 1907.
88 MORPHOLOGY
fore, in the most favourable position for photosynthesis. Whether belonging
to the Myxophyceae or the Chlorophyceae, they form a green band, straight
and continuous in some forms, in others somewhat broken up into groups.
In certain species they push up at intervals among the cortical cells, as in
Gyropkora and in Parmelia tristis. In Solorina crocea a regular series of
gonidial pyramids rises towards the upper surface. The green cells are
frequently more dense at some points than at others, and they may pene-
trate in groups well into the medulla.
The fungal tissue of the gonidial zone is composed of hyphae which
have thinner walls, and are generally somewhat loosely interlacing. In
Peltigera^ the gonidial hyphae are so connected by frequent branching and
by anastomosis that a net-like structure is formed, in the meshes of which
the algae — a species of Nostoc — are massed more or less in groups. In
lichens with a plectenchymatous cortex, the cellular tissue may extend
downwards into the gonidial zone and the gonidia thus become enmeshed
among the cells, a type of formation well seen in the squamulose species,
Dermatocarpon lachneum and Heppia Guepini, where the massive plecten-
chyma of both the upper and lower cortices encroaches on the pith. In
Endocarpon and in Psoroma the gonidia are also surrounded by short cells.
A similar type of structure occurs in Cora Pavonia, one of the Hymeno-
lichenes: the gonidial hyphae in that species form a cellular tissue in which
are embedded the blue-green Chroococcus cells2.
D. MEDULLA AND LOWER CORTEX
a. MEDULLA. The hyphal tissue of the dorsi ventral thallus that lies
between the gonidial zone and the lower cortex or base of the plant is
always referred to as the medulla or pith. It is, as a rule, by far the most
considerable portion of the thallus. In Parmelia caperata (Fig. 49), for
instance, the lobes of which are about 300 /it thick, over 200 p of the space
is occupied by this layer. It varies however very largely in extent in
different lichens according to species, and also according to the substratttm.
In another Parmelia with a very thin thallus, P. alpicola growing on quart-
zite, the medulla measures scarcely twice the width of the gonidial zone.
It forms a fairly massive tissue in some of the crustaceous lichens in some
Pertusariae and Lecanorae— attaining a width of about 600 /*.
Nylander3 distinguished three types of medullary tissue in lichens:
(1) felted, which includes all those of a purely filamentous structure;
(2) cretaceous or tartareous, more compact than the felted, and containing
granular or crystalline substances as in some Pertusariae; and lastly
(3) the cellular medulla in which the closely packed hyphae are divided
1 Meyer '9°2- 2 See p. 52. 3 Nylander l8s8.
STRATOSE THALLUS
89
into short cells and a kind of plectenchyma is formed, as in Lecanora
(Psoromd) hypnorum, in Endocarpon, etc.
Fig. 49. Parmelia caperala Ach. (S. H., Photo.}.
The felted medulla is characteristic of most lichens and is formed of
loose slender branching septate hyphae with thickish walls. This interwoven
hyphal texture provides abundant air-spaces.
Hue1 has noted that the walls of the medullary hyphae in Parmeliae are
smooth, unless they have been exposed to great extremes of heat or cold,
when they become wrinkled or scaly. They are very thick-walled in Pelti-
gera (Fig. 50).
Fig. 50. Hyphae .from lower medulla of Peltigera canina DC. x 600.
1 Hue 1898.
MORPHOLOGY
b. LOWER CORTEX. In some foliose lichens such as Peltigera there is
no special tissue developed on the under surface. In Lobaria pulmonaria
large patches of the under surface are bare, and the medulla is exposed to
the outer atmosphere, sheltered only by its position. In some other lichens
the lowermost hyphae lie closer together and a kind of felt of almost parallel
filaments is formed, generally darker in colour, as in Lecanora lentigera, and
in some species of Physcia.
Most frequently however the tissues of the upper cortex are repeated on
the lower surface, though differing somewhat in detail. In all of the brown
Parmeliae, according to Rosendahl1, the structure is identical for both
cortices, though the upper develops now hairs, now isidia, breathing pores,
etc., while the lower produces rhizinae. The amorphous mucilaginous cuticle
so often present on the upper surface is absent from the lower, the walls
of the latter being often charged instead with dark-brown pigments.
c. HYPOTHALLIC STRUCTURES. An unusual development of hyphae
from the lower cortex occurs i-n the genera Anzia and Pannoparmelia — both
closely related to Parmelia — whereby a
loose sponge-like hypothallus of anasto-
mosing reticulate strands is formed. In
one of the simpler types, Anzia colpodes,
a North American species, the hyphae
passing out from the lower medulla be-
come abruptly dark-brown in colour, and
are divided into short thick-walled cells.
Frequent branching and anastomosis of
these hyphae result in the formation of
a cushion-like structure about twice the
bulk of the thallus. In another species
from Australia (A. Japonica) there is a
lower cortex, distinct from the medulla,
consisting of septate colourless hyphae
with thick walls. From these branch out
free fi laments, similar in structure but dark
in colour, which branch and anastomose
as in the previous species.
In Pannoparmelia the lower cortex
and the outgrowths from it are several
cells thick; they may be thick- walled as
in Anzia, or they may be thin-walled as
described and figured by Darbishire2 in
Fig. 51. Pannoparmelia anzioides Darb.
Vertical section of thallus and hypo-
thallus. 0, cortex ; b, gonidial zone ;
i, medulla; d, lower cortex; e, hypo-
thallus. x ca. 450 (after Darbishire).
Rosendahl 1907.
2 Darbishire 1912.
STRATOSE THALLUS 91
P annoparmelia anzioides, a species from Tierra del Fuego (Fig. 51). A some-
what dense interwoven felt of hyphae occurs also in certain parts of the
under surface of Parmelia physodes*.
This peculiar structure, regarded as a hypothallus, is probably of service
in the retention of moisture. The thick cell-walls in most of the forms
suggest some such function.
E. STRUCTURES FOR PROTECTION AND ATTACHMENT
Such structures are almost wholly confined to the larger foliose and
fruticose lichens and are all of the same simple type ; they are fungal
in origin and very rarely are gonidia associated with them.
a. CILIA. In a few widely separated lichens stoutish cilia are borne,
mostly on the margins of the thallus lobes, or on the margins of the apo-
Fig. 52. Usneaflorida Web. Ciliate apothecia (S. H., Pkoto.).
thecia (Fig. 52). They arise from the cortical cells or hyphae, several of
which grow out in a compact strand which tapers gradually to a point.
Cilia vary in length up to about I cm. or even longer. In some lichens they
1 Porter 1919.
92
MORPHOLOGY
retain the colour of the cortex and are greyish or whitish-grey, as in Physcia
ciliaris or in Physcia hispida (Fig. 1 10). They provide a yellow fringe to
the apothecia of Physcia chrysophthalma and a green fringe to those of
Usnea fiorida. They are dark-brown or almost black in Parmelia perlata
var. ciliata and in P. cetrata, etc. as also in Gyrophora cylindrica. The fronds
of Cetraria islandica and other species of the genus are bordered with short
spinulose brown hairs whose main function seems to be the bearing of
"pycnidia" though in many cases they are barren (Fig. 128).
Superficial cilia are more rarely formed than marginal ones, but they are
characteristic of one not uncommon British species, Parmelia proboscidea
(P. pilosella Hue). Scattered over the surface of that lichen are numerous
crowded groups of isidia which, frequently, are prolonged upwards as dark-
brown or blackish cilia. Nearly every isidium bears a small brown spot on
the apex at an early stage of growth. Similar cilia are sparsely scattered
over the thallus, but their base is always a rather stouter grey structure,
which suggests an isidial origin. Cilia also occur on the margin of the lobes.
As lichens are a favourite food of snails, insects, etc., it is considered
that these structures are protective in function, and that they impede, if
they do not entirely prevent, the larger marauders in their work of destruction.
b. RHIZINAE. Lichen rootlets are mainly for the purpose of attachment
and have little significance as organs of absorption. They have been noted
in only one crustaceous lichen, Varicellaria microsticta1, an alpine species
that spreads over bark or soil, and which is further distinguished by being
Fig. 53. Rhizoid of Parmelia exasferata Carroll (P. aspidota Rosend.). A, hyphae growing out
from lower cortex x 450. B, tip of rhizoid with gelatinous sheath x 335 (after Rosendahl).
provided with a lower cortex of plectenchyma. In foliose lichens they are
frequently abundant, though by no means universal, and attach the spreading
fronds to the support. They originate, as Schwendener2 pointed out, from
the outer cortical cells, exactly as do the cilia, and are scattered over the
1 Darbishire 1897. 2 Schwendener 1860.
STRATOSE THALLUS
93
under surface or are confined to special areas. Rosendahl1 has described
their development in the brown species of Parmeliae: the under cortex in
these lichens is formed of a cellular plectenchyma with thickish walls ; the
rootlets arise by the outgrowth of several neighbouring cells from some slight
elevation near the edge of the thallus. Branching and interlacing of these
growing rhizinal hyphae follow, the outermost frequently spreading outwards
at right angles to the axis, and forming a cellular cortex. The apex of the
rhizoid is generally an enlarged tuft of loose hyphae involved in mucilage
(Fig- 53), a provision for securing firmer cohesion to the support; or the
tips spread out as a kind of sucker. Not unfrequently neighbouring "rootlets"
are connected by mucilage at the tips, or by outgrowths of their hyphae,
and a rather large hold-fast sheath is formed.
In species of Peltigera (Fig. 54) the rhizinae are confined to the veins
or ridges (Fig. 55); they are thickish at the base, and are generally rather
Fig. 54. Peltigera canina DC. (S. H., Photo ).
rig- 55-
Under surface with veins and
rhizoids (after Reinke).
long and straggling. Meyer2 states that the central hyphae are stoutish
and much entangled owing to the branching and frequent anastomosis of
one hypha with another; the peripheral terminal branches are thinner-walled
and free. These rhizinae vary in colour from white in Peltigera canina to
brown or black in other species. Most species of Peltigera spread over grass
or mosses, to which they cling by these long loose "rootlets."
Lichen rhizinae, distinguished by Reinke3 as "aerial rhizinae," are more
1 Rosendahl 1507.
2 Meyer 1902.
3 Reinke 1895, p. 186.
94 MORPHOLOGY
or less characteristic of all the species of Parmelia with the exception of
those belonging to the subgenus Hypogymnia in which they are of very rare
occurrence, arising, according to Bitter1, only in response to some external
friction. They are invariably dark-coloured, rather short, about one to a
few millimetres in length, and are simple or branched. The branches may
go off at any angle and are sometimes curved back at the ends in anchor-
like fashion. The Parmeliae grow on firm substances, trees, rocks, etc., and
the irregularities of their attaching structures are conditioned by the obstacles
encountered on the substratum. Not unfrequently the lobes are attached
by the rhizinae to underlying portions of the thallus.
In the genus Gyrophora, the rhizinae are simple strands of hyphae
(G. polyrhizd) or they are corticate structures (G. murina, G. spodochroa
and G. vellea\ They are also present in species of Solorina, Ricasolia,
Sticta and Physcia and very sparingly in Cetraria (Platysma).
c. HAPTERA. Sernander2 has grouped all the more distinctively aerial
organs of attachment, apart from rhizinae, under the term "hapteron" and he
has described a number of instances in which cilia and even the growing
points of the thallus may become transformed to haptera or sucker-like
sheaths.
The long cilia of Physcia ciliaris occasionally form haptera at their tips
where the hyphae are loose and in active growing condition. Contact with
some substance induces branching by which a spreading sheath arises; a
plug-like process may also be developed which pierces the substance en-
countered— not unfrequently another lobe of its own thallus. The long
flaccid fronds of Evernia furfuracea are frequently connected together by
bridge-like haptera which rise at any angle of the thallus or from any part
of the surface.
The spinous hairs that border the thalline margins in Cetraria may also,
in contact with some body — often another frond of the lichen — form a
hapteron, either while the spermogonium, which occupies the tip of the
spine, is still in a rudimentary stage, or after it has discharged its spermatia.
The small sucker sheath may in that case arise either from the apex of the
cilium, from the wall of the spermogonium or from its base. By means of
these haptera, not only different individuals become united together, but
instances are given by Sernander in which Cetraria islandica, normally a
ground lichen, had become epiphytic by attaching itself in this way to the
trunk of a tree (Pinus sylvestris}.
In Alectoria, haptera are formed at the tip of the thallus filament as an
apical cone-like growth from which hyphae may branch out and penetrate
any convenient object. A species of this genus was thus found clinging to
1 Bitter 1901. 2 Sernander 1901.
STRATOSE THALLUS 95
stems of Betula nana. Apical haptera are very frequent in Cladonia rangi-
ferina and Cl. sylvatica, induced here also by contact. These two plants, as
well as several species of Cetraria, tend, indeed, to become entirely epiphytic
on the heaths of the Calluna formations. Haptera similar to those of Alectoria
occur in Usnea, Evernia, Ramalina and Cornicularia (Cetraria). In Evernia
prunastri var. stictoceros, a heath form, the fronds become attached to the
stems and branches of Erica tetralix by hapteroid strands of slender glutinous
hyphae which persist on the frond of the lichen after it is detached as
small very dark tubercles surmounted, as Parfitt1 pointed out, by a dark-
brown grumous mass of cells. Plug-like haptera may be formed at the base
of Cladoniae which attach them to each other and to the substratum. The
brightly coloured fronds of Letharia vulpina are attached to each other in
somewhat tangled fashion by lateral bridges or by fascicles of hyphae dark-
brown at the base but colourless at the apices, exactly like aerial adventitious
rhizinae. They grow out from the fronds generally at or near the tips and
lay hold of a neighbouring frond by means of mucilage. These haptera are
evidently formed in response to friction. Haptera along with other lichen
attachments have received considerable attention from Gallic2. He finds
them arising on various positions of the lichen fronds and has classified
them accordingly.
After the haptera have become attached, they increase in size and strength
and supply a strong anchorage for the plant; the point of contact frequently
forms a basis for renewed growth while the part beneath the hapteron may
gradually die off. Haptera are more especially characteristic of fruticose
lichens, but Sernander considers that the rhizinae of foliose species may
function as haptera. They are important organs of tundra and heath
formations as they enable the lichens to get a foothold in well-lighted
positions, and by their aid the fronds are more able to resist the extreme
tearing strains to which they are subjected in high and unsheltered moor-
lands.
F. STRENGTHENING TISSUES OF STRATOSE LICHENS
Squamulose and foliose lichens grow mostly in close relation with the
support, and the flat expanding thallus, as in the Parmeliae, is attached at
many points to the substance — tree, rock, etc. — over which the plants spread.
Special provision for support is therefore not required, and the lobes remain
thin and flaccid. Yet, in a number of widely different genera the attachment
to the substratum is very slight, and in these we find an adaptation of
existing tissues fitted to resist tearing strains, resistance being almost
invariably secured by the strengthening of the cortical layers.
1 Parfitt in Leighton 1871, p. 470. 2 Gallic 1915.
96 MORPHOLOGY
a. BY DEVELOPMENT OF THE CORTEX. Such a transformation of tissue
is well illustrated in Heppia Guepini. The thallus consists of rigid squamules
which are attached at one point only ; the cortex of both surfaces is plecten-
chymatous and very thick and even the medulla is largely cellular.
The much larger but equally rigid coriaceous thallus of Dermatocarpon
miniatum (Fig. 56) has also a single central attachment or umbilicus, and
Fig- 56. Dermatocarpon miniatum Th. Fr. (S. H., Photo.).
both cortices consist of a compact many-layered plectenchyma. The same
structure occurs in Umbilicaria pitstnlata and in some species of Gyrophora,
which, having only a single central hold-fast, gain the necessary stiffening
through the increase of the cortical layers.
In the Stictaceae there are a large number of widely-expanded forms,
and as the attachment depends mostly on a somewhat short tomentum,
strength is obtained here also by the thick plectenchymatous cortex of both
surfaces. When areas denuded of tomentum and cortex occur, as in Lobaria
pulmonaria, the under surface is not sensibly weakened, since the cortical
tissue remains connected in a stout and firm reticulation.
b. BY DEVELOPMENT OF VEINS OR NERVES. Certain ground lichens
belonging to the Peltigeraceae have a wide spreading thallus often with
very large lobes. The upper cortex is a many-layered plectenchyma, but
the under surface is covered only by a loose felt of hyphae which branch
out into a more or less dense tomentum. As the firm upper cortex continues
to increase by intercalary growth from the branching upwards of hyphae
from the meristematic gonidial zone, there occurs an extension of the upper
STRATOSE THALLUS 97
thallus with which the lower cannot keep pace1. A little way back from
the edge, the result of the stretching is seen in the splitting asunder of the
felted hyphae of the under surface, and in the consequent formation of a
reticulate series of ridges known as the veins or nerves ; they represent the
original tomentose covering, and are white, black or brown, according to the
colour of the tomentum itself. The naked ellipsoid interstices show the
white medulla, and, if the veins are wide, the colourless areas are correspond-
ingly small. Rhizinae are formed on the nerves in several of the species,
and anchor the thallus to the support. In Peltigera canina, the under surface
is almost wholly colourless, the veins are very prominent (Fig. 55), and are
further strengthened by the growth and branching of the parallel hyphae of
which they are composed. They serve to strengthen the large and flabby
thallus and form a rigid base for the long rhizinae by which the lichen clings
to the grass or moss over which it grows.
The most perfect development of strengthening nerves is to be found in
HydrotJiyria venosa*, a rather rare water lichen that occurs in the streams of
North America. It consists of fan-like lobes of thin structure, the cortex
being only about one cell thick. The fronds are about 3 cm. wide and they
are contracted below into a stalk which serves to attach the plant to the
substratum. Several fronds may grow together in a dense tuft, the expanded
upper portion floating freely in the water. Frequently the plants form a
dense growth over the rocky beds of the stream.
At the point where the stalk expands into the free erect frond, there
arise a series of stout veins which spread upwards and outwards. They are
definitely formed structures and not adaptations of pre-existing tissues :
certain hyphae arise from the medulla at the contracted base of the frond,
take a radial direction and, by increase, become developed into firm strands.
The individual hyphae also increase in size, and the swelling of the nerve
gives rise to a ridge prominent on both surfaces. They seldom anastomose
at first but towards the tips they become smaller and spread out in delicate
ramifications which unite at various points. There is no doubt, as Bitter1
points out, that the nerves function as strengthening tissues and preserve the
frond from the strain of the water currents which would, otherwise, tear apart
the delicate texture.
1 Bitter 1899. 2 Sturgis 1890.
7-
98
MORPHOLOGY
III. RADIATE THALLUS
i. CHARACTERS OF RADIATE THALLUS
In the stratose dorsiventral thallus, there is a widely extended growing
area situated round the free margins of the thallus. In the radiate thallus
of the fruticose or filamentous lichens, growth is confined to an apical region.
Attachment to the substratum is at one point only — the base of the plant —
thus securing the exposure of all sides equally to light. The cortex
surrounds the fronds, and the gonidia (mostly Protococcaceae) lie in a zone
or in groups between the cortex and the medulla. It is the highest type of
vegetative development in the lichen kingdom, since it secures the widest
room for the gonidial layer, and the largest opportunity for photosynthesis.
Shrubby upright lichens consist mostly of strap-shaped fronds, either
simple or branched, which may be broadened to thin bands (Fig. 57) or
may be narrowed and thickened till they are almost cylindrical. The fronds
vary in length according to the species from a few millimetres upwards:
Fig. 57. Roccellafuciformis DC.
RADIATE THALLUS
99
those of Roccella have been found measuring 30 cm. in length ; those of
Ramalina reticulata, the largest of all the American lichens, extend to con-
siderably more.
Lichens of filamentous growth are more or less cylindrical (Fig. 58).
They are in some species upright and of moderate length^ but in a few
Fig. 58. Usnea barbata Web. (S. H., Photo.},
pendulous forms they grow to a great length : specimens of Usnea longissima
have been recorded that measured 6 to 8 metres from base to tip.
The radiate type of thallus occurs in most of the lichen groups but most
frequently in the Gymnocarpeae. In gelatinous Discolichens it is repre-
sented in the Lichinaceae. It is rare among Pyrenocarpeae : there is one
very minute British lichen in that series, Pyrenidium actinellum, and one
from N. America, Pyrenothamnia, that are of fruticose habit.
2. INTERMEDIATE TYPES OF THALLUS
Between the foliose and the fruticose types, there are intermediate forms
that might be, and often are, classified now in one group and now in the
other. These are chiefly : Physcia (Anaptychia) dliaris, Ph. leucomelas and
the species of Evernia.
7—2
100
MORPHOLOGY
In the two former the habit is more or less fruticose as the plants are
affixed to the substratum at a basal point, but the fronds are decumbent and
the internal structure is of the dorsi ventral type : there is an upper "fibrous"
cortex of closely compacted parallel hyphae, a gonidial zone — the gonidia
lying partly in the cortex and partly among the loose hyphae of the
medulla — and a lower cortex formed of a weft of hyphae which also run
somewhat parallel to the surface. Both species are distinguished by the
numerous marginal cilia, either pale or dark in colour. These two lichens
are greyish-coloured on the upper surface and greyish or whitish below.
Evernia furfuracea with a basal attachment1, and with a partly horizontal
and partly upright growth, has a dorsiventral thallus, dark greyish-green
above and black beneath, with occasional rhizinae towards the base. The
cortex of both surfaces belongs to the "decomposed" type; the gonidial
zone lies below the upper surface, and the medullary tissue is of loose hyphae.
In certain forms of the species isidia are abundant on the upper surface,
a character of foliose rather than of fruticose lichens. E. furfuracea grows
on trees and very frequently on palings.
Fig. 5Q. Evernia prunastri Ach. (M. P., Photo.}.
1 See p. 108.
RADIATE THALLUS 101
E. prunastri, the second species of the genus, is more distinctly upright in
habit, with a penetrating basal hold-fast and upright strap-shaped branching
fronds, light-greyish green on the "upper" surface and white on the other
(Fig. 59). The internal structure is sub-radiate; both cortices are "decom-
posed"; the gonidial zone consists of somewhat loose groups of algae, very
constant below the "upper" surface, with an occasional group in the pith
near to the lower cortex in positions that are more exposed to light. There
is also a tendency for the gonidial zone to pass round the margin and spread
some way along the under side. The medulla is of loose arachnoid texture
and the whole plant is very limp when moist. It grows on trees, often in
dense clusters.
3. FRUTICOSE AND FILAMENTOUS THALLUS
A. GENERAL STRUCTURE OF THALLUS
The conditions of strain and tension in the upright plant are entirely
different from those in the decumbent thallus, and to meet the new require-
ments, new adaptations of structure are provided either in the cortex or in
the medulla.
CORTICAL STRUCTURES. With the exception of the distinctly plec-
tenchymatous cortex, all the other types already described recur in fruticose
lichens; in various ways they have been modified to provide not only covering
but support to the fronds.
a. The fastigiate cortex. This reaches its highest development in
Roccella in which the branched hyphal tips, slightly clavate and thick-walled,
lie closely packed in palisade formation at right angles to the main axis
(Fig. 45). They afford not only bending power, but give great consistency
to the fronds. The cortex is further strengthened in R. fuciformis* by the
compact arrangement of the medullary hyphae that run parallel with the
surface, and among which occur single thick-walled filaments. The plant
grows on maritime rocks in very exposed situations ; and the narrow strap-
shaped fronds, as stated above, may attain a length of 30 cm., though usually
they are from 10 to i8cm. in height. The same type of cortex, but less
highly differentiated, affords a certain amount of stiffness to the cylindrical
much weaker fronds of Thamnolia.
b. The fibrous cortex. This type is found in a number of lichens with
long filamentous hanging fronds. It consists of parallel hyphae, rarely septate
and rarely branched, but frequently anastomosing and with strongly thick-
ened "sclerotic" walls. Such a cortex is the only strengthening element in
Alectoria, and it affords great toughness and flexibility tc .the thong-like
1 Darbishire 1808.
102
MORPHOLOGY
thallus. It is also present in Ramalina (Alectoria) thrausta, a species with
slender fronds (Fig. 60).
Fig. 60. Alectoria thrausta Ach. A, transverse section of frond;
a, cortex; b, gonidia; c, arachnoid medulla x 37. B, fibrous
hyphae from longitudinal section of cortex, x 430 (after Brandt).
II
'!!'•»
In Usnea longissima the cortex both of the fibrillose branchlets and of
the main axis is fibrous, and is composed of narrow thick-walled hyphae
which grow in a long spiral round
the central strand. The hyphae
become more frequently septate
further back from the apex (Fig. 6l).
Such a type of cortex provides an
exceedingly elastic and efficient pro-
tection for the long slender thallus.
The same type of cortex forms
the strengthening element in the
fruticose or partly fruticose members
of the family Physciaceae. One of
\\\es>e.,Teloschistesflavicans, is a bright
yellow filamentous lichen with a
somewhat straggling habit. The
fronds are very slender and are either
cylindrical or slightly flattened. The
vi
it
Usnea longissima Ach.
sections of outer cortex.
the middle portion of
Schulte).
Longitudinal
A, near the apex; B,
fibril, xjs^ (after
RADIATE THALLUS
103
hyphae of the outer cortex are compactly fibrous; added toughness is
given by the presence of some longitudinal strands of hyphae in the central
pith.
Another still more familiar grey lichen, Physcia ciliaris, has long flat
branching fronds which, though dorsiventral in structure, are partly upright
in habit. Strength is secured as in Teloschistes by the fibrous upper cortex.
Other species of Physciae are somewhat similar in habit and in structure.
In Dendrographa leucophaea, a slender strap-shaped rock lichen, Darbi-
shire1 has described the outer cortex as composed of closely compacted
parallel hyphae resembling the strengthening cortex of Alectoria and very
different from the fastigiate cortex of the Roccellae with which it is usually
classified.
B. SPECIAL STRENGTHENING STRUCTURES
a. SCLEROTIC STRANDS. This form of strengthening tissue is charac-
teristic of Ramalina. With the exception of R. thrausta (more truly an
Alectoria} all the species have a rather weak cortical layer of branching
intricate thick-walled hyphae, regarded by Brandt2 as plectenchymatous,
but more correctly by Hue3 as "decomposed" on account of the gelatinous
walls and diminishing lumen of the irregularly arranged cells.
In R. evernioides, a plant with very wide flat almost decumbent fronds
of soft texture, in R. ceruchis and in R. homalea there is a somewhat compact
medulla which gives a slight stiffness to the thallus. The other species of
the genus are provided with strengthening mechanical tissue within the
cortex formed of closely united sclerotic hyphae that run parallel to the
surface (Fig. 62). In a transverse section of the thallus, this tissue appears
A B
Fig. 62. Ramalina minuscula Nyl. A, transverse section
of frond x 37; B, longitudinal strengthening hyphae of
inner cortex x 430 (after Brandt).
1 Darbishire 1895. 2 Brandt 1906. 3 Hue 1906.
104
MORPHOLOGY
sometimes as a continuous ring which may project irregularly into the pith
(R. calicaris) ; more frequently it is in the form of strands or bundles which
alternate with the groups of gonidia (R. siliquosa, R. Curnozvii, etc.). In
R. fraxinea these strands may be scarcely discernible in young fronds, though
sometimes already well developed near the tips. Occasionally isolated strands
of fibres appear in the pith (R. Curnowii\ or the sclerotic projections may
even stretch across the pith to the other side (R. strepsilis} (Fig. 75 B).
In the Cladoniae support along with flexibility is secured to the upright
podetium by the parallel closely packed hyphae that form round the
hollow cylinder a band called the "chondroid" layer from its cartilage-like
consistency.
b. CHONDROID AXIS. The central medullary tissue in Ramalina is, with
few exceptions, a loose arachnoid structure ; often the fronds are almost
hollow. In one species of Usnea, U. Taylori, found in polar regions, there
is a similar loose though very circumscribed medullary and gonidial tissue
in the centre of the somewhat cylindrical thallus, and a wide band of sclerotic
fibres towards the cortex.
Fig. 63 A.
branch.
longissi
A, (Jinea barbata Web. Longitudinal section of filament with young adventitious
«, chondroid axis; /;, gonidial tissue; c, cortex, x too (after Schwendener). B, U.
<na Ach. Hyphae from central axis x 525 (after Schulte .
In all other species of Usnea the medulla itself is transformed into a
strong central strand of long-celled thick-walled hyphae closely knit together
by frequent anastomoses (Fig. 63 A). This central strand of the Usneas is
known as the "chondroid axis." A narrow band of loose air-containing
hyphae and a gonidial zone lie round the central axis between it and the
outer cortex (Fig. 63 A, b). At the extreme apex, the external cortical hyphae
grow in a direction parallel with the long axis of the plant, but further back,
they branch out at right angles and become swollen and mostly "decom-
posed " as in the cortex of Ramalina.
RADIATE THALLUS
105
In Letharia (L. vulpina, etc.) the structure is midway between Ramalina
and Usnea : the central axis is either a solid strand of chondroid hyphae or
several separate strands.
Fig. 63 B. Usnea lo ngissima Ach. A, transverse section of fibril x 85. B, a, chondroid axis;
b, gonidial tissue; c, cortex x 525 (after Schulte).
In three other genera with upright fruticose thalli, Sphaerophorus, Ar-
gopsis and Stereocaulon, rigidity is maintained by a medulla approaching the
chondroid type. In Sphaerophorus the species may have either flattened or
cylindrical branching stalks, but in all of them, the centre is occupied by
longitudinal strands of hyphae. Argopsis, a monotypic genus from Ker-
guelen, has a cylindrical branching thallus with a strong solid axis; it is
closely allied to Stereocaulon, a genus of familiar moorland lichens. The
central tissue of the stalks in Stereocaulon is also composed of elongate,
thick-walled conglutinate hyphae, formed into a strand which is, however,
not entirely solid.
C. SURVEY OF MECHANICAL TISSUES
Mechanical tissues scarcely appear among fungi, except perhaps as
stoutish cartilaginous hyphae in the stalks of some Agarics (Collybiae, etc.),
or as a ring of more compact consistency round the central hyphae of
rhizomorphic strands. It is practically a new adaptation of hyphal structure
confined to lichens of the fruticose group, where there is the same require-
ment as in the higher plants for rigidity, flexure and tenacity.
Rigidity is attained as in other plants by groups or strands of mechanical
tissue situated close to the periphery, as they are so arranged in Rama-
lina and Cladonia; or the same end is achieved by a strongly developed
io6 MORPHOLOGY
fastigiate cortex as in Roccella. Bending strains to which the same lichens
are subjected, are equally well met by the peripheral disposition of the
mechanical elements.
Tenacity and elasticity are provided for in the pendulous forms either
by a fibrous cortex as in Alectoria, or by the chondroid axis in Usnea.
Haberlandt1 has recorded some interesting results of tests made by him as
to the stretching capacity of a freshly gathered pendulous species in which
the central strand was from -5 to I mm. thick. He found he could draw it
out 100 to no per cent, of its normal length before it gave way. In an
upright species the frond broke when stretched 60 to 70 per cent. In both
of the plants tested, the central strand retained its elasticity up to 20 per
cent, of stretching. The outer cortical tissue was cracked and broken in
the experiments. Schulte2 calculated somewhat roughly the tenacity of
Usnea longissima and found that a piece of the main axis 8 cm. long carried
up to 300 grms. without breaking.
D. RETICULATE FRONDS
In the upright radiate thallus, more especially among the Ramalinae,
though also among Cladoniae\\h.&z has appeared a reticulate thallus resulting
from the elongate splitting of the tissues, and due to unequal growth tension
and straining of the gelatinous cortex when swollen with moisture. In
several species of Ramalina, the strap-shaped frond is hollow in the centre ;
and strands of strengthening fibres give rise to a series of cortical ridges.
The thinner tissue between is frequently torn apart and ellipsoid openings
appear which do not however pierce beyond the central hollow. Such breaks
are irregular and accidental though occurring constantly in Ramalina
fraxinea, R. dilacerata, etc.
A more complete type of reticulation is always present in a Californian
lichen, Ramalina reticulata, in which the large flat frond is a delicate open
network from tip to base (Fig. 64). It grows on the branches of deciduous
trees and hangs in crowded tufts up to 30 cm. or more in length. Usually
it is so torn, that the real size attainable can only be guessed at. It is
attached at the base by a spreading discoid hold-fast, and, in mature plants,
consists of a stoutish main axis from which side branches are irregularly
given off. These latter are firm at the base like the parent stalk, but soon
they broaden out into very wide fronds. Splitting begins at the tips of the
branches while still young ; they are then spathulate in form with a slightly
narrower recurved tip, below which the first perforations are visible, small at
first, but gradually enlarging with the growth of the frond.
Ramalina reticulata is an extremely gelatinous lichen and the formation
1 Haberlandt 1896. 2 Schulte 1904. • See p. 120.
I08 MORPHOLOGY
of the network was supposed by Lutz1 to be entirely due to the swelling of
the tissues, or the imbibition of water, causing tension and splitting. A more
exact explanation of the phenomenon is given by Peirce2: he found that it
was due to the thickened incurved tip, which, on the addition of moisture,
swells in length, breadth and thickness, causing it to bend slightly upwards
and then curve backwards over the thallus, thus straining the part imme-
diately behind. These various movements result in the splitting of the frond
while it is young and the cortices are thin and weak.
Peirce made a series of experiments to test the capacity of the tissues
to support tensile strains. In a dry state, a piece of the lichen held a weight
up to I50grms.; when wet it broke with a weight of 3Ogrms. It was also
observed that the thickness of the frond doubled on wetting.
E. ROOTING BASE IN FRUTICOSE LICHENS
Fruticose and filamentous lichens are distinguished by their mode of
attachment to the substratum : instead of a system of rhizinae or of hairs
spread over a large area, there is usually one definite rooting base by which
the plant maintains its hold on the support.
Intermediate between the foliose and fruticose types of thallus are
several species which are decumbent in habit, but which are attached at one
(or sometimes more) definite points, with but little penetration of the under-
lying substance. One such lichen, Evernia furfuracea, has been classified
now as foliose, and again as fruticose. The earliest stage of the thallus is
in the form of a rosette-like sheath which bears rhizinae on the under
surface, very numerous at the centre of the sheath, but entirely wanting
towards the periphery. A secondary thallus of strap-shaped rather narrow
fronds rises from the sheath and increases by irregular dichotomous branch-
ing. These branches, which are considered by Zopf3 as adventitious, may
also come into contact with the substratum and produce a few rhizinae at
that point; or if the frond is more closely applied, the irritation thus
produced causes a still greater outgrowth of rhizinae and the formation of
a new base from which other fronds originate. These renewed centres of
growth are not of very frequent occurrence; they were first observed and
described by Lindau4 in another species, Evernia prunastri, and were aptly
compared by him to the creeping stolons of flowering plants.
Evernia furfuracea grows frequently on dead wood, palings, etc., as well
as on trees. E.prunastri grows invariably on trees, and has a more constantly
upright fruticose' habit; in this species also, a basal sheath is present, and
the attachment is secured by means of rhizoidal hyphae which penetrate
deeply into the periderm of the tree, taking advantage of the openings
1 Lutz 1894. 2 Peirce 1898. » Zopf 1903. * Lindau 1895.
RADIATE THALLUS
109
afforded by the lenticels. The sheath hyphae are continuous with the medul-
lary hyphae of the frond, and gonidia are frequently enclosed in the tissues ;
the sheath spreads to some extent over the surface of the bark, and round
the base of the fronds, thus rendering the attachment of the lichen to the
tree doubly secure.
Among Ramalinae, the development of the base was followed by Brandt1
in one species, R. Landroensis, an arboreal lichen from S. Tyrol. A rosette-
like sheath was formed consisting solely of strands of thick-walled hyphae
which spread over the bark. There were no gonidia included in the tissue.
A different type of attachment was found by Lilian Porter2 in corti-
colous Ramalinae — R. fraxinea, R. fastigiata, and R. pollinaria. The lichens
were anchored to the tree by strands of closely compacted hyphae longi-
tudinally arranged and continuous with the cortical hyphae. These enter
the periderm of the tree by cracks or lenticels, and by wedge action cause
extensive splitting. The strands may also spread horizontally and give rise
to new plants. The living tissues of the tree were thus penetrated and
injured, and there was evidence that hypertrophied tissue was formed and
caused erosion of the wood.
Several Ramalinae — R. siliquosa, R. Curnowii, etc. — grow on rocks,
often in extremely exposed situations, in isolated tufts or in crowded swards
(Fig. 65). The separate tufts are not unfrequently connected at the base by
Fig. 6;. Ramalina siliquosa A. L. Sm., on rocks, reduced (M. P., Photo.).
1 Brandt 1906. 2 Porter 1916.
IIO MORPHOLOGY
a crustaceous thallus. It is possible also to see on the rock, here and there,
small areas of compact thalline granules that have scarcely begun to put out
the upright fronds. These granules are corticate on the upper surface and
contain gonidia; from the lower surface, slender branching hyphae in rhizoid-
like strands penetrate down between the inequalities and separable particles
of the rock, if the formation is granitic. They frequently have groups of
gonidia associated with them, and they continue to ramify and spread, the
pure white filaments often enough enclosing morsels of the rock. The
upright fronds are continuous with the base and are thus securely anchored
to the substratum.
On a smooth rock surface such as quartzite a continuous sward o*f Rama-
Una growth is impossible. The basal hyphae being unable to penetrate the
even surface of the rock, the attachment is slight and the plants are easily
dislodged. They do however succeed, sometimes, in taking hold, and small
groups of fronds arise from a crustaceous base which varies in depth from
•5 to i mm. The tissues of this base are very irregularly arranged : towards
the upper surface loose hyphae with scattered groups of algae are traversed
by strands of gelatinized sclerotic hyphae similar to the strengthening tissues
of the upright fronds, while down below there are to be found not only
slender hyphae, but a layer of gonidia visible as a white and green film on
the rock when the overlying particles are scaled off.
Darbishire1 found that attachment to the substratum by means of a
basal sheath was characteristic of all the genera of Roccellaceae. He looks
on this sheath, which is the first stage in the development of the plant, as
a primary or proto-thallus, analogous to the primary squamules of the
Cladoniae, and he carries the analogy still further by treating the upright
fronds as podetia. The sheath of the Roccellaceae varies in size but it is
always of very limited extent; it is mainly composed of medullary hyphae,
and gonidia may or may not be present. The whole structure is permanent
and important, and is generally protected by a well-developed upper cortex
similar in structure to that of the upright' thallus, i.e. of a fastigiate type.
There is no lower cortex.
The two British species of Roccella — R. fuciformis and R. phycopsis —
grow on maritime rocks, the latter also occasionally on trees. In R. fuci-
formis, the attaching sheath is a flat structure which slopes up a little round
the base of the upright frond. It is about 2 mm. thick, the cortex occupying
about 40 /A of that space; a few scattered gonidia are present immediately
below. The remaining tissue of the sheath is composed of firmly wefted
slender filaments. Towards the lower surface, there is a more closely com-
pacted dark brown layer from which pass out the hyphae that penetrate
the rock.
1 Darbishire 1898.
RADIATE THALLUS in
The sheath of R. phycopsis is a small structure about 3 to 4 mm. in width
and 1*5 mm. thick. A few gonidia may be found below the dense cortical
layer, but they tend to disappear as the upright fronds become larger and
the shade, in consequence, more dense. Lower down the hyphae take an
intensely yellow hue; mixed with them are also some brown filaments.
A somewhat larger sheath 7 to 8 mm. wide forms the base of R. tinctoria.
In structure it corresponds — as do those of the other species — with the ones
already described.
In purely filamentous species such as Usnea there is also primary sheath
formation : the medullary hyphae spread out in radiating strands which
force their way wherever possible into the underlying substance; on trees
they enter into any chink or crevice of the outer bark like wedges ; or they
ramify between the cork cells which are split up by the mere growth pressure.
By the vertical increase of the base, the fronds may be hoisted up and
an intercalary basal portion may arise lacking both gonidia and cortical
layer. Very frequently several bases are united and the lichen appears to
be of tufted habit.
A basal sheath provides a similar firm attachment for Alectoria jubata
and allied species: these are slender mostly dark brown lichens which hang
in tangled filaments from the branches of trees, rocks, etc.
These attaching sheaths differ in function as well as in structure from
the horizontal thallus of the Cladoniaceae. They may be more truly com-
pared with the primary thallus of the red algae Dumontia and Phyllophora
which are similarly affixed to the substratum, while upright fronds of
subsequent formation bear the fructifications.
IV. STRATOSE-RADIATE THALLUS
i. STRATOSE OR PRIMARY THALLUS
A. GENERAL CHARACTERISTICS
This series includes the lichens of one family only, the Cladoniaceae, the
genera of which are characterized by the twofold thallus,
one portion being primary, horizontal and stratose, the
other secondary and radiate, the latter an upright simple
or branching structure termed a "podetium" which nar-
rows above, or widens to form a trumpet-shaped cup or
"scyphus" (Fig. 66). The apothecia are terminal on the
pocletium or on the margins of the scyphi ; in a few species
they are developed on the primary thallus. Some degree
of primary thallus-formation has been demonstrated in all Fig. 66. Cladonia
, , r ., ™, pyxidata Hoffrn.
the genera, if not in all the species of the family. The Basai squamule and
^eiius Cladina was established to include those species podetium. a, apo-
thecia; s, spermo-
of Cladonia in which, it was believed, only a secondary gonia (after Krabbe).
ii2 MORPHOLOGY
podetial thallus was present, but Wainio1 found in Cladonia sylvatica a
granular basal crust and, in Cladonia uncialts, minute round scales with crenate
margins measuring from -5 to I mm. in width. In some species (subgenus
Cladina) the primary thallus is quickly evanescent, in others it is granular
or squamulose and persistent. Where the basal thallus is so much reduced
as to be practically non-existent, apothecia are rarely developed and soredia
are absent Renewal of growth in these lichens is secured by the dispersal
of fragments of the podetial thallus; they are torn off and scattered by the
wind or by animals, and, if suitable conditions are met, a new plant arises.
Cladonia squamules vary in size from very small scales as in Cl. uncialis
to the fairly large foliose fronds of Cl.foliacea which extend to 5 cm. in length
and about i cm. or more in width. It is interesting to note that when the
primary thallus is well developed, the podetia are relatively unimportant
and frequently are not formed. As a rule the squamules are rounded or
somewhat elongate in form with entire or variously cut and crenate margins.
They may be very insignificant and sparsely scattered over the substratum,
or massed in crowded swards of leaflets which are frequently almost upright.
In colour they are bluish-grey, yellowish or brownish above, and white
beneath (red in Cl. miniata], frequently becoming very dark-coloured towards
the rooting base. These several characteristics are specific and are often of
considerable value in diagnosis. In certain conditions of shade or moisture,
squamules are formed on the podetium ; they repeat the characters of the
basal squamules of the species.
B. TISSUES OF THE PRIMARY. THALLUS
The stratose layers of tissue in the squamules of Cladonia are arranged
as in other horizontal thalli.
a. CORTICAL TISSUE. In nearly all these squamules the cortex is of
the "decomposed" type. In a few species there is a plectenchymatous
formation — in Cl. nana, a Brazilian ground species, and in two New Zealand
species, CL enantia f. dilatata and Cl. Neo-Zelandica. The principal growing
area is situated all round the margins though generally there is more activity
at the apex. Frequently there is a gradual perishing of the squamule at the
base which counterbalances the forward increase.
The upper surface in some species is cracked into minute areolae; the
cracks, seen in section, penetrate almost to the base of the decomposed
gelatinous cortex. They are largely due to alternate swelling and contraction
of the gelatinous surface, or to extension caused, though rarely, by intercalary
growth from the hyphae below. The surface is subject to weathering and
peeling as in other lichens; but the loss is constantly repaired by the upward
growth of the meristematic hyphae from the gonidial zone ; they push up
1 Wainio 1880.
STRATOSE-RADIATE THALLUS 113
between the older cortical filaments and so provide for the expansion as
well as for the renewal of the cortical tissue.
b. GONIDIAL TISSUE. The gonidia consisting of Protococcaceous algae
form a layer immediately below the cortex. Isolated green cells are not
unfrequently carried up by the growing hyphae into the cortical region, but
they do not long survive in this compact non-aerated tissue. Their empty
membranes can however be picked out by the blue stain they take with
iodine and sulphuric acid.
Krabbe1 has described the phases of development in the growing region :
he finds that differentiation into pith, gonidial zone and cortex takes place
some little way back from the edge. At the extreme apex the hyphae lie
fairly parallel to each other; further back, they branch upwards to form the
cortex, and to separate the masses of multiplying gonidia, by pushing
between them and so spreading them through the whole apical tissue. The
gonidia immediately below the upper cortex, where they are well-lighted,
continue to increase and gradually form into the gonidial zone; those that
lie deeper among the medullary hyphae remain quiescent, and before long
disappear altogether.
Where the squamules assume the upright position (as in Cladonia cei~vi-
corms), there is a tendency for the gonidia to pass round to the lower
surface, and soredia are occasionally formed.
c. MEDULLARY TISSUE. The hyphae of the medulla are described by
Wainio as having long cells with narrow lumen, and as being encrusted
with granulations that may coalesce into more or less detachable granules;
in colour they are mostly white, but pale-yellow in Cl.foliacea and blood-red
in Cl. miniata, a subtropical species. They are connected at the base of the
squamules with a filamentous hypothallus which penetrates the substratum
and attaches the plant. In a few species rhizinae are formed, while in others
the hyphae of the podetium grow downwards, towards and into the sub-
stratum as a short stout rhizoid.
d. SOREDIA. Though frequent on the podetia, soredia are rare on the
squamules, and, according to Wainio2, always originate at the growing
region, from which they spread over the under surface — rather sparsely in
Cl. cariosa, Cl. squamosa, etc., but abundantly in Cl. digitata and a few others.
In some instances, they develop further into small corticate areolae on the
under surface (Cl. cocci/era, Cl. pyxidata and Cl. squamosd).
1 Krabbe 1891. 2 Wainio 1897.
II4 MORPHOLOGY
2. RADIATE OR SECONDARY THALLUS
A. ORIGIN OF THE PODETIUM
The upright podetium, as described by Wainio1 and by Krabbe2, is a
secondary product of the basal granule or squamule. It is developed from
the hyphae of the gonidial zone, generally where a crack has occurred in the
cortex and rather close to the base or more rarely on or near the edge of
the squamule (Cl. verticillata, etc.). At these areas, certain meristematic
gonidial hyphae increase and unite to form a strand of filaments below the
upper cortex but above the gonidial layer, the latter remaining for a time
undisturbed as to the arrangement of the algal cells.
This initial tissue — the primordium of the podetium — continues to grow
not only in width but in length: the basal portion grows downwards and
at length displaces the gonidial zone, while the upper part as a compact
cylinder forces its way through the cortex above, the cortical tissue, however,
taking no part in its formation ; as it advances, the edges of the gonidial
and cortical zones bend upwards and form a sheath distinguishable for some
time round the base of the emerging podetium.
Even when the primary horizontal thallus is merely crustaceous, the
podetia take origin similarly from a subcortical weft of hyphae in an areola
or granule.
B. STRUCTURE OF THE PODETIUM
a. GENERAL STRUCTURE. In the early stages of development the
podetium is solid throughout, two layers of tissue being discernible — the
hyphae forming the centre of the cylinder being thick-walled and closely
compacted, and the hyphae on the exterior loosely branching with numerous
air-spaces between the filaments.
In all species, with the exception of Cl. solida, which remains solid during
the life of the plant, a central cavity arises while the podetium is still quite
short (about i to i-5 mm. in Cl. pyxidata and Cl. degenerans). The first
indication of the opening is a narrow split in the internal cylinder, due to
the difference in growth tension between the more free and rapid increase
of the external medullary layer and the slower elongation of the chondroid
tissue at the centre. The cavity gradually widens and becomes more com-
pletely tubular with the upward growth of the podetium ; it is lined by
the chondroid sclerotic band which supports the whole structure (Fig. 67).
b. GONIDIAL TISSUE. In most species of Cladoniaceae, a layer of goni-
dial tissue forms a more or less continuous outer covering of the podetium,
1 Wainio 1880. 2 Krabbe 1891.
STRATOSE-RADIATE THALLUS
thus distinguishing it from the purely hyphal stalks of the apothecia in
Caliciaceae. Even in the genus Baeomyces,
while the podetia of some of the species
are without gonidia, neighbouring species
are provided with green cells on the up-
right stalks clearly showing their true
affinity with the Cladoniae. In one British
species of Cladonia {Cl. caespiticia) the
short podetium consists only of the fibrous
chondroid cylinder, and thus resembles the
apothecial stalk of Baeomyces rufus, but
in that species also there are occasional
surface gonidia that may give rise to
squamules.
Krabbe1 concluded from his observa-
tions that the podetial gonidia of Cladonia
arrived from the open, conveyed by wind,
water or insects from the loose sored ia that
are generally so plentiful in any Cladonia
colony. They alighted, he held, on the
growing stalks and, being secured by the
free-growing ends of the exterior hyphae,
they increased and became an integral part of the podetium. In more
recent times Baur2 has recalled and supported Krabbe's view, but Wainio3,
on the contrary, claims to have proved that in the earliest stages of the
podetium the gonidia were already present, having been carried up from
the gonidial zone of the primary thallus by the primordial hyphae. Increase
of these green cells follows normally by cell-division or sporulation.
Algal cells have been found to be common to different lichens, but in
Cladoniae Chodat4 claims to have proved by cultures that each species
tested has a special gonidium, determined by him as a species of Cystococcus,
which would render colonization by algae from the open much less probable.
In addition, the fungal hyphae are specific, and any soredia (with their
combined symbionts) that alighted on the podetium could only be utilized
if they originated from the same species; or, if they were incorporated, the
hyphae belonging to any other species would of necessity die off and be
replaced by those of the podetium.
c. CORTICAL TISSUE. In some species a cortex of the decomposed type
of thick-walled conglutinate hyphae is present, either continuous over the
whole surface of the podetium, as in Cl. gracilis (Fig. 68), or in interrupted
stage of central tube and of podetial
squamulesx 100 (after Krabbe).
1 Krabbe t!
2 Baur 1904.
3 Wainio 1880.
Chodat 1913.
8—2
MORPHOLOGY
Fig. 68. Cladonia gracilis Hoffm. (S. H., Photo.).
Fig. 69. Cladonia pyxtdata Hoftm. (S. H., Photo.]
STRATOSE-RADIATE THALLUS
117
areas or granules as in Cl. pyxidala (Fig. 69) and others. In Cl. degenerans,
the spaces between the corticated areolae are filled in by loose filaments
without any green cells. CL rangiferina, Cl. sylvatica, etc. are non-corticate,
being covered all over with a loose felt of intricate hyphae.
In the section Clathrinae (Cl. retepora, etc.) the cortex is formed of
longitudinal hyphae with thick gelatinous walls.
d. SOREDlA. Frequently the podetium is coated in whole or in part by
granules of a sorediate character — coarsely granular in Cl. pyxidata, finely
pulverulent in CL fimbriata. Though fairly constant to type in the different
species, they are subject to climatic influences, and, when there is abundant
moisture, both soredia and areolae develop into squamules on the podetium.
A considerable number of species have thus a more or less densely squamu-
lose "form" or "variety."
C. DEVELOPMENT OF THE SCYPHUS
Two types of podetia occur in Cladonia : those that end abruptly and
are crowned when fertile by the apothecia or spermogonia (pycnidia), or if
sterile grow indefinitely tapering gradually to a point (Fig. 70); and those
Fig. 70. Cladonia furcata Schrad. Sterile thallus (S.H., Photo.'].
that widen out into the trumpet-shaped or cup-like expansion called the
scyphus (Fig. 69). Species may be constantly scyphiferous or as constantly
ascyphous; in a few species, and even in individual tufts, both types of
podetium may be present.
n8 MORPHOLOGY
Wainio1, who has studied every stage of development in the Cladoniae,
has described the scyphus as originating in several different ways:
a. FROM ABORTIVE APOTHECIA. In certain species the apothecium
appears at a very early stage in the development of the podetium of which
it occupies the apical region. Owing to the subsequent formation of the
tubular cavity in the centre of the stalk, the base of the apothecium may
eventually lie directly over the hollow space and, therefore, out of touch
with the growing assimilating tissues; or even before the appearance of the
tube, the wide separation between the primordium of the apothecium and
the gonidia, entailing deficient nutrition, may have produced a similar effect.
In either case central degeneration of the apothecium sets in, and the
hypothecial filaments, having begun to grow radially, continue to travel in
the same direction both outwards and upwards so that gradually a cup-
shaped structure is evolved — the amphithecium of the fruit without the
thecium.
The whole or only a part of the apothecium may be abortive, and the
scyphus may therefore be entirely sterile or the fruits may survive at the
edges. The apothecia may even be entirely abortive after a fertile com-
mencement, but in that case also the primordial hyphae retain the primitive
impulse not only to radial direction, but also to the more copious branching,
and a scyphus is formed as in the previous case. It must also be borne in
mind that the tendency in many Cladonia species to scyphiform has become
hereditary.
Baur2, in his study of Cl. pyxidata, has taken the view that the origin of
the scyphus was due to a stronger apical growth of the hyphae at the
circumference than over the central tubular portion of the podetium, and
that considerable intercalary growth added to the expanding sides of the cup.
Scyphi originating from an abortive apothecium are characteristic of
species in which the base is closed (Wainio's Section Clausae\ the tissue in
that case being continuous over the inside of the cup as in Cl. pyxidata,
CL cocci/era and many others.
b. FROM POLYTOMOUS BRANCHING. Another method of scyphus forma-
tion occurs in Cl. amaurocrea and a few other species in which the branching
is polytomous (several members rising from about the same level). Con-
crescence of the tissues at the base of these branches produces a scyphus ;
it is normally closed by a diaphragm that has spread out from the different
bases, but frequently there is a perforation due to stretching. These species
belong to the Section Perviae.
c. FROM ARRESTED GROWTH. In most cases however where the
scyphus is open as in Cl.furcata, Cl. sguamosa, etc., development of the cup
1 Wainio 1897. 2 Baur 1904.
STRATOSE-RADIATE THALLUS 119
follows on cessation of growth, or on perforation at the summit of the
podetium. Round this quiescent portion there rises a circle of minute
prominences which carry on the apical development. As they increase in
size, the spaces between them are bridged over by lateral growth, and the
scyphus thus formed is large or small according to the number of these
outgrowths. Apothecia or spermogonia may be produced at their tips, or
the vegetative development may continue. Scyphi formed in this manner
are also open or "pervious."
d. GONIDIA OF THE SCYPHUS. Gonidia are absent in the early stages
of scyphus formation when it arises from degeneration of the apical
tissues, either fertile or vegetative ; but gradually they migrate from the
podetium, from the base of young outgrowths, or by furrows at the edge, and
so spread over the surface of the cup. Soredia may possibly alight, as
Krabbe insists that they do, and may aid in colonizing the naked area.
Their presence, however, would only be accidental ; they are not essential,
and scyphi are formed in many non-sorediate species such as Cl. vertidllata.
The cortex of the scyphus becomes in the end continuous with that of the
podetium and is always similar in type.
e. SPECIES WITHOUT SCYPHI. In species where the whole summit of
the podetium is occupied by an apothecium, as in Cl. bellidiflora, no scyphus
is formed. There is also an absence of scyphi in podetia that taper to a
point. In those podetia the hyphae are parallel to the long axis and remain
in connection with the external gonidial layer so that they are unaffected
by the central cavity. Instances of tapering growth are also to be found
in species that are normally scyphiferous such as Cl. fimbriata subsp. jil?u/a,
and Cl. cornuta, as well as in species like Cl. rangiferina that are constantly
ascyphous.
The scyphus is considered by Wainio1 to represent an advanced stage
of development in the species or in the individual, and any conditions that
act unfavourably on growth, such as excessive dryness, would also hinder
the formation of this peculiar lichen structure.
D. BRANCHING OF THE PODETIUM
Though branching is a constant feature in many species, regular dicho-
tomy is rare; more often there is an irregular form of polytomy in which one
of the members grows more vigorously than the others and branches again,
so that a kind of sympodium arises, as in Cl. rangiferina, Cl. sylvatica, etc.
Adventitious branches may also arise from the podetium, owing to some
disturbance of the normal growth, some undue exposure to wind or to too
i Wainio 1897.
120 MORPHOLOGY
great light, or owing to some external injury. They originate from the
gonidial tissue in the same way as does the podetium from the primary
thallus; the parallel hyphae of the main axis take no part in their develop-
ment.
In a number of species secondary podetia arise from the centre of the
scyphus — constantly in Cl. verticillata and Cl. cervicornis, etc., accidentally
or rarely in Cl. foliacea, Cl. pyxidata, CL fimbriata, etc. Wainio1 has stated
that they arise when the scyphus is already at an advanced stage of growth
and that they are to be regarded as adventitious branches.
The proliferations from the borders of the scyphus are in a different
category. They represent the continuity of apical growth, as the edges of
the scyphus are but an enlarged apex. These marginal proliferations thus
correspond to polytomous branching. In many instances their advance is
soon stopped by the formation of an apothecium and they figure more as
fruit stalks than as podetial branches.
E. PERFORATIONS AND RETICULATION OF THE PODETIUM
Perforations in the podetial wall at the axils of the branches are constant
in certain species such as Cl. rangiferina, CL uncialis, etc. They are caused
by the tension of the branches as they emerge from the main stalk.
A tearing of the tissue may also arise in the base of the scyphus, due to its
increase in size, which causes the splitting of the diaphragm at the bottom
of the cup.
Among the Cladoniae the reticulate condition recurs now and again.
In our native Cladonia cariosa the splitting of the podetial wall is a constant
character of the species, the carious condition being caused by unequal
growth which tears apart the longitudinal fibres that surround the central
hollow.
A more advanced type of reticulation arises in the group of the Clathrinae
in which there is no inner chondroid cylinder. In Cladonia aggregata, in
which the perforations are somewhat irregular, two types of podetia have
been described by Lindsay2 from Falkland Island specimens: those bearing
apothecia are short and broad, fastigiately branched upwards and with
reticulate perforations, while podetia bearing spermogonia are slender, elon-
gate and branched, with fewer reticulations. An imperfect network is also
characteristic of CL Sullivani, a Brazilian species. But the most marvellous
and regular form of reticulation occurs in Cl. retepora, an Australian lichen
(Fig. 71): towards the tips of the podetia the ellipsoid meshes are small,
but they gradually become larger towards the base. In this species the
outer tissue, though of parallel hyphae, is closely interwoven and forms
1 Wainio 1897. 2 Lindsay 1859, P- 171-
STRATOSE-RADIATE THALLUS 121
a continuous growth at the edges of the perforations, giving an unbroken
smooth surface and checking any irregular tearing. The enlargement of
the walls is solely due to intercalary growth. The origin of the reticulate
structure in the Clathrinae is unknown, though it is doubtless associated
Fig. 71. Cladonia retepora Fr. From Tasmania.
with wide podetia and rendered possible by the absence of an internal
chondroid layer. The reticulate structure is marvellously adapted for the
absorption of water: Cl. retepora, more especially, imbibes and holds moisture
like a sponge.
F. ROOTING STRUCTURES OF CLADONIAE
The squamules of the primary thallus are attached, as are most squa-
mules, to the supporting substance by strands of hyphae which may be
combined into simple or branching rhizinae and penetrate the soil or the
wood on which the lichen grows. There is frequently but one of these
rooting structures and it branches repeatedly until the ultimate branchlets
end in delicate mycelium. Generally they are grey or brown and are not
122 ' MORPHOLOGY
easily traced, but when they are orange-coloured, as according to Wainio1
they frequently are in Cladonia miniata and Cl. digitata, they are more
readily observed, especially if the habitat be a mossy one.
In Cl. alpicola it has been found that the rooting structure is frequently
as thick as the podetium itself. If the podetium originates from the basal
portion of the squamule, the hyphae from the chondroid layer, surrounding
the hollow centre, take a downward direction and become continuous with
the rhizoid. Should the point of insertion be near the apex of the squamule,
these hyphae form a nerve within the squamule or along the under surface,
and finally also unite with the rhizoid at the base, a form of rooting charac-
teristic of Cl. cartilaginea, Cl. digitata and several other species.
Mycelium may spread from the rhizinae along the surface of the sub-
stratum and give rise to new squamules and new tufts of podetia, a method
of reproduction that is of considerable importance in species that are
generally sterile and that form no soredia.
Many species, especially those of the section Cladina, soon lose all
connection with the substratum, there being a continual decay of the lower
part of the podetia. As apical growth may continue for centuries, the
perishing of the base is not to be wondered at.
G. HAPTERA
The presence of haptera in Cladoniae has already been alluded to. They
occur usually in the form of cilia or rhizinae2, but differ from the latter in
their more simple regular growth being composed of conglutinate parallel
hyphae. They arise on the edges of the squamules or of the scyphus, but
in Cl. foliacea and Cl. ceratophylla they are formed at the points of the
podetial branches (more rarely in Cl. cervicornis and Cl. gracilis). By the aid
of these rhizinose haptera the squamule or branch becomes attached to any
substance within reach. They also aid in the production of new individuals
by anchoring some fragment of the thallus to a support until it has grown
to independent existence and has produced new rhizinae or holdfasts. They
are a very prominent feature of Cl. verticillaris f. penicillata in which they
form a thick fringe on the edges of the squamules, or frequently grow out
as branched cilia from the proliferations on the margins of the scyphus.
H. MORPHOLOGY OF THE PODETIUM
In the above account, the podetia have been treated as part of the
vegetative thallus, seeing that, partly or entirely, they are assimilative and
absorptive organs. This view does not, however, take into account their
origin and development, in consideration of which Wainio3 and later Krabbe4
1 Wainio 1897. 2 Wainio l897) p< 9 3 Wainio I8g0i 4 Krabbe ,g9r>
STRATOSE-RADIATE THALLUS 123
considered them as part of the sporiferous organ. This view was also held
by some of the earliest lichenologists: Necker1, for instance, constantly
referred to the upright structure as "stipes"; Persoon2 included it, under
the term "pedunculus," as part of the "inflorescence" of the lichen, and
Acharius3 established the name "podetium" to describe the stalk of the
apothecium in Baeomyces.
Later lichenologists, such as Wallroth4, looked on the podetia as advanced
stages of the thallus, or as forming a supplementary thallus. Tulasne5
described them as branching upright processes from the horizontal form,
and Koerber6 considered them as the true thallus, the primary squamule
being merely a protothallus. By them and by succeeding students of lichens
the twofold character of the thallus was accepted until Wainio and Krabbe
by their more exact researches discovered the endogenous origin of the
podetium, which they considered was conclusive evidence of its apothecial
character: they claimed that the primordium of the podetium was homolo-
gous with the primordium of the apothecium. Reinke7 and Wainio are in
accord with Krabbe as to the probable morphological significance of the
podetium, but they both insist on its modified thalline character. Wainio
sums up that: "the podetium is an apothecial stalk, that is to say an
elongation of the conceptacle most frequently transformed by metamorphosis
to a vertical thallus, though visibly retaining its stalk character." Sattler8,
one of the most recent students of Cladonia, regards the podetium as evolved
with reference to spore-dissemination, and therefore of apothecial character.
His views are described and discussed in the chapter on phylogeny.
Reinke and others sought for a solution of the problem in Baeomyces,
one of the more primitive genera of the Cladoniaceae. The thallus, except
in a few mostly exotic species, scarcely advances beyond the crustaceous
condition; the podetia are short and so varied in character that species
have been assigned by systematists to several different genera. In one of
them, Baeomyces roseus, the podetium or stalk originates according to
Nienburg9 deep down in the medulla of a fertile granule as a specialized
weft of tissue; there is no carpogonium nor trichogyne formed ; the hyphae
that grow upward and form the podetium are generative filaments and give
rise to asci and paraphyses. In a second species, B. rufus (Sphyridium\ the
gonidial zone and outer cortex of a thalline granule swell out to form a
thalline protuberance; the carpogonium arises close to the apex, and from
it branch the generative filaments. Nienburg regards the stalk of B. roseus
as apothecial and as representing an extension of the proper margin10 (ex-
cipulmn propriuwi), that of B. rufus as a typical vegetative podetium.
1 Necker 1871. 2 Persoon 1794. 3 Acharius 1803. 4 Wallroth 1829, p. 61.
8 Tulasne 1852. <* Koerber 1855. 7 Reinke 1894. 8 Sattler 1914.
9 Nienburg 1908. 10 See p. 183.
i24 MORPHOLOGY
In the genus Cladonia, differentiation of the generative hyphae may
take place at a very early stage. Wainio1 observed, in CL caespiticia, a
trichogyne in a still solid podetium only 90 /x in height; usually they appear
later, and, where scyphi are formed, the carpogonium often arises at the
edge of the scyphus. Baur2 and Wolff3 have furnished conclusive evidence
of the late appearance of the carpogonium in CL pyxidata, Cl. degenerans,
CL furcata and CL gracilis: in all of these species carpogonia with tricho-
gynes were observed on the edge of well-developed scyphi. Baur draws the
conclusion that the podetium is merely a vertical thallus, citing as additional
evidence that it also bears the spermogonia (or pycnidia), though at the
same time he allows that the apothecium may have played an important part
in its phylogenetic development. He agrees also with the account of the
first appearance of the podetium as described by Krabbe, who found that
it began with the hyphae of the gonidial zone branching upwards in a quite
normal manner, only that there were more of them, and that they finally
pierced the cortex. Krabbe also asserted that in the early stages the podetia
were without gonidia and that these arrived later from the open as colonists,
in this contradicting Wainio's statement that gonidia were carried up from
the primary thallus.
It seems probable that the podetium — as Wainio and Baur both have
stated — is homologous with the apothecial stalk, though in most cases it is
completely transformed into a vertical thallus. If the view of their formation
from the gonidial zone is accepted, then they differ widely in origin from
normal branches in which the tissues of the main axis are repeated in the
secondary structures, whereas in this vertical thallus, hyphae from the
gonidial zone alone take part in the development. It must be admitted
that Baur's view of the podetium as essentially thalline seems to be strength-
ened by the formation of podetia at the centre of the scyphus, as "in CL
verticillata, which are new structures and are not an elongation of the
original conceptacular tissue. It can however equally be argued that the
acquired thalline character is complete and, therefore, includes the possibility
of giving rise to new podetia.
The relegation of the carpogonium to a position far removed from the
base or primordium of the apothecium need not necessarily interfere with
the conception of the primordial tissue as homologous with the conceptacle;
but more research is needed, as Baur dealt only with one species, CLpyxidata,
and Gertrude Wolff confined her attention to the carpogonial stages at the
edge of the scyphus.
The Cladoniae require light, and inhabit by preference open moorlands,
naked clay walls, borders of ditches, exposed sand-dunes, etc. Those with
large and persistent squamules can live in arid situations, probably because
1 Wainio 1897. 2 Baur 1904. 3 Wolff 1905.
STRATOSE-RADIATE THALLUS 125
the primary thallus is able to retain moisture for a long time1. When the
primary thallus is small and feeble the podetia are generally much branched
and live in close colonies which retain moisture. Sterile podetia are long-
lived and grow indefinitely at the apex though the base as continually
perishes and changes into humus. Wainio2 cites an instance in which the
bases of a tuft of Cl. alpestris had formed a gelatinous mass more than a
decimetre in thickness.
I. PlLOPHORUS AND STEREOCAULON
These two genera are usually included in Cladoniaceae on account
of their twofold thallus and their somewhat similar fruit formation.
They differ from Cladonia in the development of the podetia which are
not endogenous in origin as in that genus, but are formed by the growth
upwards of a primary granule or squamule and correspond more nearly to
Tulasne's conception of the podetium as a process from the horizontal
thallus. In Pilophorus the primary granular thallus persists during the life
of the plants; the short podetium is unbranched, and consists of a some-
what compact medulla of parallel hyphae surrounded by a looser cortical
tissue, such as that of the basal granule, in which are embedded the algal
cells. The black colour of the apothecium is due to the thick dark hypo-
thecium.
Stereocaulon is also a direct growth from a short-lived primary squamule3.
The podetia, called " pseudopodetia " by Wainio, are usually very much
branched. They possess a central strand of hyphae not entirely solid, and
an outer layer of loose felted hyphae in which the gonidia find place. A
coating of mucilage on the outside gives a glabrous shiny surface, or, if
that is absent, the surface is tomentose as in St. tomentosum. In all the
species the podetia are more or less thickly beset with small variously
divided squamules similar in form to the primary evanescent thallus. Gall-
like cephalodia are associated with most of the species and aid in the work
of assimilation.
Stereocaulon cannot depend on the evanescent primary thallus for attach-
ment to the soil. The podetia of the different species have developed various
rooting bases: in St. ramulosum there is a basal sheath formed, in St. coral-
hides a well-developed system of rhizoids4.
1 Aigret 1901. 2 Wainio 1897. 3 Wainio 1890, p. 67. 4 Reinke 1895.
126 MORPHOLOGY
V. STRUCTURES PECULIAR TO LICHENS
i. AERATION STRUCTURES
A. CYPHELLAE AND PSEUDOCYPHELLAE
The thallus of Stictaceae has been regarded by Nylander1 and others as
one of the most highly organized, not only on account of the size attained
by the spreading lobes, but also because in that family are chiefly found
those very definite cup-like structures which were named "cyphellae" by
Acharius2. They are small hollow depressions about \ mm. or more in
width scattered irregularly over the under surface of the thallus.
a. HISTORICAL. Cyphellae were first pointed out by the Swiss botanist,
Haller3. In his description of a lichen referable to Sticta fuliginosa he
describes certain white circular depressions " to be found among the short
brown hairs of the under surface." At a later date Schreber4 made these
" white excavated points " the leading character of his lichen genus Sticta.
In urceolate or proper cyphellae, the base of the depression rests on the
medulla; the margin is formed from the ruptured cortex and projects slightly
inwards over the edge of the cup. Contrasted with these are the pseudo-
cyphellae, somewhat roundish openings of a simpler structure which replace
the others in many of the species. They have no definite margin ; the inter-
nal hyphae have forced their way to the exterior and form a protruding
tuft slightly above the surface. Meyer5 reckoned them all among soredia;
. but he distinguished between those in which the medullary hyphae became
conglutinated to form a margin (true cyphellae) and those in which there
was a granular outburst of filaments (pseudocyphellae). He also included
a third type, represented in Lobaria pulmonaria on the under surface of
which there are numerous non-corticate, angular patches where the pith is
laid bare (Fig. 72). Delise6, writing about the same time on the Sticteae,
gives due attention to their occurrence, classifying the various species of
Sticta as cyphellate or non-cyphellate.
Acharius had limited the name " cyphella " to the hollow urceolate bodies
that had a well-defined margin. Nylander7 at first included under that
term both types of structure, but later8 he classified the pulverulent " soredia-
like " forms in another group, the pseudocyphellae. As a rule they bear no
relation to soredia, and algae are rarely associated with the protruding
filaments. Schwendener9, and later Wainio10, in describing Sticta aurata from
Brazil, state, as exceptional, that the citrine-yellow pseudocyphellae of that
species are sparingly sorediate.
1 Nylander 1858, p. 63. '2 Acharius 1810, p. 12. 3 Haller 1768, p. 85.
4 Schreber 1791, p. 768. 6 Meyer 1825, p. 148. s Delise 1822. 7 Nylander 1858, p. 14.
8 Nylander 1860, p. 333. 9 Schwendener 1863, p. 169. 10 Wainio 1890, I. p. 183.
STRUCTURES PECULIAR TO LICHENS
127
b. DEVELOPMENT OF CYPHELLAE. The cortex of both surfaces in the
thallus of Sticta is a several-layered plectenchyma of thick-walled closely
Fig. 72. Lobaria pulnionaria Hoffm. Showing pitted surface, a, under surface.
Reduced (S. H., Photo.}.
packed cells, the outer layer growing out into hairs on the under surface of
most of the species. Where either cyphellae or pseudocyphellae occur, a
more or less open channel is formed between the exterior and the internal
tissues of the lichen. In the case of the cyphellae, the medullary hyphae
which line the cup are divided into short roundish cells with comparatively
thin -walls (Fig. 73). They form a tissue sharply differentiated from the
Fig. 73. Sticta damaecornis Nyl. Transverse section
of thallus with cyphella x 100.
loose hyphae that occupy the medulla. The rounded cells tend to lie in
vertical rows, though the arrangement in fully formed cyphellae is generally
128 MORPHOLOGY
somewhat irregular. The terminal empty cells are, loosely attached and as
they are eventually abstricted and strewn over the inside of the cup they
give to it the characteristic white powdery appearance.
According to Schwendener1 development begins by an exuberant growth
of the medulla which raises and finally bursts the cortex; prominent cyphellae
have been thus formed in Sticta damaecornis (Fig. 73). In other species
the swelling is less noticeable or entirely absent. The opening of the cup
measures usually about \ mm. across, but it may stretch to a greater width.
c. PsEUDOCYPHELLAE. In these no margin is formed, the cortex is
simply burst by the protruding filaments which are of the same colour —
yellow or white — as the medullary hyphae. They vary in size, from a minute
point up to 4 mm. in diameter.
d. OCCURRENCE AND DISTRIBUTION. The genus Sticta is divided into
two sections : (i) Eusticta in which the gonidia are bright-green algae, and
(2) Stictina in which they are blue-green. Cyphellae and pseudocyphellae
are fairly evenly distributed between the sections; they never occur together.
Stizenberger2 found that 36 species of the section Eusticta were cyphellate,
while in 43 species pseudocyphellae were formed. In the section Stictina
there were 38 of the former and only 31 of the latter type. Both sections of
the genus are widely distributed in all countries, but they are most abundant
south of the equator, reaching their highest development in Australia and
New Zealand.
In the British Isles Sticta is rather poorly represented as follows:
\Eusticta (with bright-green gonidia).
Cyphellate: 5. damaecornis.
Pseudocyphellate: S. aurata.
\Stictina (with blue-green gonidia).
Cyphellate: S.fidiginosa, S. limbata, S. sylvatica, S. Dufourei.
Pseudocyphellate: 5. intricata van Thouarsii, S. crocata.
Structures resembling cyphellae, with an overarching rim, are sprinkled
over the brown under surface of the Australian lichen, Heterodea Miilleri;
the thallus is without a lower cortex, the medulla being protected by thickly
woven hyphae. Heterodea was at one time included among Stictaceae,
though now it is classified under Parmeliaceae. Pseudocyphellae are also
present on the non-corticate under surface of Nephromium tomentosum,
where they occur as little white pustules among the brown hairs; and the
white impressed spots on the under surface of Cetraria Islandica and allied
species, first determined as air pores by Zukal3, have also been described by
Wainio4 as pseudocyphellae.
1 Schwendener 1863, p. 169. 2 Stizenberger 1895. 3 Zukal 1895, p. 1355. 4 Wainio 1909.
STRUCTURES PECULIAR TO LICHENS
129
There seems no doubt that the chief function of these various structures
is, as Schwendener1 suggested, to allow a free passage of air to the assimi-
lating gonidial zone. Jatta2 considers them to be analogous to the lenticels
of higher plants and of service in the interchange of gases — expelling car-
bonic acid and receiving oxygen from the outer atmosphere. It is remarkable
that such serviceable organs should have been evolved in so few lichens.
4. Parmelia exasperata Carroll. Ver-
tical section of thallus. a, breathing- pores;
l>, rhizoid. x 60 (after Rosendahl).
B. BREATHING-PORES
a. DEFINITE BREATHING-PORES. The cyphellae and pseudocyphellae
described above are confined to the under surface of the thallus in those
lichens where they occur. Distinct breathing-pores of a totally different
structure are present on the upper
surface of the tree-lichen, Parmelia
aspidota (P. exasperata}, one of the
brown-coloured species. They are
somewhat thickly scattered as isidia-
or cone-like warts over the lichen
thallus (Fig. 74) and give it the char-
acteristically rough or "exasperate"
character. They are direct outgrowths
from the thallus, and Zukal3, who dis-
covered their peculiar nature and func-
tion, describes them as being filled with a hyphal tissue, with abundant
air-spaces, and in direct communication with the medulla ; gonidia, if
present, are confined to the basal part. The cortex covering these minute
cones, he further states, is very thin on the top, or often wanting, so that
a true pore is formed which, however, is only opened after the cortex else-
where has become thick and horny. Rosendahl4, who has re-examined these
"breathing-pores," finds that in the early stage of their growth, near the
margin or younger portion of the thallus, they are entirely covered by the
cortex. Later, the hyphae at the top become looser and more frequently
septate, and a fine net-work of anastomosing and intricate filaments takes
the place of the closely cohering cortical cells. These hyphae are divided
into shorter cells, but do not otherwise differ from those of the medulla.
Rosendahl was unable to detect an open pore at any stage, though he
entirely agrees with Zukal as to the breathing function of these structures.
The gonidia of the immediately underlying zone are sparsely arranged and
a few of them are found in the lower half of the cone; the hyphae of the
medulla can be traced up to the apex.
Schwendener 1863, p. 169.
2 Jatta 1889, p. 4*
4 Rosendahl 1907.
3 Zukal 1895, p. 1357-
S. L.
130
MORPHOLOGY
Zukal1 claims to have found breathing-pores in Cornicularia (Parmelid)
tristis and in several other Parmeliae, notably
in Parmelia stygia. The thallus of the latter
species has minute holes or openings in the
upper cortex, but they are without any definite
form and may be only fortuitous.
Zukal1 published drawings of channels of
looser tissue between the exterior and the
pith in Oropogon Loxensis and in Usnea bar-
bata. He considered them to be of definite
service in aeration. The fronds of Ramalina
dilacerata by stretching develop a series of
elongate holes. Reinke2 found openings in
Ramalina Eckloni which pierced to the centre
of the thallus, and Darbishire3 has figured
a break in the frond of another species, R.
fraxinea (Fig. 75 A), which he has designated
as a breathing-pore. Finally Brandt4, in his
careful study of the anatomy of Ramalinae,
has described as breathing- pores certain open
areas usually of ellipsoid form in the compact
cortex of several species: in R. strepsilis
(Fig. 75 B) and R. Landroensis, and in the
British species, R. siliquosa and R. fraxinea. These openings are however
mostly rare and difficult to find or to distinguish from holes that may
be due to any accident in the life of the lichen. It is noteworthy that
Fig. 75 A. Ramalina fraxinea Ach.
A, surface view of frond, a, air-
res; />, young apothecia. x \i.
. transverse section of part of
frond, a, breathing- pore \f, strength-
ening fibres, x 37 (after Brandt).
Fig- 75 B- Ramalina strepsilis Zahlbr. Transverse section
of part of frond showing distribution of: a, air-pores, and
f, strengthening fibres, x 37 (after Brandt).
Rosendahl found no further examples of breathing-pores in the brown
Parmeliae that he examined in such detail. No other organs specially
adapted for aeration of the thallus have been discovered.
b. OTHER OPENINGS IN THE THALLUS. Lobaria is the only genus of
Stictaceae in which neither cyphellae nor pseudocyphellae are formed ; but
in two species, L. scrobiculata and L. pulmonaria, the lower surface is marked
1 Zukal 1895. 2 Reinke 1895, p. 183. 3 Darbishire 1901. 4 Brandt 1906.
STRUCTURES PECULIAR TO LICHENS 131
with oblong or angular bare convex patches, much larger than cyphellae.
They are exposed portions of the medulla, which at these spots has been
denuded of the covering cortex. Corresponding with these bare spots there
is a pitting of the upper surface.
A somewhat similar but reversed structure characterizes Umbilicaria
pustulata, which as the name implies is distinguished by the presence of
pustules, ellipsoid swellings above, with a reticulation of cavities below.
Bitter1 in this instance has proved that they are due to disconnected centres
of intercalary growth which are more vigorous on the upper surface and
give rise to cracks in the less active tissue beneath. These cracks gradually
become enlarged ; they are, as it were, accidental in origin but are doubtless
of considerable service in aeration.
In some Parmeliae there are constantly formed minute round holes,
either right through the apothecia (P. cetrata, etc.), or through the thallus
(P. pertusd). Minute holes are also present in the under cortex of Par-
melia vittata and of P. enteromorpha, species of the subgenus Hypogymnia.
Nylander2, who first drew attention to these holes of the lower cortex,
described them as arising at the forking of two lobes ; but though they do
occur in that position, they as frequently bear no relation to the branching.
Bitter's3 opinion is that they arise by the decay of the cortical tissues in
very limited areas, from some unknown cause, and that the holes that pierce
right through the thallus in other species may be similarly explained.
Still other minute openings into the thallus occur in Parmelia vittata,
P. obscurata and P. farinacea var. obscurascens. In the two latter the open-
ings like pin-holes are terminal on the lobes and are situated exactly on
the apex, between the pith and the gonidial zone; sometimes several holes
can be detected on the end of one lobe. Further growth in length is checked
by these holes. They appear more frequently on the darker, better illumi-
nated plants. In Parmelia vittata the terminal holes are at the end of
excessively minute adventitious branches which arise below the gonidial
zone on the margin of the primary lobes. All these terminal holes are
directed upwards and are visible from above.
Bitter does not attribute any physiological significance to these very
definite openings in the thallus. It has been generally assumed that they
aid in the aeration of the thallus; it is also possible that they may be of
service in absorption, and they might even be regarded as open water con-
ductors.
1 Bitter 1899. 2 Nylander i8742. 3 Bitter i9Oi2.
9-2
I32 MORPHOLOGY
C. GENERAL AERATION OF THE THALLUS
Definite structures adapted to secure the aeration of the thallus in a
limited number of lichens have been described above. These are the breathing-
pores of Parmelia exasperata and the cyphellae and pseudocyphellae of the
Stictaceae, with which also may be perhaps included the circumscribed
breaks in the under cortex in some members of that family.
Though lichens are composed of two actively growing organisms, the
symbiotic plant increases very slowly. The absorption of water and mineral
salts must in many instances be of the scantiest and the formation of carbo-
hydrates by the deep-seated chlorophyll cells of correspondingly small
amount. Active aeration seems therefore uncalled for though by no means
excluded, and there are many indirect channels by which air can penetrate
to the deeper tissues.
In crustaceous forms, whether corticate or not, the thallus is often deeply
seamed and cracked into areolae, and thus is easily pervious to water and
air. The growing edges and growing points are also everywhere more or
less loose and open to the atmosphere. In the larger foliose and fruticose
lichens, the soredia that burst an opening in the thallus, and the cracks
that are so frequent a feature of the upper cortex, all permit of gaseous
interchange. The apical growing point of fruticose lichens is thin and porous,
and in many of them the ribs and veins of their channelled surfaces entail
a straining of the cortical tissue that results in the formation of thinner
permeable areas. Zukal1 devoted special attention to the question of aeration,
and he finds evidenceof air-passages through empty spermogonia and through
the small round holes that are constant in the upper surface of certain foliose
species. He claims also to have proved a system of air-canals right through
the thallus of the gelatinous Collemaceae. Though his proof in this instance
is somewhat unconvincing, he establishes the abundant presence of air in
the massively developed hypothecium of Collema fruits. He found that the
carpogonial complex of hyphae was always well supplied with air, and that
caused him to view with favour the suggestion that the function of the
trichogyne is to provide an air-passage. In foliose lichens, the under surface
is frequently non-corticate, in whole or in part; or the cortex becomes
seamed and scarred with increasing expansion, the growth in the lower
layers failing to keep pace with that of the overlying tissues, as in Umbili-
caria pustulata.
It is unquestionable that the interior of the thallus of most lichens con-
tains abundant empty spaces between the loose-lying hyphae, and that these
spaces are filled with air.
1 Zukal 1895, p. 1348.
STRUCTURES PECULIAR TO LICHENS 133
2. CEPHALODIA
A. HISTORICAL AND DESCRIPTIVE
The term " cephalodium" was first used by Acharius1 to designate cer-
tain globose apothecia (pycnidia). At a later date he applied it to the
peculiar outgrowths that grow on the thallus of Peltigera aphthosa, already
described by earlier writers, along with other similar structures, as " cor-
puscula," " maculae," etc. The term is now restricted to those purely vege-
tative gall-like growths which are in organic connection with the thallus of
the lichen, but which contain one or more algae of a different type from the
one present in the gonidial zone. They are mostly rather small structures,
and they take various forms according to the lichen species on which they
occur. They are only found on thalli in which the gonidia are bright-green
algae (Chlorophyceae) and, with a few exceptions, they contain only blue-
green (Myxophyceae). Cephalodia with bright-green algae were found by
Hue2 on two Parmeliae from Chili, in addition to the usual blue-green forms;
the one contained Urococcus, the other Gloeocystis. Several with both types
of algae were detected also by Hue2 within the thallus of Aspicilia spp.
Florke3 in his account of German lichens described the cephalodia that
grow on the podetia of Stereocaulon as fungoid bodies, "corpuscula fungosa."
Wallroth4, who had made a special study of lichen gonidia, finally established
that the distinguishing feature of the cephalodia was their gonidia which
differed in colour from those of the normal gonidial zone. He considered
that the outgrowths were a result of changes that had arisen in the epidermal
tissues of the lichens, and, to avoid using a name of mixed import such as
" cephalodia," he proposed a new designation, calling them " phymata " or
warts.
Further descriptions of cephalodia were given by Th. M. Fries5 in his
Monograph of Stereocaulon and Pilophorus\ but the greatest advance in
the exact knowledge of these bodies is due to Forssell6 who made a com-
prehensive examination of the various types, examples of which occurred,
he found, in connection with about TOO different lichens. Though fairly
constant for the different species, they are not universally so, and are some-
times very rare even when present, and then difficult to find. A striking
instance of variability in their occurrence is recorded for Ricasolia amplis-
sima (Lobaria laciniatd) (Fig. 76). The cephalodia of that species are
prominent upright branching structures which grow in crowded tufts irregu-
larly scattered over the surface. They are an unfailing and conspicuous
specific character of the lichens in Europe, but are entirely wanting in North
American specimens.
1 Acharius 1803. 2 Hue 1904 and 1910. 3 Florke 1815, IV. p. 15.
4 Wallroth 1825, p. 678. 5 Th. M. Fries 1858. 6 Forssell 1884.
134
MORPHOLOGY
As cephalodia contain rather dark-coloured, blue-green algae, they are
nearly always noticeably darker than the thalli on which they grow, varying
from yellowish-red or brown in those of Lecanora gelida to pale-coloured in
Fig. 76. Ricasolia amplissima de Not. (Lobaria ladniata Wain.) on oak, reduced. The dark
patches are tufts of branching cephalodia (A. Wilson, Photo.}.
Lecidea consentiens^ , a darker red in Lecidea panaeola and various shades
of green, grey or brown in Stereocanlon, Lobaria (Ricasolia}, etc. They form
either flat expansions of varying size on the upper surface of the thallus,
rounded or wrinkled wart-like growths, or upright branching structures.
On the lower surface, where they are not unfrequent, they take the form of
small brown nodules or swellings. In a number of species packets of blue-
green algae surrounded by hyphae are found embedded in the thallus,
either in the pith or immediately under the cortex. They are of the same
nature as the superficial excrescences and are also regarded as cephalodia.
1 Leigh ton 1869.
STRUCTURES PECULIAR TO LICHENS 135
B. CLASSIFICATION
Forssell has drawn up a classification of these structures, as follows :
I. CEPHALODIA VERA.
1. Cephalodia epigena (including perigena) developed on the upper
outer surface of the thallus, which are tuberculose, lobulate, clavate or
branched in form. These are generally corticate structures.
2. Cephalodia hypogena which are developed on the under surface
of the thallus; they are termed "thalloid" if they are entirely superficial,
and "immersed" when they are enclosed within the tissues. They are non-
corticate though surrounded by a weft of hyphae. Forssell further includes
here certain placodioid (lobate), granuliform and fruticose forms which
develop on the hypothallus of the lichen, and gradually push their way up
either through the host thallus, or, as in Lecidea panaeola, between the thalline
granules.
Nylander1 arranged the cephalodia known to him in three groups:
(i) Ceph. epigena, (2) Ceph. hypogena and (3) Ceph. endogena. Schneider2
still more simply and practically describes them as Ectotrophic (external),
and Endotrophic (internal).
II. PSEUDOCEPHALODIA.
These are a small and doubtful group of cephalodia which are apparently
in very slight connection with the host thallus, and show a tendency to
independent growth. They occur as small scales on Solorina bispora3 and
vS". spongiosa and also on Lecidea pallida. Forssell has suggested that the
cephalodia of Psoroma hypnorum and of Lecidea panaeola might also be in-
cluded under this head.
Forssell and others have found and described cephalodia in the following
families and genera:
Sphaerophoraceae.
Sphaerophorus (S. stereocauloides).
Lecideaceae.
Lecidea (L. panaeola, L, consentiens, L. pelobotrya, etc.).
Cladoniaceae.
Stereocaulon, Pilophorus and Argopsis.
Pannariaceae.
Psoroma (P. hypnoruiri).
Peltigeraceae.
Peltigera (Peltidea), Nephroma and Solorina.
1 Nylander 1878. 2 Schneider 1897. 3 Hue 1910.
i36 MORPHOLOGY
Stictaceae.
Lob aria, Sticta.
Lecanoraceae.
Lecania (L. lecanorina), Aspicilia1.
Physciaceae.
Placodium bicolor*.
C. ALGAE THAT FORM CEPHALODIA
The algae of the cephalodia belong mostly to genera that form the
normal gonidia of other lichens. They are:
Stigonema, — in Lecanora gelida, Stereocaulon, Pilophorus robustus, and
Lecidea pelobotrya.
Scytonema, — a rare constituent of cephalodia.
Nostoc.. — the most frequent gonidium of cephalodia. It occurs in those
of the genera Sticta, Lobaria, Peltigera, Nephroma, Solorina and Psoroma;
occasionally in Stereocaulon and in Lecidea pallida.
Lyngbya and Rivularia, — rarely present, the latter in Sticta oregana*.
Chroococcus and Gloeocapsa, — also very rare.
Scytonema, Chroococcus, Gloeocapsa and Lyngbya are generally found
in ^combination with some other cephalodia-building alga, though Nylander4
found Scytonema alone in the lobulate cephalodia of Sphaerophorus stereo-
cauloides, a New Zealand lichen, and the only species of that genus in which
cephalodia are developed; and Hue1 records Gloeocapsa as forming internal
cephalodia in two species of Aspicilia, Bornet5 found Lyngbya associated
with Scytonema in the cephalodia of Stereocaulon ramulosum, and, in the
same lichen, Forssell6 found, in the several cephalodia of one specimen,
Nostoc, Scytonema, and Lyngbya, while, in those of another, Scytonema and
Stigonema were present. In the latter instance these algae were living free
on the podetium. Forssell6 also determined two different algae, Gloeocapsa
magma and Chroococcus tttrg-idus,preseni in a cephalodium on Lecidea panaeola
var. elegans.
As a general rule only one kind of alga enters into the formation of the
cephalodia of any species or genus. A form of Nostoc, for instance, is in-
variably the gonidial constituent of these bodies in the genera, Lobaria, Sticta,
etc. In other lichens different blue-green algae, as noted above, may occupy
the cephalodia even on the same specimen. Forssell finds alternative algae
occurring in the cephalodia of:
Lecanora gelida and Lecidea illita contain either Stigonema or Nostoc;
Lecidea panaeola, with Gloeocapsa, Stigonema or Chroococcus;
1 Hue 1910. 2 Tuckerman 1875. 3 Schneider 1897, p. 58. * Nylander 1869.
5 Bornet 1873, p. 72. « Forssell 1885, p. 24.
STRUCTURES PECULIAR TO LICHENS 137
Lecidea pelobotrya, with Stigonema or Nostoc;
Pilophorus robustus, with Gloeocapsa, Stigonema, or Nostoc.
Fig. 77. Lecanora gelida Ach. #, lobate cephalodia
x 1 2 (after Zopf ).
Riddle1 has employed cephalodia with their enclosed algae as diagnostic
characters in the genus Stereocaulon. When the alga is Stigonema, as in
5. pascJiale, etc., the cephalodia are generally very conspicuous, grey in
colour, spherical, wrinkled or folded, though sometimes black and fibrillose
(S. denudatuni). Those containing Nostoc are, on the contrary, minute and
are coloured verdigris-green (S. tomentosum and 5. alpinuni).
Instances are recorded of algal colonies adhering to, and even penetrating,
the thallus of lichens, but as they never enter into relationship with the
lichen hyphae, they are antagonistic rather than symbiotic and have no
relation to cephalodia.
D. DEVELOPMENT OF CEPHALODIA
a. EcTOTROPHIC. Among the most familiar examples of external cepha-
lodia are the small rather dark-coloured warts or swellings that are scattered
irregularly over the surface of Peltigera (Peltidea) aphthosa. This lichen has
a grey foliose thallus of rather large sparingly divided lobes; it spreads
about a hand-breadth or more over the surface of the ground in moist up-
land localities. The specific name " aphthosa " was given by Linnaeus to
1 Riddle 1910.
i38 MORPHOLOGY
the plant on account of the supposed resemblance of the dotted thallus to
the infantile ailment of " thrush." Babikoff l has published an account of
the formation and development of these Peltidea cephalodia. He determined
the algae contained in them to be Nostoc by isolating and growing them on
moist sterilized soil. He observed that the smaller, and presumably younger,
excrescences were near the edges of the lobes. The cortical cells in that
position grow out into fine septate hairs that are really the ends of growing
hyphae. Among the hairs were scattered minute colonies of Nostoc cells
lying loose or so closely adhering to the hairs as to be undetachable (Fig.
78 A). In older stages the hairs, evi-
dently stimulated by contact with the
Nostoc, had increased in size and sent
out branches, some of which penetrated
the gelatinous algal colony; others,
spreading over its surface, gradually
formed a cortex continuous with that
of the thallus. The alga also increased,
and the structure assumed a rounded or
lentiform shape. The thalline cortex
immediately below broke down, and
the underlying gonidial zone almost
Fig. 78 A. Hairs of Peltigera aphthosaVIi\\&. 7 S S
associated with Nostoc colony much mag- wholly died off and became absorbed.
nified (after Babikoff). The hyphae of the cephalodium had
meanwhile penetrated downwards as root-like filaments, those of the thallus
growing upwards into the new overlying tissue (Fig. 78 B). The foreign
alga has been described as parasitic, as it draws from the lichen hyphae the
necessary inorganic food material; but it might equally well be considered
as a captive pressed into the service of the lichen to aid in the work of assi-
milation or as a willing associate giving and receiving mutual benefit.
Th. M. Fries2 had previously described the development of the cephalodia
in Stereocaulon but failed to find the earliest stages. He concluded from his
observations that parasitic algae were common in the cortical layer of the
lichens, but only rarely formed the " monstrous growths " called cephalodia.
b. ENDOTROPHIC. Winter3 examined the later stages of internal cepha-
lodine formation in a species of Sticta. The alga, probably a species of
Rivularia, which gives origin to the cephalodia, may be situated immediately
below the upper cortex, in the medullary layer close to the gonidial zone,
or between the pith and the under cortex. The protuberance caused by the
increasing tissue, which also contains the invading alga, arises accordingly
either on the upper or the lower surface. In some cases it was found that
the normal gonidial layer had been pushed up by the protruding cephalodium
1 Babikoff 1878. 2 Th. M. Fries 1866. 3 Winter 1877.
STRUCTURES PECULIAR TO LICHENS
139
and lay like a cap over the top. The cephalodia described by Winter are
endogenous in origin, though the mature body finally emerges from the
interior and becomes either epigenous or hypogenous. Schneider1 has fol-
lowed the development of a somewhat similar endotrophic or endogenous type
Fig. 788. Peltigera aphthosa Willd. Vertical section of thai lus and
cephalodium x 480 (after Babikoff).
in Sticta oregana due also to the presence of a species of Rivularia. How
the alga attained its position in the medulla of the thallus was not observed.
Both the algal cells of internal cephalodia and the hyphae in contact
with them increase vigorously, and the newly formed tissue curving upwards
or downwards appears on the outside as a swelling or nodule varying in
size from that of a pin-head to a pea. On the upper surface the gonidial
zone partly encroaches on the nodule, but the foreign alga remains in the
centre of the structure well separated from the thalline gonidia by a layer
of hyphae. The group is internally divided into small nests of dark-green
algae surrounded by strands of hyphae (Fig. 79). The swellings, when they
Fig. 79. Nephroma expallidum Nyl. Vertical section
of thallus. a, endotrophic cephalodium x 100 (after
Forssell).
1 Schneider 1807.
1 40 MORPHOLOGY
occur on the lower surface of the lichen, correspond to those of the upper
in general structure, but there is no intermixture of thalline gonidia. That
Nostoc cells can grow and retain the power to form chlorophyll in adverse
conditions was proved by Etard and Bouilhac1 who made a culture of the
alga on artificial media in the dark, when there was formed a green pigment
of chlorophyll nature.
Endotrophic cephalodia occur in many groups of lichens' Hue2 states
that he found them in twelve species of Aspicilia. As packets of blue-green
algae they are a constant feature in the thallus of Solorinae. The species of
that genus grow on mossy soil in damp places, and must come frequently
in contact with Nostoc colonies. In Solorina crocea an interrupted band of
blue-green algae lies below the normal gonidial zone and sometimes replaces
it — a connecting structure between cephalodia and a true gonidial zone.
c. PSEUDOCEPHALODIA. Under this section have been classified those
cephalodia that are almost independent of the lichen thallus though to some
extent organically connected with it, as for instance that of Lecidea panaeola
which originate on the hypothallus of the lichen and maintain their position
between the crustaceous granules.
The cephalodia of Lecanora gelida, as described by Sernander3, might
also be included here. He watched their development in their native habitat,
an exposed rock-surface which was richly covered with the lichen in all
stages of growth. Two kinds of thallus, the one containing blue-green algae
(Chroococcus}, the other bright-green, were observed on the rock in close
proximity. At the point of contact, growth ceased, but the thallus with
bright-green algae, being the more vigorous, was able to spread round and
underneath the other and so gradually to transform it to a superficial flat
cephalodium. All such thalli encountered by the dominant lichen were
successively surrounded in the same way. The cephalodium, growing more
slowly, sent root-like hyphae into the tissue of the underlying lichen, and
the two organisms thus became organically connected. Sernander considers
that the two algae are antagonistic to each other, but that the hyphae can
combine with either.
The pseudocephalodia of Usnea species are abortive apothecia; they are
surrounded at the base by the gonidial zone and cortex of the thallus, and
they contain no foreign gonidia.
E. AUTOSYMBIOTIC CEPHALODIA
Bitter4 has thus designated small scales, like miniature thalli, that develop
constantly on the upper cortex of Peltigera lepidophora, a small lichen not
uncommon in Finland, and first recorded by Wainio as a variety of Peltigera
1 Etard and Bouilhac 1898. 2 Hue I9,o 3 Sernander 1907. * Bitter 1904.
STRUCTURES PECULIAR TO LICHENS 141
canina. The alga contained in the scales is a blue-green Nostoc similar to
the gonidia of the thallus. Bitter1 described the development as similar to
that of the cephalodia of Peltigera aphthosa, but the outgrowths, being lobate
in form, are less firmly attached and thus easily become separated and dis-
persed ; as the gonidia are identical with those of the parent thallus they
act as vegetative organs of reproduction.
Bitter's work has been criticized by Linkola2 who claims to have dis-
covered by means of very thin microtome sections that there is a genetic
connection between the scales and the underlying thallus, not only with the
hyphae, as in true cephalodia, but with the algae as well, so that these out-
growths should be regarded as isidia.
In the earliest stages, according to Linkola, a small group of algae may
be observed in the cortical tissue of the Peltigera apart from the gonidial
zone and near the upper surface. Gradually a protruding head is formed
which is at first covered over with a brown cortical layer one cell thick. The
head increases and becomes more lobate in form, being attached to the thallus
at the base by a very narrow neck and more loosely at other parts of the
scale. In older scales, the gonidia are entirely separated from those of the
thallus, and a dark-brown cortex several cells in thickness covers over the
top and sides; there is a colourless layer of plectenchyma beneath. At this
advanced stage the scales are almost completely superficial and correspond
with the cephaloidal rather than with the isidial type of formation. The
algae even in the very early stages are distinct from the gonidial zone and
the whole development, if isidial, must be considered as somewhat abnormal.
3. SOREDIA
A. STRUCTURE AND ORIGIN OF SOREDIA
Soredia are minute separable parts of the lichen thallus, and are com-
posed of one or more gonidia which are clasped and surrounded by the
lichen hyphae (Fig. 80). They occur on the sur-
face or margins of the thallus of a fairly large
number of lichens either in a powdery excrescence
or in a pustule-like body comprehensively termed
a "soralium" (Fig. 81). The soralia vary in form Fig. 80. Soredia. a, of Phystia
and dimensions according to the species. Each fuiveruitntaXyl.-b, tiRama-
hnafartnacea Ach. x 600.
individual soredium is capable of developing into
a new plant; it is a form of vegetative reproduction characteristic of lichens.
Acharius3 gave the name " soredia " to the powdery bodies with reference
to their propagating function; he also interpreted the soredium as an "apo-
thecium of the second order." But long before his time they had been
1 Bitter 1904. 2 Linkola 1913. 3 Acharius, 1798, p. xix, and 1810, pp. 8 and 10.
I42 MORPHOLOGY
observed and commented on by succeeding botanists: first by Malpighi1
who judged them to be seeds, he having seen them develop new plants; by
Fig. 81. Vertical section of young soralium of Evernia Jurfuracea
var. soralifera Bitter x 60 (after Bitter).
Micheli2 who however distinguished between the true fruit and those seeds;
and by Linnaeus3 who considered them to be the female organs of the
plant, the apothecia being, as he then thought, the male organs. Hedwig4,
on the other hand, regarded the apothecia as the seed receptacles and the
soredia as male bodies. Sprengel's5 statement that they were "a subtile
germinating powder mixed with delicate hair-like threads which take the
place of seeds" established finally their true function. Wallroth6, who was
the first really to investigate their structure and their relation to the parent
plant, recognized them as of the same type as the "brood-cells" or gonidia;
and as the latter, he found, could become free from the thallus and form a
green layer on trees, walls, etc., in shady situations, so the soredia also
could become free, though for a time they remained attached to the lichen
and were covered by a veil, i.e. by the surrounding hyphal filaments. Koer-
ber7 also gave much careful study to soredia, their nature and function. As
propagating organs he found they were of more importance than spores,
especially in the larger lichens.
According to Schwendener8, the formation of soredia is due to increased
and almost abnormal activity of division in the gonidial cell; the hyphal
filament attached to it also becomes active and sends out branches from the
cell immediately below the point of contact which force their way between
the newly divided gonidia and finally surround them. A soredial "head"
1 Malpighi, 1686, p. 50, pi. 27, fig. 106. 2 Micheli 1729, pp. 73, 74. 3 Linnaeus 1737, p. 325.
4 Hedwig 1798. 6 Sprengel 1807, Letter xxili. 6 Wallroth 1825, I. p. 595.
7 Koerber 1841. 8 Schwendener 1860.
STRUCTURES PECULIAR TO LICHENS
of smaller or larger size is thus gradually built up on the stalk filament or
filaments, and is ultimately detached by the breaking down of the slender
support.
a. SCATTERED SOREDIA. The simplest example of soredial formation
may be seen on the bark of trees or on palings when the green coating of
algal cells is gradually assuming a greyish hue caused by the invasion of
hyphal lichenoid growth. This condition is generally referred to as " leprose "
and has even been classified as a distinct genus, Lepra or Lepraria.
Somewhat similar soredial growth is also associated with many species of
Cladonia, the turfy soil in the neighbourhood of the upright podetia being
often powdered with white granules. Such soredia are especially abundant
in that genus, so much so, that Meyer1, Krabbe2 and others have maintained
that the spores take little part in the propagation of species. The under
side of the primary thallus, but more frequently the upright podetia, are
often covered with a coating of soredia, either finely furfuraceous, or of larger
growth and coarsely granular, the size of the soredia depending on the
number of gonidia enclosed in each " head."
Soredia are only occasionally present on the apothecial margins: the
rather swollen rims in Lobaria scrobiculata are sometimes powdery-grey, and
Bitter3 has observed soredia, or rather soralia, on the apothecial margins of
Parmelia vittata; they are very rare, however, and are probably to be ex-
plained by excess of moisture in the surroundings.
b. ISIDIAL SOREDIA. In a few lichens soredia arise by the breaking
down of the cortex at the tips of the thalline outgrowths termed "isidia."
In Parmelia verruculifera, for instance, where the coralloid isidia grow in
closely packed groups or warts, the upper part of the isidium frequently
becomes soredial. In that lichen the younger parts of the upper cortex
bear hairs or trichomes, and the individual soredia are also adorned with
hairs. The somewhat short warted
isidia of P. subaurifera may become
entirely sorediose, and in P.farinacea
the whole thallus is covered with isidia
transformed into soralia. The trans-
formation is constant and is a distinct
specific character. Bitter3 considers
that it proves that no sharp distinction
exists between isidia and soralia, at
least in their initial stages.
c. SOREDIA AS BUDS. Schwen-
dener4 has described soredia in the
Fig. 82. Usttea barbata Web. Longitudinal
section of filament and base of "soredial"
branch x 40 (after Schwendener).
