x . CONTENTS 



2. RADIATE OR SECONDARY THALLUS 



I'AOE 



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 PODE- 



TIUM . ....... 120 



F. ROOTING STRUCTURES OF CLADONIAE . . .121 



G. HAPTERA ... . ... 122 



H. MORPHOLOGY OF THE PODETIUM . . 122 



I. PlLOPHORUS AND STEREOCAULON .... 12$ 



V. STRUCTURES PECULIAR TO LICHENS 

 i. 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 



