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