PLATE IS 



A. — Overwintering on seed: Natural infections on cotyledons of seedling grown in 

 steamed sand from commercial seed which had been kept in storage for seven 

 months after harvesting. Experiment of March 3, 1917. Enlarged about i^ times. 



B.— Picker dissemination. Infection resulting from inoculation of a cucumber 

 leaf at 7.30 a. m. by rubbing with the hand immediately after touching diseased 

 exudate -bearing leaves. 



C. — Dissemination by rain. The older leaves in the center of the row were badly 

 infected during a rainy period. Young leaves on the sides of the row which developed 

 during a rainless period are comparatively free from the disease. Photographed by 

 Mr. W. W. Gilbert. 



