BLACK RUST OF GRAIN (PUCCINIA GRAMINIS) 397 
Rye, and Barley, and occurs on other Grasses. The presence of 
the mycelium in the host is first known through the appearance of 
reddish spots or lines on 
the stems and leaves in 
late spring or early sum- 
mer. The reddish spots 
or lines are regions of 
spore production. They 
are pustules or blister- 
like structures caused by 
masses of spore-bearing 
hyphae which push up 
the epidermis until it is 
finally ruptured (Fig. 
358). The reddish color 
of the pustules is due to 
the reddish color of the 
spores. These spores are 
known as the “summer 
spores’? or uredospores. 
The uredospores, which 
are produced in great 
& Z ] 
eS 
Fic. 353.— Wheat Rust as it appears on 
Wheat. Left, portion of a Wheat plant, 
showing the pustules on the stem and leaf; 
right, a much enlarged section through a pus- 
tule, showing the summer spores (X 200). 
numbers, are scattered by the wind, thus reaching other host 
plants into which they grow 
hyphae and thereby infect. 
They are chiefly responsible 
for the rapid spread of the 
disease during summer. 
Later in the summer, when 
the grain is ripening and the 
food for the Fungus becomes 
scarce, the same mycelia pro- 
duce heavy-walled, two-celled 
spores, known as winter spores 
Fic. 354. — A section through a pus- OF teleutospores (F ig. 354). 
tule in late summer, showing the winter These spores are dark in color, 
spores or teleutospores. X about 200. giving the pustules a dark ap- 
pearance — whence the name 
Black Rust. They pass the winter on the straw, ground, or wher- 
ever they happen to fall. 
The following spring, each cell of the 
