GROUP I. THALLOPHYTA : FUNGI : BASIDIOMYCETES. 



311 



membrane (the velum) which extended from the stipe to the mar- 

 gin of the pileus, enclosing the hymenial cavity (Fig. 222). 



The stipe consists of a number of closely-packed branching 

 hyphse, which, at its apex, spreads out to form the tissue of the 

 pileus. In the pileus, the hyphee branch repeatedly, the hyphse 

 towards the lower 

 surface forming the 

 lamellae. Each la- 

 mella (Fig. 219 B) 

 consists of a mass of 

 hyphse, constituting 

 the trama ; as the 

 hyphee approach the 

 surface of the la- 

 mella, the cells be- 

 come shorter. The 

 last cells, before 

 reaching the hymen- 

 ial layer, are very 

 short, and constitute 

 a definite layer, 

 known as the sub- 

 hymenial layer (Fig. 

 219 B C sh). The 

 terminal cells of the 

 hyphae constitute 

 the hymenial layer 

 (Fig. 219 B hy). 

 This consists of 

 somewhat elongated 

 club - shaped cell s, 

 some of which bear 

 gonidia, and are 

 termed basidia, 

 whilst the others 

 are sterile, and are 

 termed paraphyses 

 (Fig. 219 C q). 

 Each basidium de- 

 velopes at its apex four delicate outgrowths, the sterigmata, and at 

 the apex of each sterigma a single small gonidium (C s' s") is 



FIG. 219. Agaricus campestris. A Tangential section of 

 the pileus, showing the. lamellae (I) of the hymenophore. 

 B A similar section of a lamella more highly magnified ; 

 hy the hymenium ; t the central tissue called the trama. 

 C A portion of the same section more highly magnified 

 ( x 650) : q young basidia and paraphyses ; s' the first 

 formation of gonidia on a basidium ; s" more advanced 

 stages ; at s"" the gonidia have fallen off. (After Sachs.) 



