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