EXPLAXATIOX OF THE PLATE. 



a. Loaf of Vitis ccstivalis showin*; the Tinder side with the spots affected by the 

 mildew darkened. 



h. Cross-section through a leaf sliowing the threads of the fungus running between 

 the cells. 



c. "Where the threads have passed out a stoma on the underside of the leaf and 

 branched in a tree-like maimer bearing spores on their tips. 



d. One of the tips in c very highly magnified. 



c. Cells of grape with threads passing between them, all very much enlarged. 



/. Asexual spore highly magnified showing the primular protoplasmic contents 

 collecting into oval bodies. 



(J. Asexual spore less magnified with the division of the contents completed. 



h. One of the zoospores after it has escaped, and provided with two cilia. 



1,1. Haustoria or "suckers" on the embedded filaments penetrating the cells of 

 the grnpe plant. 



j. Sexual (oospore) spore separated from the tissue of the grape leaf and magni- 

 fied about 750 diameters. 



Figures '7, f/, /i, audi are copied from Dr. Farlow's plates on Peronospora in the 

 Bulletin of the Bussey Institution. 



