Ch. X] 



THE RUSTS 



465 



in the ground, or young seedlings, and later produce again 

 the mycelium and brand spores, as already described. This 

 Smut also infests Oats and Wheat, doing them great damage. 



Fig. 324. — The life cycle of the Corn Smut (Ustilago Zeae). 



Left, ear of Corn containing characteristic smutted grains; X h Middle, 

 above, the mycelium in cells of the Corn plant ; X 250. Below, tips of 

 hyphse in the grain forming the brand spores, and ripe spores ; X 250. 

 Right, a spore germinated to the promycelium, which is developing sporidia, 

 — the spores which infect new plants ; X 200. (First and last after Curtis, 

 others after Knowles.) 



Another species produces the so-called Stink Brand or Stink- 

 ing Smut of Wheat, which smells like rotting fish. 



Thus the life history of the Smuts includes two stages, — 

 one parasitic on a host, and one saprophytic on the ground. 



Order 2. Uredinales: the Rusts. These are mostly 

 internal parasites, especially of the Grass family, and are 

 visible externally only in the spore masses, of which the 

 dull red color gives the name to the group. They produce 

 several kinds of spores, and are notable for their alternating 

 stages upon different hosts, in a more complicated life cycle 

 than is known in any other plants. Some 2000 species occur, 

 including several of the most destructive plant parasites. 

 2h 