1 Meyer 1825, p. 170. 2 Krabbe 1891..
Bitter 1901. 4 Schwendener 1860, p. 137.
i44 MORPHOLOGY
genus Usnea which give rise to new branches. Many of the species in that
genus are plentifully sprinkled with the white powdery bodies. A short
way back from the apex of the filament the separate soredia show a tendency
to apical growth and might be regarded as groups of young plants still
attached to the parent branch. One of these developing more quickly
pushes the others aside and by continued growth fills up the soredial
opening in the cortex with a plug of tissue; finally it forms a complete
lateral branch. Schwendener calls them "soredial" branches (Fig. 82) to
distinguish them from the others formed in the course of the normal
development.
B. SORALIA
In lichens of foliose and fruticose structure, and in a few crustaceous
forms, the soredia are massed together into the compact bodies called soralia,
and thus are confined to certain areas of the plant surface. The simpler
soralia arise from the gonidial zone below the cortex by the active division
of some of the algal cells. The hyphae, interlaced with the green cells, are
thin-walled and are, as stated by Wainio1, still in a meristematic condition ;
they are thus able readily to branch and to form new filaments which clasp
the continually multiplying gonidia. This growth is in an upward or out-
ward direction away from the medulla, and strong mechanical pressure is
exerted by the increasing tissue on the overlying cortical layers. Finally
the soredia force their way through to the surface at definite points. The
cortex is thrown back and forms a margin round the soralium, though shreds
of epidermal tissue remain for a time mixed with the powdery granules.
a. FORM AND OCCURRENCE OF SORALIA. The term " soralium " was
first applied only to the highly developed soredial structures considered by
Acharius to be secondary apothecia; it is now employed for any circum-
scribed group of soredia. The soralia vary in size and form and in position,
according to the species on which they occur; these characters are constant
enough to be of considerable diagnostic value. Within the single genus
Parmelia, they are to be found as small round dots sprinkled over the
surface of P. dubia; as elongate furrows irregularly placed on P. sulcata; as
pearly excrescences at or near the margins of P. perlata, and as swollen
tubercles at the tips of the lobes of P.physodes (Fig. 83). Their development
is strongly influenced and furthered by shade and moisture, and, given such
conditions in excess, they may coalesce and cover large patches of the thallus
with a powdery coating, though only in those species that would have borne
soredia in fairly normal conditions.
Soralia of definite form are of rather rare occurrence in crustaceous lichens,
1 Wainio 1897, p. 32. 2 Reinke 1895, p. 380.
STRUCTURES PECULIAR TO LICHENS
145
with the exception of the Pertusariaceae, where they are frequent, and some
species of Lecanora and Placodium. They are known in only two hypo-
Fig. 83. Parmelia physodes Ach. Thallus growing horizontally ; soredia on
the ends of the lobes (S. H. , Photo.}.
Xylographa spilomatica.
Among squamulose thalli they are typical of some Cladoniae, and also of
Lecidea (Psora) ostreata, where they are produced on the upper surface to-
wards the apex of the squamule.
b. POSITION OF SORALIFEROUS LOBES. According to observations'made
by Bitter1, the occurrence of soralia on one lobe or another may depend to
a considerable extent on the orientation of the thallus. He cites the varia-
bility in habit of the familiar lichen, Parmelia physodes and its various forms,
which grow on trees or on soil. In the horizontal thalli there is much less
tendency to soredial formation, and the soredia that arise are generally
confined to branching lobes on the older parts of the thallus.
That type of growth is in marked contrast with the thallus obliged to
take a vertical direction as on a tree. In such a case the lobes, growing
downward from the point of origin, form soralia at their tips at an early
stage (Fig. 84). The lateral lobes, and especially those that lie close to the
substratum, are the next to become soraliate. Similar observations have
been made on the soraliferous lobes of Cetraria pinastri. The cause is
probably due to the greater excess of moisture draining downwards to the
lower parts of the thallus. The lobes that bear the soralia are generally
1 Bitter
:9or.
1 46
MORPHOLOGY
narrower than the others and are very frequently raised from contact with
the substratum. They tend to grow out from the thallus in an upright
Fig. 84. Parmelia physodes Ach. Thallus growing ver-
tically ; soredia chiefly on the lobes directed downwards,
reduced (M. P., Photo.').
direction and then to turn backwards at the tip, so that the opening of the
soralium is directed downwards. Bitter says that the cause of this change
in ^direction is not clear, though possibly on teleological reasoning it is of
advantage that the opening of the soralium should be protected from direct
rainfall. The opening lies midway between the upper and lower cortex, and
the upper tissue in these capitate soralia continues to grow and to form an
arched helmet or hood-covering which serves further to protect the soralium.
Similar soralia are characteristic of Physcia Jiispida (Ph. stellaris subsp.
tenella\ the apical helmet being a specially pronounced feature of that species,
though, as Lesdain1 has pointed out, the hooded structures are primarily
the work of insects. In vertical substrata they occur on the lower lobes of
the plant.
Apical soralia are rare in fruticose lichens, but in an Alpine variety of
1 Lesdain 1910.
STRUCTURES PECULIAR TO LICHENS 147
Ramalina minusctila they are formed at the tips of the fronds and are pro-
tected by an extension of the upper cortical tissues. Another instance occurs
in a Ramalina from New Granada referred by Nylander to R. calicaris var.
farinacea: it presents a striking example of the helmet tip.
c. DEEP-SEATED SORALIA. In the cases already described Schwendener1
and Nilson2 held that the algae gave the first impulse to the formation of
the soredia; but in the Pertusariaceae3, a family of crustaceous lichens, there
has been evolved a type of endogenous soralium which originates with the
medullary hyphae. In these, special hyphae rise from a weft of filaments
situated just above the lowest layer of the thallus at the base of the medulla,
the weft being distinguished from the surrounding tissue by staining blue
with iodine. A loose strand of hyphae staining the usual yellow colour rises
from the surface of the "blue" weft and, traversing the medullary tissue,
surrounds the gonidia on the under side of the gonidial zone. The hyphae
continue to' grow upward, pushing aside both the upper gonidial zone and
the cortex, and carrying with them the algal cells first encountered. When
the summit is reached, there follows a very active growth of both gonidia
and hyphae. Each separate soredium so produced consists finally of five to
ten algal cells surrounded by hyphae and measures 8/i to 13/14 in diameter.
The cortex forms a well-defined wall or margin round the mass of soredia.
A slightly different development is found in Lecanora tartarea, one of
the "crottle" lichens, which has been placed by Darbishire in Pertu-
sariaceae. The hyphae destined to form soredia also start from the weft of
tissue at the base of the thallus, but they simply grow through the gonidial
zone instead of pushing it aside.
In his examination of Pertusariaceae Darbishire found that the apothecia
also originated from a similar deeply seated blue-staining tissue, and he con-
cluded that the soralia represented abortive apothecia and really corresponded
to Acharius's "apothecia of the second order." His conclusion as to the
homology of these two organs is disputed by Bitter4, who considers that
the common point of origin is explained by the equal demand of the hyphae
in both cases for special nutrition, and by the need of mechanical support
at the base to enable the hyphae to reach the surface and to thrust back the
cortex without deviating from their upward course through the tissues.
C. DISPERSAL AND GERMINATION OF SOREDIA
Soredia become free by the breaking down of the hyphal stalks at the
septa or otherwise. They are widely dispersed by wind or water and soon
make their appearance on any suitable exposed soil. Krabbe5 has stated
1 Schwendener 1860. 2 Nilson 1903. 3 Darbishire 1897. 4 Bitter 1901, p. 191.
5 Krabbe 1891.
148 MORPHOLOGY
that, in many cases,- the loosely attached soredia coating some of the
Cladonia podetia are of external origin, carried thither by the air-currents.
Insects too aid in the work of dissemination: Darbishire1 has told us how
he watched small mites and other insects moving about over the soralia of
Pertusaria amara and becoming completely powdered by the white granules.
Darbishire1 also gives an account of his experiments in the culture of
soredia. He sowed them on poplar wood about the beginning of February
in suitable conditions of moisture, etc. Long hyphal threads were at once
produced from the filaments surrounding the gonidia, and gonidia that had
become free were seen to divide repeatedly. Towards the end of August of
the same year a few soredia had increased in size to about 450/11, in diameter,
and were transferred to elm bark. By September they had further increased
to a diameter of 520/1-, and the gonidia showed a tendency towards aggre-
gation. No further differentiation or growth was noted.
More success attended Tobler's2 attempt to cultivate the soredia of
Cladonia sp. He sowed them on soil kept suitably moist in a pot and after
about nine months he obtained fully formed squamules, at first only an iso-
lated one or two, but later a plentiful crop all over the surface of the soil.
Tobler also adds that soredia taken from a Cladonia, that had been kept for
about half a year in a dry room, grew when sown on a damp substratum.
The algae however had suffered more or less from the prolonged desiccation,
and some of them failed to develop.
A suggestion has been made by Bitter3 that a hybrid plant might result
from the intermingling of soredia from the thallus of allied lichens. He
proposed the theory to explain the great similarity between plants of Par-
melia physodes and P. tubulosa growing in close proximity. There is no
proof that such mingling of the fungal elements ever takes place.
D. EVOLUTION OF SOREDIA
Soredia have been compared to the gemmae of the Bryophytes and also
to the slips and cuttings of the higher plants. There is a certain analogy
between all forms of vegetative reproduction, but soredia are peculiar in
that they include two dissimilar organisms. In the lichen kingdom there
has been evolved this new form of propagation in order to secure the con-
tinuance of the composite life, and, in a number of species, it has almost
entirely superseded the somewhat uncertain method of spore germination
inherited from the fungal ancestor, but which leaves more or less to chance
the encounter with the algal symbiont.
From a phylogenetic point of view we should regard the sorediate lichens
as the more highly evolved, and those which have no soredia as phylo-
3 Darbishire 1907. 2 Tobler 191 12, n. 3 Bitter ipoi2.
STRUCTURES PECULIAR TO LICHENS 149
genetically young, though, as Lindau1 has pointed out, soredia are all com-
paratively recent. They probably did not appear until lichens had reached
a more or less advanced stage of development, and, considering the poly-
phyletic origin of lichens, they must have arisen at more than one point,
and probably at first in circumstances where the formation of apothecia was
hindered by prolonged conditions of shade and moisture.
That soredia are ontogenetic in character, and not, as Nilson2 has asserted,
accidental products of excessively moist conditions is further proved by the
non-sorediate character of those species oforustaceous lichens belonging to
Lecanora, Verrucaria, etc. that are frequently immersed in water. Bitter3
found that the soredia occurring on Peltigera spuria were not formed on the
lobes which were more constantly moist, nor at the edges where the cortex
was thinnest: they always emerged on young parts of the thallus a short
way back from the edge.
Bitter3 points out that in extremely unfavourable circumstances — in the
polluted atmosphere near towns, or in persistent shade — lichens, that would
otherwise form a normal thallus, remain in a backward sorediose state. He
considers, however, that many of these formless crusts are autonomous growths
with specific morphological and chemical peculiarities. They hold these
outposts of lichen vegetation and are not found growing in any other localities.
The proof would be to transport them to more favourable conditions, and
watch development.
4. ISIDIA
A. FORM AND STRUCTURE OF ISIDIA
Many lichens are rough and scabrous on the surface, with minute simple
or divided coral-like outgrowths of the same texture as the underlying thallus,
though sometimes they are darker in colour as in Evernia furfuracea. They
always contain gonidia and are covered by a cortex continuous with that
of the thallus.
This very marked condition was considered by Acharius4 as of generic
importance and the genus, Isidium, was established byhim, with the diagnostic
characters: "branchlets produced on the surface, or coralloid, simple and
branched." In the genus were included the more densely isidioid states of
various crustaceous species such as Isidium corallinum and /. Westringii,
both of which are varieties of Pertusariae. Fries5, with his accustomed insight,
recognized them as only growth forms. The genus was however still accepted
in English Floras6 as late as 1833, though we find it dropped by Taylor7 in
the Flora Hibernica a few years later.
1 Lindau 1895. 2 Nilson 1903. 3 Bitter 1904. 4 Acharius 1798, pp. 2, 87.
5 Fries 1825. 6 Hooker 1833. 7 Taylor 1836.
MORPHOLOGY
The development of the isidial outgrowth has been described by Rosen-
dahl1 in several species of Parmelia. In one of them, P. papulosa, which has
a cortical layer one cell thick, the isidium begins as a small swelling or wart
on the upper surface of the thallus. At that stage the cells of the cortex
have already lost their normal arrangement and show irregular division.
They divide still further, as gonidia and hyphae push their way up. The
full-grown isidia in this species are cylindrical or clavate, simple or branched.
They are peculiar in that they bear laterally
here and there minute rhizoids, a development
not recorded in any other isidia. The inner
tissue accords with that of the normal thallus
and there is a clearly marked cortex, gonidial
zone and pith. A somewhat analogous develop-
ment takes place in the isidia of Parmelia pro-
boscidea; in that lichen they are mostly pro-
longed into a dark-coloured cilium.
In Parmelia scortea the cortex is several
cells thick, and the outermost rows are com-
pressed and dead in the older parts of the
thallus; but here also the first appearance of
the isidium is in the form of a minute wart.
The lower layers (4 to 6) of living cortical cells
divide actively; the gonidia also share in the
new growth, and the protuberance thus formed
pushes off the outer dead cortex and emerges
: 60 (after as an isidium (Fig. 85). They are always rather
stouter in form than those of P. papulosa and
may be simple or branched. The gonidia in this case do not form a
definite zone, but are scattered through the pith of the isidium.
Here also should be included the coralloid branching isidia that adorn
the upper surface and margins of the thallus of Umbilicaria pusttilata.
They begin as small tufts of somewhat cylindrical bodies, but they some-
times broaden out to almost leafy expansions with crisp edges. Most
frequently they are situated on the bulging pustules where intercalary
growth is active. Owing to their continued development on these areas,
the tissue becomes slack, and the centre of the isidial tuft may fall out,
leaving a hole in the thallus which becomes still more open by the tension
of thalline expansion. New isidia sprout from the edges of the wound and
the process may again be repeated. It has been asserted that these structures
are only formed on injured parts of the thallus — something like gall-
formations — but Bitter2 has proved that the wound is first occasioned by
the isidial growth weakening the thallus.
1 Rosendahl 1907. 2 Bitter 1899.
Fig. 85. Vertical section of isidia of
Parmelia scortea Ach. A, early
stage; B. later stage,
Rosendahl).
STRUCTURES PECULIAR TO LICHENS 151
B. ORIGIN AND FUNCTION OF ISIDIA
Nilson1 (later Kajanus2) insists that isidia and soredia are both products
of excessive moisture. He argues that lichen species, in the course of their
development, have become adapted to a certain degree of humidity, and, if
the optimum is passed, the new conditions entail a change in the growth
of the plant. The gonidia are stimulated to increased growth, and the
mechanical pressure exerted by the multiplying cells either results in the
emergence of isidial structures where the cortex is unbroken, or, if the
cortex is weaker and easily bursts, in the formation of soralia.
This view can hardly be accepted ; isidia as well as soredia are typical
of certain species and are produced regularly and normally in ordinary
conditions; both of them are often present on the same thallus. It is not
denied, however, that their development in certain instances is furthered
by increased shade or moisture. In Evernia furfuracea isidia are more
freely produced on the older more shaded parts of the thallus. Zopf3 has
described such an instance in Evernia olivetorina (E. furfuracea)^ which
grew in the high Alps on pine trees, and which was much more isidiose
when it grew on the outer ends of the branches, where dew, rain or snow
had more direct influence. He4 quotes other examples occurring in forms
of E. furfuracea which grew on the branches of pines, larches, etc. in a damp
locality in S. Tyrol. The thalli hung in great abundance on each side of
the branches, and were invariably more isidiose near the tips, because
evidently the water or snow trickled down and was retained longer there
than at the base.
Bitter5 has given a striking instance of shade influence in Umbilicaria.
He found that some boulders on which the lichen grew freely had become
covered over with fallen pine needles. The result was at first an enormous
increase of the coralline isidia, though finally the lichen was killed by the
want of light.
Isidia are primarily of service to the plant in increasing the assimilating
surface. Occasionally they grow out into new thallus lobes. The more
slender are easily rubbed off, and, when scattered, become efficient organs
of propagation. This view of their function is emphasized by Bitter who
points out that both in Evernia furfuracea and in Umbilicaria pustulata
other organs of reproduction are rare or absent. Zopf3 found new plants
of Evernia furfuracea beginning to grow on the trunk of a tree lower
down than an old isidiose specimen. They had developed from isidia which
had been detached and washed down by rain.
1 Nilson 1903. a Kajanus (Nilson) 1911. 3 Zopf 1903. 4 Zopf 19052.
5 Bitter 1899.
1 52 MORPHOLOGY
VI. HYMENOLICHENS
A. SUPPOSED AFFINITY WITH OTHER PLANTS
Lichens in which the fungal elements belong to the Hymenomycetes
are confined to three tropical genera. They are associated with blue-green
algae and are most nearly related to the Thelephoraceae among fungi. The
spores are borne, as in that family, on basidia.
The best known Hymenolichen, Cora Pavonia (Fig. 86), was discovered
by Swartz1 during his travels in the W. Indies (1785-87) growing on trees
Fig. 86. Cora Pavonia Fr. (after Mattirolo).
in the mountains of Jamaica, and the new plant was recorded by him as
Ulva montana. Gmelin2 also included it in Ulva in close association with
Ulva (Padind) Pavonia, but that classification was shortly after disputed by
Woodward3 who thought its affinity was more nearly with the fungi and
suggested that it should be made the type of a new genus near to Boletus
(Polystictus} versicolor. Fries4 in due time made the new genus Cora, though
he included it among algae; finally N.ylander5 established the lichenoid
character of the thallus and transferred it to the Lecanorei.
It was made the subject of more exact investigation by Mattirolo6 who
1 Swartz 1788. 2 Gmelin 1791. 3 Woodward 1797. 4 Fries 1825.
5 Nylander 1855. 6 Mattirolo 1881.
HYMENOLICHENS
153
recognized its affinity with Thelephora, a genus of Hymenomycetes. Later
Johow1 went to the West Indies and studied the Hymenolichens in their
native home. The genera and species described by Johow have been
reduced to Cora and Dictyonema ; a new genus Corella has since been added
by Wainio2.
Johow found that Cora grew on the mountains usually from 1000 to
2000 ft. above sea-level. As it requires for its
development a cool damp climate with strong
though indirect illumination, it is found
neither1 in sunny situations nor in the depths
of dark woods. It grows most freely in diffuse
light, on the lower trunks and branches of
trees in open situations, but high up on the
stem where the vegetation is more dense.
It stands out from the tree like a small thin
bracket fungus, one specimen placed above
another, with a dimidiate growth similar to
that of Polystictus versicolor. Both surfaces
are marked by concentric zones which give
it an appearance somewhat like Padina Pa-
vonia. These zones indicate unequal inter-
calary growth both above and below. The
whole plant is blue-green when wet, greyish-
white when dry, and of a thin membranaceous
consistency.
B. STRUCTURE OF THALLUS
There is no proper cortex in any of the
genera, but in Cora there is a fastigiate
branching of the hyphae in parallel lines
towards the upper surface; just at the outside
they turn and lie in a horizontal direction,
and, as the branching becomes more profuse,
a rather compact cover is formed. The goni-
dia, which consist of blue-green Chroococcus
cells, lie at the base of the upward branches
and they are surrounded with thin-walled short-celled hyphae closely inter-
woven into a kind of cellular tissue. The medulla of loose hyphae passes
over to the lower cortex, also of more or less loose filaments. The outermost
cells of the latter very frequently grow out into short jagged or crenate
processes (Fig. 87).
1 Johow 1884. 2 Wainio 1890.
Fig. 87. Cora Pavonia Fr. Vertical
section of thallus. a, upper cortex ;
b, gonidial layer; t, medulla and
lower cortex of crenate cells; d, tuft
of fertile hyphae. x 160. e, basidia
and spores x 1000 (after Johow).
154 MORPHOLOGY
In Corella, the mature lichen is squamulose or consists of small lobes; in
Dictyonema there is a rather flat dimidiate expansion; in both the alga is
Scyt0nema,thetrichomes of which largely retain their form and are surrounded
by parallel growths of branching hyphae. The whole tissue is loose and
spongy.
Corella spreads over soil on a white hypothallus without rhizinae. In
the other two genera which live on soil, or more frequently on trees, there
is a rather extensive formation of hold-fast tissue. When the dimidiate
thallus grows on a rough bark, rhizoidal strands of hyphae travel over it
and penetrate between the cracks; if the bark is smooth, there is a more
continuous weft of hyphae. In both cases a spongy cushion of filamentous
tissue develops at the base of the lichen between the tree and the bracket
thallus. There is also in both genera an encrusting form which Johow
regarded as representing a distinct genus Laudatea, but which Moller found
to be merely a growth stage. Moller1 judged from that and from other
characteristics that the same fungus enters into the composition of both
Cora and Dictyonema and that only the algal constituents are different.
C. SPORIFEROUS TISSUES
As in Hymenomycetes, the spores of Hymenolichens are exogenous,
and are borne at the tips of basidia which in these lichens are produced on
the under surface of the thallus. In Cora the fertile filaments may form a
continuous series of basidia over the surface, but generally they grow out
in separate though crowded tufts. As these tufts broaden outwards, they
tend to unite at the free edges, and may finally present a continuous
hymenial layer. Each basidium bears four sterigmata and spores (Fig. 87 e}\
paraphyses exactly similar to the basidia are abundant in the hymenium.
In Dictyonema the hymenium is less regular, but otherwise it resembles that
of Cora. No hymenium has as yet been observed in Corella; it includes, so
far as known, one species, C. brasiliensis , which spreads over soil or rocks.
1 Moller 1893.
CHAPTER IV
REPRODUCTION
I. REPRODUCTION BY ASCOSPORES
A. HISTORICAL SURVEY
THE earliest observations as to the propagation of lichens were made by
Malpighi1 who recorded the presence of soredia on the lichen plant and
noted their function as reproductive bodies. He was followed after a con-
siderable interval by Tournefort2 who placed lichens in a class apart owing
to the form of the fruit: "This fruit," he writes, "is a species of bason or
cup which seems to take the place of seeds in these kinds of plants." He
figures Ramalina fraxinea and Physcia ciliaris, both well fruited specimens,
and he represents the " minute dust " contained in the fruits as subrotund
in form. The spores of Physcia ciliaris are of a large size and dark in colour
and were undoubtedly seen by Tournefort. Morison3, in his History of
Oxford Plants, published very shortly after, dismissed Tournefort's "seeds"
as being too minute to be of any practical interest.
Micheli4, with truer scientific insight, made the fruiting organs the subject
of special study. He decided that the apothecia were floral receptacles,
receptacula florum, and that the spores were the " flowers " of the lichen. He
has figured them in a vertical series in situ, in a section of the disc of Solorina
saccata6 and also in a species of Pertusaria5, in both of which plants the
ascospores are unusually large. He adds that he had not so far seen the
" semina."
Micheli's views were not shared by his immediate successors. Dillenius6
scarcely believed that the spores could be " flowers " and, in any case, he
concluded that they were too minute to be of any real significance in the
life of the plant.
Linnaeus7, and after him Necker8, Scopoli9 and others describe the apo-
thecia as the male, the soredia as the female organs of lichens. These old
time botanists worked with very low powers of magnification, and easily went
astray in the interpretation of imperfectly seen phenomena.
Koelreuter10, a Professor of Natural History in Carlsruhe, who pub-
lished a work on The discovered Secret of Cryptogams, next hazarded the
opinion that the seeds of lichens originated from the substance of the pith,
and that the overlying cortical layer supplied the fertilizing sap. Hoffmann11
1 Malpighi 1686. 2 Tournefort 1694. 3 Morison 1699. 4 Micheli 1729.
3 Micheli, Pis. 52 and 56. B Dillenius 1741. 7 Linnaeus 1737. 8 Necker 1771, p. 257.
" Scopoli 1772. 10 Koelreuter 1777. u Hoffmann 1784.
156 REPRODUCTION
devoted a great deal of attention to lichen fructification and he also thought
that fertilization must take place within the tissue of the lichens. He
regarded the soredia as the true seeds, while allowing that a second series
of seeds might be contained in the scutellae (apothecia).
A distinct advance was made by Hedwig1, a Professor of Botany in
Leipzig, towards the end of the eighteenth century. He followed Tourne-
fort in selecting Physcia ciliaris for research, and in that plant he describes
and figures not only the apothecia with the dark-coloured septate spores,
but also the pycnidia or spermogonia which he regarded as male organs.
The soredia, typically represented and figured by him on Parmelia physodes,
he judged to be " male flowers of a different type."
Acharius2 did not add much to the knowledge of reproduction in lichens,
though he takes ample note of the various fruiting structures for which he
invented the terms apothecia, perithecia and soredia. Under still another
term gongyli he included not only spores, but the spore guttulae as well as
the gonidia or cells forming the soredia.
Hornschuch3 of Greifswald described the propagation of the lower lichens
as being solely by means of a germinating " powder " ; the more highly or-
ganized forms were provided with receptacles or apothecia containing spores
which he considered as analogous to flowers rather than to fruits. The im-
portant contributions to Lichenology of Wallroth4 and Meyer5 close this
period of uncertainty: the former deals almost exclusively with the form
and character of the vegetative thallus and the function of the " reproductive
gonidia." Meyer, a less prolix writer, very clearly states that the method of
reproduction is twofold: by spores produced in fruits, or by the germinating
granules of the soredia.
B. FORMS OF REPRODUCTIVE ORGANS
From the time of Tournefort, considerable attention had been given to
the various forms of scutellae, tuberculae, etc., as characters of diagnostic
importance. Sprengel6 grouped these bodies finally into nine different types
with appropriate names which have now been mostly superseded by the
comprehensive terms, apothecia and perithecia. A general classification on
the lines of fruit development was established by Luyken7, who, following
Persoon's8 classification of fungi, and thus recognizing their affinity, summed
up all known lichens as Gymnocarpeae with open fruits, and Angiocarpeae
with closed fruits.
a. APOTHECIA. As in discomycetous fungi, the lichen apothecium is
in the form of an open concave or convex disc, but generally of rather small
1 Hedwig 1784. 2 Acharius 1810. 3 Hornschuch 1821. 4 Wallroth 1825.
6 Meyer 1825. 6 Sprengel 1804. ? Luyken 1809. « Persoon 1801.
REPRODUCTIVE ORGANS
157
size, rarely more than I cm. in diameter (Fig. 88); there is no development
in lichen fruits equal to the cup-like ascomata of the larger Pezizae. In
Fig. 88. Lecanora subfusca Ach. A, thallus and apothecia x 3 ;
B, vertical section of apothecium. a, hymenium; b, hypo-
thecium; c, thalline margin or amphithecium ; of, gonidia.
x 60 (after Reinke).
most cases the lichen apothecium retains its vitality as a spore-bearing
organ for a considerable period, sometimes for several years, and it is
strengthened and protected by one or more external margins of sterile
tissue. Immediately surrounding the fertile disc there is a compact wall of
interwoven hyphae. In some of the shorter-lived soft fruits, as in Biatora,
this hyphal margin may be thin, and may gradually be pushed aside as the
disc develops and becomes convex, but generally it forms a prominent rim
round the disc and may be tough or even horny, and often hard and car-
bonaceous. This wall, which is present, to some extent, in nearly all lichens,
is described as the "proper margin." A second "thalline margin" containing
gonidia is present in many genera1: it is a structure peculiar to the lichen
apothecium and forms the amphithecium.
At the base of the apothecium there is a weft of light- or dark-coloured
hyphae called the hypothecium> which is continued up and round the sides
as the parathecium merging into the "proper margin." It forms the lining
of a cup-shaped hollow which is filled by the paraphyses, which are upright
closely packed thread-like hyphae, and by the'spore-containing asci or thecae,
these together constituting the thecium or hymenium. The paraphyses
are very numerous as compared with the asci ; they are simple or branched,
1 See also p. 166.
I58 REPRODUCTION
frequently septate, especially towards the apex, and mostly slender, varying in
width from 1-4/4, though Hue describes paraphyses in Aspicilia atroviolacea
as 8-12/u, thick. They may be thread-like throughout their length, or they
may widen towards the tips which are not infrequently coloured. Small
apical cells are often abstricted and lie loose on the epithecium, giving at
times a pruinose or powdered character to the disc. In some genera there
is a profuse branching of the paraphyses to form a dense protective epithecium
over the surface of the hymenium as in the genus Arthonia.
The apothecia may be sessile and closely adnate to or even sunk in the
thallus, or they may be shortly stalked. The thalline margin shares generally
the characters of the thallus; the disc is mostly of a firm consistency and is
light or dark in colour according to genus or species ; most frequently it is
some shade of brown. Marginate apothecia, i.e. those with a thalline margin,
are often referred to as "lecanorine," that being a distinctive feature of
the genus Lecanora. In the immarginate series, with a proper margin
only, the texture may be soft and waxy, termed "biatorine" as in Biatora;
or hard and carbonaceous as in the genus Lecidea, and is then described as
"lecideine."
In the subseries Graphidineae, the apothecium has the form of a very
flat, roundish or irregular body entirely without
a margin, called an "ardella" as in Arthonia;
or more generally it is an elongate narrow
"lirella," in which the disc is a mere slit
"> between two dark-coloured proper margins.
The hypothecium of the lirellae is sometimes
much reduced and in that case the hymenium
rests directly on a thin layer above the thalline
tissue as in Graphis elegans (Fig. 89).
Lichen fruits require abundant light, and
plants growing in the shade are mostly sterile.
B Naturally, therefore, the reproductive bodies
Fig. 89. Graphis elegans Ach. A,. , f , , , .,,
thallus and lirellae; B, vertical are lo be found on the best illuminated parts
section of furrowed lirella. x ca. of the thallus. In crustaceous and in most
foliose forms, they are variously situated on
the upper surface, wherever the light falls most directly. In the genera
Nephromium and Nephromopsis, on the contrary, they arise on the under sur-
face, though at the extreme margin, but as the fertile lobes eventually turn
upwards the apothecia as they mature become fully exposed. In shrubby
or fruticose lichens their position is lateral on the fronds, or more frequently
at or near the tips.
b. PERITHECIA. The small closed perithecium is characteristic of the
Pyrenocarpeae which correspond with the Pyrenomycetes among fungi. It
REPRODUCTIVE ORGANS 159
is partially or entirely immersed in the thallus or in the substratum on
which the lichen grows, and is either a globose or conical body wholly
surrounded by a hyphal wall, when it is de-
scribed as "entire" (Fig. 90), or it is somewhat
hemispherical in form and the outer wall is
developed only on the upper exposed part:
a type of perithecium usually designated by
the term "dimidiate." As the perithecial wall
gives sufficient protection to the asci, the
paraphyses are of less importance and are
frequently very sparingly produced, or they
may even be dissolved and used up at an early
stage. The thallus of the Pyrenocarpeae is
often extremelyreduced, and the perithecia are F'g- 9°- A. e^'^ perithecium of
J l Poiina ohvacea A. L.Sm. x ca.4o;
then the only Visible portion of the lichen. B, dimidiate perithecium of Acro-
A few lichens among Graphidineae and
Pyrenocarpeae grow in a united body generally looked on as a stroma;
but Wainio1 has demonstrated that as the fruiting bodies give rise to this
structure by agglomeration — by the cohesion of their margins — it can only
be regarded as a pseudostroma. Two British genera of Pyrenolichens,
Mycoporum and Mycoporellum, exhibit this pseudo-stromatoid formation.
C. DEVELOPMENT OF REPRODUCTIVE ORGANS
As most known lichens belong to the Ascolichens, the study of develop-
ment has been concentrated on that group. Tulasne2 was the first to make
a microscopic study of lichen tissues and he described in considerable detail
the general anatomical structure of apothecia and perithecia. Later, Fuisting:i
traced the development of a number of perithecia through their different
stages of growth, but his most interesting discovery was made in Lecidea
fumosa, a crustaceous Discolichen with an areolate thallus in which the
apothecia are seated on the fungal hyphae between the areolae. In the very
early stages represented by a complex of slender hyphae, he observed an
unbranched septate filament with short cuboid cells, richer in contents than
the surrounding filaments and somewhat similar to the structure known to
mycologists as "Woronin's hypha," which is an ascogonial structure. These
specialized cells disappeared as the hymenium began to form.
1 Wainio 1890. • Tulasne 1852. 3 Fuisting 1868.
i6o
REPRODUCTION
i. DISCOLICHENS
a. CARPOGONIA OF GELATINOUS LICHENS. Stahl's1 work on various
Collemaceae followed on the same lines as that of Fuisting. The first species
selected by him for examination, Collema (Leptogium) microphyllum, is a
gelatinous lichen which grows on old trunks of poplars and willows. It has
a small olive-green thallus which, in autumn, is crowded with apothecia;
the spermogones or pycnidia appear as minute reddish points on the edge of
the thallus. Within the thallus, and midway between the upper and lower
surface, there arises, as a branch from a vegetative hypha, a many-septate
filament coiled in spiral form at the base, with the free end growing upwards
and projecting a short distance above the surface and occasionally forked
(Fig. 91). The tip-cell is slightly swollen and covered with a mucilaginous
.6
Fig. 91. Collema microphyllum Ach. Vertical section of
thallus. a, carpogonium ; b, trichogyne. x 350 (after
Stahl).
coat continuous with the mucilage of the thallus. The whole structure,
characterized by the larger size and by the richer contents of its cells, was
regarded by Stahl as a carpogonium, the coiled base representing the asco-
gonium, the upright hypha functioning as the receptive organ or trichogyne,
comparable to that of the Florideae. The spermatia, which mature at this
early stage of carpogonial development, are expelled from a neighbouring
spermogonium on the addition of moisture and easily reach the protruding
trichogyne. They adhere to the mucilaginous wall of the end-cell, and, in
two or three instances, Stahl found that copulation had taken place. As the
affixed spermatium was empty, he concluded that the contents had passed
over into the trichogyne, and that the nucleus had travelled down to the
ascogonium. Certain degenerative changes that followed seemed to confirm
1 Stahl 1877.
REPRODUCTION IN DISCOLICHENS
161
the view that there had been fertilization: the cells of the trichogynej had
lost their turgidity and at the same time the cross-walls had swollen con-
siderably and stood out like knots in the
hypha (Fig. 92). The ascogonial cells had
also increased not only in size but in number
by intercalary division, so that the spiral
arrangement became obscured. Ascogenous
hyphae arose from the ascogonial cells, and
asci cut off by a basal septum were finally
formed from these hyphae. Lateral branches
from below the septum also formed asci.
Stahl's observations were repeated and
extended by Borzi1 on another of the Colle-
maceae, Collema nigrescens. In that plant the
foliaceous thallus is of thin texture and has
a distinct cellular cortex. The carpogonia
were found at varying depths near to the cor-
tical region; the ascogonium, of two and a
half to four spirals, consisted often to fifteen
cells with very thin walls, the trichogyne of
five to ten cells, the terminal cell projecting
above the thallus. Borzi also found spermatia
fused with the tip-cell.
A further important contribution was made by Baur" in his study of
Collema crispum*. There occur in nature two forms of this lichen, one of
them crowded with apothecia and spermogonia, the other with a more
luxuriant thallus, but with few apothecia and no spermogonia. On the latter
almost sterile form Baur found in spring and again in autumn immense
numbers of carpogonia — about one thousand in a medium sized thallus —
which nearly all gradually lost the characteristics of reproductive organs,
and, anastomising with other hyphae, became part of the vegetative system.
In a few cases in which, presumably, a spermatium had fused with a tricho-
gyne, very large apothecia had developed.
As the first-mentioned form was always crowded with apothecia in every
stage of development, as well as with carpogonia and spermogonia, it seemed
natural to conclude that the difference was entirely due to the presence or
absence of spermatia in sufficient numbers to ensure fertilization. The
period during which copulation is possible passes very rapidly, though
subsequent development is slow, occupying about half-a-year from the time
of fertilization to the formation of the first ascus.
1 Borzi 1878. 2 Baur 1898.
3 Fiinfstiick (1902) suggests that the lichen worked at by Baur is Collema cheileuni Ach.
Fig. 92. Collema microphyllum Ach.
Carpogonium and trichogyne after
copulation x 500 (after Stahl).
I62 REPRODUCTION
Baur confirmed Stahl's observations on the various developmental
changes. In several instances he found a spermatium fused with the tricho-
gyne, though he could not see continuity between the lumina of the fusing
cells. After copulation with the spermatium the trichogyne nucleus, which
occupied the lower third of the terminal cell, had disappeared, and the
plasma contents had acquired a deeper tint; the other trichogyne cells,
which had also lost their nuclei, were partly collapsed owing to the pressure
of the surrounding tissue, and openings were plainly visible through some
of the swollen septa, especially of the lower cells. In addition the ascogonial
cells, all of which were uninucleate, had increased in number by intercalary
division. Plasma connections were opened from cell to cell, but only in the
primary septa, the later formed cell-membranes being continuous. Asco-
genous hyphae had branched out from the ascogonium as a series of
uninucleate cell rows from which the asci finally arose.
Baur's interpretation was that the first cell of the ascogonium reached
by the male nucleus after its passage down through the cells of the trichogyne
represented the egg-cell, and that, after fusion, the resultant nucleus divided,
and a daughter nucleus passed on to the other auxiliary-cells. No male
nucleus nor fusion of nuclei was, however, observed by him, and his deduc-
tions rest on conjecture.
Krabbe1 and after him Maule2 found in Collema pulposum reproductive
organs similar to those described by Stahl, but in a recent paper on an
American form of that species a peculiar condition has been described
by Freda Bachmann3. She4 found that the spermatia originated, not in
spermogonia, but as groups of cells budded off from vegetative hyphae
within the tissue of the lichen and occupying the same position as spermo-
gonia, i.e. the region close below the upper surface. The trichogynes, therefore,
never emerged into the open, but travelled towards these internal spermatia,
and fusion with them was effected. The changes that afterwards took place
in the carpogonial cells were similar to those that had been recognized by
Stahl and Baur as consequent on fertilization.
Additional cytological details have been published in a subsequent
paper5: after fusion with the spermatium the terminal cell of the trichogyne
collapsed, its nucleus became disintegrated and the cross septa of the lower
trichogyne cells became perforated, these perforations being closed again at
a later stage by a gelatinous plug. The nuclear history is more doubtful :
the disappearance of the nuclei from the spermatium and from the terminal
cell of the trichogyne was noted; two nuclei were seen to be present in the
penultimate cell, and these the author interpreted as division products of the
1 Krabbe 1883. 2 Maule 1891. 3 F. Bachmann 1912.
4 This species of Collema has been described as Collemodes Bachmanniantim by Bruce Fink 1918.
5 F. Bachmann 1913.
REPRODUCTION IN DISCOLICHENS 163
original cell nucleus. In the same cell, lying close against the lower septum
and partly within the opening, there was a mass of chromatin material which
might be the male nucleus migrating downwards. The next point of interest
was observed in the twelfth cell from the tip in which there were two nuclei,
a larger and a smaller, the latter judged to be the male cell, the small size
being due to probable division of the spermatium nucleus either before or
after leaving the spermatium. It is stated however that the spermatium
was always uninucleate. Meanwhile the cells of the ascogonium had
increased in size, the perforations of the septa between the cells became
more evident, and their nuclei persisted. In one cell at this stage two nuclei
were present, one of the two presumably a male nucleus; no fusion of nuclei
was observed in the ascogonial cells. Later the cross walls between the
cells were seen to have disappeared more completely and migration of
nuclei had taken place, so that some of the cells appeared to be empty while
others were multinucleate. Considerable multiplication of the nuclei occurred
before the ascogenous hyphae were formed : twelve nuclei were observed in
a part of the ascogonium which was just beginning to give off a branch.
Several branches might arise from one cell, and their cells were either uni-
or binucleate, the nuclei being larger than those of the vegetative hyphae.
The formation of the asci was not distinctly seen, but young binucleate
asci were not uncommon. The fusion of the two nuclei was followed by
the enlargement of the ascus and the subsequent nuclear division for spore
formation. In the first heterotypic division twelve chromosomes, double the
number observed in the vegetative nucleus, were counted on the equatorial
plate. In the third division they were reduced to the normal number of six,
from which F. Bachmann concludes that a twofold fusion must have taken
place — in the ascogonium and again in the ascus.
Spiral or coiled ascogonia were observed by Wainio1 in the gelatinous
crustaceous genus Pyrenopsis, but the trichogynes did not reach the surface.
In Lichina-, a maritime gelatinous lichen where the carpogonia occur in
groups, trichogynes have not been demonstrated.
A peculiarity of some gelatinous lichens noted by Stahl3 and others in
species of Pkysma, and by Forssell4 in Pyrenopsis and Psorotichia, is the
development of carpogonia at the base of, and within the perithecial walls
of old spermogonia. No special significance is however attached to this
phenomenon, and it is interesting to note that a similar growth was observed
by Zukal5 in a pyrenomycetous fungus, Pleospora collematum, a harmless
parasite on PJiysma compactum and other Collemaceae. The structures in-
vaded were true pycnidia of the fungus as the minute spores were seen to
germinate. A " Woronin's hypha " at the base of several of these pycnidia
developed asci which pushed up among the spent sporophores.
1 Wainio i. 1890. 2 Wolff 1905. 3 Stahl 1877. 4 Forssell 1885'-. a Zukal 1887, p. 42.
II 2
1 64
REPRODUCTION
b. CARPOGONIA or NON-GELATINOUS LICHENS. The soft loose tissue
of the gelatinous lichens is more favourable for the minute study of apo-
thecial development than the closely interwoven hyphae of non-gelatinous
forms, but Borzi1 had already extended the study to species of Parmelia,
Anaptychia, Sticta, Ricasolia and Lecanora, and in all of them he succeeded
in establishing the presence of ascogonia and trichogynes. After him a
constant succession of students have worked at the problem of reproduction
in lichens.
Lindau2 published results of the examination of a considerable series of
lichens. In Anaptychia (Physcia) ciliaris, Physcia stellaris, Ph. pulverulenta,
Ramalina fraxinea, Placodium (Lecanora) saxicolum, Lecanora subfusca and
Lecidea enteroleuca he demonstrated the presence of ascogonia with tricho-
gynes. In Parmelia tiliacea and in Xanthoria parietina he found ascogonia
but failed to see trichogynes. In none of the species examined by him did
he observe any fusion between the trichogyne and a spermatium.
In Anaptychia ciliaris he was able to pick out extremely early stages by
staining with a solution of chlor-zinc-iodine. Maule3 applied the same test
to Physcia pulverulenta, but found that to be successful the reaction required
some time. Certain cells of the hyphae — mostly
terminal cells — in the lower area of the gonidial
zone and even occasionally in the pith (according
to Lindau) coloured a deep brown, while the
ordinary thalline hyphae were tinted yellow.
He assumed that these were initial ascogonial
cells on account of the richer plasma contents,
and also because of the somewhat larger size of
the cells. In the same region of the thallus
young carpogonia were observed as outgrowths
from vegetative hyphae, though the trichogynes
had not yet reached the surface.
At a more advanced stage the carpogonia
were seen to be embedded in the gonidial zone
and occurred in groups. The cells of the asco-
gonium, easily recognized by the darker stain,
were short and stout, measuring about 6-8 /j, in
length and 4*4 p, in width. They were arranged
in somewhat indistinct spirals; but the crowding
of the groups resulted in a confused intermingling of the various generative
filaments. The trichogynes composed of longer narrower cells rose above
the hyphae of the cortex; they also stained a deep brown and the projecting
cell was always thin-walled. Lindau frequently observed spermatia very
1 Borzi 1878. 2 Lindau 1888. 3 Maule 1891.
Fig. 93. Pkyscia pulverulenta Nyl.
Vertical section of thallus and
carpogonium before fertilization.
a, outer cortex; b, inner cortex;
c, gonidial 1 ayer ; d, medulla,
x ca. 540 (after Darbishire).
REPRODUCTION IN DISCOLICHENS
165
firmly attached to the trichogyne cell but without any plasma connection
between the two. The changes in the trichogyne described by Stahl and
Baur in Collemaceae were not seen in Anaptychia\ the peculiar swelling of
the septa seems to be a phenomenon confined to gelatinous lichens. During
the trichogyne stage in this lichen the vegetative hyphae from the medulla
grow up and surround the young carpogonia, and, at the same time, very
slender hyphae begin to branch upwards to form the paraphyses. Darbi-
shire's1 examination of Physcia pulvernlenta demonstrated the presence of
the coiled ascogonium and the trichogyne in that species (Fig. 93).
Baur1 has also given the results of an examination of Anaptychia. He
frequently observed copulation between the spermatium and the tip- of the
trichogyne, but not any passage of nucleus or contents. After copulation
the ascogonial cells increased in size and became irregular in form, and
open communication was established between them (Fig. 94). There was
no increase in their number by intercalary division as in Collema. After
Fig. 94. Physcia {Anaptychia) ciliaris DC. Vertical
section of developing ascogonium. a, paraphyses ;
b, ascogonial hyphae; c, ascogonial cells, x 800 (after
Baur).
producing ascogenous hyphae the cells were seen to have lost their contents
and then to have gradually disappeared. The fertile hyphae, which now
took a blue colouration with chlor-zinc-iodine, gradually spread out and
1 Darbishire 1900. 2 Baur 1904.
1 66 REPRODUCTION
formed a wide-stretching hymenium. Several carpogonia took part in the
formation of one apothecium.
The tissue below the ascogonium meanwhile developed vigorously, form-
ing a weft of encircling hyphae, while the upper branches grew vertically to-
wards the cortex. Gonidia in contact with the developing fruit also increased,
and, with the hyphae, formed the exciple or thalline margin. The growth
upward of the paraphyses raises the overlying cortex which in Anaptychia
is " fibrous "; it gradually dies off and allows the exposure of the disc, though
small shreds of dead tissue are frequently left. In species such as those of
Xanthoria where the cortex is of vertical cell-rows, the apothecial hyphae
simply push their way between the cell-rows and so through to the open.
Baur found the development of the apothecium somewhat similar in the
crustaceous corticolous lichen, Lecanora subfusca. After a long period of
sterile growth, spermogonia appeared in great abundance, and, a little later,
carpogonia in groups of five to ten ; the trichogynes emerged very slightly
above the cortex; they were now branched. The ascogonia were frequently
a confused clump of cells, though sometimes they showed distinct spirals.
The surrounding hyphae had taken a vertical direction towards the cortex
at a still earlier stage, and the brown tips were visible on the exterior before
the trichogynes were formed. The whole growth was extremely slow.
In Physcia stellaris the carpogonia occurred in groups also, though Lin-
dau1 thinks that, unlike Anaptychia (Physcia} ciliaris, only one is left to form
the fruit. Only one, according to Darbishire2, entered into the apothecium
in the allied species, Physcia pulverulenta. In the latter plasma connections
were visible from cell to cell of the trichogyne, and, after copulation with
the spermatium, the ascogonial cells increased in size — though not in number
— and the plasma connections between them became so wide that the asco-
gonium had the appearance of an almost continuous multinucleate cell or
coenogamete3. As in gelatinous lichens, each of these cells gave rise to
ascogenous hyphae.
c. GENERAL SUMMARY. The main features of development described
above recur in most of the species that have been examined.
(i) The carpogonia arise in a complex of hyphae situated on the under
side of, or immediately below the gonidial zone. Usually they vary in number
from five to twenty for each apothecium, though as many as seventy-two
have been computed for Icmadophila ericetorum*, and Wainio5 describes
them as so numerous in Coccocarpia pellita var., that their trichogynes covered
some of the young apothecia with a hairy pile perceptible with a hand lens,
though at the same time other apothecia on the same specimens were
bsolutely smooth.
1 Lindau 1888. 2 Darbishire 1900. 3 See also p. 180. 4 Nienburg 1908. 5 Wainio i. 1890.
REPRODUCTION IN DISCOLICHENS 167
(2) The trichogynes, when present, travel up through the gonidial and
cortical regions of the thallus; Darbishire1 observes that in Physcia pulveru-
lenta, they may diverge to the side to secure an easier course between the
groups of algae. They emerge above the surface to a distance of about 1 5/i
or less; after an interval they collapse and disappear. Their cells, which are
longer and narrower than those of the ascogonium, are uninucleate and vary
in number according to species or to individual lichens. Baur2 thought that
possibly several trichogynes in succession might arise from one ascogonium.
(3) How many carpogonia share in the development of the apothecium
is still a debated question. In Collema only one is
functional. Baur3 was unable to decide if one or
more were fertilized in Parmelia acetabulum, and
in Usnea Nienburg4 found that, out of several, one
alone survived (Fig. 95). But in Anaptychia ciliaris
and in Lecanora subfusca Baur3 considers it proved
that several share in the formation of the apothecium.
In this connection it is interesting to note that,
according to Harper5 and others, several ascogonia
enter into one Pyronema fruit.
(4) The ascogonial cells, before and after ferti-
lization, are distinguished from the surrounding F'g; 95- Vsneabarbata\jl&>.
° ~ Carpogonium with tricho-
hyphae by a reaction to various stains, which is dif- gynex uoo (after Nien-
ferent from that of the vegetative hyphae, and also burs)-
by the shortness and width of their cells. The whole of the apothecial primor-
dium is generally recognizable by the clear shining appearance of the cells.
(5) *The ascogonia do not always form a distinct spiral; frequently they
lie in irregular groups. Each cell is uninucleate and may ultimately produce
ascogenous hyphae, though in Anaptychia Baur3 noted that some of the
cells failed to develop.
(6) The hyphae from the ascogonial cells spread out in a complex layer
at the base of the hymenium, and send up branches which form the asci,
either, as in most Ascomycetes, from the penultimate cell of the fertile branch,
or from the last cell, as in Sphyridium (Baeomyces rufus)* and in Baeomyces
roseus. The same variation has been observed in fungi — in a species of
Peziza6, in which it is the end-cell of the branch that becomes the mother-
cell of the ascus; but this deviation from the normal is evidently of rare
occurrence either in lichens or fungi.
d. HYPOTHECIUM AND PARAPHYSES. The hypothecium is the layer of
hyphae that subtends the hymenium, and is formed from the complex of
1 Darbishire 1900. 2 Baur 1901. 3 Baur 1904. 4 Nienburg 1908.
5 Harper 1900. 6 Guilliermond 1904, p. .60.
1 68 REPRODUCTION
hyphae that envelope the first stages of the carpogonia. It is vegetative in
origin and distinct from the generative system.
In lichens belonging to the Collemaceae, the paraphyses rise from the
branching of the carpogonial stalk-cell immediately below the ascogonium1,
but have no plasma connection with it. They are thus comparable in origin
with the paraphyses of many Discomycetes.
In several genera in which the algal constituents are blue-green, such as
Stictina, Pannaria, Nephroma, Ricasolia and Peltigera, Sturgis2 found that
reproduction was apogamous and also that asci and paraphyses originated
from the same cell-system : a tuft of paraphyses arose from the basal cell
of the ascus, or an ascus from the basal cell of a paraphysis. These results
are at variance with those of most other workers, but the figures drawn by
Sturgis seem to be clear and convincing.
Again in Usnea barbata, as described by Nienburg3., the ascogonial cells,
after the disappearance of the trichogyne, branch profusely not only up-
wards towards the cortex but also downwards and to each side The upward
branches give rise normally to the asci, the lower branches produce the sub-
hymenium and later the paraphyses, and the two systems are thus genetically
connected, though they remain distinct from each other, and asci are never
formed from the lower cells.
In most heteromerous lichens, however, the origin of the paraphyses 'is
exclusively vegetative: they arise as branches from the primordial complex
that forms the covering hyphae of the ascogonium both above and below.
Schwendener4 had already pointed out the difference in origin between the
two constituents of the hymenium in one of his earlier studies on the de-
velopment of the apothecium, and this view has been repeatedly confirmed
by recent workers, except by Wahlberg5 who has insisted that they rise from
the same cells as the asci, a statement disproved by Baur6. The paraphyses
originate not only from the covering hyphae, but from vegetative cells in
close connection with the primordium. In this mode of development, lichens
diverge from fungi, but even in these a vegetative origin for the paraphyses
has been pointed out in Lachnea scutellata? where they branch from the
hyphae lying round the ascogonium.
There is no general rule for the order of development. In Lecanora sub-
fusca Baur6 found that vertical filaments had reached the surface by the time
the trichogyne was formed, and their pointed brown tips gave a ready clue
to the position of the carpogonia. In Lecidea enteroleuca* they show their
characteristic form and arrangement before there is any trace of ascus
formation. In Solorina* they are well formed before the ascogenous
hyphae appear. In other lichens such as Placodium saxicolum*, Peltigera
1 Baur 1899. « Sturgis 1890. 3 Nienburg 1908. 4 Schwendener 1864. 5 Wahlberg 1902.
6 Baur 1904. 7 Brown 1911. 8 Moreau 1916. 9 Lindau 1888.
REPRODUCTION IN DISCOLICHENS 169
rufescens1 and P. malacea* the two systems — paraphyses and ascogonium —
grow simultaneously, though in P. horizontalis the ascogonium has dis-
appeared by the time the paraphyses are formed. In the genus Nephroma,
in Physcia stellaris and in Xanthorina parietina the paraphyses are also late
in making their appearance.
In most instances, the paraphyses push their way up between the cortical
cells which gradually become absorbed, or they may stop short of the sur-
face as in Nephromium tomentosum*. The overlying layer of cortical cells in
that case dies off gradually and in time disappears. Such an apothecium is
said to be " at first veiled." Later formed paraphyses at the circumference
of the apothecium form the parathecium, which is thus continuous with the
hypothecium.
e. VARIATIONS IN APOTHECIAL DEVELOPMENT. Lichens are among
the least stereotyped of plants : instances of variation have been noted in
several genera.
aa. PARMELIAE. A somewhat complicated course of development has
been traced by Baur2 in Parmelia acetabulum. In that lichen the group of
three to six carpogonia do not lie free in
the gonidial tissue, but originate nearer
the surface (Fig. 96) and are surrounded
from the first by a tissue connected with,
and resembling the tissue of the cortex.
In the several ascogonia, there are more
cells and more spirals than in Collema
or in Physcia, and all of them are some-
what confusedly intertwined. The tri-
chogynes are composed of three to five
cells and project 10 to I5ytt above the
surface. When further development be-
gins, the ascogonial cells branch out and
form a primary darker layer or hypo- x 55° (after Baur).
thecium above which extends the subhymenium, a light-coloured band of
loosely woven hyphae. Branches from the ascogonial hyphae at a later stage
push their way up through this tissue and form above it a second plexus of
hyphae — the base of the hymenium. Baur considers this a very advanced
type of apothecium; he found it also present in Parmelia saxatilis, though,
in that species, the further growth of the first ascogonial layer was more
rapid and the secondary plexus and hymenium were formed earlier in the
life of the apothecium. He has also stated that a similar development occurs
in other genera such as Usnea, though Nienburg's3 work scarcely confirms
that view.
1 Funfsttick 1884. * Baur 1904. 3 Nienburg 1908.
i ;o
REPRODUCTION
In the brown Parmeliae, Rosendahl1 found the same series of apothecial
tissues, but he interprets the course of development somewhat differently:
the basal dark layer or hypothecium he found to be of purely vegetative
origin ; above it extended the lighter-coloured subhymenium ; the ascogenous
hyphae were present only in the second layer of dark tissue immediately
under the hymenium.
In most lichens the primordium of the apothecium arises towards the
lower side of the gonidial zone, the hyphae of which retain the meristematic
character. In Parmeliae, as was noted by Lindau2 in P. tiliacea, and by
Baur3 and Rosendahl1 in other species, the carpogonial groups are formed
above the gonidial zone, either immediately below the cortex as in P. glabra-
tula, or in a swelling of the cortex itself as in P. aspidota, in which species
the external enlargement is visible by the time the trichogynes reach the
surface. In P. glabra, with a development entirely similar to that of P. as-
pidota, no trichogynes were seen at any stage. The position of the primordium
close under the cortex is also a feature of Ramalina fraxinea as described
by G. Wolff4. The trichogynes in that species are fairly numerous.
A further peculiarity in Parmelia acetabulum attracted Baur's3 attention.
Carpogonia with trichogynes are extremely numerous in that species as are
the spermogonia, the open pores of which are to be found everywhere between
the trichogynes, and yet fertilization can occur but rarely, as disintegrating
carpogonia are abundant and very few apothecia are formed. Baur makes
the suggestion that possibly cross-fertilization may be necessary, or that the
spermatia, in this instance, do not fertilize and that development must
therefore be apogamous, in which case the small number of fruits formed is
due to some unknown cause. Fiinfstuck5 thought that degeneration of the
carpogonia had not gone so far, but that a few had acquired the power to
develop apogamously. In Parmelia saxatilis only a small percentage of
carpogonia attain to apothecia, although spermogonia are abundant and in
close proximity, but in that species, unlike P. acetabulum, a large number
reach the earlier stages of fruit formation ; the more vigorous apothecia seem
to inhibit the growth of those that lag behind.
bb. PERTUSARIAE. In Pertusaria, the apothecial primordium is situated
immediately below the gonidial zone; the cells have a somewhat larger
lumen and thinner walls than those of the vegetative hyphae. In the asco-
gonium there are more cells than in Parmelia acetabulum] the trichogynes
are short-lived, and several carpogonia probably enter into the formation of
each apothecium ; the paraphyses arise from the covering hyphae. So far the
course of development presents nothing unusual. The peculiar pertusarian
feature as described by Krabbe6, and after him by Baur7, does not appear
1 Rosendahl 1907. 2 Lindau 1888. 3 Baur 1904. 4 Wolff 1905.
5 Funfstiick 1902. 6 Krabbe 1882. 7 Baur 1901.
REPRODUCTION IN DISCOLICHENS
171
till a later stage. By continual growth in thickness of the overlying
thallus, the apothecia gradually become submerged and tend to degenerate;
meanwhile, however, a branch from the ascogonial hyphae at the base of
the hymenium pushes up along one side and forms a secondary ascogonial
cell-plexus over the top of the first-formed disc. A new apothecium thus
arises and remains sporiferous until it also comes to lie in too deep a position,
when the process is repeated. Sometimes the regenerating hypha travels to
the right or left away from the original apothecium, it may be to a distance
of 2 mm. or according to Fiinfstiick even considerably farther. Funfstiick1 has
gathered indeed from his own investigations that such cases of regeneration
are by no means rare : ascogenous hyphae, several centimetres long, destined
to give rise to new apothecia are not unusual, and their activity can be recog-
Fig. 97. Rhizocarpon petrae um Massal. Concentrically arranged apothecia, reduced
(J. Adams, Photo.}.
nized macroscopically by the linear arrangement of the apothecia in such
lichens as RJiizocarpon (petraeuwi) concentricum (Fig. 97).
In Variolaria, a genus closely allied to or generally included in Per-
tusaria, Darbishire2 has described the primordial tissue as taking rise almost
at the base of the crustaceous thallus: strands of delicate hyphae, staining
1 Ftinfstiick 1902. 2 Darbishire 1897.
172
REPRODUCTION
blue with iodine, mount upwards from that region through the medulla and
gonidial zone1. The ascogonium does not appear till the surface is almost
reached.
cc. GRAPHIDEAE. Several members of the Graphidaceae were studied
by G. Wolff2: she demonstrated the presence of carpogonia with emerging
trichogynes in Graphis elegans, a species which is distinguished by the deeply
furrowed margins of the lirellae (Fig. 89). Before the carpogonia appeared
it was possible to distinguish the cushion-like primordial tissue of the apo-
thecium in the thallus which is almost wholly immersed in the periderm
layers of the bark on which it grows. The trichogynes were very sparingly
septate, and a rather large nucleus occupied a position near the tip of the
terminal cell. The dark carbonaceous outer wall makes its appearance in
this species at an early stage of development along the sides of the lirellae,
but never below, as there is always a layer of living cells at the base. After
the first-formed hymenium is exhausted, these basal cells develop a new
apothecium with a new carbonaceous wall that pushes back the first-formed,
leaving a cleft between the old and the new. This regenerating process,
somewhat analogous to the formation of new apothecia in Pertusaria, may
be repeated in Graphis elegans as many as five times, the traces of the older
discs being clearly seen in the channelled margins of the lirellae.
dd. CLADONIAE. The chief points of interest in the Cladoniae are the
position of the apothecial primordia and the function of the podetium,
which are discussed later3. Krabbe4 deter-
mined not only the endogenous origin of
the podetium but also the appearance of
fertile cells in the primordium (Fig. 98).
Both frequently take rise where a crack
occurs in the cortex of the primary squa-
mule, the cells of the gonidial tissue being
especially active at these somewhat ex-
posed places. The fertile hyphae elongate
and branch within the stalk of the de-
veloping podetium, sometimes very early,
or not until there is a pause in growth,
when carpogonia are formed. As a rule
trichogynes emerge in great numbers2, generally close to, or rather below,
the spermogonia. In Cl. pyxidata* the carpogonia are characterized by the
large diameter of the cells— three to five times that of the vegetative hyphae.
Though most of the trichogynes disappear at an early stage, some of them
may persist for a considerable period. As development proceeds, the vege-
tative hyphae interspersed among the ascogonial cells grow upwards, slender
1 See also p. 147. » Wolff 1905. 3 See Chap. VII. « Krabbe 1883 and 1891. s Baur 1904.
— d
Fig. 98. Cladonia decorticata Spreng. Ver-
tical section of squamule and primordium
of podetium. a, developing podetium;
b, probably fertile hyphae; c, cortical
tissue ; </, gonidial cells, j x 600 (after
Krabbe).
REPRODUCTION IN DISCOLICHENS
173
branches push up between them and gradually a compact sheath of para-
physes is built up. The ascogenous hyphae meanwhile spread radially at
the base of the paraphyses and the asci begin to form. The apothecia may
be further enlarged by intercalary growth, and this vigorous development
of vegetative tissue immediately underneath raises the whole fruit structure
well above the surface level.
Sattler1 in his paper on Cladoniae* cites as an argument in favour of
fertilization the relative positions of carpogonia and spermogonia on the
podetia. The carpogonia with their emerging trichogynes being situated
rather below the spermogonia. Both organs, he states, have been demon-
strated in eleven species; he himself observed them in the primordial podetia
of Cladonia botrytes and of Cl. Floerkeana.
2. PYRENOLICHENS
a. DEVELOPMENT OF THE PERITHECIUM. It is to Fuisting3 that we
owe the first account of development in the lichen perithecium. Though
he failed to see the earlier stages (in Verrucaria Dufourii), he recognized
the primordial complex of hyphae in the gonidial zone of the thallus, from
which originated a vertical strand of hyphae destined to form the tubular
neck of the perithecium. Growth in the lower part is in abeyance for
a time, and it is only after the neck is formed, and the fruiting body is
widened by the ingrowth of external hyphae, that the asci begin to branch
up from the tissue at the base.
b. FORMATION OF CARPOGONIA. Stahl4 had indicated that not only
in gymnocarpous but also in angiocarpous »
lichens, it would be found that carpo-
gonia were formed as in Collema. Baur3
justified this surmise, and demonstrated the
presence of ascogonia in groups of three to
eight, with trichogynes that reached the
surface in Endocarpon {Dermatocarpon) mi-
niatum (Fig. 99). It is one of the few
foliaceous Pyrenolichens, and the leathery
thallus is attached to the substratum by a
central point, thus allowing in the thallus
not only peripheral but also intercalary
growth, the latter specially active round the
point of basal attachment; carpogonia may
be found in any region where the tissue is Fig. 99. Dermatocarpon miniatum
, 3 . „. Th. Fr. Vertical section of thallus
newly formed, and at any season. I he upper
cortex is composed of short-celled thick-
1 Sattler 1914. ~ See Chap. VII. 3 Fuisting 18
and carpogonial group x 600 (after
Baur).
4 Stahl 1877.
Baur 1904.
i74 REPRODUCTION
walled hyphae, with branching vertical to the surface, and so closely packed
that there is an appearance of plectenchyma ; the medullary hyphae are
also thick-walled but with longer cells. The carpogonia of this species
arise as a branch from the vegetative hyphae and are without special covering
hyphae, so frequent a feature in other lichens. The trichogynes bore their
nay through the compact cortex and rise well above the surface. After they
have disappeared — presumably after fertilization — the vegetative hyphae
round and between the ascogonia become active and travel upwards slightly
converging to a central point. The asci begin to grow out from the asco-
genous hyphae of the base before the vertical filaments have quite pierced
the cortex.
Pyrenula nitida has also been studied by Baur1. It is a very common
species on smooth bark, with a thin crustaceous thallus immersed among
the outer periderm cells. Unlike most other lichens, it forms carpogonia
in spring only, from February to April. A primordial coil of hyphae lies at
the base of the gonidial layer, and, before there is any appearance of carpo-
gonia, a thick strand of hyphae is seen to be directed upwards, so that a
definite form and direction is given to the perithecium at a very early stage.
The ascogonial cells which are differentiated are extremely small, and, like
those of all other species examined, are uninucleate. There are five to ten
carpogonia in each primordium ; the trichogynes grow up through the hyphal
strand and emerge 5-10 /* above the surface. After their disappearance, a
weft of ascogenous tissue is formed at the base, and, at the same time, the
surrounding vegetative tissue takes part in the building up of a plecten-
chymatous wall of minute dark-coloured cells. Further development is
rapid and occupies probably only a few weeks.
In many of the pyrenocarpous lichens — Verrucariae and others — the
walls of the paraphyses dissolve in mucilage as the spores become mature,
a character associated with spore ejection and dispersal. In some genera
and species, as in Pyrenula, they remain intact.
D. APOGAMOUS REPRODUCTION
Though fertilization by an externally produced male nucleus has not
been definitely proved there is probability that, in some instances, the fruit
may be the product of sexual fusion. There are however a number of genera
and species in which the development is apogamous so far as any external
copulation is possible and the sporiferous tissue seems to be a purely vege-
tative product up to the stage of ascus formation.
In Phlyctis agelaea Krabbe2 found abundant apothecia developing nor-
mally and not accompanied by spermogonia; in Phialopsis rubra studied
1 Baur 1901. 2 Krabbe 1882.
APOGAMOUS REPRODUCTION 175
also by him the primordium arises among the cells of the periderm on which
the lichen grows, and he failed to find any trace of a sexual act. In his
elaborate study of Gloeolichens Forssell1 established the presence of carpo-
gonia with trichogynes in two species — Pyrenopsis phaeococca and P. impolita,
but without any appearance of fertilization; in all the others examined, the
origin of the fruit was vegetative. Wainio2 records a similar observation in
a species of Pyrenopsis in which there was formed a spiral ascogonium and
a triehogyne, but the latter never reached the surface.
Neubner3 claimed to have proved a vegetative origin for the asci in the
Caliciaceae; but he overlooked the presence of spermogonia and his conclu-
sions are doubtful.
Fiinfstuck4 found apogamousdevelopment inPeltigera(\r\c\\idmgPeltidea)
and his results have never been disputed. The ascogonial cells are surrounded
at an early stage by a weft of vegetative hyphae. No trichogynes are formed
and spermogonia are absent or very rare in the genus, though pycnidia with
macrospores occur occasionally.
Some recent work by Darbishire5 on the genus supplies additional details.
The apothecial primordium always originated near the growing margin of
the thallus, where certain medullary hyphae were seen to swell up and stain
more deeply than others. These at first were uninucleate, but the nuclei
increased by division as the cells became larger, and in time there was
formed a mass of closely interwoven cells full of cytoplasm. " No coiled
carpogonia can be made out, but these darkly stained cells form part of a
connected system of branching hyphae coming from the medulla further
back." Long unbranched multiseptate hyphae — evidently functionless tri-
chogynes— travelled towards the cortex but gradually died off. Certain of
the larger cells — the " ascogonia " — grew out as ascogenous hyphae into
which the nuclei passed in pairs and finally gave rise to the asci.
These results tally well with those obtained by M. and Mme Moreau6,
though they make no mention of any triehogyne. They found that the
terminal cells of the ascogenous hyphae were transformed into asci, and the
two nuclei in these cells fused — the only fusion that took place. In Nephro-
mtum, one of the same family, the case for apogamy is not so clear; but
Fiinfstuck found no trichogynes, and though spermogonia were present on
the thallus, they were always somewhat imperfectly developed.
Sturgis7 supplemented these results in his study of other lichens con-
taining blue-green algae. In species of Heppia, Pannarta, Hydrothyria,
Stictina and Ricasolia, he failed to find any evidence of fertilization by
spermatia.
Solorina, also a member of Peltigeraceae, was added to the list of
1 Forssell 1885. 2 Wainio 1890, p. x. 3 Neubner 1893. 4 Fiinfstuck 1884.
5 Darbishire 1913. 6 Moreau 1915. 7 Sturgis 1890.
i76 REPRODUCTION
apogamous genera by Metzger1 and his work was confirmed and amplified
by Baur2: certain hyphae of the gonidial zone branch out into larger asco-
gonial cells which increase by active intercalary growth, by division and by
branching, and so gradually give rise to the ascogenous hyphae and finally
to the asci. Baur looked on this and other similar formations as instances
of degeneration from the normal carpogonial type of development. Moreau3
(Fernand and Mme) have also examined Solorina with much the same
results: the paraphyses rise first from cells that have been produced by the
gonidial hyphae; later, ascogenous hyphae are formed and spread horizontally
at the base of the paraphyses, finally giving rise at their tips to the asci.
Metzger1 had further discovered that spermogonia were absent and tricho-
gynes undeveloped in two very different crustaceous lichens, Acarospora
(Lecanora) glaucocarpa and Verrucaria calciseda, the latter a pyrenocarpous
species and, as the name implies, found only on limestone.
Krabbe4 had noted the absence of any fertilization process in Gyrophora
vellea. At a later date, Gyrophora cylindrica was made the subject of exact
research by Lindau5. In that species the spermogonia (or pycnidia) are
situated on the outer edge of the thallus lobes; a few millimetres nearer the
centre appear the primordia of the apothecia, at first without any external
indication of their presence. The initial coil which arises on the lower side
of the gonidial zone consists of thickly wefted hyphae with short cells, slightly
thicker than those of the thallus. It was difficult to establish their connec-
tion with the underlying medullary hyphae since these very soon change to a
brown plectenchyma. From about the middle of the ascogonial coil there
rises a bundle of parallel stoutish hyphae which traverse the gonidial zone
and the cortex and slightly overtop the surface. They are genetically con-
nected at the base with the more or less spirally coiled hyphae, and are similar
to the trichogynes described in other lichens. Lindau did not find that they
had any sexual significance, and ascribed to them the mechanical function of
terebrators or borers. The correctness of his deductions has been disputed by
various workers: Baur2 looks on these "trichogynes" as the first paraphyses.
The reproductive organs in Stereocaulon were examined by G. Wolff6, and
the absence of trichogynes was proved, though spermogonia were not wanting.
She also failed to find any evidence of fertilization in Xanthoria parietina,
in which lichen the ascogenous hyphae branch out from an ascogonium that
does not form a trichogyne.
Rosendahl7, as already stated, could find no trichogynes in Parmelia
glabra. In Parmelia obscurata, on the contrary, Bitter8 found that carpogonia
with trichogynes were abundant and spermogonia very rare. In other species
of the subgenus, Hypogymnia, he has pointed out that apothecia are either
1 Metzger 1903. 2 Baur 1904. 3 Moreau 1916. 4 Krabbe 1882. 5 Lindau 1899.
6 Wolff 1905. 7 Rosendahl 1907. 8 Bitter i9oi2.
DISCUSSION OF LICHEN REPRODUCTION 177
absent or occur but seldom, while spermogonia are numerous, and he concludes
that the spermatia must function as spores or conidia. Baur1 however does
not accept that conclusion; he suggests as probable that the male organs
persist longer in a functionless condition than do the apothecia.
Still more recently Nienburg2 has described the ascogonium of Baeo-
myces sp. and also of Sphyridium byssoides (Baeomyces rufus) as reduced
and probably degenerate. His results do not disprove those obtained by
Krabbe3 on the same lichen {Sphyridium fungiforme). The apothecia are
terminal on short stalks in that species. When the stalk is about '5 mm. in
height, sections through the tip show numerous primordia (12 to 15) ranged
below the outer cortex, though only one, or at most three, develop further.
These ascogonial groups are connected with each other by delicate filaments,
and Nienburg concluded that they were secondary products from a primary
group lower down in the tissue. Spirals were occasionally seen in what he
considered to be the secondary ascogonia, but usually the fertile cells lie in
loose uncoiled masses; isolated hyphae were observed to travel upwards
from these cells, but they never emerged above the surface.
Usnea macrocarpa — if Schulte's4 work may be accepted — is also apo-
gamous, though in Usnea barbata Nienburg2 found trichogynes (Fig. 95)
and the various developments that are taken as evidence of fertilization.
Wainio5 had demonstrated emergent straight trichogynes in Usnea laevis
but without any sign of fertilization.
E. DISCUSSION OF LICHEN REPRODUCTION
In Ascolichens fertilization by the fusion of nuclei in the ascogonium
is still a debated question. The female organ or carpogonium, as outlined
above, comprises a twisted or spirally coiled multiseptate hypha, with a
terminal branch regarded as a trichogyne which is also multiseptate, and
through which the nucleus of the spermatium must travel to reach the
female cell. It is instructive to compare the lichen carpogonium with that of
other plants.
a. THE TRICHOGYNE. In the Florideae, or red seaweeds, in which the
trichogyne was first described, that organ is merely a hair-like prolongation
of the egg-cell and acts as a receptive tube. It contains granular proto-
plasm but no nucleus and terminates in a shiny tip covered with mucilage.
The spermatium, unlike that of lichens, is a naked cell, and being non-motile
is conveyed by water to the tip of the trichogyne to which it adheres; the
intervening wall then breaks down and the male nucleus passes over. After
this process of fertilization a plug of mucilage cuts off the trichogyne, and
it withers away.
1 Baur 1904. - Xienburg 1908. 3 Krabbe 1882. 4 Schulte 1904. 5 Wainio 1890.
S. L. 12
i78 REPRODUCTION
In Coleochaete, a genus of small fresh- water green algae, a trichogyne is
also present in some of the species: it is again a prolongation of an oogonial
cell.
In the Ascomycetes, certain cells or cell-processes associated with the
ascogonium have been described as trichogynes or receptive cells. In one
of the simpler types, Monascus1, the " trichogyne" is a cell cut off from the
ascogonial cell. When fertilization takes place, the wall between the two
cells breaks down to allow the passage of the male nucleus, but closes up
when the process is effected. In Pyronema confluens* it is represented by a
process from the ascogonial cell which fuses directly with the male cell. A
more elaborate "trichogyne " has been evolved in Lachnea stercorea*, another
Discomycete: in that fungus it takes the form of a 3~5-septate hypha with
a longer terminal cell; it rises from some part of the ascogonial cell but has
no connection with any process of fertilization, so that the greater elaboration
of form is in this case concomitant with loss of function.
In the Laboulbeniaceae, a numerous and very peculiar series of Asco-
mycetes that live on insects, there are, in nearly all of the reproductive bodies,
a carpogonial cell, a trichophoric cell and a trichogyne. The last-named
organ is in some genera a simple continuous cell, in others it is septate and
branched, occasionally it is absent4. The male cells are spermatia of two
kinds, exogenous or endogenous, and the plants are monoecious or dioecious.
Laboulbeniaceae have no connection with lichens. Faull5, a recent worker
on the group, states that though he observed spermatia attached to the tri-
chogynes, he was not able to demonstrate copulation (possibly owing to
over-staining), nor could he trace any migration of the nucleus through the
trichophoric cell down to the carpogonial cell. In two species of Labotdbenia
that he examined there were no antheridia, and the egg-cell acquired its
second nucleus from the neighbouring trichophoric cell. These conjugate
nuclei divided simultaneously and the two daughter nuclei passed on to the
ascus and fused, as in other Ascomycetes, to form the definitive nucleus.
Convincing evidence as to the importance of the trichogyne in fungi was
supposed, until lately, to be afforded by the presence and functional activity
of that organ associated with spermogonia in a few Pyrenomycetes — in
Poronia, Gnomonia and Polystigma. Poronia was examined by M. Dawson6
who found that a trichogyne-like filament distinct from the vegetative hyphae
rose from the neighbourhood of the ascogonial cells. It took an upward
course towards the exterior, but there was no indication that it was ever
receptive. In Gnomonia erythrostoma and in Polystigma rubrum spermogonia
with spermatia — presumably male organs — are produced in abundanceshortly
before the ascosporous fruit is developed. The spermatia in both cases exhibit
1 Schikorra 1909. 2 Harper 1900. 3 Fraser 1907. 4 Thaxter 1912.
5 Faull 1911. 6 Dawson 1900.
DISCUSSION OF LICHEN REPRODUCTION 179
the characters of male cells, i.e. very little cytoplasm and a comparatively large
nucleus that occupies most of the cell cavity, along with complete incapacity
to germinate. Brooks1 found in Gnomonia that tufts of the so-called tricho-
gynes originated near the ascogonial cells, but they were " mere continuations
of ordinary vegetative hyphae belonging to the coil." They are septate and
reach the surface, and the tip-cell is longer than the others as in the lichen
trichogyne.
A somewhat similar arrangement is present in Polystigma, in which
Blackman and Welsford2 have proved that the filaments, considered as tri-
chogynes by previous workers, are merely vegetative hyphae. A trichogyne-
like structure is also present in Capnodium, one of the more primitive Pyreno-
mycetes, but it has no sexual significance.
Lindau3 in his paper on Gyrophora suggested that the trichogyne in
lichens acted as a " terebrator " or boring apparatus, of service to the deeply
immersed carpogonium in enabling it to reach the surface. Van Tieghem4
explained its presence on physiological grounds as necessary for respiration,
a view also favoured by Zukal5, while Wainio6 and Steiner7 see in it only an
" end-hypha," the vigorous growth of which is due to its connection with
the well-nourished cells of the ascogonium.
Lindau's view has been rejected by succeeding writers: as has been
already stated, it is the paraphyses that usually open the way outward for
the apothecium. Van Tieghem's theory has been considered more worthy
of attention and both Dawson and Brooks incline to think that the projecting
filaments described above may perform some service in respiration, even
though primarily they may have functioned as sexual receptive organs.
There is very little support to be drawn from fungi for the theory that
the presence of a trichogyne necessarily entails fertilization by spermatia.
Lichens in this connection must be judged as a class apart.
It has perhaps been too lightly assumed that the trichogyne in lichens
indicates some relationship with the Florideae8. Such a view might be possible
if we could regard lichens and Florideae as derived from some common
remote ancestor, though even then the difference in spore production — in
one case exogenous, and in the other in asci and therefore endogenous —
would be a strong argument against their affinity. But all the evidence goes
to prove that lichens are late derivatives of fungi and have originated from
them at different points. Fungi are interposed between lichens and any
other ancestors, and inherited characters must have been transmitted through
them. F. Bachmann's suggestion9 that Collema pulposum should be regarded
" as a link between aquatic red algae and terrestrial ascomycetes such as
Pyronema and the mildews " cannot therefore be accepted. It seems more
1 Brooks 1910. 2 Blackman and Welsford 1912. 3 Lindau 1899. * Van Tieghem 1891.
5 Zukal 1895. 6 Wainio 1890. 7 Steiner 1901. 8 See also Chap. VII. 9 F. Bachmann 1913.
i8o REPRODUCTION
probable that the lichen trichogyne is a new structure evolved in response
to some physiological requirement — either sexual or metabolic — of the deeply
embedded fruit primordium.
b. THE ASCOGONIUM. In fungi there is usually one cell forming the
ascogonium, a coenogamete, which after fertilization produces ascogenous
hyphae. There are exceptions, such as Cutting1 found in Ascophanus carneus,
in which it is composed of several cells in open contact by the formation of
wide secondary pores in the cell-walls. In lichens the ascogonium is divided
into a varying number of uninucleate cells. Darbishire2 (in Physcia) and
Baur3 (in Anaptychia) have described an opening between the different cells,
after presumed fertilization, that might perhaps constitute a coenogamete.
Ascogenous hyphae arise from all, or nearly all the cells, whether fertilized by
spermatia or not, and asci continue to be formed over a long period of time.
There may even be regeneration of the entire fruiting body as described in
Graphis elegans and in Pertusaria, apparently without renewed fertilization.
Spermogonia (or pycnidia) and the ascosporous fruits generally grow on
the same thallus, though not unfrequently only one of the two kinds is
present. As the spermogonia appear first, while the apothecia or perithecia
are still in the initial stages, that sequence of development seems to add
support to the view that their function is primarily sexual; but it is equally
valid as a proof of their pycnidial nature since the corresponding bodies in
fungi precede the more perfect ascosporous fruits in the life-cycle.
The differences in fertility between the two kinds of thallus in Collema
crispum may be recalled4. Baur considered that development of the carpo-
gonia was dependant on the presence of spermatia: a strong argument for
the necessity of fertilization by these. The conditions in Parmelia acetabulum,
also recorded by Baur, lend themselves less easily to any conclusion. On
the thallus of that species the spermogonia and carpogonia present are out
of all proportion to the very few apothecia that are ultimately formed.
Though Baur suggested that cross-fertilization might be necessary, he admits
that the development may be vegetative and so uninfluenced by the presence
or absence of spermatia.
It is the very frequent occurrence of the trichogyne as an integral part of
the carpogonium that constitutes the strongest argument for fertilization by
spermatia. There is a possibility that such an organ may have been uni-
versal at one time both in fungi and in lichens, and that it has mostly
degenerated through loss of function in the former, as it has disappeared in
many instances in lichens. Again, there is but a scanty and vestigial record
of spermogonia in Ascomycetes. They may have died out, or they may
have developed into the asexual pycnidia which are associated with so many
species. If we take that view we may trace the same tendency in lichens, as
1 Cutting 1909. 2 Darbishire 1900. 3 Baur I9<>4> 4 See p. l6l.
DISCUSSION OF LICHEN REPRODUCTION 181
for instance in the capacity of various spermatia to germinate, though in
lichen spermogonia there has been apparently less change from the more
primitive condition. It is also possible that some process of nuclear fusion,
or more probably of conjugation, takes place in the ascogonial cells, and
that in the latter case the only fusion, as in some (or most) fungi, is between
the two nuclei in the ascus.
If it be conceded that fully developed carpogonia with emergent tricho-
gynes, accompanied by spermogonia and spermatia, represent fertilization,
or the probability of fertilization, then the process may be assumed to take
place in a fairly large and widely distributed series of lichens. Copulation
between the spermatium and the trichogyne has been seen by Stahl1, Baur2
and by F. Bachmann3 in Collema. In Physcia pulverulenta Darbishire4 could
not prove copulation in the earlier stages, but he found what he took to be
the remains of emptied spermatia adhering to the tips of old trichogynes.
Changes in the trichogyne following on presumed copulation have been
demonstrated by several workers in the Collemaceae, and open communi-
cation as a result of fertilization between the cells of the ascogonium has
been described in two species. This coenocytic condition of the ascogonium
(or archicarp), considered by Darbishire and others as an evidence of fer-
tilization, has been demonstrated by Fitzpatrick8 in the fungus Rhizina
undulata. The walls between the cells of the archicarp in that Ascomycete
became more or less open, so that the ascogenous hyphae growing from the
central cells were able easily to draw nutrition from the whole coenocyte,
but no process of fertilization in Rhizina preceded the breaking down of the
septa and no fusion of nuclei was observed until the stage of ascus. formation.
The real distinction between fertile and vegetative hyphae lies, according
to Harper6, in the relative size of the nuclei. F. Bachmann speaks of one
large nucleus in the spermatium of Collema pulposum which would indicate
sexual function. There is however very little nuclear history of lichens known
at any stage until the beginning of ascus formation, when fusion of two nuclei
certainly take place as in fungi to form the definitive nucleus of the ascus.
The whole matter may be summed up in Fiinfstiick's7 statement that:
" though research has proved as very probable that fertilization takes place,
it is an undoubted fact that no one has observed any such process."
F. FINAL STAGES OF APOTHECIAL DEVELOPMENT
The emergence of the lichen apothecium from the thallus, and the form
it takes, are of special interest, as, though it is essentially fungal in structure,
it is subject to various modifications entailed by symbiosis.
1 Stahl 1877. 2 Baur 1898. 3 F. Bachmann 1912 and 1913. 4 Darbishire 1900.
5 Fitzpatrick 1918. 6 Harper 1900. 7 Fiinfstttck 1902.
Ig2 REPRODUCTION
a. OPEN OR CLOSED APOTHECIA. Schwendener1 drew attention to two
types of apothecia directly influenced by the thallus: those that are closed
at first and only open gradually, and those which are, as he says, open from
the first. The former occur in genera and species in which the thallus has a
stoutish cortex, as, for instance, in Lobaria where the young fructification
has all the appearance of an opening perithecium. The open apothecia
(primitus apertd) are found in non-corticate lichens, in which case the pioneer
paraphyses arrive at the surface easily and without any converging growth.
Similar apothecia are borne directly on the hypothallus at the periphery, or
between the thalline areolae, and they are also characteristic of thin or slender
thalli as in Coenogonium.
In both types of apothecium, the paraphyses .pierce the cortex (Fig. 100)
and secure the emergence of the developing ascomata.
Fig. 100. Physcia ciliaris DC. Vertical section of apothe-
cium still covered by the cortex, a, paraphyses ; b, hypo-
thecium ; c, gonidia of thallus and amphithecium. x 150
(after Baur).
b. EMERGENCE OF THE ASCOCARP. Hue2 has taken up this subject in
recent years and has described the process by which the vegetative hyphae
surrounding the fruit primordium, excited to active growth by contact with
the generative system, take part in the later stages of fruit formation. The
primordium generally occupies a position near to, or just within, the upper
medulla, and the hyphae in contact with it soon begin to branch freely in a
vertical direction, surrounding the developing fruit and carrying it upwards
generally to a superficial position. The different methods of the final emer-
gence give two very distinct types of mature apothecium: the lecideine in
which the gonidial zone takes no part in the upward growth, and the leca-
norine into which the gonidia enter as an integral part.
In the lecideine series (Fig. 101) the encircling hyphae from the upper
medulla rise as a compact column through the gonidial zone to the surface
of the thallus ; they then spread radially before curving up to form the outer
1 Schwendener 1864. 2 Hue 1906.
DEVELOPMENT OF APOTHECIA
183
wall or " proper margin " round the spore-bearing disc. The branching of
the hyphae is fastigiate with compact
shorter branches at the exterior. In
such an apothecium gonidia are ab-
sent both below thehypothecium and
in the margins.
In lecanorine development the
ascending hyphae from the medulla,
in some cases, carry with them algal
cells which multiply and spread as a second gonidial layer under the hypo-
thecium (Fig. 102). These hyphae may also spread in a radial direction
while still within the thallus and give rise to an " immersed " apothecium
which is lecanorine as it encloses gonidia within its special tissues, for
example, in Acarospora and Solorina. But in most cases the lecanorine fruit
is superficial and not unfrequently it is raised on a short stalk (Usnea, etc.);
Fig. 10 1. Lecidea parasema Ach. Vertical section
of thallus and apothecium with proper margin
only x ca. 50.
Fig. 102. Lecanora far/area Ach. Vertical section of apo-
thecium. a, hymenium ; b, proper margin or parathecium ;
c, thalline margin or amphithecium. x 30 (after Reinke).
both the primary gonidial zone of the thallus and the outer cortex are asso-
ciated with the medullary column of hyphae from the first and grow up
along with it, thus providing the outer part of the apothecium, an additional
" thalline margin " continuous with the thallus itself. It is an advanced
type of development peculiar to lichens, and it provides for fertility of long
continuance which is in striking contrast with the fugitive ascocarps of the
Discomycetes.
The distinction between lecideine and lecanorine apothecia is of great
value in classification, but it is not always easily demonstrable; it is
occasionally necessary to examine the early stages, as in the more advanced
the thalline margin may be pushed aside by the turgid disc and become
practically obliterated.
I84 REPRODUCTION
The " proper margin " reaches its highest development in the lecideine
and graphideine types. It is less prominent or often almost entirely replaced
when the thalline margin is superadded, except in genera such as Thelotrema
and Diploschistes which have distinct " double margins."
There is an unusual type of apothecium in the genus Gyrophora. The
fruit is lecideine, the thalline gonidia taking no part in the development.
The growth of the initial ascogenous tissue,
according to Lindau1, is constantly towards
the periphery of the disc so that a weak
spot arises in the centre which is promptly
filled by a vigorous sterile growth of para-
^^^^ , physes. This process is repeated from new
Fig. 103. Apothecial gyrose discs of r J
Gyrophora cylindrica. Ach. x 12 (after centres again and again, resulting in the
Lmdau)- irregularly concentric lines of sterile and
fertile areas of the "gyrose" fruit (Fig. 103). The paraphyses soon become
black at the tips. Asci are not formed until the ascogenous layer has ac-
quired a certain degree of stability, and spores are accordingly present only
in advanced stages of growth.
G. LICHEN ASCI AND SPORES
a. HISTORICAL. The presence of spores, as such, in the lichen fruit was
first established by Hedwig2 in Anaptychia (Physcia) ciliaris. He rightly
judged the minute bodies to be the "semina" of the plant. In that species
they are fairly large, measuring about 50 /A long and 24 /j, thick, and as they
are very dark in colour when mature, they stand out conspicuously from the
surrounding colourless tissue of the hymenium. Acharius3 also took note of
these "semina" and happily replaced the term by that of "spores." They
may be produced, he states, in a compact nucleus {Sphaerophoron\ in a naked
disc (Calicium), or they may be embedded in the disc (Opegrapha and'Leadea).
Sprengel4 opined that the spores — which he figures — were true seeds, though
he allows that there had been no record of their development into new plants.
Luyken5 made a further contribution to the subject by dividing lichens into
gymnocarpous and angiocarpous forms, according as the spores, enclosed
in cells or vesicles (thecae), were borne in an open disc or in a closed peri-
thecium.
In his Systema of lichen genera Eschweiler6, some years later, described
and figured the spores as " thecae " enclosed in cylindrical asci. FeV in
contemporary works gave special prominence to the colour and form of the
spores in all the lichens dealt with.
1 Lindau 1899. '2 Hedwig 1784. 3 Acharius 1803. 4 Sprengel 1807.
5 Luyken 1809. 6 Eschweiler 1824. 7 Fee 1824.
LICHEN ASCI AND SPORES
185
Hi^^lBr '
m
b. DEVELOPMENT OF THE ASCUS. The first attempt to trace the origin
and development of lichen asci and spores was made by Mohl1. He describes
the mother-cell (the ascus) as filled at first with a clouded granular sub-
stance changing later into a definite number — usually eight — of simple or sep-
tate spores. Dangeard2 included the lichens Borrera {Physcia} ciliaris and
Endocarpon (Dermatocarpon) miniatum among the plants that he studied
for ascus and spore development. He found that in lichens, as in fungi, the
ascus arose usually from the penultimate cell of a crooked hypha (Fig. 104)
and that it contained at first two nuclei
derived from adjoining cells. These nuclei
are similar in size to those of the vegetative
hyphae, and in each there is a large nucleo-
lus with chromatin material massed on one
side. Fusion takes place, as in fungi, between
the two nuclei, and the secondary or defi-
nitive nucleus thus formed divides suc-
cessively to form the eight spore-nuclei.
Baur3 and Nienburg4 have confirmed Dan-
geard's results as regards lichens, and Ren£
Maire5 has also contributed important cyto-
logical details on the development of the
spores. In Anaptychia {Physcia) ciliaris he
found that the fused nucleus became larger
and that a synapsis stage supervened during
which the long slender chromatin filaments
became paired, and at the same time shorter and thicker. The nuclear mem-
brane disappeared as the chromatin filaments were united in masses joined
together by linin threads which also disappeared later. At the most advanced
stage observed by Maire there was visible a nucleolus embedded in a con-
densed plasma and surrounded by eight medianly constricted filaments
destined to form the equatorial plate. A few isolated observations were also
made on the cytology of the ascus in Peltigera canina, in which lichen the
preceding ascogonial development is wholly vegetative. The secondary
nucleus was seen to contain a chromatin mass and a large nucleolus; in
addition two angular bodies of uncertain signification were associated with
the nucleolus, each with a central vacuole. The nucleolus disappeared in the
prophase of the first division and four double chromosomes were then plainly
visible. The succeeding phases of the first and the second nuclear division
were not seen, but in the prophase of the third it was possible to distinguish
four chromatin masses outside the nucleolus. The slow growth of the lichen
plant renders continuous observation extremely difficult.
1 Mohl 1833. 2 Dangeard 1894. 3 Baur 1904. * Nienburg 1908. 5 Maire 1905.
Fig. 104. Developing asci of Physcia
ciliaris DC. x 800 (after Baur).
1 86 REPRODUCTION
F. Bachmann1 was able to make important cytological observations in
her study of Collema pulposum. As regards the vegetative and ascogonial
nuclei, five or perhaps six chromosomes appeared on the spindle when the
nucleus divided. In the asci, the usual paired nuclei were present in the
early stages and did not fuse until the ascus had elongated considerably.
After fusion the definitive nucleus enlarged with the growth of the ascus
and did not divide until the ascus had attained full size. The nucleolus was
large, and usually excentric, and there were at first a number of chromatin
masses on an irregular spirem. In synapsis the spirem was drawn into a
compact mass, but after synapsis, "the chromatin is again in the form of
a knotty spirem." In late prophases the chromosomes, small ovoid bodies,
were scattered on the spindle; later they were aggregated in the centre,
and, in the early metaphase, about twelve were counted now split longi-
tudinally. There were thus twice as many chromosomes in the first division
in the ascus as in nuclear divisions of the vegetative hyphae. F. Bachmann
failed to see the second division ; there were at least five chromosomes in the
third division.
Considerable importance is given to the number of the chromosomes in
the successive divisions in the ascus since they are considered to be proof of
a previous double fusion — in the ascogonium and again in the ascus — necessi-
tating, therefore, a double reduction division to arrive at the gametophytic
or vegetative number of five or six chromosomes in the third division in the
ascus. There have been too few observations to draw any general conclusions.
c. DEVELOPMENT OF SPORES. The spore wall begins to form, as in
Ascomycetes, at the apex of the nucleus with the curving over of the astral
threads, the nucleus at that stage presenting the figure of a flask the neck
of which is occupied by the centrosome. The final spore-nucleus, as observed
by Maire, divides once again in Anaptychia and division is followed by the
formation of a median septum, the mature spore being two-celled. In
Peltigera the spore is at first ovoid, but both nucleus and spore gradually elon-
gate. The fully formed spore is narrowly fusiform and by repeated nuclear
division and subsequent cross-septation it becomes 4- or even 5-6-celled.
The spores of lichens are wholly fungoid, and, in many cases, form a
parallel series with the spores of the Ascomycetes. Markings of the epispore,
such as reticulations, spines, etc., are rarely present (Solorina spongiosa),
though thickening of the wall occurs in many species (Pertusariae, etc.), a
peculiarity which was first pointed out by Mohl2 who contrasted the spore
walls with the delicate membranes of other lichen cells. Some spores,
described as "halonate," have an outer gelatinous covering which probably
prevents the spore from drying up and thus prolongs the period of possible
germination. Both asci and spores are, as a rule, more sparingly produced
1 Bachmann 1913. 2 Mohl 1833.
LICHEN ASCI AND SPORES 187
than in fungi; in many instances some or all of the spores in the ascus
are imperfectly formed, and the full complement is frequently lacking,
possibly owing to some occurrence of adverse conditions during the long
slow development of the apothecium. In the larger number of genera and
species the spores are small bodies, but in some, as for instance in the
Pertusariae and in some Pyrenocarpeae, they exceed in size all known fungus
spores. In Varicellaria microsticta, a rare crustaceous lichen of high moun-
tains, the solitary i -septate spore measures up to 350/4 in length and 1 15 /* in
width. Most spores contain reserve material in the form of fat, etc., many are
dark-coloured; Zukal1 has suggested that the colour may be protective.
Their ejection from the ascus at maturity is caused by the twofold
pressure of the paraphyses and the marginal hyphae on the addition of
moisture. The spores may be shot up at least I cm. from the disc2.
d. SPORE GERMINATION. Meyer3 was the first who cultivated lichen
spores and the dendritic formation which he obtained by growing them on
a smooth surface was undoubtedly the prothallus (or hypothallus) of the
lichen. Actual germination was however not observed till Holle4 in 1846
watched and figured the process as it occurs in Physcia ciliaris.
Spores divided by transverse septa into two or more cells, as well as
those that have become "muriform" by transverse and longitudinal septation,
may germinate from each cell.
e. MuLTINUCLEATE SPORES. These spores, which are all very large,
occur in several genera or subgenera: in Lecidea subg. Mycoblastus (Fig. 105),
Lecanora subg. Ochrolechia and in Pertusariaceae. Tulasne5 in his experi-
Fig. 105. Multinucleate spore of Lecidea Fig. 106. Germination of multinucleate
(Mycoblastus) sanguinaria Ach. x 540 spore of Ochrolechia pallescens Koerb.
(after Zopf). x 390 (after de Bary).
ments with germinating spores found that in Lecanora parella (Ochrolechia
pallescens^} germinating tubes were produced all over the surface of the
spore (Fig. 106). De Bary8 verified his observations in that and other species
and added considerable detail : about twenty-four hours after sowing spores
of Ochrolechia pallescens, numerous little warts arose on the surface of the
1 Zukal 1895. 2 Fee 1824. 3 Meyer 1825. 4 Holle 1849.
* Tulasne 1852. 6 De Bary 1866-1867.
i88 REPRODUCTION
spore which gradually grew out into delicate hyphae. All these spores
contain fat globules and finely granular protoplasm with a very large number
of minute nuclei; the presence of the latter has been demonstrated by
Haberlandt1 and later by Zopf2 who reckoned about 200 to 300 in the
spore of Mycoblastus sanguinarius. These nuclei had continued to multiply
during the ripening of the spore while it was still contained in the ascus2.
Owing to the presence of the large fat globules the plasma is confined to
an external layer close to the spore wall; the nuclei are embedded in the
plasma and are connected by strands of protoplasm. The epispore in some
of these large spores is extremely developed: in some Pertusariae it
measures 4-5 /* in thickness.
/ POLARIBILOCULAR SPORES. The most peculiar of all lichen spores
are those termed polaribilocular — signifying a two-celled spore of which the
median septum has become so thickened that the cell-cavities with their
contents are relegated to the two poles of the spore, an open canal frequently
connecting the two cell-spaces (Fig. 107). Other terms have been suggested
and used by various writers to describe this unusual
character such as blasteniospore3, orculiform4 and
placodiomorph5 or more simply polarilocular.
The polarilocular colourless spore is found in
a connected series of lichens — crustaceous, foliose
and fruticose (Placodium, Xanthoria, TeloscMstes).
In another series with a darker thallus (Rinodina
and Physcia) the spore is brown-coloured, and the
Fig. 107. Polarilocular spores, median septum cuts across the plasma-connection.
a, Xanthoria parietina Th. T , , , ...
Fr. ; b, Kinodina roboris Th. ^n other respects the brown spore is similar to the
MrV ^My^.Pu!™™1™*" colourless one and possesses a thickened wall with
Nyl.; d, Physcia cihans DC.
x6oo. reduced cell-cavities.
The method of cell-division in these spores resembles that known as
" cleavage by constriction," in which the cross wall arises by an ingrowth
from all sides of the cell; in time the centre is reached and the wall is com-
plete, or an open pore is left between the divided cells. Cell "cleavage"
occurs frequently among Thallophytes, though it is unknown among the
higher plants. Among Algae it is the normal form of cell-division in Clado-
phora and also in Spirogyra, though in the latter the v/all passes right across
and.xruts through the connecting plasma threads. Harper6 found "cleavage
by constriction " in two instances among fungi : the conidia of Erysiphe and
the gametes of Sporodinia are cut off by a septum which originates as a
circular ingrowth of the outer wall, comparable, he considers, with the cell-
division of Cladophora.
1 Haberlandt 1887. 2 Zopf iy)^ a Massalongo 1852. 4 Koerber 1855.
6 Wainio i. 1890, p. 113. • Harper 1899.
LICHEN ASCI AND SPORES 189
The development of the thickened wall of polarilocular spores has been
studied by Hue1, who contends however that there is no true septation in
the colourless spores so long as the central canal remains open. According
to his observations the wall of the young spore is formed of a thin tegument,
everywhere equal in thickness, and consisting of concentric layers. This
tegument becomes continually thicker at the equator of the spore by the
addition of new layers from the interior, and the protoplasmic contents are
compressed into a gradually diminishing space. In the end the wall almost
touches at the centre, and the spore consists of two polar cell-cavities with
a narrow open passage between. A median line pierced by the canal is
frequently seen. In a few species there is a second constriction cleavage
and the spore becomes quadrilocular.
Hue insists that this spore should be regarded as only one-celled; for
though the walls may touch at the centre, he says they never coalesce. He
has unfortunately given no cytological observations as to whether the spore
is uni- or binucleate.
In Xanthoria parietina, one of the species with characteristic polari-
bilocular spores, germination, it would seem, takes place mostly at one end
only of the spore, though a germinating tube issues at both ends frequently
enough to suggest that the spore is binucleate and two-celled. The absence
of germination from one or other of the cells only may probably be due to
the drain on their small resources. Hue has cited the rarity of such instances
of double germination in support of his view of the one-celled nature of the
spore. He instances that out of fifteen spores, Tulasne2 has figured only
three that have germinated at each end; Bornet3 figures one in seven with
the double germination and Bonnier4 one in sixteen spores.
Further evidence is wanted as to the nuclear history of these hyaline
spores. In the case of the brown spores, which show the same thickening
of the wall and restricted cell-cavity, though with a distinct median septum,
nuclear division was observed by Rend Maire5 before septation in one such
species, Anaptychia ciliaris.
II. SECONDARY SPORES
A. REPRODUCTION BY OIDIA
In certain conditions of nutrition, fungal hyphae break up into separate
cells, each of which functions as a reproductive conidium or oidhim, which
on germination forms new hyphae. Neubner6 has demonstrated a similar
process in the hyphae of the Caliciaceae and compares it with the oidial
formation described by Brefeld7 in the Basidiomycetes.
1 Hue 191 12. 2 Tulasne 1852. 3 Bornet 1873. 4 Bonnier i8892.
5 Maire 1905. 6 Neubner 1893. 7 Brefeld 1889.
REPRODUCTION
The thallus of this family of lichens is granular or furfuraceous ; it never
goes beyond the Lepra stage of development1. In some species it is scanty,
in others it is abundant and spreads over large areas of the trunks of old
trees. It is only when growth is especially luxuriant that oidia are formed.
Neubner was able to recognize the oidial condition by the more opaque
appearance of the granules, and under the microscope he observed the
hyphae surrounding the gonidia gradually fall away and break up into
minute cylindrical cells somewhat like spermatia in size and form. There
was no question of abnormal or unhealthy conditions, as the oidia were
formed in a freely fruiting thallus.
The gonidia associated with the oidial hyphae also showed unusual
vitality and active division took place as they were set free by the breaking
up of the encircling hyphae. The germination of the oidia provides an
abundance of hyphal filaments for the rapidly increasing algal cells, and
there follows a widespread development of the lichen thallus.
Oidial formation has not been observed in any other family of lichens.
B. REPRODUCTION BY CONIDIA
a. INSTANCES OF CONIDIAL FORMATION. It is remarkable that the
type of asexual reproduction so abundantly represented in fungi by the large
and varied group of the Hyphomycetes is prac-
tically absent in lichens. An exception is to be
found in a minute gelatinous lichen that grows on
soil. It was discovered by Bornet2 and called by
him Arnoldia (Physmd) minutula. From the thallus
rise up simple or sparingly branched colourless
conidiophores which bear at the tips globose brown
conidia(Fig. 108). Bornet3 obtained these conidia
by keeping very thin sections of the thallus in a
drop of water2.
Yet another instance of conidial growth is given
by Steiner4. He had observed that the apothecia
on plants of Caloplaca aurantia var. callopisma
Stein, differed from those of normal appearance
in the warted unevenness of the disc and also in
being more swollen and convex, the thalline margin
being almost obliterated. He found, on micro-
scopical examination, that the hymenium was
occupied by paraphyses and by occasional asci,
the latter seldom containing spores, and being
2 Bornet 1873.
Conidia developed
om thallus of Arnoldia mi-
nutula Born.
Bornet).
See p. 143.
x 950 (after
3 Bornet's observations have not been repeated, and it is possible that he may have been dealing
with a parasitic hyphomycetous fungus. 4 Steiner 1901.
LICHEN ASCI AND SPORES 191
usually more or less collapsed. The component parts of the apothecium
were entirely normal and healthy, but the paraphyses and the few asci were
crushed aside by the intrusion of numerous slender unbranched septate
conidiophores. Several of these might spring from one base and the hypha
from which they originated could be traced some distance into the ascogenous
layer, though a connection with that cell-system could not be demonstrated.
While still embedded in the hymenium, an ellipsoid or obovate swelling
began to form at the apex of the conidiophore; it became separated from
the stalk by a septum and later divided into a two-celled conidium.
The conidiophore increased in length by intercalary growth and finally
emerged above the disc; the mature conidium was pyriform and measured
1 5-20 /z, x 9-11 yu,
Steiner regarded these conidia as entirely abnormal; pycnidia with
stylospores are unknown in the genus and they were not, he alleges, the
product of any parasitic growth.
b. COMPARISON WITH HYPHOMYCETES. The conidial form of fructi-
fication in fungi, known as a Hyphomycete, is generally a stage in the life-
cycle of some Ascomycete; it represents the rapid summer form of asexual
reproduction. The ascospore of the resting fruit-form in many species ger-
minates on any suitable matrix and may at once produce conidiophores and
conidia, which in turn germinate, and either continue the conidial generation
or proceed to the formation of the perfect fruiting form with asci and asco-
spores.
