240, MANUAL OF FRUIT DISEASES 
withers, turns brown or red, and finally shrivels into a mummy 
(Fig. 63). Diseased fruits shell very easily. 
Cause. 
The downy-mildew pathogene is a fungus, Plasmopara 
Vitecola. It has both a sexual and an asexual stage, the former 
Fic. 63. — Downy-mildew on grape-berries. 
represented by oospores, the latter by conidia. It is generally 
agreed that the oospores carry the fungus through the winter 
in the old fallen leaves. In the spring these oospores germinate, 
forming a conidiophore, on which is borne another spore, a 
conidium. The conidium in turn, at maturity, germinates, 
but instead of forming a germtube, its contents break up into 
