APPLE DISEASES 69 



spores, are discharged. The wind carries them to the red cedar 

 where they cause the formation of the cedar-apple. It is not 

 definitely known whether the seciospores germinate in the fall 

 or in the spring, but at any rate mycelium develops from the 

 germtube and the cedar leaf-tissues are stimulated as are those 

 of the apple. As a result of this over-growth a gall is formed. 

 This is the cedar-apple. It will be observed that one year 

 elapses between the inoculation of the apple and the appearance 

 of the gall on the cedar. This gall continues to grow through- 

 out the summer and by fall has attained its full size. The next 

 spring brown horns push out over the surface of the gall; 

 these horns are composed of another kind of spores telio- 

 spores. With the advent of spring rains the horns become 

 gelatinous and the teliospores germinate. This occurs approx- 

 imately two years after the first inoculation of the apple. A 

 peculiar germtube is produced by the teliospores one which 

 is four-celled and which is called a promycelium. Four spo- 

 ridia, or basidiospores, are developed on each promycelium; 

 each sporidium is discharged at maturity and is blown to the 

 apple. Thus the complete life-cycle involves a period of about 

 two years. 



The teliospores do not all germinate at once. As already 

 noted, during a wet period they germinate and produce sporidia. 

 If the air then becomes dry, the sporidia are snapped away and 

 caught by the wind. With the return of rainy weather the 

 process of gelatinization of the horns and germination of the 

 teliospores is repeated. As evaporation occurs the second crop 

 of sporidia is disseminated. In certain years there may be 

 but one crop, in others there may be as many as six crops. 

 The number and frequency of these yields of sporidia are deter- 

 mined by the weather conditions. The air must remain highly 

 humid for at least six hours in order to allow gelatinization, 

 germination, and sporidial production ; but within this short 

 period a great number of sporidia may be produced and with 