Such a form of transient reproduction is almost impossible in lichens, as
the hypna produced by the germinating lichen ascospore has little vitality
without the algal symbiont. In natural conditions development practically
ceases in the absence of symbiosis. When union between the symbionts
takes place, and growth becomes active, thallus construction at once com-
mences. But in certain conditions of shade and moisture, only the rudiments
of a lichen thallus are formed, known as a leprose or sorediose condition.
Soredia also arise in the normal life of many lichens. As the individual
granules or soredia may each give rise to a complete lichen plant, they may
well be considered as replacing the lost conidial fructification.
C. CAMPYLIDIUM AND ORTHIDIUM
Mu'ller1 has described under the name Campy lidium a supposed new type
of asexual fructification which he found on the thallus of tropical species of
Gyalecta, Lofadium, etc., and which he considered analogous to pycnidia and
spermogonia. Wainio2 has however recognized the cup-like structure as a
fungus, CypJiella aeruginascens Karst, which grows on the bark of trees and
occasionally is parasitic on the crustaceous thallus of lichens. Wainio has
1 Miiller 1881. 2 Wainio 1890, n. p. 27.
1 92
REPRODUCTION
also identified the plant, Lecidea irregnlaris, first described by Fe'e1, as also
synonymous with the fungus.
Another name Orthidium was proposed by M tiller2 for a type of fructi-
fication he found in Brazil which he contrasts or associates with Campylidium.
It has an open marginate disc with sporophores bearing acrogenous spores.
He found it growing in connection with a thin lichen thallus on leaves and
considered it to be a form of lichen reproduction. Possibly Orthidium is
also a Cyphella.
III. SPERMOGONIA OR PYCNIDIA
A. HISTORICAL ACCOUNT OF SPERMOGONIA
The name spermogonium was given by Tulasne3 to the " punctiform
conceptacles " that are so plentifully produced on many lichen thalli, on the
assumption that they were the male organs of the plant, and that the spore-
like bodies borne in them were non-motile male cells or spermatia.
The first record of their association with lichens was made by Dillenius l,
who indicates the presence of black tubercles on the thallus of Physcia
dliaris. He figures them also on several species of Cladonia, on Ramalina
and on Dermatocarpon, but without any suggestion as to their function.
Hed wig's5 study of the reproductive organs of the Linnaean Cryptogams
included lichens. He examined Physcia dliaris, a species that not only is
quite common but is generally found in a fruiting condition and with very
prominent spermogonia,and has been therefore a favourite lichen for purposes
of examination and study. Hedwig describes and figures not only ^he apo-
thecia but also those other bodies which he designates as "punctula mascula,"
or again as " puncta floris masculi." In his later work he gives a drawing
of Lichen (Gyrophord) proboscideus, with two of the spermogonia in section.
Acharius6 included them among the lichen structures which he called
" cephalodia": he described them as very minute tubercles rising up from
the substance of the thallus and projecting somewhat above it. He also
figures a section through two " cephalodia " of Physda dliaris. Fries7 looked
on them as being mostly " anamorphoses of apothecia, the presence of
abortive fruits transforming the angiocarpous lichen to the appearance of a
gymnocarpous form." Wallroth8 assigned the small black fruits to the com-
prehensive fungus genus Sphaeria or classified lichens bearing spermogonia
only as distinct genera and species (Pyrenothea and Thrornbiuni). Later
students of lichens— Schaerer9, Flotow10, and others — accepted Wallroth's
interpretation of their relation to the thallus, or they ignored them altogether
in their descriptions of species.
1 Fee 1873. 2 Miiller 1890. 3 Tulasne 1851. * Dillenius 1741. *> Hedwig 1784 and 1789.
6 Acharius 1 8 10. 7 Fries 1831. 8 Wailroth 1825. 9 Schaerer 1823-1842. 10 Flotow 1850.
SPERMOGONIA 193
B. SPERMOGONIA AS MALE ORGANS
Interest in these minute "tubercles" and their enclosed "corpuscles"
was revived by Itzigsohn1 who examined them with an improved microscope.
He macerated in water during a few days that part of the thallus on which
they were developed, and, at the end of the time, discovered that the
solution contained large numbers of motile bodies which he naturally took
to be the corpuscles from the broken down tubercles. He claimed to have
established their function as male motile cells or spermatozoa. The discovery
seemed not only to prove their sexual nature, but to link up the reproduction
of lichens with that of the higher cryptogams. The tubercles in which the
" spermatozoa " were produced he designated as antheridia. More prolonged
maceration of the tissue to the very verge of decay yielded still larger numbers
of the " spermatozoa " which we now recognize to have been motile bacilli.
Tulasne2 next took up the subject, and failing to find the motile cells,
he wrongly insisted that Itzigsohn had been misled by mere Brownian
movement, but at the same time he accepted the theory that the minute
conceptacles were spermogonia or male organs of lichens. He also pointed
out that their constant occurrence on the thallus of practically every species
of lichen, and their definite form, though with considerable variation, rendered
it impossible to regard them as accidental or of no importance to the life of
the plant. He compared them with fungal pycnidia such as Phyllosticta or
Septoria which outwardly they resembled, but whereas the pycnidial spores
germinated freely, the spermatia of the spermogonia, as far as his experience
went, were incapable of germination.
C. OCCURRENCE AND DISTRIBUTION
a. RELATION TO THALLUS AND APOTHECIA. We owe to Tulasne3 the
first comparative study of lichen spermogonia. He described not only
their outward form, but their minute structure, in a considerable number
of representative species. A few years later Lindsay4 published a memoir
dealing with the spermogonia of the larger foliose and fruticose lichens, and,
in a second paper, he embodied the results of his study of an equally ex-
tensive selection of crustaceous species. Lindsay's work is unfortunately
somewhat damaged by faulty determination of the lichens he examined, and
by lack of the necessary discrimination between one thallus and another of
associated and intermingled species. Both memoirs contain, however, much
valuable information as to the forms of spermogonia, with their spermatio-
phores and spermatia, and as to their distribution over the lichen thallus.
Though spermogonia are mostly found associated with apothecia, yet
1 Itzigsohn 1850. - Tulasne 1851. 3 Tulasne 1852. 4 Lindsay 1859 and 1872.
S. L. 13
194
REPRODUCTION
in some lichens, such as Cerania ( Thamnolia) vermicularis, they are the only
sporiferous organs known. Not unfrequently crustaceous thalli bear sper-
mogonia only, and in some Cladoniae, more especially in ascyphous species,
spermogonia are produced abundantly at the tips of the podetial branches
(Fig. 109), while apothecia are exceedingly rare. Usually they occur in
scattered or crowded groups, more rarely they are solitarj'. Very often they
are developed and the contents dispersed before the apothecia reach the
surface of the thallus; hence the difficulty in relating these organisms, since
the mature apothecium is mostly of extreme importance in determining the
species.
Fig. 109. C/adomafurcataSchrad. Branched
podetium with spermogonia at the tips
. (after Krabbe).
Fig. no. Physcia hispida Tuckerm. Ciliate
frond, a, spermogonia ; 6, apothecia. x ca. 5
(after Lindsay).
In a very large number of lichens, both crustaceous and foliose, the
spermogonia are scattered over the entire thallus (Fig. 1 10). covering it more
or less thickly with minute black dots, as in Parmelia conspersa. In other
instances, they are to some extent confined to the peripheral areas as in
Parmelia physodes ; or they occur on the extreme edge of the thallus as in
the crustaceous species Lecanora glaucoma (sordidd). In Pyrenula nitida
they grow on the marginal hypothallus, usually on the dark line of demar-
cation between two thalli.
They tend to congregate on, and indeed are practically restricted to the
SPERMOGONIA
195
better lighted portions of the thallus. On the fronds of foliose forms, they
appear, for instance, on the swollen pustules of Umbilicaria pustulata, while
in Lobaria pulmonaria, they are mostly lodged in the ridges that surround
the depressions in the thallus. In Parmelia conspersa, Urceolaria (Diplo-
schistes) scruposa and some others, they occasionally invade the margins of
the apothecium or even the apothecial disc as in Lichina. Forssell1 found
that a spermogonium had developed among cells of Gloeocapsa that covered
the disc of a spent apothecium of Pyrenopsis haematopis.
In fruticose lichens such as Usnea, Ramalina, etc. they occur near the
apex of the fronds, and in Cladonia they occupy the tips of the ascyphous
podetia or the margins of the scyphi. In some Cladoniae, however, spermo-
gonia are produced on the basal squamules, more rarely on the squamules
that clothe the podetia.
b. FORM AND SIZE. Spermogonia are specifically constant in form, the
same type being found on the same lichen species all over the globe. The
larger number are entirely immersed and are ovoid or roundish (Fig. 1 1 1 A)
or occasionally somewhat flattened bodies (Nephromium laevigatum),ov again,
but more rarely, they are irregular in outline with an infolding of the walls
that gives the interior a chambered form (Fig. 1 1 1 B) (Lichina pygmaed) ; but
all of these are only visible as minute points on the thallus.
B
Fig. in. Immersed spermogonia. A, globose in Parmelia
acetabulum Dub. x 600 ; B, with infolded walls in Lecidea
(Psora) testacea Ach. x 144 (after Gliick).
A second series, also immersed, are borne in small protuberances of the
thallus. These very prominent forms are rarely found in crustaceous lichens,
but they are characteristic of such well-known species as Ramalina fraxinea,
Xanthoria parietina, Ricasolia ampltssima, Baeomyces roseus, etc. Other sper-
mogonia project slightly above the level of the thallus, as in Cladonia papillaria
and Lecidea lurida; while in a few instances they are practically free, these
last strikingly exemplified in Cetraria islandica where they occupy the
small projections or cilia (Fig. 112) that fringe the margins of the lobes; they
are free also in most species of Cladonia.
1 Forssell 1885.
13—2
REPRODUCTION
In size they vary from such minute bodies as those in Parmelia exasperata
which measure 25-35 p, in diam., up to nearly I mm. in Lobaria laetevirens.
As a rule, they range from about 150/4
to 400 fj, across the widest part, and are
generally rather longer than broad. They
open above by a small slit or pore called
the ostiole about 20 yu, to I oo /x wide which
is frequently dark in colour. In one in-
stance, in Icmadophila aeruginosa, Nien-
burg1 has described a spermogonium with
a wide opening, the spermatiophores
being massed in palisade formation along
the bottom of a cup-like structure.
c. COLOUR OF SPERMOGONIA. Though
usually the ostiole is visible as a darker
point than the surrounding tissue, sper-
mogonia are often difficult to locate un-
less the thallus is first wetted, when they become visible to slight magnification.
They appear as black points in many Parmeliae,Physciae,Roccellae, etc., though
even in these cases they are often brown when moistened. They are dis-
tinctly brown in some Cladoniae, in Nephromium, and in some Physciae\
orange-red or yellow in Placodium and concolorous with the thallus in
Usnea, Ramalina, Stereocaulon, etc.
Fig
j. 112. rree spermogonia in spmous
cilia of Cetraria islandica Ach. A, part
of frond; B, cilia, x 10.
D. STRUCTURE
a. ORIGIN AND GROWTH. The spermogonia (or pycnidia) of lichens
when mature are more or less hollow structures provided with a distinct
wall or " perithecium," sometimes only one cell thick and then not easily de-
monstrable, as in Physcia speciosa, Opegrapha vulgata, Pyrenula nitida, etc.
More generally the " perithecium " is composed of a layer of several cells
with stoutish walls which are sometimes colourless, but usually some shade
of yellow to dark-brown, with a darker ostiole. The latter, a small slit or
pore, arises by the breaking down of some of the cells at the apex. After
the expulsion of the spermatia, a new tissue is formed which completely
blocks up the empty spermogonium. In filamentous lichens such as Usnea
a dangerous local weakening of the thallus is thus avoided.
Spermogonia originate from hyphae in or near the gonidial zone. The
earliest stages have not been seen, but Moller2 noted as the first recogniz-
able appearance or primordium of the "pycnidia" in cultures of Calicium
trachelinum a ball or coil of delicate yellowish-coloured hyphae. At a more
1 Nienburg roo8. 2 Moller 1887.
SPERMOGONIA 197
advanced stage the sporophores (or spermatiophores) could be traced as
outgrowths from the peripheral hyphae, directed in palisade formation
towards the centre of the hyphal coil about 20-30 (j. long and very slender
and colourless. They begin to bud off spermatia almost immediately, as it
has been found that these are present in abundance while the developing
spermogonium is still wholly immersed in the thallus. Meanwhile there is
gradually formed on the outside a layer of plectenchyma which forms
the wall. Additional spermatiophores arise from the wall tissue and push
their way inwards between the ranks of the first formed series. The sper-
mogonium slowly enlarges and stretches and as the spermatiophores do not
grow any longer a central hollow arises which becomes packed with sper-
matia (or spores) before the ostiole is open.
A somewhat similar process of development is described by Sturgis1 in
the spermogonia of Ricasolia amplissima, in which species the primordium
arises by a profuse branching of the medullary hyphae in certain areas close
to the gonidial zone. The cells of these branching hyphae are filled with oily
matter and gradually they build up a dense, somewhat cylindrical body
which narrows above to a neck-like form. The growth is upwards through
the gonidial layer, and the structure widens to a more spherical outline. It
finally reaches the outer cortex when some of the apical cell membranes
are absorbed and a minute pore is formed. The central part becomes hollow,
also by absorption, and the space thus left is lined and almost filled with
multicellular branches of the hyphae forming the wall; from the cells of
this new tissue the spermatia are abstricted.
b. FORMS AND TYPES OF SPERMATIOPHORES. The variations in form of
the fertile hyphae in the spermogonium were first pointed out by Nylander-
who described them as sterigmata3. He considered the differences in
branching, etc. as of high diagnostic value, dividing them into two groups:
simple "sterigmata" (or spermatiophores), with non-septate hyphae, and
arthrosterigmata, with jointed or septate hyphae.
Simple " sterigmata " comprise those in which the spore or spermatium is
borne at the end of a secondary branch or sterigma, the latter having arisen
from a cell of the upright spermatiophore or from a simple basal cell. The
arthrosterigmata consist of " short cells almost as broad as they are long,
much pressed together, and appearing almost agglutinate especially toward
the base; they fill almost the whole cavity of the spermogonium." The
arthrosterigmata may grow out into the centre of the cavity as a single
cell-row, as a loose branching network, or, as in Endocarpon, they may form
1 Sturgis 1890. 2 Nylander. 1858, pp. 34, 35.
3 Nylander, Crombie and others apply the term "sterigma" to the whole spermatiophore. In
the more usual restricted sense, it refers only to the short process from which the spermatium is
abstricted.
REPRODUCTION
a tissue filling the whole interior. Each cell of this tissue that borders on
a cavity may bud off a spermatium either directly or from the end of a
short process.
The most important contributions on the subject of spermogonia in
recent years are those of Gliick1 and Steiner2. Gliick, who insisted on the
0
7ig- 1 13 A- Types of lichen " sporophores " and pycnidiospores. i ,
Pdtigera rufescens fioffm. x 910; 2, Lecidea (Psora) testacea Ach.
x 1200; 3, Cladonia cariosa Spreng. x 1000; 4, Pyrenula nitida
Ach. x 1130; 5, Parmelia trtstis Nyl. x 700; 6, Lobaria pulmo-
naria Hoffm. x jooo (after Gliick).
1 Gluck 1899., • 2 Steiner 1901.
SPERMOGONIA 199
"pycnidial" non-sexual character of the organs, recognized eight types of
"sporophores" differing in the complexity of their branching or in the form
of the "spores" (Fig. 1 13 A):
1. The Peltigera type: the sporophores consist of a basal cell bearing
one or more long sterigmata and rather stoutish ellipsoid spores. (These
are true pycnidia.)
2. The Psora type: a more elongate simple sporophore with sterigmata
and oblong spores.
3. The Cladonia type: a branching sporophore, each branch with sterig-
mata and oblong spores.
4. The Squamaria type (called by Gliick Placodiuni) : also a branching
sporophore but with long sickle-like bent spores.
5. The Parmelia type: a more complicated system of branching and
anastomosing of the sporophores, with oblong spores.
6. and 7. The Sticta and Physcia types: in both of these the sporo-
phores are multiseptate; they consist of a series of radiately arranged
hyphae rising from a basal tissue all round the pycnidium. They anasto-
mose to form a network and bud off " spermatia " from the free cells or
rather from minute sterigmata. In the Physcia type there is more general
anastomosis of the sporophores and frequently masses of sterile cells along
with the fertile members occupy the centre of the pycnidium. The sper-
matia of these and the following Endocarpon type are short cylindrical
bodies (Fig.- 1138).
7
Fig. 1136. 7, Physcia ciliaris DC. x 600; 8, Endocarpon sp. x 600
(after Gliick).
8. Endocarpon type: the pycnidium is filled by a tissue of short broad
cells, with irregular hollow spaces lined by fertile cells similar to those of
the Sticta and Physcia types.
200 REPRODUCTION
The three last named types of sporophores represent Nylander's section
of arthrosterigmata. Steiner has followed Nylander in also arranging the
various forms into two leading groups. The first, characterized by the
secondary branch or "sterigma," he designates "exobasidial"; the second,
comprising the three last types in which the spores are borne directly on
the cells of the sporophore or on very short processes, he describes as " endo-
basidial." Steiner also introduces a new term, fulcrum > for the sporophore.
The pycnidia in which these different sporophores occur are not, as a
rule, characteristic of one family. Peltigera type is found only in one family
and the Cladonia type is fairly constant in Cladoniae, but "Psora" pycnidia
are found on very varying lichens among the Lecideaceae, Verrucariaceae
and others. The Squamaria type with long bent spores is found not only in
Squamaria (Gliick's Placodium) but also in Lecidea, Roccella, Pyrenula, etc.
Parmelia type is characteristic of many Parmeliae and also of species of
Evernia, Alectoria, Platysma and Cetraria. The Sticta type occurs in Gyro-
phora, Umbilicaria, Nephromium and Lecanora as well as in Sticta and in one
species at least of Collema. To the Physcia type belong the pycnidia of most
Physciaceae and of various Parmeliae, and to the closely related Rndocarpon
type the pycnidia of Endocarpon and of Xanthoria parietina.
c. PERIPHYSES AND STERILE FILAMENTS. In a few species, Roccella
tinctoria,Pertusariaglobulifera,&\ic.,shor\. one-celled sterile hyphae are formed
within the spermogonium near the ostiole, towards which they converge.
They correspond to the periphyses in the peri-
thecia of some Pyrenolichens, Verrucaria, etc.
(described by Gibelli1 as spermatiophores); they
are also present in some of the Pyrenomycetes
(Sordaria, etc.), and in many cases replace the
paraphyses in function when these have broken
down. Sterile hyphae also occur, towards the base,
mingled with the fertile spermatiophores (Fig.
4. Sterile filaments in 114). These latter were first described and figured
SS°5ST mLh'mfgnified b7 Tulasne2 in the spermogonia of Ramalina
(after Lindsay). fraxinea as stoutish branching filaments, rising
from the same base as the spermatiophores but much longer, and frequently
anastomosing with each other. They have been noted also in Usnea bar-
bata and in several species of Parmelia, and have been compared by Ny-
lander3 to paraphyses. They are usually colourless, but, in the Parmeliae,
are often brownish and thus easily distinguished from the spermatio-
phores. It has been stated that these filaments are sometimes fertile. Similar
sterile hyphae have been recorded in the pycnidia of fungi, in Sporocladus
(Hendersonia) lichenicola (Sphaeropsideae) by Corda4 who described them as
1 Gibelli 1866. 2 Tulasne 1852. 3 Nylander 1858. 4 Corda 1839.
SPERMOGONIA 201
paraphyses, and also in Steganosporium cellulosum (Melanconieae). These
observations have been confirmed by Allescher1 in his recent work on Fungi
Imperfecti. Keiszler2 has described a P/wma-\ike pycnidium parasitic on
the leprose thallus of Haematomma elatinum. It contains short slender
sporophores and, mixed with these, long branched sterile hyphae which
reach to the ostiole and evidently function as paraphyses, though Keiszler
suggests that they may be a second form of sporophore that has become
sterile. On account of their presence he placed the fungus in a new genus
L icJienophoma.
E. SPERMATIA OR PYCNIDIOSPORES
a. ORIGIN AND FORM OF SPERMATIA. Lichen spermatia arise at the
tips of the sterigmata either through simple abstriction or by budding. In
the former case — as in the Squamaria type — a delicate cross-wall is formed
by which the spermatium is separated off. When they arise by budding,
there is first a small clavate sacrlike swelling of the end of the short process or
sterigma which gradually grows out into a spermatium on a very narrow base.
This latter formation occurs in the Sticta, Physcia and Endocarpon types.
Ny lander3 has distinguished the following forms of spermatia:
1. Ob-clavate, the ^road end attached to the sterigma as in Usneae,
Cetraria glauca and C. juniperina.
2. Acicular and minute but slightly swollen at each end, somewhat
dumb-bell like, in Cetraria nivalis, C. cucullata, Alectoria, Evernia and some
Parmeliae, frequently borne on "arthrosterigmata."
3. Acicular, cylindrical and straight, the most common form ; these occur
in most of the Lecanorae, Cladoniae, Lecideae, Graphideae, Pyrenocarpeae
and occasionally they are budded off from arthrosterigmata.
4. Acicular, cylindrical, bent; sometimes these are very long, measuring
up to 40 //.; they are found in various Lecideae, Lecanorae, Graphideae,
Pyrenocarpeae, and also in Roccella, Pilophorus and species of Stereocaulon.
5. Ellipsoid or oblong and generally very minute; they are borne on
simple sterigmata and are characteristic of the genera Calicium, Chaenotheca,
Lichina,Ephebe,ofi\\e. small genus Glypholecia and of a few species tfLecanora
and Lecidea.
In many instances there is more or less variation of form and of size in
the species or even in the individual. There are no spherical spermatia.
b. SIZE AND STRUCTURE. The shortest spermatia in any of our British
lichens are those of Lichina pygmaea which are about i'4/A in length and
the longest are those of Lecanora crassa which measure up to 39 ft. In width
they vary from about O'5/tt to 2/z. The mature spermogonium is filled with
1 Allescher 1901-3. 2 Keiszler 1911. 3 Nylander 1858, p. 37-
202 REPRODUCTION
spermatia and, generally, with a mass of mucilage that swells with moisture
and secures their expulsion.
The spermatia of lichens are colourless and are provided with a cell-wall
and a nucleus. The presence of a nucleus was demonstrated by Holier1 in
the spermatia of Calicium parietinum, Opegrapha atra, Collema micropkyllum,
C.pulposum and C. Hildenbrandii, and by Istvanffi 2 in those of Buellia puncti-
formis (B. myriocarpa), Opegrapha subsiderella, Collema Hildenbrandii, Cali-
cium trachelinum,Pertusaria communis andArt&oma communis (A. astroided).
Istvanffi made use of fresh material, fixing the spermatia with osmic acid,
and in all of these very minute bodies he demonstrated the presence of a
nucleus which stained readily with haematoxylin and which he has figured
in the spermatia of Buellia punctiformis as an extremely small dot-like
structure in the centre of the cell. On germination, as in the cell-multi-
plication of other plants, the nucleus leads the way. Germination is preceded
by nuclear division, and each new hyphal cell of the growing mycelium
receives a nucleus.
c. GERMINATION OF SPERMATIA (pycnidiospores). The strongest argu-
ment in favour of regarding the spermatia of lichens as male cells had always
been the impossibility of inducing their germination. That difficulty had at
length been overcome by Moller1 who cultivated them in artificial solutions,
and by that means obtained germination in nine different lichen species.
He therefore rejected the commonly employed terms spermatia and spermo-
gonia and substituted pycnoconidium and pycnidia. Pycnidiospore has
been however preferred as more in accordance with modern fungal termi-
nology. His first experiment was with the "spermatia" of Buellia punctiformis
(B. myriocarpa) which measure about 8-10/1. in length and about 3 ^ in
width, and are borne directly on the septate spermatiophores (arthrosterig-
mata). In a culture drop, the spore had swelled to about double its size by
the second or third day, and germination had taken place at both ends, the
membrane of the spore being continuous with that of the germinating tube.
In a short time cross septa were formed in the hyphae which at first were
very close to each other. While apical growth advanced these first formed
cells increased in width to twice the original size and, in consequence, became
slightly constricted at the septa. In fourteen days a circular patch of my-
celium had been formed about 280/1 in diameter. The development exactly
resembled that obtained from the ascospores of the same species grown in the
absence of gonidia. The largest thallus obtained in either case was about
2mm. in diameter after three months' growth. The older hyphae had a
tendency to become brownish in colour; those at the periphery remained
colourless. In Opegrapha subsiderella the development, though equally
1 Moller 1887. 2 Istvanffi 1895.
SPERMOGONIA 203
successful, was very much slower. The pycnidiospores (or spermatia) have
the form of minute bent rods measuring 57 /t x 1-5 /i. Each end of the spore
produced slender hyphae about the fifth or sixth day after sowing. In four
weeks, the whole length of the filament with the spore in the middle was
300/1. In four months a patch of mycelium was formed 2 mm. in diameter.
Growth was even more sluggish with the pycnidiospores of Opegrapha atra.
In that species they are rod-shaped and 5-6/4 long. Germination took place on
the fifth or sixth day and in fourteen days a germination tube was produced
about five times the length of the spore. In four weeks the first branching
was noticed and was followed by a second branching in the seventh week.
In three months the mycelial growth measured 200-300/4 across.
Germination was also observed in a species of Arthonia, the spores of
which had begun to grow while still in the pycnidium. The most complete
results were obtained in species of Calicium : in C. parietinum the spores,
which are ovoid, slightly bent, and brownish in colour, swelled to an almost
globose shape and then germinated by a minute point at the junction of spore
and sterigma, and also at the opposite end; very rarely a third germinating
tube was formed. Growth was fairly rapid, so that in four weeks there was
a loose felt of mycelium measuring about 2 cm. x i cm. and I mm. in depth.
Parallel cultures were carried out with the ascospores and the results in both
cases were the same; in five or six weeks small black points appeared, which
gradually developed to pycnidia with mature pycnidiospores from which
further cultures were obtained.
On C. trachelinum, which has a thin greyish-white thallus spreading over
old trunks of trees, the pycnidia are usually abundant. Lindsay had noted
two different kinds and his observation was confirmed by Moller. The
spores in one pycnidium are ovoid, measuring 2-5-3 /u, x J'S"2^; m tne
other rarer form, they are rod-shaped and 5~7/t long. In the artificial
cultures they both swelled, the rod-like spores to double their width before
germination, and sometimes several tubes were put forth. Growth was slow,
but of exactly the same kind from these two types of spores as from the
ascospores. At the end of the second month pycnidia appeared on all the
cultures, in each case producing the ovoid type of spore.
In a second paper Moller1 recorded the partially successful germination
of the "spermatia" of Collema (Leptogium) microphyllum, the species in which
Stahl had demonstrated sexual reproduction. Growth was extraordinarily
slow : after a month in the culture solution the first swelling of the sper-
matium prior to germination took place, and some time later small processes
were formed in two or three directions. In the fourth month a branched
filament was formed.
Moller's experiments with ascospores and pycnidiospores were primarily
1 Moller 1888.
204 REPRODUCTION
undertaken to prove that the lichen hyphae were purely fungal and parasitic
on the algae. A series of cultures were made by Hedlund1 in order to
demonstrate that the pycnidiospores were asexual reproductive bodies ;
they were grown in association with the lichen alga and their germination
was followed up to the subsequent formation of a lichen thallus.
d. VARIATION IN PYCNIDIA. On the thallus of Catillaria denigrata
(Biatorina synothed) Hedlund found that there were constantly present two
types of pycnidia: the one with short slightly bent spores 4-8 yu, x 1*5 //,, the
other with much longer bent spores 10-20 ft x 1-5 p; there. were numerous
transition forms between the two kinds of spores. Germination took place
by the prolongation of the spore ; the hypha produced became septate and
branches were soon formed. Hedlund found that frequently germination
had already begun in the spores expelled from the spermogonium. In newly
formed thalline areolae it was possible to trace back the mycelium to innu-
merable germinating spores of both types, long and short.
Lindsay had recorded more than one form of spermogonium on the
same lichen thallus, the spermatia varying considerably in size; but he was
most probably dealing with the mixed growth of more than one species.
The observations of Moller and Hedlund on this point are more exact, but
the limits of variation would very well include the two forms found by
Moller in Calicium tradielinum ; and in the different pycnidia of Catillaria
denigrata Hedlund not only observed transition stages between the two
kinds of spores, but the longer pycnidiospores, as he himself allows, indicated
the elongation prior to germination : there is no good evidence of more than
one form in any species.
F. PYCNIDIA WITH MACROSPORES
Tulasne2 records the presence on the lichen thallus of "pycnidia" as
well as of "spermogonia"; the former producing stylospores, larger bodies
than spermatia, occasionally septate and containing oil-drops or guttulae.
These spores are pyriform or ovoid in shape and are always borne at the
tips of simple sporophores. He compared the pycnidia with the fungus
genera Cytospora, Septoria, etc. As a rule they occur on lichens with a
poorly developed thallus, on some species of Lecanora, Lecanactis, Cali-
cium, Porina, in the family Strigulaceae and in Peltigera.
There is no morphological difference between pycnidia and spermogonia
except that the spermatia of the latter are narrower ; but the difference is
so slight that, as Steiner has pointed out, these organs found on Lecanora
piniperda, L. Sambuci and L. effusa have been described at one time as
containing microconidia (spermatia), at another macroconidia (stylospores).
1 Hedlund 1892. 2 Tulasne 1852.
SPERMOGONIA 205
He also regards as macrospores those of the pycnidia of Calicium tra-
chelinum which Moller was able to germinate so successfully, and all the
more so as they were brownish in colour, true microspores or spermatia
being colourless.
Miiller1 has recorded some observations on the pycnidia and stylospores
of the Strigulaceae, a family of tropical lichens inhabiting the leaves of
the higher plants. On the thallus of Strigula elegans var. tremula from
Madagascar and from India, he found pycnidia with stylospores of abnormal
dimensions measuring 18-26/4 in length and 3 /A in width, and with I to 7
cross septa. In Strigula complanata var. genuina the stylospores were 2-8-
septate and varied from 7-65 /* in length, some of the spores being thus
ten times longer than others, while the width remained the same. Miiller
considers that in these cases the stylospore has already grown to a septate
hypha while in the pycnidium. As in the pycnidiospores, described later
by Hedlund, the spores had germinated by increase in length followed by
septation.
The spermogonia of Strigula, which are exactly similar to the pycnidia
in size and structure, produce spermatia, measuring about 3/4 x 2/*, and it is
suggested by Miiller that the stylospores may represent merely an advanced
stage of development of these spermatia. Both organs were constantly
associated on the same thallus ; but whereas the spermogonia were abundant
on the younger part of the thallus at the periphery, they were almost
entirely replaced by pycnidia on the older portions near the centre, only
a very few spermogonia (presumably younger pycnidial stages) being found
in that region.
Lindsay2 has described a great many different lichen pycnidia, but in
many instances he must have been dealing with species of the "Fungi imper-
fecti" that were growing in association with the scattered granules of
crustaceous lichens. There are many fungi — Discomycetes and Pyreno-
mycetes — parasitic on lichen thalli, and he has, in some cases, undoubtedly
been describing their secondary pycnidial form of fruit, which indeed may
appear far more frequently than the more perfect ascigerous form, and might
easily be mistaken for the pycnidial fructification of the lichen.
G. GENERAL SURVEY
a. SEXUAL OR ASEXUAL. It has been necessary to give the preceding
detailed account of these various structures — pycnidia or spermogonia — in
view of the extreme importance attached to them as the possible male
organs of the lichen plant, and, in giving the results obtained by different
workers, the terminology employed by each one has been adopted as far as
1 Miiller 1885. 2 Lindsay 1859 and 1872.
2o6 REPRODUCTION
possible: those who consider them to be sexual structures call them spermo-
gonia ; those who refuse to accept that view write of them as pycnidia.
Tulasne, Nylander and others unhesitatingly accepted them as male
organs without any knowledge of the female cell or of any method of ferti-
lization. Stahl's discovery of the trichogyne seemed to settle the whole
question ; but though he had evidence of copulation between the spermatium
and the receptive cell or trichogyne he had no real record of any sexual
process.
Many modern lichenologists reject the view that they are sexual; they
regard them as secondary organs of fructification analogous to the pycnidia
so abundant in the related groups of fungi. One would naturally expect
these pycnidia to reappear in lichens, and it might be considered somewhat
arbitrary to classify pycnidia in Sphaeropsideae as asexual reproductive
organs, and then to regard the very similar structures in lichens as sexual
spermogonia. It has also been pointed out that when undoubted pycnidia
do occur on the lichen thallus, as in Calicium, Strigula, Peltigera, etc., they
in no way differ from structures regarded as spermogonia except in the size
of the pycnidiospores — and, even among these, there are transition forms.
The different types of spermatia can be paralleled among the fungal pyc-
nidiospores and the same is also true as regards the sporophores generally.
Those described as arthrosterigmata by Nylander — as endosporous by
Steiner — were supposed to be peculiar to lichens; but recently Laubert1 has
described a fungal pycnidium which grew on the trunk of an apple tree and
in which the spores are not borne on upright sporophores but are budded
off from the cells of the plectenchyma lining the pycnidium. It may be that
future research will discover other such instances, though that type of sporo-
phore is evidently of very rare occurrence among fungi.
b. COMPARISON WITH FUNGI. The most obvious spermogonia among
fungi with which to compare those of lichens occur in the Uredineae where
they are associated with the life-cycle of a large number of rust species.
They are small flask-shaped structures very much like the simpler forms of
pycnidia and they produce innumerable spermatia which are budded off from
the tips of simple spermatiophores. The mature spermatium has a delicate
cell-wall and contains a thin layer of cytoplasm with a dense nucleus which
occupies almost the whole cavity, cytological characters which, as Blackman2
has pointed out, are characteristic of male cells and are not found in any
asexual reproductive spores. If we accept Istvanm's3 description and figures
of the lichen spermatia as correct, their structure is wholly different : there
being a very small nucleus in the centre of the cell comparable in size with
those of the vegetative hyphae (Fig. 1 15).
1 Laubert 1911. 2 Blackman 1904. 3 Istvanffi 1895.
SPERMOGONIA 207
Lichen " spermatia " also differ very strikingly from the male cells of any
given group of plants in their very great diversity of form and size; but the
a
Fig. 115. a, spermatia; b, hypha produced from spermatium of
Buellia punctiformis Th. Fr. XQSO (after Istvanffi).
chief argument adduced by the opponents of the sexual theory is the capacity
of germination that has been proved to exist in a fair number of species. It
is true that germination has been induced in the spermatia of the Uredines by
several research workers — by Plowright1, Sappin-Trouffy2 and by Brefeld3 —
who employed artificial nutritive solutions (sugar or honey), but the results
obtained were not much more than the budding process of yeast cells. Bre-
feld also succeeded in germinating the " spermatia " of a pyrenomycetous
fungus, Polystigma rubntm, one of the germinating tubes reaching a length
four times that of the spore; but it is now known that all of these fungal
spermatia are non-functional, either sexually or asexually, and degenerate
soon after their expulsion, or even while still in the spermogonium.
c. INFLUENCE OF SYMBIOSIS. In any consideration of lichens it is
constantly necessary to hark back to their origin as symbiotic organisms,
and to bear in mind the influence of the composite life on their development.
After germination from the spore, the lichen hypha is so dependant on its
association with the alga, that, in natural conditions, though it persists
without the gonidia for a time, it attains to only a rather feeble growth of
mycelial filaments. In nutritive cultures, as Moller has proved, the absence
of the alga is partly compensated by the artificial food supply, and a scanty
thalline growth is formed up to the stage of pycnidial fruits. Not only in
pycnidia but in all the fruiting bodies of lichens, symbiosis has entailed
a distinct retrogression in the reproductive importance of the spores, as
compared with fungi.
In Ascomycetes, the asci constitute the overwhelming bulk of the
hymenium ; in most lichens, there are serried ranks of paraphyses with
comparatively few asci, and the spores are often imperfectly developed.
It would not therefore be surprising if the bodies claimed by Moller and
others as pycnidiospores had also lost even to a considerable extent their
reproductive capacity.
1 Plowright 1889. 2 Sappin-Trouffy 1896. 3 Brefeld 1891.
208 REPRODUCTION
d. VALUE IN DIAGNOSIS. Lichen spermpgonia have once and again
been found of value in deciding the affinity of related plants, and though
there are a number of lichens in which we have no record of their occurrence,
they are so constant in others, that they cannot be ignored in any true
estimation of species. Nylander laid undue stress on spermogonial characters,
considering them of almost higher diagnostic value than the much more
important ascosporous fruit. They are, after all, subsidiary organs, and
often — especially in crustaceous species — they are absent, or their relation
to the species under examination is doubtful.
CHAPTER V
PHYSIOLOGY
I. CELLS AND CELL PRODUCTS
ANY study of cells or cell- membranes in lichens should naturally include
those of both symbionts, but the algae though modified have not been
profoundly changed, and their response to the influences of the symbiotic
environment has been already described in the discussion of lichen gonidia.
The description of cells and their contents refers therefore mainly to the
fungal tissues which form the framework of the plant ; they have been
transformed by symbiosis to lichenoid hyphae in some respects differing
from, in others resembling, the fungal hyphae from which they are derived.
A. CELL-MEMBRANES
a. CHITIN. It was recognized by workers in the early years of the
nineteenth century that the substance forming the cell-walls of fungal
hyphae differed very markedly from the cellulose of the membranes in other
groups of plants, the blue colouration with iodine and sulphuric acid so
characteristic of cellulose being absent in most fungi. Various explanations
were suggested ; but it was always held that the doubtful substance was a
cellulose containing something peculiar to fungi, this view being strengthened
by the fact that, after long treatment with potash, a blue reaction was
obtained. It was called fungus-cellulose by De Bary1 in order to distinguish
it from true cellulose.
It was not till a much later date that any exact work was done on the
fungal cell, and that Gilson2 by his researches was able to prove that the
membranes of fungi contained probably no cellulose, or, "if cellulose were
present, it was in a different condition from the cellulose of other plants."
Winterstein3 followed with the results of his examination of fungus-cellulose:
he found that it contained nitrogen and therefore differed very considerably
from typical plant cellulose. Gilson4 published a second paper dealing
entirely with fungal tissues in which he also established the presence of
nitrogen, and added that this nitrogenous compound resembled in various
ways the chitin8 of animal cells. He further discovered that by heating it
with potash a substance was obtained that took a reddish-violet stain when
treated with* iodine and weak sulphuric acid. This substance, called by him
mycosin, was proved later to be similar to chitosan5, a product of chitin.
1 De Bary 1866, p. 7. 2 Gilson 1893. 3 Winterstein 1893. 4 Gilson 1894.
5 The chemical formula of chitin \» given as CaoHiooNgOas, that of chitosan as CuH^NaOio-
S. L. 14
210 PHYSIOLOGY
Escombe1 analysed the hyphal membranes of Cetraria and found that
they consisted mainly of a body called by him lichenin and of a para-
galactan. From Peltigera he extracted a substance with physical properties
agreeing fairly well with those of chitosan, though analysis did not give
percentages reconcilable with that substance; the yield however was very
small. No lichenin was detected.
Van Wisselingh2 examined the hyphae of lichens as well as of fungi and
experimented with a considerable number of both types of plants. He
succeeded in proving the presence of chitin in the higher fungi (Basidio-
mycetes and Ascomycetes) and in lichens with one or two exceptions
. (Cladonia and Cetraria}. Though in some the quantity found was exceed-
ingly small, in others, such as Peltigera, the walls of the hyphae were
extremely chitinous. More recently Wester3 has gone into the question as
regards lichens, and he has practically confirmed all the results previously
obtained by Wisselingh. In some species, as for instance in Cladonia rangi-
ferina, Cl. squamosa, Cl. gracilis, Ramalina calicaris, Solorina crocea and
others, he found that chitin existed in large quantities, while in Evernia
prunastri, Usnea florida, U. artiailata, Sticta damaecornis and Parmelia
saxatilis very little was present. The variation in the amount present may
be very great even in the species of one genus : none for instance has been
detected in Cetraria islandica nor in C. nivalis while it is abundant in other
Cetrariae. There is also considerable variation in quantity in different
individuals of the same species, and even in different parts of the thallus
of one lichen. Factors such as habitat, age of the plant, etc., may, however,
account to a considerable extent for the differences in the results obtained.
b. LICHENIN AND ALLIED CARBOHYDRATES. It has been proved, as
already stated, that chitin is present in the hyphal cell-walls of all the lichens
examined except in those of Cetraria islandica (Iceland Moss), C. nivalis
and, according to Wester3, in those of Bryopogon (Alectoriae). In these
lichens another substance of purely carbohydrate nature is the chief consti-
tuent of the cell-walls which swell up when soaked in water to a colourless
gelatinous substance.
Berzelius4 first drew attention to the peculiar qualities of this lichen
product, and, recognizing its resemblance in many respects to ordinary starch,
he called it " lichen-starch " or " moss-starch." More exact observations were
made later by Guerin-Varry5 who described its properties and showed by
his experiments that it contained no admixture of either starch or gum. He
adopted the name lichenin for this organic soluble part of Iceland Moss.
An analysis of lichenin was made by Mulder6 who detected in addition to
lichenin, which coloured yellow with iodine, small quantities of a blue-
1 Escombe 1896. 2 Wisselingh 1898 3 Wester 1909. 4 Berzelius 1813.
5 Guerin-Varry 1834. s Mulder 1838.
CELLS AND CELL PRODUCTS 211
colouring substance which could be dissolved out from the lichenin and
which he considered to be true starch. Berg1 also demonstrated the com-
pound nature of lichenin: he isolated two isomerous substances with the
formula C6 H10 O5. The name " isolichenin " was given to the second blue-
colouring substance by Beilstein2 in 1881.
More recently Escombe3 has chemically analysed the cell-wall of Cetraria
islandica: after the elimination of fat, oil, colouring matter and bitter consti-
tuents he found that there remained the compound lichenin, an anhydride of
galactose with the formula C6 H10O5, which, as stated above, consists of two
substances lichenin and isolichenin4; the latter is soluble in cold water and
gives a blue reaction with iodine, lichenin is only soluble in hot water and is
not coloured blue. Both are derivatives of galactose, a sugar found in a great
number of organic tissues and substances, among others in gums.
Lichenin has also been obtained by Lacour5 from Lecanora esculenta, an
edible desert lichen supposed to be the manna of the Israelites. Wisselingh6
tested the hymenium of thirteen different lichens for lichenin. He found it
in the walls of the ascus of all those he examined except Graphis. Everniin,
a constituent of Evernia prunastri, was isolated and described by Stude7.
It is soluble in water and, though considered by Czapek8 to be identical
with lichenin, it differs, according to Ulander", in being dextro-rotatory to
polarized light; lichenin on the contrary is optically inactive. Escombe3
also obtained a substance from Evernia which he considered to be comparable
with chitosan. Usnein which has been extracted6 from Usnea barbata
may also be identical with lichenin, but that has not yet been established.
Ulander9 examined chemically the cell-walls of a fairly large number of
lichens. Cetraria islandica, C. aculeata and Usnea barbata, designated as
the " Cetraria group," contained soluble mucilage-forming substances similar
to lichenin. A second " Cladonia group " which included Cl. rangiferina
with the variety alpestris, Stereocaulon paschale and Peltigera aphthosa yielded
almost none. After the soluble carbohydrates were removed by hot water,
the insoluble substances were hydrolysed and the "Cetraria group" was found
to contain abundant d-glucose with small quantities of d-mannose and
d-galactose; the "Cladonia group," abundant d-mannose and d-galactose with
but little d-glucose. Hydrolysis was easier and quicker with the former group
than with the latter.
Besides these, which rank as hexosans, Ulander found small quantities
of pentosans and methyl pentosans. All these substances which are such
important constituents of the hyphal membranes of lichens are classed by
Ulander as hemicelluloses of the same nature as mannan, galactan and dex-
tran, or as substances between hemicellulose and the glucoses represented
1 Berg 1873. - Beilstein ex Errera 1882, p. 16 (note). 3 Escombe 1896. 4 Wiesner 1900.
5 Lacour 1880. 6 Wisselingh 1898. 7 Stude 1864. 8 Czapek 1905, I. p. 515. 9 Ulander 1905.
14—2
212 PHYSIOLOGY
by lichenin, everniin, etc. They are doubtless reserve stores of food material,
and they are chiefly located in the cell-walls of the medullary hyphae which
are often so thick as almost to obliterate the lumen of the cells. Ulander
made no test for chitin in his researches.
Ulander's results have been confirmed by those obtained by K. Miiller1.
In Cladonia rangiferina, Muller found that the cell-membranes of the hyphae
contained, as hemicelluloses, pentosans in small quantities and galactan, but
no lichenin and very little chitin. In Evernia prunastri hemicelluloses formed
the chief constituents of the thallus, and from it he was able to isolate
galactan soluble in weak hot acid, and everniin soluble in hot water, the
latter with the formula C7Hi5O6, a result differing from that obtained by
Stiide2 who has given it as C9H14O7; chitin was also present in small
quantities. In Ramalina fraxinea, the soluble part of the thallus (in hot
water) differed from everniin and might probably be lichenin. Cetraria
islandica was also analysed and yielded various hemicelluloses, chiefly
dextran and galactan, with less pentosan. No chitin has ever been found in
this lichen. In testing minute quantities of material for chitin, Wisselingh3
heated the tissue in potash to i6o°C. The potash was then gradually re-
placed by glycerine and distilled water; the precipitate was placed on a slide
and the preparation stained under the microscope by potassium-iodide-iodine
and weak sulphuric acid. Chitin, if present, would have been changed by
the potash to mycosin which gives a violet colour with the staining solution.
It has been stated by Schellenberg4 that these lichen membranes may
become lignified. He obtained a red reaction with phloroglucine test
for lignin in Cetraria islandica and Cladonia furcata. Further research is
required.
c. CELLULOSE. Several workers claim to have found true cellulose in
the cell-walls of the hyphal tissues of a few lichens ; but the more careful
analyses of Escombe5 Wisselingh3 and Wester6 have disproved their results.
The cell-walls of all the gonidia, however, are formed of cellulose, or according
to Escombe of glauco-cellulose, except those of Peltigera in which Wester
found neither cellulose nor chitin. Czapek7 suggests that the blue reaction
with iodine characteristic of the cell-walls in some apothecia, of the asci and
of the hyphae in cortex or medulla in a few instances, may be due to the
presence of carbohydrates of the nature of galactose. Moreau8 in a recent
paper terms the substance that gives a blue reaction with iodine at the tips
of the asci " amyloid." In Peltigera the ascus tip is occupied by such a plug
of amyloid which at maturity is projected like a cork from the ascus and
may be found on the surface of the hymenium.
1 Muller 1905. 2 Stude 1864. 3 Wisselingh 1898. 4 Schellenberg 1896.
5 Escombe 1896. 6 Wester 1909. 7 Czapek 1905, I. p. 515. 8 Moreau 1916.
CELLS AND CELL PRODUCTS 213
B. CONTENTS AND PRODUCTS OF THE FUNGAL CELLS
a. CELL-SUBSTANCES. The cells of lichen hyphae contain protoplasm
and nucleus with glucoses. It is doubtful if starch has been found in fungal
hyphae ; it is replaced, in some of the tissues at least, by glycogen, a carbo-
hydrate (C6 H10 Os) very close to, if not identical with, animal glycogen, a
substance which is soluble in water and colours reddish-brown (wine-red)
with iodine. Errera1 first detected its presence in Ascomycetes where it is
associated with the epiplasm of the cells, more especially of the asci, and he
considered it to be physiologically homologous with starch. He included
lichens, as Ascomycetes, in his survey of fungi and quotes, in support of his
view that lichen hyphae also contain glycogen, a statement made by Schwen-
dener2 that "the contents of the ascogenous hyphae of Coenogonium Linkii
stain a deep-brown with iodine." Errera also instances the red-brown reaction
with iodine, described by de Bary3, as characteristic of the large spores of
Ochrolechia (Lecanora}pallescens, while the germinating tubes of these spores
become yellow with iodine like ordinary protoplasm. Glycogen has been,
so far, found only in the cells of the reproductive system.
Iodine was found by Gautier4 in the gonidia of Parmelia and Peltigera,
i.e. both in bright-green and blue-green algae. The amount was scarcely
calculable.
Herissey5 claims to have established the presence of emulsin in a large
series of lichens belonging to such widely separated genera as Cladonia,
Cetraria, Evernia, Peltigera, Perttisaria, Parmelia, Ramalina, and Usnea. It
is a ferment which acts upon amygdalin, though its presence has been
proved in plants such as lichens where no amygdalin has been found*.
Diastase was demonstrated in the cells of Roccella tinctoria, R. Montagnei
and oiDendrographa leucophaea by Ronceray7 who states that, in conjunction
with air and ammonia, it forms orchil, the well-known colouring substance
of these lichens. Diastatic ferments have also been determined8 in Usnea
florida, Physcia parietina, Parmelia perlata and Peltigera canina.
b. CALCIUM OXALATE. Oxalic acid (C2H2O4) is an oxidation product
of alcohol and of most carbohydrates and in combination is a frequent
constituent of plant cells. Knop9 held that it was formed in lichens by the
reduction and splitting of lichen acids, though, as Zopf10 has pointed out,
these are generally insoluble. Hamlet and Plowright11 demonstrated the
presence of free oxalic acid in many families of fungi including Pezizae and
Sphaeriae. The acid combines with calcium to form the oxalate (CaC2O4),
which in the crystalline form is very common in lichens. In the higher
1 Errera 1882. 2 Schwendener 1862, p. 231. 3 De Bary 1866-1867, p. 211. 4 Gautier 1899.
5 Herissey 1898. 6 Czapek 1905, II. p. 257. ' Ronceray 1904. 8 Zopf in Schenk 1890, p. 448.
9 Knop 1872. 10 Zopf 1907. u Hamlet and Plowright 1877.
2i4 PHYSIOLOGY
plants the crystals are formed within the cell, but in lichens they are always
deposited on the outer surface of the hyphal membranes, mainly of the
medulla and the cortex.
Calcium oxalate was first detected in lichens by Henri Braconnot1, who
extracted it by treating the powdered thallus of a number of species (Pertu-
saria communis, Diploschistes scruposus, etc.) with different reagents. The
quantity present varies greatly in lichens : Zopf2 found that it was abundant
in all the species inhabiting limestone, and states that in such plants the
more purely lichenic acids are relatively scarce. Errera3 has calculated the
amount of calcium oxalate in Lecanora esculenta, a desert lime-loving
lichen, to be about 60 per cent, of the whole substance of the thallus.
Euler4 gives for the same lichen even a larger proportion, 66 per cent, of
the dry weight. In Pertusaria communis, a corticolous species, the oxalate
occurs as irregular crystalline masses in the medulla (Fig. 116) and has
been calculated as 47 per cent, of the
whole substance. Other crustaceous species
such as Diploschistes scrufiosus, Haema-
tomma coccineum, H. ventosum, Lecanora
saxicola, Lecanora tartarea, etc., contain
large amounts either in the form of octa-
hedral crystals or as small granules.
• Ro«»dahl' has recently made obser-
gonidia; c, medulla; rf, crystal of cal- vations as to the presence of the oxalate
ciuni oxalate. x ca. 100. ., in /• i i_ r> /• r\c
in the thallus of the brown Parmehae. Of
the fourteen species examined by him, eleven contained calcium oxalate as
octahedral crystals or as small prisms, often piled up in thick irregular
masses. Usually the crystals were located in the medullary part of the
thallus, but in two species, Parmelia verruculifera and P. papulosa, they
were abundant on the surface cells of the upper cortex.
c. IMPORTANCE OF CALCIUM OXALATE TO THE LICHEN PLANT. It is
natural to conclude that a substance of frequent occurrence in any group of
plants is of some biological significance, and suggestions have not been
lacking as to the value of oxalic acid or of calcium oxalate in the economy
of the lichen thallus. Oxalic acid is known to be one of the most efficient
solvents of argillaceous earth and of iron oxides likely to be in the soil.
These materials are also conveyed to the thallus as air-borne dust, and would
thus, with the aid of the acid, be easily dissolved and absorbed. As a direct
proof of this, Knop6 has stated that lichen-ash always contains argillaceous
earth. According to Kratzmann7, aluminium, a product of clay, is stored
up in various lichens. He proved the amount in the ash of Umbilicaria
1 Braconnot 1825. 2 Zopf 1907. 3 Errera 1893. 4 Euler 1908, p. 7.
6 Rosendahl 1907. 6 Knop 1872. 7 Kratzmann 1913.
CELLS AND CELL PRODUCTS 215
pustulata to be 4/46 per cent., in Usnea barbata 179 pe.r cent., in U. longissima
considerable quantities while in Roccella tinctoria it occurred in great abun-
dance. It was also abundant in Diploschistes scruposus, 28' 17 per cent.; it
declined in Variolaria (Pertusaria) dealbata to 777 per cent., in Cladonia
rangiferina to 176-2-12 per cent, and in Ramalina fraxinea to r8 per cent.
Calcium oxalate is directly advantageous to the thallus by virtue of the
capacity of the crystals to reduce or prevent evaporation, as has been
pointed out by Zukal1. A like service afforded by crystals to the leaves of
the higher plants in desert lands has been described by Kerner2. These
are frequently encrusted with lime crystals which allow the copious night
dews to soak underneath them to the underlying cells, while during the day
they impede, if they do not altogether check, evaporation.
Calcium oxalate crystals are insoluble in acetic acid, soluble in hydro-
chloric acid without evolution of gas; they deposit gypsum crystals in
a solution of sulphuric acid.
C. OIL-CELLS
a. OIL-CELLS OF ENDOLITHIC LICHENS. Calcicolous immersed lichens
are able to dissolve the lime of the substratum, and their hyphae penetrate
more or less deeply into the rock. In some forms the entire thallus may
thus be immersed, the fruits alone being visible on the surface of the stone.
In two such species, Verrncaria calciseda and Petractis (Gyalecta) exantJie-
matica, Steiner3 detected peculiar sphaeroid or barrel-shaped cells that
differed from the other hyphal cells of the thallus, not only in their form,
but in their greenish-coloured contents. Similar cells were found by Zukal4
in another immersed (endolithic) lichen, Verrucaria rupestris f. rosea. He
describes them as roundish organs crowded on the hyphae and filled with a
greenish shimmering protoplasm. He5 found the same types of sphaeroid
and other swollen cells in the immersed thallus of several calcicolous lichens
and he finally determined the contents as fat in the form of oil. He found
also that these fat-cells, though very frequent, were not constantly present
even in the same species. His observations were confirmed by Hulth6 for
a number of allied crustaceous lichens that grow not only on limestone but
on volcanic rocks. In them he found a like variety of fat-cells — intercalary or
torulose cells, terminal sphaeroid cells and hyphae containing scattered oil-
drops. Bachmann7 followed with a study of the thallus of purely calcicolous
lichens. The specialized oil-cells were fairly constant in the species he
examined, and, as a rule, they were formed either in the tissues immediately
below, or at some distance from, the gonidial zone. Funfstuck8 has also
1 Zukal 1895, p. 1311. - Kerner and Oliver 1894, p. 235. 3 Steiner 1881. 4 Zukal 1884.
5 Zukal 1886. 6 Hulth 1891. 7 Bachmann 1892. 8 Funfstuck 1895.
216
PHYSIOLOGY
published an account .of various oil-cells in a large series of calcicolous
lichens (Fig. 117).
The occurrence of oil- (or fat-) cells is not dependent on the presence of any
particular alga as the gonidium of
the lichen. Funfstuck 1 has described
the immersed thallus of Opegrapha
saxicola as one of those richest in
fat-cells. The gonidia belong to the
a filamentous alga Trentepohlia um-
brina and form a comparatively
thin layer about 160/4 thick near
the upper surface; isolated algal
branches may grow down to 350/4
into the rock, while the fungal ele-
ments descend to 1 1-5 mm., and
though the very lowest hyphae were
without oil — as were those imme-
diately beneath the gonidia — the
interlying filaments, he found, were
crowded with oil-cells. Sphaeroid
terminal cells were not present.
Fiinfstiick1 has re-examined the
thallus of Petractis exanthematica,
an almost wholly immersed lichen
with a gelatinous gonidium, a species
of Scytonema. The thallus is homoio-
merous : the alga forms no special
zone, it intermingles with the hy-
phae dowrn to the very base of the
thallus; the hyphae are extremely
slender and at the base they measure
only about I/A in width. Oil-cells
are abundant in the form of inter-
calary cells about 3-5/4 in thickness. Nearer the surface sphaeroid cells
are formed on short lateral outgrowths ; they measure 14-16/4 in diameter
and occur in groups of 15 to 20. The superficial part of the thallus is a
mere film ; the hyphae composing it are slightly stouter and more thickly
interwoven.
Bachmann2 and Lang3 have further described the anatomy of endolithic
thalli especially with reference to oil-cells, and have supplemented the
researches of previous workers. New methods of cutting the rock in thin
1 Fiinfstiick 1899. 2 Bachmann 1904' . 3 Lang 1906.
Fig. 117. Lecidea immersa Ach. A, sphaeroid
fat-cells from about 8 mm. below the surface
x 550. B, oil-hyphae in process of emptying :
a, sphaercid cells containing oil ; b, cells with
oil-globules x 600 (after Fiinfstiick).
CELLS AND CELL PRODUCTS
217
slices and of dissolving away the lime enabled them to see the tissues in
their relative positions. In these immersed lichens, as described by them and
by previous writers, and more especially in calcicolous species, the gonidial
zone of Protococcaceous algae lies near the surface of the rock, and is
mingled with delicate, thin-walled hyphae which usually do not contain oil.
The more deeply immersed layer is formed of a weft of equally thin-walled
hyphae, some of the cells of which are swollen and filled with fat globules.
These oil-cells may occur at intervals along the hyphae or they may form
an almost continuous row. In addition, strands or bundles of hyphae (Fig.
1 1 8) containing few or many oil globules traverse the tissue, and true
Fig. r 1 8. Biatorella (Sarcogyne) simplex Br. and Rostr.
a, sphaeroid oil-cells ; b, strand of oil-hyphae from
10-15 mm. below the surface, x 585 (after Lang).
sphaeroid cells are generally present. These latter arise in great numbers
on short lateral branchlets, usually near the tip of a filament and the groups
of cells are not unlike bunches of grapes. Sometimes the oil-cells are massed
together into a complex tissue. Hyphae from this layer pierce still deeper
into the rock and constitute the rhizoidal portion of the thallus. They also
produce sphaeroid oil-cells in great abundance (Fig. 119). In the immersed
Fig. 119. Biatorella pruinosa Mudd. a, complex of sphaeroid
oil-cells from lomm. below the surface; t>, hypha of sphaeroid
cells also from inner part of the thallus. x 585 (after Lang).
218 PHYSIOLOGY
thallus of Sarcogyne (Biatorella) pruinosa Lang1 estimated the gonidial zone
as 1 75-200 /A in thickness, while the colourless hyphae penetrated the rock
to a depth of quite 15 mm.
b. OIL-CELLS OF EPILITHIC LICHENS. The general arrangement of the
tissues and the occurrence and form of the oil-cells vary in the different
species according to the nature of the substratum. This has been clearly
demonstrated by Bachmann2 in Aspicilia (Lecanora} calcarea, an almost
exclusively calcareous lichen as the name implies.
On limestone, he found sphaeroid cells formed in
great abundance on the deeply penetrating rhi-
zoidal hyphae (Fig. 120). On a non-calcareous
brick substratum3, a specimen had grown which of
necessity was epilithic. The cortex and gonidial
Fig. 120. Lecanora (Aspi- zone together were 40 ft thick; immediately below
cilia) cah-area Sommerf. there were hyphae with irregular cells free from oil ;
Early stage of sphaeroid
cell formation x 175 (after lower still there was formed a compact tissue of
globose fat-cells. In this case the calcareous lichen
still retained the capacity to form oil-cells on the non-calcareous impene-
trable substance.
Very little oil is formed, as a rule, in the cells of siliceous crustaceous
lichens which are almost wholly epilithic, but Bachmann found a tissue of
oil-cells in the thallus of Lecanora caesiocinerea, from Labrador, on a granite
composed of quartz, orthoclase and traces of mica. A thallus of the same
species collected in the Tyrol, though of a thicker texture, contained no oil.
Bachmann3 suggests no explanation of the variation.
On granite, rhizoidal hyphae penetrate the rock to a slight extent
between the different crystals, but only in connection with the mica4 are
typical sphaeroid cells formed.
More or less specialized oil-cells have been demonstrated by Fiinfstiick5
in several superficial (epilithic) lichens which grow on a calcareous sub-
stratum, as for instance Lecanora (Placodium] decipiens, Lecanora crassa and
other similar species. The oil in these lichens is usually restricted to more or
less swollen or globose cells; but it may also be present in the ordinary
hyphae as globules. Zukal6 found that the smooth little round granules
sprinkled over the thallus of the soil-lichens, Baeomyces roseus and B. nifus,
contained in the hyphae typical sphaeroid oil-cells and that they were
specially well developed in specimens from Alpine situations. In still another
soil-lichen, Lecidea granulosa, shimmering green oil was found in short-celled
torulose hyphae.
Rosendahl's7 researches on the brown Parmeliae resulted in the unex-
1 Lang 1906, p. 171. 2 Bachmann 1892. 3 Bachmann 1904 1. 4 Bachmann 1904 *.
6 Fiinfstuck 1895. « Zukal 1895, p. 1372. » ROSendahl 1907.
CELLS AND CELL PRODUCTS 219
pected discovery of specialized oil-cells situated in the cortices — upper and
lower — of five species out of fourteen which he examined. In one of the
species, P.papulosa, they also occurred in the cortex of the rhizoids. The
oil-cells were thinner-walled and larger than the neighbouring cortical cells ;
they were clavate or ovate in form and sometimes formed irregular external
processes. They were more or less completely filled with oil which coloured
brown with osmic acid, left a fat stain on paper and, when extracted, burned
with a shining reddish flame. These oil-cells were never formed in the
medulla nor in the gonidial region.
c. SIGNIFICANCE OF OIL-FORMATION. Zukal1 regarded the oil stored
in these specialized cells as a reserve product of service to the plant in the
strain of fruit-formation, or in times of prolonged drought or deprivation of
light. According to his observations fat was most freely formed in lichens
when periods of luxuriant growth alternated with periods of starvation. He
cites, as proof of his view, the frequent presence of empty sphaeroid cells,
and the varying production of oil affected by the condition, habitat, etc. of
the plant. Fiinfstiick2, on the other hand, considers the oil of the sphaeroid
and swollen cells as an excretion, representing the waste products of meta-
bolism in the active tissue, but due chiefly to the presence of an excess of
carbonic acid which, being set free by the action of the lichen acids on the
carbonate of lime, forms the basis of fat-formation. He points out that the
development of fat-cells is always greater in endolithic species in which the
gonidial layer — the assimilating tissue — is extremely reduced. In epilithic
lichens with a wide gonidial zone, the formation of oil is insignificant. He
states further that if the oil were a direct product of assimilation, the cells
in which it is stored would be found in contact with the gonidia, and that
is rarely the case, the maximum of fat production being always at some
distance.
Fiinfstuck tested the correctness of his views by a prolonged series of
growth experiments; he removed the gonidial layer in an endolithic lichen,
and found that fat storage continued for some time afterwards, its production
being apparently independent of assimilative activity. The correctness of
his deductions was further proved by observations on lichens from glacier
stones. In such unfavourable conditions the gonidia were scanty or absent,
having died off, but the hyphae persisted and formed oil. He3 also placed
in the dark two quick-growing calcicolous lichens, Verrucaria calciseda and
Opegrapha saxicola. At the end of the experiment, he found that they had
increased in size without using up the fat. Lang4 also is inclined to reject
Zukal's theory, seeing that the fat is formed at a distance from the tissues
— reproductive and others — in need of food supply. He agrees with Fiinf-
stiick that the oil is an excretion and represents a waste-product of the plant.
1 Zukal 1895. 2 Fiinfstuck 1896. 3 Fiinfstuck 1899. 4 Lang 1906.
220 PHYSIOLOGY
Considerable light is thrown on the subject of oil-formation by the results
of recent researches on the nutrition of algae and fungi. Beijerinck1 made
comparative cultures of diatoms taken from the soil, and he found that so
long as culture conditions were favourable, any fat that might be formed
was at once assimilated. If, however, some adverse influence checked the
growth of the organism while carbonic acid assimilation was in full vigour,
fat was at once accumulated. The adverse influence in this case was the
lack of nitrogen, and Beijerinck considers it an almost universal rule in plants
and animals, that where there is absence of nitrogen, in a culture otherwise
suitable, fat-oils will be massed in those cells which are capable of forming
oil. He observed that in two of the cultures of diatoms the one which alone
was supplied with nitrogen grew normally, while the other, deprived of
nitrogen, formed quantities of oil-drops. Wehmer2recordsthe same experience
in his cultural study of Aspergillus. Sphaeroid fat-cells, similar to those
described by Zukal in calcicolous lichens, were formed in the hyphae of a
culture containing an overplus of calcium carbonate, and he judged, entirely
on morphological grounds, that these were not of the nature of reserve-storage
cells.
Stahel3 has definitely established the same results in cultures of other
filamentous fungi. In an artificial culture medium in which nitrogen was
almost wholly absent, the cells of the mycelium seemed to be entirely
occupied byoil-drops, and this fatty condition he considered to be a symptom
of degeneration due to the lack of nitrogen. These experiments enable us
to understand how the hyphae of calcicolous lichens, buried deep in the
substratum, deprived of nitrogen and overweighted with carbonic acid, may
suffer from fatty degeneration as shown by the formation of" sphaeroid-cells."
The connection between cause and effect is more obscure in the case of
lichens growing on the surface of the soil, such as Baeomyces roseus, or of
tree lichens such as the brown Parmeliae, but the same influence — lack of
sufficient nitrogenous food — may be at work in those as well as in the endo-
lithic species, though to a less marked extent
It seems probable that the capacity to form oil- or fat-cells has become
part of the inherited development of certain lichen species and persists
through changes of habitat as exemplified in Lecanora calcarea*.
In considering the question of the formation and the function of fat in
plant cells, it must be remembered that the service rendered to the life of
the organism by this substance is a very variable one. In the higher plants
(in seeds, etc.) fat undoubtedly functions in the same way as starch and
other carbohydrates as a reserve food. It" is evidently not so in lichens, and
in one of his early researches, Pfeffer8 proved that similarly oil was only
1 Beijerinck 1904. * Wehmer 1891. 3 Stahel 1911. * See p. 218.
5 Pfeffer 1877.
CELLS AND CELL PRODUCTS 221
an excretion in the cells of hepatics. He grew various species in which oil-
cells occurred in the dark and then tested the cell contents. He found that
after three months of conditions in which the formation of new carbohydrates
was excluded, the oil in the cells, instead of having served as reserve material,
was entirely unchanged and must in that instance be regarded as an
excretion.
D. LICHEN-ACIDS
a. HISTORICAL. The most distinctive and most universal of lichen pro-
ducts are the so-called lichen-acids, peculiar substances found so far only in
lichens. They occur in the form of crystals or minute granules deposited in
greater or less abundance as excretory bodies on the outer surface of the
hyphal cells. Though usually so minute as scarcely to be recognized as
crystals, yet in a fairly large series their form can be clearly seen with a
high magnification. Many of them are colourless; others are a bright yellow,
orange or red, and give the clear pure tone of colour characteristic of some
of our most familiar lichens.
The first definite discovery of a lichen-acid was made towards the begin-
ning of the nineteenth century and is due to the researches of C. H. Pfaff1.
He was engaged in an examination of Cetraria islandica, the Iceland Moss,
which in his time was held in high repute, not only as a food but as a tonic.
He wished to determine the chemical properties of the bitter principle con-
tained in it, which was so much prized by the Medical Faculty of the period,
though the bitterness had to be removed to render palatable the nutritious
substance of the thallus. He succeeded in isolating an acid which he tested
and compared with other organic acids and found that it was a new substance,
nearest in chemical properties to succinic acid. In a final note, he states
that the new :< lichen-acid," as he named it, approached still nearer to boletic
acid, a constituent of a fungus, though it was distinct from that substance
also in several particulars. The name " cetrarin " was proposed, at a later
date, by Herberger2 who described it as a " subalkaloidal substance, slightly
soluble in cold water to which it gives a bitter taste; soluble in hot water,
but, on continued boiling, throwing down a brown powder which is slightly
soluble in alcohol and readily soluble in ether." Knop and Schnederman3
found that Herberger's "cetrarin" was a compound substance and contained
besides other substances " cetraric acid " and lichesterinic acid. It has now
been determined by Hesse4 as fumarprotocetraric acid (C<j2 H^ O^), a deri-
vative of which is cetraric acid or triaethylprotocetraric acid with the formula
C54H39O24(OC2H6)3 and not C2oHi8O9 as had been supposed. Cetraric acid
has not yet been isolated with certainty from any lichen5.
1 Pfaff 1826. 2 Herberger 1830. s Knop and Schnederman 1846. 4 Hesse 1904.
5Zopf 1907, p. 179.
222 PHYSIOLOGY
After this first isolation of a definite chemical substance, further research
was undertaken, and gradually a number of these peculiar acids were recog-
nized, the lichens examined being chiefly those that were of real or supposed
economic value either in medicine or in the arts. In late years a wider
chemical study of lichen products has been vigorously carried on, and the
results gained have been recently arranged and published in book form by
Zopf1. Many of the statements on the subject included here are taken from
that work. Zopf gives a description of all the acids that had been discovered
up to the date of publication, and the methods employed for extracting each
substance. The structural formulae, the various affinities, derivatives and
properties of the acids, with their crystalline form, are set forth along with
a list of the lichens examined and the acids peculiar to each species. In
many instances outline figures of the crystals obtained by extraction are
given. For a fuller treatment of the subject, the student is referred to the
book itself, as only a general account can be attempted here.
b. OCCURRENCE AND EXAMINATION OF LICHEN-ACIDS. Acids have
been found, with few exceptions, in all the lichens examined. They are
sometimes brightly coloured and are then easily visible under the microscope.
Generally their presence can only be determined by reagents. Over 140
different kinds have been recognized and their formulae determined, though
many are still imperfectly known. As a rule related lichen species contain
the same acids, though in not a few cases one species may contain several
different kinds. In growing lichens, they form I to 8 per cent, of the dry
weight, and as they are practically, while unchanged, insoluble in water, they
are not liable to be washed out by rain, snow or floods. Their production
seems to depend largely on the presence of oxygen, as they are always
found in greatest abundance on the more freely aerated parts of the thallus,
such as the soredial hyphae, the outer rind or the loose medullary filaments.
They are also often deposited on the exposed disc of the apothecium, on the
tips of the paraphyses, and on the wall lining the pycnidia. They are absent
from the thallus of the Collemaceae, these being extremely gelatinous lichens
in which there can be little contact of the hyphae with the atmosphere.
No free acids, so far as is known, are contained in Sticta fuliginosa, but
a compound substance, trimethylamin, is present in the thallus of that lichen.
It has also been affirmed that acids do not occur in any Peltigera nor in
two species of Nephromium, but Zopf1 has extracted a substance peltigerin
both from species of Peltigera and from the section Peltidea.
For purposes of careful examination freshly gathered lichens are most
serviceable, as the acids alter in herbarium or stored specimens. It is well,
when possible, to use a fairly large bulk of material, as the acids are often
present in small quantities. The lichens should be dried at a temperature
* Zopf .907.
CELLS AND CELL PRODUCTS 223
not above 40° C. for fear of changing the character of the contained sub-
stances, and they should then be finely powdered. When only a small
quantity of material is available, it has been recommended that reagents
should be applied and the effect watched under the microscope with a low
power magnification. This method is also of great service in determining
the exact position of the acids in the thallus.
In microchemical examination, Senft1 deprecates the use of chloroform,
ether, etc., seeing that their too rapid evaporation leaves either an amorphous
or crystalline mass of material which does not lend itself to further examina-
tion. He recommends as more serviceable some oil solution, preferably
"bone oil" (neat's-foot oil), in which a section of the thallus should be broken
up under a cover-glass and subjected to a process of slow heating; some
days must elapse before the extraction is complete. The surplus oil is then
to be drained off, the section further bruised and the substance examined.
Acids in bulk should be extracted by ether, acetone, chloroform,
benzole, petrol-ether and lignoin or by carbon bisulphide. Such solvents as
alcohols, acetates and alkali solutions should not be used as they tend to
split up or to alter the constitution of the acids. For the same reason, the
use of chloroform is to a certain extent undesirable as it contains a percentage
of alcohol. Ether and acetone, or a mixture of both, are the most efficient
solvents, and all acids can be extracted by their use, if the material is left
to soak a sufficient length of time, either in the cold or warmed. It is
however advisable to follow with a second solvent in case any other acid
should be present in the tissues. Concentrated sulphuric acid dissolves out
all acids but often induces colour changes in the process.
All known lichen-acids form crystals, though the crystalline form may
alter with the solution used. After filtering and distilling, the residue will
be found to contain a mixture of these crystals along with other substances,
which may be removed by washing, etc.
c. CHARACTER OF ACIDS. Many lichen-acids are more or less bitter to
the taste; they are usually of an acid nature though certain of the substances
are neutral, such as zeorin, a constituent of various Lecanoraceae.Physciaceae
and Cladoniaceae, stictaurin, originally obtained from Sticta aurata, lei-
phemin, from Haematonima coccineum, and others.
A large proportion are esters or alkyl salts formed by the union of an
alcohol and an acid; these are insoluble in alkaline carbonates. It is con-
sidered probable that the fungus generates the acid, while the alcohol arises
in the metabolic processes in the alga. It has indeed been proved that the
alcohol, erythrit, is formed in at least two algae, Protococcus vulgaris and
Trentepohlia jolithns ; and the lichen-acid, erythrin (CaoH^do), obtained
from species of Roccella in which the alga is Trentepohlia, is, according to
1 Senft 1907.
224 PHYSIOLOGY
Hesse, the erythrit ester of lecanoric acid (C16 H14 O7), a very frequent consti-
tuent of lichen thalli. It is certain that the interaction of both symbionts is
necessary for acid production. This was strikingly demonstrated by Tobler1
in his cultural study of the lichen thallus. He succeeded in growing, to a
limited extent, the hyphal part of the thallus of Xanthoria parietina on
artificial media; but the filaments remained persistently colourless until he
added green algal cells to the culture. Almost immediately thereafter the
characteristic yellow colour appeared, proving the presence of parietin,
formerly known as chrysophanic acid. Tobler's observation may easily be
verified in plants from natural habitats. A depauperate form of Placodittm
citrinum consisting mainly of a hypothallus of felted hyphae, with minute
scattered granules containing algae, was tested with potash, and only the
hyphae immediately covering the algal granules took the stain; the hypo-
thallus gave no reaction.
It has been suggested2 that when a decrease of albumenoids takes place,
the quantity of lichen-acid increases, so that the excreted substance should
be regarded as a sort of waste product of the living plant, "rather than as a
product of deassimilation." The subject is not yet wholly understood.
d. CAUSES OF VARIATION IN QUANTITY AND QUALITY OF LICHEN-
ACIDS. Though it has been proved that lichen-acids are formed freely all
the year round on any soil or in any region, it happens occasionally that
they are almost or entirely lacking in growing plants. Schwarz3 found this
to be the case in certain plants of Lecanora tartarea, and he suggests that
the gyrophoric acid contained in the outer cortex of that lichen had been
broken up by the ammonia of the atmosphere into carbonic acid and orcin
which is soluble in water, and would thus be washed away by rain. It has
also been shown by Schwendener4 and others that the outer layers of the
older thallus in many lichens slowly perish, first breaking up and then peeling
off; the denuded areas would therefore have lost, for some time at least,
their particular acids. Fiinfstuck5 considers that the difference in the presence
and amount of acid in the same species of lichen may be due very often
to variation in the chemical character of the substratum, and this view tallies
with the results noted by Heber Howe6 in his study of American Ramali-
nae. He observed that, though all showed a pale-yellow reaction with potash,
those growing on mineral substrata gave a more pronouncedly yellow colour.
M. C. Knowles7 found that in Ramalina scopulontm the colour reaction
to potash varied extremely, being more rapid and more intense, the more
the plants were subject to the influence of the sea-spray.
Lichen-acids are peculiarly abundant in soredia, and as, in some species,
1 Tobler 1909. 2 Keegan 1907. 3 Schwarz 1880, p. 264. 4 Schwendener 1863, p. 180.
8 FiinfstUck 1902. 6 Heber Howe 1913. 7 Knowles 1913.
CELLS AND CELL PRODUCTS 225
the thallus forms these outgrowths, or even becomes leprose more freely in
damp weather, the amount of acids produced may depend on the amount of
moisture in the atmosphere.
Their formation is also strongly influenced by light, as is well shown by
the varying intensity of colour in some yellow thalli. Placodium elegans,
always a brightly coloured lichen, changes from yellow to sealing-wax red
in situations exposed to the full blaze of the sun. Haematomma ventosum,
though greenish-yellow in lowland situations is intensely yellow in the high
Alps. The same variation of colour is characteristic of Rhizocarpon geo-
graphicum which is a bright citron-yellow at high altitudes, and becomes
more greenish in hue as it nears the plains. The familiar foliose lichen
Xanthoriaparietina is a brilliant orange-yellow in sunny situations, but grey-
green in the shade, and then yielding only minute quantities of parietin.
West1 and others have noted its more luxuriant growth and brighter colour
when it grows in positions where nitrogenous food is plentiful, such as the
roofs of farm-buildings, which are supplied with manure-laden dust, and
boulders by the sea-shore frequented by birds.
e. DISTRIBUTION OF ACIDS. Some acids, so far as is known, are only to
be found in one or at most in very few lichens, as for instance cuspidatic
acid which is present in Ramalina cuspidata, and scopuloric acid, a constituent
of Ramalina scopulorum, the acids having been held to distinguish by their
reactions the one plant from the other.
Others of these peculiar products are abundant and widely distributed.
Usninic acid, one of the commonest, has been determined in some 70 species
belonging to widely diverse genera, and atranorin, a substance first discovered
in Lecanora atra, has been found again many times; Zopf gives a list of
about 73 species or varieties from which it has been extracted. Another
widely distributed acid is salazinic acid which has been found by Lettau2 in
a very large number of lichens.
E. CHEMICAL GROUPING OF LICHEN-ACIDS
Most of these acids have been provisionally arranged by Zopf in groups
under the two great organic series: I. The Fat series; and II. The Benzole
or Aromatic series.
I. LICHEN-ACIDS OF THE FAT SERIES
Group i. Colourless substances soluble in alkali, the solution not coloured
by iron chloride. Exs. protolichesterinic acid (C^H^O^ obtained from species
of Cetraria, and roccellic acid (C^H^O^ from species of Roccella, from
Lecanora tartarea, etc.
1 West, W. 1905. 2 I-ettau 1914.
S. L. I5
226 PHYSIOLOGY
Group 2. Neutral colourless substances insoluble in alkalies, but soluble
in alcohol, the solution not coloured by iron chloride. Exs. zeorin (C^H^O^,
a product of widely diverse lichens, such as Lecanora (Zeord) sulphured,
Haematomma coccineum, Physcia caesia, Cladonia deformis, etc. and barbatin
(C9H14O), a product of Usnea barbata.
Group 3. Brightly coloured acids, yellow, orange or red, all derivatives
of pulvinic acid (Ci8H12O5), a laboratory compound which has not been found
in nature. The group includes among others vulpinic acid (C19Hi4O5) from
the brilliant yellow Evernia (Letharia) vulpina, stictaurin (CseH^Og) deposited
in orange-red crystals on the hyphae of Sticta aurata, and rhizocarpic acid
(CaeHaoOg) chiefly obtained from Rhizocarpon geographicum : it crystallizes
out in slender citron-yellow prisms.
Group 4. Only one acid, usninic (Ci8H]6O7), a derivative of acetylacetic
acid, is placed in this group. It is of very wide-spread occurrence, having
been found in at least 70 species belonging to very different genera and
families of crustaceous shrubby and leafy lichens. Zopf himself isolated it
from 48 species.
Group 5. The thiophaninic acid (d2H6O9) group representing only a
small number. They are all sulphur-yellow in colour and soluble in alcohol,
the solution becoming blackish-green or dirty blue on the addition of iron
chloride, with one exception, that of subauriferin obtained from the yellow-
coloured medulla of Parmelia subaurifera which stains faintly wine-red in
an iron solution. Thiophaninic acid, which gives its name to this group,
occurs in Pertusaria lutescens and P. Wulfenii, both of which are yellowish
crustaceous lichens growing mostly on the trunks of trees.
II. LICHEN-ACIDS OF THE BENZOLE SERIES
The larger number of lichen-acids belong to this series, of which 94 at
least are already known. They are divided into two subseries: I. Orcine
derivatives, and II. Anthracene derivatives.
SUBSERIES I. ORCINE DERIVATIVES
Zopf specially insists that the grouping of this series must be regarded
as only a provisional arrangement of the many lichen-acids that are included
therein. All of them are split up into orcine and carbonic acid by ammonia
and other alkalies. On exposure to air, the ammoniacal or alkaline solution
changes gradually into orceine, the colouring principle and chief constituent
of commercial orchil. Orcine is not found free in nature. The orcine sub-
series includes five groups:
Group i. The substances in this group form, with hypochlorite of lime
("CaCl"), red-coloured compounds which yield, on splitting, orsellinic acid.
Zopf enumerates seven acids as belonging to this group, among which is
CELLS AND CELL PRODUCTS 227
lecanoric acid (Ci6H14O7), found in many different lichens, e.g. Roccella tinc-
toria, Lecanora tartarea, etc.: whenever there is a differentiated pith and
cortex it occurs in the pith alone. Erythrin (CaoH^Ojo), a constituent of the
British marine lichen Roccella fuciformi 's, also belongs to this orsellinic group.
Group 2. Substances which also form red products with CaCl, but do
not break up into orsellinic acid. Among the most noteworthy are olivetoric
acid (C21H26O7), a constituent of Evernia furfur acea, perlatic acid (C^H^Ou,)
and glabratic acid (C^H^On), which are obtained from species of Parmelia.
Group 3. Contains three acids of somewhat restricted occurrence. They
do not form red products with CaCl, and they yield on splitting everninic
acid. They are: evernic acid (Ci7H16O7), found in Evernia prunastri var.
vulgaris, ramalic acid (C17H16O7) in Ramalina pollinaria, and umbilicaric acid
(CasH^On) in species of Gyrophora.
Group 4. The numerous acids of this group are not easily soluble and
have a very bitter taste. They are not coloured by CaCl ; when extracted
with concentrated sulphuric acid, the solution obtained is reddish-yellow or
deep red. Among the most frequent are fumarprotocetraric acid (C^H^Oss),
the bitter principle of Cetraria islandica, Cladonia rangiferina^ etc., psoromic
acid (CaoHuOg), obtained from Alectoria implexa, Lecanora varia, Cladonia
pyxidata and many other lichens, and salazinic acid (Ci9HuO10), recorded by
Zopf as occurring in Stereocaulon salazinum and in several Parmeliae, but
now found by Lettau1 to be very wide-spread. He used micro-chemical
methods and detected its presence in 72 species from twelve different families.
The distribution of the acid in the thallus varies considerably.
Group 5. This is called the atranorin group from one of the most im-
portant members. They are colourless substances and, like the preceding
group, are not affected by CaCl, but when split they form bodies that colour
a more or less deep red with that reagent. Atranorin (C19Hi8O8) is one of
the most widely spread of all lichen-acids; it occurs in Lecanoraceae, Par-
meliaceae, Physciaceae and Lecideaceae. Barbatinic acid (C19H^O7), another
member, is found in Usnea ceratina, Alectoria ochroleuca and in a variety of
Rhizocarpon geographicum. A very large number of acids more or less fully
studied belong to this group.
SUBSERIES II. ANTHRACENE DERIVATIVES
The constituents of this subseries are derived from the carbohydrate
anthracene, and are characterized by their brilliant colours, yellow, red.brown,
red-brown or violet-brown. So far, only ten different kinds have been isolated
and studied. Parietin2 (Cj6H12O5), one of the best known, has been extracted
{wn\Xanthoriaparietina,Placodium murorum and several other bright-yellow
1 Lettau 1914.
8 Parietin differs chemically from chrysophanic acid of Rheum, etc.
15 — 2
228 PHYSIOLOGY
lichens; solorinic acid (C16H14O5) occurs in orange-red crystals on the hyphae
of the pith and under surface of Solorina crocea; nephromin (C16H12O6) is
found in the yellow medulla of Nephromium lusitanicum ; rhodocladonic acid
(C12H8O6 or C14H10O7) is the red substance in the apothecia of the red-fruited
Cladoniae.
There are, in addition, a short series of coloured substances which are of
uncertain position. They are imperfectly known and are of rare occurrence.
An acid containing nitrogen has been extracted from Roccella fuciformis,
and named picroroccellin1 (C^HssNgOs). It crystallizes in comparatively large
prisms, has an exceedingly bitter taste, and is very sparingly soluble. It is
the only lichen-acid in which nitrogen has been detected.
One acid at least, belonging to the Fat series, vulpinic acid, which gives the
greenish-yellow colour to Letharia vulpina, has been prepared synthetically
by Volkard2.
F. CHEMICAL REAGENTS AS TESTS FOR LICHENS
The employment of chemical reagents as colour tests in the determination
of lichen species was recommended by Nylander3 in a paper published by
him in 1866. Many acids had already been extracted and examined, and
as they were proved to be constant in the different species where they
occurred, he perceived their systematic importance. As an example of the
new tests, he cited the use of hypochlorite of lime, a solution of which,
applied directly to the thallus of species of Roccella, produced a bright-red
"erythrinic" reaction. Caustic potash was also found to be of service in
demonstrating the presence of parietin in lichens by a beautiful purple
stain. Many lichenologists eagerly adopted the new method, as a sure and
ready means of distinguishing doubtful species ; but others have rejected
the tests as unnecessary and not always to be relied on, seeing that the
acids are not always produced in sufficient abundance to give the desired
reaction, and that they tend to alter in time.
The reagents most commonly in use are caustic potash, generally indi-
cated by K ; hypochlorite of calcium or bleaching powder by CaCl ; and
a solution of iodine by I. The sign -f signifies a colour reaction, while —
indicates that no change has followed the application of the test solution.
Double signs ^ or any similar variation indicate the upper or lower parts of
the thallus affected by the reagent. In some instances the reaction only
follows after the employment of two reagents represented thus: K (CaCl) +.
In such a case the potash breaks up the particular acid and compounds are
formed which become red, orange, etc., on the subsequent application of
hypochlorite of lime.
1 Stenhouse and Groves 1877. 2 Volkard 1894. 3 Nylander 1866.
CELLS AND CELL PRODUCTS 229
As an instance of the value of chemical tests, Zopf cites the reaction of
hypochlorite of lime on the thallus of four different species of Gyrophora,
the "tripe de roche": —
Gyrophora torrefacta CaCl + .
„ polyrhiza CaCl +.
„ proboscidea CaCl ±.
„ erosa CaCl I.
It must however be borne in mind that these species are well differentiated
and can be recognized, without difficulty, by their morphological characters.
Experienced systematists like Weddell refuse to accept the tests unless
they are supported by true morphological distinctions, as the reactions are
not sufficiently constant.
G. CHEMICAL REACTIONS IN NATURE
Similar colour changes may often be observed in nature. The acids of
the exposed thallus cortex are not unfrequently split up by the gradual
action of the ammonia in the atmosphere, one of the compounds thus set
free being at the same time coloured by the alkali. Thus salazinic acid, a
constituent of several of our native Parmeliae, is broken up into carbonic
acid and salazininic acid, the latter taking a red colour. Fumarprotocetraric
acid is acted on somewhat similarly, and the red colour may be seen in
Cetraria at the base of the thallus where contact with soil containing
ammonia has affected the outer cortex of the plant. The same results are
produced still more effectively when the lichen comes into contact with
animal excrement.
Gummy exudations from trees which are more or less ammoniacal may
also act on the thallus and form red-coloured products on contact with the
acids present. Lecanora (Aspicilta) cinerea is so easily affected by alkalies
that a thin section left exposed may become red in time owing to the
ammonia in the atmosphere.
II. GENERAL NUTRITION
A. ABSORPTION OF WATER
Lichens are capable of enduring almost complete desiccation, but though
they can exist with little injury through long periods of drought, water is
essential to active metabolism. They possess no special organs for water
conduction, but absorb moisture over their whole surface. Several inter-
dependent factors must therefore be taken into account in considering the
question of absorption : the type of thallus, whether gelatinous or non-
gelatinous, crustaceous,foliose or fruticose,as also the nature of the substratum
and the prevailing condition of the atmosphere.
23o t PHYSIOLOGY
a. GELATINOUS LICHENS. The algal constituent of these lichens is
some member of the Myxophyceae and is provided with thick gelatinous
walls which have great power of imbibition and swell up enormously in
damp surroundings, becoming reservoirs of water. Species of Collema, for
instance, when thoroughly wet, weigh thirty-five times more than when
dry1. There are no interstices in the thallus and frequently no cortex in
these lichens, but the gelatinous substance itself forms on drying an outer
skin that checks evaporation so that water is retained within the thallus
for a longer period than in non-gelatinous forms. They probably always
retain some amount of moisture, as they share with gelatinous algae the
power of revival after long desiccation.
Gelatinous lichens are entirely dependent on a surface supply of water:
their hyphae — or rhizinae when present — rarely penetrate the substratum.
b. CRUSTACEOUS NON-GELATINOUS LICHENS. The lichens with this
type of thallus are in intimate contact with the substratum whether it be
soil, rock, tree or dead wood. The hyphae on the under surface of the
thallus function primarily as hold-fasts, but if water be retained in the
substratum, the lichen will undoubtedly benefit, and water, to some extent,
will be absorbed by the walls of the hyphae or will be drawn up by capillary
attraction. In any case, it could only be surface water that would be avail-
able, as lichens have no means of tapping any deeper sources of supply.
Lichens are, however, largely independent of the substratum for their
supply of water. Sievers2, who gave attention to the subject, found that
though some few crustaceous lichens took up water from below, most of
them absorbed the necessary moisture on the surface or at the edges of the
thallus or areolae, where the tissue is looser and more permeable. The
swollen gelatinous walls of the hyphae forming the upper layers of such
lichens are admirably adapted for the reception and storage -of water,
though, according to Zukal3, less hygroscopic generally than in the larger
forms. Beckmann4 proved this power of absorption, possessed by the upper
cortex, by placing a crustaceous lichen, Haematomma sp., in a damp
chamber: he found after a while that water had been taken up by the cortex
and by the gonidial zone, while the lower medullary hyphae had remained dry.
Herre5 has recorded an astonishing abundance of lichens from the desert
of Reno, Nevada, and these are mostly crustaceous forms, belonging to
a limited number of species. The yearly rainfall of the region is only about
eight or ten inches, and occurs during the winter months, chiefly as snow.
It is during that period that active vegetation goes on; but the plants still
manage to exist during the long arid summer, when their only possible
water supply is that obtained from the moisture of the atmosphere during
the night, or from the surface deposit of dews.
1 Jumelle 1892. 2 Sievers 1908. 3 Zukal 1895. 4 Beckmann 1907. 5 Herre 1911-.
GENERAL NUTRITION 231
c. FOLIOSE LICHENS. Though many of the leafy lichens are provided
with a tomentum of single hyphae, or with rhizinae on the under surface,
the principal function of these structures is that of attaching the thallus.
Sievers1 tested the areas of absorption by placing pieces of the thallus of
Parmeliae, of Evernia furfuracea, and of Cetraria glauca in a staining
solution. After washing and cutting sections, it was seen that the coloured
fluid had penetrated by the upper surface and by the edge of the thallus,
as in crustaceous forms, but not through the lower cortex.
By the same methods of testing, he proved that water penetrates not
only by capillarity between the closely packed hyphae, but also within the
cells. A considerable number of lichens were used for experiment, and
great variations were found to exist in the way in which water was taken
up. It has been proved that in some species of Gyrophora water is absorbed
from below: in those in which rhizinae are abundant, water is held by them
and so gradually drawn up into the thallus; the upper cortex in this genus
is very thick and checks transpiration. Certain other northern lichens such
as Cetraria islandica, Cladonia rangiferin'a, etc., imbibe water very slowly,
and they, as well as Gyrophora, are able to endure prolonged wet periods.
That foliose lichens do not normally contain much water was proved by
Jumelle2 who compared the weight of seven different species when freshly
gathered, and after being dried ; he found that the proportion of fresh weight
to dry weight showed least variation in Parmelia acetabulum, as ri4 to i ;
in Xanthoria parietina it was as i'2i to I.
d. FRUTICOSE LICHENS. There is no water-conducting tissue in the
elongate thallus of the shrubby or filamentous lichens, as can easily be tested
by placing the base in water: it will then be seen that the submerged parts
alone are affected. Many lichens are hygroscopic and become water-logged
when placed simply in damp surroundings. The thallus of Usnea, for
instance, can absorb many times its weight of water: a mass of Usnea
filaments that weighed 3'8 grms. when dry increased to 13-3 grms. after
having been soaked in water for twelve hours. Schrenk3, who made the
experiment, records in a second instance an increase in weight from
3-97 grms. to in 8 grms. The Cladoniae retain large quantities of water in
their upright hollow podetia. The Australian species, Cladonia retepora, the
podetium of which is a regular network of holes, competes with the Sphagnum
moss in its capacity to take up water.
To conclude : as a rule, heteromerous, non-gelatinous lichens do not
contain large quantities of water, the weight of fresh plants being generally
about three times only that of the dry weight. Their ordinary water content
is indeed smaller than that of most other plants, though it varies at once
with a change in external conditions. It is noteworthy that a number of
1 Sievers 1908- * Jumelle 1892. 3 Schrenk 1898.
232 PHYSIOLOGY
lichens have their habitat on the sea-shore, constantly subject to spray from
the waves, but scarcely any can exist within the spray of a waterfall,
possibly because the latter is never-ceasing.
B. STORAGE OF WATER
The gonidial algae Gloeocapsa, Scytonema, Nostoc, etc. among Myxophy-
ceae, Palmella and occasionally Trentepohlia among Chlorophyceae, have
more or less gelatinous walls which act as a natural reservoir of water for
the lichens with which they are associated. In these lichens the hyphae
for the most part have thin walls, and the plectenchyma when formed — as
below the apothecium in' Collema granuliferum, or as a cortical layer in
Leptogium — is a thin-walled tissue. In lichens where, on the contrary,
the alga is non-gelatinous — as generally in Chlorophyceae — or where the
gelatinous sheath is not formed as in the altered Nostoc of the Peltigera
thallus, the fungal hyphae have swollen gelatinous walls both in the pith
and the cortex, and not only imbibe but store up water.
Bonnier1 had his attention directed to this thickening of the cell-walls
as he followed the development of the lichen thallus. He made cultures
from the ascospore of Physcia (Xanthoria) parietina and obtained a
fair amount of hyphal tissue, the cell-walls of which became thickened,
but more slowly and to a much less extent than when associated with the
gonidia.
He noted also that when his cultures were kept in a continuously moist
atmosphere there was much less thickening, scarcely more than in fungi
ordinarily; it was only when they were grown under drier conditions with
necessity for storage, that any considerable swelling of the walls took place.
Further he found that the thallus of forms cultivated in an abundance of
moisture could not resist desiccation as could those with the thicker
membranes. These latter survived drying up and resumed activity when
moisture was supplied.
C. SUPPLY OF INORGANIC FOOD
As in the higher plants, mineral substances can only be taken up when
they are in a state of solution. Lichens are therefore dependent on the sub-
stances that are contained in the water of absorption : they must receive their
inorganic nutriment by the same channels that water is conveyed to them.
a. FoLIOSE AND FRUTICOSE LICHENS. These larger lichens are provided
with rhizinae or with hold-fasts, which are only absorptive to a very limited
extent ; the main source of water supply is from the atmosphere and the
salts required in the metabolism of the cell must be obtained there also —
1 Bonnier 1889*.
GENERAL NUTRITION 233
from atmospheric dust dissolved in rain, or from wind -borne particles de-
posited on the surface of the thallus which may be gradually dissolved and
absorbed by the cortical and growing hyphae. That substances received
from the atmospheric environment may be all important is shown by the
exclusive habitat of some marine lichens; the Roccellae, Lichinae, some
species of Ramalina and others which grow only on rocky shores are almost
as dependent on sea-water as are the submerged algae. Other lichens, such
as Hydrothyria venosa and Lecanora lacustris, grow in streams, or on boulders
that are subject to constant inundation, and they obtain their inorganic food
mainly, if not entirely, from an aqueous medium.
Though lichens cannot live in an atmosphere polluted by smoke, they
thrive on trees and walls by the road-side where they are liable to be almost
smothered by soil-dust. West1 has observed that they flourish in valleys
that are swept by moisture laden winds more especially if near to a high-
way, where animal excreta are mingled with the dust. The favourite habitats
of Xanthoria parietina are the walls and roofs of farm-buildings where the
dust must contain a large percentage of nitrogenous material ; or stones by
the sea-shore that are the haunts of sea-birds. Sandstede2 found on the
island of Riigen that while the perpendicular faces of the cliffs were quite
bare, the tops bore a plentiful crop of Lecanora saxicola, Xanthoria lychnea
and Candellariella mtellina. He attributed their selection of habitat to the
presence of the excreta of sea-birds. As already stated the connection of
foliose and fruticose lichens with the substratum is mainly mechanical but
occasionally a kind of semiparasitism may arise. Friedrich3 gives an instance
in a species of Usnea of unusually vigorous development. It grew on bark
and the strands of hyphae, branching from the root-base of the lichen,
had reached down to the living tissue of the tree-trunk and had penetrated
between the cells by dissolving the middle lamella. It was possible to find
holes pierced in the cell-walls of the host, but it was difficult to decide if
the hyphae had attacked living cells or were merely preying on dead material.
Lindau4 held very strongly that lichen hyphae were non-parasitic, and merely
split apart the tissues already dead, and the instance recorded by Friedrich
is of rare occurrence5.
That the substratum does have some indirect influence on these larger
lichens has been proved once and again. Uloth6, a chemist as well as a
botanist, made analyses of plants of Evernia prunastri taken from birch bark
and from sandstone. Qualitatively the composition of the lichen substances
was the same, but the quantities varied considerably. Zopf7 has, more
recently, compared the acid content of a form of Evernia furfuracea on rock
with that of the same species growing on the bark of a tree. In the case of
1 West 1905. 2 Sandstede 1904. 3 Friedrich 1906. 4 Lindau 1895*.
6 See p. 109. 6 Uloth 1861. " Zopf 1903.
234 PHYSIOLOGY
the latter, the thallus produced 4 per cent, of physodic acid and 2'2 per cent,
of atranorin. In the rock specimen, which, he adds, was a more graceful plant
than the other, the quantities were 6 per cent, of physodic acid, and 275 per
cent, of atranorin. In both cases there was a slight formation of furfuracinnic
acid. He found also that specimens of Evernia prunastri on dead wood
contained 8*4 per cent, of lichen-acids, while in those from living trees there
was only 4^4 per cent, or even less. Other conditions, however, might have
contributed to this result, as Zopf1 found later that this lichen when very
sorediate yielded an increased supply of atranoric acid.
Ohlert2, who made a study of lichens in relation to their habitat, found
that though a certain number grew more or less freely on either tree, rock
or soil, none of them was entirely unaffected. Usnea barbata, Evernia pru-
nastri and Parmelia physodes were the most indifferent to habitat; normally
they are corticolous species, but Usnea on soil formed more slender filaments,
and Evernia on the same substratum showed a tendency to horizontal growth,
and became attached at various points instead of by the usual single base.
b. CRUSTACEOUS LICHENS. The crustaceous forms on rocks are in a
more favourable position for obtaining inorganic salts, the lower medullary
hyphae being in direct contact with mineral substances and able to act
directly on them. Many species are largely or even exclusively calcicolous,
and there must be something in the lime that is especially conducive to
their growth. The hyphae have been traced into the limestone to a depth
of 15 mm.s and small depressions are frequently scooped out of the rock by
the action of the lichen, thus giving a lodgement to the foveolate fruit.
On rocks mainly composed of silica, the lichen has a much harder sub-
stance to deal with, and one less easily affected by acids, though even silica
may be dissolved in time. Uloth4 concluded from his observations that the
relation of plants to the substratum was chemical even more than physical,
so far as crustaceous species were concerned. He found that the surface of
the area of rock inhabited was distinctly marked : even such a hard substance
as chalcedony was corroded by a very luxuriant lichen flora, the border of
growth being quite clearly outlined. The corrosive action is due he con-
sidered to the carbon dioxide liberated by the plant, though oxalic acid, so
frequent a constituent of lichens, may also share in the corrosion. Egeling5
made similar observations in regard to the effect of lichen growth on granite
rocks; and he further noticed that pieces of glass, over which lichens had
spread, had become clouded, the dulness of the surface being due to a multi-
tude of small cracks eaten out by the hyphae. Buchet6 also gives an instance
of glass which had been corroded by the action of lichen hyphae. It formed
1 Zopf 1907. 2 Ohlert 1871. 3 See p. 75. 4 Uloth 1861.
5 Egeling 1881. « Buchet 1890.
GENERAL NUTRITION 235
part of an old stained window in a chapel that was obscured by a lichen
growth which adhered tenaciously. When the window was taken down and
cleaned, it was found that the surface of the glass was covered with small,
more or less hemispherical pits which were often confluent. The different
colours in the picture were unequally attacked, some of the figures or draperies
being covered with the minute excavations, while other parts were intact.
It happened also, occasionally, that a colour while slightly corroded in one
pane would be uninjured in another, but the suggestion is made that there
might in that case have been a difference in the length of attack by the
lichen. The selection of colours by the lichens might also be influenced by
some chemical or physical characters.
Bachmann1 found that on granite there is equally a selection of material
by the hyphae: as a rule they avoid the acid silica constituents; while they
penetrate and traverse the grains of mica which are dissolved by them
exactly as are lime granules.
On another rock consisting mainly of muscovite and quartz he2 found
that crystals of garnet embedded in the rock were reduced to a powder by
the action of the lichen. He concludes that the destroying action of the
hyphae is accelerated by the presence of carbon dioxide given off by the
lichen, and dissolved in the surrounding moisture. Lang3 and Stahlecker4
have both come to the conclusion that even the quartz grains are corroded
by the lichen hyphae. Stahlecker finds that they change the quartz into
amorphous silicic acid, and thus bring it into the cycle of organic life. Chalk
and magnesia are extracted from the silicates where no other plant could
procure them. Lichens are generally rare on pure quartz rocks, chiefly,
however, for the mechanical reason that the structure is of too close a grain
to afford a foothold.
D. SUPPLY OF ORGANIC FOOD
a. FROM THE SUBSTRATUM. The Ascomycetous fungi, from which so
many of the lichens are descended, are mainly saprophytes, obtaining their
carbohydrates from dead plant material, and lichen hyphae have in some
instances undoubtedly retained their saprophytic capacity. It has been
proved that lichen hyphae, which naturally could not exist without the
algal symbiont, may be artificially cultivated on nutrient media without the
presence of gonidia, though the chief and often the only source ot carbon
supply is normally through the alga with which the hyphae are associated
in symbiotic union.
A large number of crustaceous lichens grow on the bark of trees, and
their hyphae burrow among the dead cells of the outer bark using up the
1 Bachmann 1904. 2 Bachmann 1911. 3 Lang 1903. 4 Stahlecker 1906.
236 PHYSIOLOGY
material with which they come in contact Others live on dead wood, palings,
etc. where the supply of disintegrated organic substance is even greater ; or
they spread over withered mosses and soil rich in humus.
b. FROM OTHER LICHENS. Bitter1 has recorded several instances ob-
served by him of lichens growing over other lichens and using up their
substance as food material. Some lichens are naturally more vigorous than
others, and the weaker -or more slow growing succumb when an encounter
takes place. Pertusaria globulifera is one of these marauding species; its
habitat is among mosses on the bark of trees, and, being a quick grower, it
easily overspreads its more sluggish neighbours. It can scarcely be considered
a parasite, as the thallus of the victim is first killed, probably by the action
of an enzyme.
Lecanora subfusca and allied species which have a thin thallus are
frequently overgrown by this Pertusaria and a dark line generally precedes
the invading lichen; the hyphae and the gonidia of the Lecanorae are first
killed and changed to a brown structureless mass which is then split up by
the advancing hyphae of the Pertusaria into small portions. A little way
back from the edge of the predatory thallus the dead particles are no longer
visible, having been dissolved and completely used up. Pertusaria amara
also may overgrow Lecanorae, though, generally, its onward course is
checked and deflected towards a lateral direction; if however it is in a young
and vigorous condition, it attacks the thallus in its path, and ahead of it
appears the rather broad blackish line marking the fatal effect of the enzyme,
the rest of the host thallus being unaffected. Neither Pertusaria seems to
profit much, and does not grow either faster or thicker; the thallus appears
indeed to be hindered rather than helped by the encounter. Biatora (Lecidea)
quernea with a looser, more furfuraceous thallus is also killed and dissolved
by Pertusariae; but if the Biatora is growing near to a withering or dead
lichen it, also, profits by the food material at hand, grows over it and uses it up.
