396 THALLOPHYTES 



duced by the division of hyphac as described in Oat Smut. 

 When the spores are mature, the skin-like covering breaks, thus 

 allowing the spores to be scattered. Some spores pass the winter 

 on the old stalks. Others pass the winter on the ground or wher- 

 ever they happen to fall. In the spring the chlamydospores ger- 

 minate and produce the promycelia and basidiospores. The 

 basidiospores are blown to the Corn and are able to grow hyphae 

 into the tender regions of the plant and start the disease. Treat- 

 ment of the seed Corn is, therefore, of little value in combatting 

 Corn Smut. In what way can Corn Smut be controlled? 



Rusts (Uredinales).^ — Like the Smuts, the Rusts are internal 

 parasites and only their spore masses are visible externally. 

 They are so named on account of the red color of their spore 

 masses. There are about 2000 species of Rusts and they attack 

 nearly all kinds of plants but more especially members of the 

 Grass family. Although regarded as degraded parasites, they 

 are more complex than the Smuts, for they have more kinds of 

 spores and many of them have alternating stages upon different 

 hosts. For example, it is well known that Wheat Rust and the 

 Common Barberry bush (Berheris vulgaris) are associated. They 

 are associated because the Wheat Rust lives one stage of its life 

 cycle on the Wheat and the other on the Barberry. Each kind 

 of Rust lives on only certain hosts and the alternating hosts are 

 plants very different in kind, as those of the Wheat Rust 

 illustrate. 



Rusts, although directly affecting only limited areas of tissue 

 around the places of attack, commonly attack the host in so 

 many places that they weaken the host and thereby prevent grain 

 plants from yielding normally. The financial loss to the farmer 

 due to Rusts is considerably more than that caused by Smuts. 

 Some years the loss in the United States due to the Black Rust 

 exceeds $15,000,000. The Black Rust of which six forms are 

 distinguished is the most important one of the Rusts. 



Black Rust of Grain (Puccinia graminis). — The Black Rust, 

 sometimes called Red Rust, is a dreaded pest on Wheat, Oats, 



' Investigations of Rusts. Bulletin 65, Bureau of Plant Industry, U. S. 

 Dept. Agriculture, 1904. 



Lessons from the Grain Rust Epidemic of 1904. Farmers' Bulletin 219, 

 U. S. Dept. Agriculture, 1905. 



Rust of Cereals. Bulletin 109, South Dakota Agr. Exp. Sta., 1908. 



