286 



PLANT DISEASES 



fall on the leaves of a barberry, they perish and are 

 wasted. 



The mycelium in the leaf of the barberry soon 

 produces another kind of spore which may be called the 



FIG. 147. Spores of Wheat Rust. 



, a cluster of winter spores of wheat rust (Puccinia graminis) on wheat plant; 2, a winter 

 spore germinating to a thread of four cells (promycelium-basidium), each of which 

 bears a small spore (sporidium) on a stalk. The winter spore germinates in the spring 

 while still in the straw or on the ground. The sporidia are blown by the wind to another 

 plant, and there germinate, as seen in 3 and 4 4, shows the germination of a sporidium 

 on a barberry leaf; here infection will soon take place; 5, a germinating summer spore 

 of wheat rust, showing germ tubes which on a wheat plant can cause infection. All 

 magnified. 1-5, after Ward. 



spring spore, produced in May or June in this country. 

 The spring spores are produced in chains and look very 



