PLATE 40 

 Bacterium marginale: 



A. — A head of lettuce showing the marginal infection on tender leaves in center. 

 Inoculated by spraying on March 2, 191 7. Photographed on March 16, 191 7. 



B. — Four lettuce leaves inoculated by spraying February 21, 1917. Photographed 

 on February 23, 1917. Many of the infections are tiny spots not visible in the 

 illustration — for example, on the leaf next to the smallest leaf at the right there are 

 75 such spots. 



