8 BULLETIN 120, U. S. DEPARTMENT OF AGRICULTURE. 
Very early in the season there is a period when great numbers of 
what appear to be mild infections establish themselves and cause 
a characteristic crinkling of the foliage. These infections soon die 
out and the damage done is not particularly serious, though it is 
undoubtedly of some importance. 
The climatic conditions of the Pajaro Valley offer excellent oppor- 
tunity for the establishment and progress of the mildew. The fogs 
furnish excellent moisture conditions for the germination of the 
spores, and it is probable that the somewhat peculiar climatic condi- 
Fic. 3.—A perithecium of Podosphaera leucotricha, showing the two types of appendages. 
Magnified 90 times. (After Grout.) 
tions of the valley influence the character of the foliage in a way to 
make it more than normally susceptible to infection. The result is 
that unless proper protection by spraying is provided, 90 per cent of 
the foliage of Yellow Newtowns and Yellow Bellflowers may become 
diseased before the end of the growing season. 
The summer spores, or conidia, that have just been discussed serve 
only to spread the summer infections. They are not long lived, and 
therefore are not capable of carrying the mildew over from fall until 
the next spring. Furthermore, the mycelium on the twigs dies 
