THALLOPHYTES : FUNGI 
281 
wall, and forms what is called the " black rust," which ap- 
pears late in the summer on wheat stubble. These spores 
are the resting spores, which last through the winter and 
germinate in the following spring. They are called teleuto- 
spores, meaning the " last spores " of the growing season. 
They are also called " winter spores," to distinguish them 
from the uredospores or " summer spores." At first this 
teleutospore-bearing mycelium was not recognized to be 
identical with the uredospore-bearing mycelium, and it was 
called Puccinia. This name is now 
retained for the whole polymorphous 
plant, and wheat rust is Puccinia 
graminis. This mycelium on the 
wheat, with its summer spores and 
winter spores, is but one stage in 
the life history of wheat rust. 
In the spring the teleutospore 
germinates, each cell developing a 
small few-celled filament (Fig. 252). 
From each cell of the filament a 
little branch arises which develops 
at its tip a small spore, called a spo- 
ridium, which means "spore-like." 
This little filament, which is not a 
parasite, and which bears sporidia, 
is a second phase of the wheat rust, 
really the first phase of the growing 
season. 
The sporidia are scattered, fall 
upon barberry leaves, germinate, and 
develop a mycelium which spreads 
through the leaf. This mycelium produces sporophores 
which emerge on the under surface of the leaf in the 
form of chains of reddish-yellow conidia (Fig. 253). These 
chains of conidia are closely packed in cup-like receptacles, 
and these reddish-yellow cup-like masses are often called 
FIG. 252. Wheat rust, show- 
ing a teleutospore germina- 
ting and forming a short fil- 
ament, from four of whose 
cells a spore branch arises, 
the lowest one bearing at 
its tip a sporidium. After 
H. MARSHALL WARD. 
