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

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