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
PRINTED IN GREAT BRITAIN
PREFACE
The publication of this volume has been delayed owing to war conditions,
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 lichenological 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 1
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
1. GONIDIA IN RELATION TO THE THALLUS
A. HISTORICAL ACCOUNT OF LICHEN GONIDIA 21
B. GONIDIA CONTRASTED WITH ALGAE 22
C. CULTURE EXPERIMENTS WITH THE LICHEN THALLUS 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
_f._ Affinities of lichen gonidia
B. NUTRITION OF LICHEN FUNGI 44
C. SYMBIOSIS OF OTHER PLANTS 45
II. LICHEN HYPHAE
A. ORIGIN OF HYPHAE 46
B. DEVELOPMENT OF LICHENOID HYPHAE 47
C. CULTURE OF HYPHAE WITHOUT GONIDIA 49
D. CONTINUITY OF PROTOPLASM IN HYPHAL CELLS 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
1. CRUSTACEOUS LICHENS
A. GENERAL STRUCTURE 70
B. SAXICOLOUS LICHENS 70
_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 77
_a._ Epiphloeodal lichens
_b._ Hypophloeodal lichens
2. SQUAMULOSE LICHENS
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
_b._ Chondroid axis
C. SURVEY OF MECHANICAL TISSUES 105
D. RETICULATE FRONDS 106
E. ROOTING BASE IN FRUTICOSE LICHENS 108
IV. STRATOSE-RADIATE THALLUS
1. STRATOSE OR PRIMARY THALLUS
A. GENERAL CHARACTERISTICS 111
B. TISSUES OF PRIMARY THALLUS 112
_a._ Cortical tissue
_b._ Gonidial tissue
_c._ Medullary tissue
_d._ Soredia
2. RADIATE OR SECONDARY THALLUS
A. ORIGIN OF THE PODETIUM 114
B. STRUCTURE OF THE PODETIUM 114
_a._ General structure
_b._ Gonidial tissue
_c._ Cortical tissue
_d._ Soredia
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 PODETIUM 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
1. 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
3. SOREDIA
A. STRUCTURE AND ORIGIN OF SOREDIA 141
_a._ Scattered soredia
_b._ Isidial soredia
_c._ Soredia as buds
B. SORALIA 144
_a._ 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
1. 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
2. PYRENOLICHENS
_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
_f._ 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
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
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 245
_a._ Colour given by the algal constituent
_b._ 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
_c._ Dispersal of fruticose lichens
D. ERRATIC LICHENS 258
E. PARASITISM 260
_a._ General statement
_b._ Antagonistic symbiosis
_c._ Parasymbiosis
_d._ Parasymbiosis of fungi
_e._ Fungi parasitic on lichens
_f._ 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._ Gloeolichens
_b._ Ephebaceae and Collemaceae
_c._ Pyrenidiaceae
_d._ Heppiaceae and Pannariaceae
_e._ Peltigeraceae and Stictaceae
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._ Cladoniaceae
1. Origin of Cladonia
2. Evolution of the primary thallus
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
_f._ Müller-Argau
_g._ Reinke
_h._ Zahlbruckner
B. FAMILIES AND GENERA OF ASCOLICHENS 311
C. HYMENOLICHENS 342
II. NUMBER AND DISTRIBUTION
1. 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
CHAPTER IX
ECOLOGY
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
_f._ 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
B. LICHENS AS MEDICINE 405
_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 DISTILLING 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 describe 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, 119 _et passim_.
=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, 11, 133
_et passim_.
=Chrondroid=, hard and tough like cartilage, a term applied to
strengthening strands of hyphae, 104, 114.
=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.), 11, 126.
=Decomposed=, term applied to cortex formed of gelatinous indistinct
hyphae (amorphous), 73-81 _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.
=Discoid=, disc-like, an open rounded apothecium, 156.
=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, 13, 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.
=Hymenolichens=, 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.
