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