FUNGI: THE RUST FUNGI 



283 



here is called a sorus. The epidermis is ruptured by the growth 

 pressure of the hyphae and spores, and thus the spores are set 



n 



Fig. 251. 



Wheat leaf with red 

 rust. Natural size. 



Fig. 252. Fig. 253. Fig. 254. 



Portion of leaf Natural Enlarged, 



enlarged to show sori. size. 



Figs. 251-252. Puccinia graminis, red-rust stage (uredo stage). 

 Figs. 253-255. Black rust of wheat, showing sori of teieutospores. 



Fig. 255. 

 Single 

 sorus. 



free. These uredospores are carried by the wind to other w r heat 

 plants, starting new centers of the disease, and thus several suc- 



Fig. 256. Fig. 257. Fig. 258. 



Uredospores of wheat rust, Germinating uredo- Germ tube entering the leaf 



one showing remnant of the spore of wheat rust. (After through a stoma. 



pedicel. Marshall-Ward.) 



cessive crops of uredospores are formed in one season. The 

 uredo stage is the propagative stage. 



