230 Diseases of Truck Crops 



recently studied by Smith and Bryan, * who described 

 it as a new disease occurring in the Eastern and 

 Middle-Western States. 



Symptoms. The trouble is characterized by angu- 

 lar brown spots which tear or drop out when dry 

 (fig. 40 b), giving a ragged appearance to the infected 

 leaves. In the eariy stages, a bacterial exudate 

 collects in drops on the lower surface of the spots. 

 These exudates usually dry and become whitish. 

 It seems that angular leaf spots attack only the f oU- 

 age but rarely the fruit. 



The Organism. The parasite is a short rod with 

 rounded ends (fig. 40 c), occurring singly, or in pairs 

 with a decided constriction; and occasionsiUy in 

 chains of twelve individuals or more. It is motile by 

 means of polar flagella, produces capsules on agar 

 and milk; no spores, and no gas is formed. The or- 

 ganism completely Hquefies gelatine in about three 

 or four weeks. 



Damping off, see Pythium, p. 43. 



Downy Mildew 



Caused by Pseudoperonospora cubensis (B. and C.) 

 Rost. 



Downy mildew is prevalent in New Jersey, New 

 York, Florida, Texas, and possibly other States. It 



' Smith, E. W., and Bryan, M. K., IT. S. Dept. of Agr., Jour. Agr. 

 Research, 6 : 465-476, 1915. 



