DEVELOPMENT OF PLANTS 



263 



are several very widely distributed and familiar families of the 

 Agaricales, 'distinguished by the arrangement and distribution of 

 the hymenium. 



A. Thelephoraceae. — ^These fungi form membranous, leathery 



Fig. 171. Structure of a mushroom: A and B, cross and longitudinal 

 sections of a portion of the stipe, showing the character and arrangement 

 of the hyphae that make up the mushroom. C, tangential view of the gills 

 — p, pileus; h, hymenium appearing as a dark band on the surface of the 

 gills. D, a portion of the hymenium enlarged — b, basidia; pa, paraphyses; 

 s, basidiospores. 



or woody incrustations or shell-like structures or branching 

 bodies on soil or wood (Fig. 172, A, B). The hymenium forms 

 a smooth or slightly wrinkled surface on the under side or ex- 

 posed surface of the fungus. 



