266 



THE FUNGI 



--cap 



a stalk (stipe), which in some genera arises from a cup (volva) 

 and is expanded above into the cap (pileus). The under surface 



of the cap bears many thin plates 

 which hang down in a radiating ar- 



o o 



rangernent and are called gills. The 

 gills illustrate very well the struc- 

 ture and position of the basidia on 

 a fruiting surface, or hymenium, 

 and cross sections are shown in Fig. 

 238. It will be seen that the basidia 

 are the swollen terminal cells of a 

 compact mesh of hypha?, and that 

 each bears a group of four spores 

 on short stalks or sterigmata. 



The toadstool is really a fructi- 

 fication. It is attached to an ex- 

 tensive mass of mycelium, which 



i/ 



is the vegetative portion of the 

 plant. This mycelium generally 

 lives saprophytically in the soil, 

 frequently around buried roots of 

 trees, but there are some para- 

 sitic gill fungi (Plate VI) which 

 cause the decay and final death of 



valuable timber. The toadstool 



FIG. 237. A group of mushrooms j -\ * -\ , p 



develops trom an accumulation or 

 (Armillaria mellea) 



hyphse in small structures called 

 buttons (Fig. 237, c, c f , c"). The 

 cap region with the gills and stalk 

 become differentiated within the 



blltton > and ^Hy break Ollt from 



the surrounding envelope and ex- 

 pand in a few hours to their full size ; hence the expression a 

 " mushroom growth." The remains of the envelope are found in 

 some forms as scales on the top of the cap (see mature mushroom 



my, mycelial attachment ; c, c', c", 

 young stages called buttons; 

 mature mushroom with expanded 

 cap (pileus) shown above; st, 

 stem (stipe) ; g, gills; r, ring. 



