DISEASES OF COTTON 



273 



cannot fail to be well distributed over its various parts. Since 

 the number of spots arising on the bolls is comparatively few in 

 the circumstances it is a matter of great interest to know what 

 determines the occurrence of an infection 



Edgerton reports that infections similar to those of natural 

 occurrence and situated mostly near the apex of the boll are 

 readily produced by dropping a bacterial suspension into the 

 open flower. He obtained 45 per cent, of infections appearing in 

 12-14 days in field trials of this method, the controls remaining 

 healthy. 



It is possible that many of the natural infections have their 

 origin in the flower, and it is suggested that transfer of the 

 bacteria by insects may play a part in the process. At what 

 stage the basal infections are produced is not clear ; they do not 

 appear to be correlated with infestations of angular leaf-spot 

 on the adjacent bracts. Nor is it evident whether the occasional 

 occurrence of spots with a fresh appearance on full-sized bolls 

 is due to late or to delayed infection. 



Influence of External Conditions. 



Like other subjects in connection with the disease, this re- 

 quires a good deal of further study ; losses are heavy and general 

 in wet seasons and are usually very small in dry weather. Under 

 certain conditions, however, which are not understood, severe 

 local damage may occur in what may be regarded as a normal 

 or good season. Thus in St. Vincent in November, 1917, a 

 single field on an estate had a general infestation of the bolls of 

 the first picking, and was giving 10 per cent, of stained lint due 

 to this disease, while adjacent fields differing only in being 

 planted a few weeks later were practically free. In early January, 

 igi8, in dry weather, a field of cotton in Barbados in the stage of 

 full secondary growth was seen heavily infested with bacterial 

 boll disease and black arm There was little or no angular 

 leaf-spot in the fohage present, which was all new. 



In such dry weather infestations the bacterium itself is more 

 directly responsible for the damage done than in wet weather, 

 when the occupation of the spots by secondary organisms is 

 the rule. 



Resistance and Control. 



It is uncertain at present what relations exist between the 

 prevalence of bacteriad boll disease and of angular leaf-spot. 

 From direct or indirect causes certain types of smooth-boiled 

 perennial cottons occurring in these islands are certainly much 

 more susceptible to the boU disease than Sea Island, an awkward 

 fact for those who claim an all-embracing immunity for the 

 so-called native cottons. 



Attempts to reduce the amount of the disease, whether by the 



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