396 THALLOPHYTES 
duced by the division of hyphae 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 (Berberis 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, 
1 Investigations of Rusts. Bulletin 65, Bureau of Plant Industry, U. 8. 
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. 
