THE ANGULAR LEAF-SPOT OF COTTON: VARIABILITY 



337 



than others? Is it worse on lowlands than on uplands? Is it 

 modified in any way by methods of culture? Are fungi as- 

 sociated with it? Try mixed infections. Study the effect of 

 the disease on seedlings in the hothouse and in the field. 



Transmission. — This disease is probably transmitted on the 

 seed, but we have as yet no experimental proof of this. Can 

 you help to clear up the situation? Once established in the 

 field, is it ever spread except by the wind during rain storms? 



Fig. 259. — A. Bacterium malvacearum, Col. 4 (Arizona isolation), after 43 

 days in milk at 25°C. Casein precipitated by a lab ferment. B. Check tube. 

 Milk dried out about one-fourth. 



Read Faulwetter's paper and look tor wind-driven paths of 

 infection. Kellerman reports similar paths ot citrus canker. 



Does the disease occur on weeds, or on any other cultivated 

 plants? Try inoculations on okra, abutilon and hollyhock by 

 spraying. 



