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 exciospores 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. 
Tf 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 
