LIFE HISTORIES OF FUNGI 273 



it attacks some of the most valuable of all agricultural 

 crops (wheat, oats, rye, barley, etc.), causing, at times, 

 millions of dollars worth of damage.* It is difficult to 

 understand because it is heteroscious — that is, lives alter- 

 nately on two different plants, the barberry and the grain. 

 For many years the form on the grain was supposed to 

 be quite another plant from that on the barberry, which 

 was called Mcidium berberidis. 



266. Life History. — a. Red Rust Stage. — The mycelium 

 of red rust (uredo stage) grows between the cells of the 

 stem and leaves of the wheat, or other grain, and finally 

 during the summer, numerous sporophores, bearing red 

 spores (urediniospores), break through the epidermis 

 (Fig. 198), producing reddish or rusty-looking dots and 

 lines, whence the name "rust" for the. plant. The one- 

 celled uredinio-spores are easily blown by the wind in 

 great numbers to other wheat plants, where they germ- 

 inate, and thus spread the rust widely and rapidly. 



b. Black Rust Stage. — In late summer the same myce- 

 lium develops an entirely different kind of spore, two- 

 celled, and black. These are the final spores of the season, 

 the teliospores (or teleuto spores), and in them the nuclear 

 fusions occur. They rest over winter, and germinate 

 the following spring, each cell usually sending forth a 

 hypha commonly composed of four cells, which constitute 

 the basidium (promycelium) . Each of these cells produces 

 a tiny sporophore, bearing at its tip a single basidiospore 

 (sporidium). Reduction occurs during germination. 



c. Barberry Stage. — The basidiospores are blown by the 



* The financial loss from wheat-rust in the United States amounted 

 to $67,000,000 in 1891; in 1904 the loss in North Dakota, South Dakota, 

 and Minnesota alone was estimated at $25,000,000. 

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