GROUPS OF PLANTS. 



35 



are somewhat spherical or ellipsoidal, and are generally separate, 

 but are sometimes united into a mass forming the so-called 

 " spore balls." These are resting spores and upon germination 

 (Fig. 23) produce a promycelium or basidium which becomes 

 septate and from each cell of which conidia called sporidia arise. 

 The sporidia are formed in succession one after another and the 

 process continues for some time. On germination they bud like 



Fig. 22. Corn smut (Usiilago Maydis) showing several gall-like masses of smut 



full of spores. 



yeast, forming new conidia, or when nutrition is not abundant 

 they may form, a mycelium, which is usually the case when they 

 germinate on a host plant. 



Corn Smut. One of the Smut Fungi, namely, Ustilago 

 Maydis, which develops on Indian corn (Fig. 22), is used in medi- 

 cine. It forms rather large gall-like masses on all parts of the 

 plant, including the root, stem and leaves, and both staminate and 

 pistillate flowers. The spores (Fig. 23) are at first a dark olive- 

 green, but on maturity are dark brown. They are sub-spherical, 

 have prominent spines, and vary from 8 to 15 microns in diameter. 



