FUNGI, THE RUST FUNGI 



3*3 



463. The red rust of wheat (uredo stage). The aecidio- 

 spores from the cluster cup on the barberry are carried by the 

 wind to the wheat (also to the other cereals and some grasses). 

 Here they germinate and the mycelium enters at a stomate and 

 produces the intercellular mycelium. At certain points under the 

 epidermis of the leaf, or stem, a group of short spore-bearing 



B 



Fig. 273. 



A, section through sorus of black rust of wheat, showing teleutospores. B, mycelium bear- 

 ing both telcutosporcs and uredospores. (After de Bary.) 



hyphae are formed, each of which bears a broadly elliptical spore 

 with minute warts on the wall. These spores are the uredospores. 

 They are yellowish in color. The pustule formed here is called a 

 sorus. The epidermis is ruptured by the growth pressure of the 

 hyphae and spores, and thus the spores are set free. These uredo- 

 spores are carried by the wind to other wheat plants, starting 

 new centers of the disease, and thus several successive crops of 

 uredospores are formed in one season. The uredo stage is the 



