CONTENTS ix 



2. SQUAMULOSE LICHENS 



I'AGE 



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 

 i. 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 



