BACTEEIA WHICH CAUSE PLANT DISEASES 403 



Morphology — The organism is about 0.5X1.5m, motile 

 by means of peritrichous flagella; stains readily with 

 ordinary aniline dyes and is Gram-negative. 



Cultural Characters. — In broth there is abundant dirty 

 white sediment, the reaction usually becomes alkaline. Milk 

 is rendered alkaline, casein is dissolved without precipita- 

 tion. On agar the growth is smooth, slightly viscous, first 

 whitish, then yellowish and finally brown. Gelatin shows 

 little or no liquefaction ; on potato the growth is white and 

 later brownish to black on a browned medium. Neither 

 acid nor gas are produced from the carbohydrates. 



Pathogenesis. — The disease is characterized by sudden 

 wilting or shriveling of the foliage, the softer parts of the 

 plant also wilt rapidly. The fibrovascular bundles of the 

 stem become stained brownish and microscopically are 

 found to be filled with bacteria. The wilting is most evi- 

 dent in the young plants. Older woody plants may turn 

 yellow and die without wilting. The organism may invade 

 the parenchymatous tissues and cause rotting. The potato 

 tubers infected with the organism show brownish discolora- 

 tion in the ring of fibrovascular bundles. 



Eewinia tracheiphila 



Synonym. — Bacillus trackeiphilus. 



This organism is the specific cause of a wilt disease of 

 cucurbits, particularly of cucumber, squash, cantaloupe and 

 pumpkin. In this disease the foliage shows a sudden wilt- 

 ing and shriveling because the fibrovascular bundles are 

 stopped by the large masses of white, sticky, rod-shaped 

 organisms. 



Morphology. — The organism is a rod, motile by means 

 of peritrichous flagella, about 0.£m in diameter and from 

 1.2-2.5;u in length. It stains readily and is Gram-negative. 



It is probable that the disease is spread largely through 

 insects, particularly by the cucumber beetle. The organism 



