152 



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, etc. 

 The stage on the apple-tree is the clus- 

 ter-cup stage, the cluster-cups occurring 

 on the under surface of the leaves; the 

 mycelium also attacks and ruins the 

 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 and in- 

 fect the apples. Attempts 

 are made to check the ap- 

 ple-rust by destroying the 

 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 oospores (sexually formed spores) have been 

 observed; but a process in the life-history representing a 

 sexual act has been discovered in some forms. 



FIG. 144. A cedar-apple. 