Bitter has also observed lichens overgrown by Haematomma sp. ; the growth
of that lichen is indeed so rapid that few others can withstand its approach.
Another common rock species, Lecanora sordida (L. glaucoma), has a
vigorous thallus that easily ousts its neighbours. Rhizocarpon geographicu m,
a slow-growing species, is especially liable to be attacked ; from the thallus
of L. sordida the hyphae in strands push directly into the other lichen in a
horizontal direction and split up the tissues, the algae persist unharmed for
some time, but eventually they succumb and are used up; the apothecia,
though more resistant than the thallus, are also gradually undermined and
hoisted up by the new growth, till finally no trace of the original lichen is
left. Lecanora sordida is however in turn invaded by Lecidea insularis
(L. intumescens} which is found forming small orbicular areas on the
1 Bitter 1899.
GENERAL NUTRITION 237
Lecanora thallus. It kills its host in patches and the dead material mostly
drifts away. On any strands that are left Candellariella vitellina generally
settles and evidently profits by the dead nutriment. It does not spread to
the living thallus. Lecanora polytropa also forms colonies on these vacant
patches, with advantage to its growth.
Even the larger lichens are attacked by these quick-growing crusts.
Pertitsaria globulifera spreads over Parmelia perlata and P. physodes,
gradually dissolving and consuming the different thalline layers; the lower
cortex of the victim holds out longest and can be seen as an undigested
black substance within the Pertitsaria thallus for some time. As a rule,
however, the lichens with large lobes grow over the smaller thalli in a purely
mechanical fashion.
c. FROM OTHER VEGETATION. Zukal1 has given instances of association
between mosses and lichens in which the latter seemed to play the part of
parasite. The terricolous species Baeomyces rufus (Sphyridium) and Biatora
decolorans, as well as forms of Lepraria and Variolarta, he found growing
over mosses and killing them. Stems and leaves of the moss Plagiothecium
sylvaticum were grown through and through by the hyphae of a Pertusaria,
and he observed a leaf of Polytrichum commune pierced by the rhizinae of
a minute Cladonia squamule. The cells had been invaded and the neigh-
bouring tissue was brown and dead.
Perhaps the most voracious consumer of organic remains is Lecanora
tartarea, more especially the northern form frigida. It is the well-known
cud-bear lichen of West Scotland, and is normally a rock species. It has
an extremely vigorous thickly crustaceous and quick-growing thallus, and
spreads over everything that lies in its path — decaying mosses, dead leaves,
other lichens, etc. Kihlman2 has furnished a graphic description of the way
it covers up the vegetation on the high altitudes of Russian Lapland. More
than any other plant it is able to withstand the effect of the cold winds that
sweep across these inhospitable plains. Other plant groups at certain seasons
or in certain stages of growth are weakened or killed by the extreme cold
of the wind, and, immediately, a growth of the more hardy grey crust of
Lecanora tar tar ea begins to spread over and take possession of the area
affected — very frequently a bank of mosses, of which the tips have been
destroyed, is thus covered up. In the same way the moorland Cladoniae,
C. rangiferina (the reindeer moss) and some allied species, are attacked.
They have no continuous cortex, the outer covering of the long branching
podetia being a loose felt of hyphae; they are thus sensitive to cold and
liable to be destroyed by a high wind, and their stems, which are blackened
as decay advances, become very soon dotted with the whitish-grey crust of
the more vigorous and resistant Lecanora.
1 Zukal 1879. 2 Kihlman 1890.
238 PHYSIOLOGY
III. ASSIMILATION AND RESPIRATION
A. INFLUENCE OF TEMPERATURE
a. HIGH TEMPERATURE. It has been proved that plants without chloro-
phyll are less affected by great heat than those that contain chlorophyll.
Lichens in which both types are present are more capable of enduring high
temperatures than the higher plants, but with undue heat the alga succumbs
first. In consequence, respiration, by the fungus alone, can go on after
assimilation (photosynthesis) and respiration in the alga have ceased.
Most Phanerogams cease assimilation and respiration after being sub-
jected for ten minutes to a temperature of 50° C. Jumelle1 made a series of
experiments with lichens, chiefly of the larger fruticose or foliaceous types,
with species ofRamatitia, Physcia and Parmelia, also with Evernia prunastri
and Cladonia rangiferina. He found that as regards respiration, plants
which had been kept for three days at 45° C., fifteen hours at 50°, then five
hours at 60°, showed an intensity of respiration almost equal to untreated
specimens, gaseous interchange being manifested by an absorption of oxygen
and a giving up of carbon dioxide.
The power of assimilation was more quickly destroyed : as a rule it
failed after the plants had been subjected successively to a temperature of
one day at 45° C., then three hours at 50° and half-an-hour at 60°. The
assimilating green alga, being less able to resist extreme heat, as already
stated, succumbed more quickly than the fungus. Jumelle also gives the
record of an experiment with a crustaceous lichen, Lecidea (Lecanora) sul-
phurea, a rock species. It was kept in a chamber heated to 50° for three
hours and when subsequently placed in the sunlight respiration took place
but no assimilation.
Very high temperatures may be endured by lichen plants in quite natural
conditions, when the rock or stone on which they grow becomes heated by
the sun. Zopf2 tested the thalli of crustaceous lichens in a hot June, under
direct sunlight, and found that the thermometer registered 55°C.
b. Low TEMPERATURE. Lichens support extreme cold even better than
extreme heat. In both cases it is the power of drying up and entering at
any season into a condition of lowered or latent vitality that enables them
to do so. In winter during a spell of severe cold they are generally in a
state of desiccation, though that is not always the case, and resistance to
cold is not due to their dry condition. The water of imbibition is stored in
the cell-walls and it has been found that lichens when thus charged with
moisture are able to resist low temperatures, even down to — 40° C. or - 50°
as well as when they are dry. Respiration in that case was proved by
1 Jumelle 1892. - Zopf 1890, p. 489.
ASSIMILATION AND RESPIRATION 239
Jumelle1 to continue to — 10°, but assimilation was still possible at a tem-
perature of — 40° : Evernia prunastri exposed to that extreme degree of cold,
but in the presence of light, decomposed carbon dioxide and gave off
oxygen.
B. INFLUENCE OF MOISTURE
a. ON VITAL FUNCTIONS. Gaseous interchange has been found to vary
according to the degree of humidity present1. In lichens growing in sheltered
positions, or on soil, there is less complete desiccation, and assimilation and
respiration may be only enfeebled. Lichens more exposed to the air — those
growing on trees, etc. — dry almost completely and gaseous interchange may
be no longer appreciable. In severe cold any water present would become
frozen and the same effect of desiccation would be produced. At normal
temperatures, on the addition of even a small amount of moisture the
respiratory and assimilative functions at once become active, and to an in-
creasing degree as the plant is further supplied with water until a certain
optimum is reached, after which the vital processes begin somewhat to
diminish.
Though able to exist with very" little moisture, lichens do not endure
desiccation indefinitely, and both assimilation and respiration probably cease
entirely during very dry seasons. A specimen of Cladonia rangiferina was
kept dry for three months, and then moistened: respiration followed but it
was very feeble and assimilation had almost entirely ceased. Somewhat
similar results were obtained with Ramalina farinacea and Usiiea barbata.
In normal conditions of moisture, and with normal illumination, assimi-
lation in lichens predominates over respiration, more carbon dioxide being
decomposed than is given forth; and Jumelle has argued from that fact,
that the alga is well able to secure from the atmosphere all the carbon
required for the nutrition of the whole plant. The intensity of assimilation,
however, varies enormously in different lichens and is generally more powerful
in the larger forms than in the crustaceous : the latter have often an extremely
scanty thallus and they are also more in contact with the substratum — rock,
humus or wood — on which they may be partly saprophytic, thus obtaining
carbohydrates already formed, and demanding less from the alga.
An interesting comparison might be made with fungi in regard to which
many records have been taken as to their possible duration in a dry state,
more especially on the viability of spores, i.e. their persistent capacity of
germination. A striking instance is reported by Weir2of the regeneration of the
sporophores of Polystictus sanguineus, a common fungus of warm countries.
The plant was collected in Brazil and sent to Munich. After about two years
in the mycological collection of the University, the branch on which it grew
1 Jumelle 1892. 2 Weir 1919.
24o PHYSIOLOGY
was exposed in the open among other branches in a wood while snow still
lay on the ground. In a short time the fungus revived and before the end
of spring not only had produced a new hymenium, but enlarged its hymenial
surface to about one-fourth of its original size and had also formed one
entirely new, though small, sporophore.
b. ON GENERAL DEVELOPMENT. Lichens are very strongly influenced
by abundance or by lack of moisture. The contour of the large majority of
species is concentric, but they become excentric owing to a more vigorous
development towards the side of damper exposure, hence the frequent one-
sided increase of monophyllous species such as Umbilicariapustulata. Wainio1
observed that species of Cladonia growing in dry places, and exposed to full
sunlight, showed a tendency not to develop scyphi, the dry conditions
hindering the full formation of the secondary thallus. As an instance may
be cited Cl.foliacea, in which the primary thallus is much the most abundantly
developed, its favourite habitat being the exposed sandy soil of sea-dunes.
Too great moisture is however harmful: Nienburg2 has recorded his
observations on Sphyridium (Baeomyces rufus): on clay soil the thallus was
pulverulent, while on stones or other dryer substratum it was granular —
warted or even somewhat squamulose.
Parmeliaphysodes rarely forms fruits, but when growing in an atmosphere
constantly charged with moisture8, apothecia are more readily developed,
and the same observation has been made in connection with other usually
barren lichens. It has been suggested that, in these lichens, the abrupt change
from moist to dry conditions may have a harmful effect on the developing
ascogonium.
The perithecia of Pyrenula nitida are smaller on smooth bark4 such as
that of CoryluS) Carpinus, etc., probably because the even surface does not
retain water.
IV. ILLUMINATION OF LICHENS
A. EFFECT OF LIGHT ON THE THALLUS
As fungi possess no chlorophyll, their vegetative body has little or no
use for light and often develops in partial or total darkness. In lichens the
alga requires more or less direct illumination; the lichen fungus, therefore,
in response to that requirement has come out into the open : it is an adapta-
tion to the symbiotic life, though some lichens, such as those immersed
in the substratum, grow with very little light. Like other plants they are
sensitive to changes of illumination: some species are shade plants, while
others are as truly sun plants, and others again are able to adapt themselves
to varying degrees of light.
1 Wainio 1897, p. 16. 2 Nienburg 1908. 3 Metzger 1903. * Bitter 1899.
ILLUMINATION OF LICHENS 241
Wiesner1 made a series of exact observations on what he has termed
the " light-use " of various plants. He took as his standard of unity for the
higher plants the amount of light required to darken photographic paper in
one second. When dealing with lichens he adopted a more arbitrary standard,
calculating as the unit the average amount of light that lichens would receive
in entirely unshaded positions. He does not take account of the strength or
duration of the light, and the conclusions he draws, though interesting and
instructive, are only comparative.
a. SUN LICHENS. The illumination of the Tundra lichens is reckoned
by Wiesner as representing his unit of standard illumination. In the same
category as these are included many of our most familiar lichens, which
grow on rocks subject to the direct incidence of the sun's rays, such as, for
instance, Parmelia conspersa, P. prolixa, etc. Physcia tcnella (Jiispidd) is also
extremely dependent on light, and was never found by Wiesner under £ of
full illumination. Dermatocarpon miniatum, a rock lichen with a peltate
foliose thallus, is at its best from \ to £ of illumination, but it grows well in
situations where the light varies in amount from I to ^?. Psora (Lecidea)
lurida, with dark-coloured crowded squamules, grows on calcareous soil
among rocks well exposed to the sun and has an illumination from I to ^,
but with a poorer development at the lower figure. Many crustaceous rock
lichens are also by preference sun-plants as, for instance, Verrucaria calciseda
which grows immersed in calcareous rocks but with an illumination of. I
to \\ in more shady situations, where the light had declined to ^, it was
found to be less luxuriant and less healthy.
Sun lichens continue to grow in the shade, but the thallus is then reduced
and the plant is sterile. Zukal has made a list of those which grow best with
a light-use of I to T\j, though they are also found not unfrequently in habitats
where the light cannot be more than -£•$. Among these light-loving plants
are the Northern Tundra species of Cladonia, Stereocanlon, Cetraria, Par-
melia, Umbilicaria, and Gyrophora, as also Xanthoria parietina, Placodium
elegans, P. murorum, etc., with some crustaceous species such as Lecanora
atra, Haematomma ventosum, Diploschistes scruposus, many species of Leci-
deaceae, some Collemaceae and some Pyrenolichens.
Wiesner's conclusion is that the need of light increases with the lowering
of the temperature, and that full illumination is of still more importance in
the life of the plants when they grow in cold regions and are deprived of
warmth: sun lichens are, therefore, to be looked for in northern or Alpine
regions rather than in the tropics.
b, COLOUR-CHANGES DUE TO LIGHT. Lichens growing in full sunlight
frequently take on a darker hue. Cetraria islandica for instance in an open
situation is darker than when growing in woods; C. aculeata on bare sand-
1 Wiesner 1895.
S. L. 16
242 PHYSIOLOGY
dunes is a deeper shade of brown than when growing entangled among
heath plants. Parmelia saxatilis when growing on exposed rocks is fre-
quently a deep brown colour, while on shaded trees it is normally a light
bluish-grey.
An example of colour-change due directly to light influences is given by
Bitter1. He noted that the thallus of Parmelia obscurata on pine trees, and
therefore subject only to diffuse light, grew to a large size and was of a light
greyish-green colour marked by lighter-coloured lines, the more exposed
lobes being always the most deeply tinted. In a less shaded habitat or in full
sunlight the lichen was distinguished by a much darker colour, and the lobes
were seamed and marked by blackish lines and spots. Bruce Fink2 noted a
similar development of dark lines on the thallus of certain rock lichens
growing in the desert, more especially on Parmelia conspersa, Acarospora
xanthophana and Lecanora muralis. He attributes a protective function to
the dark colour and observes that it seemingly spreads from centres of con-
tinued exposure, and is thus more abundant in older parts of the thallus.
He contrasts this colouration with the browning of the tips of the fronds of
fruticose lichens by which the delicate growing hyphae are protected from
intense light.
Gallic3 finds that protection against too strong illumination is afforded
both by white and dark colourations, the latter because the pigments catch
the light rays, the former because it throws them back. The white colour
is also often due to interspaces filled with air which prevent the penetration
of the heat rays.
A deepening of colour due to light effect often visible on exposed rock
lichens such as Parmelia saxatilis is more pronounced still in Alpine and
tropical species: the cortex becomes thicker and more opaque through the
cuticularizing and browning of the hyphal membranes, and the massing of
crystals on the lighted areas. The gonidial layer becomes, in consequence,
more reduced, and may disappear altogether. Zukal4 found instances of
this in species of Cladonia, Parmelia, Roccella, etc. The thickened cortex
acts also as a check to transpiration and is characteristic of desert species
exposed to strong light and a dry atmosphere.
Bitter5 remarked the same difference of development in plants of Parmelia
physodes : he found that the better lighted had a thicker cortex, about 20-
30 jj, in depth, as compared with 15-22/4 or even only 12/u, in the greener
shade-plants, and also that there was a greater deposit of acids in the more
highly illuminated cortices, thus giving rise to the deeper shades of colour.
Many lichens owe their bright tints to the presence of coloured lichen-
acids, the production of which is strongly influenced by light and by clear
air. Xanthoria parietina becomes a brilliant yellow in the sunlight: in the
1 Bitter 1901, p. 465. 2 Fink 1909. 3 Gallic 1908. 4 Zukal 1896. s Bitter 1901.
ILLUMINATION OF LICHENS 243
shade it assumes a grey-green hue and yields only small quantities of
parietin. Placodium elegans, normally a brightly coloured yellow lichen,
becomes, in the strong light of the high Alps, a deep orange-red. Rhizo-
carpon geographicum is a vivid citrine-yellow on high mountains, but is
almost green at lesser elevations.
c. SHADE LICHENS. Many species grow where the light is abundant
though diffuse. Those on tree-trunks rarely receive direct illumination and
may be generally included among shade-plants. Wiesner found that corti-
colous forms of Parmelia saxatilis grew best with an illumination between £
and y^ of full light, and Pertusaria amara from ^ to ^j both of them could
thrive from ^ to 3^, but were never observed on trees in direct light. Physcia
ciliaris, which inhabits the trunks of old trees, is also a plant that prefers
diffuse light. In warm tropical regions, lichens are mostly shade-plants:
Wiesner records an instance of a species found on the aerial roots of a tree
with an illumination of only -^.
In a study of subterranean plants, Maheu1 takes note of the lichens that
he found growing in limestone caves, in hollows and clefts of the rocks, etc.
A fair number grew well just within the opening of the caves; but species
such as Cl. cervicornis, Placodium murorum and Xanthoria parietina ceased
abruptly where the solar rays failed. Only a few individuals of one or two
species were found to remain normal in semi-darkness: Opegrapha hapalea
and Verrucaria muralis were found at the bottom of a cave with the thallus
only slightly reduced. The nature of the substratum in these cases must
however also be taken into account, as well as the light influences: lime-
stone for instance is a more favourable habitat than gypsum ; the latter, being
more readily soluble, provides a less permanent support.
Maheu has recorded observations on growth in its relation to light in
the case of a number of lichens growing in caves.
Physcia obscura grew in almost total darkness; Placodium murorum
within the cave had lost nearly all colour; Placodium variabile var. deep
within the cave, sterile; Opegrapha endoleuca in partial obscurity; Verrucaria
rupestris f. in total obscurity, the thallus much reduced and sterile; Verru-
caria rupestris in partial obscurity, the asci empty; Homodium (Collema}
granuliferum in the inmost recess of the cave, sterile, and the hyphae more
spongy than in the open.
Siliceous rocks in darkness were still more barren, but a few odd lichens
were collected from sandstone in various caves : Cladonia squamosa, Parmelia
perlata var. ciliata, Diploschistes scruposus, Lecidea grisella, Collema nigrescens
and Leptogium lacerum.
d. VARYING SHADE CONDITIONS. It has been frequently observed
that on the trees of open park lands lichens are more abundant on the side
1 Maheu 1906.
16— 2
244 PHYSIOLOGY
of the trunk that faces the prevailing winds. Wiesner1 remarks that spores
and soredia would more naturally be conveyed to that side; but there are
other factors that would come into play: the tree and the branches frequently
lean away from the wind, giving more light and also an inclined surface that
would retain water for a longer period on the windward side2. Spores and
soredia would also develop more readily in those favourable conditions.
In forests there are other and different conditions: on the outskirts,
whether northern or southern, the plants requiring more light are to be found
on the side of the trunk towards the outside; in the depths of the forest,
light may be reduced from ^^ to ^^, and any lichens present tend to be-
come mere leprose crusts. Krempelhuber3 has recorded among his Bavarian
lichens those species that he found constantly growing in the shade: they
are in general species of Collemaceae and Caliciaceae, several species of
Peltigera (P. venosa, P. horizontalis and P. polydactyla) ; Solorina saccata ;
Gyalecta Flotovii, G. cupularis; Pannaria microphylla, P. triptophylla, P.
brunnea; Icmadophila aeruginosa, etc.
B. EFFECT ON REPRODUCTIVE ORGANS
In the higher plants, it is recognized that a certain light-intensity is
necessary for the production of flowers and fruit. In the lower plants, such
as lichens, light is also necessary for reproduction; it is a common observation
that well-lighted individuals are the most abundantly fruited. In the higher
fungi also, the fruiting body is more or less formed in the light.
a. POSITION AND ORIENTATION OF FRUITS WITH REGARD TO LIGHT.
There is an optimum of light for the fruits as well as for the thallus in each
species of lichen : in most cases it is the fullest light that can be secured.
Zukal4 finds an exception to that rule in species of Peltigera: when
exposed to strong sunlight, the lobes, fertile at the tips, curve over so that
to some extent the back of the apothecium is turned to the light; with
diffuse light, the horizontal position is retained and the apothecia face up-
wards. In the closely allied genera Nephroma, Nephromium and Nephro-
mopsis, the apothecia are produced on the back of the lobe at the extreme
tip, but as they approach maturity the fertile lobes turn right back and they
become exposed to direct illumination. In a well-developed specimen the
full-grown fruits may thus become so prominent all over the thallus, that
it is difficult to realize they are on reversed lobes. In one species of Cetraria
(C. cucullatd) the rarely formed apothecia are adnate to the back of the lobe;
but in that case the margins of the strap-shaped fronds are incurved and
connivent, and the back is more exposed than the front.
In Ramalina the frond frequently turns at a sharp angle at the point of.
1 Wiesner 1895. a R. Paulson, ined. 3 Krempelhuber 1861. 4 Zukal 1896, p. in.
ILLUMINATION OF LICHENS 245
insertion of the apothecium which is thus well exposed and prominent; but
Zukal1 sees in this formation an adaptation to enable the frond to avoid
the shade cast by the apothecium which may exceed it in width. In most
lichens, however, and /especially in shade or semi-shade species, the repro-
ductive organs are to be found in the best-lighted positions.
b. INFLUENCE OF LIGHT ON COLOUR OF FRUITS. Lichen-acids are
secreted freely in the apothecium from the tips of the paraphyses which give
the colour to the disc, and as acid-formation is furthered by the sun's rays,
the well-lighted fruits are always deeper in hue. The most familiar examples
are the bright-yellow species that are rich in chrysophanic acid (parietin).
Hedlund2 has recorded several instances of varying colour in species of
Micarea (Biatorina, etc.) in which very dark apothecia became paler in the
shade. He also cites the case of two crustaceous species, Lecidea helvola and
L. sulphnrella, which have white apothecia in the shade, but are darker in
colour when strongly lighted.
V. COLOUR OF LICHENS
The thalli of many lichens, more especially of those associated with blue-
green gonidia, are hygroscopic, and it frequently happens that any addition
of moisture affects the colour by causing the gelatinous cell-walls to swell,
thus rendering the tissues more transparent and the green colour of the
gonidia more evident. As a general rule it is the dry state of the plant that
is referred to in any discussion of colour.
In the large majority of species the colouring is of a subdued tone — soft
bluish-grey or ash-grey predominating. There are, ho\vever, striking ex-
ceptions, and brilliant yellow and white thalli frequently form a conspicuous
feature of vegetation. Black lichens are rare, but occasionally the very dart
brown of foliaceous species such as Gyrophora or of crustaceous species such
as Verrncaria maura or Buellia atrata deepens to the more sombre hue.
A. ORIGIN OF LICHEN-COLOURING
The colours of lichens may be traced to several different causes.
a. COLOUR GIVEN BY THE ALGAL CONSTITUENT. As examples may
be cited most of the gelatinous lichens, Ephebaceae, Collemaceae, etc. which
owe, as in Collema, their dark olivaceous-green appearance, when somewhat
moist, to the enclosed dark -green gonidia, and their black colour, when dry,
to the loss of transparency. When the thallus is of a thin texture as in
Collema nigrescens, the olivaceous hue may remain constant. Leptogiutn
Burgessii, another thin plant of the same family, is frequently of a purplish
1 Zukal 1896. 2 Hedlund 1892, p. 11.
246 PHYSIOLOGY
hue owing to the purple colour of the gonidial Nostoc cells. The dull-grey
crustaceous thallus of the Pannariaceae becomes more or less blue-green
when moistened, and the same change has been observed in the Hymeno-
lichens, Cora, etc.
In Coenogonium, the alga is some species of Trentepohlia, a filamentous
genus mostly yellow, which often gives its colour to the slender lichen
filaments, the covering hyphae being very scanty. Other filamentous species,
such as Usnea barbata, etc., are persistently greenish from the bright-green
Protococcaceous cells lying near the surface of the thalline strands. Many
of the furfuraceous lichens are greenish from the same cause, especially when
moist, as are also the larger lichens, Physcia ciliaris, Stereocaulons, Cladonias
and others.
b. COLOUR DUE TO LICHEN-ACIDS. These substances, so characteristic
of lichens, are excreted from the hyphae, and lie in crystals on the outer
walls; they are generally most plentiful on exposed tissues such as the
cortex of the upper surface or the discs of the apothecia. Many of these
crystals are colourless and are without visible effect, except in sometimes
whitening the surface, strikingly exemplified in Thamnolia vermicularis1 ;
but others are very brightly coloured. These latter belong to two chemical
groups and are found in widely separated lichens2 :
1 . Derivatives of pul vinic acid which are usually of a bright-yellow colour.
They are the colouring substance of Letharia vulpina, a northern species, not
found in our islands, of Cetraria pinastri and C. juniperina* which inhabit
mountainous or hilly regions. The crustaceous species, Lecidea lucida and
Rhizocarpon geographicum, owe their colour to rhizocarpic acid.
The brilliant yellow of the crusts of some species of Caliciaceae is due to
the presence of the substance calycin, while coniocybic acid gives the greenish
sulphur-yellow hue to Coniocybe furfuracea. Epanorin colours the hyphae
and soredia of Lecanora epanora a citrine-yellow and stictaurin is the deep-
yellow substance found in the medulla and under surface of Sticta aurata
and 5. crocata.
2. The second series of yellow acids are derivatives of anthracene. They
include parietin, formerly described as chrysophanic acid, which gives the
conspicuous colour to Xanthoriae<sx\& to various wall lichens; solorinic acid,
the crystals of which cover the medullary hyphae and give a reddish-grey
tone to the upper cortex of Solorina crocea, and nephromin which similarly
colours the medulla of Nephromium lusitanicum a deep yellow, the colour of
the general thallus being, however, scarcely affected. In this group must
also be included the acids that cause the yellow colouring of the medulla in
Parmelia subaurifera and the yellowish thallus of some Pertusariae.
1 Zopf 1893. * Zopf 1907. 3 Zopf 1892.
COLOUR OF LICHENS 247
In many cases, changes in the normal colouring1 are caused by the
breaking up of the acids on contact with atmospheric or soil ammonia.
Alkaline salts are thus formed which may be oxidized by the oxygen in
the air to yellow, red, brown, violet-brown or even to entirely black humus-
like products which are insoluble in water. These latter substances are
frequently to be found at the base of shrubby lichens or on the under surface
of leafy forms that are closely appressed to the substratum.
c. COLOUR DUE TO AMORPHOUS SUBSTANCES. These are the various
pigments which are deposited in the cell-walls of the hyphae. The only
instance, so far as is known, of colours within the cell occurs in Baeomyces
roseus, in which species the apothecia owe their rose-colour to oil-drops in
the cells of the paraphyses, and in Lecidea coarctata where the spores are
rose-coloured when young. In a few instances the colouring matter is
excreted (Arthonia gregaria and Diploschistes ocellatus); but Bachmann2,
who has made an extended study of this subject and has examined 120
widely diversified lichens, found that with few exceptions the pigment was
in the membranes.
Bachmann was unable to determine whether the pigments were laid down
by the protoplasm or were due to changes in the cell-wall. The middle
layer, he found, was generally more deeply coloured than the inner one,
though that was not universal. In other cases the outer sheath was the
darkest, especially in cortices one to two cells thick such as those of Parmelia
olivacea, P . fuliginosa and P. revoluta, and in the brown thick-walled spores
of Physcia stellaris and of Rhizocarpon geographicum. Still another variation
occurs in Parmelia tristis in which the dark cortical cells show an outer
colourless membrane over the inner dark wall.
The coloured pigments are mainly to be found in the superficial tissues,
but if the thallus is split by areolation, as in crustaceous lichens, the internal
hyphae may be coloured like those of the outer cortex wherever they are
exposed. The hyphae of the gonidial layer are persistently colourless, but
the lower surface and the rhizoids of many foliose lichens are frequently
very deeply stained, as are the hypothalli of crustaceous species.
The fruiting bodies in many different families of lichens have dark
coloured discs owing to the abundance of dark-brown pigment in the para-
physes. In these the walls, as determined by Bachmann, are composed
generally of an inner wall, a second outer wall, and the outermost sheath
which forms the middle lamella between adjacent cells. In some species
the second wall is pigmented, in others the middle lamella is the one deeply
coloured. The hymenium of many apothecia and the hyphae forming the
amphithecium are often deeply impregnated with colour. The wall hyphae
1 Knop 1872. 2 Bachmann 1890.
248 PHYSIOLOGY
of the pycnidia are also coloured in some forms; more frequently the cells
round the opening pore are more or less brown.
The presence of these coloured substances enables the cell-wall to resist
chemical reactions induced by the harmful influences of the atmosphere or
of the substratum. The darker the cell-wall and the more abundant the
pigment, the less easily is the plant injured either by acids or alkalies. The
coloured tips of the paraphyses thus give much needed protection to the
long lived sporiferous asci, and the dark thalline tissues prevent premature
rotting and decay.
d. ENUMERATION OF AMORPHOUS PIGMENTS:
1. Green. Bachmann found several different green pigments: "Lecidea-
green," colouring red with nitric acid, is the dark blue-green or olive-green
(smaragdine) of the paraphyses of many apothecia in the Lecideaceae, and
may vary to a lighter blue; it appears almost black in thalline cells1.
" Aspicilia-green " occurs in the thalline margin and sometimes in the
epithecium of the fruits of species of Asp i cilia; it becomes a brighter green
on the application of nitric acid. " Bacidia-green," also a rare pigment,
becomes violet with the same acid; it is found in the epithecium of Bacidia
muscorum and Bacidia acclinis (Lecideaceae). " Thalloidima-green " in the
apothecia of some species of Biatorina is changed to a dirty-red by nitric
acid and to violet by potash. Still another termed " rhizoid-green " gives
the dark greenish colour to the rhizoids of Physciapulverulenta and P. aipolia
and to the spores of some species of Physcia and Rhizocarpon. It becomes
more olive-green with potash.
2. Blue. A very rare colour in lichens, so far found in only a few species,
Biatora (Lecidea} atrofusca, Lecidea sanguinaria and Aspicilia flavida f.
coerulescens. It forms a layer of amorphous granules embedded in the outer
wall of the paraphyses, becoming more dense towards the epithecium. A
few granules are also present in the hymenium.
3. Violet. " Arthonia-violet" as it is called by Bachmann is a constituent
of the tissues of A rtlwnia gregaria, occurring in minute masses always near
the cortical cells; it is distinct from the bright cinnabarine granules present
in every part of the thallus.
4. Red. Several different kinds of red have been distinguished: " Ur-
ceolaria-red," visible as an interrupted layer on the upper side of the medulla
in the thallus of Diploschistes ocellatus, a continental species with a massive,
crustaceous, whitish thallus that shows a faint rose tinge when wetted.
" Phialopsis-red " is confined to the epithecium of the brightly coloured
1 A similar reaction with nitric acid is produced on the blue hypothalline hyphae of Placynthium
nigrum.
COLOUR OF LICHENS 249
apothecia of Phialopsis rubra. " Lecanora-red," by which Bachmann desig-
nates the purplish colour of the hymenium, is an unfailing character of
Lecanora atra\ the colouring substance is lodged in the middle lamella of
the paraphysis cells; it occurs also in Rhizocarpon geographicum and in Rk.
viridiatrum\ it becomes more deeply violet with potash. M. C. Knowles1
noted the blue colouring of Rh. geographicum growing in W. Ireland near
the sea and she ascribed it to an alkaline reaction. Two more rare pigments,
" Sagedia-red " and " Verrucaria-red," are found in species of Verrucaria-
ceae. These tinge the calcareous rocks in which the lichens are embedded
a beautiful rose-pink. They are scarcely represented in our country.
5. Brown. A frequent colouring substance, but also presenting several
different kinds of pigment which may be arranged in two groups:
(1) Substances with some characteristic chemical reaction. These
are of somewhat rare occurrence: " Bacidia-brown " in the middle lamella
of the paraphyses of Bacidia fuscorubella stains a clear yellow with acids
or a violet colour with potash ; " Sphaeromphale-brown," which occurs
in the perithecia and in the cortex of Staurothele clopismoides, becomes
deep olive-green with potash, changing to yellow-brown on the application
of sulphuric acid ; " Segestria-brown " in Porina lectissima changes to a
beautiful violet colour with sulphuric acid, while " Glomellifera-brown,"
which is confined to the outer cortical cells of the upper surface of Parmelia
glomellifera, becomes blue with nitric and sulphuric acids, but gives no re-
action with potash. Rosendahl2 confirmed Bachmann's discovery of this
colour and further located it in corresponding cells of Parmelia prolixa and
P. locarensis.
(2) Substances with little or no chemical reaction. There is only
one such to be noted: " Parmelia-brown," usually a very dark pigment, which
is lodged in the outer membranes of the cells. It becomes a clearer colour
with nitric acid, and if the reagent be sufficiently concentrated, some of the
pigment is dissolved out. Some tissues, such as the lower cortex of some
Panneliae, maybe so impregnated and hardened, that nothing short of boiling
acid has any effect on the cells; membranes less deeply coloured and changed,
such as the cortex of the Gyrophorae, become disintegrated with such drastic
treatment. With potash the colour becomes darker, changing from a clear
brown to olivaceous-brown or -green, or in some cases, as in a more faintly
coloured epithecium, to a dirty-yellow, but the lighter colour produced there
is largely due to the swelling up of the underlying tissues to which the potash
penetrates readily between the paraphyses.
" Parmelia-brown " is a colouring substance present in the dark epi-
thecium and hypothecium of the fruits of many widely diverse lichens, and
1 Knowles 1915. 2 Rosendahl 1907.
250 PHYSIOLOGY
in the cortical cells and rhizoids of many thalli. In some plants the thallus
is brown both above and below, in others, as in Parmelia revoluta, etc. only
the under surface is dark-coloured.
e. COLOUR DUE TO INFILTRATION. There are several crustaceous lichens
that are rusty-red, the colour being due to the presence of iron. These
lichens occur on siliceous rocks of gneiss, granite, etc., and more especially
on rocks rich in iron. Iron as a constituent of lichens was first demonstrated
by John1 in Ramalina fraxinea and R. calicaris. Grimbel2 proved that the
colour of rust lichens was due to an iron salt, and Molisch3 by microscopic
examination located minute granules of ferrous oxide as incrustations on
the hyphae of the upper surface of the thallus. Molisch held that the rhizoids
or penetrating hyphae dissolved the iron from the rocks by acid secretions.
Rust lichens however grow on rocks that are frequently under water in which
the iron is already present.
Among " rusty " lichens are the British forms, Lecanora lacustris, the
thallus of which is normally white, though generally more or less tinged
with iron; it inhabits rocks liable to inundation. L. Dicksonii owes its fer-
ruginous colour to the same influences. Lecidea contigua vax.flavicunda and
L. confluens f. oxydata are rusty conditions of whitish-grey lichens.
Nilson4 found rusty lichens occurring frequently in the Sarak-Gebirge,
more especially on glacier moraines where they were liable, even when un-
covered by snow, to be flooded by water from the higher reaches. It is the
thallus that is affected by the iron, rarely if ever are apothecia altered in
colour.
1 John 1819. 2 Grimbel 1856. 3 Molisch 1892. 4 Nilson 1907.
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CHAPTER VI
BIONOMICS
A. GROWTH AND DURATION
LICHENS are perennial plants mostly of slow growth and of long continuance ;
there can therefore only be approximate calculations either as to their rate
of increase in dimensions or as to their duration in time. A series of some-
what disconnected observations have however been made that bear directly
on the question, and they are of considerable interest.
Meyer1 was among the first to be attracted by this aspect of lichen life,
and after long study he came to the conclusion that growth varied in
rapidity according to the prevailing conditions of the atmosphere and
the nature of the substratum ; but that nearly all species were very slow
growers. He enumerates several, — Lichen ( X anthoria) parietinus, L. (Par-
melia) tiliaceus.L. (Rhizocarpori)geographicus, L.(Haematommd) ventosus,aind
L. (Lecanoro) saxicolus, — all species with a well-defined outline, which, after
having attained some considerable size, remained practically unchanged for
six and a half years, though, in some small specimens of foliose lichens, he
noted, during the same period, an increase of one-fourth to one-third of their
size in diameter. In one of the above crustaceous species, .£. ventosus,the speci-
men had not perceptibly enlarged in sixteen years, though during that time
the centre of the thallus had been broken up by weathering and had again
been regenerated.
Meyer also records the results of culture experiments made in the open;
possibly with soredia or with thalline scraps: he obtained a growth of
X anthoria parietina (on wrought iron kept well moistened), which fruited in
the second year, and in five years had attained a width of 5-6 lines (about
i cm.) ; Lecanora saxicola growing on a moist rock facing south grew 4-7 lines
in six and a half years, and bore very minute apothecia.
Lindsay2 quotes a statement that a specimen of Lobaria pulmonaria had
been observed to occupy the same area of a tree after the lapse of half a
century. Berkeley3 records that a plant of Rhizocarpon geographicum remained
in much the same condition of development during a period of twenty-five
years. The latter is a slow grower and, in ordinary circumstances, it does
not fruit till about fifteen years after the thallus has begun to form. Weddell4,
also commenting on the long continuance of lichens, says there are crustaceous
species occupying on the rock a space that might be covered by a five-franc
piece, that have taken a century to attain that size.
Phillips5 on the other hand argues against the very great age of lichens,
1 Meyer 1825, p. 44. 2 Lindsay 1856. 3 Berkeley 1857. * Weddell 1869. 5 Phillips 1878.
GROWTH AND DURATION 253
and suggests 20 years as a sufficient time for small plants to establish them-
selves on hard rocks and attain full development. He had observed a small
vigorous plant of Xanthoria parietina that in the course of five years had
extended outwards to double its original size. The centre then began to
break up and the whole plant finally disappeared.
Exact measurements of growth have been made by several observers.
Scott Elliot1 found that a Pertusaria had increased about half a millimetre
from the ist February to the end of September. Vallot2 kept under obser-
vation at first three then five different plants of Parmelia saxatilis during a
period of eight years : the yearly increase of the thallus was half a centimetre,
so that specimens of twenty centimetres in breadth must have been growing
from forty to fifty years.
Bitter's3 observations on Parmelia physodes agree in the main with those
of Vallot: the increase of the upper lobes during the year was 3-4 mm. In
a more favourable climate Heere found that Parmelia caperata (Fig. 49) on
a trunk ofAescu/us in California had grown longitudinally 1*5 cm. and trans-
versely i cm. The measurements extended over a period of seven winter
months, five of them being wet and therefore the most favourable season of
growth. In warm regions lichens attain a much greater size than in tem-
perate or northern countries, and growth must be more rapid.
A series of measurements was also made by Heere4 on Ramalina reti-
culata (Fig. 64), a rapid growing tree-lichen, and one of the largest American
species. The shorter lobes were selected for observation, and were tested
during a period of seven months from September to May, five of the months
being in the wet season. ' There was great variation between the different
lobes but the average increase during that period was 41 per cent.
Krabbe5 took notes of the colonization of Cladonia rangiferina (Fig. 127)
on burnt soil : in ten years the podetia had reached a height of 3 to 5 cm.,
giving an annual growth of about 3-5 mm. It is not unusual to find speci-
mens in northern latitudes 18 inches long (50 cm.), which, on that computa-
tion, must have been 100 to 160 years old; but while increase goes on at the
apex of the podetia, there is constant perishing at the base of at least as
much as half the added length and these plants would therefore be 200 or
300 years old. Reinke6 indeed has declared that apical growth in these
Cladina species may go on for centuries, given the necessary conditions of
good light and undisturbed habitat.
Other data as to rate of growth are furnished by Bonnier7 in the account
of his synthetic cultures which developed apothecia only after two to three
years. The culture experiments of Darbishire8 and Tobler9 with Cladonia
soredia are also instructive, the former with synthetic spore- and alga-cultures
1 Scott Elliot 1907. * Vallot 1896. 3 Bitter 1901. * Heere 1904. s Krabbe 1891, p. 131.
6 Reinke 1894, p. 18. 7 Bonnier, see p. 29. 8 Darbishire, see p. 148. 9 Tobler, see p. 148.
254 BIONOMICS
having obtained a growth of soredia in about seven months; the latter,
starting with soredia, had a growth of well-formed squamules in nine months.
It has been frequently observed that abundance of moisture facilitates
growth, and this is nowhere better exemplified than in crustaceous soil-
lichens. Meyer found that on lime-clay soil which had been thrown up from
a ditch in autumn, lichens such as Gyalecta geoica were fully developed the
following summer. He gives an account also of another soil species, Verru-
caria (Thrombium) epigaea, which attained maturity during the winter half
of the year. Stahl1 tells us that Thelidium minutulum, a pyrenocarpous soil-
lichen, with a primitive and scanty thallus, was cultivated by him from spore
to spore in the space of three months. Such lichens retain more of the
characteristics of fungi than do those with a better developed thallus. Rapid
colonization by a soil-lichen was also observed in Epping Forest by Paulson2.
In autumn an extensive growth of Lecidea uliginosa covered as if with a dark
stain patches of soil that had been worn bare during the previous spring.
The lichen had reached full development and was well fruited.
These facts are quite in harmony with other observations on growth
made on Epping Forest lichens. The writers3 of the report record the finding
of " fruiting lichens overspreading decaying leaves which can scarcely have
lain on the ground more than two or three years; others growing on old
boots or on dung and fruiting freely; others overspreading growing mosses."
They also cite a definite instance of a mass of concrete laid down in 1903
round a surface-water drain which in 1910 — seven years later — was covered
with Lecanora galactina in abundant fruit; and of another case of a Portland
stone garden -ornament, new in 1904, and, in 1910, covered with patches of
a fruiting Verrucaria (probably V. nigrescens}. Both these species, they add,
have a scanty thallus and generally fruit very freely.
A series of observations referring to growth and "ecesis" or the spreading
of lichens have been made by Bruce Fink4 over a period of eight years. His
aim was mainly to determine the time required for a lichen to re-establish
itself on areas from which it had been previously removed. Thus a quadrat
of limestone was scraped bare of moss and of Leptogium lacerum, except
for bits of the moss and particles of the lichen which adhered • to the
rock, especially in depressions of the surface. After four years, the moss
was colonizing many small areas on which grew patches of the lichen 2 to
10 mm. across. Very little change occurred during the next four years.
Numerous results are also recorded as to the rate of growth, the average
being i cm. per year or somewhat under. The greatest rate seems to have
been recorded for a plant of Peltigera canina growing on " a mossy rock
along a brook in a low moist wood, well-shaded." A plant, measuring 10
by 14 cm., was deprived of several large apothecia. The lobes all pointed
1 Stahl 1877, p. 34. 2 Paulson 1918. 3 Paulson and Thompson 1913. 4 Fink 1917.
GROWTH AND DURATION 255
in the same direction, and the plant increased 175 cm. in one year. Two
other plants, deprived of their lobes, regenerated and increased from 2 and
5 cm. respectively to 3^5 and 6 cm. No other measurements are quite so
high as these, though a plant of Parmelia caperata (sterile), measuring from
I to 2 cm. across, reached in eight years a dimension of 10 by 13 cm. Other
plants of the same species gave much slower rates of increase. A section of
railing was marked bearing minute scattered squamules of Cladonia pityrea.
After two years the squamules had attained normal size and podetia were
formed 2 to 4 mm. long.
Several areas of Verrucaria muralis were marked and after ten months
were again measured; the largest plants, measuring 2*12 by 2^4 cm. across,
had somewhat altered in dimensions and gave the measurements 2'2 by
3 cm. Some crustose species became established and produced thalli and
apothecia in two to eight years. Foliose lichens increased in diameter from
°'3 to 3'5 cm- Per year- So far as external appearance goes, apothecia are
produced in one to eight years; it is concluded that they require four to
eight years to attain maturity in their natural habitats.
B. SEASON OF FRUIT FORMATION
The presence of apothecia (or perithecia) in lichens does not always
imply the presence of spores. In many instances they are barren, the spores
having been scattered or not yet matured ; the disc in these cases is composed
of paraphyses only, with possible traces of asci. In any month of the year,
however, some lichens may be found in fruit.
Baur1 found, for instance, that Parmelia acetabulum developed carpogonia
the whole year round, though somewhat more abundantly in spring and
autumn. Pertusaria communis similarly has a maximum period of fruit-
formation at these two seasons. This is probably true of tree-lichens
generally: in summer the shade of the foliage would inhibit the formation
of fruits, as would the extreme cold of winter ; but were these conditions
relaxed spore-bearing fruits might be expected at any season though perhaps
not continuously on the same specimen.
An exception has been noted by Baur in Pyrenula nitida, a crustaceous
tree Pyrenolichen. He found carpogonia only in February and April, and
the perithecia matured in a few weeks, presumably at a date before the trees
were in full leaf; but even specimens of Pyrenula are not unusual in full
spore-bearing conditions in the autumn of the year.
To arrive at any true knowledge as to the date and duration of spore
production, it would be necessary to keep under observation a series of one
species, examining them microscopically at intervals of a few weeks or months
1 Baur 1901.
256 BIONOMICS
and noting any conditions that might affect favourably or unfavourably the
reproductive organs. A comparison between corticolous and saxicolous
species would also be of great interest to determine the influence of the
substratum as well as of light and shade. But in any case it is profitable to
collect and examine lichens at all seasons of the year, as even when the
bulk of the spores is shed, there may remain belated apothecia with a few
asci still intact.
C. DISPERSAL AND INCREASE
The natural increase of lichen plants may primarily be sought for in the
dispersal of the spores produced in the fruiting-bodies. These are ejected,
as in fungi, by the pressure of the paraphyses on the mature ascus. The
spores are then carried away by wind, water, insects, etc. In a few lichens
gonidia are enclosed in the hymen ium and are ejected along with the spores,
but, in most, the necessary encounter with the alga is as fortuitous, and
generally as certain, as the pollination of anemophilous flowers. A case of
dispersal in Sagedia microspora has been described by Miyoshi1 in which
entire fruits, small round perithecia, were dislodged and carried away
by the wind. The addition of water caused them to swell enormously and
brought about the ejection of the spores. Areas covered by the thallus
are also being continually enlarged by the spreading growth of the hypo-
thallus.
a. DISPERSAL OF CRUST ACEOUS LICHENS. These lichens are distributed
fairly equally on trees or wood (corticolous) and on rocks (saxicolous). Some
species inhabit both substrata. As regards corticolous lichens that live on
smooth bark such as hazel or mountain-ash, the vegetative body or thallus
is generally embedded beneath the epidermis of the host. Soredia are absent
and the thallus is protected from dispersal. In these lichens there is rather
an abundant and constant formation of apothecia or perithecia.
Other species that affect rugged bark and are more superficial are less
dependent on spore production. The thallus is either loosely granular, or is
broken up into areolae. The areolae are each a centre of growth, and with
an accession of moisture they swell up and exert pressure on each other.
Parts of the thallus thus become loosened and are dislodged and carried
away. If anchored on a suitable substratum they grow again to a complete
lichen plant. Sorediate lichens are dependent almost wholly on these bud-
like portions for increase in number ; soredia are easily separated from
the parent plant, and easily scattered. Darbishire2 noted frequently that
small Poduridae in moving over the surface of Pertusaria amara became
powdered with soredia and very evidently took a considerable part in the
dissemination of the species.
1 Miyoshi 1901. 2 Darbishire 1897, p. 657.
DISPERSAL AND INCREASE 257
Crustaceous rock lichens are rarely sorediate, but they secure vegetative
propagation l by the dispersal of small portions of the thallus. The thalli most
securely attached are cracked into small areolae which, by unequal growth,
become very soon lop-sided, or, by intercalary increase, form little warts and
excrescences on their surface. These irregularities of development give rise
to more or less tension which induces a loosening of the thallus from the
substratum. Weather changes act similarly and gradually the areolae are
broken off. Loosening influence is also exercised by the developing fruits,
the expanding growth of which pushes aside the neighbouring tissues. Wind
or water then carries away the thalline particles which become new centres
of growth if a suitable substratum is reached.
b. DISPERSAL OF FOLIOSE LICHENS. It is a matter of common obser-
vation that, in foliose lichens where fruits are abundant, there are few or no
soredia and vice versa. In either case propagation is ensured. In addition
to these obvious methods of increase many lichens form isidia, outgrowths
from the thallus which are easily detached. Bitter2 considers for instance
that the coralloid branchlets, which occur in compact tufts on the thallus of
Uinbilicaria pustulata, are of immense service as organs of propagation.
Apothecia and pycnidia are rarely present in that species, and the plant
thus falls back on vegetative production. Slender crisp thalline outgrowths,
easily separable, occur also on the edges of lobes, as in species of Peltigera,
Platysvia, etc.
Owing to the gelatinous character of lichen hyphae, the thallus quickly
becomes soft with moisture and is then easily torn and distributed by wind,
animals, etc. The action of lichens on rocks has been shown to be of a
constantly disintegrating character, and the destruction of the supporting
rock finally entails the scattering of the plant. This cause of dispersal is
common to both crustaceous and foliose species. The older central parts of
a lichen may thus have disappeared while the areolae on lobes of the cir-
cumference are still intact and in full vigour.
As in crustaceous lichens the increase in the area of growth may take
place by means of the lichen mycelium which, originating from the rhizinae
in contact with the substratum, spreads as a hypothallus under the shelter
of the lobes and far beyond them. When algae are encountered a new lobe
begins to form. The process can be seen perhaps most favourably in
lichens on decaying wood which harbours moisture and thus enables the
wandering hyphae to retain life.
c. DISPERSAL OF FRUTICOSE LICHENS. Many of these lichens are
abundantly fruited; in others soralia are as constantly developed. Species
of Usnea, Alectoria, Ramalina and many Cladoniae are mainly propagated
1 Beckmann 1907. '* Bitter 1899.
S. L. I 7
258 BIONOMICS
by soredia. They are all peculiarly liable to be broken and portions of the
thallus scattered by the combined action of wind and rain.
Peirce1 found that Ramalina reticulata (Fig. 65), of which the fronds are
an open network, was mainly distributed by the tearing of the lichen in high
wind. This takes place during the winter rains, when not only the lichen is
wet and soft in texture, but when the deciduous trees are bare of leaves, at
a season, therefore, when the drifting thalline scraps can again catch on to
branch or stem. A series of observations on the dispersal of forms of long
pendulous Usneas was made by Schrenk2. In the Middle and North Atlantic
States of America these filamentous species rarely bear apothecia. The
high winds break and disperse them when they are in a wet condition. They
generally grow on Spruces and Firs, because the drifting filaments are more
easily caught and entangled on short needles. The successive wetting and
drying causes them to coil and uncoil, resulting in a tangle impossible to
unravel, which holds them securely anchored to the support.
D. ERRATIC LICHENS •
In certain lichens, there is a tendency for the thallus to develop excres-
cences of nodular form which easily become free and drift about in the wind
while still living and growing. They are carried sometimes very long distances,
and fall in thick deposits over localities far from their place of origin. The
most famous instance is the " manna lichen," Lecanora esculenta, which has
been scientifically examined and described by Elenkin3. He distinguishes
seven different forms of the species: f. esculenta, f. affznis, f. alpina, and
f. fnttiadosa-foliacea which are Alpine lichens, the remainder, f. desertoides,
f. foliacea and f. esculenta-tarquina, grow on the steppes or in the desert4.
Elenkin3 adds to the list of erratic lichens a variety of Parmelia mollius-
cula along with P. ryssolea from S. Russia, from the Asiatic steppes and
from Alpine regions. Mereschkovsky5 has also recorded from the Crimea
Parmelia vagans, probably derived from P. conspersa f. vaga (f. nov.). It
drifts about in small rather flattened bits, and, like other erratics, it never
fruits.
Meyer6 long ago described the development of wandering lichens : scraps
that were torn from the parent thallus continued to grow if there were
sufficient moisture, but at the same time undergoing considerable change in
appearance. The dark colour of the under surface disappears in the frequently
altered position, as the lobes grow out into narrow intermingling fronds
iorming a more or less compact spherical mass ; the rhizoids also become
modified and, if near the edge, grow out into threadlike structures which
Peirce 1898. 2 Schrenk 1898. 3 Elenkin 1901. 4 See Chap. X.
5 Mereschkovsky 1918. 6 Meyer 1825, p. 44.
ERRATIC LICHENS
259
bind the mass together. Meyer says that " wanderers " have been noted as
belonging to P annelid acetabuluin, Platysma glaucum and Anaptychiaciliaris.
The most notable instance in Britain of the " erratic " habit is that of
Parmelia revoluta var. concentrica (Fig. 121), first found on Melbury Hill
li"
Fig. 121. Parmelia revoluta var. concentrica Cromb. a, plant on flint with detached fragment;
b, upper surface of three specimens ; c, three specimens as found on chalk downs ; d, speci
in section showing central cavity (S. H., Photo.}.
17 — 2
26o BIONOMICS
near Shaftesbury, Dorset, and described as " a spherical unattached lichen
which rolls on the exposed downs." It has recently been observed on the
downs near Seaford in Sussex, where, however, it seems to be confined to a
small area about eight acres in extent which is exposed to south-west winds.
The lichen is freely distributed over this locality. To R. Paulson and Somer-
ville Hastings1 we owe an account of the occurrence and origin of the revo-
luta wanderers. The specimens vary considerably in shape and size, and
measure from I to 7 cm. in longest diameter. Very few are truly spherical,
some are more or less flattened and many are quite irregular. The revolute
edges of the overlapping lobes give a rough exterior to the balls, which
thereby become entangled amongst the grass, etc., and movement is impeded
or prevented, except in very high winds. Crombie2 had suggested that the
concentric plant originated from a corticolous habitat, but no trees are near
the Seaford locality. Eventually specimens were found growing on flints in
the immediate neighbourhood. While still on the stone the lichen tends
to become panniform, a felt of intermingling imbricate lobes is formed,
portions of which, in time, become crowded out and dislodged. When
scattered over the ground, these are liable to be trampled on by sheep or
other animals and so are broken up; each separate piece then forms the
nucleus of new concentric growth.
Crombie2 observed at Braemar, drifting about on the detritus of Morrone,
an analogous structure in Parmelia omphalodes. He concluded that nodular
excrescences of the thallus had become detached from the rocks on which
the lichen grew; while still attached to the substratum Parmelia omphalodes
and the allied species, P. saxatilis, form dense cushion-like masses.
E. PARASITISM
a. GENERAL STATEMENT. The parasitism of Strigula complanata, an
exotic lichen found on the leaves of evergreen trees, has been already
described3; Dufrenoy4 records an instance of hyphae from a Parmelia thallus
piercing pine-needles through the stomata and causing considerable injury.
Lichen hyphae have attacked and destroyed the protonemata of mosses.
Cases have also been recorded of Usnea and Ramalina penetrating to the living
tissue of the tree on which they grew, and there may be other similar para-
sitisms ; but these exceptions serve to emphasize the independent symbiotic
growth of lichens.
There are however some lichens belonging to widely diverse genera that
have retained, or reverted to, the saprophytic or parasitic habit of their fungal
ancestors, though the cases that occur are generally of lichens preying on
1 Paulson and Somerville Hastings 1914. 2 Crombie 1872. 8 See p. 35.
* Dufrenoy 1918.
PARASITISM 261
other lichens. The conditions have been described as those of " antagonistic
symbiosis " when one lichen is hurtful or fatal in its action on the other, and
as " parasymbiosis " when the association does little or no injury to the host.
The parasitism of fungi on lichens, though falling under a different category,
in many instances exhibits features akin to parasymbiosis.
The parasitism of fungus on fungus is not unusual; there are instances
of its occurrence in all the different classes. In the Phycomycetes there are
genera wholly parasitic on other fungi such as Woronina and other Chytri-
diaceae ; Piptocephahts, one of the Mucorini, is another instance. Cicinnobolus,
one of the Sphaeropsideae, preys on Perisporiae ; a species of Cordyceps is
found on Elaphomyces, and Orbilia coccinella on Polyporus\ while among
Basidiomycetes, Nyctalis, an agaric, grows always on Russula.
There are few instances of lichens rinding a foothold on fungi, for the
simple reason that the latter are too short lived. On the perennial Polyporeae
a few have been recorded by Arnold1, but these are not described as doing
damage to the host. They are mostly species of Lecidea or of allied genera.
Kupfer2 has also listed some 15 different lichens that he found on Lenzites sp.
b. ANTAGONISTIC SYMBIOSIS. In discussing the nutrition of lichens3
note has been taken of the extent to which some species by means of enzymes
destroy the thallus of other lichens in their vicinity and then prey on the
dead tissues. A constantly cited4 example is that of Lecanora atriseda which
in its early stages lives on the thallus of Rhizocarpon geographicum inhabiting
mountain rocks. A detailed examination of the relationship between these
two plants was made by Malme and later by Bitter5. Both writers found
that the Lecanora thallus as it advanced caused a blackening of the Rhizo-
carpon areolae, the tissues of which were killed by the burrowing slender
filaments of the Lecanora, easily recognized by their longer cells. The invader
thereafter gradually formed its own medulla, gonidial layer and cortex right
over the surface of the destroyed thallus. Lecidea insularis (L. intumescens)
similarly takes possession of and destroys the thallus of Lecanora glaucoma
and Malme4 strongly suspects that Bnellia verruculosa and B. aethalea may
be living on the thallus of Rhizocarpon distinctum with which they are
constantly associated.
Other cases of facultative parasitism have been studied by Hofmann6,
more especially three different species, Lecanora dispersa, Lecanora sp. and
Parmelia hyperopta, which were found growing on the thick foliose thailus
of Dermatocarpon miniatum. These grew, at first independently, on a wall
along with many examples of Endocarpon on to which they spread as oppor-
tunity offered. The thallus of the latter was in all cases distorted, the area
occupied by the invaders being finally killed. The attacking lichens had
1 Arnold 1874. °- Kupfer 1894. 3 See p. 236. * Malme 1895.
5 Bitter 1899. 6 Hofmann 1906.
262 BIONOMICS
benefited materially by the more nutritive substratum : their apothecia were
more abundant and their thallus more luxuriant. The gonidia especially
had profited; they were larger, more brightly coloured, and they increased
more freely. Hoffmann offers the explanation that the strain on the algae of
providing organic food for the hyphal symbiont was relaxed for the time,
hence their more vigorous appearance.
Arthonia subvarians is always parasitic on the apothecia of Lecanora
galactina, and Almquist1 discovered that the hymenium of the host alone is
injured, the hypothecium and excipulum being left intact.
The " parasitism " of Pertusaria globulifera on Parmelia perlata and
P.physodes, as described by Bitter2, may also be included under antagonistic
symbiosis. The hyphae pierce the Parmdia thallus, break it up and gradually
absorb it. Chemical as well as mechanical influences are concerned in the
work of destruction as both the fungus and the alga of the victim are dissolved.
Lecanora tartarea already dealt with as a marauding lichen3 over decaying
vegetation may spread also to living lichens. Fruticose soil species, such as
Cetraria aculeata and others, die from the base and the Lecanora gains
entrance to their tissues at the decaying end which is open.
Arnold4 speaks of these facultative parasites that have merely changed
their substratum as pseudo-parasites, and he gives a list of instances of such
change. In many cases it is rather the older thalli that are taken possession
of, and, in nearly every case, the invader is some crustaceous species. The
plants attacked are generally ground lichens or more particularly those that
inhabit damp localities, such as Peltigera or Cladonia or certain bark lichens.
Drifting soredia or particles of a lichen would easily take hold of the host
thallus and develop .in suitable conditions. To give a few of the instances
observed, there have been found, by Arnold, Crombie and others:
on Peltigera canina: Callopisma cerina, Rinodina turfacea var., Bilimbia
obscurata and Lecanora aurella;
on Peltigera aphthosa: Lecidea decolorans;
on Cladoniae: Bilimbia microcarpa, Bacidia Beckhausii and Urceolaria
scruposa, etc.
Urceolaria (Diploschistes) has a somewhat bulky crustaceous thallus which
may be almost evanescent in its semi-parasitic condition, the only gonidia
retained being in the margin of the apothecia. Nylander5 found isolated
apothecia growing vigorously on Cladonia squamules.
Hue6 describes Lecanora aspidophora f. errabunda, an Antarctic lichen, as
not only a wanderer but as a "shameless robber." It is to be seen everywhere
on and about other lichens, settling small glomeruli of apothecia here and
1 Almquist 1880. 2 Bitter 1899. 3 See p. 237. 4 Arnold 1874.
6 Nylander 1852. 6 Hue 1915.
PARASITISM 263
there on the thallus of Umbilicariae or between the areolae of Buelliac, and
always too vigorous to be ousted from its position.
Bacidia flavovirescens has been regarded by some lichenologists1 as a
parasite on Baeomyces, but recent work by Tobler2 seems to have proved
that the bright green thallus is that of the Bacidia.
c. PARASYMBIOSIS. There are certain lichens that are obligative parasites
and pass their whole existence on an alien thallus. They may possibly have
degenerated from the condition of facultative parasitism as the universal
history of parasitism is one of increased dependence on the host, and of
growing atrophy of the parasite, but, in the case of lichens, there is always
the peculiar symbiotic condition to be considered : the parasite produces its
own vigorous hyphae and normal healthy fruits, it often claims only a share
of the carbohydrates manufactured by the gonidia. The host lichen is not
destroyed by this parasymbiosis though the tissues are very often excited
to abnormal growth by the presence of the invading organism.
Lauder Lindsay3 was one of the first to study these "microlichens" as
he called them, and he published descriptions of those he had himself
observed on various hosts. He failed however to discriminate between lichens
and parasitic fungi. It is only by careful research in each case that the
affinity to fungi or to lichens can be determined; very frequently the whole
of them, as possessing no visible thallus, have been classified with fungi, but
that view ignores the symbiosis that exists between the hyphae of the
parasite and the gonidia of the host.
Parasitic lichens are rather rare on gelatinous thalli ; but even among
these, a few instances have been recorded. Winter4 has described a species
of LeptorapJtis, the perithecia of which are immersed in the thallus of Physma
franconicum. The host is wholly unaffected by the presence of the parasite
except for a swelling where it is situated. The foreign hyphae are easily
distinguishable; they wander through the thallus of the host with their free
ends in the mucilage of the gonidial groups from which they evidently
extract nourishment. Species of the lichen genus Obryznm are also parasitic
on gelatinous lichens.
The parasitic genus Abrothallus* has been the subject of frequent stud}-.
There are a number of species which occur as little black discs on various
thalli of the large foliose lichens. They were first of all described as parasitic
fungi, later Tulasne6 affirmed their lichenoid nature as proved by the struc-
ture, consistence and long duration of the apothecia. Lindsay7 wrote a
monograph of the genus dealing chiefly with Abrothallus Smithii (Buellia
P armeliarunt) and A. oxysporus, with their varieties and forms that occur on
1 Th. Fries 1874, p. 343. "- Tobler 191 12. 3 Lindsay i8692. 4 Winter 1877.
5 Abrothallus has been included in the lichen genus Buellia. 6 Tulasne 1852.
7 Lindsay 1856.
264 BIONOMICS
several different hosts. In some instances the thallus is apparently quite
unaffected by the presence of Abrothallus, in others, as in Cetraria glauca,
there is considerable hypertrophy produced, the portion of the thallus on
which the parasites are situated showing abnormal growth in the form of
swellings or pustules which may be regarded as gall-formations. Crombie1
points this out in a note on C. glauca var. ampullacea, figured first by
Dillenius, which is merely a swollen condition due to the presence of
Abrothallus.
The internal structure and behaviour of Abrothallus has more recently
been followed in detail by Kotte2. He recognized a number of different
species growing on various thalli of Parmelia and Cetraria, but Abrothallus
Cetrariae was the only one that produced gall-formation. The mycelium of
the parasite in this instance penetrates to the medulla of the host lichen as
a loose weft of hyphae which are divided into more or less elongate cells.
These send out side branches, which grow towards the algal cells, and by
their short-celled filaments clasp them exactly in the same way as do the
normal lichen hyphae. Thus in the neighbourhood of the parasite an algal
cell may be surrounded by the hyphae not only of the host, but also by
those of Abrothallus. The two different hyphae can generally be distin-
guished by their reaction to iodine: in some cases Abrothallus hyphae take
the stain, in others the host hyphae. In addition to apothecia, spermogonia
or pycnidia are produced, but in one of the species examined by Kotte,
Abrothallus Peyritschii on Cetraria caperata, there was no spermogonial
wall formed. The hyphae also penetrate the host soredia or isidia, so that
on the dispersal of these vegetative bodies the perpetuation of both organisms
is secured in the new growth.
Abrothallus draws its organic food from the gonidia in the same way as
the host species, and possibly the parasitic hyphae obtain also water and
inorganic food along with the host hyphae. They have been traced down
to the rhizinae and may even reach the hypothallus, but no injury to the
host has been detected. It is a case of joint symbiosis and not of parasitism.
Microscopic research has therefore justified the inclusion of these and other
forms among lichens.
d. PARASYMBIOSIS' OF FUNGI. There occur on lichens, certain parasites
classed as fungi which at an early stage are more or less parasymbionts of
the host ; as growth advances they may become parasitic and cause serious
damage, killing the tissues on which they have settled.
Zopf3 found several instances of such parasymbiosis in his study of
fungal parasites, such as Rhymbocarpus punctiformi s, a minute Discomycete
which inhabits the thallus of Rhizocarpon geographicum. By means of
staining reagents he was able to trace the course of the parasitic hyphae,
1 Crombie 1894. 2 Kotte 1910. 3 Zopf 1896.
PARASITISM 265
and found that they travelled towards the gonidia and clasped them lichen-
wise without damaging them, since these remained green and capable of
division. At no stage was any harm caused to the host by the alien
organism. Another instance he observed was that of Conida rubescens on
the thallus of Rhizocarpon epipolium. By means of fine sections through the
apothecia of Conida and the thallus of the host, he proved the presence of
numerous gonidia in the subhymenial tissue, these being closely surrounded
by the hyphae of the parasite, and entirely undamaged : they retained their
green colour, and in size and form were unchanged. Zopf1 at first described
these parasites as fungi though later1 he allows that they may represent
lower forms of lichens.
Tobler2 has added two more of these parasymbiotic species on the border
line between lichens and fungi, similar to those described by Zopf. One of
these, Phacopsis vulpina, belonging to the fungus family Celidiaceae, is
parasitic on Letharia vulpina. The fronds of the host plant are considerably
altered in form by its presence, being more branched and curly. Where
the parasite settles a swelling arises filled with its hyphae, and the host
gonidia almost disappear from the immediate neighbourhood, only a few
"nests" being found and these very mucilaginous. These nests as well as
single gonidia are surrounded by Phacopsis hyphae which have gradually
displaced those of the Letharia thallus. The gonidia are excited to division
and increase in number on contact with either lichen or fungus hyphae, but
in the latter case the increase is more abundant owing doubtless to a more
powerful chemical irritant in the fungus. As development advances, the
Phacopsis hyphae multiply to the exclusion of both lichen hyphae and
gonidia from the area of invasion. Finally the host cortex is split, the
fungus bursts through, and the tissue beneath the parasite becomes brown
and dead. Phacopsis begins as a "parasymbiont," then becomes parasitic,
and is at last saprophytic on the dead cells. The hyphae travel down into
the medulla of the host and also into the soredial outgrowths, and are
dispersed along with the host. The effect of Verrucula on the host thallus
may also be cited3.
Tobler gives the results of his examination of still another fungus, Kar-
schia destructans. It becomes established on the thallus of Chaenotheca
cJnysoceptiala and its hyphae gradually penetrate down to the underlying
bark (larch). The lichen thallus beneath the fungus is killed, but gonidia in
the vicinity are sometimes clasped : Karschia also is thus a parasymbiont,
then a parasite, and finally a saprophyte.
Elenkin4 describes certain fungi which to some extent are parasymbionts.
One of these, Conidclla urceolata n.sp., grew on forms of Lecanora esculenta.
The other, a stroma-forming species, had invaded the thallus of Parmelia
1 Zopf 1898, p. 249. 2 Tobler 191 12. 3 See p. 276. 4 Elenkin 1901-.
266 BIONOMICS
molliuscula, where it caused gall-formation. As the growth of the gall was
due to the co-operation of the lichen gonidia, the fungus must at first have
been a parasymbiont. Only dead gonidia were present in the stroma; prob-
ably they had been digested by the parasite. Because of the stroma Elenkin
placed the fungus in a new genus, Trematosphaeriopsis.
e. FUNGI PARASITIC ON LICHENS. A solution or extract of lichen
thallus is a very advantageous medium in which to grow fungi. It is there-
fore not surprising that lichens are a favourite habitat for parasitic fungi.
Stahl1 has noted that the lichens themselves flourish best where there is
frequent moistening by rain or dew with equally frequent drying which
effectively prevents the growth of fungi. Species of Peltigera are however
able to live in damp conditions : without being injured, they have been
observed to maintain their vigour when cultivated in a very moist hot-
house while all the other forms experimented with were attacked and finally
destroyed by various fungi.
Lindsay2 devoted a great deal of attention to the microscopic study of
the minute fruiting bodies so frequently present on lichen thalli and published
descriptions of microlichens, microfungi and spermogonia. He and others
naturally considered these parasitic organisms to be in many cases either
the spermogonia or pycnidia of the lichen itself. It is often not easy to
determine their relationship or their exact systematic position ; many of
them are still doubtful forms.
There exists however a very large number of fully recognized parasitic
microfungi belonging to various genera. Lindsay discovered many of them.
Zopf3 has given exact descriptions of a series of forms, with special reference
to their effect on the host thallus. In an early paper he described a species,
Pleospora collematum, that he found on Physma compactum and other Colle-
maceae. The hyphae of the parasite differed from those of the host in being
of a yellow colour; they did not penetrate or spread far, being restricted to
rhizoid-like filaments at the base of their fruiting bodies (perithecia and
pycnidia). Their presence caused a slight protuberance but otherwise did
no harm to the host ; the Nostoc cells in their immediate vicinity were even
more brightly coloured than in other parts of the thallus. In another paper4
he gives an instance of gall-formation in Collema pulposum induced by the
presence of the fungus Didymosphaeria pulposi. Small protuberances were
formed on the margins of the apothecia, more rarely on the lobes of the
thallus, each one the seat of a perithecium of the fungus. No damage was
done to either constituent of the thallus.
Agyrium flavescens grows parasitically on the under surface of Peltigera
polydactyla. M. and Mme Moreau5 found that the hyphae of the fungus
spread between the medullary filaments of the lichen; no haustoria were
1 Stahl 1904. 2 Lindsay 1859, 1869, 1871. 3 Zopf 1896. 4 Zopf 1898. 6 Moreau I9i63.
PARASITISM 267
observed. The mature fruiting body had no distinct excipulum, but was
surrounded by*a layer of dead lichen cells.
It is not easy to determine the difference between parasites that are of
fungal nature and those that are lichenoid ; but as a general rule the fungi
may be recognized by their more transient character, very frequently by
their effect on the host thallus, which is more harmful than that produced
by lichens, and generally by their affinity to fungi rather than to lichens.
Opinions differ and will continue to differ on this very difficult question.
The number of such fungi determined and classified has gradually
increased, and now extends to a very long list. Even as far back as 1896
Zopf reckoned up 800 instances of parasitism of 400 species of fungi on
about 350 different lichens and many more have been added. Abbe Vouaux1
is the latest writer on the subject, but his work is mostly a compilation of
species already known. He finds representatives of these parasites in nine
families of Pyrenomycetes and six of Discomycetes. He leaves out of account
the much debated Coniocarps, but he includes with fungi all those that have
been proved to be parasymbiotic, such as Abrotliallus.
A number of fungus genera, such as Conida, etc., are parasitic only on
lichens. Most of them have one host only; others, such as Tichothecium
pygmaeum, live on a number of different thalli. Crustaceous species are often
selected by the parasites, and no great damage, if any, is caused to these
hosts, except when the fungus is seated on the disc of the apothecium, so
that the spore-bearing capacity is lessened or destroyed.
In some of the larger lichens, however, harmful effects are more visible.
In Lobaria pulmonaria, the fruits of which are attacked by the Discomycete,
Celidium Stictarum-, there is at first induced an increased and unusual forma-
tion of lichen apothecia. These apothecia are normally seated for the most
part on the margins of the lobes or pustules, but when they are invaded by
the fungus, they appear also in the hollows between the pustules and even
on the under surface of the thallus. In the large majority of cases the
fungus is partly or entirely embedded in the thallus; the gonidia in the
vicinity may remain green and healthy, or all the tissues in the immediate
neighbourhood of the parasite may be killed.
/. MYCETOZOA PARASITIC ON LICHENS. Mycetozoa live mostly on
decayed wood, leaves, humus, etc. One minute species, L isterella paradoxa,
always inhabits the podetia of Cladonia rangiferina. Another species,
Hymenobolina parasitica, was first detected and described by Zukal3 as a
true parasite on the thallus of Physciaceae; it has since been recorded in the
British Islands on Parmeliae*. This peculiar organism differs from other
mycetozoa in that the spores on germination produce amoebae. These unite
to form a rose-red plasmodium which slowly burrows into the lichen thallus
1 Vouaux 1912, etc. 2 Bitter 1904. 3 Zukal 1893. 4 Lister 1911.
268 BIONOMICS
and feeds on the living hyphae. It is a minute species, but when abundant
the plasmodia can just be detected with the naked eye as rosy specks
scattered over the surface of the lichen. Later the grey sporangia are
produced on the same areas.
F. DISEASES OF LICHENS
a. CAUSED BY PARASITISM. Zopf l has stated that of all plants, lichens
are the most subject to disease, reckoning as diseases all the instances of
parasitism by fungi or by other lichens. There are however only rare
instances in which total destruction or indeed any permanent harm to the
host is the result of such parasitism. At worst the trouble is localized and
does not affect the organism as a whole. Some of these cases have been
already noted under antagonistic symbiosis or parasymbiosis. Several
instances have however been recorded where real injury has been caused
by the penetration of some undetermined fungus mycelium. Zukal2 records
two such observed by him in Parmelia encansta and Physcia villosa : the
thallus of the former was dwarfed and deformed by the presence of the alien
mycelium, the latter was excited to abnormal proliferation.
b. CAUSED BY CROWDING. Lichens suffer frequently from being over-
grown by other lichens ; they may also be crowded out by other plants.
My attention was called by Mr P. Thompson to a burnt plot of ground in
Epping Forest, which, after the fire, had been colonized by Peltigera spuria.
In the course of a few years, other vegetation had followed, depriving the
lichen of space and light and gradually driving it out. When last examined
only a few miserable specimens remained, and these were reduced in vitality
by an attack of the lichen parasite Illosporium carneum.
c. CAUSED BY ADVERSE CONDITIONS. Zukal considers as pathological,
at least in origin, the cracking of the thallus so frequent in crustaceous
lichens as well as in the more highly developed forms. As the cracks are
beneficial in the aeration of the plant, they can hardly be regarded as
symptoms of a diseased condition. The more evident ringed breaks in the
cortex of Usneae, due probably to wind action, have more reason to be so
regarded ; they are most pronounced in Usnea articulata, where the portions
bounded by the rings are contracted and swollen, and a hollow space is
formed between the cortex and the central axis. The swellings that are
produced ®n lichen thalli, such as those of Umbilicaria and some species of
Gyrophora, due to intercalary growth are normal to the plant, though occasion-
ally the swollen weaker portions may become ruptured and the cortex be
thrown off. As pathological also must be regarded the loss of cortex some-
times occasioned by excessive soredial formation at the margins of the lobes:
1 Zopf 1897. 2 Zukal Xg96) p< 258.
DISEASES OF LICHENS 269
the upper cortex may be rolled back and eventually torn away; the gonidial
layer is exposed and transformed into soredia which are swept away by the
wind and rain, till finally only traces of the lower cortex are left.
Zukal1 has instanced, as a case of diseased condition observed by him,
the undue thickening of the cortex in Pertusaria communis whereby the
formation of the fruiting bodies is inhibited and even vegetative development
is rendered impossible. There arrives finally a stage when splitting takes
place and the whole thallus breaks down and disappears. As a rule however
there need be no limit to the age of the lichen plant. There is no vital
point or area in the thallus ; injury of one part leaves the rest unhurt, and
any fragment in growing condition, if it combines both symbionts, can carry
on the life of the plant, the constant renewal of gonidia preventing either
decay or death. Barring accidents many lichens might exist as long as the
world endures.
G. HARMFUL EFFECT OF LICHENS
One lichen only, Strigula complanata, a tropical species, has been proved
to be truly and constantly parasitic. It grows'on the surface of thick leathery
leaves such as those of Camellia-, etc. and the alga and fungus both penetrate
the epidermis and burrow beneath the cuticle and outer cells, causing them
to become brown. It undoubtedly injures the leaves.
Friedrich3 has given an isolated instance of the hold-fast hyphae of Usnea
piercing through the cortex to the living tissue of the host, and not only
destroying the middle lamella by absorption, but entering the cells. The
Usnea plant was characterized by exceptionally vigorous growth. Practically
all corticolous lichens are epiphytic and the injury they cause is of an acci-
dental nature Crustaceous species on the outer bark occupy the dead
cortical layers and seem to be entirely harmless4. The larger foliose and
fruticose forms are not so innocuous: by their abundant enveloping growth
they hinder the entrance of air and moisture, and thus impede the life of
the higher plant. Gleditsch5, one of the earliest writers on Forestry, first
indicated the possibly harmful effect of lichens especially on young trees
and " in addition," he says, " they serve as cover for large numbers of small
insects which are hurtful in many ways to the trees." Lindau6 pointed out
the damage done to pine-needles by Xantkoria parietina which grew round
them like a cuff and probably choked the stomata, the leaves so clothed being
mostly withered. Dufrenoy7 states that he found the hyphae of a Parmelia
entering a pine-needle by the stomata, and that the starch disappeared from
the neighbouring parenchyma the cells of which tended to disintegrate.
It is no uncommon sight to see neglected fruit trees with their branches
crowded with various lichens, Evernia prunaslri, Ramalina farinacea, etc.
Such lichens often find the lenticels a convenient opening for their hold-fasts
1 Zukal 1896, p. 255. '2 Cunningham 1879. 3 F"edrich 1906, p. 401. * See p. 78.
5 Gleditsch 1775, p. 31. 6 Lindau 1895, p. 53. 7 Dufrenoy 1881.
27o BIONOMICS
and excercise a smothering effect on the trees. Lilian Porter1 distinctly
states that Ramalinae by their penetrating bases damage the tissues of the
trees. The presence of lichens is however generally due to unhealthy con-
ditions already at work. Friedrich2 reported of a forest which he examined,
in which the atmospheric moisture was very high, with the soil water
scarce, that those trees that were best supplied with soil water were free
from lichens, while those with little water at the base bore dead branches
which gave foothold to a rich growth of the epiphytes.
Experiments to free fruit trees from their coating of lichens were made
by Waite3. With a whitewash brush he painted over the infested branches
with solutions of Bordeaux mixture of varying strength, and found that this
solution, commonly in use as a fungicide, was entirely successful. The trees
were washed down about the middle of March, and some three weeks later
the lichens were all dead, the fruticose and foliose forms had changed in
colour to a yellowish or brownish tint and wer.e drooping and shrivelled.
Waite was of opinion that the lichens did considerable damage to the
trees, but it has been held by others that in very cold climates they may
provide protection against severe frost. Instances of damage are however
asserted by Bouly de Lesdain4. The bark of willows he found was a favourite
habitat of numerous lichens: certain species, such as Xanthoria parietina,
completely surrounded the branches, closing the stomata; others, such as
Physcia ascendens, by the mechanical strain of the rhizoids, first wet and then
dry, gradually loosened the outer bark and gave entry to fungi which com-
pleted the work of destruction.
H. GALL-FORMATION
Several instances of gall-formation to a limited extent have been already
noted as caused by parasitic fungi or lichens. Greater abnormality of develop-
ment is induced in a few species by the presence of minute animals, mites,
wood-lice, etc. Zopf5 noted these deformations of the thallus in specimens
of Ramalina Kullensis collected on the coasts of Sweden. The fronds were
frequently swollen in a sausage-like manner, and branching was hindered or
altogether prevented; apothecia were rarely formed, though pycnidia were
abundant. Here and there, on the swollen portions of the thallus, small
holes could be detected and other larger openings of elliptical outline, about
\-\\ mm. in diameter, the margins of which had a nibbled appearance.
Three types of small articulated animals were found within the openings:
species of mites, spiders and wood-lice. Mites were the most constant and
were more or less abundant in all the deformations; frequently a minute
Diplopodon belonging to the genus Polyxenus was also met with.
Zopf came to the conclusion that the gall-formation was mainly due to
the mites: they eat out the medulla and possibly through some chemical
1 Porter 1917. 2 Friedrich 1906. » Waite 1893. 4 Lesdain 1912. 5 Zopf 1907.
GALL-FORMATION 271
irritation excite the algal zone and cortex to more active growth, so that an
extensive tangential development takesplace. The small spiders mayexercise
the same power; evidently the larger holes were formed by them.
Later Zopf added to gall-deformed plants Ramalina scopnlorum van in-
crassata and R. cuspidata var. crassa. He found in the- hollow swollen fronds
abundant evidence of mites, but whether identical with those that attacked
R. Kullensis could not be determined. These two Ramalinae are maritime
species ; they are morphologically identical, as are also the deformed varieties,
and the presence of mites, excreta, etc., are plainly visible in our British
specimens.
Bouly de Lesdain1 found evidence of mite action in Ramalina far inacea
collected from Pinus sylvestris on the dunes near Dunkirk. The cortex
had been eaten off either by mites or by a small mollusc (Pupa muscorum]
and the fronds had collapsed to a more or less convex compact mass.
Somewhat similar deformations, though less pronounced, were observed in
other Ramalinae.
In Cladonia sylvatica and also in Cl. rangiformis Lesdain has indicated
ff. abortiva Harm, as evidently the result of insect attack. In both cases the
tips of the podetia are swollen, brown, bent and shrivelled.
One of the most curious and constant effects, also worked out by Lesdain,
occurs in Physcia hispida (Ph. stellaris var. tenella). In that lichen the
gonidia at the tips of the fronds are scooped out and eaten by mites, so
that the upper cortex becomes separated from the lower part of the thallus.
As the hyphae of the cortex continue to develop, an arched hood is formed
of a whitish shell-like appearance and powdery inside. Sometimes the
mites penetrate at one point only, at other times the attack is at several
places which may ultimately coalesce into one large cavity. In a crustaceous
species, Caloplaca (Placodium) citrina he found constant evidence of the
disturbing effect of the small creatures, which by their action caused the
areolae of the thallus to grow into minute adherent squamules. A patho-
logical variety, which he calls var. sorediosa, is distinguished by the presence
of cup-like hollows which are scooped out by Acarinae and are filled by
yellowish soredia. In another form, var. maritima, the margins of the areolae,
occasionally the whole surface, become powdery with a citrine yellow
efflorescence as a result of their nibbling.
Zukal2 adds to the deformations due to organic agents, the hypertrophies
and abnormalities caused by climatic conditions. He finds such irregularities
of structure more especially developed in countries with a very limited rain-
fall, as in certain districts of Chili, Australia and Africa, where changes in
cortex and rhizoids and proliferations of the thallus testify to the disturbance
of normal development.
1 Lesdain 1910. 2 Zukal 1896, p. 258.
CHAPTER VII
PHYLOGENY
I. GENERAL STATEMENT
A. ORIGIN OF LICHENS
THOUGH lichens are very old members of the vegetable kingdom, as
symbiotic plants they yet date necessarily from a time subsequent to the
evolution of their component symbionts. Phylogeny of lichens begins with
symbiosis.
The algae, which belong to those families of Chlorophyceae and Myxo-
phyceae that live on dry land, had become aerial before their association
with fungi to form lichens. They must have been as fully developed then
as now, since it is possible to refer them to the genus or sometimes even to
the species of free-living forms. The fungus hyphae have combined with a
considerable number of different algae, so that, even as regards the algal
symbiont, lichens are truly polyphyletic in origin.
The fungus is, however, the dominant partner, and the principal line of
development must be traced through it, as it provides the reproductive organs
of the plant. Representatives of two great groups of fungi are associated
with lichens: Basidiomycetes, found in only a few genera, and Ascomycetes
which form with the various algae the great bulk of lichen families. In
respect of their fungal constituents lichens are also polyphyletic, and more
especially in the Ascolichens which can be traced back to several starting
points. But though lichens have no common origin, the manner of life is
common to them all and has influenced them all in certain directions: they
are fitted for a much longer existence than that of the fungi from which they
started; and both the thallus and the fruiting bodies — at least in the sub-
class Ascolichens — can persist through great climatic changes, and can pass
unharmed through prolonged periods of latent or suspended vitality.
Another striking note of similarity that runs through the members of this
sub-class, with perhaps the exception of the gelatinous lichens, is the formation
of lichen-acids which are excreted by the fungus. These substances are
peculiar to lichens and go far to mark their autonomy. The production of
the acids and the many changes evolved in the vegetative thallus suggest the
great antiquity of lichens.
ORIGIN OF LICHENS 273
B. ALGAL ANCESTORS
It is unnecessary to look far for the algae as they have persisted through
the ages in the same form both without and within the lichen thallus. By
many early lichenologists the free-living algae, similar in type to lichen algae,
were even supposed to be lichen gonidia in a depauperate condition and
were, for that reason, termed by Wallroth " unfortunate brood-cells." In the
condition of symbiosis they may be considerably modified, but they revert
to their normal form, and resume their normal life-history of spore production,
etc., under suitable and free culture. The different algae taking part in
lichen-formation have been treated in an earlier chapter1.
C. FUNGAL ANCESTORS
a. HVMENOLICHENS. The problem of the fungal origin in this sub-class
is comparatively simple. It contains but three genera of tropical lichens which
are all associated with Myxophyceae, and the fungus in them, to judge from
the form and habit of the plants, is a member of the Thelephoraceae. It
may be that Hymenolichens are of comparatively recent origin and that the
fungi belonging to the Basidiomycetes had, in the course of time, become
less labile and less capable of originating a new method of existence. What-
ever the reason, they lag immeasurably behind Ascomycetes in the formation
of lichens.
b. ASCOLICHENS. Lichens are again polyphyletic within this sub-class.
The main groups from which they are derived are evident. Whether there
has been a series of origins within the different groups or a development
from one starting point in each it would be difficult to determine. In any
case great changes have taken place after symbiosis became established.
The main divisions within the Ascolichens are related to fungi thus:
Series I. Pyrenocarpineae I
„ . \ to Pyrenomycetes.
2. Comocarpmeae )
3. Graphidineae to Hysteriaceae.
4. Cyclocarpineae to Discomycetes.
II. THE REPRODUCTIVE ORGANS
A. THEORIES OF DESCENT IN ASCOLICHENS
It has been suggested that ascomycetous fungi, from which Ascolichens
are directly derived, are allied to the Florideae, owing to the appearance of
a trichogyne in the carpogonium of both groups. That organ in the red sea-
weeds is a long delicate cell in direct communication with the egg-cell of
the carpogonium. It is a structure adapted to totally submerged conditions,
and fitted to attach the floating spermatia.
1 See p. 51.
S.L. 18
274 PHYLOGENY
In fungi there is also a structure considered as a trichogyne1, which, in
the Laboulbeniales, is a free, simple or branching organ. There is no other
instance of any similar emergent cell or cells connected with the ascogonium
of the Ascomycetes, though the term has been applied in these fungi to
certain short hyphal branches from the ascogonium which remain embedded
in the tissue. In the Ascomycetes examined all traces of emergent receptive
organs, if they ever existed, have now disappeared ; in some few there are
ipossible internal survivals which never reach the surface.
In Ascolichens, on the contrary, the "trichogyne," a septate hyphal
branch extending upwards from the ascogonium, and generally reaching the
open, has been demonstrated in all the different groups except, as yet,- in
the Coniocarpineae which have not been investigated. Its presence is a
strong point in the argument of those who believe in the Floridean ancestry
of the Ascomycetes. It should be clearly borne in mind that Ascolichens
are evolved from the Ascomycetes: these latter stand between them and
any more remote ancestry.
In the Ascomycetes, there is a recognized progression of development
in the form of the sporophore from the closed perithecium of the Pyreno-
mycetes and possibly through the vHysteriaceae, which are partially closed,
to the open ascocarp of the Discomycetes. If the fungal and lichenoid
" trichogyne " is homologous with the carpogonial organ in the Florideae,
then it must have been retained in all the groups of Ascomycetes as an
emergent structure, and as such passed on from them to their lichen
derivatives. Has that organ then disappeared from fungi since symbiosis
began ? There is no trace of it now, except as already stated in Laboul-
beniales with which lichens are unconnected.
Were Ascolichens monophyletic in origin, one could more easily suppose
that both the fungal and lichen series might have started at some early stage
from a common fungal ancestor possessing a well-developed trichogyne
which has persisted in lichens, but has been reduced to insignificance in
fungi, while fruit development proceeded on parallel lines in both. There is
no evidence that such progression has taken place among lichens ; the theory
of a polyphyletic origin for the different series seems to be unassailable. At
the same time, there is no evidence to show in which series symbiosis started
first.
It is more reasonable to accept the polyphyletic origin, as outlined above,
from forms that had already lost the trichogyne, if they ever really possessed
it, and to regard the lichen trichogyne as a new organ developing in lichens
in response to some requirement of the deep-seated ascogonium. Its sexual
function still awaits satisfactory proof, and it is wiser to withhold judgment
as to the service it renders to the developing fruit.
1 See p. \li et seq.
REPRODUCTIVE ORGANS 275
B. RELATION OF LICHENS TO FUNGI
a. PYRENOCARPINEAE. In Phycolichens (containing blue-green gonidia)
and especially in the gelatinous forms, fructification is nearly always a more
or less open apothecium. The general absence of the perithecial type is
doubtless due to the gelatinous consistency of the vegetative structure; it is
by the aid of moisture that the hymenial elements become turgid enough
to secure the ejection of the spores through the narrow ostiole of the peri-
thecium, and this process would be frustrated were the surrounding and
enveloping thallus also gelatinous. There is only one minutely foliose or
fruticose gelatinous family, the Pyrenidiaceae, in which Pyrenomycetes are
established, and the gonidia, even though blue-green, have lost the gelatinous
sheath and do not swell up.
In Archilichens (with bright-green gonidia), perithecial fruits occur
frequently ; they are nearly always simple and solitary; in only a few families
with a few representatives, is there any approach to the stroma formation so
marked among fungi. The single perithecium is generally semi-immersed
in the thallus. It may be completely surrounded by a hyphal " entire " wall,
either soft and waxy or dark coloured and somewhat carbonaceous. In
numerous species the outer protective wall covers only the upper portion
that projects beyond the thallus, and such a perithecium is described as
" dimidiate," a type of fruit occurring in several genera, though rare among
fungi.
As to internal structure, there is a dissolution and disappearance of the
paraphyses in some genera, their protective function not being so necessary
in closed fruits, a character paralleled in fungi. There is a great variety of
spore changes, from being minute, simple and colourless, to varied septation,
general increase in size, and brown colouration. The different types may
be traced to fungal ancestors with somewhat similar spores, but more
generally they have developed within the lichen series. From the life of the
individual it is possible to follow the course of evolution, and the spores of
all species begin as simple, colourless bodies; in some genera they remain
so, in others they undergo more or less change before reaching the final
stage of colour or septation that marks the mature condition.
As regards direct fungal ancestors, the Pyrenocarpineae, with solitary
perithecia, are nearest in fruit structure to the Mycosphaerellaceae, in which
family are included several fungus genera that are parasitic on lichens such
as Ticothecium, Mullerella, etc. In that family occurs also the genus Stigmatea,
in which the perithecia in form and structure are very similar to dimidiate
Vernicariae.
Zahlbruckner1 has suggested as the starting point for the Verrucariaceae
1 Zahlbruckner 1903.
18— 2
276 PHYLOGENY
the fungus genus Verrncula. It was established by Steiner1 to include two
species, V. cahirensis and V. aegyptica, their perithecia being exactly similar
to those of Verrucaria? in which genus they were originally placed. Both
are parasitic on species of Caloplaca (P lacodium}. The former, on C. gilvella,
transforms the host thallus to the appearance of a minutely lobed Placodium ;
the latter occupies an island-like area in the centre of the thallus of Caloplaca
interveniens, and gives it, with its accompanying parasite, the character of
an Endopyrenium (Dermatocarpon), while the rest of the thallus is normal
and fertile.
Zahlbruckner may have argued rightly, but it is also possible to regard
these rare desert species as reversions from an originally symbiotic to a purely
parasitic condition. Reinke came to the conclusion that if a parasitic
species were derived directly from a lichen type, then it must still rank as
a lichen, a view that has a direct bearing on the question. The parallel
family of Pyrenulaceae which have Trentepohlia gonidia is considered by
Zahlbruckner to have originated from the fungus genus Didymella.
Compound or stromatoid fructifications occur once and again in lichen
families; but, according to Wainio3, there is no true stroma formation, only
a pseudostroma resulting from adhesions and agglomerations of the thalline
envelopes or from cohesions of the margins of developing fruit bodies.
These pseudostromata are present in the genera Chiodecton and Glyphis
(Graphidineae) and in Trypethelium, Mycoporium, etc. (Pyrenocarpineae).
This view of the nature of the compound fruits is strengthened, as Wainio
points out, by the presence in certain species of single apothecia or perithecia
on the same specimen as the stromatoid fruits.
b. CONIOCARPINEAE. This subseries is entirely isolated. Its peculiarity
lies in the character of the mature fruit in which the spores, owing to the
early breaking down of the asci, lie as a loose mass in the hymenium, while
dispersal is delayed for an indefinite time. This type of fruit, termed a
mazaedium by Acharius, is in the form of a stalked or sessile roundish head
— the capitulum — closed at first and only half-open at maturity rarely, as in
Cyphelium, an exposed disc. There is a suggestion, but only a suggestion, of a
similar fructification in the tropical fungus Camillea in which there is some-
times a stalk with one or more perithecia at the tip, and in some species early
disintegration of the asci, leaving spore masses4. But neither in fungi nor in
other lichens is there any obvious connection with Coniocarpineae. In some
of the genera the fungus alone forms the stalk and the wall of the capitulum ;
in others the thallus shares in the fruit-formation growing around it as an
amphithecium.
The semi-closed fruits point to their affinity with Pyrenolichens, though
1 Steiner 1896. 2 Muller-Argau 1880. 3 Wainio 1890, p. xxiii. 4 Lloyd 1917.
REPRODUCTIVE ORGANS 277
they are more advanced than these judging from the thalline wall that is
present in some genera and also from the half-open disc at maturity. The
latter feature has influenced some systematists to classify the whole subseries
among Cyclocarpineae. The thallus, as in Sphaerophorus, reaches a high
degree of fruticose development ; in other genera it is crustaceous without
any formation of cortex, while in several genera or species it is non-existent,
the fruits being parasites on the thalli of other lichens or saprophytes on
dead wood, humus, etc. These latter — both parasites and saprophytes —
are included by Rehm1 and others among fungi, which has involved the
breaking up of this very distinctive series. Rehm has thus published as
Discomycetes the lichen genera Sphinctrina, Cyp helium, Coniocybe, Ascoliunit
Calicium and Stenocybe, since some or all of their species are regarded by
him as fungi.
Reinke2 in his lichen studies states that it might not be impossible for
a saprophytic fungus to be derived from a crustaceous lichen — a case of
reversion — but that no such instance was then known. More exact studies3
of parasymbiosis and antagonistic symbiosis have shown the wide range of
possible life-conditions, and such a reversion does not seem improbable. We
must also bear in mind that in suitable cultures, lichen hyphae can be grown
without gonidia: they develop in that case as saprophytes.
On Reinke's2 view, however, that these saprophytic species, belonging to
different genera in the Coniocarpineae, are true fungi, they would represent
the direct and closely related ancestors of the corresponding lichen genera,
giving a polyphyletic origin within this group. As fungus genera he has
united them in Protocaliciaceae, and the representatives among fungi he
distinguishes, as does Wainio4, under such names as Mycocalicium and
Mycocon iocybe.
If we might consider the saprophytic forms as also retrogressive lichens,
a monophyletic origin from some remote fungal ancestor would prove a more
satisfactory solution of the inheritance problem. This view is even supported
by a comparison Reinke himself has drawn between the development of the
fructification in Mycocalicium parietinum, a saprophyte, and in his view a
fungus, and Chaenotheca cJirysocephala, a closely allied lichen. Both grow on
old timber. In the former (the fungus), the mycelium pervades the outer
weathered wood-cells, and the fruit stalk rises from a clump of brownish
hyphae; there is no trace of gonidia. ChaenotJieca chrysocephala differs in the
presence of gonidia which are associated with the mycelium in scattered
granular warts; but the fruit stalk here also rises directly from the mycelium
between the granules. The presence of a lichen thallus chiefly differentiates
between the two plants, and this thallus is not a casual or recent association;
it is constant and of great antiquity as it is richly provided with lichen-acids.
1 Rehm 1890. 2 Reinke 1894. 3 See p. 260. 4 Wainio 1890.
2;8 PHYLOGENY
Reinke has indicated the course of evolution within the series but that
is on the lines of thalline development and will be considered later.
c. GRAPHIDINEAE. This series contains a considerable variety of lichen
forms, but all possess to a more or less marked degree the linear form of
fructification termed a "lirella" which has only a slit-like opening. There
is a tendency to round discoid fruits in the Roccellae and also in the Arthoniae;
the apothecia of the latter, called by early lichenologists "ardellae," are with-
out margins. In nearly all there is a formation of carbonaceous black tissue
either in the hypothecium or in the proper margins. In some of them the
paraphyses are branched and dark at the tips, the branches interlocking to
form a strong protective epithecium. There are, however, constant exceptions,
in some particular, to any generalization in genera and in species. Miiller-
Argau's1 pronouncement might be held to have special reference to Graphi-
dineae: "that in any genus, species or groups of species are to be found
which outwardlyshew something that is peculiar, thoughof slightimportance."
The most constant type of gonidium is Trentepbhlia, but Palmella and
Phycopeltis occasionally occur. The spores are various in colour and form ;
they are rarely simple.
The genus Arthonia is derived from a member of the Patellariaceae, from
which family many of the Discomycetes have arisen. The course of develop-
ment does not follow from a closed to an open fruit ; the apothecium is open
from the first, and growth proceeds from the centre outwards, the fertile cells
gradually pushing aside the sterile tissue of the exterior. The affinity of
Xylographa (with Palmella gonidia) is to be found in Stictis in the fungal
family Stictidaceae, the apothecia of Stictis being at first closed, then open,
and with a thick margin ; Xylographa has a more elongate lirella fruit, though
otherwise very similar, and has a very reduced thallus. Rehm2 has classified
Xylographa as a fungus.
The genera with linear apothecia are closely connected with Hysteriaceae,
and evidently inherit their fruit form severally from that family. There is
thus ample evidence of polyphyletic descent in the series. Stromatoid fruits
occur in Chiodectonaceae, with deeply sunk, almost closed disc, but they
have evidently evolved within the series, possibly from a dividing up of the
lirellae.
In Graphidineae there are also forms, more especially in Arthoniaceae,
on the border line between lichens and fungi: those with gonidia being
classified as lichens, those without gonidia having been placed in corre-
sponding genera of fungi. These latter athalline species live as parasites or
saprophytes.
The larger number of genera have a poorly developed thallus; in many
of them it is embedded within the outer periderm-cells of trees, and is known
1 Muller-Argau 1862. 2 Rehm 1890.
REPRODUCTIVE ORGANS 279
as " hypophloeodal." But in some families, such as Roccellaceae, the thallus
attains a very advanced form and a very high production of acids.
The conception of Graphidineae as a whole is puzzling, but one or other
characteristic has brought the various members within the series. It is in
this respect an epitome of the lichen class of which the different groups,
with all their various origins and affinities, yet form a distinct and well-defined
section of the vegetable kingdom.
d. CYCLOCARPINEAE. This is by far the largest series of lichens. The
genera are associated with algae belonging both to the Myxophyceae and
the Chlorophyceae, and from the many different combinations are produced
great variations in the form of the vegetative body. The fruit is an emergent,
round or roundish disc or open apothecium in all the members of the series
except Pertusariaceae, where it is partially immersed in thalline " warts."
In its most primitive form, described as "biatorine" or "lecideine," it may
be soft and waxy {Biatorci) or hard and carbonaceous (Lecidea), in the latter
the paraphyses being mostly coloured at the tips ; these are either simple or
but sparingly branched, so that the epithecium is a comparatively slight
structure. The outer sterile tissue forms a protective wall or "proper margin"
which may be entirely pushed aside, but generally persists as a distinct rim
round the disc.
A great advance within the series arose when the gonidial elements of
the thallus took part in fruit-formation. In that case not only is the
hymenium generally subtended by a layer of algae, but thalline tissue con-
taining algae grows up around the fruit, and forms a second wall or thalline
margin. This type of apothecium, termed " lecanorine," is thus intimately
associated with the assimilating tissue and food supply, and it gains in
capacity of ascus renewal and of long duration. This development from
non-marginate to marginate ascomata is necessarily an accompaniment of
symbiosis.
There is no doubt that the Cyclocarpineae derive from some simple
form or forms of Discomycete in the Patellariaceae. The relationship
between that family and the lower Lecideae is very close. Rehm1 finds the
direct ancestors of Lecidea itself in the fungus genus, Patinella, in which the
apothecia are truly lecideine in character — open, flat and slightly margined,
the hypothecium nearly always dark-coloured and the paraphyses branched,
septate, clavate and coloured at the tips, forming a dark epithecium. More
definitely still he describes Patinella atroviridis, a new species he discovered,
as in all respects a Lecidea, but without gonidia.
In the crustaceous Lecideaceae, a number of genera have been delimited
on spore characters — colourless or brown, and simple or variously septate.
In Patellariaceae as described by Rehm are included a number of fungus
1 Rehm 1890.
28o PHYLOGENY
genera which correspond to these lichen genera. Only two of them —
Patinella and Patellaria — are saprophytic ; in all the other genera of the
family, the species with very few exceptions are parasitic on lichens : they
are parasymbionts sharing the algal food supply ; in any case, they thrive
on a symbiotic thallus.
Rehm unhesitatingly derives the corresponding lichen genera from these
fungi. He takes no account of the difficulty that if these parasitic (or sapro-
phytic) fungi are primitive, they have yet appeared either later in time than
the lichens on which they exist, or else in the course of ages they have
entirely changed their substratum.
He has traced, for instance, the lichen, Buellia, to a saprophytic fungus
species, Karschia lignyota, to a genus therefore in which most of the species
are parasitic on lichens and have generally been classified as parasitic lichens.
There is no advance in apothecial characters from the fungus, Karschia, to
Buellia, merely the change to symbiosis. It therefore seems more in accord-
ance with facts to regard Buellia as a genus evolved within the lichen series
from Patinella through Lecidea, and to accept these species of Karschia on
the border line as parasitic, or even as saprophytic, reversions from the
lichen status. We may add that while these brown-spored lichens are fairly
abundant, the corresponding athalline or fungus forms are comparatively
few in number, which is exactly what might be expected from plants with
a reversionary history.
Occasionally in biatorine or lecideine species with a slight thalline
development all traces of the thallus disappear after the fructification has
reached maturity. The apothecia, if on wood or humus, appear to be
saprophytic and would at first sight be classified as fungi. They have un-
doubtedly retained the capacity to live at certain stages, or in certain con-
ditions, as saprophytes.
The thallus disappears also in some species of the crustaceous genera
that possess apothecia with a thalline margin, and the fruits may be left
stranded and solitary on the normal substratum, or on some neighbouring
lichen thallus where they are more or less parasitic ; but as the thalline
margin persists, there has been no question as to their nature and affinity.
Rehm suggests that many species now included among lichens may be
ultimately proved to be fungi ; but it is equally possible that the reverse may
be the case, as for instance Bacidiaflavovirescens, held by Rehm and others to
be a parasitic fungus species, but since proved by Tobler1 to be a true lichen.
A note by Lightfoot2, one of our old-time botanists who gave lichens a
considerable place in his Flora, foreshadows the theory of evolution by
gradual advance, and his views offer a suggestive commentary on the subject
under discussion. He was debating the systematic position of the maritime
1 Tobler 191 12, p. 407. 2 Lightfoot 1777, p. 965.
REPRODUCTIVE ORGANS 281
lichen genus Lichina, considered then a kind of Fucus, and had observed
its similarity with true lichens. " The cavity," he writes, " at the top of the
fructification (in Lichind) is a proof how nearly this species of Fucus is
related to the scutellated lichens. Nature disdains to be limited to the
systematic rules of human invention. She never makes any sudden starts
from one class or genus to another, but is regularly progressive in all her
works, uniting the various links in the chain of beings by insensible con-
nexions."
III. THE THALLUS
A. GENERAL OUTLINE OF DEVELOPMENT
a. PRELIMINARY CONSIDERATIONS. The evolution of lichens, as such,
has reference mainly to the thallus. Certain developments of the fructification
are evident, but the changes in the reproductive organs have not kept pace
with those of the vegetative structures: the highest type of fruit, for instance,
the apothecium with a thalline margin, occurs in genera and species with a
very primitive vegetative structure as well as in those that have attained
higher development.
