CHAPTER III. Morphology

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