FUNGI, THE RUST FUNGI 



309 



loss to the wheat crop in the United States is estimated variously 

 from $20,000,000 to $60,000,000 annually. The yellowish or 

 blackish spore masses, often thickly scattered over parts of the 

 host, give a rusty appearance to them, hence the name. The 

 mycelium is within the host and intercellular. It sends short 

 haustoria into the cells, where they absorb nutriment. In many 

 cases it stimulates the affected part of the host to abnormal growth, 

 forming witches' brooms in one form on the balsam, or galls as in 

 the case of the cedar apples (paragraph 471), etc. Some of these 

 abnormal growths are edible, as the branches of an acacia in 



Fig. 258. 



Witches' broom on balsam (Abies balsamifera) caused by a parasitic fungus (.^cidial stage 

 of Melampsorella cerastii), from northern Michigan. 



India deformed by Mcidium esculentum, and in Scandinavia the 

 branches of the fir deformed by Mtidium corruscans. The life 

 history is very complicated in some species and is well illustrated 

 by the wheat rust. 



Wheat Rust (Puccinia graminis). 



461. The wheat rust is one of the common rusts on cereals 

 and grasses in many parts of the world, and one stage in its 

 complete life history occurs on the barberry. 



