xxxvi.] POTATO DISEASE, II. PASSIVE STATE. 305 



only, in a hibernating, septate state, is seen at D. The 

 transparent oogonia of the summer have now become 

 brownish ripe oospores or winter resting-spores of a larger 

 size. Six resting-spores are shown in the illustration, 



X- 100 



FIG. 133. 



Section through a fragment of old potato leaf, with resting-spores or 



oospores, of Peronospora infestans, Mont., in situ. 



Enlarged 100 diameters. 



two in the transparent leaf hair, three in the intercellular 

 spaces of the leaf, and one inside a spiral vessel, in which 

 position it is extremely common to find them. 



The perfectly mature resting-spores are best seen in the 

 X 