Lichens are polyphyletic as regards their algal, as well as their fungal,
ancestors, so that it is impossible to indicate a straight line of progression,
but there is a general process of thalline development which appears once
and again in the different phyla. That process, from simpler to more com-
plicated forms, follows on two lines: on the one there is the endeavour to
increase the assimilating surface, on the other the tendency to free the plant
from the substratum. In both, the aim has been the same, to secure more
favourable conditions for assimilation and aeration. Changes in structure
have been already described1, and it is only needful to indicate here the main
lines of evolution.
b. COURSE OF EVOLUTION IN HYMENOLICHENS. There is but little
trace of development in these lichens. The fungus has retained more or less
the form of the ancestral Thelephora which has a wide-spreading superficial
basidiosporous hymenium. Three genera have been recognized, the differences
between them being due to the position within the thallus, and the form of
the Scytonema that constitutes the gonidium. The highest stage of develop-
ment and of outward form is reached in Cora, in which the gonidial zone
is central in the tissue and is bounded above and below by strata of hyphae.
c. COURSE OF EVOLUTION IN ASCOLICHENS. It is in the association
with Ascomycetes that evolution and adaptation have had full scope. In
that subclass there are four constantly recurring and well-marked stages
of thalline development, (i) The earliest, most primitive stage, is the
1 See Chap. III.
282 PHYLOGENY
crustaceous: at first an accretion of separate granules which may finally be
united into a continuous crust with a protective covering of thick-walled
amorphous hyphae forming a " decomposed " cortex. The extension of
a granule by growth in one direction upwards and outwards gives detach-
ment from the substratum, and originates (2) the squamule which is, how-
ever, often of primitive structure and attached to the support, like the granule,
by the medullary hyphae. Further growth of the squamule results in (3)
the foliose thallus with all the adaptations of structure peculiar to that form.
In all of these, the principal area of growth is round the free edges of the
thallus. A greater change takes place in the advance to (4) the fruticose
type in which the more active growing tissue is restricted to the apex, and
in which the frond or filament adheres at one point only to the support, a
new series of strengthening and other structures being evolved at the same
time.
The lichen fungi associate, as has been already stated, with two different
types of algae: those combined with the Myxophyceae have been designated
Phycolichenes, those with Chlorophyceae as Archilichenes. The latter pre-
dominate, not only in the number of lichens, but also in the more varied
advance of the thallus, although, in many instances, genera and species of
both series may be closely related.
B. COMPARATIVE ANTIQUITY OF ALGAL SYMBIONTS
One of the first questions of inheritance concerns the comparative an-
tiquity of the two gonidial series: with which kind of alga did the fungus
first form the symbiotic relationship ? No assistance in solving the problem
is afforded by the type of fructification. The fungus in Archilichens is
frequently one of the more primitive Pyrenomycetes, though more often a
Discomycete, while in Phycolichens Pyrenomycetes are very rare. There
is, as already stated, no corelation of advance between the fruit and the
thallus, as the most highly evolved apothecia with well-formed thalline
margins are constantly combined with thalli of low type.
Forssell1 gave considerable attention to the question of antiquity in his
study of gelatinous crustaceous lichens in the family Pyrenopsidaceae, termed
by him Gloeolichens, and he came to the conclusion that Archilichens
represented the older combination, Phycolichens being comparatively.young.
His view is based on a study of the development of certain lichen fungi
that seem able to adapt themselves to either kind of algal symbiont. He
found1 in Euopsis (Pyrenopsis) granatina, one of the Pyrenopsidaceae, that
certain portions of the thallus contained blue-green algae, while others con-
tained Palmella, and that these latter, though retrograde in development,
1 Forssell 1885.
THE THALLUS 283
might become fertile. The granules with blue-green gonidia were stronger,
more healthy and capable of displacing those with Palmella, but not of
bearing apothecia, though spermogonia were embedded in them — a first step,
according to Forssell, towards the formation of apothecia. These granules,
not having reached a fruiting stage, were reckoned to be of a more recent
type than those associated with Palmella. In other instances, however, the
line of evolution has been undoubtedly from blue-green to more highly
evolved bright-green thalli.
The striking case of similarity between Psoroma hypnorum (bright-green)
and Pannaria rubiginosa (blue-green) may also be adduced. Forssell con-
siders that Psoroma is the more ancient form, but as the fungus is adapted
to associate with either kind of alga, the type of squamules forming the
thallus may be gradually transformed by the substitution of blue-green for
the earlier bright-green — the Pannaria superseding the Psoroma. There is
a close resemblance in the fructification — that is of the fungus — in these two
different lichens.
Hue1 shares Forssell's opinion as to the greater antiquity of the bright-
green gonidia and cites the case of Solorina crocea. In that lichen there is
a layer of bright-green gonidia in the usual dorsiventral position, below the
upper cortex. Below this zone there is a second formed entirely of blue-
green cells. Hue proved by his study of development in Solorina that the
bright-green were the normal gonidia of the thallus, and were the only ones
present in the growing peripheral areas; the blue-green were a later addition,
and appeared first in small groups at some distance from the edge of the
lobes.
The whole subject of cephalodia-development2 has a bearing on this
question. These bodies always contain blue-green algae, and are always
associated with Archilichens. Mostly they occur as excrescences, as in
Stereocaulon and in Peltigera. The fungus of the host-lichen though normally
adapted to bright-green algae has the added capacity of forming later a sym-
biosis with the blue-green. This tendency generally pervades a whole genus
or family, the members of which, as in Peltigeraceae, are too closely related
to allow as a rule of separate classification even when the algae are totally
distinct.
C. EVOLUTION OF PHYCOLICHENS
The association of lichen-forming fungi with blue-green algae may have
taken place later in time, or may have been less successful than with the
bright-green: they are fewer in number, and the blue-green type of thallus
is less highly evolved, though examples of very considerable development
are to be found in such genera as Peltigera, Sticta or Nephromium.
1 Hue 191 11. 2 See p. 133.
284 PHYLOGENY
a. GLOEOLICHENS. Among crustaceous forms the thallus is generally
elementary, more especially in the Gloeolichens (Pyrenopsidaceae). The
algae of that family, Gloeocapsa, Xanthocapsa or Chroococcus, are furnished
with broad gelatinous sheaths which, in the lichenoid state, are penetrated
and traversed by the fungal filaments, a branch hypha generally touching
with its tip the algal cell-wall. Under the influence of symbiosis, the algal
masses become firmer and more compact, without much alteration in form;
algae entirely free from hyphae are often intermingled with the others. Even
among Gloeolichens there are signs of advancing development both in the
internal structure and in outward form. Lobes free from the substratum,
though very minute, appear in the genus Paulia, the single species of which
comes from Polynesia. Much larger lobes are characteristic of Thyrea, a
Mediterranean and American genus. The fruticose type, with upright fronds
of minute size, also appears in our native genus Synalissa. It is still more
marked in the coralloid thalli of Peccania and Phleopeccania. In most of
these genera there is also a distinct tendency to differentiation of tissues,
with the gonidia congregating towards the better lighted surfaces. The only
cortex formation occurs in the crustaceous genus Forssellia in which, according
to Zahlbruckner1, it is plectenchymatous above, the thallus being attached
below by hyphae penetrating the substratum. In another genus, Anema?,
which is minutely lobate-crustaceous, the internal hyphae form a cellular
network in which the algae are immeshed. As regards algal symbionts,
the members of this family are polyphyletic in origin.
b. EPHEBACEAE AND COLLEMACEAE. In Ephebaceae the algae are
tufted and filamentous, Scytonema, Stigonema or Rivularia, the trichomes of
which are surrounded by a common gelatinous sheath. The hyphae travel
in the sheath alongside the cell-rows, and the symbiotic plant retains the
tufted form of the alga as in Lichina with Rivularia, Leptogidium with Scyto-
nema, and Ephebe with Stigonema. The last named lichen forms a tangle of
intricate branching filaments about an inch or more in length. The fruticose
habit in these plants is an algal characteristic ; it has not been acquired as a
result of symbiosis, and does not signify any advance in evolution.
A plectenchymatous cortex marks some progress here also in Lepto-
dendriscum, Leptogidium and Polychidium, all of which are associated with
Scytonema. These genera may well be derived from an elementary form
such as Thermutis. They differ from each other in spore characters, etc.,
Polychidium being the most highly developed with its cortex of two cell-
rows and with two-celled spores.
Nostoc forms the gonidium of Collemaceae. In its free state it is extremely
gelatinous and transmits that character more or less to the lichen. In the
crustaceous genus Physma, which forms the base of the Collema group or
1 Zahlbruckner 1907. 2 Reinke 1895.
THE THALLUS 285
phylum, there is but little difference in form between the thalline warts of
the lichen crust and the original small Nostoc colonies such as are to be
found on damp mosses, etc.
In Collema itself, the less advanced species are scarcely more than crusts,
though the more developed show considerable diversity of lobes, either short
and pulpy, or spreading out in a thin membrane. The Nostoc chains pervade
the homoiomerous thallus, but in some species they lie more towards the
upper surface. There is no cortex, though once and again plectenchyma
appears in the apothecial margin, both in this genus and in Leprocolletna
which is purely crustaceous.
Leptogium is a higher type than Col/etna, the thallus being distinguished
by its cellular cortex. The tips of the hyphae, lying close together at the
surface, are cut off by one or more septa, giving a one- or several-celled
cortical layer. The species though generally homoiomerous are of thinner
texture and are less gelatinous than those of Collema.
c. PVRENIDIACEAE. This small family of pyrenocarpous Phycolichens
may be considered here though its affinity, through the form of the fruiting
body, is with Archilichens. The gonidia are species of Nostoc, Scytoncma
and Stigonema. There are only five genera; one of these, Eolichcn, contains
three species, the others are monotypic.
The crustaceous genera have a non-corticate thallus, but an advance to
lobate form takes place in PlacotJielium, an African genus. The two genera
that show most development are both British: Corisciiun (Normandina),
which is lobate, heteromerous and corticate — though always sterile — and
Pyreniciium which is fruticose in habit ; the latter is associated with Nostoc
and forms a minute sward of upright fronds, corticate all round ; the peri-
thecium is provided with an entire wall and is immersed in the thallus.
If the thallus alone were under consideration these lichens would rank
with Pannariaceae.
d. HEPPIACEAE AND PANNARIACEAE. The next stage in the develop-
ment of Phycolichens takes place through the algae, Scytonema and Nostoc,
losing not only their gelatinous sheaths, but also, to a large extent, their
characteristic forms. Chains of cells can frequently be observed, but accurate
and certain identification of the algal genus is only possible by making
separate cultures of the gonidia.
Scytonema forms the gonidium of the squamulose Heppiaceae consisting
of the single genus Heppia. The ground tissue of the species is either
wholly of plectenchyma with algae in the interstices, or the centre is occupied
by a narrow medulla of loose filaments.
In the allied family Pannariaceae, a number of genera contain Scytonema
or Nostoc, while two, Psoroma and Psoromaria, have bright-green gonidia.
286 PHYLOGENY
The thallus varies from crustaceous or minutely squamulose, to lobes of
fair dimension in Parmeliella and in Hydrothyria venosa, an aquatic lichen.
Plectenchyma appears in the upper cortex of both of these, and in the
proper margin of the apothecia, while the under surface is frequently provided
with rhizoidal filaments. '
These two families form a transition between the gelatinous, and mostly
homoiomerous thallus, and the more developed entirely heteromerous thallus
of much more advanced structure. The fructification in all of them, gelatinous
and non-gelatinous, is a more or less open apothecium, sometimes immar-
ginate, and biatorine or lecideine, but often, even in species nearly related
to these, it is lecanorine with a thalline amphithecium. Rarely are the spori-
ferous bodies sunk in the tissue, with a pseudo-perithecium, as in Phylliscum.
It would be difficult to trace advance in all this group on the lines of fruit
development. The two genera with bright-green gonidia, Psoroma and
Psoromaria, have been included in Pannariaceae owing to the very close
affinity of Psoroma hypnorum with Pannaria rubiginosa; they are alike in
every respect except in their gonidia. Psoromaria is exactly like Psoroma,
•but with immarginate biatorine apothecia, representing therefore a lower
development in that respect.
These lichens not only mark the. transition from gelatinous to non-
gelatinous forms, but in some of them there is an interchange of gonidia.
The progression in the phylum or phyla has evidently been from blue-green
up to some highly evolved forms with bright-green algae, though there may
have been, at the beginning, a substitution of blue-green in place of earlier
bright-green algae, Phycolichens usurping as itwerethe Archilichen condition.
e. PELTIGERACEAE AND STICTACEAE. The two families just examined
marked a great advance which culminated in the lobate aquatic lichen
Hydrothyria. This lichen, as Sturgis pointed out, shows affinity with other
Pannariaceae in the structure of the single large-celled cortical layer as well
as with species of Nepkroma (Peltigeraceae). A still closer affinity may be
traced with Peltigera in the presence in both plants of veins on the under
surface. The capacity of Peltigera species to grow in damp situations may
also be inherited from a form like the submerged Hydrothyria. In both
families there are transitions from blue-green to bright-green gonidia, or
vice versa, in related species. Thus in Peltigeraceae we find Peltigera con-
taining Nostoc in the gonidial zone, with Peltidea which may be regarded
as a separate genus, or more naturally as a section of Peltigera; it contains
bright-green gonidia, but has cephalodia containing Nostoc associated with
its thallus.
The genus Nephroma is similarly divided into species with a bright-green
gonidial zone, chiefly Arctic or Antarctic in distribution, and species with
Nostoc (subgenus Nephromium) more numerous and more widely distributed.
THE THALLUS 287
Peltigera and Nephroma are also closely related in the character of the
fructification. It is a flat non-marginate disc borne on the edge of the
thallus: in Peltigera on the upper surface, in Nephroma on the under surface.
The remaining genus Solorina contains normally a layer of bright-green
algae, but, along with these, there are always present more or fewer Nosloc
cells, either in a thin layer as in S. crocea or as cephalodia in others, while,
in three species the algae are altogether blue-green.
The members of the Peltigeraceae have a thick upper cortex of plecten-
chyma and in some cases strengthening veins, and long rhizinae on the
lower side. Some of the species attain a large size, and, in some, soredia
are formed, an evidence of advance, this being a peculiarly lichenoid form
of reproduction.
The Stictaceae form a parallel but more highly organized family, which
also includes closely related bright-green and blue-green series. They are
all dorsiventral, but they are mostly attached by a single hold-fast and the
lobes in some species suggest the fruticose type in their long narrow form.
A wide cortex of plectenchyma protects both the upper and the lower
surface and a felt of hairs replaces the rhizinae of other foliose lichens. In
the genus Sticta (including the section Sticlind) special aeration organs,
cyphellae or pseudocyphellae, are provided ; in Lobaria these are replaced by
naked areas which serve the same purpose.
Nylander1 regarded the Stictaceae as the most highly developed of all
lichens, and they easily take a high place among dorsiventral forms, but it
is generally conceded that the fruticose type is the more highly organized.
In any case they are the highest reach of the phylum or phyla that started
with Pyrenopsidaceae and Collemaceae ; the lowly gelatinous thalli changing
to more elaborate structures with the abandonment of the gelatinous algal
sheath, as in the Pannariaceae, and with the replacement of blue-green by
bright-green gonidia. Reinke2, considers the Stictaceae as evolved from the
Pannariaceae more directly from the genus Massalongia. Their relationship
is certainly with Pannariaceae and Peltigeraceae rather than with Par-
meliaceae ; these latter, as we shall see, belong to a wholly different series.
D. EVOLUTION OF ARCHILICHENS
The study of Archilichens as of Phycolichens is complicated by the
many different kinds of fungi and algae that have entered into combination ;
but the two principal types of algae are the single-celled Protococcus group
and the filamentous Trenlepohtia : as before only the broad lines of thalline
development will be traced.
The elementary forms in the different series are of the simplest type — a
somewhat fortuitous association of alga and fungus, which in time bears the
1 Seep. 126. 2 Reinke 1895.
288 PHYLOGENY
lichen fructification. It has been stated that the greatest advance of all
took place with the formation of a cortex over the primitive granule,
followed by a restricted area of growth outward or upward which resulted
finally in the foliose and fruticose thalli. Guidance in following the course
of evolution is afforded by the character of the fructification, which generally
shows some great similarity of type throughout the different phyla, and
remains fairly constant during the many changes of thalline evolution.
Development starting from one or many origins advances point by point in
a series of parallel lines.
a. THALLUSOF PYRENOCARPINEAE. In this series there are two families
of algae that function as gonidia: Protococcaceae, consisting of single cells,
and Trentepohliaceae, filamentous. Phyllactidium (Cephaleuros) appears in
a single genus, Strigula, a tropical epiphytic lichen.
Associated with these types of algae are a large number of genera and
species of an elementary character, without any differentiation of tissue. In
many instances the thallus is partly or wholly embedded in the substratum.
Squamulose or foliose forms make theirappearance in Dermatocarpaceae :
in Normandina the delicate shell-like squamules are non-corticate, but in
other genera, Endocarpon, Placidiopsis, etc., the squamules are corticate and
of firmer texture, while in Dermatocarpon, foliose fronds of considerable size
are formed. The perithecial fruits are embedded in the upper surface.
In only one extremely rare lichen, Pyrenothamnia Spraguei(N. America),
is there fruticose development: the thallus, round and stalk-like at the base,
branches above into broader more leaf-like expansions.
b. THALLUS OF CONIOCARPINEAE. At the base of this series are genera
and species that are extremely elementary as regards thalline formation,
with others that are saprophytic and parasitic. The simplest type of thallus
occurs in Caliciaceae, a spreading mycelium with associated algae (Proto-
coccaceae) collected in small scattered granules, resembling somewhat a col-
lection of loose soredia. The species grow mostly on old wood, trunks of trees,
etc. In Calidwn (Chaenothecd) chrysocephalum as described by Neubner1 the
first thallus formation begins with these scattered minute granules; gradually
they increase in size and number till a thick granular coating of the sub-
stratum arises, but no cortex is formed and there is no differentiation of tissue.
The genus Cyphelium (Cypheliaceae) is considered by Reinke to be more
highly developed, inasmuch as the thalline granules, though non-corticate,
are more extended horizontally, and, in vertical section, show a distinct
differentiation into gonidial zone and medulla. The sessile fruit also takes
origin from the thallus, and is surrounded by a thalline amphithecium, or
rather it remains embedded in the thalline granule. A closely allied tropical
1 Neubner 1893.
THE THALLUS 289
genus Pyrgillus has reached a somewhat similar stage of development, but
with a more coherent homogeneous thallus, while in Tylophoron, also tropical
or subtropical, the fruit is raised above the crustaceous thallus but is thickly
surrounded by a thalline margin. The alga of that genus is Trentepolilia,
a rare constituent of Coniocarpineae.
A much more advanced formation appears in the remaining family
Sphaerophoraceae. In Calycidium, a monotypic New Zealand genus, the
thallus consists of minute squamules, dorsiventral in structure but with a
tendency to vertical growth, the upper surface is corticate and the mazaedial
apothecia — always open — are situated on the margins. Tlwlurna dissimilis,
(Scandinavian) still more highly developed, has two kinds of rather small
fronds corticate on both surfaces, the one horizontal in growth, crenulate in
outline, and sterile, the other vertical, about 2 mm. in height, hollow and
terminating in a papilla in which is seated the apothecium.
Two other monotypic subtropical genera form a connecting link with
the more highly evolved forms. In the first, Acroscyphus sphaerophoroides,
the fronds are somewhat similar to the fertile ones of Tholurna, but they
possess a solid central strand and the apical mazaedium is less enveloped by
the thallus. The o\\\er,Pleurocybe madagascarea, has narrow flattish branching
fronds about 3 cm. in height, hollow in the centre and corticate with marginal
or surface fruits.
The third genus, Sphaerophorus, is cosmopolitan ; three of the species are
British and are fairly common on moorlands, etc. They are fruticose in
habit, being composed of congregate upright branching stalks, either round
or slightly compressed and varying in height from about I to 8 cm. The
structure is radiate with a well-developed outer cortex, and a central strand
which gives strength to the somewhat slender stalks. The fruits are lodged
in the swollen tips and are at first enclosed; later, the covering thallus splits
irregularly and exposes the hymenium.
Coniocarpineae comprise only a comparatively small number of genera
and species, but the series is of unusual interest as being extremely well
defined by the fruit-formation and as representing all the various stages of
thalline development from the primitive crustaceous to the highly evolved
fruticose type. With the primitive thallus is associated a wholly fungal
fruit, both stalk and capitulum, which in the higher forms is surrounded and
protected by the thallus. Lichen-acids are freely produced even in crustaceous
forms, and they, along with the high stage of development reached, testify to
the great antiquity of the series.
c. THALLUS OF GKAPHIDINEAE. As formerly understood, this series
included only crustaceous forms with an extremely simple development of
thallus, fungi and algae— whether Palmellaceae, etc., or more frequently
Trentepohliaceae — growing side by side either superficially or embedded in
s. L. '9
290 PHYLOGENY
tree or rock, the presence of the vegetative body being often signalled only
by a deeper colouration of the substratum. The researches of Almquist,
and more recently of Reinke and Darbishire, have enlarged our conception
of the series, and the families Dirinaceae and Roccellaceae are now classified
in Graphidineae.
Arthoniaceae, Graphidaceae and Chiodectonaceae are all wholly crus-
taceous. The first thalline advance takes place in Dirinaceae with two allied
genera, Dirina and Dirinastrum. Though the thallus is still crustaceous, it
is of considerable thickness, with differentiation of tissues: on the lower
side there is a loosely filamentous medulla from which hyphae pierce the
substratum and secure attachment. Trentepokliagomfaa. lie in a zone above
the medulla, and the upper cortex is formed of regular palisade hyphae
forming a " fastigiate cortex." It is the constant presence of Trentepohlia
algae as well as the tendency to ellipsoid or lirellate fruits that have in-
fluenced the inclusion of Dirinaceae and Roccellaceae in the series.
The thallus of Dirinaceae is crustaceous, while the genera of Roccellaceae
are mostly of an advanced fruticose type, though in one, Roccellina, there is
a crustaceous thallus with an upright portion consisting of short swollen
podetia-like structures with apothecia at the tips ; and in another, Roccello-
grapha, the fronds broaden to leafy expansions. They are nearly all rock-
dwellers, often inhabiting wind-swept maritime coasts, and a strong basal
sheath has been evolved to strengthen their foothold. In some genera the
sheath contains gonidia; in others the tissue is wholly of hyphae — in nearly
every case it is protected by a cortex.
In the upright fronds the structure is radiate: generally a rather loose
strand of hyphae more or less parallel with the long axis of the plant forms
a central medulla. The gonidia lie outside the medulla and just within the
outer cortex. The latter, in a few genera, is fibrous, the parallel hyphae
being very closely compacted; but in most members of the family the
fastigiate type prevails, as in the allied family Dirinaceae.
d. THALLUS OF CYCLOCARPINEAE. This is by far the largest and most
varied series of Archilichens. It is derived, as regards the fungal constituent,
from the Discomycetes, but in these fungi, the vegetative or mycelial body
gives no aid to the classification which depends wholly on apothecial
characters. In the symbiotic condition, on the contrary, the thallus becomes
of extreme importance in the determination of families, genera and species.
There has been within the series a great development both of apothecial
and of thalline characters in parallel lines or phyla.
A A. LECIDEALES. The type of fruit nearest to fungi in form and origin
occurs in the Lecideales. It is an open disc developed from the fungal sym-
biont alone, the alga taking no part. There are several phyla to be considered.
THE THALLUS 291
aa. COENOGONIACEAE. There are two types of gonidial algae in this
family, and both are filamentous forms, Trentepohlia in Coenogonium and
Cladophora in Racodium. The resulting lichens retain the slender thread-like
form of the algae, their cells being thinly invested by the hyphae and both
symbionts growing apically. The thalline filaments are generally very
sparingly branched and grow radially side by side in a loose flat expansion
attached at one side by a sheath, or the strands spread irregularly over the
substratum. Plectenchyma appears in the apothecial margin in Coenogonium.
Fruiting bodies are unknown in Racodium.
Coenogoniaceae are a group apart and of slight development, only the
one kind of thallus appearing; the form is moulded on that of the gonidium,
and is, as Reinke1 remarks, perfectly adapted to receive the maximum of
illumination and aeration.
bb. LECIDEACEAE AND GYROPHORACEAE. The origin of this thalline phylum
is distinct from that of the previous family, being associated with a different
type of gonidium, the single-celled alga of the Protococcaceae.
The. more elementary species are of extremely simple structure as
exemplified in such species as Lecidea (Biatora) uliginosa or Lecidea granu-
losa. These lichens grow on humus-soil and the thallus consists of a spreading
mycelium or hypothallus with more or less scattered thalline granules con-
taining gonidia, but without any defined structure. The first advance takes
place in the aggregation and consolidation of such thalline granules and
the massing of the gonidia towards the light, thus substituting the hetero-
merous for the homoiomerous arrangement of the tissues. The various
characters of thickness, areolation, colour, etc. of the thallus are constant and
are expressed in specific diagnoses. Frequently an amorphous cortex of
swollen hyphae provides a smooth upper surface and forms a protective
covering for such long-lived species as Rhizocarpon geographicum, etc.
The squamulose thallus is well represented in this phylum. The squa-
mules vary in size and texture but are mostly rather thick and stiff. In
Lecidea ostreata they rise from the substratum in serried rows forming a
dense sward; in L. decipiens, also a British species, the squamules are still
larger, and more horizontal in direction ; they are thick and firm and the
upper cortex is a plectenchyma of cells with swollen walls. Solitary hyphae
from the medulla pass downwards into the support.
Changes in spore characters also arise in these different thalline series,
as for instance in genera such as Biatorina and Buellia, the one with colour-
less, the other with brown, two-celled spores. These variations, along with
changes in the thallus, are of specific or generic importance following the
significance accorded to the various characters.
In one lichen of the series, the monotypic Brazilian genus Spltaerophoropsis
1 Reinke 1895, p. no.
19—2
292 PHYLOGENY
stereocauloides, the thallus is described by Wainio1 as consisting of minute
clavate stalks of interwoven thick-walled hyphae, with gelatinous algae, like
Gloeocapsa, interspersed in groups, though with a tendency to congregate
towards the outer surface.
The highest development along this line of advance is to be found in the
Gyrophoraceae, a family of lichens with a varied foliose character and dark
lecideine apothecia. The thallus may be monophyllous and of fairly large
dimensions or polyphyllous; it is mostly anchored by a central stout hold-
fast and both surfaces are thickly corticate with a layer of plectenchyma;
the under surface is mostly bare, but may be densely covered with rhizina-
like strands of dark hyphae. They are all northern species and rock-dwellers
exposed to severe extremes of illumination and temperature, but well
protected by the thick cortex and the dark colouration common to them all.
cc. CLADONIACEAE. This last phylum of Lecideales is the most interesting
as it is the most complicated. It possesses a primary, generally sterile,
thallus which is dorsiventral and crustaceous, squamulose or in some in-
stances almost foliaceous, along with a secondary thallus of upright radiate
structure and of very varied form, known as the podetium which bears at
the summit the fertile organs.
A double thallus has been suggested in the spreading base, containing
gonidia, of some radiate lichens such as Roccella, but the upright portion
of such lichens, though analogous, is not homologous with that of
Cladoniaceae.
The algal cells of the family belong to the Protococcaceae. Blue-green
algae are associated in the cephalodia of Pilophorus and Stereocaulon.
The primary thallus is a feature of all the members, though sometimes very
slight and very short-lived, as in Stereocaulon or in the section Cladina of
the genus Cladonia. Where the primary thallus is most largely developed,
the secondary (the podetium) is less prominent.
This secondary thallus originates in two different ways: (i) the primary
granule may grow upward, the whole of the tissues taking part in the new
development; or (2) the origin may be endogenous and proceed from the
hyphae only of the gonidial zone: these push upwards in a compact fascicle,
as in the apothecial development of Lecidea, but instead of spreading outward
on reaching the surface, they continue to grow in a vertical direction and
form the podetium. In origin this is an apothecial stalk, but generally it is
clothed with gonidial tissue. The gonidia may travel upwards from the
base or they may possibly be wind borne from the open. The podetium
thus takes on an assimilative function and is a secondary thallus.
The same type of apothecium is common to all the genera ; the spores
1 Wainio 1890.
THE THALLUS 293
are colourless and mostly simple, but there are also changes in form and
septation not commensurate with thalline advance, as has been already noted.
Thus in Gomphillus, with primitive thallus and podetium, the spores are
long and narrow with about 100 divisions.
1. ORIGIN OF CLADONIA. There is no difficulty in deriving Cladoniaceae
from Lecidea, or, more exactly, from some crustaceous species of the section
Biatora in which the apothecia — as in Cladoniaceae — are waxy and more
or less light-coloured and without a thalline margin. In only a very few
isolated instances has a thalline margin grown round the Cladonia fruit.
There are ten genera included in the Cladoniaceae, of which five are
British. Considerable study has been devoted to the elucidation of develop-
mental problems within the family by various workers, more especially in the
large and varied genus Cladonia which is complicated by the presence of
the two thalli. The family is monophyletic in origin, though many subordi-
nate phyla appear later.
2. EVOLUTION OF THE PRIMARY THALLUS. At the base of the series we
find here also an elementary granular thallus which appears in some species
of most of the genera. In Gomphillus, a monospecific British genus, the
granules have coalesced into a continuous mucilaginous membrane. In
Baeomyces, though mostly crustaceous, there is an advance to the squamulose
type in B. placophyllus, and in two Brazilian species described by Wainio,
one of which, owing to the form of the fronds, has been placed in a separate
genus Hcteromyces. The primary thallus becomes almost foliose also in
Gymnoderma coccocarpum from the Himalayas, with dorsiventral stratose
arrangement of the tissues, but without rhizinae. The greatest diversity
is however to be found in Cladonia where granular, squamulose and almost
foliose thalli occur. The various tissue formations have already been
described1.
3. EVOLUTION OF THE SECONDARY THALLUS. Most of the interest
centres round the development and function of the podetium. In several
genera the primordium is homologous with that of an apothecium ; its
elongation to an apothecial stalk is associated with delayed fructification,
and though it has taken on the function of the vegetative thallus, the purpose
of elongation has doubtless been to secure good light conditions for the
fruit, and to facilitate a wide distribution of spores : therefore, not only in
development but in function, its chief importance though now assimilative
was originally reproductive. The vegetative development of the podetium is
correlated with the reduction of the primary thallus which in many species
bears little relation in size or persistence to the structure produced from it,
as, for instance, in Cladonia rangiferina where the ground thallus is of the
1 See Chap. III.
294 PHYLOGENY
scantiest and very soon disappears, while the podetial thallus continues to
grow indefinitely and to considerable size.
4. COURSE OF PODETIAL DEVELOPMENT. In Baeomyces the podetial
primordium is wholly endogenous in some species, but in others the
outer cortical layer of the primary thallus as well as the gonidial hyphae
take part in the formation of the new structure which, in that case, is simply
a vertical extension of the primary granule. This type of podetium — called
by Wainio1 a pseudopodetium — also recurs in Pilophorus and in Stereocanlon.
To emphasize the distinction of origin it has been proposed to classify these
two latter genera in a separate family, but in that case it would be necessary
to break up the genus Baeomyces. We may assume that the endogenous
origin of the "apothecial stalk" is the more primitive, as it occurs in the
most primitive lecideine lichens, whereas a vertical thallus is always an
advanced stage of vegetative development.
Podetia are essentially secondary structures, and they are associated
both with crustaceous and squamulose primary thalli. If monophyletic in
origin their development must have taken place while the primary thallus
was still in the crustaceous stage, and the inherited tendency to form podetia
must then have persisted through the change to the squamulose type. In
species such as Cl. caespiticia the presence of rudimentary podetia along
with large squamules suggests a polyphyletic origin, but Wainio's1 opinion is
that such instances may show retrogression from an advanced podetial form,
and that the evidence inclines to the monophyletic view of their origin.
The hollow centre of the podetium arises in the course of development
and is common to nearly all advanced stages of growth. There are how-
ever some exceptions : in Glossodium aversum, a soil lichen from New
Granada, and the only representative of the genus, a simple or rarely forked
stalk about 2 cm. in height rises from a granular or minutely squamulose
thallus. The apothecium occupies one side of the flattened and somewhat
wider apex. There is no external cortex and the central tissue is of loose
hyphae. In Thysanothecium Hookeri, also a monotypic genus from Australia,
the podetia are about the same height, but, though round at the base, they
broaden upwards into a leaf-like expansion. The central tissue below is of
loose hyphae, but compact strands occur above, where the apothecium
spreads over the upper side. The under surface is sterile and is traversed
by nerve-like strands of hyphae.
5. VARIATION IN CLADONIA. It is in this genus that most variation is to
be found. Characters of importance and persistence have arisen by which
secondary phyla may be traced within the genus: these are mainly (i) the
relative development of the horizontal and vertical structures, (2) formation
1 Wainio 1897.
THE THALLUS 295
of the scyphus and branching of the podetium, with (3) differences in colour
both in the vegetative thallus and in the apothecia.
Wainio has indicated the course of evolution on the following lines :
(i) the crustaceous thallus is monophyletic in origin and here as elsewhere
precedes the squamulose. The latter he considers to be also monophyletic,
though at more than one point the more advanced and larger foliose forms
have appeared : (2) the primitive podetium was subulate and unbranched,
and the apex was occupied by the apothecium. Both scyphus and branching
are later developments indicating progress. They are in both cases associated
with fruit-formation — scyphi generally arising from abortive apothecia1,
branching from aggregate apothecia. In forms such as Cl. fimbriata, where
both scyphiferous and subulate sterile podetia are frequent, the latter (sub-
species fibula) are retrogressive, and reproduce the ancestral pointed pode-
tium. (3) In subgen. Cenomyce, with a squamulose primary thallus, there is
a sharp division into two main phyla characterized by the colour of the
apothecia, brown in Ochrophaeae — the colour being due to a pigment — and
red in Cocciferae where the colouring substance is a lichen-acid, rhodocladonic
acid. In the brown-fruited Ochrophaeae there are again several secondary
phyla. Two of these are distinguished primarily by the character of the
branching : (a) the Chasmariae in which two or several branches arise from
the same level, entailing perforation of the axils (Cl. furcata, Cl. rangi-
formis, Cl. squamosa, etc.), the scyphi also are perforated. They are further
characterized by peltate aggregate apothecia, this grouping of the apothecia
according to Wainio being the primary cause of the complex branching,
the several fruit stalks growing out as branches. The second group (&), the
Clausae, are not perforated and the apothecia are simple and broad-based
on the edge of the scyphus (Cl. pyxidata, Cl. fimbriata, etc.), or on the tips
of the podetia (Cl. cariosa, Cl. leptophylla, etc.). A third very small group
also of Clausae called (c} Foliosae has very large primary squamules and
reduced podetia (Cl. foliacea, etc.), while finally (d) the Ochroleucae, none of
which is British, have poorly developed squamules and variously formed
yellowish podetia with pale-coloured apothecia.
The Cocciferae represent a phylum parallel in development with the
Ochrophaeae. The species have perhaps most affinity with the Clausae, the
vegetative thallus — both the squamules and the podetia — being very much
alike in several species. Wainio distinguishes two groups based on a differ-
ence of colour in the squamules, glaucous green in one case, yellowish in
the other.
6. CAUSES OF VARIATION. External causes of variation in Cladonia are
chiefly humidity and light, excess or lack of either effecting changes which
may have become fixed and hereditary. Minor changes directly traceable
1 See Chap. III.
296 PHYLOGENY
to these influences are also frequent, viz. size of podetia, proliferation and the
production more or less of soredia or of squamules on the podetia, though
only in connection with species in which these variations are already an
acquired character. The squamules on the podetium more or less repeat
the form of the basal squamules.
/. PODETIAL DEVELOPMENT AND SPORE-DISSEMINATION. In a recent
paper by Hans Sattler1 the problem of podetial development in Cladonia
is viewed from a different standpoint. He holds that as the podetia are
apothecial stalks, their service to the plant consists in the raising of the
mature fruit in order to secure a wide distribution of the spores, and that
changes in the form of the podetium are therefore but new adaptations for
the more efficient discharge of this function.
Following out this idea he regards as the more primitive forms those in
which both the spermogonia, as male reproductive bodies, and the carpogonia
occur on the primary thallus, ascogonia and trichogynes being formed before
the podetium emerges from the thallus. Fertilization thus must take place
at a very early period, though the ultimate fruiting stage may be long
delayed. Sattler considers that any doubt as to actual fertilization is without
bearing on the question, as sexuality he holds must have originally existed
and must have directed the course of evolution in the reproductive bodies.
In this primitive group, called by him the "Floerkeana" group, the podetia
are always short and simple, they are terminated by the apothecium and
no scyphi are formed (Cl. Floerkeana, Cl. leptophylla, Cl. cariosa, Cl. caespi-
ticia, Cl. papillaria, etc.).
In his second or "pyxidata" group, he places those species in which the
apothecia are borne at the edge of a scyphus. That structure he follows
Wainio in regarding as a morphological reaction on the failure of the first
formed apical apothecium: it is, he adds, a new thallus in the form of a
spreading cup and bears, as did the primary thallus, both the female primordia
and the spermogonia. In some species, such as Cl. foliacea, there may be
either scyphous or ascyphous podetia, and spermogonia normally accompany
the carpogonium appearing accordingly along with it either on the squamule
or on the scyphus.
As the pointed podetia are the more primitive, Sattler points out that
they may reappear as retrogressive structures, and have so appeared in the
"pyxidata" group in such species as Cl. fimbriata. He refers to Wainio's
statement that the abortion of the apothecium being a retrogressive anomaly,
while scyphus formation is an evolutionary advance, the scyphiferous species
present the singular case, "that a progressive transmutation induced by
a retrogressive anomaly has become constant."
1 Sattler 1914.
THE THALLUS 297
His third group includes those forms that grow in crowded tufts or
swards such as Cl. rangiferina, Cl.furcata, Cl. gracili s, etc. They originate,
as did the pyxidata group, in some Floerkeana-\\\i& form, but in the "rangi-
ferina" group instead.of cup-formation there is extensive branching. In the
closely packed phalanx of branches water is retained as in similar growths
of mosses, and moist conditions necessary for fertilization are thus secured
as efficiently as by the water-holding scyphus.
Sattler in his argument has passed over many important points. Above
all he ignores the fact that whatever may have been the original nature
and function of the podetium, it has now become a thalline structure and
provides for the vegetative life of the plant, and that it is in its thalline
condition that the many variations have been formed ; the scyphus is not,
as he contends, a new thallus, it is only an extension of thalline characters
already acquired.
8. PILOPHORUS, STEREOCAULON AND ARGOPSIS. These closely related
genera are classified with Cladonia as they share with it the twofold thallus
and the lecideine apothecia. The origin of the podetium being different
they may be held to constitute a phylum apart, which has however taken
origin also from some Biatora form.
The primary thallus is crustaceous or minutely squamulose and the
podetia of Pilophorus, which are short and unbranched (or very sparingly
branched), are beset with thalline granules. The podetia of Stereocaulon
and Argopsis are copiously branched and are more or less thickly covered
with minute variously divided leaflets. Cephalodia containing blue-green
algae occur on the podetia of these latter genera; in Pilophorus they are
intermixed with the primary thallus.
The tissue systems are less advanced in these genera than in Cladonia :
there, is no cortex present either in Pilophorus or in Argopsis or in some
species of Stereocaulon, though in others a gelatinous amorphous layer
covers the podetia and also the stalk leaflets. The stalks are filled with
loose hyphae in the centre.
BB. LECANORALES. This second group of Cyclocarpineae is distinguished
by the marginate apothecium, a thalline layer providing a protecting amphi-
thecium. The lecanorine apothecium is of a more or less soft and waxy
consistency, and though the disc is sometimes almost black, neither hypo-
thecium nor parathecium is carbonaceous as in Lecidea. The affinity of
Lecanora is with sect. Biatora, and development must have been from a
biatorine form with a persistent thallus. The margin or amphithecium
varies in thickness: in some species it is but scanty and soon excluded by
the over-topping growth of the disc, so that a zone of gonidia underlying
the hypothecium is often the only evidence of gonidial intrusion left in
fully formed fruits.
298 PHYLOGENY
The marginate apothecium has appeared once and again as we have
seen. It is probable however that its first development was in this group of
lichens, and even here there may have been more than one origin as there
is certainly more than one phylum.
aa. COURSE OF DEVELOPMENT. At the base of the series, the thallus is
of the crustaceous type somewhat similar to that of Lecidea, but there are
none of the very simple primitive forms. Lecanora must have originated
when the crustaceous lecideine thallus was already well established. Its
affinity is with Lecidea and not with any fungus: where the thallus is
evanescent or scanty, its lack is due to retrogressive rather than to primitive
characters.
bb. LECANORACEAE.. A number of genera have arisen in this large family,
but they are distinguished mainly if not entirely by spore characters, and
by some systematists have all been included in the one genus Lecanora,
since the changes have taken place within the developing apothecium.
There is one genus, Harpidium, which is based on thalline characters,,
represented by one species, H. rutilans, common enough on the Continent,
but not yet found in our country. It has a thin crustaceous homoiomerous
thallus, the component hyphae of which are divided into short cells closely
packed together and forming a kind of cellular tissue in which the algae are
interspersed. The dorsiventral stratose arrangement prevails however in the
other genera and a more or less amorphous " decomposed " cortex is fre-
quently present. The medulla rests on the substratum.
With the stouter thallus, there is slightly more variety of crustaceous
form than in Lecideaceae: there occurs occasionally an outgrowth of the
thalline granules as in Haematomma ventosum which marks the beginning
of fruticulose structure. Of a more advanced structure is the thallus of
Lecanora esculenta, a desert lichen which becomes detached and erratic, and
which in some of its forms is almost coralline, owing to the apical growth of
the original granules or branches: a more or less radiate arrangement of
the tissues is thus acquired.
The squamulose type is well represented in Lecanora, and the species
with that form of thallus have frequently been placed in a separate genus,
Squamaria. These squamules are never very large; they possess an upper,
somewhat amorphous, cortex; the medulla rests on the substratum, except
in such a species as Lecanora lentigera, where they are free, a sort of fibrous
cortex being formed of hyphae which grow in a direction parallel with the
surface. In none of them are rhizinae developed.
cc. PARMELIACEAE. The chief advance, apart from size, of the squamulose
to the foliose type is the acquirement of a lower cortex along with definite
organs of attachment which in Parmeliaceae are invariably rhizoidal and
THE THALLUS 299
are composed of compact strands of hyphae extending from the cells of
the lower cortex.
In the genus Parmelia rhizinae are almost a constant character, though
in a few species, such as Parmelia physodes, they are scanty or practically
absent. It is not possible, however, to consider that these species form a
lower group, as in other respects they are highly evolved, and rhizinae may
be found at points on the lower surface where there is irritation by friction.
Soredia and isidia occur frequently and, in several species, almost entirely
replace reproduction by spores. In one or two northern or Alpine species,
P. stygia and P.pubescens, the lobes are linear or almost filamentous. They
are retained in Parmelia because the apothecia are superficial on the fronds
which are partly dorsiventral, and because rhizinae have occasionally been
found. Some of the Parmeliae attain to a considerable size ; growth is centri-
fugal and long continued.
Two monotypic genera classified under Parmeliaceae, Physcidia and
Heterodea, are of considerable interest as they indicate the bases of parallel
development in Parmelia and Cetraria. The former, a small lichen, is corti-
cate only on the upper surface, and without rhizinae; and from the description,
the cortex is of a fastigiate character. The solitary species grows on bark
in Cuba; it is related to Parmelia, as the apothecia are superficial on the
lobes. The second, Heterodea Mulleri, a soil-lichen from Australasia, is more
akin to Cetraria in that the apothecia are terminal. The upper surface is
corticate with marginal cilia, the lower surface naked or only protected by
a weft of brownish hyphae amongst which cyphellae are formed ; pseudo-
cyphellae appear in Cetraria.
The genus Cetraria contains very highly developed thalline forms, either
horizontal (subgenus Platysma), or upright (Eiicetraria}. Rhizinae are scanty
or absent, but marginal cilia in some upright species act as haptera. Cetraria
aculeata is truly fruticose with a radiate structure.
An extraordinary development of the under cortex characterizes the
genera Anzia1 and Pannoparmelia: rhizinae-like strands formed from the
cortical cells branch and anastomose with others till a wide mesh of a
spongy nature is formed. They are mostly tropical or subtropical or Austra-
lasian, and possibly the spongy mass may be of service in retaining moisture.
A species of Anzia has been recorded by Darbishire2 from Tierra del Fuego.
dd. USNEACEAE. As we have seen, the change to fruticose structure
has arisen as an ultimate development in a number of groups; it reaches
however its highest and most varied form in this family. Not only are there
strap-shaped thalli, but a new form, the filamentous and pendulous, appears;
it attains to a great length, and is fitted to withstand severe strain. The
1 See p. 90. * Darbishire 1912.
3oo PHYLOGENY
various adaptations of structure in these two types of thallus have already
been described1.
In Parmelia itself there are indications of this line of development in
P. stygia, with short stiff upright branching fronds, and in P. pubescens,
with its tufts of filaments, but these two species are more or less dorsiventral
in structure and do not rise from the substratum. In Cetraria also there
is a tendency towards upright growth and in C. aculeata even to radiate
structure. But advance in these directions has stopped short, the true line
of evolution passing through species like Parmelia physodes with raised, and
in some varieties, tubular fronds, and the somewhat similar species P. Kamt-
schadalis with straggling strap-like lobes, to Evernia. That genus is a true
link between foliose and fruticose forms and has been classified now with
one series, now with the other.
In Evernia furfuracea, the lobes are free from the substratum except
when friction causes the development of a hold-fast and the branching out
of new lobes from that point. It is however dorsiventral in structure, the
under surface is black and the gonidial zone lies under the upper cortex.
Evernia prunastri is white below and is more fruticose in habit, the long
fronds all rising from one base. They are thin and limp, no strengthening
tissue has been evolved, and they tend to lie over on one side; both surfaces
are corticate and gonidia sometimes travel round the edge, becoming fre-
quently lodged here and there along the under side.
The extreme of strap-shaped fruticose development is reached in the
genus Ramalina. In less advanced species such as R. evernioides there is a
thin flat expansion anchored to the substratum at one point and alike on
both surfaces. In R.fraxinea the fronds may reach considerable width (var.
ampliata), but in that and in most species there is a provision of sclerotic
strands to support and strengthen the fronds. One of those best fitted to
resist bending strains is R. scopulorum (siliquosd) which grows by preference
on sea-cliffs and safely withstands the maximum of exposure to wind or
weather.
The filamentous structure appears abruptly, unless we consider it as
foreshadowed by Parmelia pubescens. The base is secured by strong sheaths
of enduring character; tensile strains are provided for either by a chondroid
axis, as in Usnea, or by cortical development, as in Alectoria; the former
method of securing strength seems to be the most advantageous to the plant
as a whole, since it leaves the outer structures more free to develop, and there
is therefore in Usnea a greater variety of branching and greater growth in
length, which are less possible with the thickened cortex of Alectoria.
ee. PHYSCIACEAE. There remains still an important phylum of Lecano-
rales well defined by the polarilocular spores2. It also arises from a Biatora
1 See p. 101. 2See p. 188.
THE THALLUS 301
species and forms a parallel development. Even in this phylum there are two
series : one with colourless spores and mostly yellow or reddish either in
thallus or apothecium, and the other with brown spores and with cinereous-
grey or brown thalli. The dark spores are in many of the species typically
polarilocular, though in some the median septum is riot very wide and no
canal is visible. Practically all of the lighter coloured forms contain parietin
either in thallus or apothecia or in both ; it is absent in the dark-spored series.
Among the lighter coloured forms it is difficult to decide which of these
two striking characteristics developed first, the acid or the peculiar spore.
Probably the acid has the priority: there is one common rock lichen in this
country, Placodium rupestre (Lecanora irrubata\ which gives a strong red
acid reaction with potash, but in which the spores are still simple, and the
'fruit structure in the biatorine stage. Another species, PI. luteoalbum, with a
purplish reaction in the fruit only, shows septate spores but with only a
rather narrow septum. The development continues through biatorine forms
to lecanorine with a fully formed thalline margin. Among these latter we
encounter PI. nivale which is well provided with acid but in which the spores
have become long and fusiform with little trace of the polar cells or central
canal. We must allow here also for reversions, and wanderings from the
straight road.
From crustaceous the advance is normal and simple to squamulose forms
which in this phylum maintain a stiff regularity of thalline outline termed
"effigurate"; the squamules, developing from the centre, extend outwards in a
radiate-stellate manner. There are also foliose thalli in the genus Xanthoria
and fruticose in Teloschistes. The cortex in the former horizontal genus is of
plectenchyma, and no peculiar structures have emerged. In Teloschistes the
cortex is of compact parallel hyphae (fibrous) which form the strengthening
structure of the narrow compressed fronds (T.flavicans}.
In the brown-spored series there is a considerable number of species that
are crustaceous united in the genus Rinodina, all of which have marginate
apothecia. One of them, Rinodina oreina, approaches in thalline structure the
effigurate forms of Placodium; while in R. isidioides, a rare British species,
there is an isidioid squamulose development.
Among foliose genera, the tropical genus Pyxine is peculiar in its almost
lecideine fruit, a few gonidia occurring only in the early stages; its affinity
with Physcia holds, however, through the one-septate brown spores with very
thick walls and the reduced lumen of the cells. The more simple type of
fruit may be merely retrogressive.
Pliyscia, the remaining genus, is mainly foliose and with dorsiventral
thallus. A few species have straggling semi-upright fronds and these have
sometimes been placed in a separate genus Anaptychia. Only one " Anap-
tychia" Ph. intricata, has a radiate structure with fibrous cortex all round ;
in the others the upper cortex alone is fibrous— of long parallel hyphae —
302
PHYLOGENY
but that character appears in nearly every one of the horizontal species as
well, sometimes in the upper, sometimes in the lower cortex.
In Physcia the horizontal thallus is of smaller dimensions than in Par-
melia, and never becomes so free from the substratum: it is attached by
rhizinae and soredia appear frequently. Very often the circular effigurate
type of development prevails.
It is difficult to trace with any certainty the origin of this series of the
phylum. Some workers have associated it with the purely lecideine genus,
Buellia, but the brown septate spores of the latter are of simple structure,
though occasionally approaching the Rinodina type. There are also
differences in the thallus, that of Buellia, especially when it is saxicolous,
inclining to Rhizocarpon in form. It is more consistent with the outer and
inner structure to derive Rinodina from some crustaceous Placodium form
with a marginate apothecium, therefore from a form of fairly advanced
development. As the parietin content disappeared — perhaps from the pre-
ponderance of other acids — the colouration changed and the spores became
dark-coloured.
Many genera and even families, such as Thelotremaceae, etc., have
necessarily been omitted from this survey of phylogeny in lichens, but the
tracing of the main lines of development has indicated the course of evolu-
tion, and has demonstrated not only the close affinity between the members
of this polyphyletic class of plants, as shown in the constantly recurring
thalline types, but it has proved the extraordinary vigour gained by both
the component organisms through the symbiotic association.
The principal phyla1, developing on somewhat parallel lines, are given in
the appended table :
ARCHILICHENS
Phyla
Crustose
Squamulose
Foliose
Fruticose
Pyrenolichens
Coniocarpineae
Verrucariaceae
Caliciaceae
Dermato
Sphaero
carpaceae
jhoraceae
Sphaerophoraceae •
TArthoniaceae
|
Graphidineae \ Graphidaceae
Roccellaceae
^Dirinaceae
Cyclocarpineae
ILecideaceae Gyrophoraceae
Coenogoniaceae
Lecideales
(filamentous gonidia)
Cladoniaceae
. »
Lecanorales
(primary and secondary thalli)
Lecanoraceae
Parmeliaceae
Usneaceae
Polariloculares
{Colourless spores
Placodium
Xanthoria
Teloschistes
Brown spores
Rinodina, Pyxine
Physcia j Physcia (Anaptychia)
1 Dr Church (1920) has published a new conception of the origin of lichens. See postscript at
the end of the volume, p. 421.
THE THALLUS
303
SCHEME OF SUGGESTED PROGRESSION IN LICHEN STRUCTURE
PYRENOCARPINEAE
CONIOCARPINEAE
PYRENOCARPEAE
CONIOCARPEAE
Pyrenothamniaceae
Dermatocarpaceae
Dermatocarpaceae
Verrucariaceae
(Protococcaceae)
Phyllopy
Pyreni
(Trent
reniaceae
laceae
-Pohtia)
Sphaerophorus
I Pilophorus
Pleurocybe Acroscyphus
Calycidium Tholurna
Cyphelium Tylophoron Tylophorella
i , 1
Caliciaceae Pyrgillus
(Protococcaceae) (Trentepoklia)
CYCLOCARPINEAE
PHYCOLICHENS (CYANOPHILI)
Stictaceae
1
Peltigeraceae
l_
Hydrothyria
Peccania Phloeopeccania
Pannariaceae
Leptodendriscum and
1
Synalissa
Thyrea 1
Leptogidium
Polychidium
1
Heppiaceae
P 'r
Leptogium
Pauha 1
|
L_J
Collema
Pyrenopsidaceae Thermutis
Physma
(Gloeocapsci)
. (Scytonsma)
(No*toc)
LECIDEALES
LECANORALES POLARILOCULARES
Usneae
Stereocaulon Eucetraria Ramalina
Ochropheae Cocciferae
Evernia Teloschistes
Gyrophoraceae
Cladbnia Pilophoro
Cetraria Parmelia
(Platysma) physodes
Parme-
Xantnoria
Physcia
sect.
Anaptychia
Physcia
{Sect. Psora
Sect. Eulecidea
Heterodea Physcidia lEuplacodium
^ecanora sect. -I \ ICallopisma
Squamaria JPlacodium \ Rinod
i I | IBUstenU |
Lecanora Colourless spores
Sect. Biatora
I
Lecidea
(Protococcaceae)
CHAPTER VIII
SYSTEMATIC
I. CLASSIFICATION
A. WORK OF SUCCESSIVE SYSTEMATISTS
SINCE the time when lichens were first recognized as a separate class —
as members of the genus Lichen by Tournefort1 or as "Musco-fungi"
by Morison2, — many schemes of classification have been outlined, and the
history of the science of lichenology, as we have seen, is a record of attempts
to understand their puzzling structure, and to express that understanding
by relating them to each other and to allied classes of plants. The great
diversity of opinion in regard to their affinities is directly due to their
composite nature.
a. DILLENIUS AND LINNAEUS. The first systematists were chiefly im-
pressed by their likeness to mosses, hepatics or algae. Dillenius* in the
Historia Muscorum grouped them under the moss genera: — IV. Usnea,
V. Coralloides and VI. Lichenoides. Linnaeus4 classified them among algae
under the general name Lichen, dividing them into eight orders based on
thalline characters in all but one instance, the second order being distin-
guished from the first by bearing scutellae. The British botanists of the
latter part of the eighteenth century — Hudson, Lightfoot and others — were
content to follow Linnaeus and in general adopted his arrangement.
b. ACHARIUS. Early in the nineteenth century Acharius, the Swedish
Lichenologist, worked a revolution in the classification of lichens. He gave
first place to the form of the thallus, but he also noted the fundamental
differences in fruit-formation: his new system appeared in the Methodus
Lichenum5 with an introduction explaining the terms he had introduced,
many of them in use to this day.
Diagnoses of twenty-three genera are given with their included species.
The work was further extended and emended in Lichenographia Uni-
versalis* and in the Synopsis Lichenum1. In his final arrangement the
family "Lichenes" is divided into four classes, three of which are charac-
terized solely by apothecial characters; the fourth class has no apothecia.
They are as follows :
Class I. Idiothalami with three orders, Homogenei, Heterogenei and Hyperogenei :
the apothecia differ in texture and colouration from the thallus: Lecidea, Opegrapha,
Gyrophora, etc.
Class II. Coenothalami, with three orders, Phymaloidei, Discoidei and Cephaloidei.
1 Tournefort 1694. 2 Morison 1699. 3 Dillenius 1741. 4 Linnaeus 1753.
6 Acharius 1803. 6 Acharius 1810. 7 Acharius 1814.
FAMILIES AND GENERA 305
The apothecia are partly formed from the thallus: Lecanora, Parme/ta, etc. The
Pyrenolichens are also included by him in this class, because "the thallus surrounds and
is concrete with the partly or wholly immersed apothecia."
Class III. Homothalami with two orders, Scutellati and Peltati. The apothecia are
formed from the cortical and medullary tissue of the thallus : Ramalina, Usnea, Collema,
etc.
Class IV. Athalami, with but one sterile genus, Lepraria.
The orders are thus based on the form of the fruit; the genera in the
Synopsis number 41. Large genera such as Lecanora with 132 species are
divided into sections, many of which have in turn been established as
genera, by S. F. Gray in 1821, and later by other systematists.
The Synopsis was the text-book adopted by succeeding botanists for
some 40 years with slight alterations in the arrangement of classes, genera,
etc.
Wallroth1 and Meyer2 followed with their studies on the lichen thallus,
and Wallroth's division into "Homoiomerous" and "Heteromerous" was
accepted as a useful guide in the maze of forms, representing as it did
a great natural distinction.
c. SCHAERER. This valiant lichenologist worked continuously during
the first half of the nineteenth century, but with very partial use of the
microscope. His last publication in 1850, an Enumeration of Swiss Lichens,
was the final declaration of the older school that relied on field characters.
His classification is as follows :
Class I. Lichenes Discoidei, with ten orders from Usneacei to Graphidei ; fruits
open.
Class II. Lichenes Capitati, with three orders: Calicioidei, Sphaerophorei and Cla-
doniacei ; fruits stalked.
Class III. Lichenes Verrucarioidei, with three orders: Verrucarii, Pertusarii and
Endocarpei : fruits closed.
An "Appendix" contains descriptions of Crustacei and Fruticulosi, all
sterile forms, except Coniocarpon and Arthonia, which seem out of place,
and finally a "Corollarium" of gelatinous lichens all classified under one
genus Collema.
d. MASSALONGO AND KOERBER. As a result of their microscopic
studies, these two workers proposed many changes based on fruit and
spore characters, and Koerber in the Systema Lichenum Germaniae (1855)
gave expression to these views in his classification. He also made use of
Wallroth's distinctions of "homoiomerous" and "heteromerous," thus dividing
lichens at the outset into those mostly with blue-green and those with bright-
green gonidia.
1 Wallroth 1825. * Meyer '825-
3o6 SYSTEMATIC
The following is the main outline of Koerber's classification:
Series I. Lichenes Heteromerici.
Order I. Lich. Thamnoblasti (fruticose).
Order II. Lich. Phylloblasti (foliose).
Order III. Lich. Kryoblasti (crustaceous).
Series II. Lichenes Homoeomerici.
Order IV. Lich. Gelatinosi.
Order V. Lich. Byssacei.
With the exception of Order V all are subdivided into two sections,
"gymnocarpi" with open fruits and "angiocarpi" with closed fruits, a
distinction that had long been recognized both in lichens and in fungi.
e. NYLANDER. The above writers had been concerned with the inter-
relationships of lichens ; Nylander, who was now coming forward as a
lichenologist of note, gave a new turn to the study by dwelling on their
relation to other classes of plants. Without for a moment conceding that
they were either algal or fungal, he yet insisted on their remarkable affinity
to algae on the one hand, and to fungi on the other, and he sought to make
evident this double connection by his very ingenious scheme of classfication1.
He began with what we may call "algal lichens," those associated with
blue-green gonidia in the family "Collemacei"; he continued the series to
the most highly evolved foliose forms and then wound up with those that
are most akin to fungi, that is, those with least apparent thalline formation
— according to him — the " Pyrenocarpei."
In his scheme, which is the one followed by Leighton and Crombie, the
"family" represents the highest division; series, tribe, genus and species
come next in order. We have thus :
Fam. I. Collemacei.
Fam. II. Myriangiacei (now reckoned among fungi).
Fam. III. Lichenacei.
This last family, which includes the great bulk of lichens, is divided into
the following series: I. Epiconiodei; II. Cladoniodei; III. Ramalodei ;
IV. Phyllodei; V. Placodei; VI. Pyrenodei. It is an ascending series up
to the Phyllodei, or foliaceous lichens, which he considers higher in develop-
ment than the fruticose or filamentous Ramalodei. The Placodei include
four tribes on a descending scale, the Lecanorei, Lecidinei, Xylographidei
and Graphidei. The classification is almost wholly based on thalline form,
except for the Pyrenodei in which are represented genera with closed fruits,
there being one tribe only, the Pyrenocarpei.
Nylander claims however to have had regard equally to the reproductive
system and was the first to give importance to the spermogonia. The
classification is coherent and easy to follow, though, like all classifications
1 Nylander 1854.
FAMILIES AND GENERA 307
based on imperfect knowledge, it is not a little artificial ; also while magnify-
ing the significance of spermogonia and spermatia, he overlooked the much
more important characters of the ascospores.
/. Mt)LLER(-ARGAU). In preparing his lists of Genevan lichens (1862),
Miiller realized that Nylander's series was unnatural, and he found as he
studied more deeply that lichens must be ranged in parallel or convergent
but detached groups. He recognized three main groups :
1. Eulichens, divided into Capitularieae, Discocarpeae and Verru-
caroideae.
2. Epiconiaceae.
3. Collemaceae.
He suggested that, in relation to other plants, Eulichens approach
Pezizae, Hysteriaceae and Sphaeriaceae; Epiconiaceae have affinity with
Lycoperdaceae, while Collemaceae are allied to the algal family Nosto-
caceae. These three groups of Eulichens, he held, advanced on somewhat
parallel lines, but reached a very varied development, the Discocarpeae
attaining the highest stage of thalline form. M tiller accepted as characters
of generic importance the form and structure of the fruiting body, the
presence or absence of paraphyses, and the septation, colour, etc. of the spores.
A few years later (1867) the composite nature of the lichen thallus was
announced by Schwendener, and, after some time, was acknowledged by
most botanists to be in accordance with the facts of nature. Any system
of classification, therefore, that claims to be a natural one, must, while
following as far as possible the line of plant development, take into account
the double origin of lichens both from algae and fungi, the essential unity
and coherence of the class being however proved by the recurring similarity
between the thalline types of the different phyla. As Muller had surmised:
"they are a series of parallel detached though convergent groups."
g. REINKE. The arrangement of Ascolichens on these lines was first
seriously studied by Reinke1, and his conclusions, which are embodied2 in
the Lichens of Schleswig-Holstein, have been largely accepted by succeeding
workers. He recognizes three great subclasses: I. Coniocarpi; 2. Disco-
carpi; 3. Pyrenocarpi.
The Coniocarpi are a group apart, but as their fruit is at first entirely
closed — at least in some of the genera — the more natural position for them
is between Discocarpi and Pyrenocarpi. It is in the arrangement of the
Discocarpi that variation occurs. Reinke's arrangement of orders and
families in that subclass is as follows :
Subclass 2. Discocarpi.
Order I. GRAMMOPHORI: Fam. GRAPHIDACEI and XYLOGRAPHACEI.
1 Reinke 1894, '95, '96. 2 Darbishire and Fischer- Benzon 1901.
20 2
3o8 SYSTEMATIC
Order II. LECIDEALES: Fam. GYALECTACEI, LECIDEACEI, UMBILICARI-
ACEI and CLADONIACEI.
Order III. PARMELIALES: Fam. URCEOLARIACEI, PERTUSARIACEI, PAR-
MELIACEI, PHYSCIACEI, TELOSCHISTACEI and ACAROSPORACEI.
Order IV. CYANOPHILI: Fam. LICHINACEI, EPHEBACEI, PANNARIACEI,
Sr/CTAC£f, PELTIGERACEI, COLLEMACEI and OMPHALARIACEI.
The orders represent generally the principal phyla or groups, the families
subordinate parallel phyla within the orders. The first three orders are
stages of advance as regards fruit development ; the Cyanophili are a group
apart.
Wainio1 rendered great service to Phylogeny in his elaborate work on
Cladoniaceae, the most complicated of all the lichen phyla. He also drew
up a scheme of arrangement in his work on Brazil Lichens2. There is in
it some divergence from Reinke's arrangement, as he tends to give more
importance to the thallus than to fruit characters as a guide. He places, for
instance, Gyrophorei beside Parmelei and at a long distance from his Lecidei.
The Cyanophili group of families he has interpolated between Buelliae
(Physciaceae) and Lecideae. Many workers approve of Wainio's classifica-
tion but it presents some difficult problems.
h, ZAHLBRUCKNER. The systematist of greatest weight in recent times
is A. Zahlbruckner, who is responsible for the systematic account of lichens
in Engler and Prantl's Naturlichen Pflanzenfamilien. It is difficult to
express the very great service he has rendered to Lichenology, in that and
other world-wide studies of lichens. The sketch of lichen phylogeny as
given in the present volume owes a great deal to the sound and clear
guidance of his work, though his conclusions may not always have been
accepted. The classification in the Pflanzenfamilien is the one now gene-
rally followed.
The class Lichenes is divided by Zahlbruckner3 into two subclasses,
I. Ascolichens and II. Hymenolichens. He gives a third class, Gastero-
lichens4, but as it was founded on error5, it need not concern us here. The
Ascolichens are by far the more important. These are subdivided into:
Series I. PYRENOCARPEAE, with perithecial fruits.
Series 2. GYMNOCARPEAE, with apothecial fruits.
These are again broken up into families, and in the arrangement and
sequence of the families Zahlbruckner indicates his view of development
and relationship. They occur in the following order:
1 Wainio 1887, '94, '97. 2 Wainio 1890. 3 Zahlbruckner 1907.
4 Massee 1887. 5 Fischer 1890.
FAMILIES AND GENERA 309
SERifcs i. PYRENOCARPEAE
ALGAL CELLS PROTOCOCCACEAE OR PALMELLA.
MORIOLACEAE \
EPIGLOEACEAE \, Thallus crustaceous, perithecia solitary
VERRUCARIACEAE]
DERMATOCARPACEAE. Thallus squamulose or foliose.
P YRENO THA MNIA CEA E. Thallus fruticose.
ALGAL CELLS PRASIOLA.
VI. MASTOIDIACEAE.
ALGAL CELLS TRENTEPOHLIA.
VII. PYRENULACEAE }
VIII. PARATHELIACEAEY Thallus crustaceous, perithecia occurring singly.
IX. TRYPE^HELIACEAE\ .
X. ASTROTHELIACEAE}' Thallus crustaceous, perithecia united (stromatoid).
J XI. MYCOPORACEAE. Thallus crustaceous, perithecia in compact groups with a
common outer wall.
XII. PHYLLOPYREN1ACEAE. Thallus minutely foliose.
ALGAL CELLS PHYLLACTIDIUM OR MYCOIDEA.
XIII. STRIGULACEAE. Tropical leaf-lichens. ,,*-.
ALGAL CELLS NOSTOC OR SCYTONEMA.
XIV. PYRENIDIACEAE. Thallus minutely squamulose or fruticose.
SERIES 2. GYMNOCARPEAE
Subseries i. Coniocarpineae, with subperithecial fruits.
Subseries 2. Graphidineae, with elongate, narrow fruits.
Subseries 3. Cyclocarpineae, with round open fruits.
SUBSERIES i. CONIOCARPINEAE
This is a well-defined group, peculiar in the disappearance of the asci at an early stage
so that the spores lie like a powder in the globose partly closed fruits. Algal cells, bright-
green ; Protococcaceae. There are only three families :
XV. CALICIACEAE. Thallus crustaceous, apothecia stalked.
XVI. CYPHELIACEAE. Thallus crustaceous, apothecia sessile.
XVII. SPHAEROPHORACEAE. Thallus foliose or fruticose, apothecia sessile.
SUBSERIES 2. GRAPHIDINEAE
This subseries comes next in the form of fruit development ; generally the apothecia
are elongate, with a narrow slit-like opening, so that a transverse section shows almost a
perithecial outline. Algal cells are mostly Trentepohlia.
XVII!. ARTHONIACEAE. Thallus crustaceous, apothecia oval or linear, flat.
XIX. GRAPHIDACEAE. Thallus crustaceous, apothecia linear, raised.
XX. CHIODECTONACEAE. Thallus crustaceous, apothecia generally immersed in
a stroma.
DIRINACEAE. Thallus crustaceous, corticate above, apothecia round.
ROCCELLACEAE. Thallus fruticose, apothecia round or elongate.
SUBSERIES 3. CYCLOCARPINEAE
A large and very varied group ! In most of the families the algal cells are bright-green
(Chlorophyceae), in some they are blue-green (Cyanophyceae), these latter corresponding
to Reinke's order Cyanophili. The apothecia, as the name implies, are round and open ;
the "Cyanophili" have been placed by Zahlbruckner after those families in which the
3io
SYSTEMATIC
XXIII.
XXIV.
XXV.
> XXVI.
XXVII.
XXVIII.
apothecium has no thalline margin. They form a phylum distinct from those that precede
and those that follow.
The first family of the Cyclocarpineae, the Lecanactidaceae, is often placed under
Graph idineae; in any case it forms a link between the two subseries.
i. Lecideine group (apothecia without a thalline margin).
LECANACTIDACEAE. Thallus crustaceous. Algal cells Trentepohlia.
Apothecium with carbonaceous hypothecium or parathecium.
PILOCARPACEAE. Thallus crustaceous. Algal cells Protococcaceae. Apo-
thecia with a dense rather dark hypothecium.
CHRYSOTHRICACEAE. Thallus felted, loose in texture. Algal cells Pal-
mella^ Protococcaceae or Trentepohlia. Apothecia with or without a thalline
margin. The affinity of the "Family" seems to be with Pilocarpaceae.
\ Thallus crustaceous. Algal cells in the first Tren-
THELOTREMACEAE [ tepohlia; in the second Protococcaceae. In both
DIPLOSCHISTAChAE( there are prominent double margins round the
' apothecium.
ECTOLECHIACEAE. Thallus very primitive in type. Algal cells Proto-
coccaceae. Apothecia with or without a thalline margin. Nearly related to
Chrysothricaceae.
GYALECTACEAE. Thallus crustaceous. Algal cells Trentepohlia, Phyllac-
tidium or rarely Scytonema. Apothecia biatorine, i.e. of soft consistency and
without gonidia.
COENOGONIACEAE. Thallus confusedly filamentous (byssoid). Algal cells
Trentepohlia or Cladophora. Apothecia biatorine.
LECIDEACEAE. Thallus crustaceous or squamulose. Algal cells Proto-
coccaceae. Apothecia biatorine (soft), or lecideine (carbonaceous).
PHYLLOPSORACEAE. Thallus squamulose or foliose. Algal cells Proto-
coccaceae. Apothecia biatorine or lecideine.
CLADONIACEAE. Thallus twofold. Algal cells Protococcaceae. Apo-
thecia biatorine or lecideine.
GYROPHORACEAE. Thallus foliose. Algal cells Protococcaceae. Apo-
thecia lecideine.
ACAROSPORACEAE. Thallus primitive crustaceous, squamulose or foliose.
Algal cells Protococcaceae. Apothecia with or without a thalline margin ;
very various, but always with many-spored asci.
2. Cyanophili group.
In this group the classification depends almost entirely on the nature of the algal
constituents. The apothecia are in most genera provided with a thalline margin.
a. More or less gelatinous when moist.
XXXVI. EPHEBACEAE. Algal cells Scytonema or Stigonema. Thallus minutely
fruticose or filamentous.
XXXVII. PYRENOPSIDACEAE. Algal cells Gloeocapsa (Gloeocapsa, Xanthocapsa
or Chroococcus}. Thallus crustaceous, minutely foliose or fruticose.
XXXVIII. LICHINACEAE. Algal cells Rivularia. Thallus crustaceous, squamulose
or minutely fruticose.
XXXIX. COLLEMACEAE. Algal cells Nostoc. Thallus crustaceous, minutely fruti-
cose, or squamulose to foliose.
XL. HEPPIACEAE. Algal cells Scytonema. Thallus generally squamulose
and formed of plectenchyma.
XXX.
XXXI.
XXXII.
XXXIII.
XXXIV.
XXXV.
FAMILIES AND GENERA 311
b. Not gelatinous when moist.
^~\ XLl. PANNARIACEAE. Algal cells Nostoc, Scytonema or rarely bright-green,
Protococcaceae. Thallus crustaceous, squamulose or foliose.
XLll. STICTACEAE. Algal cells Nostoc or Protococcaceae. Thallus foliose,
and very highly developed, corticate on both surfaces.
XLIII. PELTIGERACEAE. Algal cells Nostoc or Protococcaceae. Thallus
foliose, corticate above.
3. Lecanorine group (apothecia with a thalline margin).
The remaining families have all bright-green gonidia and nearly always apothecia
with a thalline margin. The group includes several distinct phyla :
XLIV. PERTUSARIACEAE. Thallus crustaceous. Apothecia, one or several
immersed in thalline tubercles ; spores mostly very large.
XLV. LECANORACEAE. Thallus crustaceous or squamulose. Apothecia mostly
superficial.
XLVI. PARMELIACEAE. Thallus foliose, rarely almost fruticose or filamentous.
Apothecia scattered over the surface or marginal, sessile.
' XLVI I. USNEACEAE. Thallus fruticose or filamentous. Apothecia sessile or
shortly stalked.
N] XLVI 1 1. CALOPLACACEAE. Thallus crustaceous, squamulose or minutely fruti-
cose. Apothecia with polarilocular colourless spores.
XLIX. TELOSCHISTACEAE. Thallus foliose or fruticose. Apothecia with
polarilocular colourless spores.
L. BUELLIACEAE. Thallus crustaceous or squamulose. Apothecia (lecideine
or lecanorine) with two-celled, thick-walled brown spores (polarilocular in
part).
LI. PHYSCIACEAE. Thallus foliose, rarely partly fruticose. Apothecia with
two-celled thick-walled brown spores (polarilocular in part).
Subclass 2. Hymenolichens.
There are only three closely related genera of Hymenolichens, Cora, Corella and
Dictyonema with Chroococcus or Scytonema algae.
There is reason to dissent from the arrangement in one or two instances which will
be pointed out in the following examination of families and genera.
B. FAMILIES AND GENERA OF ASCOLICHENS
The necessity for a well-reasoned and well-arranged system of classifica-
tion is self-evident: without a working knowledge of the plants that are
the subject of study no progress can be made. The recognition of plants
as isolated individuals is not sufficient, it must be possible to place them in
relation to others; hence the importance of a natural system. In identifying
species artificial aids, such as habitat and substratum, are also often of great
value, and a good working system should take account of all characteristics.
Lichen development is the result of two organisms mutually affecting
each other, but as the fungus provides the reproductive system, it is the
dominant partner : the main lines of classification are necessarily determined
3i2 SYSTEMATIC
by fruit characters. The algae occupy a subsidiary position, but they also
are of importance in shaping the form and structure of the thallus. The
different phyla are often determined by the presence of some particular alga ;
it is in the delimitation of families that the algal influence is of most effect.
Zahlbruckner's system gives due weight to the inheritance from both
fungus and alga with, however, the fungus as the chief factor in development,
and as his work is certain to be generally followed by modern lichenologists,
it is the one of most immediate interest. His scheme has been accepted in
the following more detailed account of families and genera, and for the
benefit of home workers those that have not so far been recorded from the
British Isles have been marked with an asterisk.
It cannot be affirmed that nomenclature is as yet firmly established in
lichenology. Both on historical grounds and on those of convenience, the
subject is one of extreme importance, and interest in it is one of the main
avenues by which we secure continuity with the past, and by which we are
able to realize not only the difficulty, but the romance of pioneer work.
Besides, there can be no exchange of opinion between students nor assured
knowledge of plants, until the names given to them are beyond dispute.
According to the ruling of the Brussels Botanical Congress in 1910,
Linnaeus's1 list of lichens in the Species Plantarum has been selected as the
basis of nomenclature, but since his day many new families, genera and
species have been described and often insufficiently delimited. It is not
easy to decide between priority, which appeals to the historical sense, and
recent use which is the plea of convenience. Here also it seems there can
be no rigid decision; the one aim should be to arrive at a conclusion
satisfactory to all, and accepted by all.
In the following necessarily brief account of families and genera, the
"spermogonia" or "pycnidia" have in most cases been left out of account,
as in many instances they vary within the family and occasionally even
within the genus. Their taxonomic value is not without importance, but,
in the general systematic arrangement, they are only subsidiary characters.
An account of them has already been given, and for more detailed state-
ments the student is referred to purely systematic works.
There are two main types of spore production in the "pycnidia" which
have been shortly described by Steiner2 as "exobasidial" and "endobasidial."
In the former the sporophores are simple or branched filaments, at the
apices of which a short process grows out and buds off a pycnidiospore;
in the latter the spores are budded directly from cells lining the walls or*
filling the cavity of the pycnidium. The exobasidial type is more simply
rendered in the following pages by "acrogenous," the endobasidial by
"pleurogenous" spore production. In many cases the "spermogonia" or
1 Linnaeus 1753. 2 Steiner 1901.
FAMILIES AND GENERA 313
"pycnidia" are still imperfectly known. In designating the gonidial algae,
the more comprehensive Protococcaceae has been substituted for Protococcus,
as in many cases the alga is* probably not Protococcus as now understood,
but some other genus of the family1.
SUBCLASS I. ASCOLICHENS
SERIES I. PYRENOCARPINEAE
It is on mycological grounds that Pyrenocarpineae are placed at the
base of lichen classification. There is no evidence that the series was first
in time.
I. MORIOLACEAE
This family was described by Norman2 in 1872 from specimens col-
lected by himself in Norway or in the Tyrol, on soil or more frequently on
trees. There seems to have been no further record, and Zahlbruckner,
while accepting the family, suggests that an examination or revision may
be necessary.
The thallus is crustaceous. The algal cells, Protococcaceae, occur either
in groups (sometimes stalked) surrounded by a plectenchymatous wall and
called by Norman "goniocysts," or they form nests in the thallus termed
"nuclei" which are surrounded by a double wall of plectenchyma, colourless
in the interior and brown outside. Norman invented the term "Allelositis-
mus," which , may be rendered "mutualism," to indicate this peculiar form
of thallus. The species of Spheconisca are fairly numerous on poplars, willows
and conifers:
Algae in ;'goniocysts" i. *Moriola Norm.3
Algae in double-walled "nuclei" ... 2. *Spheconisca Norm.
II. EPIGLOEACEAE
The family consists of but one genus and one species, Epigloea bactrospora,
and, according to Zahlbruckner, further examination is necessary to make
certain as to the lichenoid nature of the plant.
Zukal4 found the perithecia scattered over the leaves of mosses, and he
alleges that hyphae connected with the perithecium were closely associated
with the alga, Palmella botryoides, and were causing it no harm. Along with
the perithecia he also found minute pycnidia. The "thallus" is of a gelatinous
nature and homoiomerous in structure; the perithecia are soft and clear-
coloured with many-spored asci and colourless one-septate spores.
The small globose pycnidia contain simple sporophores and acrogenous
straight or slightly bent rod-like spores.
Asci many-spored ; spores one-septate, i. *Epigloea Zukal.
1 See p. 56. 2 Norman 1872 and '74.
3 Genera marked with an asterisk have not been found in the British Isles. 4 Zukal 1890.
3i4 SYSTEMATIC
III. VERR UCARIA CEA E
In all the genera of this family the thallus is crustaceous, and, with very
few exceptions, the species are saxicolous or terricolous. The thallus is
variable within the crustaceous limits, and may be superficial and very
conspicuous, almost imperceptible, or wholly immersed in the substratum.
The algal cells are Protococcaceae, and in two of the genera the green cells
penetrate the hymenium and grow in rows alongside of the asci. The
perithecia are small roundish structures scattered over the thallus, the base
immersed, but the upper portion generally projecting. An outer dark-
coloured wall surrounds the whole perithecium (entire) or only the upper
exposed portion (dimidiate) ; it opens above by a pore or ostiole more or
less prominent.
In some of the genera the paraphyses become dissolved at an early
stage, and somewhat similar filaments near the ostiole, termed periphyses,
aid in the expulsion of the spores. The spores vary in septation, colour
and size, and these variations have served to delimit the genera which
have been formed from the original very large genus Verrucaria. The ascus
may be 1-2-, 4- or 8-spored. In only one genus is it many-spored
( Trimmatothele).
The genera are as follows :
Perithecia with simple ostioles.
Paraphyses disappearing early, or wanting.
Spores simple, ellipsoid I. Verrucaria Web.
Spores simple, elongate vermiform 2. Sarcopyrenia Nyl.
Spores simple, numerous in the ascus 3. *Trimmatothele Norm.
Spores i-3-septate 4. Thelidium Massal.
Spores murifbrm (with transverse and longitudinal divisions).
Without hymenial gonidia 5. Polyblastia Massal.
With hymenial gonidia 6. Staurothele Norm.
Paraphyses present.
Spores simple.
Without hymenial gonidia 7. Thrombium Wallr.
With hymenial gonidia 8. *Thelenidia Nyl.
Spores 3-septate, broadly ellipsoid 9. *Geisleria Nitschke.
Spores acicular, many-septate 10. Gongylia Koerb.
Spores muriform u. Microglaena Lonnr.
Perithecia with a wide ring round the ostiole.
Spores muriform; paraphyses unbranched 12. *Aspidothelium Wain.
Spores elongate, many-septate; paraphyses branched 13. *Aspidopyrenium Wain.
IV. DERMATOCARPACEAE
In this family there is a much more advanced thalline development —
generally squamulose or with some degree of foliose structure, though in
the genus Endocarpon, some of the species are little more than crustaceous.
FAMILIES AND GENERA 315
The gonidia are bright-green Protococcaceae (according to Chodat, Cocco-
botrys in Dermatocarpori). In Endocarpon they appear in the hymenium.
The least developed in structure is Normandina : the thallus of the
single species consists of delicate shell-like squamules which are non-
corticate above and below. In the other genera there is a cortex of
plectenchyma.
The perithecia are almost wholly immersed, and open above by a straight
ostiole. The fructification of Dacampia is considered by some lichenologists
to be only a parasite on the white thickish squamulose thallus with which
it is associated.
Hymenial gonidia present.
Spores muriforrn I. Endocarpon Hedw.
Hymenial gonidia absent.
Thallus non-corticate 2. Normandina Wain.
Thallus corticate.
Spores simple, colourless 3. Dermatocarpon Eschw.
Spores simple, brown 4. *Anapyrenium Miill.-Arg.
Spores elongate-septate, colourless 5. *Placidiopsis Beltr.
Spores elongate-septate, brown 6. *Heterocarpon Miill.-Arg.
Spores muriforrn, colourless 7. *Psoroglaena Miill.-Arg.
Spores muriforrn, brown 8. Dacampia Massal.
V. PYRENOTHAMNIACEAE
Thallus more or less fruticose and corticate on both surfaces. Algal
cells Protococcaceae.
Only two genera are included in this family : Nylanderiella with one
species from New Zealand, with a small laciniate thallus up to 15 mm. in
height, partly upright, partly decumbent, and attached to the substratum by
basal rhizinae ; the other small genus, Pyrenothamnia, belongs to N. America ;
the thallus has a short rounded stalk which expands above to an irregular
frond. The perithecia are immersed in the fronds.
Spores colourless, i-septate i. *Nylanderiella Hue1.
Spores brown, muriforrn 2. *Pyrenothamnia Tuckerm.
VI. MASTOIDEACEAE
A family containing one genus and one species, with a wide distribution,
having been found in Siberia, on the Antarctic continent (Graham's Land),
as also in Tierra del Fuego, South Georgia, South Shetland Islands and
Kerguelen. The thallus is foliose, of small thin lobes, and without rhizinae.
Algal cells Prasiola-. The perithecia are globose and partly project from
the thallus; the asci are 8-spored; the paraphyses are mucilaginous and
partly dissolving.
Spores elongate-fusiform, simple, colourless ...i. *Mastoidea Hook, and Harv.
1 Hue 1914. 2 Hue 1909.
3i6 SYSTEMATIC
VII. PYRENULACEAE
This family of crustaceous lichens differs from Verrucariaceae chiefly in
the gonidium which is a species of Trentepohlia. Genera and species are
largely corticolous and the thallus is inconspicuous, often developing within
the substratum. The perithecia, like those of Verrucariae, are immersed or
partly emergent and have an entire or dimidiate outer wall. They are
scattered over the thallus except in Anthracothecium where they are often
coalescent. This genus is tropical or subtropical except for one species
which inhabits S.W. Ireland.
Paraphyses are variable, and in some species tend to disappear, but do
not dissolve in mucilage. The spores are generally colourless, only in one
monotypic genus, C&ccotrema, are they simple. The cells into which the
spore is divided differ in form according to the genus.
Paraphyses branched and entangled or wanting.
Perithecia opening above by stellate lobes i. *Asteroporum Miill.-Arg.
Perithecia opening by a pore.
Spores variously septate.
Spore cells cylindrical or cuboid.
Spores colourless, elongate or ovate i-5-septate 2. Arthopyrenia Massal.
Spores colourless, filiform I -multi-septate 3. Leptorhaphis Koerb.
Spores colourless, muriform 4. Polyblastropsis A. Zahlbr.
Spores brown, ovoid or elongate 2-5-septate ... 5. Microthelia Koerb.
Spore cells globose or lentiform, 3-multi-septate 6. *Pseudopyrenula Miill.-Arg.
Paraphyses unbranched free.
Spore cells cylindrical or cuboid.
Perithecia beset with hairs 7. *Stereochlamys Miill.-Arg.
Perithecia naked.
Asci disappearing ; spores elongate multi-
septate, colourless 8. *Belonia Koerb.
Asci persistent.
Spores simple, ellipsoid, colourless 9. *Coccotrema Miill.-Arg.
Spores elongate, i-multi-septate, colourless... 10. Porina Miill.-Arg.
Spores elongate, i -multi -septate, brown u. Blastodesmia Massal.
Spores muriform, colourless 12. *Clathroporina Miill.-Arg.
Spores elongate, 2-3-septate, colourless 13. Thelopsis Nyl.
Spore cells globose or lentiform.
Spores elongate, i-5-septate, brown 14. Pyrenula Massal.
Spores muriform, brown 15. Anthracothecium Massal. -
VIII. PARATHELIACEAE
This family is peculiar in that the perithecia open by a somewhat
elongate ostiole that slants at an oblique angle. The algal cells are Trente-
pohlia. Genera and species are endemic in tropical or subtropical regions
of the Western hemisphere, though a species of Pleurotrema has been found
in subantarctic America. They are corticolous and the thallus is either
FAMILIES AND GENERA 317
superficial or embedded. The genera are arranged according to spore
characters :
Spores elongate, 2- or more-septate.
Spore cells cylindrical, colourless i. *Pleurotrema Miill.-Arg.
Spore cells globose-lentiform.
Spores colourless 2. *Plagiotrema Miill.-Arg.
Spores brown 3. *Parathelium Miill.-Arg.
Spores muriform.
Spores colourless 4. *Campylothelium Mull.-Arg.
Spores brown 5. *Pleurothelium Miill.-Arg.
IX. TR YPE THEL I A CEA E
This and the following two families are distinguished by the pseudo-
stroma or compound fruit, a character rare among lichens, though the true
stroma is frequent in Pyrenomycetes in such genera as Dothidea, Valsa, etc.
The genera are crustaceous and corticolous and occur with few exceptions
in tropical or subtropical regions, mostly in the Western Hemisphere.
Several grow on officinal bark (Cinchona, etc.). Algal cells are Trentepohlia.
As in many tropical lichens, the spores are large. The genera are based
chiefly on spore characters, on septation, and on the form of the spore
cells :
Spore cells cylindrical or cuboid.
Spores colourless, elongate, multi-septate i. *Tomasiella Miill.-Arg.
Spores colourless, muriform 2. *Laurera Rehb.
Spores brown, muriform 3. *Bottaria Massal.
Spore cells globose-lentiform.
Spores colourless, elongate, multi-septate 4. *Tr\ pethelium Spreng.
Spores brown, elongate, multi-septate 5. Melanotheca Miill.-Arg.
X. ASTROTHELIACEAE
The perithecia are either upright or inclined, and occur usually in
radiate groups. They are free or united in a stroma, and the elongate
ostioles open separately or coalesce in a common canal. The genera are
all crustaceous, with Trentepohlia gonidia. They are tropical or subtropical,
mostly in the Western Hemisphere; but species of Parmentaria and Astro-
thelium have been recorded also from Australia.
The spores are all many-celled and the form of their cells is a generic
character :
Spores elongate, multi-septate.
Spore cells cylindrical I- *Lithothelium Miill.-Arg.
Spore cells globose-lentiform.
Spores colourless 2. *Astrothelium Trev.
Spores brown ••••3- *Pyrenastrum Eschw.
' Spores muriform.
Spores colourless 4- *Heufleria Trev.
Spores brown 5- *Parmentaria Fe'e.
3i8 SYSTEMATIC
XL MYCOPORACEAE
A small family with only two genera which are found in both Hemi-
spheres ; species of both occur in Great Britain. They are all corticolous.
The perithecia are united into a partially chambered fruiting body surrounded
by a common wall, but opening by separate ostioles. The thallus is thinly
crustaceous, with Palmella gonidia in Mycoporum, and Trentepohlia in
Mycoporellum. The spores are colourless or brown in both genera :
Spores muriform i. Mycoporum Flot.
Spores elongate, multi-septate 2. Mycoporellum A. Zahlbr.
XII. PHYLLOPYRENIACEAE
Thallus foliose with both surfaces corticate and attached by rhizinae.
Algal cells Trentepohlia. There is but one genus, Lepolichen, which has a
laciniate somewhat upward growing thallus. Two species, both from South
America, have been described, L. granulatus Miill.-Arg. and L. coccophora
Hue. The latter has been recently examined by Hue1 who finds, on the
thalli, cephalodia which are peculiar in containing bright-green gelatinous
algae either Urococcus or Gloeocystis, one of the few instances known of
chlorophyllaceous algae forming part of a cephalodium. Gloeocystis may be
the only alga present in the cephalodium ; Urococcus is always accompanied
by Scytonema.
The perithecia are immersed in thalline tubercles :
Spores colourless, simple, ovoid or ovoid-elongate I. *Lepolichen Trevis.
XIII. STRIGULACEAE
A family of epiphyllous lichens inhabiting and disfiguring coriaceous
evergreen leaves, or occasionally fern leaves in tropical or subtropical regions.
The algae associated are Mycoidea and Phycopeltis (Phyllactidium). The
only truly parasitic lichen, Strigula, belongs to this family: the alga precedes
the lichen on the leaves and is gradually invaded by the hyphae of the
lichen and altered in character. The small black perithecia are scattered
over the surface. In Strigula the lichen retains the spreading rounded form
of the alga. The other genera are more irregular.
Thallus orbicular in outline I. *Strigula Fries.
Thallus irregular.
Perithecia without hairs.
Spores colourless.
Spores elongate, multi-septate 2. *Phylloporina Mull.-Arg.
Spores muriform 3. *Phyllobathelium Miill.-Arg.
Spores brown.
Spores simple 4. *Haplopyrenula Miill.-Arg.
Spores elongate, [-3-septate 5. *Microtheliopsis Miill.-Arg.
Perithecia beset with stiffhairs 6. *Trichothelium Miill.-Arg.
1 Hue 1905.
FAMILIES AND GENERA 319
XIV. PYRENWIACEAE
The only family of Pyrenocarpineae associated with blue-green algae.
The genera of Pyrenidiaceae are all monotypic, only one is common and
of wide distribution, Coriscium (Normandina Nyl.). Pyrenidium is the only
member that has a fruticose thallus, and that is of minute dimensions.
Eolichen Heppii, found and described by Zukal, is a doubtful lichen. " Lopho-
thelium " Stirton is a case of parasitism of a fungus, Ticothecium, on the
squamules of Stereocaulon condensatum.
Algal cells Scytonema or Stigonema.
Thallus crustaceous1; spores simple, colourless i. *Rhabdopsora Mull.-Arg.
Thallus crustaceous ; spores i-septate, colourless 2. *Eolichen Zuk.
Thallus crustaceous ; spores muriform, brown 3. *Pyrenothrix Riddle2.
Thallus squamulose ; spores numerous, simple 4. *Placothelium Miill.-Arg.
Algal cells Nostoc.
Thallus crustaceous; spores filiform, simple, colourless 5. *Hassea A. Zahlbr.
Thallus fruticose ; spores elongate, 3-septate, brown ...6. Pyrenidium Nyl.
Algal cells Microcystis (Polycoccus).
Thallus squamulose ; fructification unknown 7. Coriscium Wainio.
SERIES II. GYMNOCARPEAE
SUBSERIES i. Coniocarpineae
This small subseries is marked by the peculiar "mazaedium" type of
fruit with its disappearing asci. It forms a connecting link between the
families with perithecia and those with apothecia. The thallus is crustaceous
or fruticose, often poorly developed and sometimes absent. The algal cells
are Protococcaceae or rarely Trentepohlia.
XV. CALICEACEAE
The thallus is thinly crustaceous, sometimes brightly coloured, some-
times absent, taking no part in the formation of the fruits; these have
upright stalks with a small capitulum, and often look like minute nails.
One genus, Sphinctrina, is parasitic on the thallus of other lichens, mostly
Pcrtusariae.
Fruits with slender stalks.
Spores simple.
Spores colourless i. Coniocybe Ach.
Spores brown 2. Chaenotheca Th. Fr.
Spores septate, brown.
Spores i-septate 3. Calicium De Not.
Spores 3-7-septate 4- Stenocybe Nyl.
Fruits with short thick stalks.
Spores globose, brown (parasitic) 5- Sphinctrina Fries.
Spores i-septate, brown 6. *Pyrgidium Nyl.
1 Zahlbr., in Hedwigia, LIX. p. 301, 1917. * Riddle 1917.
320 SYSTEMATIC
XVI. CYPHELIACEAE
Thallus crustaceous. Algal cells Protococcaceae or Trentepohlia. Apo-
thecia sessile, more widely open than in the previous family; in some genera
the thallus forms an outer apothecial margin. The genera Farriola from
Norway and Tylophorella from New Granada are monotypic. The British
genus Cyphelium has been known as Trachytia.
Thallus with Protococcaceae.
Spores colourless, simple i. *Farriola Norm. •
Spores brown, i-3-septate (rarely simple or muriform) ...2. - Cyphelium Th. Fr.
Thallus with Trentepohlia.
Spores simple, many in the ascus 3. *Tylophorella Wainio.
Spores 8 in the ascus.
Apothecia with a thalline margin 4. *Tylophoron Nyl.
Apothecia without a thalline margin 5. *Pyrgillus Nyl.
XVII. SPHAEROPHORACEAE
The most highly evolved family of the subseries, as regards the thallus.
Algal cells Protococcaceae. In Tkolurna, a small lichen endemic in Scan-
dinavia, there is a double thallus : one of horizontal much-divided squa-
mules, the other swollen, upright, terminating in the capitulum. The fruit
is lateral in Calycidium, a squamulose form from New Zealand, and in
Pleurocybe from Madagascar, with stiff strap-shaped fronds. All the genera
are monotypic except Sphaerophorus, of which genus ten species are recorded,
some of them with a world-wide distribution. The spores are brown and
simple or I -septate.
Thallus squamulose and upright i. *Tholurna Norm.
Thallus wholly squamulose 2. *Calycidium Stirton.
Thallus fruticose.
Fronds hollow in the centre 3. *Pleurocybe Miill.-Arg.
Fronds not hollow.
Fruit without a thalline margin 4. *Acroscyphus Lev.
Fruit inclosed in the tip of the fronds 5. Sphaerophorus Pers.
SUBSERIES i. Graphidineae
In this subseries are included five families that differ rather widely from
each other both in thallus and apothecia; the latter are more or less
carbonaceous and mostly with a proper margin only. Families and genera
are widely distributed, though most abundant in warm regions. Algal cells
mostly Trentepohlia.
A comprehensive study of the apothecia of this series by Bioret1 gives
some interesting results in regard to the paraphyses: in Arthonia they are
irregular in direction and much-branched ; in Opegrapha, the paraphyses
are vertical and parallel with more regular branching ; Stigmatidium (Entero-
1 Bioret 1914.
FAMILIES AND GENERA 321
graplia} resembles Opegrapha in this respect as does also Platygrapha, a
genus of Lecanactidaceae, while in Grapliis the paraphyses are vertical,
unbranched and free; Melaspilea paraphyses are somewhat similar to those
of Gr aphis.
XVIII. ARTHONIACEAE
The thallus of Arthoniaceae is corticolous with few exceptions and is
very inconspicuous, being largely embedded in the substratum. The
apothecia (ardellae) are round, irregular or stellate, without any margin,
the hymenium being protected by the dense branching of the paraphyses
at the tips.
A rthonia is abundant everywhere. The species of the other genera belong
mostly to tropical or subtropical countries. Arthoniopsis is similar to
Arthonia in the character of the fruits, but the gonidium is a Phycopeltis,
and it is only found on leaves. SynartJionia with peculiar stromatoid fruc-
tification is monotypic; it occurs in Costa Rica.
Thallus with Trentepohlia gonidia.
Apothecia scattered.
Spores elongate i- or pluri-septate i. Arthonia Ach.
Spores muriform 2. Arthothelium Massal.
Apothecia stromatoid.
Spores elongate, multi-septate 3. *Synarthonia Mull.-Arg.
Thallus with Pahnella gonidia.
Spores i- or more-septate 4. Allarthonia Nyl.
Spores muriform 5- *Allarthothelium Wain.
Thallus with Phycopeltis gonidia.
Spores elongate I- or more-septate 6. *Arthoniopsis Miill.-Arg.
XIX. GRAPHIDACEAE
Thallus crustaceous, inconspicuous, partly immersed, mainly growing
on bark but occasionally on dead wood or stone. Algal cells chiefly
Trentepohlia, very rarely Palniella or Phycopeltis (epiphyllous). Apothecia
(lirellae) carbonaceous more or less linear, opening by a narrow slit with
a well-developed proper margin except in Gymnographa, a monotypic
Australian genus. In two genera, the fruit is of a compound nature, several
parallel discs occurring in one lirella: these are Ptychographa (on bark in
Scotland) and Diplogramma (Australia), both are monotypic. They must
not be confused with Graphis elegans and allied species in which the sterile
carbonaceous margin is furrowed. Two tropical genera associated with
Phycopeltis are epiphyllous.
Graphidaceae are among the oldest recorded lichens, attention having
been drawn to them since early times by the resemblance of the lirellae on
the bark of trees to hieroglyphic writing.
322 SYSTEMATIC
Thallus with Palmetto, gonidia.
Apothecia single.
Hypothec) urn dark-brown.
Spores simple i. Lithographa Nyl.
Hypothecium colourless or brownish.
Spores colourless.
Spores simple 2. Xylographa Fries.
Spores elongate 3-8-septate 3. *Aulaxina Fee.
Spores brown.
Spores i -septate 4. Encephalographa Massal.
Spores pluri-septate, then muriform 5. *Xyloschistes Wain.
Apothecia compound.
Spores simple, colourless 6. Ptychographa Nyl.
Spores pluri-septate, colourless 7. *Diplogramma Miill.-Arg.
Thallus with Trentepohlia gonidia.
Spores elongate i -multi-septate, the cells longer than wide.
Spores brown.
Spores i-(rarely more)-septate 8. Melaspilea Nyl.
Spores 3-septate (apothecia rudimentary) 9. *Gymnographa Miill.-Arg.
Spores colourless.
Spores acicular, coiled (many in the ascus) 10. *Spirographa A. Zahlbr.
Spores fusiform, straight n. Opegrapha Humb.
Spores muriform. ,
Spores elongate, central cells finally muriform 12. *Dictyographa Miill.-Arg.
Spores elongate, septate, cells wider than long.
Paraphyses unbranched, filiform.
Spores multi-septate, colourless 13. Graphis Adans.
Spores multi-septate, brown 14. Phaeographis Miill.-Arg.
Spores muriform, colourless 15. Graphina Miill.-Arg.
Spores muriform, brown 16. Phaeographina Miill.-Arg.
Paraphyses clavate, warted at tips 17. *Acanthothecium Wain.
Paraphyses branched, interwoven above 18. *Helminthocarpon Fe"e.
Thallus with Phycopeltis gonidia (epiphyllous).
Spores elongate, 3-9-septate, colourless 19. *Opegraphella Miill.-Arg.
Spores elongate, i-septate, brown 20. *Micrographa Miill.-Arg.
XX. CHIODECTONACEAE
Specially distinguished in this subseries by the grouping of the somewhat
rudimentary apothecia in pseudostromata in which they are almost wholly
immersed. In form they are roundish or linear; the spores are septate or
muriform. The thallus is thinly crustaceous and continuous : in Glyphis,
Sarcographa and Sarcographina there is an amorphous upper cortex, the
other genera are non-corticate. Algal cells are Trentepohlia with the
exception of two epiphyllous genera associated with Phycopeltis.
Genera and species are mostly tropical. Sderophyton with five species
is represented in Europe by a single British specimen, S. circumscriptum.
The form of the paraphyses is a distinguishing character of the genera.
FAMILIES AND GENERA 323
Thallus with Trentepohlia gonidia.
Paraphyses free, unbranched.
Spore cells short or almost globose.
Spores elongate, multi-septate, colourless i. Glyphis Fe"e.
Spores elongate, multi-septate brown 2. *Sarcographa Fe"e.
Spores muriform, brown 3. *Sarcographina Miill.-Arg.
Spore cells longer and cuboid.
Spores muriform, colourless 4. *Enterodictyon Miill.-Arg.
Paraphyses branched, interwoven above.
Spores elongate, multi-septate, colourless 5. Chiodecton Ach.
Spores elongate, multi-septate, brown 6. Sclerophyton Eschw.
Spores muriform, colourless 7. *Minksia Miill.-Arg.
Spores muriform, brown 8. *Enterostigma Miill.-Arg.
Thallus with Phycopeltis gonidia (epiphyllous).
Paraphyses free.
Spores unequally 2-celled, colourless 9. *Pycnographa Miill.-Arg.
Paraphyses branched, interwoven above.
Spores elongate, multi-septate, colourless 10. *Mazosia Massal.
XXI. DlRINACEAE
A small family, which is associated with and often included under
Graphidaceae. The thallus is crustaceous and corticate on the upper
surface, the cortex being formed of palisade hyphae. Algal cells Trente-
polilia. Apothecia are rounded or with a tendency to elongation, and, in
addition to a thin proper margin, possess a stout thalline margin ; the
hypothecium is thick and carbonaceous. There are two genera : Dirina
with twelve species has a wide distribution ; Dirinastrum is monotypic and
occurs on maritime rocks in Australia. In both the spores are elongate-
septate, differing only in colour :
Spores colourless I. Dirina Fr.
Spores brown 2. *Dirinastrum Miill.-Arg.
XXII. ROCCELLACEAE
The Roccellaceae differ from the preceding Dirinaceae chiefly in the
fruticose thallus which is more or less characteristic of all the genera, though
in Roccellographa it expands into foliose dimensions and in Roccellina is
reduced to short podetia-like processes from a crustose base. The fronds —
mostly long and strap-shaped — are protected in most of the genera by
a cortex of compact palisade hyphae; in a few the outer hyphae are parallel
with the long axis. The medulla is of parallel hyphae, either loose or
compact. The algal cells are Trentepohlia.
The apothecia are lateral except in Roccellina where they occur at the
tips of the short upright fronds, and only in Roccellaria is there no thalline
margin. They are superficial in all of the genera except Roccellographa, in
which they are immersed and almost closed, recalling the perithecia-like
324 SYSTEMATIC
fruits of Chiodecton (sect. Enterographa). The spores are elongate, narrow,
pluri-septate, and colourless or brownish, except in Darbishirella in which
they are ovoid, 2-septate and brown.
The affinity of Dirinaceae and Roccellaceae with Graphidaceae was first
indicated by Reinke1 and elaborated later by Darbishire2 in his monograph
of Roccellaceae. The apothecia in some species of Dirina are ellipsoid rather
than round ; in several genera of Roccellaceae they are distinctly lirellate,
and in Roccella itself some species have ellipsoid fruits. The fruticose thallus
is predominant in Roccellaceae, but its evolution from the crustaceous type
may be traced through Roccellina which is partly crustaceous and only
imperfectly fruticose.
In most of the genera only one species is recorded. Roccella, represented
by twelve species, is well known for its dyeing properties, and has a wide
distribution. Like other Graphidineae they are mainly plants of warm
regions, mariy of them exclusively maritime rock-dwellers.
The following synopsis of the genera is the one given by Darbishire in
his monograph.
Cortex fastigate, of palisade hyphae.
Spores colourless.
Hypothecium black-carbonaceous.
Apothecia round.
Thallus fruticose I. Roccella DC.
Thallus crustaceous-fruticose 2. *Roccellina Darbish.
Apothecia lirellate 3. *Reinkella Darbish.
Hypothecium colourless.
Gonidia present under the hypothecium 4. *Pentagenella Darbish.
Gonidia absent from hypothecium 5. *Combea De Not.
Spores brown or brownish.
Medulla of parallel somewhat loose hyphae 6. *Schizopelte Th. Fr.
Medulla solid, black 7. *Simonyella Steiner.
Cortex fibrous, of parallel hyphae.
