68 Rusts [CH. 
The fungus has now reached the stage when it 
leaves the wheat plant and seeks a new host. Before 
its life history was known it was held by farmers that 
barberry hedges caused the wheat near them to become 
rusted. This story aided de Bary in following out its 
further development. He found that it was possible 
to infect the barberry plant by means of the secondary 
spores formed from the teleutospores. He also found 
that the fungus produced on the barberry had a totally 
different appearance from the rust of wheat which 
produced it, but on infecting wheat with the spores 
from the barberry it became rusted. Two kinds of 
spores are produced on the barberry but only one of 
them takes part in the reproduction of the fungus. 
These are known as aecidiospores, and are borne in 
a chain-like manner. A series of these chains is 
enclosed in a kind of ball near the lower surface of the 
barberry leaf. After a time the ball bursts and a 
kind of cup is produced which can be seen with 
the naked eye (see Fig. 24). The aecidiospores are 
yellowish, spherical, and almost as large as the uredo- 
spores. On germination they send out a simple tube 
which is capable of infecting wheat. The aecidium 
cups appear on the barberry in the early spring. This 
is not a case of one fungus giving rise to another fungus 
as the aecidiospores cannot infect other barberry 
plants. The different spores are stages of the fungus 
Puccinia graminis. 
The damage done to the wheat plant consists in 
reducing the yield, as some of the food which should 
have gone to swell the grain is taken by the fungus, and 
the amount of food manufactured is lessened by the 
destruction of some of the chlorophyll in the leaves and 
