298 



STRUCTURE AND LIFE HISTORIES 



These diseases are caused by fungi of the genus Ustilago} 

 The species are often named from the plant affected, 

 for example Ustilago Avenm on oats (Avena, Fig. 220), 



Fig. 220. — Panicles of oats (Avena sativa), with the grains almost com- 

 pletely destroyed and replaced by the oat smut {Ustilago Avena). 



Ustilago Triticl on barley (Triticum), Ustilago ZecB on 

 corn {Zea, Fig. 221). The mycelium extends through the 



1 A Hemibasidiomycete. 