Apothecia round.
Hypothecium black-carbonaceous.
Apothecia with thalline margin ; . . . 8. *Dendrographa Darbish.
Apothecia with proper margin 9. *Roccellaria Darbish.
Hypothecium colourless 10. *Darbishirella A. Zahlbr.
Apothecia lirellate II. *Ingaderia Darbish.
SUBSERIES 3. CYCLOCARPINEAE
This last subseries includes the remaining twenty-nine families of Asco-
lichens. They are very varied both in the fungal and the algal symbionts.
The fruit is more or less a discoid open apothecium. The gonidia belong to
different genera of Myxophyceae and Chlorophyceae, but the most frequent
are Protococcaceae. Families are based largely on thalline structure.
1 Reinke 1895. 2 Darbishire 1898.
FAMILIES AND GENERA 325
XXIII. LECANACTIDACEAE
By many systematists this family is included under Graphidineae on
account of the fruit structure which in some of the forms is carbonaceous
and almost lirellate, and also because the algal symbiont is Trentepohlia.
The thallus is primitive, being thinly crustaceous and non-corticate ; the
apothecium has a black carbonaceous hypothecium in two of the genera,
Lecanactis and Schismatomma (Platygrapha)\ in the third genus, Melam-
pydiwn, it is colourless. The latter is monotypic, and the spores become
muriform. In the other genera they are elongate and multi-septate.
Apothecia with prominent proper margin i. Lecanactis Eschw.
Apothecia with thin proper margin 2. *Melampydium Miill.-Arg.
Apothecia with thalline margin 3. Schismatomma Flot.
XXIV. PlLOCARPACEAE
A small family with but one genus, Pilocarpon. It is distinguished as
one of the few epiphyllous genera of lichens associated with Protococcaceous
gonidia and with a distribution extending far beyond the tropics. The best
known species, P. leucoblepJiarum, encircles the base of pine-needles with
a white felted crust, or inhabits coriaceous evergreen leaves. Another species
lives on fern leaves. The fruit is a discoid apothecium with a dark carbona-
ceous hypothecium and proper margin, and with a second thalline margin.
The paraphyses are branched and interwoven above.
Spores elongate, 3-septate, colourless i. Pilocarpon Wain.
XXV. CHRYSOTRICHACEAE
This family now, according to Hue1, includes two genera, Crocynia and
Chrysothrix. In both there is a thallus of interlaced hyphae with Protococ-
caceous algae scattered through it or in groups. The structure is thus
homoiomerous, and Hue has suggested for it a new series, "Intertextae."
The only British species, Crocynia lanuginosa, first placed by Nylander2 in
Amphiloma and later transferred by him to Leproloma*, has a soft crustaceous
lobate thallus, furfuraceous on the surface; no fructification has been found.
A West Indian species, C. gossypina, has discoid apothecia with a thalline
margin. There is only one species of Chrysothrix, Ch. nolitangere, which
forms small clumps or tufts on the spines of Cactus in Chili. The structure
is somewhat similar to that of Crocynia.
Spores colourless, simple i- Crocynia Nyl.
Spores colourless, 2-3-septate 2. *Chrysothrix Mont.
1 Hue 1909. 2 Nylander 1855. 3 Nylander 1883.
326 SYSTEMATIC
t
XXVI. THELOTREMACEAE
A tropical or subtropical family of which the leading characteristic is
the deeply sunk disc of the apothecium : it has a proper hyphal margin,
and, round that, an overarching thalline margin. The apothecia occur singly,
or they are united in a kind of pseudostroma : in Tremotylium several grow
together, while in Polystroma each new apothecium develops as an outgrowth
from the thalline margin of the one already formed, so that an upright,
r branching succession of fruits is built up. It is a very unusual type of lichen
fructification, with one species, P. Ferdinandezii, found in Spain and in
Guiana.
The thallus in all the genera is crustaceous with an amorphous (decom-
posed) cortex; or it is non-corticate. The algal cells are Trentepohlia except
in Phyllophthalmaria, an epiphyllous genus associated with the alga Phyco-
peltis. In Polystroma the alga is unknown.
Only one genus is represented in the British Isles.
Apothecia growing singly.
Thallus with Trentepohlia gonidia.
Paraphyses numerous, unbranched, free.
Spores colourless.
Spores elongate, 2- or multi-septate i. *Ocellularia Spreng.
Spores muriform 2. Thelotrema Ach.
Spores brown.
Spores elongate, septate .3. *Phaeotrema Miill.-Arg.
Spores muriform 4. *Leptotrema Mont.
Paraphyses scanty, branched.
Spores muriform, brown 5- *Gyrostomum Fr.
Thallus with Phycopeltis gonidia 6. *Phyllophthalmaria A. Zahlbr.
Apothecia in pseudostromata.
Apothecia united in tubercles 7. *Tremotylium Nyl.
Apothecia united 'by the margins 8. *Polystroma Clem.
XXVII. DlPL OSCHIS TA CEA E
Scarcely differing from the preceding family except in the gonidia which
are Protococcaceous algae. The thallus is crustaceous and non-corticate.
The apothecia have a double margin but the outer thalline margin is less
overarching than in Thelotremaceae. The spores in the two genera are
somewhat peculiar: in Conotrema they are exceedingly long and divided
by parallel septa into thirty to forty small cells ; in Diploschistes ( Urceolaria)
they are large, muriform and brown. Conotrema contains two corticolous
species ; Diploschistes about thirty species mostly saxicolous. Both genera
are represented in the British Isles.
Spores elongate, multi-septate, colourless i. Conotrema Tuck.
Spores muriform, brown 2. Diploschistes Norm.
FAMILIES AND GENERA 327
XXVIII. ECTOLECHIACEAE
A family of tropical epiphyllous lichens that are associated with Proto-
coccaceous gonidia. The thallus is primitive in character, mostly a weft of
hyphae with intermingled algal cells, described as homoiomerous.
The apothecia are without a thalline margin, and with a scarcely
developed proper margin : their affinity is with the Lecideaceae, though in
two genera, Lecaniella and ArtJiotJieliopsis, there are gonidia below the
hypothecium, a character of Lecanoraceae. The genera are nearly all
monotypic ; in Sporopodium has been included Lecidea phyllocJiaris YVainio
(Sect. Gonotheciuni), which is distinguished by hymenial gonidia.
Apothecia at first covered by a "veil."
Spores elongate, colourless, septate i. *Asterothyrium Mull.-Arg.
Apothecia uncovered from the first.
Gonidia not present below the hypothecium.
Paraphyses unbranched, free.
Spores muriform 2. *Lopadiopsis Wain.
Paraphyses branched.
Spores i-septate 3. *Actinoplaca Mi.ill.-Arg.
Spores elong'ate, multi-septate 4. *Tapellaria Miill.-Arg.
Spores muriform 5. *Sporopodium Mont.
(ionidia present below the hypothecium.
Spores elongate, 2-septate 6. *Lec'aniella Wain.
Spores muriform 7. *Arthotheliopsis Wain.
XXIX. GYALECTACEAE
The algal cells in this family are filamentous; either Myxophyceae
(Scytoneina) or Chlorophyceae ( Trentepohlia or Phyllactidium). The thallus
is crustaceous, and in some cases homoiomerous, as in Petractis, where the
alga, Scytonema, penetrates the substratum as deeply as the hyphae. Mono-
phiale, a tropical genus, possesses two kinds of gonidia : the species that
grow on bark or mosses are associated with Trentepohlia ; others that have
invaded the surface of leathery evergreen leaves resemble most epiphyllous
lichens in being associated with the leaf alga Phyllactidium (Phycopeltis).
Some species of Trentepohlia exhale when moist an odour of violets. This
scent is retained in at least one genus, Jonaspis.
The apothecia are superficial, and are soft, waxy and bright-coloured,
with prominent margins which are however entirely hyphal : the affinity is
therefore with Lecideaceae. In one genus, Sagiolechia, the fruit is carbona-
ceous and dark coloured. The spores of all the genera are colourless.
Apothecia waxy, bright-coloured.
Thallus with Scytonema. gpnidia.
Spores elongate, 3-septate i. Petractis Fr.
328 SYSTEMATIC
Thallus with Trentepholia gonidia.
Asci 6-8-spored.
Spores simple 2. Janaspis Th. Fr.
Spores i-septate 3. *Microphiale A. Zahlbr.
Spores septate or muriform 4. Gyalecta Ach.
Asci i2-many-spored.
Spores i-septate 5. *Ramonia Stizenb.
Spores fusiform or acicular, many-septate ...6. Pachyphiale Lonnr.
Apothecia carbonaceous.
Spores elongate, 2-3-septate 7. *Sagiolechia Massal.
XXX. COENOGONIA CEA E
There are only two genera in this small family, Coenogonium with Trente-
pohlia gonidia, and Racodium with Cladophora. Both genera follow the algal
form and are filamentous. In Coenogonium the filaments are sometimes
matted into a loose felted expansion. The genus is mainly tropical or
subtropical and mostly rather light-coloured. There is only one British
species, C. ebeneum1, a sterile form, in which the hyphae are very dark-brown ;
it often covers large areas of stone or rock with its sooty-like creeping
filaments.
Racodium includes 2 (?) species. One of these, R. rupestre, is sterile and
resembles C, ebeneum in form and colour.
The apothecia of Coenogonium are waxy and light-coloured ; they are
borne laterally on the filaments; the spores are simple or I -septate.
Thallus with Trentepohlia gonidia i. Coenogonium Ehrenb.
Thallus with Cladophora gonidia 2. Racodium Fr.
XXXI. LECIDEACEAE
One of the largest lichen families as regards both genera and species,
and of world-wide distribution. The algal cells are Protococcaceae. The
thallus is mostly crustaceous but it becomes squamulose in Psora, a section
of Lecidea\ and in Sphaerophoropsis, a Brazilian genus, there are small
upright fronds or stalks with lateral apothecia. The prevailing colour of
the thallus is some shade of grey, but it ranges from white or yellow to
dark-brown or almost black. Cephalodia appear in some of the species.
The apothecia have a proper margin only, no gonidia taking part in the
fruit-formation. They may be soft and waxy (biatorine) or hard and
carbonaceous (lecideine). The genera are mainly based on spore characters
which are very varied.
The arrangement of genera given below follows that of Zahlbruckner ;
in several instances, both as to the limitations of genera and to the nomen-
clature, it differs from that of British text-books, though the general principle
of classification is the same.
1 Lorrain Smith 1906.
FAMILIES AND GENERA 329
Thallus crustaceous non-corticate.
Spores simple.
Spores small, thin-walled.
Spores colourless i. Lecidea Ach.
Spores brown 2. *Orphniospora Koerb.
Spores large, thick-walled 3. Mycoblastus Norm.
Spores i -septate.
Spores small, thin-walled 4. Catillaria Th. Fr.
Spores large, thick-walled 5. Megalospora Mey. and Flot.
Spores elongate, 3-multi-septate.
Spores elongate, narrow, thin-walled 6. Bacidia A. Zahlbr.
Spores elongate, large and thick- walled 7. Bombyliospora De Not.
Spores muriform.
Spores colourless; on trees 8. Lopadium Koerb.
Spores colourless to brown ; on rocks 9. Rhizocarpon Th. Fr.
Thallus warted or squamulose, corticate.
Spores elongate, i-y-septate, thin- walled 10. Toninia Th. Fr.
Thallus of upright podetia-like small fronds.
Spores ellipsoid, becoming I -septate n. *Sphaerophoropsis Wain.
XXXII. PHYLLOPSORACEAE
A small family of exotic lichens with a somewhat more developed thallus
than that of the Lecideaceae, being in both of the genera squamulose or
almost foliose.
The apothecia are without a thalline margin ; they are biatorine or
lecideine ; the hypothecium is formed of plectenchyma and is purple-red
in one species, Phyllopsora furfuracea. The two genera differ only in spore
characters. There are fifteen species, mostly corticolous, belonging to
Pliyllopsora ; only one, from New Zealand, is recorded for Psorella.
Spores simple i. *Phyllopsora Miill.-Arg.
Spores elongate, septate 2. *Psorella Miill.-Arg.
XXXIII. CLADONIACEAE
Associated with Lecideaceae in the type of apothecium, but differing
widely in thallus formation. The latter is of a twofold type : the primary
thallus is crustaceous, squamulose, or very rarely foliose ; the secondary
thallus or podetium, upright, simple or branched, is terminated by the
apothecia, or broadens upwards to cup-like scyphi. Algal cells, Protococ-
caceae, according to Chodat, Cystococcus.
Much attention has been given to the origin and development of the
podetia in this family. They are superficial on granule or squamule
except in the monotypic Himalayan genus Gymnoderma where they are
marginal on the large leaf-like lobes. Though in origin the podetia are
doubtless fruit stalks, they have become in most cases vegetative in function.
330 SYSTEMATIC
The fruits are coloured yellowish, brown or red (or dark and carbonaceous
in Pilophorus), and are borne on the tips of the branches or on the margins
of the scyphi. In Glossodium and Thysanothecium — the former from New
Granada, the latter from Australia — the apothecia occupy one side of the
widened surface at the tips.
Cephalodia are developed on the primary thallus of Pilophorus, and on
the podetia of Stereocaulon and Argopsis.
Podetia simple, short, not widening upwards.
Podetial stalks naked.
Primary thallus thin, continuous I. Gomphillus Nyl.
Primary thallus granular or squamulose ... 2. Baeomyces Pers.
Primary thallus foliose.
Podetia superficial 3. *Heteromyces Miill.-Arg.
Podetja marginal 4. *Gymnoderma1 Nyl.
Podetial stalks granular, squamulose 5. Pilophorus Th. Fr.
Podetia short, widening upwards.
Podetia simple above, rarely divided ... 6. *Glossodium Nyl.
Podetia lobed, leaf-like 7. *Thysanothedum Berk. & Mont.
Podetia elongate, variously branched, or scy-1 0
' \ 8. Cladoma Hill,
phous and hollow J
Podetia elongate, not scyphous, the stalks solid.
Spores elongate, septate 9. Stereocaulon Schreb.
Spores muriform 10. *Argopsis Th. Fr.
XXXIV. GYROPHORACEAE
A small family of foliose lichens allied to Lecideaceae by the character
of the fruit — a superficial apothecium in the formation of which the gonidia
take no share. There are only three genera, distinguished by differences in
spore and other characters. Dermatiscum has light-coloured thallus and
fruits ; of the two species, one occurs in Central Europe, the other in North
America. Umbilicaria and GyropJiora are British; they are dark-coloured
rock-lichens and are extremely abundant in Northern regions where they
are known as "tripe de roche." Algal cells Protococcaceae.
Umbilicaria, Dermatiscum, and some species of Gyrophora are attached
to the substratum by a central point. Other species of Gyrophora are
rhizinose. In all there is a cortex of plectenchyma above and below. In
Gyrophora the thallus may be monophyllous as in Umbilicaria, or poly-
phyllous and with or without rhizinae. New lobes frequently arise from
protuberances or warts on the older parts of the thallus. At the periphery,
in most species, growth is equal along the margins, in G. erosa2 the edge is
formed of numerous anastomosing lobes with lateral branching, the whole
forming a broadly meshed open network. Further back the tissues become
continuous owing to the active growth of the lower tissue or hypothallus,
1 Neophyllis Wils. is synonymous with Gymnoderma. 2 Lindau 1 899.
FAMILIES AND GENERA 331
which grows out from all sides and meets across the opening. The overlying
layers, with gonidia, follow more slowly, but they also in time become
continuous, so that the "erose" character persists only near the periphery.
This forward growth of the lower thallus occurs in other species, though to
a much less marked degree.
There is abundant detritus formation in this family; the outer layers of
the cortex are continually being sloughed, the dead tissues lying on the
upper surface as a dark gelatinous layer, continuous or in small patches.
On the under surface the cast-off cortex gathers into a loose confused mass
of dead tissues.
Asci 8-spored.
Spores mostly simple (disc gyrose) i. Gyrophora Ach.
Spores i-septate 2. *Dermatiscum Nyl.
Asci i-2-spored.
Spores muriform 3. Umbilicaria Hoffrn.
XXXV. ACAROSPORACEAE
Thallus foliose, squamulose or crustaceous, sometimes scarcely developed.
Algal cells Protococcaceae.
Into this family Zahlbruckner has gathered the genera in which the
asci are many-spored, as he considers that a character of great importance
in determining relationship, but he has in doing so overlooked other very
great differences. The fruit-bodies are round and completely enclosed in
a thalline wall in Thelocarpon, which has however no perithecial wall. They
have a proper margin only (lecideine) in Biatorella, and a thalline margin
(lecanorine) in the remaining genera. In Acarospora the apothecia are sunk
in the thallus. Stirton's genus Cryptothecia^ is allied to Tfielocarpon in the
fruit-formation, but the basal thallus is well developed and the spores are
few in number and variously divided.
Thallus none.
Apothecia (or perithecia) in thalline warts i. Thelocarpon Nyl.
Thallus crustaceous.
Apothecia lecideine ; spores simple 2. Biatorella Th. Fr.
Apothecia lecanorine ; spores septate 3. *Maronea Massal.
Thallus of small squamules 4. Acarospora Massal.
Thallus almost foliose, attached centrally 5. *Glypholecia Nyl.
XXXVI. EPHEBACEAE
A family of very simple structure either filamentous, foliose or crustaceous.
The algal cells which give a dark colour to the thallus are Stigonema or
Scytonema, members of the blue-green Myxophyceae, and consist of minute
simple or branched filaments — single cell-rows in Scytonema, compound in
Stigonema.
1 Stirton 1877, p. 164.
332 SYSTEMATIC
In some of the genera the lichen hyphae travel within the gelatinous
sheath of the filaments, both algae and hyphae increasing by apical growth
so that filaments many times the length of the alga are formed as in
Ephebe. In others the filaments scarcely increase beyond the normal size
of the alga as in Thermutis (Gonionema); or the gelatinous algal cells may
be distributed in a stratum of hyphae.
The apothecia are minute and almost closed; they may be embedded
in swellings of the thallus, or are more or less superficial. The spores are
rather small, colourless and simple or I -septate.
The lichens of this family are rock-dwellers and are mostly to be found
in hilly or Alpine regions. A tropical species, Leptogidium dendriscum, occurs
in sterile condition in south-west Ireland. There are few species in any of
the 'genera.
Algal cells Scytonema.
Thallus minutely fruticose, non-corticate I. Thermutis Fr.
Thallus minute, of felted filaments, cortex one) „_ ,,7 .
> 2. *Leptodendnscum Wain,
cell thick I
Thallus of elongate filaments, cortex of several cells 3. Leptogidium Nyl.
Thallus foliose or fruticose, cellular throughout 4. Polychidium Ach.
Thallus crustaceous, non-corticate 5. Porocyphus Koerb.
Algal cells Stigonema.
Thallus minutely fruticose, non-corticate 6. Spilonema Born.
Thallus of long branching .filaments.
Spores septate ; paraphyses wanting 7. Ephebe Fr.
Spores simple ; paraphyses present 8. Ephebeia Nyl.
Thallus crustaceous; upper surface non-corticate,! . . .
. \ 9. *Pterygtopsis Wain,
lower surface corticate J
XXXVII. P YRENOPSIDA CEA E
In this family are included gelatinous lichens of which the gonidium is
a blue-green alga with a thick gelatinous coat, either Gloeocapsa (including
Xanthocapsd) or Chroococcus. In Gloeocapsa and Chroococcus the gelatinous
envelope is often red, in Xanthocapsa it is yellow, and these colours persist
more or less in the lichens, especially in the outer layers.
The thallus is in many cases a formless gelatinous crust of hyphal
filaments mingling with colonies of algal cells as in Pyrenopsis; but small
fruticose tufts are characteristic of Synalissa, and larger foliose and fruticose
thalli appear in some exotic genera. A plectenchymatous cortex is formed
on the thallus of Forssellia, a crustaceous genus from Central Europe, with
two species only; the whole thallus is built up of a kind of plectenchyma
in some others, but in most of the genera there is no tissue formed.
The apothecia, as in Ephebaceae, are generally half-closed.
FAMILIES AND GENERA 333
Thallus with Gloeocapsa gonidia.
Thallus crustaceous.
Spores simple i. Pyrenopsis Nyl.
Spores i-septate 2. -Cryptothele Forss.
Thallus shortly fruticose 3. Synalissa Fr.
Thallus lobate, centrally attached 4. *Phylliscidium Forss.
Thallus with Chroococcus gonidia.
Thallus crustaceous 5. Pyrenopsidium Forss.
Thallus lobate, centrally attached 6. *Phylliscum Nyl.
Thallus with Xanthocapsa gonidia.
Thallus crustaceous.
Thallus non-corticate.
Spores simple.
Apothecia open, asci 8-spored 7. Psorotichia Forss.
Apothecia covered, asci many-spored 8. *Gonohymenia Stein.
Spores i -septate.
Apothecia closed 9. *Collemopsidium Nyl.
Thallus with plectenchymatous cortex 10. *Forssellia A. Zahlbr.
Thallus lobate, centrally attached.
Spores simple.
Thallus plectenchymatous throughout u. *Anema Nyl.
Thalline tissue of loose hyphae 12. *Thyrea Massal.
Cortex of upright parallel hyphae 13. *Jenmania Wacht.
Spores i -septate.
Thalline tissue of loose hyphae 14. *Paulia Fe"e.
Thallus fruticose.
Thallus without a cortex 15. *Peccania Forss.
Thallus with cortex of parallel hyphae 16. *Phloeopeccania Stein.
XXXVIII. LlCHlNACEAE
The only family of lichens associated with Rivularia gonidia, the
trichomes of which retain their filamentous form to some extent in the
more highly developed genera; they lie parallel to the long axis of the
squamule or of the frond except in LicJiinella in which genus they are
vertical to the surface. The thallus may be crustaceous, or minutely foliose,
or fruticose; in all cases it is dark-brown in colour, and the gelatinous
character is evident in the moist condition. The best known British genus
is Licliina which grows on rocks by the sea.
The apothecia are more or less immersed in the tissue; in Pterygium and
Steinera they are open and superficial (the latter monotypic genus confined
to Kerguelen). They are also open in Lichinella and Homopsella^ both very
rare genera. The spores are colourless and simple except in Pterygium arid
Steinera where they are elongate, and i-3-septate.
Thallus crustaceous squamulose.
Apothecia immersed in thalline warts i. *Calothricopsis Wain.
Apothecia superficial, with thalline margin 2. *Steinera A. Zahlbr.
Apothecia superficial, without a thalline margin 3. Pterygium Nyl.
334 SYSTEMATIC
Thallus of small fruticose fronds.
Gonidia occupying the central strand 4. *Lichinodium Nyl.
Gonidia not in the centre.
Apothecia immersed 5. Lichina Ag.
Apothecia superficial.
Paraphyses present 6. *Lichinella Nyl.
Paraphyses absent 7. *Homopsella Nyl.
XXXIX. CoLLEMACEAE
The most important family of the gelatinous lichens and the most
numerous. Collema is historically interesting as having first suggested the
composite thallus. Algal cells, Nostoc, which retain the chain-like form
except in Leprocollema, a doubtful member of the family. The thallus varies
from indeterminate crusts to lobes of considerable size ; occasionally the
lobes are narrow and erect, forming minute fruticose structures. In the
more primitive genera the thallus is non-corticate, but in the more evolved,
the apical cells of the hyphae coalesce to form a continuous cellular cortex,
one or more cells thick, well marked in some species, in others rudimentary;
the formation of plectenchyma also occurs occasionally in the apothecial
tissues of some non-corticate species.
The apothecia are superficial except in Pyrenocollema, a monotypic genus
of unknown locality. They are generally lecanorine, with gonidia entering
into the formation of the apothecium : in some genera they are lecideine or
biatorine, being formed of hyphae alone. The spores are colourless and vary
in form, size and septation.
Apothecia immersed ; spores fusiform, i-septate i. *Pyrenocollema Reinke.
Apothecia superficial.
Thallus without a cortex.
Spores simple, globose or ellipsoid.
Thallus crustaceous 2. *Leprocollema Wain.
Thallus largely squamulose-fruticose.
Apothecia lecideine (dark-coloured) 3. *Leciophysma Th. Fr.
Apothecia lecanorine 4. Physma Massal.
Spores variously septate or muriform.
Apothecia biatorine (light-coloured) 5. *Homothecium Mont.
Apothecia lecanorine 6. Collema Wigg.
Thallus with cortex of plectenchyma.
Spores simple.
Spores globose 7. Lemmopsis A. Zahlbr.
Spores ellipsoid, with thick subverrucose wall... 8. *Dichodium Nyl.
Spores vermiform, spirally curved 9. *Koerberia Massal.
Spores variously septate or muriform.
Apothecia biatorine (light-coloured) 10. *Arctomia Th. Fr.
Apothecia lecanorine u. Leptogium S. F. Gray.
FAMILIES AND GENERA 335
XL. HEPPIACEAE
A family belonging to the "blue-green" series as it is associated with
a gelatinous alga, Scytonema, but is of almost entirely cellular structure and
is non-gelatinous. The thallus is squamulose or minutely foliose, or is formed
of narrow almost fruticose lobes; the apothecia are semi-immersed; the asci
are 4-many-spored.
Heppia is a wide-spread genus both in northern and tropical regions
with about forty species that live on soil or rock. So far, no representative
has been recorded in our Islands.
Spores simple, colourless, globose or ellipsoid i. *Heppia Naeg.
Spores muriform, colourless, ellipsoid 2. *Amphidium1 Nyl.
X L I . PA N\A RIACEAE
The members of this family are also non-gelatinous, though for the most
part associated with blue-green gelatinous algae, Nostoc or Scytonema. The
gonidia are bright-green in the genera Psoroma and Psoromaria, the former
often included under Lecanora, but too closely resembling Pannaria to be
dissociated from that genus.
The -thallus varies from being crustaceous to squamulose or foliose, and
has a cortex of plectenchyma on the upper and sometimes also on the
lower surface. The apothecia are superficial or lateral and with or without
a thalline margin (lecanorine or biatorine), the spores are colourless.
Zahlbruckner has included Hydrotkyria in this family. It is a monotypic
aquatic genus found in North America and very closely allied to Peltigera.
The British species of the genus, familiarly known as Coccocarpia, have
been placed under Parmeliella, the former name being restricted to the
tropical or subtropical species first assigned to Coccocarpia and distinguished
by the cortex, the hyphae forming it lying parallel with the surface though
forming a regular plectenchyma.
An Antarctic lichen TJielidea corrugata with Palmetto, gonidia is doubt-
fully included: the thallus is foliose, the apothecia biatorine with colourless
i -septate spores.
Thallus with bright-green gonidia.
With Palmetto, i. *Thelidea Hue.
With Protococcaceae.
Apothecia non-marginate (biatorine) 2. *Psoromaria Nyl.
Apothecia marginate 3. Psoroma Nyl.
Thallus with Scytonema gonidia.
Apothecia marginate, spores i-septate 4. Massalongia Koerb.
Apothecia non-marginate ; spores simple.
Upper surface smooth 5. *Coccocarpia Pers.
Upper surface felted 6. *Erioderma Fe"e.
1 A. Zalilbruckner, in Oesterr. hot. Zeitschr. 1919, p- 163.
336 SYSTEMATIC
Thallus with Nostoc gonidia.
Apothecia marginate ; spores simple 7. Pannaria Del.
Apothecia non-marginate ; spores various.
Thallus crustaceous or minutely squamulose ... 8. Placynthium Ach.
Thallus squamulose, cortex indistinct 9. *Lepidocollema Wain.
Thallus squamulose or foliose, cortex cellular ...10. Parmeliella Miill.-Arg.
Thallus foliose, thin veined below 11. *Hydrothyria Russ.
XLII. STICTACEAE
Thallus foliose, mostly horizontal, with a plectenchymatous cortex on
both surfaces, a tomentum of hair-like hyphae taking the place of rhizinae
on the lower surface. Algal cells Protococcaceae or Nostoc. Cephalodia and
cyphellae or pseudocyphellae often present. Apothecia superficial or lateral ;
spores colourless or brown, variously septate.
The highly organized cortex and the presence of aeration organs —
cyphellae or pseudocyphellae — which are almost solely confined to the
genus Sticta give this family a high position as regards vegetative develop-
ment. The two genera are of wide distribution, but Sticta is more abundant
in the Southern Hemisphere. Lobaria pulmonaria is one of our largest
lichens.
Under surface dotted with cyphellae or pseudo-}
, I. Sticta Schreb.
cyphellae ...
Under surface without these organs 2. Lobaria Schreb.
XLII I. PELTIGERACEAE
A family of heteromerous foliose lichens containing in some instances
blue-green (Nostoc), in others bright-green (Protococcaceae) gonidia, and
thus representing a transition between these two series. They have large
or small lobes and grow on the ground or on trees.
Cephalodia, either ectotrophic (Peltidea) or endotrophic (Solorina), occur
in the family and further exemplify the capacity of the fungus hyphae to
combine with different types of algae.
The upper surface is a wide cortex of plectenchyma, which in some
forms (Nephromium) is continued below. In the non-corticate under surface
of Peltigera, the lower hyphae grow out in hairs or rhizinae, very frequently
brown in colour. Intercalary growth of the upper tissues stretches the
thallus and tears apart the lower under surface so that the hair-bearing
areas become a network of veins, with the white exposed medulla between.
In Peltigera canina there is further growth and branching of the hyphae in
the veins, adding to the bulk of the interlacing ridges.
From all other foliose lichens Peltigeraceae are distinguished by the
flat wholly appressed or peltate apothecia without a thalline margin which
arise mostly on the upper surface, but in Nephromium on the extreme
FAMILIES AND GENERA 337
margin of the under surface, the tip of the fertile lobe in that case is turned
back as the apothecium matures, so that the fruit eventually faces the light.
In Nephroma has been included Eunephroma with bright-green gonidia and
Nephromium with blue-green.
Bitter1 has recorded the finding of apothecia on the under surface of
Peltigera malacea and not at the margin, as in Nephromium. The plant was
otherwise normal and healthy. Solorinella, from Central Europe and
Asteristion from Ceylon are monotypic genera with poorly developed thalli.
Thallus poorly developed.
Asci 6-8-spored; spores 3-5 -septate i. *Asteristion Leight.
Asci many-spored ; spores i-septate 2. *Solorinella Anzi.
Thallus generally well developed.
Apothecia superficial, sunk in the thallus 3. -Solorina Ach.
Apothecia terminal on upper surface of lobes 4. Peltigera Willd.
Apothecia terminal on lower surface of lobes 5. Nephroma Ach.
XLIV. PERTUSARIACEAE
Thallus crustaceous, often rather thick and with an amorphous cortex
on the upper surface. Algal cells Protococcaceae. Apothecia solitary or
several immersed in thalline warts, generally with a narrow opening which
barely exposes the disc, and which in one genus, Perforaria, is so small as
almost to constitute a perithecium ; spores are often very large and with
thick walls; some if not all are multinucleate and germinate at many points.
In the form of the fruit, this family stands between Pyrenocarpeae and
Gymnocarpeae, though more akin to the latter. Perforaria, with two species,
belongs to New Zealand and Japan. Pertusaria has a world-wide distri-
bution, and Varicellaria, a monotypic genus, with a very large two-celled
spore, is an Alpine plant, recorded from Europe and from Antarctic
America.
Spores simple.
Apothecia with pore-like opening I. *Perforaria Miill.-Arg.
Apothecia with a wider opening 2. Pertusaria DC.
Spores i-septate 3. Varicellaria Nyl.
XLV. LECANORACEAE
Thallus mostly crustaceous, occasionally squamulose or very rarely
minutely fruticulose. The squamulose thallus is corticate above, the under
surface appressed and attached to the substratum by penetrating hyphae,
often effigurateat the circumference. Algal cells Protococcaceae. Apothecia
well distinguished by the thalline margin; spores colourless, simple or
variously septate or muriform.
1 Bitter 1904*.
338 SYSTEMATIC
Lecanora, Ochrolechia, Lecania, Haematomma and Phlyctis are cosmo-
politan genera, some of them with a very large number of species; the other
genera are more restricted in distribution and generally with few species.
The genus Candelariella is of uncertain position; the spores are 8 or
many in the ascus and are simple or I -septate, and not unfrequently become
polarilocular as in Caloplacaceae, but there is no parietin present.
Algae distributed through the thallus. Spores simple i. *Harpidium Koerb.
Algae restricted to a definite zone.
Spores simple.
Thallus grey, white or yellowish.
Spores rather small \2. Lecanora Ach.
Spores large 3. Ochrolechia Massal.
Thallus bright yellow.
Spores simple or I -septate 4. Candelariella Miill.-Arg.
Spores i-septate (rarely pluri-septate).
Paraphyses free.
Thallus squamulose, effigurate 5. Placolecania Zahlbr.
Thallus crustaceous.
Apothecial disc brownish 6. Lecania Zahlbr.
Apothecial disc flesh-coloured 7. Icmadophila Trevis.
Paraphyses branched, intricate 8. *Calenia Miill.-Arg.
Spores elongate, pluri-septate.
Apothecia superficial 9. Haematomma Massal.
Apothecia immersed.
Paraphyses free 10. *Phlyctella Miill.-Arg.
Paraphyses branched, intricate 11. *Phlyctidia Miill-Arg.
Spores muriform.
Apothecia superficial 12. *Myxodictyon Massal.
Apothecia immersed 13. Phlyctis Wallr.
XLVI. PARMELIACEAE
A very familiar family of foliose lichens. Genera and species are dorsi-
ventral and stratose in structure, though some Cetrariae are fruticose in
habit. Algal cells are Protococcaceae; in Physcidia they are Palmellae, In
every case the upper surface of the thallus is corticate and generally of
plectenchyma, the lower being somewhat .similar, but in Heterodea and
Physcidia, monotypic Australasian genera, the upper cortex is of branching
hyphae parallel with the surface, the lower surface being non-corticate.
The Parmeliae are mostly provided with abundant rhizinae; in Cetrariae
and Nephromopsis these are very sparingly present, while in Anzia (including
Pannop annelid) the medulla passes into a wide net-like structure of anasto-
mosing hyphae.
In Heterodea, cyphellae occur on the under surface as in Stictaceae; and
in Cetraria islandica bare patches have been described as pseudocyphellae.
The latter lichen is one of the few that are of value as human food. Special
aeration structures are present on the upper cortex of Parmelia aspidota.
FAMILIES AND GENERA 339
Thallus non-corticate below.
Apothecia terminal I. *Heterodea Nyl.
Apothecia superficial 2. *Physcidia Tuck.
Thallus spongy below 3. *Anzia Stizenb.
Thallus corticate below.
Asci poly-spored 4. Candelaria Massal.
Asci 8-spored.
Spermatia acrogenous 5. Parmeliopsis Nyl.
Spermatia pleurogenous.
Apothecia superficial 6. Parmelia Ach.
Apothecia lateral.
Apothecia on upper surface 7. Cetraria Ach.
Apothecia on lower surface 8. *Nephromopsis Miill.-Arg.
XLVII. USNEACEAE
This also is a familiar family of lichens, Usnea barbata the "bearded moss"
being one of the first lichens noted and chronicled. Algal cells Protococ-
caceae. Structure radiate, the upright or pendulous habit characteristic of
the family securing all-round illumination. Special adaptations of the cortex
or of the internal tissues have been evolved to strengthen the thallus against
the strains incidental to their habit of growth as they are attached in
nearly all cases by one point only, by a special sheath, or by penetrating
hold-fasts.
Apothecia are superficial or marginal and sometimes shortly stalked ;
spores are simple or variously septate.
Ranialina and Usnea, the most numerous, are cosmopolitan genera;
Alectoria inhabits northern or hilly regions.
The genus Evernia, also cosmopolitan, represents a transition between
foliose and fruticose types; the fronds of the two species, though strap-
shaped and generally upright, are dorsiventral and stratose, the gonidia
for the most part lying beneath one surface; the other (lower) surface is
either white or very dark-coloured. Everniopsis, formed of thin branching
strap-shaped fronds, is also dorsiventral.
A number of genera, TJiamnolia, Siphu/a, etc. are of podetia-like structure,
generally growing in swards. Several of them have been classified with
Cladoniae, but they lack the double thallus. One of these, Endocena, a
sterile monotypic Patagonian lichen, with stiff hollow coralloid fronds, was
classified by Hue1 along with SipJiula\ recently he has transferred it to his
family Polycaulionaceae2 based on Polycauliona regale (Placodium frustu- ^
losnin Darbish.), and allied to Placodium Sect. T/iamnoma3. In recent studies
Hue has laid most stress on thalline characters. He places the new family
between "Ramalinaceae" and " Alectoriaceae." Dactylinaarctica is a common
Arctic soil-lichen.
1 Hue 1892. 2 Hue 1914. 3 Tuckerman 1872, p. 107.
22 — 2
340 SYSTEMATIC
Thallus strap- shaped.
Structure dorsiventraL
Greyish-green above I. Evernia Ach.
Whitish-yellow above 2. *Evemiopsis NyL
Structure radiate alike on both surfaces.
Fronds grey; medulla of loose hyphae 3. Ramalina Ach.
Fronds yellow ; medulla traversed by strands 4. *Letharia A. Zahlbr.
Thallus filamentous.
Medulla a strong "chondroid" strand 5. Usnea DilL
Medulla of loose hyphae.
Spores simple 6. Alectoria Ach.
Spores muriform, brown 7. *Oropogon Fr.
Thallus of upright podetia-like fronds.
Fronds rather long (about two inches), tapering,^ 8. Thamnolia Ach. (Cerania
white I S. F. Gray).
Fronds shorter, blunt
Medulla solid 9. *Siphula Fr.
Medulla partly or entirely hollow.
Fronds swollen and tall (about two inches) 10. *Dactylina NyL
Fronds coralloid, entangled n. *Endocena Cromb.
Fronds short, upright 12. *Dufourea NyL
XLVIII. CALOPLACACEAE
In this family Zahlbruckner has included the squamulose or crustaceous
lichens with colourless polarilocular spores, relegating those with more
highly developed thallus or with brown spores to other families. He has
also substituted the name Caloplaca for the older Placodium, the latter being,
as he considers, less well defined.
Algal cells are Protococcaceae. The thallus is mostly light-coloured,
generally some shade of yellow, and, with few exceptions, contains parietin,
which gives a purple colour on the application of potash. The squamulose
forms are closely appressed to the substratum, and have often a definite
rounded outline (effigurate). The spores have a thick median septum with
a loculus at each end and a connecting canal1.
In Blastenia the outer thalline margin is obscure or absent — though
gonidia are frequently present below the hymenium. Caloplacaceae occur
all over the globe: they are among the most brilliantly coloured of all
lichens. Polycauliona Hue1 possibly belongs here: though based on thalline
rather than on spore characters, one species at least has polarilocular spores.
Apothecia with a distinct thalline margin i. Caloplaca Th. Fr.
Apothecia without a thalline margin 2. Blastenia Th. Fr.
1 See p. 188. » Hue 1908.
FAMILIES AND GENERA 341
XLIX. TELQSCHISTACEAE
PolariJocular colourless spores are the distinguishing feature of this
family as of the Caloplacaceae. Algal cells Protococcaceae. The thallus
of Teloschistaceae is more highly developed, being either foliose or fruticose,
though never attaining to very large dimensions. The cortex of Xanthoria
( foliose) is plectenchymatous, that of Teloschistes (fruticose) is fibrous. The
species of both genera are yellow- or greenish-yellow due to the presence of
the lichen-acid parietiru
Both genera have a wide distribution over the globe, more especially in
maritime regions.
Thallus foliose i. Xanthoria Th. Fr.
Thallus fruticose 2. Teloschistes Norm.
L. B CELL! ACE AE
A family of crustaceous lichens distinguished by the brown two-celled
spores. Algal cells Protococcaceae. Zahlbruckner has included here Bufllia
and Rinodina; the former with a distinctly lecideine fruit and with thinly
septate spores; the latter lecanorine and with spores of the polarilocular
type, with a very wide central septum pierced in most of the species by
a canal which may or may not traverse the middle lamella of the wall.
Rinodina is closely allied to Physciaceae, while Buellia has more affinity
with Lecideaceae and is near to Rhizocarpon.
Both genera are of world-wide distribution.
Apothecia lecideine, without a thalline margin i. Buellia De Xot.
Apothecia lecanorine, with a thalline margin 2. Rinodina MassaL
LI. PHYSCIACEAE
Thallus foliose or partly fruticose, and generally attached by rhizinae.
Algal cells Protococcaceae. The spores resemble those of Rinodina, dark-
coloured with a thick septum and reduced cell-lumina. As in that species
there may be a second septum in each cell, giving a 3-septate spore; but
that is rare.
Pyxine, a tropical or subtropical genus, is lecanorine only in the very
early stages; it soon loses the thalline margin. Anaptychia is differentiated
from Physria by the subfruticose habit though the species are nearly all
dorsiventral in structure, only a few of them being truly radiate and corticate
on both surfaces. The upper cortex of Anaptychia is fibrous, but that
character appears also in most species of Physcia either on the upper or the
lower side. Physcia and Anaptychia are widely distributed.
Thalline margin absent in apothecia I. *Pyxine XyL
Thalline margin present in apothecia.
Thallus foliose 2. Physcia Schreb.
Thallus fruticose 3- Anaptychia Koerb.
342 SYSTEMATIC
C. *HYMENOLICHENS
Fungus a Basidiomycete, akin to Thelephora. Algal cells Scytonema or
Chroococcus. Thallus crustaceous, squamulose or foliose. Spores colourless,
produced on basidia, on the under surface of the free thallus.
The Hymenolichens1 are few in number and are endemic in tropical
or warm countries. They inhabit soil or trees.
Thallus of extended lobes.
Gonidia near the upper surface i. *Dictyonema Zahlbr.
Gonidia in centre of tissue 2. *Cora Fr.
Thallus squamulose, irregular 3. *Corella Wain.
II. NUMBER AND DISTRIBUTION OF LICHENS
i. ESTIMATES OF NUMBER
Calculations have been made and published, once and again, as to the
number of lichen species occurring over the globe or in definite areas. In
1898 Fiinfstuck stated that about 20,000 different species had been described,
but as many of them had been proved to be synonyms, and since many
must rank as forms or varieties, the number of well-authenticated species
did not then, according to his estimate, exceed 4000. Many additional
genera and species have, however, been discovered since then. In Engler
and Prantl's Pflanzenfamilien, over 50 families and nearly 300 genera find
a place, but even in these larger groupings opinions differ as to the limits
both of genera and families, and lichenologists would not all accept the
arrangement given in that volume.
Fiinfstuck has reckoned that of his estimated 4000, about 1500 are
European and of these at least 1200 occur in Germany. Probably this is
too low an estimate for that large country. Leighton in 1879 listed, in his
British Lichen Flora, 1710 in all, and, as the compilation includes varieties,
it cannot be considered as very far astray. On comparing it with Olivier's2
recent statistics of lichens, we find that of the larger fruticose and foliose
species, 310 are recognized by him for the whole of Europe, 206 of these
occurring in the British Isles. Leighton's estimate of similar species is
about 145, without including varieties now reckoned as good species. In
a more circumscribed area, Th. Fries3 described for Spitzbergen about 210
different lichens, a number that closely approximates to the 206 recent re-
cords by Darbishire4 for the same area.
A general idea of the comparative numbers of the different types of
lichens may be gathered from Hue's compilation of exotic lichens5, examined
1 See p. 152. 2 Olivier 1907. 3 Th. Fries 1867.
4 Darbishire 1909. 5 Hue 1892.
NUMBER OF LICHENS 343
or described by Nylander, and now in the Paris herbarium. There are 135
genera with 3686 species. Of these, about 829 belong to the larger foliose
and fruticose lichens (including Cladoniae)\ the remaining 2857 belong to
the smaller kinds, most of them crustaceous.
2. GEOGRAPHICAL DISTRIBUTION
A. GENERAL SURVEY
The larger foliose and fruticose lichens are now fairly well known and
described for Europe, and the knowledge of lichens in other continents is
gradually increasing. It is the smaller crustaceous forms that baffle the in-
vestigator. The distribution of all lichens over the surface of the earth is
controlled by two principal factors, climate and substratum ; for although
lichens as a rule require only support, they are most of them restricted to one
or another particular substratum, either organic or inorganic. As organisms
which develop slowly, they require an unchanging substratum, and as sun-
plants they avoid deeply shaded woodlands: their occurrence thus depends
to a large extent on the configuration and general vegetation of the country.
Though so numerous and so widely distributed, lichens have not evolved
that great variety of families and genera characteristic of the allied fungi
and algae. They conform to a few leading types of structure, and thus the
Orders and Families are comparatively few, and more or less universal.
They are most of them undoubtedly very old plants and were probably
wide-spread before continents and climates had attained their present
stability. Arnold1 indeed considers that a large part of the present-day
lichens were almost certainly already evolved at the end of the Tertiary
period, and that they originated in a warm or probably subtropical climate.
As proof of this he cites such genera as Graphis, Thelotrenia and Arthonia*
which are numerous in the tropics though rare in the colder European
countries ; and he sees further proof in the fact that many fruticose and
gelatinous lichens do not occur further north than the forest belt, though
they are adapted to cold conditions. Several genera that are abundant in
the tropics are represented outside these regions by only one or few species,
as for instance Conotrenia urceolatum and Bonibyliospora incana.
During the Ice age of the Quaternary period, not many new species can
have arisen, and such forms as were not killed off must have been driven
towards the south. As the ice retreated the valleys were again stocked with
southern forms, and northern species were left behind on mountain tops all
over the globe.
1 Arnold 1890.
2 These genera are associated with Trentepohlia algae which are numerous and abundant in
tropical climates, and their presence there may possibly account for these particular lichens.
344 SYSTEMATIC
In examining therefore the distribution of lichens, it will be found that
the distinction between different countries is relative, certain families being
more or less abundant in some regions than others, but, in general, nearly
all being represented. Certain species are universal, where similar conditions
prevail. This is especially true of those species adapted to extreme cold, as
that condition, normal in polar regions, recurs even on the equator if the
mountains reach the limit of perpetual snow ; the vertical distribution thus
follows on the lines of the horizontal.
In all the temperate countries we find practically the same families, with
some few exceptions; there is naturally more diversity of genera and species.
Genera that are limited in locality consist, as a rule, of one or few species.
In this category, however, are not included the tropical families or genera
which may be very rich in species: these are adapted to extreme conditions
of heat and often of moisture, and cannot exist outside tropical or subtropical
regions, extreme heat being more restricted as to geographical position than
extreme cold.
In the study of distribution the question which arises as to the place of
origin of such widely distributed plants is one that is difficult to solve.
Wainio1 has attempted the task in regard to Cladonia, one of the most
unstable genera, the variations of form, which are dependent on external
circumstances, being numerous and often bewildering. In his fine mono-
graph of the genus, 132 species are described and 25 of these are cosmo-
politan.
The distribution of Phanerogams is connected, as Wainio points out,
with causes anterior to the present geological era, but this cannot be the
case in a genus so labile and probably so recent as Cladonia, though some
of the species have existed long enough to spread and establish themselves
from pole to pole. Endemic species, or those that are confined to a com-
paratively limited area, are easily traced to their place of origin, that being
generally the locality where they are found in most abundance, and as
a general rule in the centre of that area, though there may be exceptions:
a plant for instance that originated on a mountain would migrate only in
one direction — towards the regions of greater cold.
The difficulty of determining the primitive. stations of cosmopolitan, or
of widely spread, species is much greater, but generally they also may be
referred to their area of greatest abundance. Thus a species may occur
frequently in one continent and but rarely in another, even where the con-
ditions of climate, etc., are largely comparable. It may therefore be inferred
that the plant has not yet reached the full extent of possible distribution in
the less frequented area. As examples of this, Wainio cites, among other
instances, Cladonia papillaria, which has a very wide distribution in Europe,
1 Wainio 1897.
DISTRIBUTION 345
but, as yet, has been found only in the eastern parts of North America; and
Cl. pycnodada, a plant which braves the climate of Cape Horn and the
Falkland Islands, but has not travelled northward beyond temperate North
America: the southern origin of that species is thus plainly indicated. Wainio
also finds that evidence of the primitive locality of a very widely spread
species may be obtained by observing the locality of species derived from
it, which are as yet of limited distribution ; presumably these arose in the
ancestral place of origin, though this indication is not always to be relied
on. If, however, the ancestral plant has given rise to several of these rarer
related species, those of them that are most closely allied to the primitive
plant would be found near to it in the original locality.
A detailed account of species distribution according to these indications
is given by Wainio and is full of interest. No such attempt has been made
to deal with any other group, and the distribution of genera and species can
only be suggested. An exhaustive comparison of the lichens of different
regions is beyond the purpose of our study and is indeed impossible as,
except in some limited areas, or for certain species, the occurrence and dis-
tribution are not fully known. It is in any case only tentatively that genera
or species can be described as local or rare, until diligent search has been
made for them over a wider field. The study of lichens from a floristic point
of view lags behind that of most other groups of plants. The larger lichen
forms have received more attention,' as they are more evident and more
easily collected ; but the more minute species are not easily detected, and,
as they are largely inseparable from their substratum of rocks, or trees, etc.,
on which they grow, they are often difficult to collect. They are also in
many instances so indefinite, or so alike in outward form, that they are
liable to be overlooked, only a m'icroscopic examination revealing the differ-
ences in fruit and vegetative structure.
Though much remains to be done, still enough is known to make the
geographical distribution of lichens a subject of extreme interest. It will be
found most instructive to follow the usual lines of treatment, which give the
three great divisions : the Polar, the Temperate and the Tropical regions
of the globe.
B. LICHENS OF POLAR REGIONS
Strictly speaking, this section should include only lichens growing within
the Polar Circles; but in practice the lichens of the whole of Greenland and
those of Iceland are included in the Arctic series, as are those of Alaska:
the latitudinal line of demarcation is not closely adhered to. With the
northern lichens may also be considered those of the Antarctic continent,
as well as those of the islands just outside the Antarctic Circle, the South
346 SYSTEMATIC
Shetlands, South Orkneys, Tierra del Fuego, South Georgia and the Falkland
Islands. During the Glacial period, the polar forms must have spread with
the advancing cold ; as the snow and ice retreated, these forms have been
left, as already stated, on the higher colder grounds, and representatives of
polar species are thus to be found very far from their original haunts. There
are few exclusively boreal genera: the same types occur at the Poles as in
the higher subtemperate zones. One of the most definitely polar species,
for instance, Usnea (Neuropogon] melaxantha grows in the whole Arctic zone,
and, in the Antarctic, is more luxuriant than any other lichen, but it has also
been recorded from the Andes in Chili, Bolivia and Peru, and from New
Zealand (South Island).
Cold winds are a great feature of both poles, and the lichens that by
structure or habit can withstand these are the most numerous ; those that
have a stout cortical layer are able to resist the low temperatures, or those
that grow in tufts and thus secure mutual protection. In Arctic and Subarctic
regions, 495 lichens have been recorded, most of them crustaceous. Among
the larger forms the most frequently met are certain species of Peltigera,
P armelia, Gyrophora, Cetraria, Cladonia, Stereocaulon and Alectoria. Among
smaller species Lecanora tartarea spreads everywhere, especially over other
vegetation, Lecanora varia reaches the farthest limits to which wood, on
which it grows, has drifted, and several species of Placodium occur con-
stantly, though not in such great abundance." Over the rocks spread also
many crustaceous Lecideaceae too numerous to mention, one of the most
striking being the cosmopolitan Rhizocarpon geographicnm.
Wainio1 has described the lichens collected by Almquist at Pitlekai in
N.E. Siberia just on the borders of the Arctic Circle, and he gives a vivid
account of the general topography. The snow lies on the ground till June
and falls again in September, but many lichens succeed in growing and
fruiting. It is a region of tundra and sand, strewn more or less with stones.
Most of the sand is bare of all vegetation; but where mosses, etc., have
gained a footing, there are also a fair number of lichens : Lecanora tartarea,
Psoroma hypnorum, with Lecideae, Parmeliae, Cladoniae, Stereocaulon alpinnm,
Solortna crocea, SpJiaeropJwrus globosus, Alectoria nigricans and Gyrophora
proboscidea. Some granite rocks in that neighbourhood rise to a height of
200 ft., and though bare of vegetation on the north side, yet, in sheltered
nooks, several species are to be found. Stunted bushes of willow grow
here and there, and on these occur always the same species : Placodium
ferrugineum, Rinodina archaea, Buellia myriocarpa and Arthopyrenia puncti-
formis. Some species such as Sphaerophorus globosus, Dactylina arctica
(a purely Arctic genus and species) and Thamnolia vermicularis are so.
abundant that they bulk as largely as other better represented genera such
1 Wainio 1909.
DISTRIBUTION 347
as Cladoniae, Lecanorae or Lecideae. On the soil, Lecanorae cover the largest
areas.
Wainio determined a large number of lichens with many new species,
but the region is colder than that of Lappland, and trees with tree-lichens
are absent, with the exception of those given above. In Arctic Siberia,
Elenkin1 discovered a new lichen Placodium subfruticulosum which scarcely
differs from Darbishire's2 Antarctic species PI. fruticulosnm (or /-*. regale);
both are distinguished by the fruticose growth of the thallus, for which reason
Hue3 placed them in a new genus, Polycauliona.
The Antarctic Zone and the neighbouring lands are less hospitable to
plant life than the northern regions, and there is practically no accumulation
of detritus. Collections have been made by explorers, and several lists have
been published which include a marvellous number of species common to
both Poles, if the subantarctic lands are included in the survey. An analytic
study of the various lists has been published by Darbishire4. He recognizes
1 06 true Antarctic lichens half of which are Arctic as well. The greater
number are crustaceous and are plants common also to other lands though
a certain number are endemic. The most abundant genera in species as
well as individuals are Lecidea and Lecanora. Several bright yellow species
of Placodium — PI. elegans, PL murorum, etc., are there as at the North Pole.
Among the larger forms, Parnieliae, Cetrariae, and Cladoniae are fairly
numerous; Usneae and Rainalinae rather uncommon, while members of the
Stictaceae are much more abundant than in the North. The common species
of Peltigera also occur in Antarctica, though P. aphthosa and P. venosa are
wanting ; both of these latter are boreal species. Darbishire adds that lichens
have so great a capacity to withstand cold, that they are only checked by
the snow covering, and were bare rocks to be found at the South Pole, he
is sure lichens would take possession of them. The most southerly point
at which any plant has been found is 78° South latitude and 162° East
longitude, in which locality the lichen Lecanora subfusca was collected by-
members of Scott's Antarctic expedition (1901-1904) at a height of 5000 ft.
A somewhat different view of the Antarctic lichen flora is indicated by
Hue3 in his account of the plants brought back by the second French
Antarctic Expedition. The collection was an extremely favourable and
important one : great blocks of stone with their communities of lichens were
secured, and these blocks were entirely covered, the crustaceous species,
especially, spreading over every inch of space.
Hue determined 126 species, but as 15 of these came from the Magellan
regions only 1 1 1 were truly Antarctic. Of these 90 are new species, 29 of
them belonging to the genus Buellia. Hue considers, therefore, that in
Antarctica there is a flora that, with the exception of cosmopolitan species,
1 Elenkin 1906. 2 Darbishire 1905. 3 Hue 1915. 4 Darbishire 1912.
348 SYSTEMATIC
is different from every other, and is special to these southern regions. Dar-
bishire himself described 34 new Antarctic species, but only 10 of these
are from true Antarctica; the others were collected in South Georgia, the
Falkland Islands or Tierra del Fuego. Even though many species are
endemic in the south, the fact remains that a remarkable number of lichens
which occur intermediately on mountain summits are common to both Polar
areas.
C. LICHENS OF THE TEMPERATE ZONES
Regions outside the Polar Circles which enjoy, on the whole, cool moist
climates, are specially favourable to lichen growth, and the recorded numbers
are very large. The European countries are naturally those in which the
lichen flora is best known. Whereas polar and high Alpine species are
stunted in growth and often sterile, those in milder localities grow and fruit
well, and the more highly developed species are more frequent. Parmeliae,
Nephromae, Usneae and Ramalinae become prominent, especially in the
more northern districts. Many Arctic plants are represented on the higher
altitudes. A comparison has been made between the lichens of Greenland
and those of Germany: of 286 species recorded for the former country, 213
have been found in Germany, the largest number of species common to
both countries being crustaceous. Lindsay1 considered that Greenland
lichens were even more akin to those of Scandinavia.
There is an astonishing similarity of lichens in the Temperate Zone all
round the world. Commenting on a list of Chicago lichens by Calkins2,
Hue3 pointed out that with the exception of a few endemic species they
resemble those of Normandy. The same result appears in Bruce Fink's4
careful compilation of Minnesota lichens, which may be accepted as typical
of the Eastern and Middle States of North Temperate America. The
genera from that region number nearly 70, and only two of these, Omphalaria
and Heppia, are absent from our British Flora. The species naturally present
much greater diversity. Very few Graphideae are reported. In other States
of North America there occurs the singular aquatic lichen, Hydrothyria
venosa, nearly akin to Peltigera.
If we contrast American lichens with these collected in South Siberia
near Lake Baikal5, we recognize there also the influence of temperate
conditions. Several species of Usnea are listed, U. barbata, U. florida,
U. hirta and U. longissima, all of them also American forms, U. longissima
having been found in Wisconsin. Xanthoria parietina, an almost cosmo-
politan lichen, is absent from this district, and is not recorded from Minnesota.
The opinion6 in America is that it is a maritime species: Tuckerman gives
1 Lindsay 1870. 2 Calkins 1896. 3 Hue 1898. * Fink 1903.
5 Wainio 1896. 6 Comm. Heber Howe.
DISTRIBUTION 349
its habitat as "the neighbourhood of a great water," and reports it from
near Lake Superior. In our country it grows at a good distance from the
sea, in Yorkshire dales, etc., but all our counties would rank as maritime
in the American sense. Lecanora tartarea which is rare in Minnesota is also
absent from the Lake Baikal region. It occurs frequently both in Arctic
and in Antarctic regions, and is probably also somewhat maritime in habitat.
Many of the Parmeliae, NepJiromiae and Peltigerae, common to all northern
temperate climes, are Siberian as are also Cladoniae and many crustaceous
species. There is only one Sticta, St. Wrightii, a Japanese lichen, recorded
by Wainio from this Siberian locality.
A marked difference as regards species is noted between the Flora of
Minnesota and that of California. Herre1 has directed attention to the
great similarity between the lichens of the latter state and those of
Europe : many European species occur along the coast and nowhere else
in America so far as is yet known ; as examples he cites, among others,
Calicium hyperellum, Lecidea quernea, L. aromatica, Gyrophora polyrhiza,
Pertusaria amara, Roccella fuciformis, R. fucoides and R. tinctoria. The
Scandinavian lichen, Letharia vulpina, grows abundantly there and fruits
freely; it is very rare in other parts of America. Herre found, however,
no specimens of Cladonia rangiferina, Cl. alpestris or CL syhatica, nor
any species of Graphis\ he is unable to explain these anomalies in distri-
bution, but he considers that the cool equable climate is largely responsible:
it is so much more like that of the milder countries of Europe than of the
states east of the Sierra Nevada. His contention is supported by a con-
sideration of Japanese lichens. With a somewhat similar climate there is
a great preponderance of European forms. Out of 382 species determined
by Nylander2, 209 were European. There were 17 Graphideae, 31 Parmeliae,
and 23 Cladoniae, all of the last named being European. These results of
Nylander's accord well with a short list of 30 species from Japan compiled
by Muller3 at an earlier date. They were chiefly crustaceous tree-lichens;
but the Cladoniae recorded are the familiar British species Cl. fimbriata,
Cl. pyxidata and CL verticillata.
With the Japanese Flora may be compared a list4 of Maingay's lichens
from China, 35 in all. Collema limosum, the only representative of Colle-
maceae in the list, is European, as are the two species of Ramalina, R.graci-
lenta and R. pollinaria ; four species of Physcia are European, the remaining
Ph. picta being a common tropical or subtropical plant. Lecanora saxicola,
L. cinerea, Placodium callopismnm and PI. citrinum are cosmopolitan, other
Lecanorae and most of the Lecideae are new. Graphis scripta, Opegrapka
subsiderella and Arthonia cinnabarina— the few Graphideae collected— are
1 Herre 1910. 2 Nylander 1890. 3 Muller 1879.
4 Nylander and Cromhie 1884.
350 SYSTEMATIC
more or less familiar home plants. Among the Pyrenocarpei, Verrucaria
(Pyrenuld) nitida occurs ; it is a widely distributed tree-lichen.
It is unnecessary to describe in detail the British lichens. Some districts
have been thoroughly worked, others have barely been touched. The flora
as a whole is of a western European type showing the influence of the Gulf
Stream, though there is also a representative boreal growth on the moorlands
and higher hills, especially in Scotland. Such species as Parmelia pubescens,
P. stygia and P. alpicola recall the Arctic Circle while Alectoriae, Cetrariae
and Gyrophorae represent affinity with the colder temperate zone.
In the southern counties such species as Sticta aurata, S. damaecornis,
Phaeographis Lyellii and Lecanora (Lecanid) holophaea belong to the flora
of the Atlantic seaboard, while in S.W. Ireland the tropical genera Lepto-
gidium and Anthracothedum are each represented by a single species. The
tropical or subtropical genus Coenogonium occurs in Great Britain and in
Germany, with one sterile species, C. ebeneum. Enterographa crassa is
another of our common western lichens which however has travelled east-
wards as far as Wiesbaden. Roccella is essentially a maritime genus of
warm climates : two species, R.fuaformtsand R.fucoides, grow on our south
and west coasts. The famous R. tinctoria is a Mediterranean plant, though
it is recorded also from a number of localities outside that region and has
been collected in Australia.
In the temperate zones of the southern hemisphere are situated the great
narrowing projections of South Africa and South America with Australia and
New Zealand. As we have seen, the Antarctic flora prevails more or less in
the extreme southern part of America, and the similarity between the lichens
of that country and those of New Zealand is very striking, especially in the
fruticulose forms. There is a very abundant flora in the New Zealand
islands with their cool moist climate and high mountains. Churchill
Babington1 described the collections made by Hooker. Stirton2 added
many species, among others Calycidium cuneatum, evidently endemic. Later,
Nylander3 published the species already known, and Hellbom4 followed
with an account of New Zealand lichens based on Berggsen's collections ;
many more must be still undiscovered. Especially noticeable as compared
with the north, are the numbers of Stictaceae which reach their highest
development of species and individuals in Australasia. They are as numerous
and as prominent as are Gyrophoraceae in the north. A genus of Parmelia-
ceae, Hetorodea, which, like the Stictae, bears cyphellae on the lower surface,
is peculiar to Australia.
A warm current from the tropical Pacific Ocean passes southwards along
the East Coast of Australia, and Wilson6 has traced its influence on the
1 Babington 1855. 2 Stirton 1875. 3 Nylander 1888. 4 Hellbom 1896.
5 Wilson 1892.
DISTRIBUTION 351
lichens of Australia and Tasmania to which countries a few tropical species
of Graphis, Chiodecton and Trypethelium have migrated. Various unusual
types are to be found there also: the beautiful Cladonia retepora (Fig. 71),
which spreads over the ground in cushion-like growths, with the genera
Thysanothecium and Neophyllis, genera of Cladoniaceae endemic in these
regions.
The continent of Africa on the north and east is in so close connection
with Europe and Asia that little peculiarity in the flora could be expected.
In comparing small representative collections of lichens, 37 species from
Egypt and 20 from Palestine, Miiller1 found that there was a great affinity
between these two countries. Of the Palestine species, eight were cosmo-
politan ; among the crustaceous genera, Lecanorae were the most numerous.
There was no record of new genera.
The vast African continent — more especially the central region — has
been but little explored in a lichenological sense; but in 1895 Stizenberger2
listed all of the species known, amounting to 1 593, and new plants and new
records have been added since that day. The familiar genera are well
represented, Nephromium, Xanthoria, Physcia, Parmelia, Ranialina and
Roccella, some of them by large and handsome species. In the Sahara
Steiner' found that genera with blue-green algae such as the Gloeolichens
were particularly abundant ; Heppia and Endocarpon were also frequent.
Algeria has a Mediterranean Flora rather than tropical or subtropical.
Flagey4 records no species of Graphis for the province of Constantine, and
only 22 species of other Graphideae. Most of the 519 lichens listed by him
there are crustaceous species. South America stretches from the Tropics
in the north to Antarctica in the south. Tropical conditions prevail over
the central countries and tropical tree-lichens, Graphidaceae.Thelotremaceae,
etc. are frequent ; further West, on the Pacific slopes, Usneae and Ramalinae
hang in great festoons from the branches, while the foliose Parmeliae and
Stictae grow to a large size on the trunks of the trees.
Wainio's8 Lie/tens du Bresil is one of the classic systematic books and
embodies the writer's views on lichen classification. There are no new
families recorded though a number of genera and many species are new,
and, so far as is yet known, these are endemic. Many of our common forms
are absent ; thus Peltigera is represented by three species only, P. leptoderma,
P. spuriella and P. Americana, the two latter being new species. Sticta
(including Stictina) includes only five species, and Coenogonium three. There
are 39 species of P armelia with 33 of Lecanora and 68 of Lecidea, many of
them new species.
1 Miiller- Argau 1884. * Stizenberger 1888-1895. 3 Steiner 1895.
4 Flagey 1892. 5 Wainio 1890.
352 SYSTEMATIC
D. LICHENS OF TROPICAL REGIONS
In the tropics lichens come under the influence of many climates : on
the high mountains there is a region of perpetual snow, lower down a gradual
change to temperate and finally to tropical conditions of extreme heat, and,
in some instances, extreme moisture. There is thus a bewildering variety
of forms. By "tropical" however the warmer climate is always implied.
Several families and genera seem to flourish best in these warm moist
conditions and our familiar species grow there to a large size. Among
crustaceous families Thelotremaceae and Graphidaceae are especially abun-
dant, and probably originated there.. In the old comprehensive genus
Graphis, 300 species were recorded from the tropics. It should be borne in
mind that Trentepohlia, the alga that forms the gonidia of these lichens, is
very abundant in the tropics. Coenogonium, a genus containing about twelve
species and also associated with Trentepohlia, is scarcely found in Europe,
except one sterile species, C. ebenenm. Other species of the genus have been
recorded as far north as Algeria in the Eastern Hemisphere and Louisiana
in the Western, while one species, C. implexum, occurs in the southern
temperate zone in Australia and New Zealand.
Of exclusively tropical lichens, the Hymenolichens are the most note-
worthy. They include three genera, Cora, Corella and Dictyonema, the few
species of which grow on trees or on the ground both in eastern and western
tropical countries.
Other tropical or subtropical forms are Oropogon loxensis, similar to
Alectoria in form and habit, but with one brown muriform spore in the
ascus; it is only found in tropical or subtropical lands. Physcidia Wrightii
(Parmeliaceae) is exclusively a Cuban lichen. Several small genera of
Pyrenopsidaceae such asjenmania (British Guiana), Paulia (Polynesia) and
Phloeopeccania (South Arabia) seem to be confined to very hot localities.
On the other hand Collemaceae are rare : Wainio records from Brazil only
four species of Collema, with nine of Leptogium.
Among Pyrenolichens, Paratheliaceae, Mycoporaceae and Astrothe-
liaceae are almost exclusively of tropical distribution, and finally the leaf
lichens with very few exceptions. These follow the leaf algae, Mycoidea,
Phycopeltis, etc., which are so abundant on the coriaceous long-lived green
leaves of a number of tropical Phanerogams. All the Strigulaceae are
epiphytic lichens. Phyllophthalmaria (Thelotremaceae) is also a leaf genus;
one of the species, Ph. coccinea, has beautiful carmine-red apothecia. The
genera of the tropical family Ectolechiaceae also inhabit leaves, but they
are associated with Protococcaceae ; one of the genera Sporopodium1 is re-
markable as having hymenial gonidia. Though tropical in the main,
1 Wainio 1890, II. p. 27 (recorded under Lecided).
DISTRIBUTION 353
epiphyllous lichens may spread to the regions beyond: Sforopodium
Caucasium and a sterile Strigula were found by Elenkin and Woronichin1
on leaves of Buxus sempervirens in the Caucasus, well outside the tropics.
Pilocarpon, an epiphytic genus, is associated with Protococcaceae ; one
of the species, P. leucoblepharum, spreads from the bark to the leaves of pine-
trees ; it is widely distributed and has also been reported in the Caucasus".
Ckrysothrix, in which the gonidia belong to the algal genus Pa/mella, grows on
Cactus spines in Chili, and may also rank as a subtropical epiphyllous lichen.
A series of lichens from the warm temperate region of Transcaucasia
investigated by Steiner3 were found to be very similar to those of Central
Europe. Lecanoraceae were, however, more abundant than Lecideaceae
and Verrucariaceae were comparatively rare.
Much of Asia lies within tropical or subtropical influences. Several
regions have received some amount of attention from collectors. From
Persia there has been published a list of 59 species determined by Miiller4;
several of them are Egyptian or Arabian plants, 1 5 are new species, but the
greater number are European.
A small collection of 53 species from India, near to Calcutta, published
by Nylander5, included a new genus of Caliciaceae, Pyrgidium (P. bengalense),
allied to Sphinctrina. He also recorded Ramalina angulosa in African species,
along with R. calicaris, R. farinacea and Parmelia perlata, f. isidiophora,
which are British. Other foliose forms, Physcia picta, Pyxine Cocoes and
P. Meissnerii are tropical or subtropical ; along with these were collected
crustaceous tropical species belonging to Lecanorae, Lecideae, Graphideae, etc.
Leighton6 published a collection of Ceylon lichens and found that Gra-
phideae predominated. Nylander7 came to the same conclusion with regard
to lichens referred to him: out of 159 species investigated from Ceylon,
there were 36 species of Graphideae. In another list8 of Labuan, Singapore
and Malacca lichens, 164 in all, he found that 56 belonged to the Graphidei,
36 to Pyrenocarpei, 14 to Thelotremei and n to Parmelei; only 15 species
were European.
On the whole it is safe to conclude from the above and other publications
that the exceptional conditions of the tropics have produced many distinc-
tive lichens, but that a greater abundance both of species and individuals is
now to be found in temperate and cold climates.
III. FOSSIL LICHENS
In pronouncing on the great antiquity of lichens, proof has been adduced
from physiological rather than from phytogeological evidence. It would
have been of surpassing interest to trace back these plants through the ages,
1 Elenkin and Woronichin 1908. 2 Jaczewski 1904. 3 Steiner 1919. 4 MUller 1891.
5 Nylander 1867. 6 Leighton 1869. ' Nylander 1900. 8 Nylander 1891.
s. L. 23
354 SYSTEMATIC
even if it were never possible to assign to any definite period the first
symbiosis of the fungus and alga ; but among fossil plants there are only
scanty records of lichens and even these few are of doubtful determination.
The reason for this is fairly obvious : not only are the primitive thalline
forms too indistinct for recognizable preservation, but all lichens are charac-
terized by the gelatinous nature of the hyphal or of the algal membranes
which readily imbibe water. They thus become soft and flaccid and unfit
to leave any impress on sedimentary rocks. It has also been pointed out by
Schimper1 that while deciduous leaves with fungi on them are abundant in
fossil beds, lichens are entirely wanting. These latter are so firmly attached
to the rock's or trees on which they grow that they are rarely dislodged, and
form no part of wind- or autumn-fall. Trunks and branches of trees lose
their bark by decay long before they become fossilized and thus all trace of
their lichen covering disappears.
The few records that have been made are here tabulated in chronological
order:
1. PALAEOZOIC. Schimper decides that there are no records of lichens
in the earlier epochs. Any allusions2 to their occurrence are held to be ex-
tremely vague and speculative.
2. MESOZOIC. Braun3 has recorded a Ramalinites lacerns from the
Keuper sandstone at Eckersdorf, though later4 he seemed to be doubtful as
to his determination. One other lichen, an Opegrapha, has been described5
from the chalk at Aix.
3. CAINOZOIC. In the brown-coal formations of Saxony Engelhardt6
finds two lichens : Ramalina tertiaria, a much branched plant, the fronds
being flat and not channelled " and of further interest that it is attached to
a carbonized stem." The second form, Lichen dichotomies, has a dichoto-
mously branching strap-shaped frond. " There is sufficient evidence that
these fronds were cylindrical and that the width is due to pressure. In one
place a channel is visible, filled with an ochraceous yellow substance."
Other records on brown coal or lignite are : Verrncarites geanthricis"1
Goepp., somewhat similar to Pyrenida nitida, found at Muskau in Silesia ;
Opegrapha Thomasiana* Goepp., near to Opegrapha varm,a.nd Graphis scripta
succinea Goepp.9 on a piece of lignite in amber beds, all of them doubtful.
Schimper has questioned, as he well might, Ludwig's10 records from
lignite from the Rhein-VVetterau Tertiary formations ; these are : Cla-
donia rosea, Lichen albineus, L. diffissus and L. orbiculatus ; he thinks they
are probably fungus mycelia. Another lichen, a Parmelia with apothecia,
1 Schimper 1869, p. 145. 2 Lindsay 1879. :i Braun 1840. * Muenster 1846, p. 26.
5 Eltingshausen and Debey 1857. 6 Engelhardt 1870 (PI. I. figs, i and 2).
7 Goeppert 1845, p. 195. 8 See Schimper 1869, pp. 145, etc.
"Goeppert and Menge 1883, t. i, fig. 3. 10 Ludwig 1859, p. 61 (t. 9, figs. 1-4), 1859-61.
FOSSIL LICHENS 355
which recalls somewhat P. saxatilis or P. conspersa, collected by Geyler
also in the brown coal of Wetterau is accepted by Schimper1 as more trust-
worthy.
More authentic also are the lichens from the amber beds of Konigsberg
and elsewhere collected by Goeppert and others. These deposits are
Cainozoic and have been described by Goeppert and Menge2 as middle
Miocene. Schimper gives the list as: Parmelia lacnnosa Meng. and Goepp.,
fragments of thallus near to P. saxatilis; Sphaerophornscoralloides; Cladonia
divaricata Meng. and Goepp.; Cl. furcata; Ramalina calicaris \zrs.fraxinea
and canaliculata ; Cornicularia aculeata, C. subpubescens Goepp., C, ochroleiica,
C. succinea Goepp., and Usnea barbata var. hirta. Schimper rather deprecates
specific determinations when dealing with such imperfect fragments.
In a later work Goeppert and Menge2 state that they have found twelve
different amber lichens and that among these are Physcia ciliaris, Parmelia
physodes and Graphis (probably G. scripta succinea) along with Peziza retinae
which is more generally classified among lichens as Lecidea (Biatorelld}
resinae.
Another series of lichens found in recent deposits in North Europe has
been described by Sernander3as "subfossil." While engaged on the investi-
gations undertaken by the Swedish Turf-Moor Commission, he noted the
alternation of slightly raised Sphagnum beds with lower-lying stretches of
Calluna and lichen moor — in some instances dense communities of Cladonia
rangiferina. In time the turf-forming Sphagnum overtopped and invaded
the drier moorland, covering it with a new formation of turf. Beneath these
layers of " regenerated turf" were found local accumulations of blackened
remains of the Cladonia still recognizable by the form and branching. Some
specimens of Cetraria islandica were also determined.
Of especial lichenological interest in these northern regions was the
Calcareous Tufa or Calc-sinter in which Sernander also found subfossil
lichens — distinct impressions of Peltigera spp. and the foveolae of endolithic
calcicolous species.
In another category he has placed Ramalina fraxinea, Graphis sp. and
Opegrapha sp., traces of which were embedded with drift in the Tufa. In
the two Graphideae the walls of apothecia and pycnidia were preserved.
Sernander considers their presence of interest as testifying to warmer con-
ditions than now prevail in these latitudes.
' Schimper in Zittel 1890. 2 Goeppert and Menge 1883. 3 Sernander 1918.
23—2
CHAPTER IX
ECOLOGY
A. GENERAL INTRODUCTION
ECOLOGY is the science that deals with the habitats of plants and their
response to the environment of climate or of substratum. Ecology in the
lichen kingdom is habitat "writ large," and though it will not be possible in
so wide a field to enter into much detail, even a short examination of lichens
in this aspect should yield interesting results, especially as lichens have
never, at any time, been described without reference to their habitat. In
very early days, medicinal Usneas were supposed to possess peculiar virtues
according to the trees on which they grew and which are therefore carefully
recorded, and all down the pages of lichen literature, no diagnosis has been
drawn up without definite reference to the nature of the substratum. Not
only rocks and trees are recorded, but the kind of rock and the kind of tree
are often specified. The important part played by rock lichens in preparing
soil for other plants has also received much attention1.
Several comprehensive works on Ecology have been published in recent
times and though they deal mainly with the higher vegetation, the general
plan of study of land plants is well adapted to lichens. A series of definitions
and explanations of the terms used will be of service :
Thus in a work by Moss2 we read " The flora is composed of the indi-
vidual species: the vegetation comprises the groupings of these species into
ensembles termed vegetation units or plant communities." And again :
1. "A plant formation is the whole of the vegetation which occurs on
a definite and essentially uniform habitat." — All kinds of plants are included
in the formation, so that strictly speaking a lichen formation is one in which
lichens are the dominant plants. Cf. p. 394. The term however is very loosely
used in the literature. A uniform habitat, as regards lichens, would be that
of the different kinds of soil, of rock, of tree, etc.
2. "A. plant association is of lower rank than a formation, and is charac-
terized by minor differences within the generally uniform habitat." — It
represents a more limited community within the formation.
3. " A plant society is of lower rank than an association, and is marked
by still less fundamental differences of the habitat." — The last-named term
represents chiefly aggregations of single species. Moss adds that: ''plant
community is a convenient and general term used for a vegetation unit of
any rank."
Climatic conditions and geographical position are included in any con-
sideration of habitat, as lichens like other plants are susceptible to external
influences.
1 See p. 392. 2 Moss 1913.
GENERAL INTRODUCTION 357
Ecological plant-geography has been well defined by Macmillan1 as
"the science which treats of the reciprocal relation between physiographic
conditions and life requirements of organisms in so far as such relations
manifest themselves in choice of habitats and method of establishment
upon them... resulting in the origin and development of plant formations."
B. EXTERNAL INFLUENCES
The climatic factors most favourable to lichen development are direct
light (already discussed)2, a moderate or cold temperature, constant moisture
and a clear pure atmosphere. Wind also affects their growth.
a. TEMPERATURE. Lichens, as we have seen, can endure the heat of
direct sunlight owing to the protection afforded by thickened cortices, colour
pigments, etc. Where such heat is so intense as to be injurious the gonidia
succumb first:i.
Lichens endure low temperatures better than other plants, their xerophytic
structure rendering them proof against extreme conditions: the hyphae
have thick walls with reduced cell lumen and extremely meagre contents.
Freezing for prolonged periods does them little injury ; they revive again
when conditions become more favourable. Efficient protection is also afforded
by the thickened cortex of such lichens as exist in Polar areas, or at high
altitudes. Thus various species of Cetrariae with a stout "decomposed"
amorphous cortex can withstand very low temperatures and grow freely on the
tundra, while Cladonia rangiferina, also a northern lichen, but without a con-
tinuous cortex, cannot exist in such cold conditions, unless in localities where
it is protected by a covering of snow during the most inclement seasons.
b. HUMIDITY. A high degree of humidity is distinctly of advantage to
the growth of the lichen thallus, though when the moist conditions are ex-
cessive the plants become turgid and soredial states are developed.
The great abundance of lichens in the western districts of the British
Isles, where the rainfall is heaviest, is proof enough of the advantage of
moisture, and on trees it is the side exposed to wind and rain that is most
plentifully covered. A series of observations on lichens and rainfall were
made by West4 and have been published since his death. He has remarked
in more than one of his papers that a most favourable situation for lichen
growth is one that is subject to a drive of wind with much rain. In localities
with an average of 216 days of rain in the year, he found abundant and
luxuriant growths of the larger foliose species. In West Ireland there were
specimens oiRicasolia laetevirens measuring 1 65 by 60 cm. I n West Scotland
with an "average of total days of rain, 225," he found plants of Ricasolia am-
plissima 150 x 90 cm. in size, of R. laetevirens 120x90 cm., while Pertusaria
1 Macmillan 1894. - See p. 240 et seq. 3 See p. 238. 4 West 1915-
358 ECOLOGY
globulifera formed a continuous crust on the trees as much as 120 x 90 cm.
Lecanora tartarea seemed to thrive exceptionally well when subject to
driving mists and rains from mountain or moorland, and was in these cir-
cumstances frequently the dominant epiphyte. Bruce Fink1 also observed
in his ecological excursions that the number of species and individuals was
greater near lakes or rivers.
Though a fair number of lichens are adapted to life wholly or partly
under water, land forms are mostly xerophytic in structure, and die off if
submerged for any length of time. The Peltigerae are perhaps the most
hydrophilous of purely land species. Many Alpine or Polar forms are
covered with snow for long periods. In the extreme north it affords more
or less protection; and Kihlman2 and others have remarked on the scarcity
of lichens in localities denuded of the snow mantle and exposed to severe
winter cold. On the other hand lichens on the high Alpine summits that are
covered with snow the greater part of the year suffer, according to Nilson3,
from the excessive moisture and the deprivation of light. Foliose and
fruticose forms were, he found, dwarfed in size; the crustaceous species had
a very thin thallus and in all of them the colour was impure. Gyrophorae
seemed to be most affected : folds and outgrowths of the thallus were formed
and the internal tissues were partly disintegrated. Lichens on the blocks
of the glacier moraines which are subject to inundations of ice-cold water
after the snow has melted, were unhealthy looking, poorly developed and
often sterile, though able to persist in a barren state. Lindsay4 noted as
a result of such conditions on Cladoniae not only sterility but also de-.
formity both of vegetative and reproductive organs ; discolouration and
mottling of the thallus and an increased development of squamules of the
primary thallus and on the podetia.
c. WIND. Horizontal crustaceous or foliose lichens are not liable to
direct injury by wind as their close adherence to the substratum sufficiently
shelters them. It is only when the wind carries with it any considerable
quantity of sand that the tree or rock surfaces are swept bare and prevented
from ever harbouring any vegetation, and also, as has been already noted,
the terrible winds round the poles are fatal to lichens exposed to the
blasts unless they are provided with a special protective cortex. After
crustaceous forms, species of Cetraria, Stereocaulon and Cladonia are best
fitted for weathering wind storms: the tufted5 cushion-like growth adopted
by these lichens gives them mutual protection, not only against wind, but
against superincumbent masses of snow. Kihlman2 has given us a vivid
account of wind action in the Tundra region. He noted numerous hollows
completely scooped out down to the sand : in these sheltered nooks he
1 Fink 1894. 2 Kihlman 1890. 3 Nilson 1907.
4 Lindsay 1869. 6 Sattler 1914.
EXTERNAL INFLUENCES 359
observed the gradual colonization of the depressions, first by a growth of
hepatics and mosses and by such ground lichens as Peltigera canina, P.
aphthosa and Nephromium arcticum ; they cover the soil and in time the
hollow becomes filled with a mass of vegetation consisting of Cladonias,
mosses, etc. On reaching a certain more exposed level these begin to wither
and die off at the tips, killed by the high cold winds. Then arrives Lecanora
tartarea, one of the commonest Arctic lichens, and one which is readily
a saprophyte on decayed vegetation. It covers completely the mound of
weakened plants which are thus smothered and finally killed. The collapse
of the substratum entails in turn the breaking of the Lecanora crust, and
the next high wind sweeps away the whole crumbling mass. How long
recolonization takes, it was impossible to find out.
Upright fruticose lichens are necessarily more liable to damage by wind,
but maritime Ramalinae and Roccellae do not seem to suffer in temperate
climates, though in regions of extreme cold fruticose forms are dwarfed and
stunted. The highest development of filamentous lichens is to be found in
more or less sheltered woods, but the effect of wind on these lichens is not
wholly unfavourable. Observations have been made by Peirce1 on two
American pendulous lichens which are dependent on wind for dissemina-
tion. On the Californian coasts a very large and very frequent species,
Ramalina reticulata (Fig. 64), is seldom found undamaged by wind. In
Northern California the deciduous oaks Quercus alba and Q. Douglasii are
festooned with the lichen, while the evergreen " live oak," Q. chrysolepis,
with persistent foliage, only bears scraps that have been blown on to it.
Nearer the coast and southward the lichen grows on all kinds of trees and
shrubs. The fronds of this Ramalina form a delicate reticulation and when
moist are easily torn. In the winter season, when the leaves are off the
trees, wind- and rain-storms are frequent ; the lichen is then exposed to
the full force of the elements and fragments and shreds are blown to other
trees, becoming coiled and entangled round the naked branches and barky
excrescences, on which they continue to grow and fruit perfectly well.
A succeeding storm may loosen them and carry them still further. Peirce
noted that only plants developed from the spore formed hold-fasts and
they were always small, the largest formed measuring seven inches in length.
Both the hold-fast and the primary stalk were too slight to resist the tearing
action of the wind.
Schrenk2 made a series of observations and experiments with the lichens
Usneaplicata and U. dasypoga, long hanging forms common on short-leaved
conifers such as spruce and juniper. The branches of these trees are often
covered with tangled masses of the lichens not due to local growth, but to
wind-borne strands and to coiling and intertwining of the filaments owing
1 Peirce 1898. 2 Schrenk 1898.
360 ECOLOGY
to successive wetting and drying. Tests were made as to the force of wind
required to tear the lichens and it was found that velocities of 77 miles per
hour were not sufficient to cause any pieces of the lichen to fly off when it
was dry; but after soaking in water, the first pieces were torn off at 50 miles
an hour. These figures are, however, considered by Schrenk to be too high
as it was found impossible in artificially created wind to keep up the condi-
tion of saturation. It is the combination of wind and rain that is so effective
in ensuring the dispersal of both these lichens.
d. HUMAX AGENCY. Though lichens are generally associated with un-
disturbed areas and undisturbed conditions, yet accidents or convulsions of
nature, as well as changes effected by man, may at times prove favourable
to their development. The opening up of forests by thinning or clearing
will be followed in time by a growth of tree and ground forms; newly
planted trees may furnish a new lichen flora, and the building of houses
and walls with their intermixture of calcareous mortar will attract a par-
ticular series of siliceous or of lime-loving lichens. A few lichens are partial
to the trees of cultivated areas, such as park-lands, avenues or road-sides.
Among these are several species of Physcia : Ph. pulverulenta, Ph. ciliaris
and Ph. stellaris, some species of Placodinm, and those lichens such as
Lecanora varia that frequently grow on old palings.
On the other hand lichens are driven away from areas of dense popula-
tion, or from regions affected by the contaminated air of industrial centres.
In our older British Floras there are records of lichens collected in London
during the eighteenth century — in Hyde Park and on Hampstead Heath — but
these have long disappeared. A variety of Lecanora galactina seems to be
the only lichen left within the London district : it has been found at Camden
Town, Netting Hill and South Kensington.
So recently as 1866, Nylander1 made a list of the lichens growing in the
Luxembourg gardens in Paris; the chestnuts in the alley of the Observatory
were the most thickly covered, and the list includes about 35 different
species or varieties, some of them poorly developed and occurring but rarely,
others always sterile, but quite a number in healthy fruiting condition. All
of them were crustaceous or squamulose forms except Parmelia acetabulum,
which was very rare and sterile; Physcia obscura var. and Ph. pulverulenta
var., also sterile; Physcia stellaris with occasional abortive apothecia and
Xantlwria parietina, abundant and fertile. In 1898, Hue2 tells us, there
were no lichens to be found on the trees and only traces of lichen growth
on the stone balustrades.
The question of atmospheric pollution in manufacturing districts and its
effect on vegetation, more especially on lichen vegetation, has received
special attention from Wheldon and Wilson1 in their account of the lichens of
1 Nylander 1866. * Hue 1898. * Wheldon and Wilson 1915.
EXTERNAL INFLUENCES 361
South Lancashire, a district peculiarly suitable for such an inquiry,as nowhere,
according to the observations, are the evil effects of impure air so evident
or so wide-spread. The unfavourable conditions have prevailed for a long
time and the lichens have consequently become very rare, those that still
survive leading but a meagre existence. The chief impurity is coal smoke
which is produced not only from factories but from private dwellings, and
its harmful effect goes far beyond the limits of the towns or suburbs, lichens
being seen to deteriorate as soon as there is the slightest deposition of coal
combustion products — especially sulphur compounds — either on the plants
or on the surfaces on which they grow. The larger foliose and fruticose
forms have evidently been the most severely affected. "While genera of
bark-loving lichens such as Calicimn, Usnea, Ramalina, Grapliis, Opegrapha,
Arthonia etc. are either wholly absent or are poorly represented in the
district," corticolous species now represent about 15 per cent, of those that
are left; those that seem best to resist the pernicious influences of the smoky
atmosphere are, principally, Lecanora varia, Parmelia saxatilis,P.pJiysodes and
to a less degree P. sulcata, P.fuliginusa var. laetevirens and Pcrtusaria ainara.
Saxicolous lichens have also suffered severely in South Lancashire; not
only the number of species, but the number of individuals is enormously
reduced and the specimens that have persisted are usually poorly developed.
The smoke-producing towns are situated in thevalley-bottoms.andthe smoke
rises and drifts on to the surrounding hills and moorlands. The authors
noted that crustaceous rock-lichens were in better condition on horizontal
surfaces such as the copings of walls, or half-buried stones, etc. than on the
perpendicular or sloping faces of rocks or walls. This was probably due
to what they observed as to the effect of water trickling down the inclined
substrata and becoming charged with acid from the rock surfaces. They
also observed further that a calcareous substratum seemed to counteract the
effect of the smoke, the sulphuric acid combining with the lime to form
calcium sulphate, and the surface-washings thus being neutralized, the
lichens there are more favourably situated. They found in good fruiting
condition, on mortar, cement or concrete, the species Lecanora urbana,
L. campestris, L. crenulata, Verrncaria mitralis, V. rupestris, Thelidinin
microcarpum and StaurotJiele hymenogonia. Some of these occurred on the
mortar of sandstone walls close to the town, "whilst on the surface of the
sandstone itself no lichens were present."
Soil-lichens were also strongly affected, the Cladoniae of the moorlands
being in a very depauperate condition, and there was no trace of Stereocanlon
or of Sphatropliorns species, which, according to older records, previously
occurred on the high uplands.
The influence of human agency is well exemplified in one of the London
districts In 1883 Crombie published a list of the lichens recorded from
362 ECOLOGY
Epping Forest during the nineteenth century. They numbered 171 species,
varieties or forms, but, at the date of publication, many had died out owing
to the destruction of the older trees ; the undue crowding of the trees that
were left and the ever increasing population on the outskirts of the Forest.
Crombie himself made a systematic search for those that remained, and
could only find some 85 different kinds, many of them in a fragmentary or
sterile condition.
R. Paulson and P. Thompson1 commenced a lichen exploration of the
Forest 27 years after Crombie's report was published, and they have found
that though the houses and the population have continued to increase round
the area, the lichens have not suffered. " Species considered by Crombie as
rare or sterile are now fairly abundant, and produce numerous apothecia.
Such are Baeomyces rufus, B. roseus, Cladonia pyxidata, Cl. macilenta var.
coronata, Cl. Floerkeana f. trachypoda, Lecanora varia, Lecidea decolorant and
Lecidea tricolor? They conclude that "some at least of the Forest lichens
are in a far more healthy and fertile condition than they were 27 years ago."
They attribute the improvement mainly to the thinning of trees and the
opening up of glades through the Forest, letting in light and air not only to
the tree trunks but to the soil. In 191 22 the authors in a second paper
reported that 109 different kinds had been determined, and these, though
still falling far short of the older lichen flora, considerably exceed the list
of 85 recorded in 1883.
C. LICHEN COMMUNITIES
Lichen communities fall into a few definite groups, though, as we shall
see, not a few species may be found to occur in several groups — species
that have been designated by some workers as "wanderers." The leading
communities are :
1. ARBOREAL, including those that grow on leaves, bark or wood.
2. TERRICOLOUS, ground-lichens.
3. SAXICOLOUS, rock-lichens.
4. OMNICOLOUS, lichens that can exist on the most varied substrata, such
as bones, leather, iron, etc.
5. LOCALIZED COMMUNITIES in which owing to special conditions the
lichens may become permanent and dominant.
In all the groups lichens are more or less abundant. In arboreal and
terricolous formations they may be associated with other plants; in saxi-
colous and omnicolous formations they are the dominant vegetation. It will
be desirable to select only a few of the typical communities that have been
observed and recorded by workers in various lands.
1 Paulson and Thompson 191 1. * Paulson and Thompson 1917.
LICHEN COMMUNITIES 363
I. ARBOREAL
Arboreal communities may be held to comprise those lichens that grow
on wood, bark or leaves. They are usually the dominant and often the sole
vegetation, but in some localities there may be a considerable development
of mosses, etc., or a mantle of protococcaceous algae may cover the bark.
Certain lichens that are normally corticolous may also be found on dead
wood or may be erratic on neighbouring rocks : Usnea florida for instance
is a true corticolous species, but it grows occasionally on rocks or boulders
generally in crowded association with other foliose or fruticose lichens.
Most of the larger lichens are arboreal, though there are many excep-
tions : Parmelia perlata develops to a large size on boulders as well as on
trees ; some species of Ramalinae are constantly saxicolous while there are
only rare instances of Roccellae that grow on trees. The purely tropical or
subtropical genera are corticolous rather than saxicolous, but species that
have appeared in colder regions may have acquired the saxicolous habit :
thus Coenogonium in the tropics grows on trees, but the European species,
C. ebeneum, grows on stone.
a. EPIPHYLLOUS. These grow on Ferns or on the coriaceous leaves of
evergreens in the tropics. Many of them are associated with Phycopeltis,
Phyllactidium or Mycoidea, and follow in the wake of these algae. Obser-
vations are lacking as to the associations or societies of these lichens whether
they grow singly or in companies. The best known are the Strigulaceae :
there are six genera in that family, and some of the species have a wide
distribution. The most frequent genus is Strigula associated with Phyco-
peltis which forms round grey spots on leaves, and is almost entirely confined
to tropical regions. Chodat1 records a sterile species, 5. Buxi, on box leaves
from the neighbourhood of Geneva.
Other genera, such as those of Ectolechiaceae, which inhabit fern scales
and evergreen leaves, are associated with Protococcaceae. Pilocarpon leuco-
blepharum with similar gonidia grows round the base of pine-needles. It is
found in the Caucasus. In our own woods, along the outer edges, the lower
spreading branches of the fir-trees are often decked with numerous plants
of Parmelia physodes, a true " plant society," but that lichen is a confirmed
"wanderer." Biatorina Bouteillei, on box leaves, is a British and Continental
lichen.
b. CORTICOLOUS. In this series are to be found many varying groups,
the type of lichen depending more on the physical nature of the bark than
on the kind of trees. Those with a smooth bark such as hazel, beech, lime,
etc., and younger trees in general, bear only crustaceous species, many of
them with a very thin thallus, often partly immersed below the surface.
1 Chodat 1912.
364 ECOLOGY
As the trees become older and the bark takes on a more rugged character,
other types of lichens gain a foothold, such as the thicker crustaceous forms
like Pertusaria, or the larger foliose and fruticose species. The moisture that
is collected and retained by the rough bark is probably the important factor
in the establishment of the thicker crusts, and, as regards the larger lichens,
both rhizinae and hold-fasts are able to gain a secure grip of the broken-up
unequal surface, such as would be quite impossible on trees with smooth bark.
Among the first t6 pay attention to the ecological grouping of corticolous
lichens was A. L. Fee1, a Professor of Natural Science and an Army doctor,
who wrote on many literary and botanical subjects. In his account of the
Cryptogams that grow on "officinal bark," he states that the most lichenized
of all the Cimhotiae was the one known as " Loxa," the bark of which was
covered with species of Parmelta, Sticta and Usnea along with crustaceous
forms of Lecanora, Lecidea, Graphis and Verrucaria. Another species, Cin-
chona cordifolia, was completely covered, but with crustaceous forms only :
species of Graphidaceae, Lecanora and Lecidea were abundant, but Trype-
thelium, Chiodecton, Pyrenula and Verrucaria were also represented. On each
species of tree some particular lichen was generally dominant:
A species of Thelotrema on Cinchona oblongifolia.
A species of Chiodecton on C. cordifolia.
A species of Sarcographa on C. condaminea.
Fries2, in his geography of lichens, distinguished as arboreal and "hypo-
phloeodal" species of Verrucariaceae, while the Graphideae, which also grew
on bark, were erumpent. Usnea barbata, Evernia prunastri, etc., though grow-
ing normally on trees might, he says, be associated with rock species.
More extensive studies of habitat were made by Krempelhuber3 in his
Bavarian Lichens. In summing up the various "formations" of lichens, he
gives lists of those that grow, in that district, exclusively on either coniferous
or deciduous trees, with added lists of those that grow on either type of tree
indifferently. Among those found always on conifers or on coniferous wood
are : Letharia vulpina, Cetraria Laureri, Pannelia aleurites and a number of
crustaceous species. Those that are restricted to the trunks and branches of
leafy trees are crustaceous with the exception of some foliose Collemaceae
such as Leptogium Hildenbrandii, Collema nigrescens, etc.
Arnold4 carried to its furthest limit the method of arranging lichens
ecologically, in his account of those plants from the neighbourhood of
Munich. He gives " formation " lists, not only for particular substrata and
in special situations, but he recapitulates the species that he found on the
several different trees. It is not possible to reproduce such a detailed survey,
which indeed only emphasizes the fact that the physical characters of the
bark are the most important factors in lichen ecology: that on smooth bark,
1 Fee 1824. 2 Fries 1831. 3 Krempelhuber 1861. 4 Arnold 1891, etc.
LICHEN COMMUNITIES 365
whether of young trees, or on bark that never becomes really rugged, there
is a preponderance of species with a semi-immersed thallus, and very
generally of those that are associated with Trentepohlia gonidia, such as
Graphidaceae or Pyrenulaceae, though certain species of Lecidea, Lecanora
and others also prefer the smooth substratum.
Bruce Fink1 has published a series of important papers on lichen com-
munities in America, some of them similar to what we should find in the
British Isles.
On trees with smooth bark he records in the Minnesota district:
Xanthoria polycarpa.
Candelaria concolor.
Parmelia olivacea, P. adglutinata.
Placodium cerinum.
Lecanora subfusca.
Bacidia fusca-rubella.
Lecidea enteroleuca.
Graphis scripta.
Arlhonia lecideella, A. dispersa.
Arthopyrenia punctiformis, A.fallax.
Pyrenula nitida, P. thelena, P. cinerella, P. leucoplaca.
On rough bark he records :
Ramalina calicaris, R. fraxinea, R . fastigiata.
Teloschistes chrysophthalmus.
Xanthoria polycarpa, X. lychnea.
Candelaria concolor.
Parmelia perforata, P. crinita, P. Borreri, P. tiliacea, P. saxatilis, P. caperata.
Physcia granulifera, Ph. pul-verulenta, Ph. stellaris, Ph. tnbacia, Ph. obscura.
Collema pycnocarpum, C. flaccidum.
Leptogium mycochroum.
Placodium aurantiacum, PL cerinum.
Lecanora subfusca.
Perlusaria leioplaca, P. velata.
Bacidia rubella, B . fuscorubella.
Leddea enteroleuca.
Rhizocarpon alboatrum, Buellia parasema.
Opegrapha varia.
Graphis scrip ta.
Arthonia lecideella, A. radiata.
A>'thopyrenia quinqueseplata, A. macrospora.
Pyrenula nitida, P. leucoplaca.
Finally, as generally representative of the commonest lichens in our
woods of deciduous trees, including both smooth- and rough-barked, the com-
munity of oak-hazel woods as observed by Watson2 in Somerset maybequoted:
Collema flaccidum.
Calicium hyperellutn.
i Fink 1902. * Watson 1909.
366 ECOLOGY
Ramalina calicaris, R. fraxinea with var. ampliata, R. fastigiata, R. farinacea and
R. pollinaria.
Parmelia saxatilis and f. furfuracea, P. caperata, P. physodes.
Physcia pulverulenta, Ph. tenella (hispida).
Lecanora subfusca, L. rugosa.
Pertusaria amara, P. globulifera, P, communis, P. Wuljenii.
Lecidea (Buellia} canescens.
Graphis scripta.
And on the soil of these woods :
Cladonia pyxidata, Cl. pungens, Cl. macilenta, Cl, pityrea, Cl. squamosa and Cl.
sylvatica.
Paulson1, from his observations of lichens in Hertfordshire, has concluded
that the presence or absence of lichens on trees is influenced to a consider-
able degree by the nature of the soil. They were more abundant in woods
on light well-drained soils than on similar communities of trees on heavier soils,
though the shade in the former was slightly more dense and therefore less
favourable to their development; the cause of this connection is not known.
c. LlGNICOLOUS. Lichens frequenting the branches of trees do not long
continue when these have fallen to the ground. This may be due to the
lack of light and air, but Bouly de Lesdain2 has suggested that the chemical
reactions produced by the decomposition of the bast fibres are fatal to them,
Lecidea parasema alone continuing to grow and even existing for some time
on the detached shreds of bark.
On worked wood, such as old doors or old palings, light and air are well
provided and there is often an abundant growth of lichens, many of which
seem to prefer that substratum : the fibres of the wood loosened by weathering
retain moisture and yield some nutriment to the lichen hyphae which burrow
among them. Though a number of lichens grow willingly on dead wood,
there are probably none that are wholly restricted to such a habitat. A few,
such as the species of Coniocybe, are generally to be found on dead roots of
trees or creeping loosely over dead twigs. They are shade lichens and fond
of moisture.
The species on palings — or " dead wood communities " — most familiar
to us in our country are :
Usnea hirta. Rinodina exigua.
Cetraria diffusa. Lecanora ff agent, L. varia and its allies.
Evernia furfuracea. Lecidea osfreata, L. parasema.
Parmelia scortia, P. physodes. Buellia myriocarpa.
Xanlhoria parietina. Cladoniaceae and Caliciaceae (several species).
Placodium cerinum.
These may be found in very varying association. It has indeed been
remarked that the dominant plant may be simply -the one that has first
1 Paulson 19 r9- 2 Lesdain 1912.
LICHEN COMMUNITIES 367
gained a footing, though the larger and more vigorous lichens tend to crowd
out the others. Bruce Fink1 has recorded associations in Minnesota :
On wood :
Teloschistes chrysophthalmus. Buellia parasema (disciformis\ B. turgescens.
Placodium cerinum. Calicium parietinum.
Lecanora Hagem, L. varia. Thelocarpon prasinellum.
Rinodina sophodes, R. exigua.
On rotten stumps and prostrate logs : Peltigera canina. Cladonia fim-
briata var. tubaeformis, Cl. gracilis, Cl. verticillata. CL symphicarpia, Cl.
macilenta, Cl. cristatella.
Except for one or two species such as Buellia turgescens, Cladonia sym-
phicarpia, etc., the associations could be easy paralleled in our own country,
though with us Peltigera canina, Cladonia gracilis and Cl. verticillata are
ground forms.
2. TERRICOLOUS
In this community other vegetation is dominant, lichens are subsidiary.
In certain conditions, as on heaths, they gain a permanent footing, in others
they are temporary denizens and are easily crowded out. As they are
generally in close contact with the ground they are peculiarly dependent
on the nature of the soil and the water content. There are several distinct
substrata to be considered each with its characteristic flora. Cultivated soil
and grass lands need scarcely be included, as in the former the processes of
cultivation are too harassing for lichen growth, and only on the more perma-
ment somewhat damp mossy meadows do we get such a species as Peltigera
canina in abundance. Some of the earth-lichens are among the quickest
growers : the apothecia of Baeomyces rosens appear and disappear within a
year. Thrombium epigaeum develops in half a year; Thelidium mtnutulum
in cultures grew from spore to spore, according to Stahl2, in three months.
There are three principal types of soil composition: (i) that in which
there is more or less of lime; (2) soils in which silica in some form or other
predominates, and (3) soils which contain an appreciable amount of humus.
Communities restricted to certain soils such as sand-dunes, etc., are
treated separately.
a. ON CALCAREOUS SOIL. Any admixture of lime in the soil, either as
chalk, limy clay or shell sand is at once reflected in the character of the
lichen flora. On calcareous soil we may look for any of the squamulose
Lecanorae or Lecideae that are terricolous species, such as Lecanora crassa,
L. lentigera, Placodium fulgens, Lecidea lurida and L. decipiens. There are
also the many lichens that grow on mortar or on the accumulated debris
mixed with lime in the crevices of walls, such as Biatorina coeruleonigricans,
species of Placodium, several species of Collema and of Verrucariaceae.
1 Fink 1896, etc. 3 Stahl 1877.
368 ECOLOGY
Bruce Fink1 found in N.W. Minnesota an association on exposed cal-
careous earth as follows :
Heppia Despreauxii. Biatora (Bacidia] muscorum.
Urceolaria scruposa. Dermatocarpon hepaticum.
Biatora (Lecidea} decipiens.
This particular association occupied the slope of a hill that was washed
by lime-impregnated water. It was normally a dry habitat and the lichens
were distinguished by small closely adnate thalli.
There are more lichens confined to limy than to sandy soil. Arnold'2
gives a list of those he observed near Munich on the former habitat :
Cladonia sylvatica f. alpestris. Urceolaria scruposa f. argillacea.
