Family Solanaceae 343 



localized to the vegetative parts. With the Irish 

 potato, the disease works underground where it also 

 penetrates the tubers. These show a yellowing and 

 blackening of the veins, finally giving way to a soft 

 rot. On squeezing, a creamy exudate oozes out from 

 the diseased veins. 



Southern wilt attacks not only the tomato, potato, 

 and eggplant, but it also causes a serious disease on 

 the tobacco, peanut, nasturtium, ragweed, im- 

 patience, verbena, plants which belong to families 

 other than the Solanaceae. 



The Organism. Pseudomonas solanacearum is a 

 medium-sized rod, with rounded ends and motile 

 by means of polar flagella. Pseudo-zooglceae are 

 common in old cultures. No spores are formed; 

 on agaragar, colonies are white, then dirty white, 

 afterwards becoming brown with age. The or- 

 ganism does not liquefy gelatin and produces no 

 gas. 



Control. Crop rotation is the safest method of con- 

 trol. All crops subject to wilt, such as potato and 

 eggplant should be left out from the rotation 

 system. 



Damping off, see Pythium, p. 43. 



Late Blight 



Caused by Phytophthora infestans (Mont.) De By. 



Late blight usually attacks the fall tomato crop. 

 It is especially prevalent during rainy weather, where 

 it may even be found in the seed bed. The trouble 



