Minnesota Plant Diseases. 



287 



mycelium does not hibernate, tliat the cluster-cups can also be 

 omitted without injury to the rust. 



It is an important fact that some O'f the injurious rusts are 

 found upon wild grass plants and infection from cereals from 

 such sources must not be overlooked. The stem rust in par- 

 ticular is dangerous on this account. It has been shown that the 

 stem rust of wheat is able to infect a half dozen or more com- 



FiG. 143. — Spores of crown rust of 

 wheat (Puccinia coronata). w. Win- 

 ter spores, with a crown of finger- 

 like protuberances at the top of each 

 spore; from the wheat plant, a. 

 Summer spores from the wheat 

 plant, c. Cluster-cup spores from 

 the alder-leaved buckthorn. Highly 

 magnified. After Arthur and Hol- 

 way. 



mon wild grasses, including squirrel tail grass (Hordeum 

 jubatum), and also that the rust from these can infect 

 wheat plants. This is a very discouraging feature, for it seems 

 almost impossible to eliminate all of these weeds. Unless 

 this is done, however, the spread of stem rust cannot be pre- 

 vented. The stem rust moreover is the most virulent rust for 

 the spore specialty is the winter spore and this is found chiefly 

 on the stems, hence the common name of stem rust. In this posi- 



