THE BROWN ROT OF SOLANACEAE : VARIABILITY 199 



Virginia and Texas? Specifically: is it in California, Maine, 

 Wisconsin, Michigan, Ohio, Kentucky or New York? Does 

 it occur in Canada? If not in these places, why not? 



Transmission. — Have you seen any indication leading you to 

 think that insects spread this disease? In 1896 I obtained 

 very successful infections on potato, using the Colorado potato 

 beetle (Leptinotarsa decemlineata) . Many narrow, dark, bacteri- 

 ally infested streaks started in the bitten places and passed 



Fig. 141. — Photomicrograph showing origin and structure of two incipient 

 roots in an inoculated diseased tomato stem. Bacterium solanacearum occurs in 

 some of the vessels at the lower left side. What stimulus sets the roots growing? 



rapidly down the stems, both stems and tubers being de- 

 stroyed. If you have opportunity watch infected fields closely 

 and if you obtain clues make some experiments. Hunger in 

 Java incriminated several insects and also thought Phytoph- 

 thora nicotiana paved the way for this parasite. Are plants on 

 wet soils more liable to it? Do the roots of the infected plants 

 usually bear nematode galls? Are plants on limestone soils 

 free from it? 



Of course, one susceptible crop should not closely follow 