Cladonia squamosa f. subsquamosa. Verrucatia (Thrombium) epigaea.
Cladonia rangiformis f. foliosa. Lecidea decipiens.
Cladonia cariosa and f. sympkicarpa. Dermatocarpon cinereum.
Peltigera canina f. soreumatica. Collema granulatum.
Solorina spongiosa. Collema tenax.
Heppia virescens. Leptogium byssinum.
Lecanora crassa.
It is interesting to note how many of these lichens specialized as to
habitat are forms of species that grow in other situations.
b. ON SILICEOUS SOIL. Lichens are not generally denizens of cultivated
soil ; a few settle on clay or on sand-banks. Cladonia fimbriata and Cl.
pyxidata grow frequently in such situations ; others more or less confined to
sandy or gravelly soil are, in the British Isles :
Baeomyces roseus. Gongylia -viridis.
Baeomyces rufus. Dermatocarpon lachneum.
Baeomyces placophyllus. Dermatocarpon hepaticum.
Endocarpon spp. Dermatocarpon cinereum.
These very generally grow in extended societies of one species only.
In his enumeration of soil-lichens Arnold2 gives 40 species that grow on
siliceous soil, as against 57 on calcareous. Many of them occurred on both.
Those around Munich on siliceous soil only were :
Cladonia cocci/era. Baeomyces rufus.
Cladonia agaridformis. Ler.idea gelatinosa.
Secoliga (Gyalecta) bryophaga. Psorotichia lutophila.
Mayfield3 in his account of the Boulder Clay lichen flora of Suffolk found
only four species that attained to full development on banks and hedgerows.
These were: Collema pidposum, Cladonia pyxidata, Cl. furcata var. corymbosa
and Peltigera polydactyla.
1 Fink 1902, etc. 2 Arnold 1891. s Mayfield 1916.
LICHEN COMMUNITIES 369
On bare heaths of gravelly soil in Epping Forest Paulson and Thompson1
describe an association of such lichens as :
Baeotnyces roseus. Cladonia macilenta.
Baeomyces rufus. Cladonia furcata.
Pycnothelia papillaria. Cetraria aculeata.
Cladonia coccifera. Peltigera spuria.
Lee idea granulosa.
And on flints in the soil : Lecidca crustnlata and Rhizocarpon confer-
voides. They found that Peltigera spuria colonized very quickly the burnt
patches of earth which are of frequent occurrence in Epping Forest, while
on wet sandy heaths amongst heather they found associated Cladonia syl-
vatica f. tennis and Cl. finibriata subsp. y^w/<7.
c. ON BRICKS, ETC. Closely allied with siliceous soil-lichens are those
that form communities on bricks. As these when built into walls are more
or less smeared with mortar, a mixture of lime-loving species also arrives.
Roof tiles are more free from calcareous matter. Lesdain2 noted that on
the dunes, though stray bricks were covered by algae, lichens rarely or never
seemed to gain a footing.
There are many references in literature to lichens that live on tiles.
A fairly representative list is given by Lettau3 of" tegulicolous " species.
Verrucaria Jiigrescens. Placodium elegans.
Lecidea coarctata. Placodium inurorum.
Candelariella iiitellina. Xantlwria parietina.
Lecanora dispersa. Rhizocarpon alboatrum var.
Lecanora galactina. Buellia myriocarpa.
Lecanora Hageni. Lecidea detnissa.
Lecanora saxicola. Physcia ascendens.
Parmelia conspersa. Physcia caesia.
Placodiuni teicholyttim. Physcia obscura.
Placodium pyraceuni. Physcia sciastrella.
Placodiuni decipiens.
Several of these are more or less calcicolous and others are wanderers,
indifferent to the substratum. Though certain species form communities on
bricks, tiles, etc., none of them is restricted to such artificial substrata.
d. ON HUMUS. Lichens are never found on loose humus, but rocks or
stumps of trees covered with a thin layer of earth and humus are a favourite
habitat, especially of Cladoniae. One such " formation " is given by Bruce
Fink4 from N. Minnesota ; with the exception of Cladonia cristatclla, the
species are British as well as American :
Cladonia furcata. Cladonia rangiferina.
Cladonia crisiatella. Cladonia untialis.
Cladonia gracilis. Cladonia alpestris.
Cladonia verticillata. Cladonia turgida.
1 Paulson and Thompson 1913. 2 Lesdain 1910-. 3 Lettau 1911, 4 Fink 1903.
S. L. 24
370 ECOLOGY
Cladonia cocci/era. Peltigera malacea.
Cladonia pyxidata. . Peltigera canina.
Cladonia fimbriata. Peltigera aphthosa.
e. ON PEATY SOIL. Peat is generally found in most abundance in
northern and upland regions, and is characteristic of mountain and moor-
land, though there are great moss-lands, barely above sea-level, even in our
own country. Such soil is of an acid nature and attracts a special type of
plant life. The lichens form no inconsiderable part of the flora, the most
frequent species being members of the Cladoniaceae.
The principal crustaceous species on bare peaty soil in the British Isles
are Lecidea uliginosa and L.granulosa. The former is not easily distinguish-
able from the soil as both thallus and apothecia are brownish black. The
latter, which is often associated with it, has a lighter coloured thallus and
apothecia that change from brick-red to dark brown or black ; Wheldon
and Wilson1 remarked that after the burning of the heath it was the first
vegetation to appear and covered large spaces with its grey thallus. Another
peat species is Icuiadophila ericetorum, but it prefers damper localities than
the two Lecideae.
To quote again from Arnold2: 24 species were found on turf around
Munich, 13 of which were Cladoniae, but only four species could be con-
sidered as exclusively peat-lichens. These were:
Cladonia Floerkeana. Thelocarpon turficolum.
Biatora terricola. Geisleria sychnogonioides.
The last is a very rare lichen in Central Europe and is generally found
on sandy soil. Arnold considered that near Munich, for various reasons,
there was a very poor representation of turf-lichens.
f. ON MOSSES. Very many lichens grow along with or over mosses,
either on the ground, 'on rocks or on the bark of trees, doubtless owing to
the moisture accumulated and retained by these plants. Besides Cladoniae
the commonest " moss " species in the British Isles are Bilimbia sabulosa,
Bacidia muscormn, Rinodina Conradi, Lecidea sanguineoatra, Pannaria
brunnea, Psoroma hypnorum and Lecanora tartarea, with species of Collema
and Leptogium and Diploschistes bryopJiilus.
Wheldon and Wilson3 have listed the lichens that they found in Perth-
shire on subalpine heath lands, on the ground, or on banks amongst mosses:
Leptogrum spp. Lecidea granule sa.
Peltigera spp. Lecidea uliginosa.
Cetraria spp. Lecidea neglecta.
Parmelia physodes. Bilimbia sabulosa.
Psoroma hypnorum. Bilimbia ligniaria.
Lecanora epibryon. Bilimbia melaena.
Lecanora tartarea. Baeomyces spp.
Lecidea coarctata. Cladonia spp.
1 Wheldon and Wilson 1907. 2 Arnold 1892, p. 34. s Wheldon and Wilson 1915.
LICHEN COMMUNITIES 371
As already described Lecanora tartarea* spreads freely over the mosses
of the tundra. Aigret2 in a study of Cladoniae notes that Cl. pyxidata, var.
neglecta chooses little cushions of acrocarpous mosses, which are particularly
well adapted to retain water. CL digitata, CLflabelliformis and some others
grow on the mosses which cover old logs or the bases of trees.
g. ON FUNGI. Some of the fungi, such as Polyporei, are long lived, and
of hard texture. On species of Lensitcs in Lorraine, Kieffer3 has recorded
15 different forms, but they are such as naturally grow on wood and can
scarcely rank as a separate association.
3. SAXICOLOUS
Lichens are the dominant plants of thisv and the following formations,
they alone being able to live on bare rock ; only when there has been formed
a nidus of soil can other plants become established.
a. CHARACTERS OF MINERAL SUBSTRATA. It has been often observed
that lichens are influenced not only by the chemical composition of the
rocks on which they grow but also by the physical structure. Rocks that
weather quickly are almost entirely bare of lichens : the breaking up of the
surface giving no time for the formation either of thallus or fruit. Close-
grained rocks such as quartzite have also a poor lichen flora, the rooting
hyphae being unable to penetrate and catch hold. Other factors, such as
incidence of light, and proximity of water, are of importance in determining
the nature of the flora, even where the rocks are of similar formation.
b. COLONIZATION ON ROCKS. When a rock surface is laid bare it
becomes covered in time with lichens, and quite fresh surfaces are taken
possession of preferably to weathered surfaces4. The number of species is
largest at first and the kind of lichen depends on the flora existing in the
near neighbourhood. Link5, for instance, has stated that Lichen candelarius
was the first lichen to appear on the rocks he observed, and, if trees were
growing near, then Lichen parietinus and Lichen tenellus followed soon after.
After a time the lichens change, the more slow-growing being crowded out
by the more vigorous. Crustaceous species, according to Malinowski8, are
most subject to this struggle for existence, and certain types from the nature
of their thallus are more easily displaced than others. Those with a deeply
cracked areolated thallus become disintegrated in the older central areas by
repeated swelling and contracting of the areolae as they change from wet
to dry conditions. Particles of the thallus are thus easily dislodged, and
bare places are left, which in time are colonized again by the same lichen
or by some invading species. There may result a bewildering mosaic of
1 See p. 358. 2 Aigret 1901. 8 Kieffer 1894. 4 Stahlecker 1906.
8 Link 1795. ° Malinowski 1911.
24—2
372 ECOLOGY
different thalli and fruits mingling together. Some forms such as Rhizo-
carpum geographicum which have a very close firm thallus do not break away.
In the course of time lichen communities come and go, and the plants of
one locality may be different from those of another for no apparent reason.
The question of colonization1 was studied by Bruce Fink2 on a "riprap"
wall of quartz, 30 years old, built to protect and brace a railway in Iowa.
Nearby was a grass swamp which supplied moisture especially to the lower
end of the wall. A few boulders were present in the vicinity, but the nearest
lichen "society" was on trees about 150 metres away and these bore corti-
colous Parmelias, Physcias, Ramalinas,Placodiums, Lecanoras and Rinodines
which were only very sparingly represented on the riprap. Moisture-loving
species never gained a footing; the extreme xerophytic conditions were
evidenced by the character of the lichens, Biatora myriocarpoides (Lecidea
sylvicola) occupying the driest parts of the wall. Lower down where more
moisture prevailed Bacidia inundata and Stereocaulon paschale were the
dominant species. Some 30 species or forms were listed of which 1 1 were
Cladonias that grew mainly on debris from the disintegration of the wall.
With the exception of two or three species the number of individuals was
very small.
Some of these lichens had doubtless come from the boulders, others from
the trees ; the Cladonias were all known to occur within a few miles, but
most of the species had been wind-borne from some distance. The Stereo-
caulon present did not exist elsewhere in Iowa ; it had evidently been
brought by the railroad cars, possibly on telegraph poles.
A similar wall on the south side of the railway, subject to even more
xerophytic conditions but with less disintegration of the surface, had a larger
number of individuals though fewer species. Only one Cladonia and one
Parmelia had gained a footing, the rest were crustaceous, Buellia myriocarpa
being one of the most frequent.
There are two types of rock of extreme importance in lichen ecology:
those mainly composed of lime (calcareous), and those in which silica or
silicates preponderate (siliceous). They give foothold to two corresponding
groups of lichen communities, calcicolous and silicicolous.
c. CALCICOLOUS. The pioneer in this section of lichen ecology is
H. F. Link, who was a Professor of Natural Science and Botany at Rostock,
then at Breslau, and finally in Berlin. He3 published in 1789, while still at
Rostock, an account of limestone plants in his neighbourhood, most of them
being lichens. In a later work he continues his Botanical Geography or
" Geology " and gives more precise details as to the plants, some of which
are essentially calcicolous though many of them he records also on siliceous
rocks.
1 See also p. 254. 2 Fink 1904. 3 Link 1789.
LICHEN COMMUNITIES 373
Most calcicolous lichens are almost completely dependent on the lime
substratum which evidently supplies some constituent that has become
necessary to their healthy growth. Calcareous rocks are usually of softer
texture than those mainly composed of silica, and not only the rhizoidal
hyphae but the whole thallus — both hyphae and gonidia— may be deeply
embedded. Only the fruits are visible and they are, in some species, lodged
in tiny depressions (foveolae) scooped out of the surface by the lichen-acids
acting on the easily dissolved lime.
Those obligate lime species may be found in associations on almost any
calcareous rock. Watson1 has given us a list of species that inhabit carboni-
ferous limestone in Britain. Wheldon and Wilson2 have described in West
Lancashire the "grey calcareous rocks blotched with black patches of Pan-
narias (Placynthium nigruni) and Verrucarias, or dark gelatinous rosettes of
Collemas. White and grey Lecanorae and Verrucariae spread extensively,
some of them deeply pitting the surface. These more sombre or colourless
species are enlivened by an intermixture of orange-yellow Physciae (Xan-
tJioriae) and Placodii by the ochrey films of Lecanora ochracea and lemon-
yellow Q{ Lecanora xantholyta. Amongst the greenish scaly crusts of Lecanora
crassa may be seen the bluish cushions of Lecidca coeruleo-nigricans, the
whole forming an exquisite blend of tints."
The flora recorded by Flagey3 on the cretaceous rocks of Algeria in the
Province of Constantine does not greatly differ, some of the species being
identical with those of our own country. Placodiums and Rinodinas were
abundant, as also Lecanora calcarea, Acarospora percaenoides and Urceolaria
actinostoma var. calcarea. Also a few Lecideae along with Verrucaria
lecideoides, V. fuscella, V. calciseda and Rndocarpon monstrosum. The rocks
of that region are sometimes so covered with lichens that the stone is no
longer visible.
Bruce Fink4 gives a typical community on limestone bluffs in Minnesota:
Pannaria (Placynthiuni) nigra. Placodium citrinnm.
Crocynia lanuginosa. Bacidia inundata.
Omphalaria pulvinata. Rhizocarpon alboatrum var.
Collema plicatile. Dennatocarpon miniatum.
Collema pustulatum. Staurothele itmbrinum.
Leptogium laceriim.
Forssell5 pointed out an interesting selective quality in the Gloeolichens
which are associated with the gelatinous algae, Chroococcns, Gloeocapsa and
Xanthocapsa. The genera containing the two former grow on siliceous rocks
with the exception of Synalissa. The genera Omphalaria, Peccania, Anema,
Psorotichia and Enchylium, in which Xanthocapsa is the gonidium, grow on
1 Watson iQiS2. 2 Wheldon and Wilson 1-907. 3 Flagey i9Ot.
4 Bruce Fink ios2. 8 Forssell 1885.
374 ECOLOGY
calcareous rocks. Collemopsidinm is the only Xanthocapsa associate that is
silicicolous.
d. SILICICOLOUS. There is greater variety in the mineral composition
and in the nature of the surface in siliceous than in calcareous rocks ; they are
also more durable and give support to a large number of slow-growing forms.
Silicon enters into the composition of many different types, from the
oldest volcanic to the most recent of sedimentary rocks. Some of these are
of hard unyielding surface on which only a few lichens are able to attach
themselves. Such a rock is instanced by Servit1 as occurring in Bohemia,
and is known as Lydite or Lydian stone, a black flinty jasper. The associa-
tion of lichens on this smooth rock was almost entirely Acarospora chloro-
phana and Rinodina oreina, which as we shall see occur again as a "desert"
association in Nevada; these two lichens grow equally well in sun or shade,
and either sheltered or exposed as regards wind and rain. Acarospora chloro-
phana, according to Malinowski2, arrives among the first on rocks newly
laid bare, and forms large societies, though in time it gives place to Lecanora
glaucoma (L. sordida}, a common silicicolous lichen.
A difference has been pointed out by Bachmann3 between the lichens
of acid and of basic rocks. The acid series, such as quartz- and granite-
porphyry, contain 70 per cent, and more of oxide of silica; the basic — diabase
and basalt — not nearly 50 per cent. He observed that Rhizocarpon geographi-
cum was the most frequent lichen of the acid porphyry, while on basalt there
were only small scattered patches. Pertusaria corallina was abundant only
on granitic rocks. On the other hand Pertusaria lactea f. cinerascens, Diplo-
scJiistes scruposus, D. bryophilus and Buellia leptodine preferred the basic sub-
stratum of diabase and basalt. In this case it is the chemical rather than the
physical character of the rocks that affects the lichen flora, as porphyry and
basalt are both close-grained, and are outwardly alike except in colouration.
Other rocks, such as granite, in which the different crystals, quartz, mica
and felspar are of varying hardness, are favourite habitats as affording not
only durability but a certain openness to the rhizoidal hyphae, though in
Shetland, West4 found the granitic rocks bare owing to their too rapid
weathering. In these rocks the softer basic constituents such as the mica are
colonized first; the quartz remains a long time naked, though in time it
also is covered. Wheldon and Wilson5 point out that the sandstone near to
intrusive igneous rocks has become close-grained and indurated and bears
Lecanora squamulosa, L. picea, Lecidea rivulosa and Rhizocarpon petraeum,
which were not seen on the unaltered sandstone. It was also observed by
Stahlecker6, that, in layered rocks, the lichen chose the surface at right
angles to the layering as the hyphae thus gain an easier entrance.
1 Servit 1910. 2 Malinowski 1911. 3 Bachmann 1914. 4 West 1912.
° Wheldon and Wilson 1913. 6 Stahlecker 1906.
LICHEN COMMUNITIES
375
It will only be possible to give a few typical associations from the many
that have been published. Crustaceous forms are the most abundant.
On granite and on quartzite not disintegrated Malinowski1 listed :
Acarospora chlorophana. Lecidea tumida.
Lecanora glaucoma. Biatorella sporostatia.
Rhizocarpon mridiatrum. Biatorella testudinea.
On granite and quartzite disintegrated :
Aspicilia cinerea.
Aspicilia gibbosa.
Aspicilia tenebrosa.
Buellia coracina.
Catillaria (Biatorina) Hochstetteri.
Rhizocarpon petraeum.
Rhizocarpon geographicum vars.
Biatorella cinerea.
Lecanora badia.
Lecanora ccnisia.
Lecidea confluens.
Lecidea f us coat r a.
Lecidea platycarpa.
Lecidea lapicida.
Hacmiitonnna ventosum.
On these disintegrated rocks there is a constant struggle for existence
between the various species ; the victorious association finally consists of
Lecanora badia, L. cenisia and Lecidea confluens with occasional growths of
the following species :
Aspicilia cinerea. Biatorella cinerea.
Haematonnna -ventosum. Lecidea platycarpa.
Rhizocarpon geographicum vars.
A number of rock associations have been tabulated by Wheldon and
Wilson2 for Perthshire. Among others they give some of the most typical
lichens on granitic and eruptive rocks :
Sphaerophorus coralloides. Gyrophora ftocculosa.
Sphaerophorits fragilis. Lecanora gelida.
Platysma Fahlunense. Lecanora atra.
Platysma commixtum. Lecanora badia.
Platysma glaucnm. Lecanora far/area.
Platysma lacunosum.
Parmelia saxatilis.
Parmelia omphalodes.
Parmelia Mougeotii.
Parmelia stygia.
Parmelia tristis.
Parmelia Ian at a.
Gyrophora proboscidea.
Gyrophora cylindrica.
Gyrophora torrefacta.
Gyrophora polyphylla.
Lecanora parella.
Lecanora ventosa.
Lecanora Dicksonii.
Lecanora cinerea.
Lecanora peliocyplia.
Pertitsaria dealbata.
Stereocaulon Delisei.
Stereocaulon evolution.
Stereocaulon coralloides.
Stereocaulon denudatum.
Psorotichia lugubris.
Lecidea insercna.
Lecidea panaeola.
Lecidea contigna.
Lecidca confluens.
Lecidca lapicida.
Lecidea plana.
Lecidea mesotropa.
Lecidea auriculata.
Lecidea didncens.
Lecidea aglaea.
Lecidea rhntlosa.
Lecidea Kochiana.
Lecidea pycnocarpa.
Buellia atrata.
Rhisocarpon Oederi.
On siliceous rocks in West Lancashire the same authors3 depict the
lichen flora as follows: "There are many grey Parmcliae and Cladoniae
1 Malinowski 1911. 2 Wheldon and Wilson 1915. 3 Wheldon and Wilson 1907.
376 ECOLOGY
with coral-like Sphaerophorei on the rocks, and on the walls smoky-looking
patches of Parmelia fuliginosa and ragged fringes of Platysma glaucum and
Evernia furfuracea. On the higher scars, flat topped tabular blocks exhibit
black scaly Gyrophoreae, dingy green Lecidea (Rhizocarpon) viridiatra and
mouse-coloured L. rivulosa. Suborbicular (whitish) patches of Pertusaria
lactea and P. dealbata enliven the general sadness of tone, and everywhere
loose rocks and stones are covered with the greyish-black spotted thallus
of Lecidea contigua."
On the Silurian series of rocks in the same district they describe a
somewhat brighter coloured flora: "First Stereocaulons invite attention,
and greenish or yellowish shades are introduced by an abundance of Lecanora
sulphured, L. polytropa, Rhizocarpon geographicmn and Parmelia conspersa,
often beautifully commingled with grey species such as Lecidea contigua
and L. stellulata, and reddish angular patches of Lecanora Dicksonii. Also
an abundance of orbicular patches of Haematomma ventosum with its
reddish-brown apothecia." A brightly coloured association on the cretaceous
sand-rocks of Saxon Switzerland has been described as "Sulphur lichens."
These have recently1 been determined as chiefly Lepraria chlorina, in less
abundance Lecidea lucida and Calicium arenarium, with occasional growths
of Coniocybe furfiiracea and Calicium corynellum.
4. OMNICOLOUS LICHENS
Some account must be taken in any ecological survey of those lichens
that are indifferent to substrata. Certain species have become so adapted to
some special habitat that they never or rarely wander ; others, on the con-
trary, are true vagabonds in the lichen kingdom and settle on any substance
that affords a foothold : on leather, bones, iron, pottery, etc. There can be
no sustenance drawn from these supports, or at most extremely little, and
it is interesting to note in this connection that while some rock-lichens are
changed to a rusty-red colour by the infiltration of iron — often from a
water medium containing iron-salts — those that live directly on iron are
unaffected.
The " wanderers " are more or less the same in every locality and they
pass easily from one support to another. Bouly de Lesdain2 made a tabula-
tion of such as he found growing on varied substances on the dunes round
Dunkirk and they well represent these omnicolous communities. It is in
such a no man's land that one would expect to find an accumulation of
derelict materials, not only favourably exposed to light and moisture, but
undisturbed for long periods and bordering on normal lichen associations
of soil, tree and stones. Arnold3 also noted many of these peculiar habitats.
1 Schade 1916. 2 Lesdain 1910. 3 Arnold 1858.
LICHEN COMMUNITIES 377
The following were noted by Lesdain and other workers :
On iron — Xanthoria parietina, Physcia obscura and var. virella, Ph.
ascendens, Placodium (fiavescens) sympageum, PL pyraceum, PL citrinum,
Candelariella vitellinum, Rinodina exigua, Lecanora campestris, L. umbrina,
L. galactina, Lecania erysibe, Bacidia inundata. Xanthoria parietina is one
of the commonest wandering species; it was found by Richard1 on an old
cannon lying near water, that was exfoliated by rust.
On tar — Lecanora nmbrina.
On charcoal — Rinodina exigua, Lecanora umbrina.
On bones — Xanthoria parietina, Physcia ascendens, Ph. tenella, Placodium
citrinum, PL lacteum, Rinodina exigua, Lecanora galactina, L. dispersa, L.
nmbrina, Lecania erysibe, L. cyrtella, Acarospora pruinosa, A. Heppii, Bacidia
inundata, B. muscorum, Verrucaria anceps, V. papillosa.
In Arctic regions in Ellesmere Land and King Oscar Land, Darbishire2
found on bones : Lecanora varia, L. Hageni, Rinodina turfacca and Buellia
parasema (disciformis). He could not trace any effect of the lichens on the
substratum.
On charcoal — Rinodina exigua, Lecanora umbrina.
On dross or clinkers — Parmelia dubia, Physcia obscura, Ph. ascendens
f. tenella, Ph. pulverulenta, Xanthoria parietina, Placodium pyraceum, PL
citrinum, Rinodina exigua, Lecanora dispersa, L. umbrina, Lecania erysibe.
On glass3 — Physcia ascendens f. tenella, Buellia canescens. Richard has
recorded the same lichens on the broken glass of walls and in addition :
Xantlioria parietina, Lecanora crenulata, L. dispersa, Lecania erysibe, Rinodina
exigua, and Buellia canescens.
On earthenware, china, etc. — Physcia ascendens f. tenella, Lecanora
umbrina, L. dispersa, Lecania (? Biatorind) cyrtella, Verrucaria papillosa,
Bacidia inundata.
On leather — Nearly fifty species or varieties were found by Lesdain on
old leather on the dunes. Cladonias, Parmelias and Physcias were well re-
presented with one Evernia and a large series of crustaceous forms. He
adds a note that leather is an excellent substratum : lichens covered most
of the pieces astray on the dunes. Similar records have been made in
Epping Forest by Paulson and Thompson4 who found Cladonia fi mbriata
var. tubaeformis and Lecidea granulosa growing on an old boot. These
authors connect the sodden condition of the leather with its attraction for
lichens.
On pasteboard — Even on such a transient substance as this Lesdain
found a number of forms, most of them, however, but poorly developed :
Cladonia furcata (thallus), Parmelia subaurifera (beginning), Xanthoria
parietina (beginning), Physcia obscura, Placodium citrinum (thallus), PL
1 Richard 1877. 2 Darbishire 1909. 3 Cf. p. 234. 4 Paulson and Thompson 1913.
378 ECOLOGY
pyraceum, Lecanora umbrina, Bacidia inundata and Polyblastia Vouauxi var.
charticola.
On linoleum — Xanthoria parietina, Physcia ascendens f. tenella, Rinodina
exigua, Lecanora umbrina.
On indiarubber — Physcia ascendens f. tenella.
On tarred cloth — Xanthoria parietina, Placodium citrinum, PI. pyraceum,
Rinodina exigua, Lecanora umbrina, Lecania erysibe, Bacidia inundata.
On felt — Bacidia inundata, B. muscorum.
On cloth (cotton, etc.) — Bacidia inundata.
On silk — Physcia ascendens, Ph. obscura, Placodium citrinum (thallus),
Lecanora umbrina, Bacidia inundata.
On cord — Physcia ascendens f. tenella, Placodium citrinum (thallus).
On excreta — One would scarcely expect to find lichens on animal
droppings, but as some of these harden and lie exposed for a considerable
time, some quick-growing species attain to more or less development on
what is, in any case, an extremely favourable habitat for fungi and for many
minute organisms. Paulson and Thompson found tiny fruiting individuals
of Cladonia macilenta and Cl. fimbriata var. tubaeformis growing on the dry
dung of rabbits in Epping Forest. On the same type of pellets Lesdain re-
cords Physcia ascendens f. leptalea, Cladonia pyxidata, Bacidia inundata and
B. muscorum ; and on sheep pellets : Physcia ascendens f. leptalea and Placo-
dium citrinum; while on droppings of musk-ox in Ellesmere Land Darbishire
found Biatorina globulosa, Placodium pyraceum, Gyalolechia subsimilis, Leca-
nora epibryon, L. verrucosa, Rinodina turfacea and even, firmly attached,
TJiamnolia vermicularis.
It would be difficult to estimate the age of these lichens, but it seems
evident that the " wanderers " are all more or less quick growers, and the
lists also prove conclusively their complete indifference to the substratum,
as the same species occur again and again on the very varied substances.
5. LOCALIZED COMMUNITIES
Lichens may be grouped ecologically under other conditions than those
of substratum. They respond very readily to special environments, and
associations arise either of species also met with elsewhere, or of species
restricted to one type of surroundings. Such associations or communities
might be multiplied indefinitely, but only a few of the outstanding ones
will be touched on.
a. MARITIME LICHENS. This community is the most specialized of any,
many of the lichens having become exclusively adapted to salt-water sur-
roundings. They are mainly saxicolous, but the presence of sea-water is the
factor of greatest influence on their growth and distribution, and they occur
LICHEN COMMUNITIES
379
indifferently on any kind of shore rock either siliceous or calcareous.
Wheldon and Wilson1 noted this indifference to substratum on the Arran
shores, where a few calcicolous species such as Verrucaria nigrescens, V.
macultfornris, Placodium tegularis and PL lobu/atuin, grow by the sea on
siliceous rocks. They suggest that the spray-washed habitat affords the
conditions, which, in other places, are furnished by limestone.
The greater or less proximity of the salt water induces in lichens, as in
other maritime plants, a distribution into belts or zones which recede
gradually or abruptly according to the slope of the shore and the reach of
the tide. Weddell2 on the Isle d'Yeu delimited three such zones : ( i ) marine,
those nearest the sea and immersed for a longer or shorter period at each
tide; (2) semi-marine, not immersed but subject to the direct action of the
waves, and (3) maritime or littoral, the area beyond the reach of the waves
but within the influence of sea-spray. In the course of his work he indicates
the lichens of each zone.
Fie. 122. Ramalina siliqtiosa A. L. Sm. Upper zone of barren plants (after M. C. Knowles,
R. Welch, Photo.}.
In Ireland, a thorough examination has been made of a rocky coast at
Howth near Dublin by M. C. Knowles3. She recognizes five distinct belts
1 Wheldon and Wilson 1913.
' Weddell 1875.
Knowles 1913.
380 ECOLOGY
beginning with those furthest from the shore though within the influence of
the salt water:
1. The Ramalina belt. 4. Verrucaria maura belt.
2. The Orange belt. 5. The belt of Marine Verrucarias.
3. Lichina Vegetation.
(i) The Ramalina belt. In this belt there are two zones of lichen vege-
tation: those in the upper zone consist mainly of barren plants of Ramalina
siliguosa1, rather dark or glaucous in colour with much branched fronds
which are incurved at the tips (Fig. 122). They are beyond the direct action
of the waves. The lower zone consists also mainly of the same Ramalina,
the plants bearing straight, stiff, simple, or slightly branched fertile fronds
of a pale-green or straw colour (Fig. 123). The pale colour may be partly
due to frequent splashings by sea-spray.
Ramalina siliquosum in both zones takes several distinct forms, according
to exposure to light, wind or spray, the effects of which are most marked in
the upper zone. The plants growing above the ordinary spray zone generally
form sward-like growths (Fig. 124); at the higher levels the sward growth
is replaced by isolated tufts with a smaller more amorphous thallus which
passes into a very small stunted condition. The latter form alone has
gained and retained a footing on the steep faces of the hard and close-
grained quartzite rocks. "On the western faces, indeed, it is the only visible
vegetation." The dwarfed tufts with lacerated fronds measuring from
\ to \ an inch in height are dotted all over the quartzites. On the sea faces
the plants are larger, but everywhere they are closely appressed to the rock
surface. At lower levels the fronds lengthen to more normal dimensions.
"On these steep rock-faces there is a complete absence of any of the
crustaceous species. The problem, therefore, as to how the Ramalina has
obtained a foothold on these very hard precipitous rocks, which are too
inhospitable even for crustaceous species is an interesting and puzzling one."
In the Ramalina zone along with the dominant species there occur
occasional tufts ofR. Cnrnowii and R. subfarinacea, the latter more especially
in shady and rather moist situations. There are also numerous foliaceous
and crustaceous lichens mingling with the Ramalina vegetation (Fig. 125),
several Parmelias, Physcia aquila, Xanthoria parietina, Buellia canescens,
B, ryssolea, Lecanora atra, L. sordida, Rhizocarpon geographicum and others.
In the main these are arranged in the following order descending towards
the sea :
1. Parmeliae. 3. Xanthoria parietina,
2. Physcia aquila. 4. Crustaceous species.
1 The two morphologically similar plants Ramalina cuspidata and R. scopulorum are here
united under the older name R. siliquosa. The distinction between the two is based on reaction
tests with potash, which give very uncertain results.
LICHEN COMMUNITIES
123. Ramalina siliqitosa A. L. Sm. Lower zone of fertile plants (after M. C. Knowles,
R. Welcli, Photo.}.
Fig. 1 24. Sward of young Ramalinae (after M. C. Knowles, R. Welch, Ph*
382
ECOLOGY
Parmelia prolixa is the most abundant of the Parmelias : it covers large
spaces of the rocks and frequently competes for room with the Ramalinas,
or in other areas with PJiyscia aquila and Lecanora parella.
A number of crustaceous species which form the sub-vegetation of the
Ramalina belt, and also on the same level, clothe the steeper rock faces
where shelter and moisture are insufficient to support the foliose forms.
"In general the sub-vegetation of the eastern and northern coasts is largely
composed of species that are common in Alpine and upland regions. This
Fig. 125. Crustaceous communities in the Ramalina belt. Lecanora atra Ach. (grey patches) and
Buellia ryssolea A. L. Sm. (dark patches). (After M. C. Knowles, R. Welch, Photo.)
is due to the steepness of the rocks and also to the colder and drier conditions
prevailing on these coasts." An association of Rhizocarpon geographicum,
Lecanora (sordida) glaucoma and Pertusaria concreta f. Westringii forms an
almost continuous covering in some places, descending nearly to sea-level.
On sunnier and moister rocks with a south and south-west aspect the
association is of more lowland forms such as Buellia colludens, B. stelhdata
Lecanora smaragdula and L. simplex f. strepsodina.
(2) The Orange belt. "Below the Ramalinas, and between them and
the sea, several deep yellow or orange-coloured lichens form a belt of varying
LICHEN COMMUNITIES 383
width all round the coast. In summer, the colour of these lichens is so
brilliant that the belt is easily recognized from a considerable distance." The
most abundant species occur mainly in the following order descending
towards the sea :
1 . Xanthoria parietina. 4. Placodium deripiens.
2. Placodium murorum. 5. Placodium lobulatum.
3. Placodium tegular is.
"On the stones and low shore rocks that lie just above the ordinary high-
tide level Placodium lobulatum grows abundantly, covering the rocks with
a continuous sheet of brilliant colour." With these brightly coloured lichens
are associated several with greyish thalli such as :
Lecanora prose choides. Biatorina lenticularis,
Lecanora uinbrina. Rinodina exigua var. demissa.
Lecanora Hageni. Opegrapha calcarea f. hctcromorpha.
Rhizocarpon alboatrum.
(3) The Lichina vegetation, and (4) The Verrucaria maura belt.
These two communities are intermingled, and it will therefore be better to
consider them together. There are only two species of Lichina on this or any
other shore, L. pygniaea and L. confiuis; the latter grows above the tide-level,
and sometimes high up on the cliffs, where it is subject to only occasional
showers of spray: it forms on the Howth coast a band of vegetation four
to five inches wide above the Verrucaria belt. Lichina pygniaea occurs
nearer the water, and therefore mixed with and below Verrucaria maura.
Those three zones were first pointed out by Xylander1 at Pornic, where
however they were all submerged at high tide.
Verrucaria maura is one of the most abundant lichens of our rocky
coasts, and is reported from Spitzbergen in the North to Graham Land in
the Antarctic. It grows well within the range of sea-spray, covering great
stretches of boulders and rocks with its dull-black crustaceous thallus. At
Howth it is submerged only by the highest spring tides. Though it is the
dominant lichen on that beach, other species such as V. memnonia, V. promi-
nula, and V. aquatilis form part of the association, and more rarely V. scotitia
along with Arthopyrenia halodytes, A. leptotera and A. Iializoa.
(5) The belt of marine Verrucarias. This association includes the
species that are submerged by the tide for a longer or shorter period each
day. The dominant species are Verrucaria microspora, V. striatnla and
V. uiucosa. Arthopyrenia halodytes is also abundant; A. halizoa and A.
marina are more rarely represented. Among the plants of Fucus spiralis,
Verrucaria mucosa, the most wide-spreading of these marine forms, is "very
conspicuous as a dark-green, almost black, band of greasy appearance
stretching along the shore." When growing in the shade, the thallus is of
a brighter green colour.
1 Nylander 1861.
384 ECOLOGY
An examination1 of the west coast of Ireland yielded much the same
results, but with a still higher " white belt " formed mainly of Lecanora
parella and L. atra which covered the rocks lying above high-water mark,
"giving them the appearance of having been whitewashed." A more
general association for the same position as regards the tide is given by
Wheldon and Wilson2 on the coasts of Arran as :
Physcia aquila. Placodium tegularis.
Xanthoria parietina. Ramalina cuspidata.
Lecanora parella. Physcia stellaris.
Lecanora atra. Physcia tenella.
Lecanora campestris. Verrucaria maura.
Placodium ferrugineum vzx.festivum.
A somewhat similar series of "formations" was determined by Sandstede3
on the coast of Riigen. On erratic granite boulders washed by the tide he
found :
Verrucaria maura. Lecanora prosechoides.
Lichina confinis. Placodium lobulatum.
While in a higher position on similar boulders :
Lecanora exigua. Lecanora parella.
Lecanora dispersa. Lecidea colludens.
Lecanora galactina. Lecidea lavata.
Lecanora sulphurea. Lecidea nigroclavata f. lenticularis.
Lecanora saxicola. Xanthoria parietina and f. aureola.
Lecanora caesiocinerea. Physcia subobscura.
Lecanora gibbosa. Physcia caesia.
Lecanora atra.
And more rarely a few species of Lecidea.
b. LICHENS OF SAND-DUNES. These lichens might be included with those
of the terricolous communities, but they really represent a maritime com-
munity of xerophytic type, subject to the influence of salt spray but not
within reach of the tide. They are sun-lichens and react to the strong light
in the deeper colour of the thallus. In such a sun-baked area at Findhorn
a luxuriant association of lichens was observed growing among short grass
and plant debris. It consisted chiefly of:
Parmelia physodes. Cladonia ceriricornis.
Evernia prunastri. . Cladonia endiinaefolia.
Cetraria aculeata. Peltigera spp.
On very arid situations the species of Cladonia are those that have a well-
developed rather thick primary thallus, probably because such a thallus is
able to retain moisture for a prolonged period4. On shifting sand, as in the
desert, there are no lichens; it is only on surfaces more or less fixed by marram
1 Knowles 1915. 2 Wheldon and Wilson 1913. 3 Sandstede 1904. 4 Aigret 1901.
LICHEN COMMUNITIES: 385
grass that lichens begin to develop, though in the cool damp weather of
autumn and winter, as observed by Wheldon and Wilson1, certain species
associated with Myxophyceae, such as Collemaceae, may make their appear-
ance, among others Leptogium scotinum, Collemodium turgidum and Collcma
ceranoides. Watson2 makes the same observation in his study of sand-dunes.
When the loose sand on the dunes of South Lancashire becomes cemented
by algae and mosses several rare Lecideae are to be found on the decaying
vegetation, and with further accumulation of humus Cladoniae appear and
spread rapidly along with several species of Peltigera and the ubiquitous Par-
melia physodes. The latter starts on dead twigs of Salix repens and spreads
on to the surrounding soil where it forms patches some inches in diameter.
The association also includes Lecidea uliginosa and Bilimbia sphacroides.
On the more inland portions of the dunes numerous rather poorly de-
veloped Cladoniae and Cetraria aculeata were associated, while on the sides
of "slacks" or "dune-pans" Colleina pulposum, Cladonia sylvatica and several
crustaceous lichens covered the soil. The wetter parts of the dunes were
not found to be favourable to lichen growth.
Sandstede3 found on the sandy shores of Riigen, from the shore upwards:
first a stretch of bare sand, then a few dune grasses with scattered scraps
of Cladoniae, Peltigerae and Cetraria aculeata. Next in order sandbanks
with Parmelia physodes, Cladonia sylvatica, Cl. alcicornis and Stereocanlon
pascliale. All these are species that occur on similar shores in the British
Islands. Sandstede adds an extensive list of maritime species observed by
him in Riigen.
A very careful tabulation of lichens at Blakeney Point in Norfolk was
made 'by McLean4 and the table on p. 386 is reproduced from his paper.
Sand, he writes, is present in all the associations and the presence or
absence of stones marks the great difference between the two formations
determined by dune and shingle.
(1) Bare sand, which is the first association listed, is an area practically
without phanerogams ; the few lichen plants, Cladonia furcata and Cetraria
aculeata f. acanthella, are attached by slight embedding in the soil.
(2) Grey dune. The sand-loving lichens of the associatipn grow in
company with Hypnnm cupressiforme and attain their greatest development.
Other species which also occur there are Parmelia physodes and Evertiia
prunastri var. stictocera.
(3) Derelict dune. This part of the dune formation occurs here and
there on the seaward margin where the grey dune has been worn down by
the wind. It is more shingly, hence the presence of stone lichens; dune
phanerogams are interspersed and with them a few fruticose lichens, such as
Cladonia furcata.
1 Wheldon and Wilson 1915. - Watson 1918'. 3 Sandstede 1904. * McLean 1915.
S. L. 25
386
ECOLOGY
(4) High shingle. The term indicates shingle aggregated into banks
lying well above all except the highest tides. A large percentage of sand
may be mixed with the stones and if no humus is present and the stones of
small size, lichens may be absent altogether. Those occurring in the "loose
shingle" are saxicolous. In the "bound shingle" where there is no grass
the stones, fixed in a mixture of sand and humus, are well covered with
lichens. With the presence of grass, a thin layer of humus covers the stones
and a dense lichen vegetation is developed both of shingle and of dune
species.
(5) Low shingle. This last association lies in the hollows among plants
of Suaeda fruticosa. Stability is high and tidal immersions regular and
frequent. The dominant factor of the association is the quantity of humus
and mud deposited around and over the stones. The lichens cover almost
every available spot on the firmly embedded pebbles. The characteristic
species of such areas are Lecanora badia and L. (Placodinm) citrina which
effect the primary colonization. To these succeed Lecanora atra and Xan-
thoria parietina. In time the mud overwhelms and partly destroys the
lichens, so that the phase of luxuriant growth is only temporary.
Lecanora badia is conspicuously abundant at the sand end of this forma-
tion. Lecanora (Placodium} citrina disappears as the mud is left behind.
Collema spp. also occur frequently on the mixture of mud and sand round
the stones. Trie species on " low shingle " are those most tolerant of sub-
mersion : Verrucaria maura is confined to this area, where it is covered by
the tide several hours each day.
FORMATION
Dune
ASSOCIATION
i. Bare Sand
•2. Grey Dune
Derelict Dune
Shingle
4. High Shingle I
Loose j
(Without sand
Bound
5. Low Shingle
PRINCIPAL SPECIES
Cetraria aculeata f. acanthella
Cladonia furcala
Cladonia rangiferina, Peltigera rufescens
Cladonia furcata, Cl. alcicomis
Cladonia furcata, Parmeliafuliginosa
Rhizocarpon confervoides
(Lecanora atra, L. galactina
With sand -I Rhizocarpon confervoides
{Lecanora citrina
(Physcia tenella, Lecanora citrina, Xanthoria parietina
\ Squamaria saxicola
I Parnielia saxatilis, P. fuliginosa
\ Cladonia rangiferina, Cl. furcata, Cl. pungens
\ Cetraria aculeata
Xanthoria parietina, Biatorina chalybeia, Lecanora atn
Aspiciliagibbosa, Buellia colludens, J'errncaria microspon
Physcia tenella, Lecanora atroflava
Rhizocarpon confervoides, Lecanora citrina var. incrustan.
L. badia, L. atra, Xanthoria parietina
Verrucaria maura
With grasses
(Without grasses
McLean adds that Xanthoria parietina in its virescent form on Suaeda
fiuticosa also endures constant immersion ; Lecanora badia does not occur
LICHEN COMMUNITIES
387
above the tidal line and Lecanora galactina does not descend below tidal
limits ; the latter is an arenicolous species and colonizes some of the loosest
and sandiest areas of shingle. Rhizocarpon confewoides is ubiquitous.
c. MOUNTAIN LICHENS. On the mountain summits of our own and
other lands are to be found lichens very similar to those of the far North
the climatic conditions being the chief factors of importance in determining
the formations. These regions are occupied by what Wheldon and Wilson1
describe as " a zone of Arctic-Alpine vegetation," and they have recorded
a series of lichen associations belonging to that zone on the schistose
summits of the Perthshire mountains. The following is one of the most
typical :
Euopsis granatina.
Sphaerophorus coralloides.
Spliaerophorus fragilis.
Gyrophora polyphylla.
Cetraria tristis.
Cetraria nii/alis.
Lecanora tartarea vvx.frigida.
Lecanora upsaliensis.
Aspicilia ocitlata.
Pertusaria dactylina.
Pertusaria glomerata.
Stereocaulon denudatum.
Parmelia saxatilis.
Parinelia omphalodes.
Parmelia lanata.
Parmelia stygia.
Stereocaulon tomentosum.
Stereocaulon alpinum.
Cladonia coccinea.
Cladonia gracilis.
Cladonia uncialis.
Cladonia destricta.
Cladonia racemosa.
Lecidea arctica.
Parmelia alpicola.
Cetraria aculeata.
Cetraria crispa.
Cetraria islandica.
Lecidea limosa.
Lecidea alpestris.
Lecidea demissa.
Lecidea tiliginosa.
Lecidea citprea.
Lecidea Berengeriana.
Lecidea cupreiformis.
Lecidea atrofusca.
Again on the summit of Ben-y-Gloe the same authors2 have recorded
" Gyrophora erosa, G. torrefacta and G. cylindrica, P annelid alpicola, Lecanora
tartarea var. frigida, Lecidea limosa and L. arctica, the last two lichens
thriving in the most bleak and exposed situations. Cladonia cen>icornis
grew in reduced squamulose cushions ; Stereocaulon and SpJiacrophorus in
very compact forms, the outer stalks prostrate, the next inclined, the central
ones erect so that points only are exposed and no lateral stress is caused by
wind storms. Erect fruticose lichens are absent in this region, being repre-
sented only by Parmelia lanata, a semi-decumbent plant, and by Tliainnolia
rcnnicularis which is prostrate on the ground except where the points of
the stalks turn up to catch the dew. Many of the Lecideae were observed to
have large fruits and very little thallus : " the hyphae ramify in the minute
interstices of the stone and the gonidia cluster under the lea of the apothecia;
this is especially the case on loose stones where conditions are extremely
dry."
On the Continent an interesting study of the lichens of high altitudes
was made by Maheu3 in the Savoyard Oberland. On the Great Casse at
1 Wheldon and Wilson 1915. 2 Wheldon and Wilson 1914.
1 Maheu 1887.
25 — :
388 ECOLOGY
a height of 3861 m. he collected four mosses and sixteen lichens. These
were :
Stereocaulon condensation, Candelaria concolor. Buellia discolor.
Gyrophora cylindrica Caloplacapyracea var . nivalis. Buellia stellulata.
Gyrophora spodochroa. Haematomma ventosum. Lecidea contigua var. steriza
Solorina crocea. Acarospora smaragdula. Lecidea confluens.
Solorina saccata. Psora decipiens. Dermatocarpon hepaticum.
Parmelia encausta.
He found that as he climbed higher and higher foliaceous species became
rarer and crustaceous more abundant. The colour of the lichens on the high
summits was slightly weakened and the thallus often reduced, but all were
fertile and the apothecia normal and sporiferous. Lichens at less high
altitudes where they emerge from the snow covering for longer periods and
enjoy light and sunshine are, as already observed, often very brightly
coloured and of luxuriant growth.
d. TUNDRA LICHENS. In phyto-geography the term "tundra" is given
to great stretches of country practically treeless and unsheltered within the
Polar climate; the tundra extends from the zone of dwarfed trees on to the
permanent ice or snow fields. The vegetation includes a few dwarfed trees,
shrubs, etc., but is mainly composed of mosses and lichens ; the latter being
the most abundant. These are true climatic lichen formations.
Leighton1, in describing lichens from Arctic America brought home by
the traveller, Sir John Richardson, quotes from the latter that : " the ter-
restrial lichens were gathered on Great Bear, and Great Slave Lakes before
starting on our summer voyages after the snow had melted.... The barren
grounds are densely covered for many hundreds of miles with Corniculariae
and Cetrariae, and where the ground is moist with Cladoniae, while the
boulders thickly scattered over the surface are clothed with Gyrophorae....
The smaller stones on the gravelly ridges of the Barren Grounds are
covered with lichens."
The accounts of tundra lichens that have been given by various travellers
deal chiefly with the more prominent terricolous forms. They have been
classified as "Cladina tundra," including Cladonia rangiferina and Sphaero-
phorus coralloides, " Cetraria tundra," and " Alectoria heath," the latter the
hardiest of all. Great swards of these lichens often alternate with naked
stony soil.
Kihlman2 has noted, as characteristic of tundra formations, the compact
cushion-like growth of the mosses which are thus enabled to store up water
and to conduct it by capillarity throughout the mass to the highest stalks.
Certain tundra lichens take on the same growth character as adaptations to
the strenuous life conditions. Cetraria glauca f. spadicea with f. congesta and
1 Leighton 1867. 2 Kihlman 1890. .
LICHEN COMMUNITIES - 389
C. crispa are examples of this compact growth : they form a soft thick carpet
of a yellowish-grey colour. Cladoniae also grow in crowded tufts, but are
generally to be found in the more sheltered positions, in valleys between
the tundra hills and in the clefts of the rocks, or between great boulders and
stones where there is also more moisture.
The same kinds of lichens occur all over these northern regions. Birger
Nilson1 gives as the principal earth-lichens in Swedish Lappland, Alectoria
ochroleuca, A. nigricans, Cetraria nivalis, C. cucullata, Cladonia uncialis,
Tkamnolia (Cerania) vermicularis and Sphaerophorus coralloides.
Darbishire2 speaks of the extensive beds of various species of Cetraria
in Ellesmere Land and King Oscar Land. Alectoria nigricans and A.oc/iro-
lenca were often found in pure communities, but even more frequently in close
company with mosses. Though these fruticose lichens are not represented
by many species in Arctic regions, they cover a very extensive area and
form a very important feature in the vegetation.
Crustaceous lichens are not wanting : Lecanom tartarea f. frigida, L.
epibryon and others are to be found in great sheets covering the mosses or
the soil, or spreading over the stones and boulders. Cold has no deterrent
effect, and their advance is only checked by the presence of perpetual snow.
e. DESERT LICHENS. The reduced rainfall of desert countries is un-
favourable to general lichen growth and only the more xerophytic species —
those with a stout cortex — can flourish in the adverse conditions of excessive
light and dryness. Lichens, however, there are, in great numbers as far as
individuals are concerned, though the variety is not great. The abundance
of the crustaceous Lecanora esculenta in the deserts of Asia has already been
noted. Flagey3 found it one of the dominant species at Biskra in the Sahara
where it grows on the1 rocks. Patouillard4 in describing the flora of Tunis
speaks of the great patches (societies) of Lecanora crassa f. deserti which at
a distance look like milk spilled on the ground, or if growing on unequal
surfaces take the aspect of plaster that has been passed over by some
wheeled vehicle. At Biskra species of Heppia grow on the sand. Steiner5
also records the frequency of Heppia and of Endocarpon in the Sahara as well
as of Gloeolichens which, as they are associated with gelatinous blue-green
algae, can endure extreme and long-continued desiccation. These lichens,
however, only form communities in clefts among the rocks where these abut
on the desert. In the great plains the sand is too mobile and too often
shifted by the sirocco to enable them to settle.
Bruce Fink6 discusses desert lichens and their adaptive characters :
crustaceous species with a stout cortex are best able to withstand the long
dry periods; conspicuously lobed thalli are lacking, as are lichens with
1 Nilson 1907. 2 Darbishire 1909. 3 Flagey 1901. 4 Patouillard 1897.
5 Steiner 1895. 6 Bruce Fink 1909.
390 ECOLOGY
fruticose structure though he thinks the latter are prevented from developing
by the exposure to high winds and driving sand storms. Herre's1 study of
the desert lichen flora at Reno, Nevada, is full of interest. The district is
situated at an altitude of 4500 feet east of the Sierra Nevada Mountains.
The annual rainfall averages 8'2i inches, and a large part falls as snow during
the winter months or as early spring rain. The summer is hot and dry and
the diurnal changes of temperature are very great. Strong drying winds
from the west or north are frequent.
At 5000 feet and upwards lichens are, in general, exceedingly abundant
on all rock substrata and represent 57 species or subspecies, only three of
these being arboreal: Buellia triphragmia occurs rarely, Xanthoria poly-
carpa is frequent on sage brush, while Candelariella cerinella though a rock-
lichen grows occasionally on the same substratum. Caloplaca (Placodiuni)
elegans is one of the most successful and abundant species and along with
Lecanora (nine forms), Acarospora (seven forms) and Lecidia (five forms) com-
prises three-fourths of the rock surface occupied by lichens. The addition
of Rinodina with two species and Gyrophora with four brings the computation
of individuals in these desert rock formations up to nine-tenths of the whole.
As the desert rocks pass to the Alpine, Gyrophora becomes easily the domi-
nant genus followed by Acarospora, Caloplaca and Lecidea,
"The colouring characteristic of the rock ledges of the desert and canon
walls is often entirely due to lichens, and in a general way they form the
only brilliant plant formations in a landscape notable for its subdued pale
monotonous tones. Most conspicuous are Acarospora chlorophana and
Caloplaca elegans, which form striking landmarks when covering great crags
and rock walls. The next most conspicuous lichens are Rinodina oreina and
Lecanora rubina and its allies, which often entirely cover immense boulders
and northerly sloping rock walls." Herre concludes that though desert con-
ditions are unfavourable to most species of lichens, yet some are perfectly
at home there and the rocks are just as thickly covered as in regions of
greater humidity and less sunshine.
f. AQUATIC LICHENS. There is only one of the larger lichens that has
acquired a purely aquatic habit, Hydrothyria venosa, a North American
plant. It grows on rocks2 in the beds of streams, covering them often with
a thick felt ; it is attached at the base and the rather narrow fronds float
freely in the current. The gonidium is Nostoc sp., and the thallus is of a
bluish-grey colour ; the fruits are small discoid reddish apothecia with an
evanescent margin. It is closely allied to Peltigerae, some of which are
moisture-loving though not truly aquatic.
The nearest approach to aquatic habit among the foliose forms in our
1 Herre 191 12. 2 See p. 97.
LICHEN COMMUNITIES 391
country is Dennatocarpon aquaticum, with thick coriaceous rather contorted
lobes; it inhabits rocks and stones in streams and lakes. Somewhat less con-
tinuously aquatic is D. ininiatum var. complicatum which grows on damp rocks
exposed to spray or occasionally to inundation. Lindsay1 has described it
" on boulders by the side of the Tay, frequently covered by the river when
flooded, and of a deep olive colour when under water": both these lichens
have a wide distribution in Europe, Africa, America and New Zealand.
In a discussion of lake shore plants Conway Macmillan2 describes on
the flat shores a Dennatocarpon zone on the wet area nearest the lake, behind
that a Biatora zone and further landward a Cladonia zone. On rounded
rocky shores the same zones followed each other but were less broad : they
were so close together that the Cladoniae, which with Stereocaulon paschale
grow in profusion on all such shores, occurred within a couple of feet of the
high-water mark.
M. C. Knowles3 reports concerning the lichen flora of some mountain
lakes in Waterford, that a band of Dennatocarpon miniatuin var. complicatum
six feet wide grew all the way round the lakes between the winter and
summer level of the water. Below that zone D, aquaticum formed another
belt mingled with the moss Fontinalis and several species of crustaceous
lichens Staurotheleae^ Polyblastiae, etc.
Bruce Fink4 gives as a typical "amphibious angiocarpous lichen forma-
tion" of wet rocks in Minnesota: Dennatocarpon aquaticum, D. miniatuin var.
complicatum, Staurotliele clopima and Verrucaria viridula. These " forma-
tions," he says, " may be seen complete in places along the shores of Ver-
million Lake and less well represented at other portions of the lake shore."
Macmillan found that on the rocky shores of Lake Superior the Dermato-
carpon zone also occurred nearest the water.
Species with closed fruits such as Pyrenolichens, or with apothecia
deeply sunk in the thallus and thus also well protected, seem to be best
adapted to the aquatic life. Such in our own country are Lecanora lacustris,
Bacidia inutidata and others, with a number of Verrncariae : V. aethiobola,
V. hydrela, V. margacea, etc.
Lettau5 gives as "formations" on rocks or boulders in the beds of streams
in Thuringia :
Verrucaria aethiobola. Bacidia inundata.
Verrucaria hydrela. Lecanora aquatica.
Dermalocarpon aquaticum.
In their ecological study of Perthshire lichens Wheldon and Wilson6
give two " formations." The first is on rocks submerged for long periods,
1 Lindsay 1856. 2 Macmillan 1894. Knowles in lift. 4 Bruce Fink 1903.
5 Lettau 191 1. * Wheldon and Wilson 1915.
392 ECOLOGY
though in dry weather the lichens may be exposed, and can withstand
desiccation for a considerable time :
Pterygium Kenmorensis. Lecidea contigua.
Collema fluviatile. • Lecidea albocoerulescens.
Lecanora lacustris. Dermatocarpon miniatum var. complicaium.
Lecanora epulotica. Dermatocarpon aquaticutil.
Bacidia inundata. Verrncaria laevata.
Rhizocarpum obscuratum. Verrucaria aethiobola.
Rhizocarpum petraeum. Verrucaria margacea.
The second group of species usually inhabits damp, shaded rocks of
ravines or large boulders by streams or near waterfalls. It includes species
of Collema, Sticta, Peltigera, Solorina, Pannaria, etc., with Opegrapha zonata,
Porina lectissima and Verrucaria nigrescens.
The last-mentioned lichen grows by preference on limestone, but in
excessive moisture1, as by the sea-side, the substratum seems to be of minor
importance.
D. LICHENS AS PIONEERS
a. SOIL-FORMERS. The part played by lichens in the "Economy of
Nature" is of very real importance: to them is allotted the pioneer work
of breaking down the hard rock surfaces and preparing a soil on which
more highly developed plants can grow. This was pointed out by Linnaeus2
who thus describes the succession of plants : "Crustaceous lichens," he
writes, "are the first foundation of vegetation. Though hitherto we have
considered theirs a trifling place among plants, nevertheless they are of
great importance at that first stage in the economy of nature. When the
rocks emerge from the seas, they are so polished by the force of the waves,
that scarcely any kind of plant could settle on them, seen more especially
near the sea. But very soon, in truth, the smallest crustaceous lichens begin
to cover those arid rocks, and are sustained by minute quantities of soil and
by imperceptible particles brought to them by rain and by the atmosphere.
These lichens in time become converted by decay into a. thin layer of
humus, so that at length imbricate lichens are able to thrust their rhizoids
into it. As these in turn change to humus by natural decay, various mosses
such as Hypnum, BryuDi and Polytrichum follow, and find suitable place
and nourishment. In time there is produced by the dying down of the
mosses such a quantity of soil that herbs and shrubs are able to establish
themselves and maintain their existence."
Similar observations have been made since Linnaeus's day, among others
by Guembel3 in his account of Lecanora ventosa. Either by the excretion of
carbon dioxide which acidifies the surrounding moisture, or by the mechanical
1 Wheldon and Wilson 1913. 2 Linnaeus 1762. 3 Guembel 1856.
LICHENS AS PIONEERS 393
action of hyphae and rhizinae, the component particles of rocks such as
granite are gradually dissolved and broken up. Rocks exposed to weather
alone are unchanged, while those covered with lichens have their surface
disintegrated and destroyed.
The decaying parts of the lichen thallus add to the soil material as
observed by Linnaeus, and in time mosses follow, and, later, phanerogams.
Goeppert1 has pointed out the succession observed on roofs of houses as:
"first some lichen such &s' Lecanora saxicola, then the moss Griuitnia pitlvi-
iiata, which forms compact cushions on which later grow Poa compressa,
small crucifers, etc."
Goeppert1 has noted as special rock-destroyers some foliaceous species,
Parmelia saxatilis, P. stygia and P. encausta, the underlying rock being
roughened and broken up by their rhizoids. Species of Gyroplwra and
Sphaerophorus have the same disintegrating effect, so that the surface of the
rock may in time lose its coherence to a depth of 2 to 4 inches. Crustaceous
species such as Lecanora polytropa, Candelariella vitellina, etc., exercise an
equally powerful solvent action, while underneath closely appressed growers
like Lecanora atra and Acarospora smaragdula the stone is converted to
a friable substance that can be sliced away with a knife.
Salter- concluded that oxalic acid was the principal agent in disintegra-
tion. He found that it acted more or less rapidly on minerals and almost
any class of saline compounds; it even attacked glass finely powdered,
though silica remained unchanged.
Bachmann3 found that granite was reduced by lichens to a clay-like
granular yellow mass in a comparatively short time, the lichen seizing on
the particles of mica first; but the spread of the lichen over the rock, he
observes, is largely directed by the amount of humidity and by the chance
of gaining a foothold. In the case of calcareous rocks he4 tested the relative
dampness of those containing lichens and those that were lichen-free. In
the former case water was absorbed more freely and retained much longer
than in the barren rock, thus encouraging further vegetation.
Lucy E. Braun5 has described the successive colonization of limestone
conglomerate in Cincinnati. The rock is somewhat resistant to erosion-
and stands out in irregular outcrops on the hillsides of the region. The
first plants to gain a footing are certain crustaceous lichens, Lccidea sp.,
Pertusaria communis, Staurothele mnbrina, Verritcana muralis and Placo-
dinin citrinum which occur as patches on the smoother and more exposed
rock faces. With these were associated small quantities of a moss, Grimmia
apocarpa. In the second stage of growth Dennatocarpon inimatiun, and, to
a lesser degree, a gelatinous Omphalaria sp. were the most prominent plants,
1 Goeppert 1860. 2 Salter 1856. 3 Bachmann 1911.
4 Bachmann 1913. 5 Braun 1917.
394 ECOLOGY
but mosses were more in evidence, and the next stage consisted almost
exclusively of mosses and hepatics with Peltigera canina. A thick layer of
humus was gradually built up by these plants on which Phanerogamous
plants were able to flourish.
In tropical countries the first vegetation to settle on bare rocks would
seem to be blue-green gelatinous algae. Three years after the eruption of
Krakatoa, dark-green layers of these plants were found by Treub1 on the
surface of the pumice and ash, and on the loose stones in the ravines of the
mountain. It was only at a later stage that lichens appeared.
b. OUTPOSTS OF VEGETATION. Lichens are the only plants that can
survive extreme conditions of cold or of heat. They grow in Polar regions
where no other vegetation could obtain sustenance ; they are to be found
at great heights on mountains all over the globe ; and, on arid desert rocks
they persist through long dry seasons, depending almost entirely on night
dews for the supply of moisture. Here we have true lichen formations in
the sense of modern ecology.
1 Treub 1888.
CHAPTER X
ECONOMIC AND TECHNICAL
A. LICHENS AS FOOD.
a. FOOD FOR INSECTS, ETC. Some of the earlier botanists made careful
observations on the important place occupied by lichens in nature as affording
food to many small animals. In 1791 Jacques Brez1 wrote his Flore des
Insectophyles, and in the list of food-plants he includes seven species of
lichens. The "insects" that frequented these lichens were species of the
genera Acarus (mites) and Phalena (moths). A few years later Persoon2
noted that lichens formed the main food supply of many insects, slugs, etc.
Zukal3, quoting from Otto Wilde {Die Pflanzen und Raupen Deutschlands,
Berlin, 1860), gives a list of caterpillars that are known to feed on and
destroy lichens.
A very considerable number of small creatures feed eagerly on lichens,
and traces of their depredations are constantly to be seen in the empty
fruit discs, and in the cortices eaten away in patches so as to expose the
white medulla. It has been argued by Zukal4 that the great formation of
acid substances in lichens is for shielding them against the attacks of
animals; Zopf5 on the contrary insists that these substances afford the plants
no real protection. He made a series of experiments with snails, feeding
them with slices of potato smeared with pure lichen acids. Many snails ate
the slices with great readiness even when covered with bitter acids such as
cetraric, or with those which are poisonous for other animals such as rhizo-
carpic and pinastrinic. The only acid they refused was.vulpinic, which is
said to be poisonous for vertebrates. The crystals of the acids passed
unchanged through the alimentary canal of the snails, and were found in
masses in the excreta. They were undissolved, but, enclosed in slime, their
sharp edges did no damage to the digestive tract.
Stahl6 however upholds Zukal's theory of the protective function of
lichen acids against the attacks of small animals. Some few snails, cater-
pillars, etc., that are omnivorous feeders consume most lichens with impunity,
and the bitter taste seems to attract rather than repel them ; but many
others he contends are certainly prevented from eating lichens by the
presence of the acids. He proved this by soaking portions of the thalli of
certain bitter species for about twenty-four hours in a one per cent, soda
solution, which was sufficiently strong to extract the acids. He found that
1 Brez 1791. 2 Persoon 1794. 3 Zukal 1895, p. 1317 (note). 4 Zukal 1895, p. 1315.
5 Zopf 1896. ' Stahl 1904.
396 ECONOMIC AND TECHNICAL
these treated specimens were in most cases preferred to fresh portions that
had been simply moistened with water.
Even the omnivorous snail, Helix hortensis, was several times observed
to touch the fresh thallus and then creep away, while it ate continuously
the soda-washed portion as soon as it came into contact with it. Calcium
oxalate, on the other hand, formed no protection ; omnivorous feeders ate
indifferently calcicolous lichens such as Aspicilia calcarea and Lecanora
saxicola, whether treated with soda or not, but would only accept lichens
with acid contents, such as Parmelia caperata, Evernia prunastri, etc., after
they had been duly soaked.
Experiments were also made with wood-lice (Oniscus murarius\ and
with earwigs (Forficula auricularia), and the result was the same : they
would only eat bitter lichens after the acids had been extracted by the soda
method. Stahl therefore concludes that acids must be regarded as eminently
adapted to protect lichens which otherwise, owing to their slowness of
growth, would scarcely escape extinction.
The gelatinous Collemaceae, as also Nostoc, the alga with which these
are associated, are unharmed by snails, etc., on account of their slippery
consistency when moist, which prevents the creatures from getting a foothold
on the thallus. These lichens however do not contain acids, and if, when
dry, they are reduced to powder and then moistened, they are eagerly eaten
both by snails and by wood-lice. Peltigera canina, on account of a disagree-
able odour it acquires on being chewed, is avoided to a certain extent, but
even so it is frequently found with much of the thallus eaten away.
Hue1 in his study of Antarctic lichens, comments on the abundance and
perfect development of the lichens, especially the crustaceous species, which
cover every inch of rock surface. He ascribes this to the absence of snails
and insects which in other regions so seriously interfere with the normal
and continuous growth of these plants.
Snails do not eat lichens when they are dry and hard, but on damp or
dewy nights, and on rainy days, all kinds, both large and small, come out
of their shells and devour the lichen thalli softened by moisture. Large
slugs (Limax) have been seen devouring with great satisfaction Pertusaria
faginea, a bitter crustaceous lichen. The same Limax species eats many
different lichens, some of them containing very bitter substances. Zopf2
observed that Helix cingulata ate ten different lichens, containing as many
different kinds of acid.
Other creatures such as mites, wood-lice, and the caterpillars of many
butterflies live on lichens, though, with the exception of the caterpillars, they
eat them only when moist. Very frequently the apothecial discs and the
soredia are taken first as being evidently the choicest portions. All lichens
1 Hue 1915. 2 Zopf 1907.
LICHENS AS FOOD 397
are, however, not equally palatable. Bitter1 observed that the insect Psocus
(Orthoptera) had a distinct preference for certain species, and restricted its
attention to them probably because of their chemical constitution. He noted
that in a large spreading thallus of GrapJiis elegans on holly, irregular bare
spots appeared, due to the ravages of insects — probably Psocus. In other
places, the thallus alone had been consumed, leaving the rather hard black
fruits (lirellae) untouched. In time the thallus of Thelotrema lepadinnm,
also a crustaceous lichen, invaded the naked areas, and surrounded the
Graphis lirellae. The new comer was not to the taste of the insects and was
left untouched.
Fetch2 says that lichens form the staple food of Termes monoccros, the
black termite of Ceylon. These ants really prefer algae, but as the supply
is limited they fall back on lichens, though they only consume those of
a particular type, or at a particular stage of development. Those with
a tough smooth cortex are avoided, preference being given to thalli with a
loose powdery surface. At the feeding ground the ants congregate on the
suitable lichens. With their mandibles they scrape off small fragments of
the thallus which they form into balls, varying in size from i'5 mm. to 2*5 mm.
in diameter. The workers then convey these to the nests in their mandibles.
It would seem that they carry about these balls of food, and allow the ants
busy in the nest to nibble off portions. Lichen balls are not used by termites
as fungi are, for "gardens."
Other observations have been made by Paulson and Thompson3 in their
study of Epping Forest lichens: "Mites of the family Oribatidae must be
reckoned among the chief foes of these plants upon which they feed, seeming
to have a special predilection for the ripe fruits. We have had excellent
specimens of PJiyscia parietina spoiled by hidden mites of this family, which
have eaten out the contents of the mature apothecia after the lichens have
been gathered. One can sometimes see small flocks of the mites browsing
upon the thallus of tree-dwelling lichens, like cattle in a meadow." The
Oribatidae, sometimes called beetle-mites, a family of Acarinae, are minute
creatures familiar to microscopists. They live chiefly on or about mosses,
but Michael4 is of opinion that a large number frequent these plants for the
fungi and lichens which grow in and about the mosses. In Michael's
Monograph of British Oribatidae, four species are mentioned as true lichen-
lovers, Leiosoma palmicinctum found on Peltigera canina and allied species ;
Cepteus ocellatus and Oribata parmeliae which live on Physciae, the latter
exclusively on Physcia (Xanthoria) parietina ; and Saitwertes maculatus
which confines itself to lichens by the sea-shore. Another species, Notaspis
lucoruni, frequents maritime lichens, but it is also found on other substrata;
1 Bitter 1899. 2 Fetch 1913. 3 Paulson and Thompson 1913.
* Michael 1884.
398
ECONOMIC AND TECHNICAL
while Tegeocranus labyrinthicus, though usually a lichen-eating species, lives
either on mosses or on lichens on walls. Zopf * reckoned twenty-nine species
of lichens, mostly the larger foliose and fruticose kinds, that were eaten by
mites. Lesdain2 in his observations on mite action notes that frequently the
thallus round the base of the perithecia of Verrucaria sp. was eaten clean
away, leaving the perithecia solitary and extremely difficult to determine.
J. A. Wheldon3 found the eggs of a species of mite, Tetranychus lapidus,
attached to the fruits of Verrucaria calciseda, Lecidea immersa and L.Metzleri,
calcicolous lichens of which the thallus not only burrows deep down into
the limestone, but the fruits form in shallow excavated pits (Fig. 126). The
\ /
Fig. 126. i, Tetranychus lapidus, enlarged; i, Verrucaria calciseda with eggs in situ, slightly
enlarged ; 3 and 4, eggs attached to lichen fruits, much magnified (after Wheldon).
eggs of this stone mite are found fairly frequently on exposed limestone
rocks, bare of vegetation, except for a few crustaceous lichens. "There is
usually a single egg, rarely two, in each pit apparently attached to the old
lichen apothecium. The eggs are very attractive objects under a lens; they
measure '5 mm. in diameter, and are disc-like with a central circular depres-
sion from which numerous ridges radiate to the circumference, like the spokes
of a wheel. When fresh, they have a white pearly lustre, becoming chalk-
white when dry and old." Wheldon's observations were made in the Carnforth
and Silverdale district of West Lancashire.
1 Zopf 1907. - Lesdain 1910. 3 Wheldon 1914.
LICHENS AS FOOD 399
A minute organism, Hymenobolina parasitica1, first described by Zukal
and doubtfully grouped among the mycetozoa, feeds, in the plasmodium
stage, on living lichens. The parasitic habit is unlike that of true mycetozoa.
It has recently been recorded from Aberdeenshire.
b. INSECT MIMICRY OF LICHENS. Paulson and Thompson2 give instances
of moth caterpillars, which not only feed on lichens, but which take on the
coloration of the lichens they affect, either in the larval or in the perfect
moth stage. "One of the most remarkable examples of this protective
resemblance to lichens is that of the larva of the geometrid moth, Cleora
/ichenaria,\\\\ich feeds upon foliose lichens growing upon tree-trunks and
palings, and being of a green-grey hue, and possessed of two little humps
on many of their body-segments, they so exactly resemble the lichens in
colour and appearance as to be extremely difficult of detection." Several
instances are recorded of moths that resemble the lichens on which they
settle : perfect examples of such similarity are exhibited at the Natural
History Museum, South Kensington, where Teras literana, Moma orion, and
other moths are shown at rest on lichen-covered bark from which they can
hardly be distinguished.
Another curious instance of suggested mimicry is recorded by G.E. Stone3.
He spotted a number of bodies on the bark of some sickly elms in Massa-
chusetts. They were about £ of an inch in diameter " with a dark centre
and a drab foliaceous margin." They were principally lodged in the crevices
of the bark and Stone collected them under the impression that they were
the apothecia of a lichen' most nearly resembling those of Physcia hypoleuca.
Some of the bodies were even attached to the thallus of a species of Physcia;
others were on the naked bark and had every appearance of lichen fruits.
Only closer examination proved their insect nature, and they were identified
as belonging to a species Gossypina Ulmi, an elm-leaf beetle common in
Europe where it causes a disease of the tree. It had been imported into
the United States and had attacked American elms.
'It is stated by Tutt4 that the larvae of many of the Psychides (Lepi-
doptera) live on the lichens of trees and walls, such as Candelaria concolor,
Xanthoria parietina, Physcia pulvenilenta and Buellia canescens, and that
their larvae pupate on their feeding grounds. Each species makes a "case"
peculiar to itself, but those of the lower families are usually covered exter-
nally with grains of sand, scraps of lichens, etc. The " case " of Narcyria
inonilifera, for instance, is somewhat raised on a flat base and is obscured
with particles of sand and yellow lichen, giving the whole a yellow appearance.
That of Luffia lapidella is roughly conical and is held up at an angle of 30°
to 45° when the larva moves. The "cases" of Bacotia septum are always
upright; they measure about 5-5 mm. in height and 275 mm. in width and
1 See also p. 267. - Paulson and Thompson 1913. 3 Stone 1896. 4 Tutt 1900, p. 107.
4oo
ECONOMIC AND TECHNICAL
present a hoary appearance from the minute particles of lichen with which
they are covered, so that the structure is not unlike the podetium of a
Cladonia.
c. FOOD FOR THE HIGHER ANIMALS. It has been affirmed, especially
by Henneguy, that many lichens, if deprived of the bitter principle they
contain, by soaking in water, or with the addition of sodium or potassium
carbonate, might be used with advantage as fodder for animals. He cites as
examples of such, Lobariapulmonaria, Everniaprunastri, Ramalinafraxinea,
R. farinacea, and R. fastigiata, all of which grow abundantly on trees, and
owe their nutritive quality to the presence of lichenin, a carbohydrate allied
to starch.
Fig. 127. Cladonia rangiferina Web. (S. H , Photo.}.
Cladonia rangiferina (Fig. 127), the well-known "reindeer moss," is,
however, the lichen of most economic importance, as food for reindeer,
cattle, etc. It is a social plant and forms dense tufts and swards of slender,
much branched, hollow stalks of a greenish-grey colour which may reach
a height of twelve inches or even more; the stalks decay slowly at the base
as they increase at the apex, so that.., very great length is never attained.
In normal conditions they neither wither nor die, and growth continues
indefinitely. It is comparatively rare in the northern or hilly regions of the
British Isles, and is frequently confused with the somewhat smaller species
Cl. sylvatica which is very common on our moorlands, a species which Zopf1
tel-ls us reindeer absolutely refuse to eat.
1 Zopf 1907, p. 372.
LICHENS AS FOOD 401
The true reindeer moss is abundant in northern countries, more especially
in forest regions1 and in valleys between the tundra hills which are more or
less sheltered from the high winds; it is independent of the substratum and
flourishes equally on barren sand and on wet turf; but grows especially well
on soil devastated by fire. For long periods it may be covered with snow
without injury and the reindeer are accustomed to dig down with horns and
hoofs in order to reach their favourite food. Though always considered as
peculiarly " reindeer " moss, deer, roebuck and other wild animals, such as
Lemming rats2, feed on it largely during the winter. In some northern
districts it is collected and stored as fodder for domestic cattle ; hot water
Fig. 128. Celraria islandica Ach. (S. H., Photo.}.
is poured over it and it is then mixed with straw and sprinkled with a little
salt. Johnson3 has reported that the richness of the milk yielded by the
small cows of Northern Scandinavia is attributed by some to their feeding
in great measure on the "reindeer moss."
When Cladonia rangiferina is scarce, a few other lichens4 are made use
of, Alectoria jubata, a brownish-black filamentous tree-lichen being one of
the most frequent substitutes. Stereocaulon paschale, which grows in large
dense tufts on the ground in mountainous regions, is also eaten by reindeer
and other animals; and Iceland moss, Cctraria islandica, is stored up in
large quantities by the Icelanders and used as fodder. Willemet5 reports it
as good for horses, oxen, cows and pigs.
1 Kihlman 1890. * Linnaeus 1762. 3 Johnson 1861.
4 Lindsay 18*6. 5 Willemet 1787.
26
402 ECONOMIC AND TECHNICAL
It is interesting to recall a discovery of prehistoric remains at the
Abbey of Schussenried on the Lake of Constance and described by F. Keller1:
under successive beds of peat and crumbly tufa, there was found a layer,
3 feet thick, containing flints, horns of reindeer and bones of various animals,
and, along with these, masses of reindeer moss ; a sufficient proof of its
antiquity as a fodder-plant.
d. FOOD FOR MAN. Lichens contain no true starch nor cellulose, but the
lichenin present in the cell-walls of the hyphae has long been utilized as
a food substance. It is peculiarly abundant in Cetraria islandica (Fig. 128),
which grows in northern countries, covering great stretches of ground with
its upright strap-shaped branching fronds of varying shades of brown. In
more southern lands it is to be found on high hills or on upland moors, but
in much smaller quantities. Commercial " Iceland moss " is supplied from
Sweden, Norway or Iceland. In the last-named country the inhabitants
harvest the lichen preferably from bare stony soil where there is no admixture
of other vegetation. They revisit the locality at intervals of three years, the
time required for the lichen to grow to a profitable size ; and they select
the wet season for the ingathering of the plants as they are more easily
detached when they are wet. If the weather should be dry, they collect it
during the night. When gathered it is cleansed from foreign matter and
washed in water to remove as much as possible of the bitter principle. It
is then dried and reduced to powder. When required, the powder is put to
macerate in water for 24 hours, or it is soaked in a weak solution of soda
or of carbonate of potassium, by which means the bitter cetraric acid is
nearly all eliminated. When boiled2 it yields a jelly which forms the basis
of various light and easily digested soups or of other delicacies prepared
by boiling in milk, which have been proved to be valuable for dyspeptics or
sufferers from chest diseases. The northern nations also make the powder
into bread, porridge or gruel. Johnson3 states in his account of " Useful
Plants " that considerable quantities of Iceland moss were formerly em-
ployed in the manufacture of sea biscuit, and that ship's bread mixed with
it was said to be less liable to the attacks of weevil than when made from
wheat flour only.
An examination of the real food value of the mucilaginous extract from
"Iceland moss" has been made by several workers. Church4 states that for
one part of flesh formers, there are eight parts of heat-givers reckoned as
starch. Brown8 isolated the two carbohydrates, lichenin and iso-lichenin.
The former, a jelly which yields on hydrolysis a large quantity of a reducing
sugar, dextrose, ferments with yeast and gives no phloroglucin reaction ;
it is unaffected by digestion and probably does not form glycogen.
1 Keller 1866. 2 Proust 1906. 3 Johnson 1861.
4 Church 1880. 5 Brown 1808.
LICHENS AS FOOD 403
Iso-lichenin is much less abundant and resembles soluble starch, but on
digestion yields only dextrins — no sugar. It may be concluded, judging
from the chemical nature of the mucilage, from the resistance of its con-
stituents to digestion and from the small amount present in the jelly, that
its nutritive value is practically nil1.
It has been stated that " reindeer moss " in times of food scarcity is
powdered and mixed with "Iceland moss" and rye to make bread in North
Finland. Johnson confirms this and cites the evidence of a Dr Clarke that:
" to our surprise we found we might eat of it with as much ease as of the
heart of a fine lettuce. It tasted like wheat-bran, but after swallowing it,
there remained in the throat and upon the palate a gentle heat, or sense of
burning, as if a small quantity of pepper had been mixed with the lichen."
The Egyptians2 have used Evernia prunastri, more rarely E. furfuracea,
in baking. In the eighteenth century fermentative agents such as yeast
were unknown to them, and these lichens, which were imported from more
northern lands, were soaked in water for two hours and the solution then
mixed with the flour to give a much appreciated flavour to the unleavened
bread.
In India3 a species of Parmelia (near to P. perlatd) known in the Telegu
language as "rathapu" or rock-flower has been used as a food, generally
prepared as a curry,by the natives in the Bellary district (Madras Presidency),
and is esteemed as a delicacy. It is also used medicinally. The collecting
of rathapu is carried on during the hot weather in April and May, and forms
a profitable business.
A note has been published by Calkins4, on the authority of a correspondent
in Japan, that large quantities of Endocarpon (Dermatocarpon) miniatum
(Fig. 56) are collected in the mountains of that country for culinary purposes,
and largely exported to China as an article of luxury. The local name is
"iwataka," meaning stone-mushroom. Properly prepared it resembles tripe.
It is possibly the same lichen under a different name, Gyrophora esculenta,
which is described by Manabu Miyoshi5 as of great food value in Japan
where it is known as "iwatake." It is a greyish-brown leathery "mono-
phyllous" plant of somewhat circular outline and fairly large size, measuring
3 to 1 3 cm. across. Fertile specimens are rare, and are smaller than the
sterile. It grows generally on the steep declivities of damp granitic rocks and
is common in various districts of Japan, being especially abundant on such
mountains as Kiso, Nikko, Kimano, etc. The face of the precipices is often
thickly covered with the lichen growth. The inhabitants collect the plants
in large quantities. They dry them and send them to the towns, where they
are sold in all vegetable stores; some are even exported to other countries.
1 Hutchinson 1916. • Forskal 1875, p- 193- * Watt l89°- * Calkins 1892.
5 Miyoshi 1893.
26—2
404
ECONOMIC AND TECHNICAL
These lichens are not bitter to the taste, nor are they irritating as are other
species of the genus. They are on the contrary quite harmless and are much
relished by the Japanese on account of their agreeable flavour, in spite of
their being somewhat indigestible. Though only determined scientifically in
recent times, this edible lichen has long been known, and the risks attending
its collection have frequently been described in Old Chinese and Japanese
writings.
Other species of Gyrophora including G. polyrhiza (Fig. 129) and
Umbilicaria, black leathery lichens which grow on rocks in northern regions,
Fig. 129. Gyrophora polyrhiza Koerb. (S.H., Photo, reduced).
have also been used as food. They are the "Tripe de Roche" or Rock Tripe
of Arctic regions, a name given to the plants by Canadian fur-hunters.
They have been eaten by travellers and others in desperate straits for food ;
but though to a certain extent nutritious, they are bitter and nauseous, and
cause severe internal irritation if the bitter acids are not first extracted by-
boiling or soaking.
Of more historical interest is the desert lichen Lecanora esculenta,
supposed to be the manna1 of the Israelites, and still called "bread from
heaven." Eversmann2 wrote an account of its occurrence and qualities, and
fuller information was given by Berkeley3: when mixed with meal to a
third of its weight it is made into bread and eaten by the desert tribes.
It grows abundantly in North Africa and in many parts of Western Asia,
on the rocks or on soil. It is easily broken off and driven into heaps by the
wind; and has been reported as covering the soil to a depth of 15 cm. to
1 See p. 422. 2 Eversmann 1825. 3 Berkeley 1849.
LICHENS AS FOOD 405
20 cm. with irregular contorted lumps varying in size from a pea to a small
nut (Fig. 130). Externally these are clear brown or whitish; the interior
is white, and consists of branching interlaced
hyphae, with masses of calcium oxalate crystals,
averaging about 60 per cent, or more of the
whole substance.
A still more exhaustive account is given by
Visiani1, who quotes the experience of a certain Fig. I30. Lecano~a fscuicnta
General Jussuf, who had tested its value in the Eversm. Loose nodules of the
Sahara as food for his soldiers. When bread
was made from the lichen alone it was friable and without consistency ; when
mixed with a tenth portion of meal it was similar to the soldiers' ordinary
bread, and had something of the same taste. The General also gave it as
fodder to the horses, some of them being nourished with the lichen and
a mixture of barley for three weeks without showing any ill effects. It is
also said that camels, gazelles and other quadrupeds eat it with advantage,
though it is in any case a very defective food.
A remarkable deposit of the lichen occurred in recent times in Mesopo-
tamia during a violent storm of hail. After the hail had melted, the ground
was seen to be covered, and specimens were sent to Errera2 for examination.
He identified it as Lecanora esculenta. In his opinion two kinds of manna
are alluded to in the Bible : in one case (Exodus xvi.) it is the sweet gum
exuded from the tamarisk that is described; the other kind (Numbers xi.),
he thinks, plainly refers to the lichen. He considers that its nutritive value
must be very low, and it can only be valued as food in times of famine.
B. LICHENS AS MEDICINE
a. ANCIENT REMEDIES. An interesting note has been published by
Muller-Argau3 which seems to trace back the medicinal use of lichens to
a very remote age. He tells us that Dr Schweinfurth, the distinguished
traveller, who made a journey through the valley of the Nile in 1864, sent
to him from Cairo a piece of lichen thallus found in a vase along with berries
of Juniperus excelsa and of Sapindus, with some other undetermined seeds.
The vase dated from the i8th Dynasty (1700 to 1600 B.C.), and the plants
contained in it must thus have lain undisturbed over 3000 years. The broken
pieces of the lichen thallus were fairly well preserved; they were extremely
soft and yellowish-white and almost entirely decorticate, but on the under
surfaces there remained a few black patches, which, on microscopical
examination, enabled Muller to identify them as scraps of Evernia furfuracea.
This lichen does not grow in Egypt, but it is still sold there along with
i Visiani 1867. 2 Errera 1893. 3 Muller-Argau 1881, p. 5*6.
406
ECONOMIC AND TECHNICAL
Cetraria islandica and some other lichens as foreign drugs. Dr Schweinfurth
considered his discovery important as proving the use of foreign remedies
by the ancient Egyptians.
b. DOCTRINE OF "SIGNATURES." In the fifteenth century A.D. there was
in the study and treatment of disease a constant attempt to follow the
guidance of nature. It was believed that Providence had scattered here and
there on plants "signatures," or resemblances more or less vague to parts
of the human body, or to the diseases to which man is subject, thus indi-
cating the appropriate specific.
Fig- I3I- Parmelia saxatilis Ach. (S. H., Photo.).
Lichens among other plants in which any "signature" could be detected
or imagined were therefore constantly prescribed : the long filaments of
Usnea barbata were used to strengthen the hair; Lobaria pulmonaria, the
true lung-wort, with its pitted reticulate surface (Fig. 72), was marked as a
suitable remedy for lung troubles ; Xanthoria parietina being a yellow lichen
was supposed to cure jaundice, and Peltigera aphthosa, the thallus of which
is dotted with small wart-like tubercles1, was recommended for children who
suffered from the "thrush" eruption.
1 See p. 138.
LICHENS AS MEDICINE 407
The doctrine reached the height of absurdity in the extravagant value
set on a lichen found growing on human skulls, "Muscus cranii humani"
or "Muscus ex cranio humano." There are a number of lichens that grow
indifferently on a variety of substances, and not infrequently on bones lying
in the open. This skull lichen1, Parnielia saxatilis ( Fig. 131) or some other,
was supposed to be worth its weight in gold as a cure for epilepsy.
Parkinson2 tells us in all confidence "it groweth upon the bare scalps of
men and women that have lyen long... in former times much accounted of
because it is rare and hardly gotten, but in our own times much more set
by, to make the 'Unguentum Sympatheticum' which cureth wounds with-
out the local application of salves... but as Crollius hath it, it should be
taken from the sculls of those that have been hanged or executed for
offences." Ray3 says that the same gruesome plant "is celebrated by several
authors as useful in haemorrhages and is said to be an ingredient of the
famous 'Unguentum Armarium4,' reported to have been invented by
Paracelsus." Another lost ointment !
c. CURE FOR HYDROPHOBIA. Still another lichen to which extraordinary
virtue was ascribed, was the very common ground species Peltigera canina
(Fig. 54), a preparation of which was used in the cure of rabies. Dillenius5
has published in full the prescription as " A certain Cure for the Bite of
a Mad Dog" which was given to him by a very celebrated physician of that
day, Dr Richard Mead, who had found it effective :
" Let the patient be blooded at the arm, nine or ten ounces. Take of
the herb called in Latin Lichen cinereus terrestris, in English Ash-coloured
ground liverwort, clean'd, dry'd and powder'd half an ounce. Of black
. pepper powder'd two drachms.
"Mix these well together and divide the Powder into four Doses, one of
which must be taken every Morning, fasting, for four Mornings successively
in half a Pint of Cow's Milk warm. After these four Doses are taken, the
Patient must go into the cold bath, or a cold Spring or River, every Morning
fasting, for a Month. .He must be dipt all over but not stay in (with his
head above water) longer than half a minute, if the Water be very cold.
After this he must go in three Times a Week for a Fortnight longer."
Lightfoot6, some forty years later, refers to this medicine as " the once
celebrated ' Pulvis antilyssus,' much recommended by the great Dr Mead."
He adds that " it is much to be lamented that the success of this medicine
has not always answered the expectation. There are instances where the
application has not prevented the Hydrophobia, and it is very uncertain
1 From an examination of old figures of the Muscus cranii, Arnold (1892, p. 53) has decided that
several kinds of lichens or hepatics are included in this designation.
2 Parkinson ,640, p. 1313- 3 ^ l686' P- "?• * Am°rCUX i;87' P' ^
5 Dillenii-s 1741, p. 202. 6 Lightfoot 1777, M. p. 846.
4o8 ECONOMIC AND TECHNICAL
whether it has been at all instrumental in keeping off that disorder." Belief in
the efficacy of the powder died out before the end of the cerjtury but the echo
of the famous remedy remains in the name Peltigera canina, the dog lichen.
d. POPULAR REMEDIES. Lichens with very few exceptions are non-
poisonous plants. They owed their repute as curative herbs to the presence
in the thallus of lichenin and of some bitter or astringent substances, which,
in various ailments, proved of real service to the patient, though they have
now been discarded in favour of more effective drugs. Some of them, on
account of their bitter taste, were frequently used as tonics to replace
Fig. 132. Pertusaria amara Nyl. on bark (S. H., Photo.'].
quinine in attacks of fever. Several species of Pertusaria, such as the bitter
P. amara (Fig. 132), and of Cladonia as well as Cetraria islandica (Fig. 128),
were recommended in cases of intermittent fever; species of Usnea and
others, as for instance Evernia furfuracea, were used as astringents in
haemorrhages; others were given for coughs, Cladonia pyxidata (Fig. 69)
being supposed to be specially valuable in whooping cough.
One of the most frequently prescribed lichens was the tree lung-wort
(Lobaria pulmonarid) (Fig. 72). It was first included among medical plants
by Dorstenius1, a Professor at Marburg; he gives a good figure and supplies
1 Dorstenius 1540.
LICHENS AS MEDICINE 409
directions for its preparation as a cure for chest complaints. The doctrine
of "signatures" influenced practitioners in its favour, but it contains lichenin
which acts as an emollient. In England, it was taken up by the famous
Dr Culpepper1, who, however, believed in astrology even more than in sig-
natures. He says : " it is of great use with many physicians to help the
diseases of the lungs and for coughs, wheesings and shortness of breath
which it cureth both in man and beast." He adds that "Jupiter seems to
own the herb." A century later we find Dr John Hill12, who was a physician
as well as a naturalist, stating that the great tree lung-wort has been at all
times famous in diseases of the breast and lungs, but by that time "it was
not much used owing to change in fashions."
The only lichen that has stood the test of time and experience as a real
remedy is Cetraria islandica, and even the " Iceland moss " is now rarely
prescribed. The first mention in literature of this famous plant occurs in
Cordus3 as the Muscus with crisp leaves. Some years later it figures among
the medicinal plants in Sibbald's4 Chronicle of the Scottish Flora, and Ray5
wrote of it about the same time as being known for its curative and ali-
mentary properties. It was Linnaeus6, and later Scopoli7, who gave it the
important place it held so long in medicine. It has been used with advantage
in many chronic affections as an emollient and tonic. Cramer8 in a lengthy
dissertation gathered together the facts pertaining to its use as a food,
a medicine and for dyeing, and he gives recipes he had himself prescribed
with marked success in many different maladies. It has been said that if
"Iceland moss" accomplished all the good it was alleged to do, it was indeed
a " Divine gift to man."
The physiological action of cetrarin (acid principle of the lichen) on
living creatures has been studied by Kobert9 and his pupils. It has not any
poisonous effect when injected into the blood, nor does it work any harm
when taken into the stomach even of small animals, so that it may be safely
given to the most delicate patients. Nearly always after small doses peri-
staltic movements in the intestines are induced which indicate that as
a drug it might be of service in the case of enfeebled organs. In larger
doses it may cause collapse in animals, but if administered as free cetraric
acid it passes through the stomach unchanged to become slowly and com-
pletely dissolved in the intestine. The mucous membrane of the intestine
of animals that had been treated with an overdose, was found to be richer
in blood so that it seems as if cetrarin might be of service in chlorosis and
in assisting digestion.
Cetrarin has also been proved to be a nerve excitant which might be
used with advantage in mental maladies.
1 Culpepper 1652. * Hill 1751. * Cordus 1561. « Sibbald 1684. s Ray 1686.
6 Linna^s 1737. 7 Scopoli 1760. 8 Cramer 1880. » Kobert 1895.
4io ECONOMIC AND TECHNICAL
C. LICHENS AS POISONS
Though the acid substances of lichens are most of them extremely
irritating when taken internally, very few lichens are poisonous. Keegan1
writing on this subject considers this quality of comparative innocuousness
as a distinctive difference between fungi and lichens and he decides that
it proves the latter to be higher organisms from a physiological point of
view: "the colouring matters being true products of deassimilation, whereas
those of fungi are decomposition or degradation waste products of the
albuminoids akin to alkaloids."
The two outstanding exceptions to this general statement are the two
Alpine species Letharia vulpina and Cetraria pinastri. The former contains
vulpinic acid in the cortical cells, the crystals of which are lemon-yellow in
the mass. Cetraria pinastri produces pinastrinic acid in the hyphae of the
medulla and the crystals are a beautiful orange or golden yellow.
These lichens, more especially Letharia vulpina, have been used by
Northern peoples to poison wolves. Dead carcasses are stuffed with
a mixture of lichen and powdered glass and exposed in the haunts of
wolves in time of frost. Henneguy2, who insists on the non-poisonous
character of all lichens, asserts that the broken glass is the fatal ingredient
in the mixture, but Kobert3, who has proved the poisonous nature of vul-
pinic acid, says that the wounds caused by the glass render the internal
organs extremely sensitive to the action of the lichen.
Kobert, Neubert4 and others have recorded the results of experiments
on living animals with these poisons. They find that Letharia vulpina either
powdered or in solution has an exciting effect on the mucous membrane.
Elementary organisms treated with a solution of the lichen succumbed
more quickly than in a solution of the acid as a salt. Kobert concluded
that vulpinic acid is a poison of protoplasm.
He further tested the effect of the poison on both cold- and warm-blooded
animals. Administered as a sodium salt, 4 mg. proved fatal to frogs. The
effect on warm-blooded animals was similar. A sodium salt, whether
swallowed or administered as subcutaneous or intravenous injections, was
poisonous. Cats were the most sensitive — hedgehogs the least — of all the
animals that were subjected to the experiments. Volkard's3 synthetic pre-
paration of vulpinic acid gave the same results as the solution directly-
extracted from the lichens.
1 Keegan 1905. 2 Henneguy 1883. 3 Kobert 1895. 4 Neubert 1893.
5 See p. 228
LICHENS IN INDUSTRY 411
D. LICHENS USED IN TANNING, BREWING AND DISTILLING
The astringent property in Cetraria islandica and in Lobaria pulmonaria
has been made use of in tanning leather. The latter lichen grows commonly
on oak and could hardly be gathered in sufficient quantity to be of com-
mercial importance. Like many other lichens it develops very slowly.
Lobaria pulmonaria has also been used to replace hops in the brewing of
beer. Gmelin1 in his journey through Siberia visited a monastery at Ussolka
where the monks employed it for this purpose. The beer tasted exactly
like that made with hops, but was more intoxicating. The lichen in that
country grew on pine-trees.
Lichens have in more modern times been used in the preparation of
alcohol. The process of manufacture was discovered by Roy'of Tonnerre,
early in the nineteenth century, and was described by Leorier2. It was
further improved by Stenberg3, a Professor of Chemistry in Stockholm.
Roy had worked with Physcia ciliaris, Ramalina fraxinea, R. fastigiata,
R. farinacea and Usnea florida, but Stenberg and distillers after his time4
made more use of Cladonia rangiferina (Fig. 127), Cetraria islandica
(Fig. 128) and Alectoria jubata.
By treatment with weak sulphuric or nitric acid the lichenin of the
thallus is transformed into glucose which on fermentation forms alcohol.
Stenberg found that 68 per cent, of the weight in Cladonia rangiferina was
a " sugar " from which a good brandy could be prepared : a kilogramme of
the lichens furnished half a litre of alcohol. The Professor followed up his
researches by establishing a distillery near Stockholm. His papers contain
full instructions as to collecting and preparing the plants. Henneguy5,
writing in 1883, stated that the fabrication of alcohol from lichens was then
a large and increasing industry in Sweden. The whole industry seems,
however, to have fallen into disuse very soon : Wainio6, quoting Hellbonv,
states that the various distilleries were already closed in 1884, because of
the exhaustion of the lichen in the neighbourhood, and the impossibility of
obtaining sufficient supplies of such slow-growing plants.
E. DYEING PROPERTIES OF LICHENS
a. LICHENS AS DYE-PLANTS. Knowledge as to the dyeing properties
of lichens dates back to a remote antiquity. It has been generally accepted
that lichen-colours are indicated by the prophet Ezekiel in his denunciation
of Tyre: "blue and purple from the Isles of Elishah was that which covered
thee." Theophrastus describes certain plants as growing in Crete, and being
1 Gmelin 1752, p. 425. 2 Leorier 1825. 3 Stenterg 1868. * Richard r 87 7.
8 Henneguy 1883. « Wainio 1887, p. 47- 7 Hellbom 1886, p. 72.
4i2 ECONOMIC AND TECHNICAL
used to dye wool, etc., and Pliny in his Phycos Thalassion is also under-
stood as referring to the lichen Roccella, "with crisp leaves, used in Crete for
dyeing garments."
Information as to the dyeing properties of certain lichens is given in most
of the books or papers dealing with these plants from the herbals onwards.
Hoffmann1 devoted a large part of his Commentatio de vario Lichenum usu
to the dye-lichens, and, illustrating his work, are a series of small rectangular
coloured blocks representing samples of woollen cloth dyed with different
lichens. There are seventy-seven of these samples with the colour names
used by French dyers.
An important treatise on the subject translated into French was also
contributed by Westring2. He desired to draw attention to the tinctorial
properties of lichens other than the Roccellae which do not grow in Sweden.
The Swedes, he states, already used four to six lichens as dye-plants, but
only for one colour. He demonstrated by his improved methods that other
colours and of finer tint could be obtained. He describes the best methods
both of extraction and of dyeing, and then follows with an account of the
different lichens likely to be of service. The treatise was subsequently
published at greater length in Swedish3 with twenty-four very fine coloured
illustrations of the lichens used, and with sample blocks of the colours to be
obtained.
b. THE ORCHIL LICHEN, ROCCELLA. The value of Roccella as a dye-
plant had been lost sight of until it was accidentally rediscovered, early in
the fourteenth century, by a Florentine merchant called Federigo. He intro-
duced its use into Florence, and as he retained the industry in his own hands
he made a large fortune, and founded the family of the Orcellarii, called
later the Rucellarii or Rucellai, hence the botanical name, Roccella. The
product was called orseille for which the English name is orchil or archil.
Another origin suggested for orchil is the Spanish name of the plant,
Orcigilia. There are a number of different species that vary in the amount
of dye-product. Most of them grow on rocks by the sea-side in crowded
bluish-grey or whitish tufts of strap-shaped or rounded stiff narrow fronds
varying in length up to about six inches or more. The main supply of
"weeds" came from the Levant until the fifteenth century when supplies
were obtained from the Canaries (long considered to produce the best
varieties), Cape Verd and the African coasts. The geographical distribution
of the Roccellae is very wide: they grow on warm sea-coasts all over the
globe, more particularly in Angola, the Cape, Mozambique, Madagascar, in
Asia, in Australia, and in Chili and Peru.
Zopf4 has proved the existence of two different colouring substances
among the Roccellas : in R. fuciformis (Fig. 57) and R. fucoides (both
1 Hoffmann 1787. 2 Westring 1792 and 1793. 3 Westring 1805-1809. 4 Zopf 1907.
LICHENS AS DYE-PLANTS
413
British species), in R. Montagnei and R.peruensis the acid present is erythrin ;
in R. tinctoria, R. portentosa and R. sinuensis it is lecanoric acid. In
R, tinctoria (Fig. 133), according to Ronceray1, the acid is located chiefly
in the gonidial layer and the soredia but
is absent from the cortex and centre. In
R. portentosa it is abundant in the cortex
and central layer, while scarcely to be
detected in the gonidial layer, and it is
wanting altogether in the soredia. In R.
Montagnei it is chiefly found in the cortex
and the gonidial layer, and is absent from
the soredia and from the medulla.
c. PURPLE DYES: ORCHIL, CUDBEAR
AND LITMUS. Orseille or orchil is formed
not only from erythrin and lecanoric acid
(orseillic acid), but also from erythrinic,
gyrophoric, evernic and ramalic acids'2 and
may be obtained from any lichen contain-
ing these substances. By the action of
ammonia the acids are split up into orcin
and carbonic acid. In time, under the
influence of ammonia and the oxygen of
the air3, orcin becomes orcein which is the
colouring principle of orchil ; the perfecting
of the process may take a month. The dye
is used for animal fibres such as wool and
silk ; it has no effect on cotton.
There are several different preparations
on the market, chiefly obtained from F ranee
and Holland ; orchil or orseille in the form of a solution, cudbear (persio of
Germany) almost the same, but manufactured into a violet-reddish powder,
and litmus (tournesol of France) which is prepared in a slightly different
manner. At one time the lichen, broken into small pieces, was soaked in
urine; a fermentation process was set up, then lime and potash with an
admixture of alum were added. The mass of material when ready was
pressed into cubes and dried in the air. Commercial litmus contains three
substances, erythrolein, erythrolitmin and azolitmin ; the last named, which
is the true litmus, is a dark brown amorphous powder soluble in water, and
forming a blue solution with alkalies.
1 Ronceray 1904. 2 Zopf 1907.
3 Zahlbruckner (1905, p. 109) quotes from Czapek a statement that orchil fermentation is brought
about by an obligate aerobic bacillus.
'33- Koccella tinctoria Ach. From
the Cape of Good Hope.
4i4 ECONOMIC AND TECHNICAL
An aqueous solution of litmus when exactly neutralized by an acid is
violet coloured ; it becomes red with the smallest trace of free acid, or blue
with free alkali. Litmus paper is prepared by steeping specially prepared
unsized paper in the dye solution. It is as a ready and sensitive indicator
of acidity or alkalinity that litmus is of so much value. According to Zopf 1
it is also used as a blueing agent in washing and as a colouring of wine.
Litmus is chiefly manufactured in Holland. Still another substance some-
what differently prepared from the same lichens is sold as French purple,
a more brilliant and durable colour than orchil.
Fig. 134. Lecanora tartarea Ach. (S. H., Photo.).
d. OTHER ORCHIL LICHENS. Though species of Roccella rank first in
importance as dye-plants, purple and blue colours are obtained, as indicated
above, from other very different lichens. Lindsay2 extracted orchil from
about twenty species. Those most in use in northern countries are on the
whole less rich in colouring substances ; they are : Umbilicaria pustulata,
species of Gyrophora, Parmelia and Pertusaria, and above all Lecanora
tartarea (Fig. 134). The last named, one of the hardiest and most abundant
1 Zopf 1907, p. 393. 2 Lindsay 1855.
LICHENS AS DYE-PLANTS 415
of rock- or soil-lichens, is chiefly used in Scotland and Sweden (hence the
name " Swedish moss") to furnish a red or crimson dye. In Scotland all
dye-lichens are called "crottles," but the term "cudbear" was given to
Lecanora tartarea (either the lichen or the dye-product); it was acquired
from a corrupt pronunciation of the Christian name of Dr Cuthbert Gordon,
a chemist, who, according to Bohler1, obtained a patent for his process of
producing the dye, or who first employed it on a great scale in Glasgow.
Johnson- remarks that the colour yielded by cudbear, if well prepared, is
a fine, clear, but not very bright purple. It is, he alleges, not permanent.
