64 Ergot and Clover Sickness [cH. 
sclerotia are only capable of living for four or five years. 
After an attack of the disease an interval longer than 
this should therefore be allowed to elapse before clover 
is sown again. Meantime the land should be kept 
free from leguminous weeds. 
CHAPTER VI 
RUSTS 
The group to which rusts belong, known as the 
Uredineae, is very widely distributed, in fact some of 
its members are present in all parts of the world where 
plants are cultivated. The term “rust” in its popular 
sense includes all diseases which cause a rusty appear- 
ance of a green plant. From a farmer’s point of view 
they are extremely important, as they bring about a 
considerable loss in his cereal crop every year. They 
are characterized by giving rise to several different kinds 
of spores, some having as many as five different kinds. 
Another peculiarity of certain members of the group 
is that some of these spores may be borne on one host, 
and other spores of the same fungus on an entirely 
different host. There are a number of rusts which 
attack our cereals, most of them belonging to the 
genus Puccinia. The differences between them are 
chiefly concerned with the number of kinds of spores, 
their characteristics, and whether they are all or only 
in part produced on the cereal host. A description of 
two of the more important species will help to give 
some idea as to what rusts are. 
Puccimia graminis. The popular name of this 