=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, 114, 293 _et
seq._
=Polarilocular=, =Polaribilocular=, two-celled spores with thick median
wall traversed by a connecting tube, 188, 340-341.
=Polytomous=, 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._
=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, 111, 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, 159, 163.
ERRATA
p. 24. _For_ Baranetsky _read_ Baranetzky.
p. 277. For _Ascolium_ read _Acolium_.
p. 318. For _Lepolichen coccophora_ read _coccophorus_.
Transcriber’s Note: The errata have been corrected.
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 foothold. 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
Ascomycetes[1], 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.
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. Luyken[2], for instance, thought that
lichens were compounded of air and moisture. Hornschuch[3] 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
account[4] 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 Dillenius[5] 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 Wallroth[6] 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 Agardh[7], 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 announcement[8] by Schwendener[9] 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 some[10], 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 Lindsay[11]
dismissed the theory as “merely the most recent instance of German
transcendentalism applied to the Lichens.” Earlier still, Nylander[12],
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 Crombie[13], wholly agreeing with his estimate of these “absurd
tales,” translates a much later pronouncement by him[14]: “All these
allegations belong to inept Schwendenerism and scarcely deserve even
to be reviewed or castigated so puerile are they—the offspring of
inexperience and of a light imagination. No true science there.”
Crombie[15] 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 Crombie[16] of one of Nylander’s papers. It is stated there that a
saxicolous alga (_Gongrosira_ Kütz.) 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, Crombie[17]
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
parasitic nature has been freshly promulgated among others by the
American lichenologist Bruce Fink[18]. The genetic origin of the gonidia
has also been restated by Elfving[19]: 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 Moreau[20].
They hold that the most characteristic lichen structures—more
particularly 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,
conditioned 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 compound 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
continual 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 understanding 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; 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 Peirce[21] 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 solution 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
French[22]: “first the lichen is put into 95 per cent. alcohol for 24
hours, then into thin celloidin and thick celloidin 24 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 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 conjointly, 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 Morison[23]. In a botanical work
published in 1700 by Tournefort[24] 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 Dillenius[25] 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 Krempelhuber[26], a German lichenologist.
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 continuous
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.
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 284 B.C., 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 physician 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 _Grete Herball_[27]. 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.
Ruel[28] of Soissons in France, Dorstenius[29], Camerarius[30] and
Tabernaemontanus[31] 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’Obel[32], a
Fleming, who spent the latter part of his life in England and is said to
have had charge of a physic garden at 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. Dodoens[33], 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 Gerard[34] 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 Schwenckfeld[35] 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 Colonna[36] and Bauhin[37]. 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’s[38] _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’s[39] _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 Merrett[40], who records in his Pinax, “Muscus
arboreus umbilicatus” (_Physcia ciliaris_), “Muscus aureus tenuissimus”
(_Teloschistes flavicans_), “Muscus caule rigido” (_Alectoria_) 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 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 Plot[41] we owe the earliest
record of _Cladonia coccifera_ which had hitherto escaped notice; it was
described and figured as a new and rare plant in the _Natural History
of Staffordshire_[41]. Plot was the first Custos 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
Morison[42], 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 work[42] 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_[43] is considered to have
commenced a new era in the study of the science. The _Catalogue_ was
followed by the _History of Plants_[44], and later by a _Synopsis of
British Plants_[45], 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 Buddle, James Petiver and
William Sherard. Buddle 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 Buddle had a church.
