36 



FU^^'GI AXD rrXGICIDES 



bisli. Then the Bordeaux mixture treatment recom- 

 mended for the preyention of apple scab will have a 

 decided influence in lessening the amount of damage. 



An account of experiments with this disease may be 

 found in Bulletin K'o. 44 of the Kentucky Agricultural 

 Experiment Station ; and of its nature in the 1889 report 

 of the same station. It is also discussed in the 1887 

 Eeport of the U. S. Department of Agriculture^ and 

 more fully in the Journal of Mycology, v. YI^ p. 164. 



The Apple Rust 



Gymnosporangmm and Roestelia 



A peculiarity of many parasitic fungi is that the 

 complete cycle of their existence is not passed upon a 

 single host-plant^ but that, instead, one phase of devel- 



riG. 19. surface view of pustule; ^, mycelium thread; germinating spore. 



Magnifiecl. 



opment occurs upon one plant, while another quite differ- 

 ent stage of existence is passed on an entirely different 

 host. A striking illustration of this is seen in the case of 

 the rusts which sometimes affect apple trees, causing the 

 leaves to become more or less blistered with orange-yel- 

 low spots. In this disease the fungus on the apple is an 

 alternating form arising from spores produced by the so- 

 called cedar -apples," or ^^cedar-balls" of cedar or juni- 



