X. THE ANGULAR LEAF-SPOT OF COTTON 



Type. — This disease is a common leaf-spot, twig-blight and 

 boll-rot of cotton, comparable with the bean blight due to 

 Bacterium phaseoli (No. VIII), the walnut blight due to Bac- 

 terium juglandis, and in some ways also with the mulberry blight 

 due to Bacterium mori (No. XI). 



Following Atkinson, the leaf-disease is commonly known 

 as the angular leaf-spot. The stem-bhght is known as "black- 

 arm" or '' gummosis," and the capsule spot as "boll-rot." These, 

 however, are only different manifestations of one disease. 



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Fig. 238. — Cotton leaves from Monetta, South Carolina, showing Atkinson's 

 angular leaf spot, due to Bacterium malvacearum. Photographed in 1903. H 



The spots on the leaves were first described in 1891-92 by 

 Geo. F. Atkinson who examined them under the microscope and 

 detected bacteria in them. He isolated a micro-organism and 

 made inoculations, but these were unsuccessful. 



Stedman ascribed the boll-rot to his green-fluorescent 

 Bacillus gossypina, but on insufficient evidence. 



The writer was the first to reproduce the disease on leaves 

 and bolls of healthy cotton plants (1900-1905) with the true 

 parasite isolated from capsule-spots and leaf-spots. He was 



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