THE WHEAT RUST 



killed. The winter spores of the rust are formed within the 



cedar apple. In the spring the inner part of the cedar apple 



becomes soft and sends out finger-like masses of jelly in 



which the winter spores germinate (Fig. 31). The small 



plants that grow from the winter spores bear sporidia within 



and on the surface of the jelly. The sporidia are distributed 



by the wind. If they fall upon leaves, flowers, young fruits, 



or twigs of the apple, 



they produce an infec- \^ 



tibn. In a few weeks, 



cluster cups begin to 



appear, mostly on the 



leaves but sometimes on 



the fruits or twigs of the 



apple (Fig. 32) ; the 



spores formed in these 



cups, often as late as 



August, which correspond 



to the spring spores of the 



wheat rust, may then 



cause a new infection of 



the red cedar. No spores 



are produced by this rust 



that correspond to the 



summer spores of the 



wheat rust. If the apple 



tree is badly diseased, its fruit crop is greatly damaged. 



Not only does the .fruit that is directly attacked fail to 



develop normally, but the diseased condition of the leaves 



affects the nutrition of the tree as a whole, and so indirectly 



checks the growth of the fruit. 



The disease of the apple trees may be absolutely prevented 

 by the removal of red cedars from the neighborhood of the 

 apple orchard. Apparently the fungus has no way of sur- 

 viving the winter except within the tissues of the red cedar. 



FIG. 32. An apple infected by the 

 spores produced as a result of the germina- 

 tion of the winter spores. The spring 

 spores produced in the little cup-like 

 structures will infect the red cedar, caus- 

 ing the formation of "cedar apples." 

 After Jones and Bartholomew. 



