386 



THALLOPHYTES 



the weather is warm and moist and sometimes the sporophore 

 attains full size in a few hours. The elongating sporophore 

 finally breaks through the covering of the button, spreads out its 

 umbrella-like top, and the characteristic sporophore appears with 

 remnants of the torn skin-like covering remaining attached. 



When mature the sporophore consists of a stalk, called stipe, 

 and the expanded umbrella-like top, called pileus. On the under 



FIG. 339. Reproductive structures of the Mushroom, Agaricus cam- 

 pestris. A, the Mushroom with a portion of its pileus cut away to show 

 the gills, g, gills; s, stipe; a, annulus. B, section through a gill, highly 

 magnified to show the basidia (b) and the basidiospores (r) . Redrawn from 

 Leavitt. 



side of the pileus are the thin radiating plates or gills bearing the 

 hymenium in which occur the basidia as shown in Figure 339. A 

 fragment of the skin-like covering of the button stage commonly 

 remains attached to the stipe, forming the annulus and in some 

 forms, as shown in Figure 337, a portion of the covering remains 

 as a cup at the base of the stipe, forming the volva. Other frag- 

 ments of the covering often remain as flecks on the outer surface 

 of the pileus. When the spores are mature, they fall from the 



