298 
STRUCTURE AND LIFE HISTORIES 
These diseases are caused by fungi of the genus Ustilago. 1 
The species are often named from the plant affected, 
for example Ustilago Avence on oats (Avena, Fig. 220), 
FIG. 220. Panicles of oats (Avena saliva), with the grains almost com- 
pletely destroyed and replaced by the oat smut (Ustilago Avena:}. 
Ustilago Tritici on barley (Triticum), Ustilago Zea on 
corn (Zea, Fig. 221). The mycelium extends through the 
1 A Hemibasidiomycete. 
