PLASMOPARA 



119 



Plasmopara viticola (Berl. and de Toni), was introduced to 

 Europe from the United States, where it is equally injurious 

 to both wild and cultivated vines. Every portion of the plant 

 above ground is attacked, but more especially the foliage, 

 where its presence is first indicated by the appearance of pale, 



FIG. 25. Basidiospora entospora. 2, 3, Sclerospora graminis, 

 conidial stage and oospore ; 4, Bremia lactucae, portion of conidial 

 stage. All highly mag. 



yellowish-green patches on the upper surface of the leaf. 

 Corresponding areas on the under surface soon become 

 covered with a delicate greyish mildew ; these patches continue 

 to* increase in size, and run into each other, until finally the 

 entire under surface is covered with mildew. Soon after this 

 stage has been reached the leaf turns yellow, then brown, 

 dries up and falls, but not before myriads of spores have been 



