258 ESSENTIALS OF BOTANY 
(b) The rough outer coating and the inner coating with (usually) 
four pits or thin places in its wall about midway of the spore. 
Fic. 183. A Germinat- 
ing Teleutospore of 
Puccinia graminis. 
a, a’, threads produced 
by the germination, 
from the ends of which 
grow short rows of 
cells which bear basid- 
tospores, 6. These are 
carried by the wind 
to the barberry host- 
plant. 
333. Black Rust, Minute Structure. — Re- 
move a small mass of the black-rust spores 
(teleutospores), mount, and examine as de- 
scribed in Sect. 832. Note: 
(a) The shape and attachment of the spores 
(Fig. 182). 
(6) The structure of the spore (composed 
of two cells) and the thickness of the cell- 
wall. Look for thin places or germinating 
pores in the cell. 
334. Life History of Wheat Rust. 
This species of rust under favorable cir- 
cumstances shifts from the barberry as 
a host-plant to wheat or other grass and 
back to the barberry again year after 
year. The cluster-cup spores are borne 
by the winds to grain or grass fields, 
where they germinate arid develop 
red-rust streaks full of uredospores. 
These spores are carried to other wheat 
plants on which they germinate, and 
so the growth of the fungus spreads. 
In late summer or autumn the same 
mycelium which earlier produced ure- 
dospores forms only teleutospores and 
the red-rust streaks turn blackish. The 
teleutospores survive the winter and 
in the spring germinate on barberry 
leaves (Fig. 183), produce a new crop 
of cluster-cup spores, and so on. Note that all these proc- 
esses of spore formation are asexual; no gametes are known. 