The Society of Apothecaries had been founded in 1617 and the members
acquired land on the river-front at Chelsea, which was extended later
and made into a Physick Garden. James Petiver[46] 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 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
contemporary botanist was Leonard Plukenet[47] 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. Malpighi[48] had noted
the presence of soredia on the thallus of some species, and regarded them
as seeds. Porta[49], 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 Élémens de Botanique_ by Tournefort[50], 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 Élémens_ was successful enough to warrant the publication a few
years later of a larger Latin edition entitled _Institutiones_[51]
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 Rupp[52] who published a Flora of plants from Jena. Among these
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)_. Buxbaum[53], in his enumeration of plants from
Halle, finds place for forty-nine lichen species, with, in addition,
eleven species of _Coralloides_; and Vaillant[54] in listing the plants
that grew in the neighbourhood 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, Dillenius[55], 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. Micheli[56], 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 work[57] 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-page[58]. 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 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
Muscorum_, 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 Crombie[59] 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’s[60] _Systematic and Descriptive list of plants indigenous
to Switzerland_. The lichens are described as without visible leaves
or stamens but with “corpuscula” instead of flowers and leaves. He
arranged his lichen species, 160 in all, under seven different Orders:
1. “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 Linnaeus[61]. The renowned Swedish botanist
rather scorned lichens as “rustici pauperrimi,” happily translated by
Schneider[62] as the “poor trash of vegetation,” but he named and listed
about 80 species. He divided his solitary genus _Lichen_ into sections:
1. “Leprosi tuberculati”; 2. “Leprosi scutellati”; 3. “Imbricati”;
4. “Foliacei”; 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
Hill[63], 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”—_Usnea_, tree mosses,
consisting of filaments only; _Platysma_, flat branched tree mosses,
such as lung-wort; _Cladonia_, the orchil and coralline mosses, such
as _Cladonia furcata_; _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 suggested by him, but among his plants are such binomials
as _Usnea compressa_, _Platysma corniculatum_, _Cladonia furcata_ and
_Cladonia tophacea_; other lichens are trinomial or are indicated, in
the way then customary, by a whole sentence. 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_[64], 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 Watson[65], 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
embarrassment, 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’s[66] _Flora Carniolica_, for
instance, published in 1760, still adhered to the old descriptive method
of nomenclature, but a second edition, issued twelve years later, is
based on the new system: it includes 54 lichen species.
About this time Adanson[67] 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, Hudson[68], 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.
Withering[69] was 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. Lightfoot[70],
whose descriptive and economic notes are full of interest, records 103
lichens in the _Flora Scotica_, and Dickson[71] 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 Weber[72] 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_, which 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 Sibthorp[73] at Oxford were
making extensive studies of plants. The latter was content to follow
Linnaeus in his treatment of lichens. Relhan[74] 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.
Extensive contributions to the knowledge of English plants generally were
made by Sir James Edward Smith[75] 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
Hoffmann[76] and Persoon[77].
For a long time little was known of the lichens of other than European
countries. Buxbaum[78] in the East, Petiver[79] and Hans Sloane[80] 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 Swartz[81] in the West Indies and Desfontaines[82]
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. Georgi[83], 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_, _Platysma glaucum_,
_Lobaria pulmonaria_, etc., which he collected from birch and pine trees.
About this time also the French scientists Willomet[84], 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
classification raised them to the rank of the other great classes of
plants.
Acharius was a country doctor at Wadstena on Lake Mälar in Sweden, as
he himself calls it, “the country of lichens.” He was attracted to the
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 work[85] 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_[86], then subsequently in
the larger _Lichenographia Universalia_[87]. 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_[88],
a more condensed work which he published 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 terminology for the structures peculiar to lichens. We owe to him
the names and descriptions of “thallus,” “podetium,” “apothecium,”
“perithecium,” “soredium,” “cyphella” and “cephalodium,” the last word
however 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 the test of time and
have been found of service in allied branches of botany.
Lichens were studied with great zest by the men of that day. Hue[89]
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. 14th, 1819). Dufour, however, had
added the comment that the illness and death might after all be merely a
coincidence.
