GROUPS OF PLANTS. 31 



Basidiomycetes. — The Basidiomycetes are the most highly 

 organized of the Fungi. The mycehum consists of white branch- 

 ing threads and is usually concealed in the substratum. In the 

 cultivation of the edible mushrooms propagation is by means of 

 the mycelium which is known commercially as " spawn." It is 

 recognized, however, that mushrooms can not be propagated in 

 this way exclusively for more than two or three years. The my- 

 celium is really the plant body, and the part which rises above the 

 surface and is commonly regarded as the toadstool or mushroom 

 (Figs. 20 and 21) is a fruit branch, or spore-producing organ. 

 When these branches first make their appearance they are in the 

 form of small solid bodies known as " buttons " (Fig. 20, I-V). 

 As growth proceeds these bodies differentiate into a stalk-like 

 portion known as the stipe (Fig. 20, st), which is directly con- 

 nected with the mycelium, and an umbrella-like portion borne at 

 the summit of the stalk, called a pileus, which at first is closed 

 down over the stalk, but later expands or opens more or less 

 widely according to the species. On the under surface of the 

 pileus, known as the hymenium, the spores are borne (Fig. 20, 

 A, B, C). In some cases the under surfa!ce is composed of 

 a series of narrow, radiating, knife-like plates, or gills, as in 

 the common edible mushroom Agaricus. On the surface of 

 the gills the basidia or spore-bearing organs arise. The basidia 

 are somewhat swollen terminal cells of the closely arranged 

 hyphae composing the gills, which bear a group of spores on 

 short stalks (Fig. 20, C). Both the basidia and spores (basidio- 

 spores) are of a characteristic size and number for the different 

 species. 



In some of the other members of the group the gills are 

 replaced by pores, as in the " pore-fungi," which are parasites on 

 trees and destructive to timber. In still other cases the under 

 surface is furnished with teeth, as in the " teeth-bearing Fungi," 

 some of which, as Hydnum repandum, form the " fairy-rings " 

 in the woods. The latter are also formed by Marasmius oreades 

 (Fig. 21, illus. 7), in which the gills are comparatively few and 

 bulge out at the middle. 



One or two types will be considered, namely, the common 

 edible mushroom and two of the poisonous group, Amanita. 



