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