38 



FUXGI AND FUXGICIDES 



per. The presence of tlie fungus causes a peculiar 

 develoj^ment of the cedar leaves, as may be seen by ref- 

 erence to Plate III, wliere a normal healthy cedar branch 

 is shown at B, and a diseased one at A. The affected 

 branch not only has the ^'apples" developed, but the 

 leaves are entirely changed in shape. Reproductive 

 spores are produced from these ^'apples;" they ger- 

 minate in a way illustrated at C, and are blown about by 

 the wind. AVhen one is carried to an apple leaf where 

 conditions favorable to germination are present, it may 



2. 



FIO. 20. APPLE KUST. 

 1, Cluster cups on under surface of leaf; 2, spores; 3, spores germinating. 



develop and produce the aj^ple rust. The affected aj^j^le 

 loaf has scurfy bunches on the under surface, the area 

 on the upper surface above these becoming orange-yel- 

 low, or sometimes almost crimson, in color. As the 

 disease progresses the leaf becomes more and more dis- 

 torted, and in case the injury affects a large proportion 

 of the leaves serious damage to the tree may result. 



The spores are produced in great numbers on the 

 orange-yellow areas of the aj^ple leaf, and are blown 



