3G 



FUXGI AXD FUXGICIDES 



bish. 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 No. 44 of the Kentucky Agricultural 

 Experiment Station ; and of its nature in the 18S9 report 

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

 Report of the IT. S. Dej^artment of Agriculture, and 

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



The Apple Rust 



Gymnosporangium and Rcestelia 



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 jihase of devel- 



FIG. 19. ^, surface view of pustiile; if, mycelium thread; (J, ^terminating spore. 



Magnified. 



opment occurs upon one plant, whiJe 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 -ap23les," or ^' cedar-balls" of cedar or juni- 



