FORAGE CROPS 393 



ease may be clearly distinguished by cutting across the stem 

 and observing whether the color of the wood is normal. 

 This discoloration, which may often be seen through the 

 translucent stem of the cowpea, is characteristic of this 

 class of diseases. The name " wilt " is somewhat mislead- 



FiG. 170. — Cowpea leaf spot (amerosporiose). Original. 



ing, as the leaves usually drop off before there is any con- 

 spicuous wilting. 



The causal fungus is carried by the plow and cultivator, 

 as evidenced by the spread of the disease lengthwise of a 

 field, and by cattle, in cases where they pass through an in- 

 fected field on their way to pasture. It may also be car- 

 ried by drainage water, and by other of the ways suggested 

 under soil diseases. The disease is now known in most of 



