76 PLANT DISEASES 



fungus. Numerous globose, thick-walled bodies, called 

 resting-spores, are produced on the mycelium present in 

 the tissues of the decaying leaves. These resting-spores 



Fig. lo.Peronospora schleideni. i, a conidiophore that has 

 emerged through a stoma of the leaf, x 300 ; 2, free conidia, 

 x 300 ; 3, a resting-spore, or oospore, x 300. 



do not germinate until the spring following their produc- 

 tion, when they inoculate the young onions and start the 

 disease afresh. During the winter the leaves containing 



