DISEASES OF CEREALS AND GRASSES 49 



(a) Rztst and Mildew of Wheat [Puccinia gram- 

 inis). 



Many varieties of wheat are attacked. 



Symptoms, — The leaves of attacked plants turn 

 a pale yellow colour in early summer, and later 

 elongated reddish-orange spots appear on the leaf, 

 sheath, and the stem. These spots turn a much 

 darker colour in the late summer (see Fig. 13). 



Fig. 13. — Rust of wheat {Pnccinia graminis) : (A) showing the small 

 pustules covering the wheat leaf; (B) section through a pustule from 

 (A); (») uredospore ; (t) teleutospore ; (5) surface cell of wheat leaf. 



Cause. — This disease is caused by the fungus 

 Puccinia graminis, which has a very interesting, 

 but complex, life history ; for it apparently usually 



4 



