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Thirty-second Annual Report 



hot water, seed treated with concentrated sulphuric acid and 

 then with mercuric chloride, seed treated with mercuric 

 chloride, and seed treated with formalin. The study should not 

 only afford information regarding the relation of alkali to 

 susceptibility of black arm and leaf spot in cotton, but also 

 facts bearing on the value of different disinfecting agents for 

 use in treating cotton seed. 



MISCELLANEOUS STUDIES 



LETTUCE ROT 



A bad outbreak of bacterial rot of lettuce occurred at Casa 

 Grande and Toltec early in the spring of 1921. The disease 

 usually affected first the outer leaves of the head, causing a 

 brown discoloration of the fibrovascular bundles, then of the 

 entire leaves, and eventually turned the head into a dark wet, 

 slimy mass. One entire field of 60 acres near Toltec was lost. 



Fig. 8. — Head of lettuce from the market, inoculated in the laboratory 

 with bacterial rot from diseased plants taken from field near Toltec. 



