138 Diseases of Greenhouse Crops 



hosts which are subject to this trouble. Of the nu- 

 merous varieties of cucumber, none shows promise 

 of resistance to the disease. 



Angular Leaf Spot 



Caused by Pseudomonas lachrymans Sm. and Bry. 



Symptoms. The trouble is characterized by an- 

 gular brown spots which tear or drop out when dry, 

 giving a ragged appearance to the infected leaves. 

 In the early stages of the disease a bacterial exudate 

 collects in drops on the lower surface of the spots. 

 This usually dries up and becomes whitish. It seems 

 that angular leaf spots usually attack only the foli- 

 age, rarely the fruit. 



The Organism. The parasite is a short rod with 

 rounded ends, occurring singly or in pairs with a 

 decided constriction, and occasionally 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 organism com- 

 pletely liquefies gelatine in about three or four 

 weeks. Little is known of methods of control. 



Damping Off, see Pythium, p. 28. 



Downy Mildew 



Caused by Fseudoperonospora cubensis (B. and 

 C.) Rost. 



Symptoms. The disease appears on the leaves 