Like other orchil substances it is without effect on cotton or linen.
f. PREPARATION OF ORCHIL. A general mode of treatment of dye-
lichens recommended by Lauder Lindsay3 for home production of orchil,
cudbear and litmus is as follows :
1. Careful washing, drying and cleansing to separate earthy and other
impurities.
2. Pulverization into a coarse or fine pulp with water.
3. Repeated addition of ammoniacal liquor of a certain strength, obtain-
able from several sources (e.g* putrid urine, gas liquor, etc.).
4. Frequent stirring of the fermenting mass so as to ensure full exposure
of every part thereof to the action of atmospheric oxygen.
5. Addition of alkalies in some cases (e.g. potash or soda), to heighten
or modify colour ; and of chalk, gypsum and other substances to impart
consistence.
/. BROWN AND YELLOW DYES. The extracting of these colours from
lichens is also a very old industry. Linnaeus found during his journey to
Lappland4, undertaken when he was quite a young man, that the women in
the northern countries made use of a brown lichen for dyeing which is
evidently Parmelia ompJialodes (Fig. 135). He describes it as a "rich
Lichenoides of a brown stercoraceous colour," and he has stated that it grew
in such abundance in the Island of Aland, that every stone was covered,
especially near the sea. In the Plantae tinctoriae* there is a record of six
other lichens used for dyeing : Lichen Roccella, L. tartareus, L. saxatilis,
L. juniperinus, L. parietinus and L. candelarius. The value of Lichen oni-
phalodes was also emphasized by Lightfoot ; the women of Scotland evidently
appreciated its dyeing properties as much as other northern peoples.
A series of memoirs on the utility of lichens written by Willemet",
Amoreux and Hoffmann, and jointly published at Lyons towards the end
of the eighteenth century, represents the views as to the economic value
of lichens held by scientific botanists of that time. All of them cite the
1 Bohler 1835, N. 10. 2 Johnson 1861. 3 Lindsay 1855. 4 Linnaeus 1711.
5 Linnaeus 1760. 6 Willemet etc. 1787.
4i6
ECONOMIC AND TECHNICAL
various dye-species, and Hoffmann, as already stated, gives illustrations of
colours that can be obtained. It has been once and again affirmed that
Parmelia saxatilis yields a red colour, but Zopf1 denies this. It contains
saxatillic acid which is colourless when extracted but on boiling gives
a clear reddish-yellow to reddish-brown solution which dyes wool and silk
directly without the aid of a mordant. Zopf1 observed the process of dyeing
Fig. 135. Parmelia oviphalodes Ach. (S. H., Photo."].
followed in South Tyrol : a layer of the lichen was placed in a cooking pot,
above this a layer of the material to be dyed, then lichen and again the
material until the pot was filled. .It was covered with water and boiled
three to four hours, resulting in a beautiful rust-brown and peculiarly fast dye.
Reddish- or rust-brown dye is also obtained from Haematomma ventosum
and H. coccineum, a yellow-brown from Parmelia conspersa (salazinic acid),
and other shades of brown from Parmelia perlata, P. physodes, Lobaria pul-
monaria and Cetraria islandica.
Yellow lichens in general furnish yellow dyes, as for instance Xanthoria
parietina which gives either brown or yellow according to treatment and
Cetraria juniperina which forms a beautiful yellow colouring substance on
* Zopf 1907.
LICHENS AS DYE-PLANTS 417
boiling. Teloschistes flavicans and Letharia vulpina yield very similar yellow
dyes, and from Lecanom parella (Fig. 39), Pertusaria melaleuca and Usnea
barbata yellow colours have been obtained. Candelariella vitellina and
Xanthoria lychnea both contain yellow colouring agents and have been
employed by the Swedes for dyeing the candles used in religious ceremonies.
g. COLLECTING OF DYE-LICHENS. Lauder Lindsay1 made exhaustive
studies of dye-lichens both in the field and in the laboratory, and recorded
results he obtained from the micro-chemical examination of 540 different
specimens. He sought to revive and encourage the use of their beautiful
colour products among country people; he has given the following practical
hints to collectors:
1. That crustaceous dwarf pale-coloured species growing on rocks, and
especially on sea-coasts, are most likely to yield red and purple dyes similar
to orchil, cudbear or litmus; while on the other hand the largest, most hand-
some foliaceous or fruticose species are least likely.
2. That the colour of the thallus is no indication of colorific power (in
orchil lichens), inasmuch as the red or purple colouring substances are the
result of chemical action on crystalline colorific "principles" previously
devoid of colour.
3. That alterations in physical characters, chemical composition and
consequently in dyeing properties are very liable to be produced by modi-
fication in the following external circumstances :
(i) Degree of moisture.
(ii) Degree of heat.
(iii) Degree of exposure to light and air.
(iv) Climate.
(v) Elevation above the sea.
(vi) Habitat ; nature of basis of support.
(vii) Age.
(viii) Seasons and atmospheric vicissitudes, etc.
August has been recommended as the best month for collecting dye-
lichens : i.e. just after the season of greatest light and heat when the
accumulation of acids will be at its maximum.
Some of the acids found useful in dyeing occur in the thalli of a large
number of lichens, many of which are too scantily developed to be of any
economic value. Thus salazinic acid which gives the effective yellow-brown
dye in Parmelia conspersa was found by Zopf in 13 species and varieties.
It has since been located by Lettau2 in 72 different lichens, many of them,
however, with poorly developed or scanty thalli, so that no technical use
can be made of them.
1 Lindsay 1855. 2 Lettau 1914.
S. L. 27
4i8 ECONOMIC AND TECHNICAL
h. LICHEN COLOURS AND SPECTRUM CHARACTERS. In a comparative
study of vegetable colouring substances, Sorby1 extracted yellow colouring
matters from various plants distinguished by certain spectrum characters.
He called them the "lichenoxanthine group" because, as he explains, "these
xanthines occur in a more marked manner in lichens than in plants having
true leaves and fronds. Orange lichenoxanthine he found in Peltigera
canina, Platysma glaucum, etc., when growing well exposed to the sun.
Lichenoxanthine he obtained from the fungus Clavaria fusiformis; it
was difficult to separate from orange lichenoxanthine. Yet another, which
he terms yellow lichenoxanthine, he obtained most readily from Physcia
(Xantfiorid) parietina. The solutions of these substances vary according to
Sorby in giving a slightly different kind of spectrum. He did not experi-
ment on their dyeing properties.
F. LICHENS IN PERFUMERY
a. LICHENS AS PERFUMES. There are a few lichens that find a place
in Gerard's2 Herball and that are praised by him as being serviceable to
man. Among others he writes of a " Moss that partakes of the bark of
which it is engendered. It is to be used in compositions which serve for
sweet perfumes and that take away wearisomeness." At a much later date
we find Amoreux3 recording the fact that Lichen {Evernia) prunastri,
known as " Mousse de Chene," was used as a perfume plant.
Though lichens are not parasitic, the idea that they owed something of
their quality to the substratum was firmly held by the old herbalists. It
appears again and again in the descriptions of medicinal lichens, and still
persists in this matter of perfumes. Hue4 states in some notes to a larger
work, that French perfumers extract an excellent perfume from Evernia
prunastri (Fig. 59) known as " Mousse des Chenes " (Oak moss), and it ap-
pears that the plants which grow on oak contain more perfume than those
which live on other trees. The collectors often gather along with Evernia
prunastri other species such as Ramalina calicaris and R. fraxinea, but these
.possess little if any scent. A still finer perfume is extracted5 from Lobaria
pulnionaria called " moss from the base of the oaks," but as it is a rarer
lichen than Evernia it is less used. Most of the Stictaceae, to which family
Lobaria belongs, have a somewhat disagreeable odour, but this one forms
a remarkable exception, which can be tested by macerating the thallus and
soaking it in spirit : it will then be found to exhale a pleasant and very
persistent scent. These lichens are not, however, used alone; they are com-
bined with other substances in the composition of much appreciated perfumes.
The thallus possesses also the power of retaining scent and, for this reason,
lichens frequently form an ingredient of potpourri.
1 Sorby 1873. 2 Gerard 1597. 3 Amoreux 1787. * Hue 1889. 5 Hue 1900.
LICHENS IN PERFUMERY 419
b. LICHENS AS HAIR-POWDER. In the days of white-powdered hair,
use was occasionally made of Ramalina calicaris which was ground down
and substituted for the starch that was more commonly employed.
In older books on lichenology constant reference is made to a hair-
powder called " Pulvis Cyprius " or " Cyprus powder " and very celebrated
in the seventeenth century. It was believed to beautify and cleanse the hair
by removing scurf, etc. Evernia prunastri was one of the chief ingredients
of the powder, but it might be replaced by P/iyscia ciliaris or by Usnea.
The virtue of the lichens lay in their capacity to absorb and retain perfume.
The powder was for long manufactured at Montpellier and was a valuable
monopoly. Its composition was kept secret, but Bauhin1 (J.) published an
account of the ingredients and how to mix them. Under the title " Pulvis
Cyprius Pretiosius" a more detailed recipe of the famous powder was given
by Zwelser2, a Palatine medical doctor. The lichen employed in his pje-
paration, as in Bauhin's, is Usnea, but that may include both Evernia and
Physcia as they are all tree plants. He gives elaborate directions as to the
cleaning of the lichen from all impurities — it is to be beaten with a stick,
washed repeatedly with limpid and pure water, placed in a linen cloth and
dried in the sun till it is completely bleached and deprived of all odour and
taste.
When well dried it was placed in a basket in alternate layers with freshly
gathered, entire flowers of roses and jasmine (or flowers of orange and citrus
when possible). The whole was compressed by a heavy weight, and each
day the flowers were renewed until the "Usnea" was thoroughly impregnated
with a very fragrant odour. It was then reduced to a fine powder and ready
for other ingredients. To each pound should be added :
li oz. powdered root of white Iris.
i^- oz. of Cyperus (a sedge).
I scruple or half drachm of musk reduced to a pulp with fragrant spirit
of roses.
\ drachm of ambergris dissolved in a scruple of genuine oil of roses, or
oil of jasmine or oranges as may be preferred.
Zwelser adds :
"This most fragrant royal powder when sprinkled on the head invigorates
by its remarkably pleasant odour; by its astringency and dryness it removes
all impurities, and, since it operates with no viscosity nor sticks firmly either
to skin or hair, it is easily removed from the hair of the head."
1 Bauhin 1650, p. 88. 2 Zwelser 1672.
27—2
420 ECONOMIC AND TECHNICAL
G. SOME MINOR USES OF LICHENS
The possibility of extracting gum or mucilage from lichens was demon
strated by the Russian scientist, Professor Georgi1, and later by Amoreux2
the method employed being successive boiling of the plants. The largei
foliose or fruticose forms were specially recommended.
At a later date, during the Napoleonic wars, the "ingenious Lore
Dundonald3," of great fame as an inventor, published an account of the
extraction process and of the application of the gum to calico-printing
staining and manufacture of paper, dressing and stiffening silks. Lore
Dundonald's aim was to replace the gum Senegal, then a monopoly of the
French, who were in possession of the Settlement of Senegambia. He tool-
out a patent for his invention, but whether the gum was successfully usec
is not recorded.
According to Henneguy4, lichen mucilage, as a substitute for gum arabic
has been used at Lyons with advantage in the fabrication of dyed materials
1 Georgi 1779. 2 Amoreux 1787. 3 Dundonald 1801. 4 Henneguy 1883.
APPENDIX
POSTSCRIPT TO CHAPTER VII1
IN a remarkable paper on The Symbiosis of Lichens-, Dr A. Henry Church
has presented a new and striking view of the origin and development of
lichens: he has sought to link them up with other classes of vegetation that,
in the great transmigration, passed from sea to land. As we know from his
TJialassiopJiyta* and the subaerial transmigration, he holds that primeval
algae of advanced form and structure were left exposed on dry land
by the gradually receding waters, and those that successfully adapted
themselves to the changed conditions formed the basis of the land flora.
A certain number of the algae lost their surface tissues containing chlorophyll
and they had perforce to secure from other organic sources the necessary
carbohydrates : they adopted a heterotrophic existence as saprophytic or
parasitic fungi. Fungi are a backward race (deteriorated according to
Dr Church) as regards their soma, but in number, distribution and variety
of spore-production, they are eminently successful plants.
Lichens are similarly regarded by Dr Church as derived from stranded
contemporaneous types of marine algae — crustaceous, foliose and fruticose,
that had also lost their chlorophyll, but by taking into association green
algal units of a lower grade they established a vicarious photosynthesis.
But, to quote his own words4, " as the alga-lichen-fungus left the sea, so it
remained : it might deteriorate, but it certainly never advanced, once the
sea factors which produced it were eliminated, it simply stopped along
these lines."
And again5 : " Lichens thus present an interesting case of an algal race
deteriorating along the lines of a heterotrophic existence, yet arrested, as it
were, on the somatic down-grade, by the adoption of intrusive algal units
of lower degree to subserve photosynthesis (much in the manner of the
marine worm Convoluted). Thus arrested, they have been enabled to retain
more definite expression of more deeply inherent factors of sea-weed habit
and construction than any other race of fungi ; though closely paralleled
by such types as Xylaria (Ascomycete) and Clavaria (Basidiomycete),
which have followed the full fungus progression as holosaprophytic on
decaying plant residues."
Dr Church's theory is of vivid interest and might be convincing were
there no possibility and no proof of advance within the symbiotic plant, but
See p. 302. 2 Jourti. Bot. LVIII. pp. 213-9 > *62~7' '970' * Bot- Memoirs* 3> Oxford, 1919.
4 Church I'M lift. 5 Journ. Bot. I.e.
422
APPENDIX
in numbers of crustaceous thalli, there is evident, by normal or abnormal1
development, the first advance to the formation of rudimentary squamules,
a condition diagnosed as subsquamulose. "Deterioration" of the lichen
plant — when it occurs owing to unfavourable conditions — is a reversion to
the leprose early stage of the association ; there is no evidence of reversion
from fruticose or foliose to squamulose. A glance at the table of lichen phyla2
shows progression again and again from the crustaceous forms onwards.
In such a phylum as Physciaceae (with colourless polarilocular spores) there
is a clear example of a closely connected series; the different types of
thallus — crustaceous, squamulose, foliose and fruticose — are all represented
and form a natural sequence, being well delimited by the unusual form of
the spore and by the presence of parietin in thallus or apothecium.
That there has been development seems absolutely certain, and that
along the lines sketched in the chapter on phylogeny. Progress has been
mainly in the thallus, but there has also been change and advance in the
reproductive organs, more especially in the spores which in several families
reach a size and septation unparalleled in fungi. That association with green
algal cells stimulated the fungus to new development is the view taken of
the lichen plant and emphasized in the present volume. But it seems more
in accordance with the polyphyletic origin and recurring parallel development
in the phyla that association began at the elementary crustaceous stage, and
that the lichen soma was gradually evolved within what is after all a very
limited and simple structure.
ADDENDUM
FOOT-NOTE TO PAGE 404
E. M. Holmes3 has published recently an account of a substance which seems in some
respects to answer to the description of manna (Exodus xvi. ; Numbers xi.) more nearly
than the generally accepted Lecanora escuhnta. The information is quoted from Swann's
book: Fighting the slave-hunters in Central Africa. The author writes (p. 116): "I was
shown a curious white substance similar to porridge. It was found early in the morning
before the sun rose. On examination it was found to possess all the characteristics of the
manna of the Israelites. In appearance it resembled coriander seed, was white in
colour like hoar frost, sweet to the taste, melted in the sun and if kept over night was full
of worms in the morning. It required to be baked if you intended to keep it for any length
of time. It looked as if it was deposited on the ground in the night." The writer has
suggested that "the substance might be mushroom spawn as, on the spot where it melted
tiny fungi sprung up the next night." Swann's statement has been confirmed by
Dr Wareham, a medical missionary from the same district, who states, however, that it is
of rare occurrence.
1 See p. 271 ante. 2 See p. 302 ante.
3 Chemist and Druggist, xcn. pp. 25-26, 1920; Bot. Abstracts, N. 903, p. 135, 1920.
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INDEX
Abrothallus De Not., 267
A. Cetrariae Kotte, 264
A. oxysporus Tul., 263
A. Peyritschii Kotte, 264
A. Smithii Tul., 263
Acanlhothedum Wain., 322
Acarinae, 271, 397
Acarospora Massal., 183, 331, 390
A. chlorophana Massal., 374, 375, 390
A. glaucocarpa Koerb. , 176
A. Heppii Koerb., 377
A. pruinosa (Sm.), 377
A. 'smara^dula Massal. , 388, 393
A.xanthophana (Nyl.), 242
Acarosporaceae, 310, 331
Acarus, 395
Acharius, i, 10, 123, 120, 133, 141, 149, 150,
185, 192, 304
Acolium, S. F. Gray, 277
Acrocordia gemmata Koerb., 152 (Fig. 906)
Acroscyphus, Lev., 320
A. sphaerophoroides Lev., 289
Actlnoplaca Miill.-Arg., 327
Acton, xix, 57
Adanson, 9
Aesculus, 253
Agardh, C- A., xx, 21
Agyrium flavescens Rehm, 266
Aigret, 125, 371, 384
Alectoria Ach., 85, 94, 101, 103, 200, 257, 300,
340, 346, 350, 352
A. implexa Nyl., 227
A.jnbata Ach ,3, in, 401, 411
A. nigncans Nyl., 346, 389
A. ochroleuca Ach., 227, 389
A. thrausta Ach., 105 (Fig. 60)
Alectoriaceae, 339
Allarthonia Nyl., 321
AUarthothelium Wain., 321
Allescher, 201
Almquist, 262
Ambergris, 419
Amoreux, 10, 407, 415, 418, 420
Amphidinm Nyl., 335
Aviphiloma Koerb., 325
Anaboena Bory, 41
Anaptychia Koerb., 341 (see Physcia)
Anapyrenium Miill.-Arg., 315
Anema Nyl., 333, 373
Angiocarpeae, 156
Anthoceros L., 41
Anthracothecium Massal., 316, 350
Anzia Stiz., 90, 299, 339
A. colpoctes Stiz., 90
A. japonica Miill.-Arg., 90
Archer, 28
Arctomia Th. Fr , 334
Argopsislh. Fr., 105, 135, 297, 330
Arnold, 18, 261, 342, 343, 364, 368, 370, 407
Arnoldea minutula Born., 190 (Fig. 108)
Arnott, Walker, 15
Artari, 39, 42
Arthonia Ach., 158, 203, 278, 305, 321, 343, 361
A. astroidea Ach., 202
A. cinnabarina Wallr. (see A. gregarid], 349
A. dispersa Nyl., 365
A. gregaria Koerb., 247, 248
A. lecideella Nyl., 365
A. pruinosa Ach., 145
A. rattiata Ach., 78, 365
A. subvarians Nyl., 262
Arthoniaceae, 59, 278, 309, 321
Arthoniopsis Miill.-Arg., 321
Arlhopyrenia Massal., 30, 316
A.fallax Am., 365
A. halizoa A. L. Sm., 383
A. haloJytes Oliv., 383
A. leptotera A. L. Sm., 383
A. macrospora Fink, 365
A. marina A. L. Sm., 383
A. punctiformis Arn., 346, 365
A. quinqueseptata Fink, 365
Arthotheliopsis Wain., 327
Artholheliuin Massal., 321
Ascolichens, 272, 273, 281, 308, 311
Ascomycetes xix, 178 et passim
Ascophanus carneus Boud. , 1 80
Aspergillus Micheli, 220
Aspicilia Massal., 133, 136, 140 (see Lecanora}
A. alroviolacea (Flot.) Hue, 158
A.fiavida (Hepp), 248
Aspidoferae, 9
Aspidopyrenium Wrain., 314
Aspidothelium Wain., 314
Aster istion Leight., 337
Asterosporum Mull.-Arg., 316
Asterothyrium Miill.-Arg., 327
Astrotheliaceae, 309, 317, 352
Astrothelium Trev. ,317
Athalami, 305
Aulaxina Fee, 322
Azolla Laur., 41 ,
Babikoff, 138
Babington, 18, 350
Bachmann, E., 35, 75, 76, 215, 216, 235, 247,
347, 393
Bachmann, Freda, 162, 179, 181, 186
Bacidia, De Not., 329
B. acdinis (Flot.), 248
B . Beckhausii Koerb., 262
B. flavovirescens Anzi, 280
B. fuscoriibella Arn., 249, 365
B. inundata Koerb., 372, 373, 377, 391, 392
B. muscorum Mudd, 248, 368, 370, 377
B. rubella Massal., 365
INDEX
449
Bacotia septum, 399
Baeotnyces Pers., 123, 293, 294, 330
B. paeminosus Krempelh., 55
B. placophyllus Ach. , 293, 368
B. roseus Pers., 123, 167, 195, 218, 247, 362,
367, 368, 369
B. rufus, DC., 123, 167, 177, 218, 237, 240,
362, 368, 369
Baranetzky, 24
Bary, de, 24, 31, 187, 209, 213
Bauhin, J., 419
Bauhin, K., 3
Baur, 51, 115, 118, 124, 161, 165, 167, i68i 169,
170, 172, 173, 174, 176, 177, 180, 181, 185,
255
Beckmann, 230, 257
Beechey, 15
Beetle-mites, 397
Beijerinck, 39, 220
Beilstein, 211
Belonia Koerb., 316
Berg, 211
Berkeley, 252, 404
Berzelius, 210
Betula nana L., 95
Bialosuknia, 57
Biatora Koerb., 158, 279, 293 (see also Lecidea),
39'
Biatorella Th. Fr., 331
B. dnerea Th. Fr., 375
B. pruinosa Mudd, 217 (Fig. 119)
B, resinae Th. Fr., 355
B. simplex Br. and Rostr., 217 (Fig. 118)
B. testudinea Massal., 375
Biatorina Massal., 245, 291
B. Bonteillei Arn., 363
B. chalybeia Mudd, 386
B. coeruleonigricans A. L. Sm., 367
B. globulosa Koerb., 378
B. lentictilaris Koerb., 383
B. prasina Syd., 33, 61
B. (denigrata) synothea Koerb., 33, 204
Bilimbia, aromatica Jatta, 349
B. incana A. L. Sm., 343
B. microcarpa Th. Fr., 262
B. obscurata Th. Fr., 262
B. sabulosa Massal., 370
B. sphaeroides Koerb., 385
Bioret, 320
Birger, see Nilson
Bitter, 64, 79, 94, 97, 131, 140, 143, 147, 148,
149, 151, 176, 240, 242, 253, 257, 261, 267,
337, 397
Blackman, 206
Blackman and Welsford, 179
Blastenia Th. Fr., 340
Blastodesmia Massal., 316
Bohler, 415
Bombyliospora De Not., 329
Bonnier, 29, 36, 47, 65, 189, 232, 253
Bornet, 27, 28, 32, 36, 61, 78, 136, 189
Borrer, 12, 14
Borrera, see Physcia
Borzi, 28, 161, 164
Botrydina vulgaris Breb. , xix, 57
Botrydium pyriforme Kiitz., 45
Bottaria Massal., 317
S. L.
Bouilhac, 42, 140
Braconnot, 214
Brandt, 103, 130
Braun, Fr., 354
Braun, L., 393
Brefeld, 189, 207
Brez, 395
Brooks, F. T., 64, 179
Brown, E. W., 402
Brown, W. H., 168
Bryopogon, see Oropogon
Bryum L., 392
Buchet, 90
Buddie, 4
Buellia, De Not., 263, 280, 291, 302, 308, 341,
347
B. aethalea Th. Fr., 261
B. atrata Mudd, 245, 375
B. canescens De Not., 80, 366, 377, 380, 399,
B. colludens Tuck., 382, 386
B. coradna Koerb., 375
B. discolor Koerb., 388
B. leptocline Koerb., 374
B. myriocarpa Mudd, 50, 346, 366, 369
B. parasema Th. Fr., 365, 367, 377
B. Parmeliarum Oliv., 263
B. pnnftiformis, 50, 202, 207 (Fig. 118)
B. ryssolea A. L. Sm., 380, 382 (Fig. 125)
B. stellulata Mudd, 382, 388
B. triphragmia Th. Fr., 390
B. turgescens Tuck., 367
B. verruculosa Mudd, 261
Buelliaceae, 311, 341
Buxbaum, 6, 10
Buxus sempervirens L., 353
Cactus, 325, 353
Calenia Miill.-Arg., 338
Caliciaceae, 62, 115, 175, 189, 244, 288, 309,
3 '9. 353, 366
Calicium De Not., 184, 201, 277, 319, 361
C. arenariitm Nyl. , 376
C. corynellum Ach., 376
C. hyferelltim Ach., 349, 365
C. parted num Ach., 202, 367
C. Irachelinum Ach., 196, 202, 204
Calkins, 348, 403
Cal/opisma, see Platodium
Calluna Salisb., 95, 355
Caloplaca Th. Fr. (see P/ae odium), 340
C. aitrantia, var. callopisma Stein., 190
C. gilvella (Nyl.), 276
C. inteneniens Miill.-Arg., 276
C. pyraceat\L. Fr., 34, 388
Caloplacaceae, 311, 340
Calothricopsis Wain., 333
Calyddium Stirt., 289, 320
C. cuneatum Stirt., 350
Camellia L., 269
Camerarius, i
Camillea Fr., 276
Campylidium ,191
Campy lot helium Miill.-Arg., 317
Candelaria Massal., 339
C. concolor Wain., 365, 388, 399
Candelariella Miill.-Arg., 338
C. cerinella A. Zahlbr., 390
450
INDEX
Candelariella vitellina Miill.-Arg., 233, 237,
369, 377, .393. 417
Capnodium Mont., 179
Carpinus Tournef., 240
Carrington, 12
Carroll, 19
Cassini, 21
Catillaria Th. Fr. (see Biatorind), 329
C. Hochstetteri Koerb., 375
Celidiaceae, 265
Cdliditim stictarum Tul., 267
Cenomyce Th. Fr., 295
Cephaleuros Kunze (see Mycoided), 59, 288
Cephaloidei, 303
Cepteus ocellatus, 397
Cerania S. F. Gray, 340
C. vermiadaris S. F. Gray, 194, 387
Cetraria Ach., 84, 94, 200, 210, 213, 225, 241,
264, 299, 346, 350, 357, 358, 370, 388, 399
C. aculeata Fr., 211, 241, 262, 299, 300, 355,
369,384,385,386, 387
C. caperata Wain., 264
C. crispa Lamy, 387, 388
C. ctuullata Ach., 201, 244, 389
C. diffusa A. L. Sm., 366
C. islandica Ach., 2, 94, 128, 195 (Fig. 112),
210, 212, 221, 227, 231, 241, 338, 355, 387,
401 (Fig. 128), 406, 408, 409, 411, 416
C. juniperina Ach., 201, 246, 416
C. Lanreri Kremp., 364
C. nivalis Ach., 201, 210, 389 .
C. pinastri S. F. Gray, 145, 246, 410
C. tristis, see Parmelia
Chaenotheca Th. Fr., 201, 319
C. chrysocephala Th. Fr., 265, 277, 288
Chalice-Moss, 3
Chambers, 43
Chasmariae, 295
Chevalier, 13
Chiodecton Miill.-Arg., 276, 320, 323, 351, 364
Chiodectonaceae, 59, 278, 309, 323
Chlorella Beij., 56"
Ch. Cladoniae Chod., 56
Ch.faginea Wille, 56 (Fig. 23 A)
Ch. lichina Chod., 56
Ch. miniata Wille, 56 (Fig. 23 A)
Ch. viscosa Chod., 56
Ch.vnlgaris Beyer., 42, 56
Chlorococcus (? Chlorococcum Fr.), 24
Chlorophyceae, xix, 51, 55-60, 61, 272, 324
Chodat, 28, 30, 43, 44, 55, 115, 329
Chroococcaceae, 25
Chroococais Naeg., 24, 52, 82, 136, 153, 284,
311- 332> 373
Ch. giganteus West, 52 (Fig. 16)
Ch. Schizodermaticus West, 52 (Fig. 16)
Ch. turgidns Naeg., 52 (Fig. 16), 136
Chroolepus Ag., see Trentepohlia
C. ebeneus Ag., 22
Chrysothricaceae, 57, 310, 325
Chrysothrix Mont., 325, 353
C. noli tangere Mont., 325
Church, A. Henry, 42 1
Church, A. Herbert, 402
Cicinnobolus Ehrenb. , 261
Cinchona L., 364
Cinchona cordaminea Humb., 364
C. cordifolia Mutis, 364
C. oblongifolia Mutis, 364
Claassen, 34
Cladina Leight, 112, 122, 253, 292
Cladonia Hill, 9, 13, 23, 38, 44, 55, 56, 80, 81,
95, 104, 106, 172, 213, 237, 241, 242, 257,
262, 329, 344, 346, 347, 355, 358, 372, 375,
385. 39V 399.' 4°8
Cl. agariciformis Wulf., 368
Cl. aggregata Ach., 120
Cl. alcicomis Floerk., 385, 386
Cl. alpestris Rabenh., 125, 211, 349, 369
Cl. alpicola Wain., 122
Cl. amaurocrea Schaer. , 1 1 8
Cl. bjllidiflora Schaer., 1 19
Cl. botrytes Willd., 173
Cl. caespiticia Floerk., 115, 124, 294, 296
Cl. cariosa Spreng., 113, 120, 295, 296,368
Cl. cartilaginea Miill.-Arg., 122
Cl. ceratophylla Spreng., 122
Cl. cervicornis Schaer., 113, 120, 122, 243,
384, 387
Cl. coca/era Willd., 113, 118,368,369,370,387
Cl. cristatdla Tuck., 367, 369
Cl. decorticata Spreng., 172 (Fig. 98)
Cl. deformis Hoffm., 226
Cl. degenerans Floerk., 114, 117, 124
Cl. destncta Nyl., 387
Cl. digitata Hoffm., 113, 122, 371
Cl. divaricata Meng. and Goepp. , 355
Cl. enautia f. dllatala Wain., 112
Cl. endiviaefolia Fr., 384
Cl.Jimbriata Fr., 51, 117, 120, 295 296, 349,
367, 368, 370, 377; Subsp.y££w/a Nyl., 119,
369
Cl. flabelliformis Wain., 371
Cl. Floerkeana Fr., 173,296, 362, 370
Cl. foliacea Willd., 112, 113, 120, 122, 240,
295, 296
Cl.furcata Schrad., 117 (Fig. 70), 118, 124,
194 (Fig. 109), 212, 295, 297, 355, 368, 369,
377, 386
Cl. gracilis Hoffm., 115 (Fig. 68), 122, 124,
210, 297, 367, 369, 387
Cl. leptophylla Floerk., 295, 296
Cl. macilenta Hoffm., 362, 366, 367, 369, 378
Cl. miniata Mey., 112, 122
Cl. nana Wain., 112
Cl. Neo-Zelandica^Nxm., 112
Cl.papillaria Hoffm., 195, 296, 344
Cl.pityrea Floerk., 255, 366
Cl. pungens Floerk. (see Cl. rangifortnis)
Cl. pycnoclada Nyl., 345
Cl. pyzidata Hoffm., 2, 44, no, lit (Fig. 66),
113, 114, 117 (Fig. 69), 118, 120, 124, 172,
227, 295, 346, 349, 362, 366, 368, 370, 371,
377. 408
Cl. racemosa Hoffm., 387
Cl. rangiferina Web., 56, 95, 117, 119, 120,
210, 211, 215, 227, 231, 237, 238, 253, 267,
293, 297, 349' 355. 357. 3^9. 386, 388, 400,
,4IX
Cl. rangiformis Hoffm., 271, 295, 366, 368, 386
Cl. retepora Fr., 117, 120 (Fig. 71), 231, 351
Cl. rosea Ludw., 354
Cl. solida Wain., 114
INDEX
Cladonia sqiiamosa Hoffm., 113, 115 (Fig. 67),
118, 210, 243, 295, 366, 368
Cl. sylvatica Hoffm., 95, 112, 117, 119, 271,
349, 366, 368, 369, 385, 400
Cl. syinphicarpia Tuck., 367
Cl. tophacea Hill, 8
Cl. tiirgida Hoffm., 369
Cl. uncialis Web. , 112, 120, 369, 387, 389
Cl. -verticillaris Fr. , 122
Cl. verticillata Floerk., 114, 119, 120, 124,
349' 36/. 369
Cladoniaceae, 135, 292, 310, 329, 366, 370
Cladoniodei, 306
Cladophora Kiitz., 35, 59, 188
C. glomerala Kiitz., 58 (Fig. 30)
Cladophoraceae, 59
Clathrhiae, 117, 120
Clathroporina Miill.-Arg., 316
C/ausae, 295
Clai'aria Vaill., 421
Cleora lichenaria, 399
Cocciferae, 295
Coccobotrys Chod., 30, 40, 56, 315
C. Vei-rucariae Chod., 57 (Fig. 24)
Coccocarpia Pers., 335
C. tnolybdaea Pers., 61
C.pellita Miill.-Arg., 166
Coccomyxa Schmidle, 56
C. Solorinae croceae Chod., 56
C. Solorinae saccatae Chod. , 56
C. sitbcllipsoidea Acton, 57 (Fig. 25)
Coccotrema Miill.-Arg., 316
Coenogoniaceae, 59, 291, 310, 328
Cocnogoniitm Ehrenb. , 23, 35,69, 182, 246, 291,
32X> 35'
C. ebeneum A. L. Sm., 22 (Fig. 3), 34, 59,
328, 350, 352, 363
C. implexum Nyl., 352
C. Linkii Ehrenb., 213
Coenothalami, 303
Coleochaete Breb., 178
Collema Wigg-, 6, 9, 21, 23, 25, 30, 48. 69, 87,
132, 165, 173, 200, 230, 284, 305, 334, 367,
392
C. reranoides Borr., 385
C. cheileum Ach., 161
C. crispum Ach., 161, 180
C. flacciditm Ach., 365
C. fitiviatile Sm., 392
C. granulatum Ach., 368
C. granuliferum Nyl., 69, 232, 243
C. Hildenbrandii Garov., 202 (see Leptogium)
C. liinostnn Ach., xx, 21, 349
C. microphyllum Ach., 160 (Fig. 91), 161
(Fig. 92), 202
C. iiigrescens Ach., 20 (Fig. 2), 101, 243, 245.
364
C plicatile, 409
C.pulposum Ach., 24, 162, 179, 186, 202, 266,
368, 385
C. pustiilatiun Ach., 373
C.pycnocarpum Nyl., 365
C. tenax Sm., 368
Collemaceae, 27, 53, 69, 160, 241, 244, 266,
284, 306, 310, 334, 364, 384, 396
Cot 'le modes Fink, 162
C. Bachinannianttm Fink, 162
Corella Wain., 153, 311, 34
C. brasiliensis Wain., 15.
Collemodiuw, see Leptogium
Collemopsidiitni Nyl., 3**, 174
Collybia, Qu61., 105
Colonna, 3
Combea De Not., 83
Conida Massal., 265, 267
C. mbescens, Arn., 265
Conidella urceolata Elenk., 265
Coniocarpi, 307
Coniocarpineae, 267, 273, 274, 276, 288. 309.
3'9
Coniocarpon DC., ^05
Coniocybe Ach., 277, 319, 366
C '. fnrfuracea Ach., 746, 376
Conotrema Tuck., 326
C. urceolatum Tuck., 343
Convolnta roscoffensis, 40
Cora Fr., 53, 246, 281, 311. 342, }H2
C. Pavonia Fr., 88, 152 (Figs. 86, 87)
Coralloidcs, 5, 6, 7, 303
Corda, 200
Cordus, 409
Cordyceps Fr., 261
342, 35*
'54
Coriscium Wain., 285, 288, 319
Cornicularia (Cetraria) Schreb., 388
C. ochroleiua Ach., 355
C. siibpitbescens Goepp.. 355
C. siiicinea Goepp., 355
Corylns Tournef., 240
Cramer, 409
Croall, 19
Crocynia Nyl., 325
C. gossypina Nyl., 325
C. laimginosa Hue, 325, 373
Crombie, xxi, 7, 18, 19, 197, 260, 262, 264, 306,
36i
Crottles, 415
Criteria Fr., 73
Cryptothecia Stirton, 331
Cryptothele Nyl., 333
Cudbear, 413, 415
Culpepper, 409
Cunningham, 35, 269
Cuppe-Moss, 3
Cupthongs, 9
Curnow, 19
Cutting, 1 80
Cyanophili, 308, 310
Cyanophyceae, 309 ; see Myxophyceae
Cycas L., 40
Cyclocarpineae, 273, 279, 290, 309, 314
Cyperus, 419
Cypheliaceae, 309, 320
Cyphelitim Th. Fr., 276, 277, 288, 320
Cyphella aeriigitiasffus Karst., 191
Cystofocctts Chod., 55. 56
C. Cladoniae fimbriatae Chofl., ;6
C. Cladoniae pixidatae Chod., 56 (Fig. 56)
Cystococciis Naeg., 24, 26, 28, 34, 115, 219
C. humifola Naeg.. 24, 27, 40, 55
Cystocoleus Thwaites, 23
Cytospora Ehrenb., 204
Czapek, 211, 413
Dacantpia Massal., 315
29—2
452
INDEX
Dactylina Nyl., 340
D. arctica Nyl., 339, 346
Dangeard, 185
Danilov, 37
Darbishire, 18, 26, 51, 64, 77, 86, 90, 92, 101,
103, no, 130, 147, 148, 166, 167, 171, 175,
180, 181, 253, 256, 299, 324, 342, 346, 347,
377. 389
Darbishire and Fischer-Benzon, 307
Darbishirella A. Zahlbr., 324
Davies, 12, 14
Dawson, 178
De Candolle, 12
Deckenbach, 59
Deer, 401
Delise, 13, 126
Dendrographa Darbish., 324
D. leucophaea Darbish., 103, 213
Dermatiscum Nyl., 331
Dermatocarpaceae, 309, 314
Dermatocarpon Eschw., 80, 81, 276, 288, 315
D. aquaticum A. Zahlbr., 391, 392
D. cinereum Th. Fr., 368
D. hepaticum Th. Fr., 368, 388
D. lachneum A. L. Sm., 88, 368
D. miniatum Th. Fr., 56, 96 (Fig. 56), 173
(Fig- 99)» 185, 241, 261, 373, 391, 392,403
Desfontaines, 10
Diatoms, 220
Dichodium Nyl., 334
Dickson, 9
Dictyographa Miill.-Arg., 322
Dictyonema A. Zahlbr., 54, 153, 311, 342, 352
Didymellq Sacc., 276
Didymosphaeria pulposi Zopf, 266
Dillenius, xx, i, 6, 155, 192, 262, 304, 407
Dioscorides, 2
Diplogramma Miill.-Arg., 322
Diplopodon, 270
Diploschistaceae, 310, 326
Diploschistes Norm., 326 <-
D. bryophilus Zahlbr., 374
D. ocellatus Norm., 247, 248, 374
D. scruposus Norm., 195, 214, 241, 243, 262,
368
Diplosphaera Bial., 57
D. C/Wa/z Bial., 57
Dirina Fr., 73, 83, 290, 323
Dirinaceae, 290, 309, 323
Dirinastrum Mull.-Arg., 290, 323
Discocarpi, 307
Discomycetes, 267, 273
Dodoens, 3
Dog-lichen, 408
Domestic animals (Oxen, horses, etc.), 401
Don, 14
Doody, 4
Dorstenius, 2, 408
Dothidea Fr., 317
Dufour, i r
Dujourea Nyl., 340
Dufrenoy, 42, 260, 269
Dumontia Lamour., 1 1 T
Dundonald, Lord, 420
Ectolechiaceae, 69, 310, 327, 352, 363
Egeling, 234
Elaphomyces Nees, 261
Elenkin, 36, 37, 258, 265, 347
Elenkin and Woronichin, 353
Elfving, xxi, 25
Encephalographa Massal., 322
Enchylium Massal., see Forssellia
Endocarpon Hedw., 62, 88, 89, 197, 200, 261,
288, 315, 35t, 389
E. monstrosum Massal., 373
E.pusillum Hedw., 28 (Figs. 5, 6)
Endocena Cromb., 339, 340
Endomyces scytonemata Zuk., 38
Englehardt, 354
Enterodictyon Miill.-Arg., 323
Enterographa Fee, 320
E. crassa Fee, 350
Enterostigma Miill.-Arg., 323
Erioderma Fee, 335
Eolichen Zuk., 285, 319
E. Heppii Zuk., 319
Ephebaceae, 54, 284, 310, 331
Ephebe Fr., 23, 25, 27, 30, 38, 68, 201, 284, 322
E. lanata Wain., see E. pubescens
E. pubescens Nyl., 23 (Fig. 3)
Ephebeia Nyl., 332
Epiconiaceae, 307
Epiconiodei, 306
Epigloea Zuk., 313
E. bactrospora Zuk., 313
Epigloeaceae, 57, 309, 313
Erica tetralix L., 95
Errera, 213, 214, 405
Erysiphe Link, 188
Eschweiler, 15, 184
Escombe, 210
Etard and Bouilhac, 42, 140
Ettingshausen and Debey, 354
Euler, 214
Eunephroma Stiz., 337
Euopsis granatina Nyl., 282, 387
-Evernia Ach., 84, 95, 99, 200, 213, 340
E.furfuracea Mann, 24, 38, 94, 99, 108, 142
(Fig. 81), 151, 227, 231. 233, 300, 366, 376,
403. 405
E. prunastri Ach., 2, 100 (Fig. 59), 108, 210,
211, 212, 227, 233, 234, 238, 2*69, 300, 364,
384, 385. 396> 4°°. 4°3> 4'8, 419
Everniopsis Nyl., 339, 340
Eversman, 404
Famintzin, 24
Farriolla Norm., 319
Faull, 178
Fee, 13, 15, 184, 187, 192, 364
Fink, Bruce, xx, 242, 254, 348, 358, 365, 367,
368, 369, 373, 389, 391
Fischer, 308
Fitting, 36
Fitzpatrick, 181
Flagey, 373, 389
Florideae, 160, 177, 273
Fldrke, 12, 13, 133
Flotow, 23, J92
Fontinalis L., 391
Forficula auricularia, 396
Forskal, 403
Forssell "
» 4°3
> 63, 65, 133, 136, 163, 175, 282, 373
INDEX
453
Forssellia A. Zahlbr., 284, 333, 373
Forster, 12, 14
Fossil Lichens, 353-355
Frank, 31, 62, 78 '
Fraser, 1 78
French, xxiii
Friedrich, 75, 233, 269, -270
Fries, E., 13, 22, 149, 364
Fries, Th. M., 17, 18, 133, 138, 152, 192, 163,
342
Fncus L., 281
F. spiralis L., 383
Fuisting, 30, 159, 173
Fiinfstiick, 18/19, 61, 75, 76, 161, 169, 170,
171, 175, 181, 216, 218, 219, 224, 342
Gage, 14
Gallic, 95, 242
Gargeaune, 45
Gasterolichens, 308
Gautier, 213
Geisleria Nitschke, 314
G. sychnogonioides Nitschke, 370
Georgi, 10, 420
Geosiphon Wettst., 45
Gerard, John, 3, 418"
Gibelli, 200
Gilson, 209
Gleditsch, 269
Gloeocapsa Kiitz., 23, 32, 55, 61, 68, 136, 195,
232, 284, 292, 332, 373
G. magma Kiitz., 52 (Fig. 17), 60, 136
G. polydermatica Kiitz., 53
Gloeocystis Naeg., 33, 57 (Fig. 28), 61, 133, 318
Gloeolichens, 175, 282, 284, 373, 389
Glos sodium Nyl., 330
G. aversiim Nyl., 294
Gltick, 198
Glyphis Fee, 276, 323
Glypholecia Nyl., 331
Gmelin, J. F., 152
Gmelin, J. G., 411
Gnomonia erythrostoma Auersw., 178
Goeppert, 354, 393
Goeppert and Menge, 354
Gomphillus Nyl., 293, 330
Gongrosira Kiitz., xxi
Gongylia Koerb., 314
G. viridis A. L. Sm., 368, 388
Gonohymenia Stein., 333
Gonothecium Wain., 31, 327
Gordon, Cuthbert, 415
Gossypina Uhnt, 399
Grammophori, 307
Graphidaceae, 59, 158, 309, 321, 351, 352, 364
Graphideae, 13, 17, 27, 34, 62, 78, 79, 172, 348,
349: 35L 353- 364
Graphidineae, 273, 278, 289, 309, 320, 365
Graphina Miill.-Arg., 322
Graphis Adans., 9, 211', 321, 322, 343, 349, 351,
355> 36*> 364
G. clegans Ach., 30, 158 (Fig. 89), 172, 180,
397
G. scripta Ach., 50, 349, 354, 365, 366
G. scripta succinea Goepp., 355
Gray, J. E., 12, 305
Crete Herball, 2
Greville, 12
Grimbel, 250
Grimmia pulvinata Sm., 393
G. apocarpa Hedw., 393
Guembel, 392
Guerin-Varry, 210
Guillermond, 167
Gunner a L., 31, 41
Gyalecta Ach., 191, 318
G. cttpularis Schaer., 244
G. Flotoi'ii Koerb., 244
G. geoica Ach., 254
G. rtibra Massal., 249
Gyalectaceae, 54, 59, 69, 310, 327
Gyalolechia Massal., 201
G. sHbsimiHs (Th. Fr.) Darb., 378
Gymnocarpeae, 156, 308, 318
Gymnoderma Nyl., 330
G. coccocarpurn Nyl., 293
Gymnographa Mull.-Arg., 322
Gyrophora Ach., 88, 96, 184, 200, 227, 231, 241,
249, 268, 304, 331, 346, 350, 376, 390, 393,
4'4.
G. cylindrica Ach., 176, 184 (Fig. 103), 375,
387
G. erosa Ach., 330, 387
G. esculent a Miyosh., 403
G. flocculosa Turn, and Borr., 375
G. murina Ach., 94
G.polyphylla Hook., 387
G. polyrhiza Koerb., 94, 349, 404 (Fig. 119)
G. proboscidea Ach., 192, 346, 375
G. spodochroa Ach., 94
G. tonefacta Cromb., 375, 387
G. vellea Ach., 74, 1 76
Gyrophoraceae, 291, 310, 330
Gyrostomum Fr., 326
Haberlandt, 106, 188
Haematomma Massal., 230, 236, 338
H. coccineum Koerb., 214, 223, 2»6
H. elatinum Koerb., 201
H. ventosum Massal., 214, 225, 241, 251, 298,
375, 37.6, 388, 393
Hagenia filtaris, 24
Haller, 7, 126
Halopyrenula Miill.-Arg., 318
Halsey, 14
Hamlet and Plowright, 213
Haniiand, 63
Harper, 167, 178, 181, 188
Harpidium Koerb., 298, 338
H. rutilans Koerb., 298
Harriman, 14
Hassea A. Zahlbr., 319
Hedlund, 32, 61, 204, 245
Hedwig, 142, 156, 184, 192
Helix hortfttsis, 396
H. cingulata, 396
Hellbom, 350, 411
HelmmthocarpoH Fee, 322
Henneguy, 410, 411, 420
Heppia Naeg., 81, 175, 285, 335, 348, 351, 389
H. DepreauxiilucV.., 368
H. Guepini Nyl., 80, 88, 96
H. virescens Nyl., 368
Heppiaceae, 54, 285, 310
454
INDEX
Herberger, 221
Herissey, 213
Herre, 230, 253, 349
Hesse, 12, 221, 224
Heterocarpon Mlill.-Arg., 315'
Heterodea Nyl., 339
H. MullertNyl., 128, 299, 339, 350
Heterogenei, 303
Heteromyces Miill.-Arg., 293, 330
Heufleria Trev., 317
Hicks, 14.
Hildenbrandtia Nardo, 73
Hill, Sir John, 8, 409
Hoffmann, 10, 154, 412, 415
Hofmann, 261
Holl, 19
Holle, 14, 46, 187
Holmes, 19, 422
Homogenei, 303
Homopsella Nyl., 334
Homothalami, 305
Homothecium Mont., 334
Hooker, 12, 15, 149
Hornschuch, xx, 156
How, 3
Howe, Heber, 85, 224, 348
Hudson, 7, 9, 303
Hue, ii, 16, 18, 33, 57, 63, 69, 73, 82, 85, 103,
133, '35. 136, 140, 188, 262, 283, 315, 325,
339. 34°> 342, 347, 348, 360, 396, 418
Hulth, 215
Hutchins, 14
Hutchinson, 403
Hydrothyria Russ., 336
H. venosa Russ., 97, 175, 233, 286, 348, 390
Hymenobolina parasitica Zuk. , 267, 399
Hymenolichens, xix, 54, 152-154, 273, 281, 308,
3".335, 342
Hymenomycetes, xix, 153 et passim
Hyphomycetes, xix, 191
Hypnum L., 392
H. cupressiforme L., 385
Hypogymnia Nyl., 94, 176
Hypoxylon Bull., 12
Hysteriaceae, 273, 307
Hysterium Tode, 12
Iceland Moss, 210, 401 et passim
Icmadophila Massal., 166, 338
/. aeruginosa Mudd, see I. ericetorum
I. ericetorum A. Zahlbr., 196, 244, 370
Illosporium carneum Fr., 268
Ingaderia Darbish., 324
Iris, white, 419
Isidium Ach., 149
'/. corallinum Ach., 149
/. Westringii Ach., 149
Istvanffi, 202, 206
Itzigsohn, 17, 23, 24, 193
Jaczewski, 353
Jasmine, oil of, 419
Jatta, 129
Jenmania Wacht., 333, 352
Jennings, Vaughan, 60
Jesuit's bark, 10
John, 250
Johnson, C. P., 401, 402
Johnson, W., 19
Johow, 153
fonaspis Th. Fr. , 328
Joshua, 19
Jumelle, 230, 238
Kajanus (Nilson), 151
Karschia Koerb., 280
K. destructans Tobl., 265
K. lignyota Sacc., 280
Keeble, 4i
Keegan, 224, 410
Keiszler, 201
Keller, 402
Kerner and Oliver, 215
Kieffer, 371
Kienitz-Gerloff, 51
Kihlman, 237, 358, 388, 401
Knop, 213, 247
Knop and Schnederman, 221
Knowles, 224, 249, 379, 384, 391
Kobert, 409, 410
Koelreuter, 155
Koerber, 14, 123, 142, 188, 305
Koerberia Massal., 334
Kotte, 264
Krabbe, 63, 113, 114, 119, 122, 123, 124, 143,
147, 162, 170, 172, 174, 176, 177, 253
Kratzmann, 214
Krempelhuber, i, 55, 244, 364
Kupfer, 261
Kutzing, 22
Laboulbenia Mont, and Robin, 178
Laboulbeniaceae, 178, 274
Lachnea scutellata Gill., 168
L. stercorea Gill., 178
Lacour, 211
Lang, 76, 216, 235
Larbalestier, 19
Laubert, 206
Laudatea Joh., 154
Laurera Reichenb., 317
Lecanactidaceae, 310, 325
Lecanactis Eschw., 204, 325
Lecania Massal., 136, 338
L. candicans A. Zahlbr., 80 (Fig. 43)
L. cyrtella Oliv. , 377
L. erysibe Mudd, 377
L. holophaea A. L. Sm., 350
Lecaniella Wain., 327
Lecanora Ach., 78, 88, 200, 298, 305, 338, 347,
349- 351, 353, 364, 365, 372, 39°
L. aquatica Koerb., 391
L. aspidophora f. errabunda Hue, 262
L. atra Ach., 63, 225, 249, 375, 380, 382 (Fig.
125), 384, 386, 393
L. atriseda Nyl., 261
L. atroflava, see Placodium
L. aurella (Hoffm.), 262
L. badia Ach., 79, 375, 386
L. caesiocinerea Nyl., 218, 384
L. calcarea Somm., 218 (Fig. 120), 373, 396
L. campestris B. de Lesd., 361, 384
L, cenisia Ach., 375
L. cinerea Somm., 229, 349, 375
INDEX
455
Lecanora dtrina Ach., see Placodium
L. coilocarpa Nyl. , 30
L.crassa Ach., 79, 81,201, 2 18,367, 368, 373,389
L. crenulata Hook., 361, 377
L. Dicksonii Nyl., 250, 375
L. dispersa Nyl., 261, 369, 377, 384
L. ejffusa Ach., 204
L. epanora Ach., 246
L. epibryon Ach., 378, 389
L. epulotica Nyl., 392
L. esculenta Eversm., 21 1, 257, 265, 298, 389,
404 (Fig. 130), 422
L. exigna, see Rinodina
L.ferrnginea Nyl., 30
L. galactina Ach., 254, 262, 360, 369, 377,
384. 386
L. gelida Ach., 135, 136, 137 (Fig. 77), 140,
375
L. gibbosa Nyl., 375, 384, 386
L, glaucoma Ach., see L. sordida
var. corrugata Nyl., 84 (Fig. 46)
L. Hageni Ach., 366, 367, 369, 377, 383
L. hypnorum Ach., see Psoroma
L. lacustris Th. Fr., 233, 250, 391, 392
L. lentigera Ach., 81, 90, 298, 367
L. muralis Schaer., 242
L. ochracea Nyl., 373
L. pallescens Mudd, 213
L. pallida Schaer., 78 '
L.parella Ach., 72, 375, 382, 384, 417
/,. peliocypha Nyl., 375
L. picea Nyl., 374
L.piniperda Koerb., 204
L. polytropa Schaer., 237, 376, 394
L. prosechoides Nyl., 383, 384
L. rubina Wain., 390
L. ragosa Nyl., 366
L. Samiuci VSyl., 204
L. saxicola Ach., 79, 80, 81, 233, 252, 349,
369, 384, 386, 393, 396
Z. simplex Nyl. (see Biatorella], 75, 77, 382
Z. smaragdula Nyl., 382
Z. sophodes Ach., 30; see Rinodina
L. sordida Th. Fr., 194, 236, 261, 374, 375,
380, 382
L. squainulosa Nyl., 374
L. sitbfusca Ach., 22, 30, 49, 65 (Fig. 34), 70
(F'g- 57). W (Fjg- 88)' l64. '66, 167, 168,
236> 347' 365> 366
L. sulphured Ach., 226, 238, 376, 384
L, tartarea Ach., 57, 147. 183 (Fig. 102), 224,
225, 227, 237, 262, 346, 358, 359, 371, 375.
387, 389, 414 (Fig. 134)
L. umbrina Massal., 377, 385
L. upsaliensis Nyl., 387
L. urbana Nyl., 361
L. varia Ach., 227, 346, 360, 36?, 362, 366,
367. 377
L. ventosa, see Haematonuna
L. verntcosa Laur., 378
L. xantholyta Nyl., 373
Lecanoraceae, 136, 311, 337, 353
Lecanorales, 297
Leddea Ach., 78, 184, 261, 279, 292, 304, 308,
328, 346, 347, 349, 351, 353. 364, 3^5, 372,
373, 385,. 39°
L. aglaea Somm., 375
Leddea albocoerulescens Ach., 392
L. alpestris Somm., 387
L. arctica Somm., 387
L. aromatica (see ftilimbia)
L. atrofusca Nyl., 248, 387
L. auriculata Th. Fr., 375
L. Berengeriana Th. Fr-.'^Sj
L. coarctata Nyl., 247
L. coeruleonigricans Schaer., 37}
L. collude us Nyl., 3*84 ; see Bui-Ilia
L. confluens Ach., 375, 388
f. oxydata Leight., 250
L. consentiens Nyl., 134, 135
L. contigna Fr., 375, 376, 388, 392
v&i.jlavicunda Nyl., 250
L. crustiilata Koerb., 369'
L. (Bilimbia) cuprea Somm., 387
L. cupreiformis Nyl., 387
L. dedpiens Ach., 291, 367, 368
L. dccolorans Floerk, see L. granulosa
L. demissa Th. Fr. , 369, 387
/,. diduccns Nyl., 375
L. enterolenca Nyl., 164, 168, 365
L.fumosa Ach., 159
L.fuscoatra Ach., 200 (Fig. 114), 375
L. gelatinosa Floerk., 368
Z. granulosa Schaer., 218, 237, 269, 291, 36:
369. 37°, 377
Z. grisella Floerk., 243
Z. helrola Th. Fr., 245
L. herbidnla Nyl., xxi
L. iltita Nyl., 136
L. iinmena Ach., 217 (Fig. 117), 398
L. inserena Nyl., 375
L. insularis Nyl., 236, 261
Z. irregiilaris Fee, 192
L. Kochiana Hepp, 375
L. lapicida Ach., 375
L. lavata Nyl., 384
L. limosa Ach., 387
L. lucida Ach., 246, 376
L. lurida Ach., 79, 195, 241, 367
Z. mesotropa Nyl., 375
L. Metzlen"T\\. Fr., 398
Z. nigroclavata Nyl., 384
Z. ostreata Schaer., 79, 145, 291, 366
L. pallida Th. Fr., 135
L.panaeola Ach., 134, 135, 136, 375
/,. parasema Ach., 183 (Fig. 101), 366
L. pelobolrya Somm., 135, 136
Z. phylliscocarpa Nyl., 31
Z. phyllocaris Wain., 31, 327
Z. plana Nyl., 375
Z. platycarpa Ach., 375
Z. pycnocarpa Koerb., 375
Z. quernea Ach., 236, 349, 386
Z. rivulosa Ach., 374, 375, 376
Z. sanguinaria Ach., 187 (Fig. 105), 248
Z. sanguineoatra Ach., 370
Z. steilitlata Tayl., 376
Z. sulphurella Hedl., 242
Z. sylvicola Flot., 372
Z. testacea Ach., 195 (Fig. in)
Z. tricolor Nyl. (Biatorina Grijfithii), 361
Z. tumida Massal., 375
Z. uliginosa Ach., 254, 291, 370, 385, 387
Z. wrnalis Ach., 66 (Fig. 35)
456
INDEX
Lecideaceae, 135, 241, 279, 291, 298, 310, 327,
328, 341, 346, 353
Lecideales, 290, 308
Leciophysma Th. Fr., 334
Leighton, 16, 17, 18, 19, 134, 306, 342, 353, 388
Leiosoma palmicinctum, 397
Lemming rats, 401
Lemmopsis A. Zahlbr., 334
Lenzites Fr., 261, 371
Leorier, 41 1
Lepidocollema Wain., 81, 336
Lepidoptera, 399
Lepolichen Trevis., 318
L. coccophora Hue, 57, 318
L. granulatus Miill.-Arg., 318
Lepra Hall., 143
L. viridis Humb., 23
Lepraria Ach., 143, 237, 305
L. botryoides, xx
L. chlorina, 376
Leprieur, 15
Leprocollema Wain., 285, 354
Leproloma Nyl., 325
Leptodendriscum Wain., 284, 332
Leptogidium Nyl., 284, 332, 350
L. dendriscum Nyl., 332
Leptogium S. F. Gray, 69, 84, 87, 232, 285, 335,
37°
L. Burgessii Mont., 245
L. byssinum Nyl., 368
L. Hildenbrandii Nyl., 364
L. lacerum S. F. Gray, 243, 254, 373
L. myochrotim Nyl., 365
L. scolimim Fr., 385
L. tnrgidum Nyl., 385
Leptorhaphis Koerb., 263, 316
Lesdain, Bouly de, 140, 270, 271, 366, 369, 376,
398
Letharia A. Zahlbr., 84, 340
L. viilpina Wain., 95, 105, 226, 228, 246, 265,
349, 364, 410, 417
Lett, 19
Lettau, 225, 227, 369, 391, 417
Lichen, xxvi, i, 5, 9, 303
Lichen albineus Ludw. , 354
Lichen candelarius L., 371, 415
Lichen dneretis terrestris, 407
Lichen dichotomus Engelh., 354
Lichen diffusus Ludw., 354
Lichen gelatinosus Rupp, 6
Lichen juniperinus L.. 415
Lichen orbiculatus Ludw., 354
Lichen parietinus L., 371, 415
Lichen Roccella L., 415
Lichen saxatilis L., 415
Lichen tartareus L., 415
Lichen tenellus Scop., 371
Lichenacei, 306
Lichenes Coralloidei etc. Hall. , 7
Lichenodium Nyl., 334
Lichenoides, i, 6, 7, 304, 415
Lichenophoma Keisz., 201
Lichenoxanthine, 418
Lichina Ag., 163, 195, 201, 233, 281, 284, 334,
383
L. confinis Ag., 383, 384
L- pygfnaea Ag., 195, 201, 383
Lichinaceae, 55, 99, 310, 333
Ltchtnella Nyl., 354
Lightfoot, 9, 280/303, 407, 415
Limax, 396
Lindau, 18, 34, 36, 48, 64, 67, 78, 108, 149, 164,
168, 170, 176, 178, 184, 233, 269, 330
Lindsay, xx, 16, 17, 19, 120, 193,203, 252, 262,
266, 348, 354, 358, 391, 401, 415, 417
Link, 371
Linkola, 141
Linnaeus, 7, 142, 154, 304, 312, 392, 401, 409,
Lister, 267
Listerellaparadoxa]2hn., 267
Lithographa Nyl., 322
Lithoicea Massal., see Verrucaria
L. lecideoides Massal., 373
Lithothelium Miill.-Arg., 317
Litmus, 413
Lobaria Schreb., 136, 182, 287, 336
L. laciniata Wain., 133, 134
L. laelevirens A. Zahlbr., 2, 196
L. pulmonaria Hoffm., 2, 3, 10, 90, 96, 126
(Fig. 127), 130, 195, 252, 267, 336, 400, 406,
408, 411, 416, 418
L. scrobiculata DC., 130, 143
L'Obel, 2
Lopadiopsis Wain., 327
Lopadium Koerb., 191, 329
Lophothelium Stirt., 319
Loxa (Cinchona), 364
Ludwig, 354
Luffia lapidclla, 399
Lung-wort, 406, 409
Lutz, 1 08
Luyken, xx, 156, 184
Lycoperdaceae, 307
Lyell, 14
Lyngbya Ag., 136
Mackay, 13
McLean, 385
Macmillan, 357, 391
Maheu, 243, 387
Maire, 185, 186, 189
Malinowski, 74, 371, 374
Malme, 261
Malpighi, 5, 142, 155
Manna, 404, 422
Marchantia L., i, 5
Maronea Massal., 331
Martindale, 19
Martius, 15
Massalongia Koerb., 287, 335
Massalongo, 16, 188, 305
Massee, 308
Mastoidea Hook, and Harv., 315
Mastoidiaceae, 60, 309, 315
Mattirolo, 152
Maule, 162, 164
Mayfield, 368
Mazosia Massal., 59, 323
Mead, Richard, 407
Megalospora Mey. and Flot., 329
Melampydium Miill.-Arg., 325
Melanotheca Miill.-Arg., 317
Melaspilea Nyl., 321, 322
INDEX
457
Mereschkovsky, 258
Merrett, 3
Metzger, 176, 240
Meyer, 13, 46, 51, 126, 143, I56, 187, 252, 258,
3°5
Micarea Fi:, see Biatorina Massal.
Michael, 397
Michaux, 14
Micheli, i, 6, 142, 155
Microcystis Kiitz., 52, 319
Microglaena Lonnr., 314
Micrographa Miill.-Arg., 322
Microphiale A. Zalilbr., 328
-Wicrotkelia Koerb. , 316
Microtheliopsis Miill.-Arg., 318
Minks, 26
Minksia Miill.-Arg., 323
Mites, 395, 397
Miyoshi, 256, 403
J\Iniu>H hornutn L. , 65 (Fig. 35)
Moebius, 62
Mohl, 185, 1 86
Molisch, 250
Moller, 49, 154, 196, 202, 203
J\Io»ia orion, 399
Monas Lens, xx
Monasats, Van Teigh. , 1 78
Montagne, 15
Moreau, xxi, 168, 175, 176, 212, 266
Moriola Norm., 313
Moriolaceae, 309, 313
Morison, i, 4, 5, 155, 304
Moss, 356
Mousse des Chenes, 418
Mudd, 16, 17, 19
Muenster, 354
Mtihlenberg, 14
Mulder, 210
Miiller(-Argau), 18, 26, 191, 192, 205, 278, 307,
353' 4°r
M filler, K.; 212
Miillerella Hepp, 275
Mitsco-fnngns, \
Mn sens, i
Must-its cranii huinani, 413
Musk, 419
Mycetozoon on Lichens, 267
Ulycoblastus Norm., 329
J/. sangitinarius Th. Fr., 188 ; see Lecidca
Mycocalicium Rehm, 277
M. parietinuin Rehm, 277
Mycoconiocybe Rehm, 277
Mycoidea Cunningh., 35, 59, 309, 318, 352, 363
.}/. parasitica Cunningh., 36, 59 (Fig. 31),
60
Mycoideaceae, 59
Mycoporaceae, 309, 318, 352
Mycoporellum Zahlbr., 159, 3x8
Mycoporum Flot., 159, 276, 318
Mycosphatrella Johans., 39
Mycosphaerellaceae, 275
Myriangiacei, 306
Myxodictyon Massal., 338
Myxophyceae, xix, *i, 52-55, 60, 68, 272, 324,
385
Narcyria monilifera, 399
Necker, 123, 154
Nees von Esenbeck, xxiv
Neophyllis Wils., 330, 351
Nephroma Ach.,63, 135, 136, 169, 244,186, 337,
348
N. expallidum Nyl., 139 (Fig. 79)
Nephromium Nyl., 63, 158, 175, 200, 122, 244,
283, 286, 337, 349, 351
N. laevigatutu Nyl., 195
N. lusitanicum Nyl., 218, 246
N. tomentosum Nyl., 87, 128, 169
Nephromopsis Miill.-Arg., 158, 244, 339
Neubert, 410
Neubner, 62, 175, 189, 188
Neuropogon Flot. and Nees, 346
Nienburg, 38, 64, 123, 166, 167, 168, 169, 177,
185, 196, 240
Nilson, 147, 151, 250, 358, 389
Norman, 16, 313
Normandina Nyl., see Corisciutn
Normandina Wain., 315
Nostoc Vauch., 20, 21, 23, 24, 26, 27, 32, 41, 53,
61, 63, 69, 136, 138, 232, 246, 266, 285,
yx^etseq., 396
N. coernlescens Lyngb., 53 (Fig. 18)
N. lichenoides Kiitz., xx, 54
N. Linckia Born., 53 (Fig. 18)
ff. sphaericum Vauch., 54
N. symbioticum, 45
Nostocaceae, 25, 53
Notaris, De, i, 15, 16
Notaspis lutontm, 397
Nyc • tails Fr., 261
Nylander, xxi, 7, 8, 16, 18, 25, 30, 52, 126, 131,
'35. 136, 152, 197, 228, 262, 306, 325, 350,
353, 3°°' 383
Nylanderitlla Hue, 315
Obryzum Wallr., 363
Ocellularia Spreng., 326
Ochrolechia Massal., 338
O. pa'.lescens Koerb., 187 (Fig. 106), 213
Ochrophaeae Wain., 295
Officinal barks, 15
Ohlert, 234
Oidia, 189
Olivier, 342
Omphalaria Dur. and Mont., 348, 3/3, 393
O. Heppii MUll., 63
O. pulvinata Nyl., 373
Oniscus, 396
Oospora Wallr., 45
Opegrapha Ach., n, 13, 35, 184, 304, 321, 321,
353- 354. 36'
O. atra Pers., 15, 202
O. calcarea Turn., 383
O. endoleuca Nyl., 243
O. hapalea Ach., 243
O. saxicola Ach., 216, 219
O. subsiderella Nyl., 50, 202, 349
O. Thomasiana Goepp., 354
0. varia Pers., 354, 365
O. vulgata Ach., 30
O. zonata Koerb., 392
Opegraphella Miill.-Arg., 322
Orbilia coccinella Karst., 261
Orchil lichen, 412, 416
458
INDEX
Oribata Parmeliae, 397
Oribatidae, 397
Oropogon Fr., 340
O. loxensisTh. Fr., 130, 210, 352
Orphniospora Koerb., 329
Orthidium, 191
Orthoptera, 397
Oscillaria Bosc., 24
Pachyphiale Lonnr., 328
Padina Pavonia Gaillon, 153
Palmella Lyngb., 24, 57, 232, 278, 282, 289, 309,
32*> 338, 353
P. botryoides Kiitz., 313
Pannaria Del., 61, 79, 81, 135, 168, 175, 336,
392
P. brunnea Massal.', 244, 370
P. microphylla Massal., 81, 244
P. pezizoides Leight., 63
P. rtibiginosa Del., 283
P. triptophylla Nyl., 244
Pannariaceae, 54, 135, 285, 287, 311, 335
Pannoparmelia Darbish., 338
P. anzioides Darbish., 90 (Fig. 51)
Paracelsus, 407
Paratheliaceae, 309, 316, 352
Parathelium Mull.-Arg., 317
Parfitt, 95
Parkinson, 3, 407
Parmelei, 353
Parmelia Ach., 84, 86, 93, 94, 95, 133, 200, 213,
227, 231, 238, 241, 242, 249, 260, 264, 267,
269, 299, 300, 305, 346, 347, 348, 349, 351,
354. 364, 372, 4M
P. acetabulum Dub., 30, 167, 169 (Fig. 90),
170, 180, 195 (Fig. in), 231, 255, 259, 360
P. adgluthiata Floerk., 365
P. aleurites Ach., 364
P. alpicola Fr., 18, 350, 387
P. aspidota Rosend. (see P. exasperata), 92 (Fig.
53). 17°. 338
P. Borreri Turn., 265 ; see P. dubia
P. caperata Ach., 88 (Fig. 49), 253, 255, 365,
366, 395
P. cetrata Ach. , 92
P. conspersa Ach., 194, 241, 242, 355, 369,
376, 416, 417
P. crinita Nyl., 365
P. dubia Schaer., 377
P. encausta Ach., 268, 388, 393
P. enteromorpha Ach., 131
P. exasperata Carroll, 62, 129 (Fig. 74), 132,
196
P.farinacea Bitt., 131, 143
P.fuligitwsa Nyl., 247, 361, 376, 386
P.glabra Nyl., 87, 170, 176
P. glabratula Lamy, 1 70
P. glomellijera Nyl., 249, 251
P. hyper opt a Ach., 261
P. isidiophora A. Zahlbr., 66
P. Kamtschadalis Eschw. , 300
P. lacunosa Meng. and Goepp., 355
P. lanata Wallr., see P. pubescens
P. locarensis Zopf., 249
P. molliuscula Ach., 265
P. Mougeotii Schaer., 375
P. obscurata DC., 64, 131, 176, 242
Parmelia olivacea Ach., 247, 365
P. omphalodes Ach., 3, 260, 37=;, 387, 415
(Fig. 135)
P. papulosa Rosend., 150, 214, 219
P. perforata Hook. (?), 365
P.perlata Ach., 92, 114, 213, 237, 243, 262,
353. 363. 403. 4i6
P. pertusa Schaer. , 131
P. physodes Ach., 64, 91, 144 (Fig. 83), 146
(Fig. 84), 156, 194, 234, 237, 242, 253, 262,
299> 355. 361, 363. 366, 384, 385, 416
P. pilosella Hue, 92
P. proboscidea Tayl., 92, 150
P. prolixa Carroll, 241, 249, 382
P. pubescens Wain., 85, 299, 300, 350, 375,
387
P. revoluta Floerk., 247, 259 (Fig. 121)
P. saxatilis Ach., 169, 170, 242, 243, 253,
260, 355, 361, 365, 366, 375, 386, 387, 393,
407 (Fig. 131), 416
P. scortea Ach., 150, 366
P. stygia Ach., 130, 299, 350, 375, 387, 393
P. subaurifera Nyl., 143, 226, 246, 377
P. sulcata Tayl., 144, 361
P. tiliacea Ach., 164, 170, 252, 365
P. tristis Wallr., 88, 130, 247, 375, 387
P. vemuulifera Nyl., 87, 143, 214
P. vittata Nyl., 131, 143
Partneliaceae 200, 287, 298, 311
Parmeliales, 308
Parmeliella Mull.-Arg., 81, 286, 336
Parmeliopsis Nyl., 339
Parmentaria Fee, 3 1 7
Patellaria Fr., 280
Patellariaceae 278
Patinella Sacc., 279
P. atryviridis Rerun, 278
Patouillard, 389
Paulia Fee, 284, 333, 352
Paulson, 244, 254, 366
Paulson and Hastings, 28, 38, 44, 56, 260
Paulson and Thompson, 254, 361, 369, 377, 397
Peccania Forss., 284, 333, 373
Peirce, xxiii, 33, 34, 108, 258, 359
Peltati, 305
Peltidea Ach., 63, 286, see Peltigera
Peltigera Willd., 3, 42, 53, 6r, 63, 88, 135, 136,
137, 168, 175, 186, 204, 212, 213, 222, 232,
242, 257, 266, 283, 286, 337, 346, 349, 355,
367, 384, 385, 392
P.americana Wain., 351
P. aphlhosa Willd., 26, 87, 133, 138 (Fig.
78 A, B), 141, 211, 262, 347, 359, 370, 406
P. canina Willd., 24, 51, 84 (Fig. 47), 87, 89
(Fig. 50), 93 (Figs. 54, 55), 97, 185, 213,
254, 262, 359, 367, 370, 394, 396, 407, 418
P. horizontalis Hoffm., 169, 244
P. lepidophora (Nyl.) Bitt., 140
P. leptoderma Nyl., 351
P. malacea Fr., 169, 370
P. polydactyla Hoffm., 51, 244, 266, 368
P. ntfescens Hoffm., 169, 386
P. spuria Leight., 268, 369
P. spuriella Wain., 351
P. venosa Hoffm., 244, 347
Peltigeraceae, 54, 135, 283, 286, 287, 311, 336
Pelvetia canaliculata Dec. and Thur., 39
INDEX
459
Pentagenella Darbish., 83, 324
Perforaria Mlill.-Arg., 337
Persio, 413
Persoon, 10, 21, 123, 156, 395
Pertusaria DC., 34, 73, 85, 86, 88, 170, 180,
186, 213, 246,253, 337, 4 [4
P. amara Ach., 148, 236, 243, 349, 361, 366,
408 (Fig. 132)
P. comtnunis DC., 50, 202, 214 (Fig. 116),
255, 269, 366, 393 •
P. concreta Nyl., 382
P. corallina (Ach.) Bachm., 374
P. dactylina Nyl., 387
P.dealbataC<com\>., 215, 375, 376
P. faginea Leight., 396
P. globulifera Nyl., 33 (Fig. 12), 236, 237, 262,
357, 366
P. glomerata Schaer., 387
P. lactea Nyl., 374, 376
P. leioplaca Schaer., 365
P. hitescens Lamy, 226
P. melaleuca Dub. ,417
P. oculata Th. Fr., 387
P. velata Nyl., 265
P. Wulfenii DC., 226, 366
Pertusariaceae, 147, 311
Petch, 397
Petiver, 4, 10
Petractis Fr., 327
P. exanthematica P'r., 61, 75, 215, 216
Peziza Dill., 157, 213, 307
/'. resinae Fr., 355
Pfaff, 221
Pfeffer, 220
Phacopsis vulpina Tobl., 265
Phaeographina Miill.-Arg., 322
Phacographis Miill.-Arg., 322
Ph. Lyellii A. Zahlbr., 350
Phaeotrema Miill.-Arg., 326
Phalena, 395
Phascum cuspidatum Schreb., 45
Phialopsis rubra Koerb., 174, 249; see Gyalecta
Phillips, 252
Phleopeccarua Stein., 284, 333, 352
Phlyctella Miill.-Arg., 338
Phlyctidia Miill.-Arg., 338
Phlyetis Wallr., 338 •
P. agelaea Koerb., 174
Phycolichens, 22, 282, 283, 285
Pliycopeltis Millard., 59, 278, 318, 321, 322, 323,
327. 352, 363
P. expansa Jenn., 35 (Fig. 13), 60 (Fig. 32)
Phyllactidium Moeb., 59, 62, 288, 309, 310, 318,
327, 363
P. tropiciim Moeb., 59
Phylliscidinm Forss., 333
Phylliscum Nyl., 286, 33}
Phyllobathelium Miill.-Arg., 318
Phyllophora Grev., 1 1 1
Phyllophthalmaria A. Zahlbr., 326, 352
Ph. coccinea A. Zahlbr., 352
Phylloporina Miill.-Arg., 318
Phyllopsora Mull.-Arg., 329
P. furfur acea A. Zahlbr., 329
Phyllopsoraceae, 310, 329
Phyilopyreniaceae, 309, 318
Phymaloidei, 304
Physda Schreb., 90, 94, 166, 186, 238, 301, 351,
37?. 399
P. aipolia Nyl., 20 (Fig. i), 249
P. aquila Nyl., 380, 382, 384
P. ascendens Bitt., 270, 369, 377
P. caesia Nyl., 226, 369, 384
P. chrysophthalma, see Teloschistes
P. ciliaris DC., 3, 46, 84 (Fig. 48), 92, 94, 99,
103, 155, 165 (Fig. 94), 166, 167, 182 (Fig.
too), 184, 185 (Fig. 104), 187, 189, 191,
243, 246, 247, 355, 360, 411, 419
P. granulifera Nyl., 365
P. hispida Tuck., 29, 92, 146, 164, 166, 169,
194 (Fig- IIO)> 24i, 271, 360, 366
P. hypoleuca Tuck., 399
P. intricata Schaer., 301
P. Uncomelas Mich., 99
P. obscura Nyl., 243, 360, 365, 369, 377
P. parietina (see Xanthoria), 29 (Figs. 7, 8)
P. picta Nyl., 349, 353
P. puherulenta Nyl., 28, 164 (Fig. 93), 166,
181, 248, 360, 365, 366, 377, 399
P. punctieulata Hue, 33
P. sciastrella Harm., 369
P. stdlaris Nyl., 29, 365, 384
P. slellaris var. teiulla Cromb. , see P. hispida
Tuck.
P. subobscura A. L. Sm., 384
P. tenella Bitt., 366, 384, 386
P. tribacia Nyl., 365
P. villosa Dub., 268
Physciaceae, 136, 200, 267, 300, 308, 311, 341
Physcidia Tuck., 299, 339
Ph. Wrightii Nyl., 352
Physma Massal., 163, 284, 334, 341
P. chalazanum Arn., 32 (Fig. 9)
P. compaction Koerb., 163, 266
P. franconicum Massal., 263
Pilocarpaceae, 310, 325
PMocarponVfain., 325, 353; see Pilophorus
P. leiicoblepharum Wain., 325, 363
Pilophorus Th. Fr., 17, 125, 133, 135, 201, 292,
294, 297, 330
P. robuslus Th. Fr., 136
Pinus sylvestris L., 94, 271
Piptocephalis De Bary, 261
Placidiopsis Beltr., 288
Placodium DC., 80, 339, 340, 346, 360, 372
P. atroflawm A. L. Sm., 386
P. aurantiacum Hepp, 365
P. bicolor Tuck., 136
P. callopismum Mer., 349
P. cerinum Hepp, 262, 365, 366, 367
P. ritrinum Hepp, 224, 271, 349, 373. 377.
P'. dedpiens Leight., 218, 369, 383
P. elegans DC., 225, 241, 34?- 3<>9» 39°
P.ferntgineum Hepp, 346, 384
P.flavescens A. L. Sm., 377
P. fruticulosum Darbish., 34?
P.fulgensS. F. Gray, 367
P. lacteum Lesil., 377
P. lobulatum A. L. Sm., 379, 382, 3»4
P. luteoalbum Hepp, 301
P. murorum DC., 42, 80 (Fig. 42), «/» *4'
243. 347, 369, 3»o
P. nivale Tuck., 301
460
INDEX
Placodium pyracewn Anzi, 369, 377
P. rupestre Br. and Rostr., 301
P. subfruticulosum Elenk., 347
P. sympageum, see P.flavescens
P. tegularis (Ehrh.) Darbish., 379, 384
P. teicholytum DC., 369
Placodium Hill (non DC.), 8
Placodium Web. (non DC.), 9
P. Garovagli (Koerb.) Fried., 8 1
P. saxicolum S. F. Gray, 146, 168; see
Lecanora
Placolecania Zahlbr., 338
Placothelium Miill.-Arg., 285, 319
Placynthium Ach., 336
P. nigrum S. F. Gray, 248, 373
Plagiothecium sylvaticum Buch. and Schimp.,
237
Plagiotrema Miill.-Arg., 317
Platygrapha Nyl. , 325
Platysma Nyl., 8, 200, 257; see Cetraria
P. commixtum Nyl., 375
P. corniculatum Hill, 8
P. Fahlunense Nyl., 375
P. glaucum Nyl., 10, 375, 376, 418
P. lacunosa Nyl., 375
Pleospora collematum Zuk., 163, 266
Pleurococcus Menegh. (?), 22, 29, 62
P. Naegeli Chod., 28
P. vulgaris Menegh., 28, 55 (Fig. 22), 223
P. vulgaris Naeg., 28
Pleurocybe Mull.-Arg., 320
P. madagascarea A. Zahlbr., 289
Pleurothelium Miill.-Arg., 317
Plenrotrema Miill.-Arg., 317
Plot, 4
Plowright, 207
Plukenet, 5
Poa eompressa L., 393
Podtiridae, 256
Polyblastia Massal., 48, 314
P. catalepta (Ach.) Fuist., 30
P. Vouauxi Lesd., 378
Polyblastiopsis Nyl., 316
Polycauliona Hue, 339, 340, 346
P. regale Hue, 339, 346
Polycaulionaceae, 339
Polychidium A. Zahlbr., 284, 332
Poly coccus Kiitz., 24
P. punctiformis Kiitz., 24, 54, 61
Polyporus Mich., 261
Polysticlus versicolor (Fr.), 152
Polystigma rubrum DC., 178, 207
Polystroma Clem., 326
P. Ferdinandezii Clem. , 326
Polytrichum L., 392
P. commune L.f 237
Polyxenus, 270
Porina Ach., 204, 316
P. lectissima A. Zahlbr., 249, 251, 392
P. olivacea A. L. Sm., 159 (Fig. 90 A)
Porocyphus Koerb., 332
PororuaVfiOA., 13, 178
Porta, 5
Porter, 109, 270
Prasiola Ag., 60, 309, 315
P.parietina Wille, 60 (Fig. 33)
Prasiolaceae, 60
Propagula, 1 1
Protocaliceaceae, 277
Protococcaceae, 55, 288, 291, 309, 310, 313 et
seq., 353« 363
Protococcus Ag., xx, 28, 56, 62, 63, 65, 287
P. botryoides Kirchn., 65
P. -viridis Ag., 22, 28, 44, 48 (Fig. 15), 55,
(Fig. 22), 65, 313
Pseudopyrenula Miill.-Arg., 316
Psocus, 397
Psora (Lecided) decipiens Hook., 388
Psorella Miill.-Arg., 329
Psoroglaena Miill.-Arg., 315
Psoroma S. F. Gray, 136, 285, 286, 335
P. hypnorum S. F. Gray, 63, 8i, 88, 89, 135,
246, 283, 370
Psoromaria Nyl., 285, 286, 335
Psorotichia Massal., 68, 163, 333, 373
Ps. higubris Dal. Tor. and Sarnth., 375
Ps. lutophila Arn., 368
Psychides, 399
Pterygiopsis Wain., 332
Pterygium Nyl., 333
Pt. Kenmorensis A. L. Sm., 392
Ptychographa Nyl., 321, 322
Pulteney, 4, 14
Pulvis antilyssus, 407
Pulvis Cyprius, 419
Pycnothelia ( Cladonia] papillaria Duf., 369
Pyrenastrum Eschw., 317
Pyrenidiaceae, 53, 54, 275, 285, 309, 319
Pyrenidium Nyl., 285, 319
P. actinellum Nyl., 99
Pyrenocarpeae, 158, 273, 308
Pyrenocarpei, 306, 307, 353
Pyrenocarpineae, 273, 275, 288, 308
Pyrenocollema Reinke, 334
Pyrenographa Miill.-Arg., 323
Pyrenolichens 159, 241, 276, 352, 391
Pyrenomycetes 158, 267, 273
Pyrenopsidaceae, 282, 284, 310, 352
Pyrenopsidium Forss., 333
Pyrenopsis Nyl., 60, 68, 163, 175, 333
P. haematopis Th. Fr., 195
P. impolita Forss., 175
P. phaeococca Tuck., 175
Pyrenothamnia Tuck., 99, 315
P. Spraguei Tuck., 288
Pyrenothamniaceae, 309, 315
renothea Ach., 192
thrix Riddle, 319
enula Ach., 200, 316
P. tinerella Fink, 365
P. leucoplaca Koerb., 365
P. nitida Ach., 174, 194, 240, 255, 350, 354,
364, 365
P. thelena Fink, 365
Pyrenulaceae, 50, 276, 309, 316, 365
Pyrgidium Nyl., 319
P. bengalense Nyl., 353
Pyrgillus Nyl., 289, 320
Pyronema Carus., 167
P. confluens1v\., 178
Pyxidium Hill, 8
Pyxine Nyl., 301, 341
P. Cocoes Nyl., 353
P. Meissnerii Tuck., 353
INDEX
461
Quercus alba, 359
Q. chrysolepis, 359
Q. Douglasii, 359
Racodium Pers., 35, 328
K. rupestre Pers., 291, 328
Radais, 42
Ramalina Ach., 3, 84, 103, no, 195, 213, 238,
244, 257, 270, 305, 340, 347, 348, 351, 359,
361, 363
R.calicaris Fr., 3, 104, 147, 210, 353, 355,
365, 366, 418, 419
A', ceruchis De Not., 103
R. Curnowii Cromb., 104, 109
A*. cuspidataN'y\,\ 225, 271 (seeR.siliquosa),^^
R. dilacerata Hoffm., 106, 130
R. Eckloni Mont., 130
R. evernioides Nyl., 103, 300
A'.farinaceaAch., 10,239, 2^9> 271,353, 3^6,
400, 411
R.fastigiata Ach., 109, 365, 366, 400, 411
R.fraxinea Ach., 104, 106, 130 (Fig. 75 A),
155, 164, 170, 195, 200, 212, 215, 300, 355,
365, 366, 400, 411. 418
A', gracilenta Ach., 349
R. homalea Ach., 103
A'. Landroensis Zopf, 109, 130
A1, mimtscula Nyl., 103 (Fig. 62), 147
R. pollinaria Ach., 109, 227, 349, 366
R. reticulata Krempelh., 33 (Fig. u), 99, 106
(Fig. 64), 253, 257, 359
A', scopulorum Ach., see R. siliquosa
R. siliqitosa A. L. Sm. , 104, 109 (Fig. 65),
130, 224, 225, 271, 300, 379 (Fig. 122), 381
(Figs. 123, 124)
A', strepsilis Zahlbr., 104, 130 (Fig. 75 B)
R. subfarinacea Nyl., 380
R. tertiaria Engelh., 354
Ramalinaceae, 339
Ramalinites lacerns Braun, 354
Ramalodei, 306
Romania Stizenb. , 328
Rathapu, 403
Ray, 4, 407, 409
Rees, 27
Rehm, 277
Reindeer, 401
Reindeer moss, 400 et passim
Reinke, 18, 31, 41, 68, 123, 125, 130, 144, 253,
277, 284, 291, 307, 324
Reinkella Uarbish., 83, 324
Relhan, 9
Rhabdopsora Mtill.-Arg., 319
Rhizina unditlata Fr. , 181
Rhizocarpon Ramond, 248, 302, 329, 341
A", alboatrum Th. Fr., 365, 369, 373, 383
A', concentricum, see R. petraettm
R. confervoides DC., 71 (Fig. 38 A, B), 369, 386
R. distinctnm Th. Fr., 261
R. epipolium (Ach.), 265
R. geographicum DC., 73, 74 (Figs. 40, 41),
226, 236, 243, 246, 249, 252, 261, 264, 291,
346, 372, 374, 376- 38o
A", obscuratum Massal., 392
A'. Oederi Koerb., 375
A', petraenm Koerb. (?), 374
Jf.petraeumM&ssai., 171 (Fig. 97), 375, 392
Rhizocarpon viridiatrum Koerb., 249, 37*,
3/6
Rhizomorpha Roth, 12
Rhymbocarpus pututiformis Zopf, 164
Ricasolia De Not., 94 (see Lobaria), 168, 175
R. amplissima De Not., 133, 134 (Fig. 76),
'95, 197- 357
R. lattevirens Leigh t., 357
Richard, 377, 411
Richardson, Dr, 6
Richardson, Sir John, 388
Riddle, 137
Rinodina S. F. Gray, 301, 302, 341, 371
A', archaea Wain., 346
A'. Conradi Koerb., 370
R. f?iS?a. s- F. Gray, 366, 367, 377, 383. 384
A', isidioides Oliv., 301
R. oreina Wain., 301, 374, 390
R. sophodes Th. Fr., 367
A', turfacea Th. Fr., 262, 377
Rivularia, 55, 136, 138, 284, 333
A'. Biasolettiana, 54 (Fig. 21)
A', minutula Born, and Fl., 54 (Fig. 21)
R. nitida Ag. , 55
Rivulariaceae, 54
Roccella DC., 3, 34, 35, 83, 103, 200, 125, 233,
242, 278, 292. 324, 351, 359, 363
R.fudformis DC., 83 (Fig. 45), 98 (Fig. 57),
101, no, 227, 228, 349, 350, 412
R.fucoidfs Wain., 349, 350
A'. Alontagnei Bel., 213, 413
R. peritensis Kremp. , 413
A', phycopsis Ach., 1 10 ; see R. fut aides
R. portentosa Mont., 413
R. sinnensis Nyl., 413
R. tinctoria DC., 213, 215, 227, 349, 350, 413
(Fig- '33)
Roccellaceae, 59, 83, no, 279, 290, 309, 333
Roccellaria Darbish., 323, 324
Roccellina Darbish., 83, 290, 323, 324
Roccellographa Stein., '83, 290', 323, 324
Rock tripe, 404
Roebuck, 401
Ronceray, 213, 413
Rosendahl, 86, 90, 93, 129, 170, 176, 214, 218,
249
Roses, spirit of, 419
Roy, 41 1
Ruel, 2
Rupp, 5
Russula Pers., 161
Sachs, 17, 23
Sagedia, see Verntcaria
S. declivum Arn., 251
Sagiolechia Massal., 328
Salix repens L., 357
Salter, 51, 393
Sandstede, 233, 384, 385
Sappin-Troufty, 207
Sarcographa Fee, 323
Sarcographina Miill.-Arg., 323
Sarcogyne ( = Biatorella) latericola Stein., 76
Sarcopyrenia Nyl., 314
Saltier, 113, 173, 296, 358
Schade, 376
Schaerer, 15, 192
462
INDEX
Schellenberg, in.
Schenk, 213
Schikorra, 178
Schimper, 354, 355
Schismatomma Flot., 325
Schizopelte Th. Fr., 83, 324
Schneider, 7, 135, 136, 139
Schreber, 126
Schrenk, 231, 258, 359
Schulte, 104, 105, 1 06, 177
Schvvarz, 224
Schweinfurth, 405
Schvveinitz, 15
Schwenckfeld, 3
Schwendener, xx, 2, 16, 17, 18, 25, 27, 36, 71,82,
86, 92, 126, 128, 129, 142, 147, 168, 213,
224, 307
Sderophyton Eschw., 323
S. circumscriptum A. Zahlbr., 322
Scopoli, 8, 21, 154, 409
Scott-Elliot, 253
Scutellati, 305
Scutovertes maculatus, 397
Scytonema Ag., 54, 57, 61, 68, 75, 136, 153,216,
232, 281, 284, yyjetseq., 318
S. mirabile Thur., 53 (Fig. 19)
Scytonemaceae, 54
Secoliga (Gyalecta) bryophaga Koerb., 368
Segestria, see Porina
Senft, 223
Septoria Fr., 204
Sernander, 94, 140, 355
Servettaz, 45
Servit, 374
Sherard, 4, 6, 7
Sibbald, 409
Sibtborp, 9
Sievers, 230
Simonyella Steiner, 324
Siphula Fr., 340
Strosiphon pulvinatus Breb. , 54
Sloane, 10
Smith, Lorrain, 328
Smith, Sir J. E., 10
Solorina Ach., 56, 63, 85, 94, 135, 136, 168, 175,
176, 183, 287, 337," 392
S. bispora Nyl., 135
S. crocea Ach., 63, 88, 140, 210, 228, 246, 287,
346, 388
S. octospora Am., 85
S. saccata Ach., 155, 244, 388
S. spongiosa Carroll, 135, 186, 368
Solorinetta Anzi, 337
Sorby, 418
Sowerby, James, 10
Speerschneider, 17, 25
Sphaeria Hall., 192, 213
Sphaeriaceae, 307
Sphaerocephalum Web., 9
Sphaerophoraceae, 135, 309, 320
Sphaerophoropsis Wain., 291, 329
S. stereocauloides Wain., 292
Sphaerophorus Pers., 83, 105, 184, 277, 289, 320,
36l» 375, 387, 393
S. foralloides Pers., 83 (Fig. 44) (see S. globo-
««). 355, 375, 387, 388, 389
S.fragihs Pers., 375, 387
Sphaerophorus globosus A. L. Sm. , 346
S. stereocauloides Nyl., 135
Sphagnum Dill., 231, 355
Spheconisca Norm., 313
Sphinctrina Fr., 277, 319, 353
Sphyriditim byssoides, 177
S.fungiforme Koerb., 177
Spilonema Born., 68, 333
Spirographa A. Zahlbr., 322
Spirogyra Link, 188
Splachnum L., 5
Sporocladus lichenicola Corda, 200
Sporodinia Link, 188
Sporopodium Mont., 327, 352
S. Caucasium Elenk. and Woron., 353
Sprengel, 21, 142, 156, 184
Squamuria DC., 200, 298
S. saxicola, see Lecanora
Stahel, 220
Stahl, 28, 30, 62, 160, 163, 173, 266, 395
Stahlecker, 76, 235, 371, 374
Staurothele'KoTm., 31, 62, 76, 314
S. clopima Th. Fr., 391
S. dopismoides Anzi, 249
S, hymenogonia A. Zahlbr., 361
S. umbrinum A. L. Sm., 373, 393
Steganosporium cellulosum Corda, 201
Steiner, 75, 179, 190, 198, 215, 276, 312, 353,
389
Steinera A. Zahlbr., 333
Stenberg, 411
Stenhouse and Groves, 228
Stenocybe Nyl., 177, 319
Stereocaulon Schreb., 17, 23, 83, 105, 125, 133,
135, '76, 201, 283, 292, 294, 297, 330, 346,
358, 361, 387
S. alpmum Laur., 137, 346, 387
S. condensation Hoffm., 319, 388
S. coral loides Fr., 125, 375
S. Delisei Borg., 375
S. denudatum Floerk., 137, 375, 387
S. evohitum Graewe, 375
S. paschale Fr., 211, 372, 385, 391, 401
S. ramulosum Ach., 125, 136
S. salazinum Borg., 227
S. tomentosum Fr. , 125, 136, 387
Stereochlamys Miill.-Arg., 316
Stic hoc occus Naeg., 62
S. bacillaris Naeg., 42
Sticta Schreb., 13, 63, 85, 86, 94, 136, 138, 200,
283, 287, 336, 350, 351, 364, 392
St. aurata Ach., 126, 128, 223, 226, 246, 350
St. crocata Ach., 128, 246
St. damaecornis Nyl., 127 (Fig. 73), 128, 210,
35°
St. Dufourei Del., 128
St. fuliginosa Ach., 126, 128, 223
St. intricata Del., 128
St. limbata Ach., 128
St. oregana Tuck., 136, 139
St. sylvalica Ach., 1 28
Stictaceae, 96, 136, 286,311, 336, 347, 350, 418
Stictidaceae, 278
Stictina Nyl., 63, 168, 175, 287
Stictis Pers., 278
Stigmatea Fr., 275
INDEX
463
Stigonema Ag., 23, 16, 54 (Fig. 20), 68, 136, 283,
284, 310 et seq., 317
.S. panniforme Kirchn. , 54
Stigonemaceae, 54
Stirton, 331, 350
Stizenberger, 18, 128
Stone, 399
StreptothriA Cohn, 45
Strigula Fr., 60, 65, 288, 318, 353, 363
S. Bitxi Chod., 363
S, complanata Mont., 35, 42, 59, 205, 260, 269
5°. t'legans Miill.-Arg., 205
Strigulaceae, 59, 60, 204, 309, 318, 363
Stiide, 2ii
Sturgis, 97, 168, 175, 197, 289
Snaeda fniticosa Forsk., 387
Swartz, 10, 152
Swedish moss, 415
Symbiosis 3 1
Synalissa Fr., 32, 33, 61, 284, 333, 373
S. symphorea Nyl., 33 (Fig. 10)
Synarthonia Miill.-Arg., 321
Tabernaemontanus, 2
Tapellaria Miill.-Arg., 327
Taylor, 13, 149
Tegeocrantis labyrinthicus, 328
Teloschistaceae, 311, 341
Teloschistes Norm., 85. 301, 341
T. chrysophthalimis, Th. Fr., 92, 365, 367
T. flaviians Norm., 3, 301, 341, 417
Teras literana, 399
7'ermes mcnoceros, 397
Termites, 397
Tetrany chits lapidus, 398 (Fig. 126)
Tetrasporaceae, 57
Thamnolia Ach. , 83, 101 (see Cerania), 246, 340,
389
Th. vermicularis Schaer., 346, 377
Thamnonia Tuck., 339
Thaxter, 178
Thelenidia Nyl., 314
Thelephora Ehrh., 281, 342
Thelephoraceae, 152, 273
Thdidea Hue, 335
Th. forrugata Hue, 335
Thelidium Massal., 314
Th. microcarpiim A. L. Sm., 361
Th. miniitiihtm Koerb., 253, 367
Thelocarpon Nyl., 331
Th. prasinelium Nyl., 367
Th. turficoium Arn., 370
Thclopsis Nyl., 316
Thelotrema Ach., 3-26, 343
Th. lepadinnm Ach., 397
Thelotremaceae, 59, 302, 310, 326, 351, 352
Thelotremei, 353
Theophrastus, i, 2, 411
Thernnitis Fr., 68, 284, 332
Tholnrna Norm., 320
Th. dissimilis Norm., 289
Thomas, N., 59
Thrambium Wallr., 192, 314
T. epigaetim Wallr., 254, 367, 368
Thwaites, 1 7
Thyrea Massal., 284, 333
Thysanothedum Berk, and Mont., 330
Thysanothecium Hookeri Berk, and Mont., 294
Ticothecium Flot., 275, 319
T. pygmaeum Koerb., 267
Tieghem, Van, 179
Tobler, 43, 50, 148, 224, 253, 263, 265, 280
Tomasiella Miill.-Arg., 317
Toni, De, 60
Toninia Th. Fr. , 329
Torrey, 14
Tournefort, i, 5, 155, 304
Tournesol, 413
Treboux, 40, 42
Trematosphaeropsis Klenk., 266
Tremotylium Nyl., 326
Trentepohlia Born., 26, 30, 34, 59, 75, 78, 131,
246, 276, 278, 287, 289, 291, 309, 316 etc.,
343. 35 2» 365
T. abietina Hansg., 65, 66
T. aurea Mart., 34, 35, 58 (Fig. 29 A), 59
T. jolt thus, 223
T. umbrina Born. ,2 2, 34, 58 (Fig. 298), 59, 62,
216
Trentepohliaceae, 59, 288, 289
Treub, 28, 394
Treveris, Peter, 2
Tricothelium Miill.-Arg., 318
Trimmatothele Norm . , 314
Tripe de Roche, 404
Trypetheliaceae, 309, 317
Trypethelium Spreng., 276, 317, 351, 364
J^ubercularia Web., 9
Tuckerman, 15, 136, 339
Tulasne, 17, 25, 46, 70, 123, 159, 187, 189, 192,
193, 200, 204, 263
Turner, Dawson, 14
Tutt, 399
Tylophorella Wain., 320
Tylophoron Nyl., 289, 320
Uhlir, 43
U lander, 21 1
Uloth, 233
Utnbilicaria., 17, 82, 200, 241, 262, 268, 331
U. pushdata Hoffm., 86, 96, 150, 195, 214,
240, 257, 414
Unguentum Armarium, 407
Unguentum sympatheticum, 407
Urceolaria Ach., 48 ; see Diploschistes
Urococats Kiitz., 57, 133, 318
Usnea Dill., i, 3, 7, 9, 83, in, 195, 213, 233,
257, 268, 269, 300, 304, 305, 340, 347, 348,
351, 361, 408, 419
U. articulala Hoffm., 210, 268
U. barbata Web., 25, 99 (Fig. 58), 104 (Fig.
63 A), 130, 143 (Fig. 82), 167 (Fig. 95),
168, 177, 200, 211, 215, 226, 234, 239, 246.
339- 348,364, 4' 7
U. ceratina Ach., 227
U. compress a Hill, 8
U. dasypoga Stiz., 359
U. flonda Web., 91 (Fig. 52), 92, 210, 213,
348, 363, 4"
U. hirta Hoffm., 348, 355, 366
U. laevis Nyl., 177
U. longissima Ach., 85, 99, 102 (Fig. 61), 105
(Fig. 638), 106, 215,348
U. tnacrocarpa Arn., 177
464 INDEX
Usnea melaxantha Ach., 346
U. plicata Web. , 359
U. Taylori Hook., 104
Usneaceae, 299, 311, 339
Vaillant, 6
Vallot, 253
Valsa Fr., 317
Varic ell aria Nyl., 337
V. microsticta Nyl., 77, 92, 187 (Fig. 126)
Variolaria Ach. (see Pertusaria), 64, 171, 237
Vaucheria sessilis DC., 65 (Fig. 34)
Ventenat, 21
Verrucaria Web. (non Pers.), 9, 174, 200, 275,
3 1 4' 364
V. aethiobola Wahlenb., 391, 392
V. anceps Koerb., 377
V. aquatilis Mudd, 383
V. cakiseda DC., 176, 215, 219, 241, 373,
398
V. Dufourii'DC., 173
V.fnscella Ach., 373
V. Hoffmanni Hepp ; f. purpurascens Arn.,
251
V. hydrela Ach., 391, 392
V. lecideoides Koerb., 373
V. mactiliformis Krempelh., 379
V. margacea Wahlenb., 391, 392
V. maura Wahlenb., 245, 383, 384, 386
V. memnonia Flot., 383
V. microspora Nyl., 256, 383, 386
V. umcosa Wahlenb., 73, 383
V. mnralis Ach., 30, 46 (Fig. 14), 70, 243,
255. 361, 393
V. nigrescent Pers., 56, 254, 369, 377, 392
V. papillosa Ach., 377
V. promimda Nyl., 383
V. rupestris Schrad., 215, 243, 361
V. scotina Wedd. , 383
V. striatula Wahlenb., 383
V. viridula Ach.', 391
Verrucariaceae, 749, 309, 314, 353, 367
Verrucarites geanthricis Goepp., 354
Verrucula Stein., 265, 276
V. aegyptica Stein., 276
V. cahirensis Stein., 276
Visiani, 405
Volkard, 228, 410
Vouaux, 267
Wahlberg, n, 168
Wahrlich, 51
Wainio, 31, 48, 70, 112, 114, 118, 120, 122, 123,
124, 125, 126, 128, 144, 153, 159, 163, 166,
175, 177, 179, 188, 191, 240,276, 277, 292,
294, 308, 344, 346, 348, 411
Waite, 270
Wallroth, xx, 13, 21, 22, 123, 133, 142, 156,
192, 3°5
Ward, Marshall, 35, 42, S9
Watson, Sir W., 8
Watson, 365, 373, 385
Watt, 403
Weber, i, 9
Weddell, 252, 379
Wehmer, 220
Weir, 239
West, G. F., 52, 54, 55, 56
West, W., 225, 233, 357, 374
Wester, 211
Westring, 412
Wettstein, 45
Wheldon, 398
Wheldon and Wilson, 360, 370, 373, 374, 379,
384. 385. 387. 39i> 392
Wiesner, 211, 241, 244
Wilde, 395
Wille, 28
Willemet, 10, 401, 415
Wilson, 350
Winter, 30, 138, 263
Winterstein, 209
Wisselingh, 211
Withering, 9
Wolff, 124, 163, 170, 172, 176
Woodward, 152
Woronin, 28
Woronina Cornu, 261
Xanthocapsa (Sect, of gloeocapsa}, 52, 63, 284,
332i 373
Xanthoria Th. Fr., 166, 246
X. lychnea Th. Fr., 233, 252, 365, 417
X. parietina Th. Fr., 3, 22, 24, 27, 28, 38, 42,
48 (Fig. 15), 50, 56, 65, 67 (Fig. 36), 86,
164, 176, 189, 195, 200, 224, 225, 227, 231,
232, 24I, 242, 253, 269, 270, 301, 341, 348,
351, 360, 369, 373, 376, 380, 383, 384, 386,
397, 406, 416, 418
X. polycarpa Oliv., 365, 390
Xylaria Hill, 12, 421
Xylographa Fr., 278, 322
X. spilomatica Th. Fr., 145
Xyloschistes Wain., 322
Zahlbruckner, A., 19, 59, 60, 66, 69, 275, 284,
3°8, 335. 413
Zopf, 19, 43, 108, 151, 188, 213, 221, 233, 238,
246, 264, 265, 266, 268, 270, 395, 396, 398,
4oo, 412, 417
Zukal, 18, 26, 38, 6r, 68, 70, 82, 128, 129, 130,
163, 179, 187, 215, 219, 230, 237, 244, 267,
268, 271, 313, 395
Zwelser, 419
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