Among contemporary botanists, we find that De Candolle[90] 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. Flörke[91], 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 Davies[92] for Wales, which adheres
to the Linnaean system, and the other by Forster[93] of lichens round
Tonbridge. Though Forster adopts the genera of Acharius, he includes
lichens among algae. A more important publication was S. F. Gray’s[94]
_Natural Arrangement of British Plants_. Gray, who was a druggist
in Walsall and afterwards a lecturer on botany in London, was only
nominally[95] the author, as it was mainly the work of his son John
Edward Gray[96], 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 _Rhizomorpha_, 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’s[97] _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_[98], 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_[99]. The two species
of Lichina are the only ones he figured, and these he took to be algae.
He[100] 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’s[101]
contributions to Smith’s _English Flora_ and Taylor’s[102] 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.
Fries[103] in his important work _Lichenographia Europaea_ more or
less followed his distinguished 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. Fée[104] published an Essay on the Cryptogams (mostly lichens)
that grew on officinal exotic barks; Flörke[105] took up the difficult
genus _Cladonia_; Wallroth[106] also wrote on _Cladonia_; Delise[107] on
_Sticta_, and Chevalier[108] 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.
Wallroth[109] 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 “morphosis” 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’s[110] 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; 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 having first observed their
germination should be given to a later botanist, Holle[111]. The works
of both Wallroth and Meyer enjoyed a great and well-merited reputation:
they were standard books of consultation for many years. Koerber[112],
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
nineteenth, 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, includes 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 (1775-1858), 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 (1798-1856), 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’s[113] _Flora_ grouped
under “Lichenaceae” were collected in such widely separated regions as
Carolina and Canada. A few years later Mühlenberg[114] included no fewer
than 184 species in his _Catalogue of North American Plants_. Torrey[115]
and Halsey[116] 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 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 Tuckerman[117]
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 Fée, 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
determination, 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 Fée[118] 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’s[119]
_Flora of Brazil_. Montagne[120] named large collections, notably those
of Leprieur collected in Guiana, and Hooker[121] 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
Schaerer[122], 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, Eschweiler[123] in his _Systema_
and Fée[124] 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. Fée, 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 Notaris[125], a Professor in
Florence, who took up the work where Fée 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 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 Massalongo[126] in Italy, by Norman[127] in
Norway, by Koerber[128] in Germany and by Mudd[129] 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.
Lindsay[130], Mudd and Leighton[131] 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 Finland[132] 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 Classification_[133] 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 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 lichens[134] and traced their
development, 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 Lindsay[135] 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 Itzigsohn[136],
Speerschneider[137], Sachs[138], Thwaites[139], and others. They devoted
their researches to some particular aspect of lichen development and
their several contributions are discussed elsewhere in this work.
Schwendener[140] 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: Leighton[141]
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 _Graphideae_[142] and
the _Umbilicarieae_[143], and Mudd[144] published a careful study of the
_British Cladoniae_. On the Continent Th. Fries[145] issued a revision
of _Stereocaulon_ and _Pilophoron_ and other writers contributed work on
smaller groups.
H. PERIOD VII. 1867 AND AFTER
Modern lichenology begins with the enunciation of Schwendener’s[146]
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.
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 Nylander[147], J.
Müller and Crombie[148]. 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 date that the truer conception of the
“consortium” or “symbiosis” was proposed. The researches undertaken to
prove or disprove the new theories come under review in Chapter II.
Stahl’s work on the development of the carpogonium in lichens gave a new
direction to study, and notable work has been done 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, Müller, Th. Fries, Stizenberger, Leighton,
Crombie and many others, and their contributions are scattered through
contemporary scientific journals. The number of recorded species is now
somewhere about 40,000, 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
monographs, 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, Fünfstück, Darbishire, Hue, and by an increasing number
of modern writers whose work is duly acknowledged under each 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
1911, 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 Lett[149] has reported 80 species and varieties
from the Mourne 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 Engler and
Prantl’s _Pflanzenfamilien_ has proved a boon to all who are interested
in the study of lichens. Fünfstück[150] prepared the introduction, an
admirable presentation of the morphological and physiological aspects of
the subject, while Zahlbruckner[151], with equal success, took charge of
the section dealing with classification.