LITE 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 hetercecious 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 (uredinios pores}, 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 teleutos pores), 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 (promyceliuni) . Each of these cells produces 
a tiny sporophor.e, 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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