158 A TEXT-BOOK OF BOTANY 
case the early spring spores infecting wheat plants rather 
than barberry leaves; and recently it has been shown 
that often the summer spores survive the severest winter 
and infect young wheat plants of the next season. 
Another well-known rust is that which attacks apple- 
trees and their relatives, the wild crab, hawthorn, ete. 
The stage on the apple-tree is the clus- 
' 3 ter-cup stage, the cluster-cups occurring 
ay on the under surface of the leaves; the 
oe mycelium also attacks and ruins the 
2 \ fruit, the cluster-cups being seen in 
™ \ connection with the diseased parts. 
The cluster-cup spores infect the cedars, 
producing swellings half 
an inch or more in diame- 
ter and known as cedar- 
apples (Fig. 144). In the 
spring these cedar-apples 
become conspicuous, espe- 
cially after a rain, when 
the jelly-like masses con- 
taining the orange-colored 
spores swell. These spores 
are blown about end in- 
feet the apples. Attempts 
are made to check the ap- 
ple-rust by destroying the 
Fie. 144.—A_ cedar-apple. cedar-trees and by spray- 
ing the apple-trees, when 
they are putting out their leaves, with a liquid that kills 
such Fungi. 
Although rusts possess several kinds of ordinary (asex- 
ual) spores, no odspores (sexually formed spores) have been 
observed; but a process in the life-history representing a 
sexual act has been diseovered in some forms. 
