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 
Fic. 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. J, 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 
