278 DISEASES OF CROP-PLANTS 



Course of the Disease. 



The seeds are liable to be infected in the boll without necessarily 

 impairing their power of germination, and when they are subse- 

 quently planted the fungus develops and produces spots or 

 marginal injury upon the cotyledons. The conidia are also 

 carried on the surface of the seed. A certain amount of damping- 

 off, and of spotting on young stems are also produced. 



The fungus continues its existence in dead spots on the 

 leaves and stems of mature plants, but does not spread to any 

 marked extent in the living tissues apart from the bolls. 



Carried over as above described the fungus only assumes 

 prominence when the bolls are formed. The first infections on 

 these produce enormous numbers of conidia, which are released 

 when wetted, and the combined effects of rain and wind, probably 

 supplemented by insect carriage, serve for their distribution, 

 and enable them to give rise in suitable weather to epidemics 

 of the disease. 



The Fungus. 



The manner of production of the conidia is that typical of the 

 anthracnoses (p. 22). The conidia are hyaline, one-celled, 

 cylindrical, generally straight but sometimes slightly curved, 

 with rounded ends, and usually slightly narrower towards the 

 middle. They measiire about 3.5-7 X 12-25 microns. The 

 measurements of the variety Barbadense are given by Lewton 

 Brain as 4-5 x 11-14 micr. 



The ascogenous (Glomerella) stage has beaked perithecia, 

 dark brown to black in colour, subglobose to p3'riform, 80-120 



X 100-160 microns, usually buried in the host tissue with only the 

 beaks protruding ; ascospores nearly elliptical, hyaline, 12-20 



X5-8 micr. ; paraphyses abundant. 



Control. 



As pointed out above, the amount of injury effected by 

 anthracnose in these islands, alone and in association with 

 bacterial boll disease, requires to be determined, Should the 

 need for control arise the most promising measures are selection 

 for resistance and the use of clean seed. In view of internal 

 infections the latter can only be secured by picking from uninjured 

 bolls. It is desirable on general grounds that all cotton seed for 

 planting should be externally disinfected. 



Curly Leaf, Chibble Leaf. 



Under certain conditions which appear to be closely con- 

 nected with the prevailing weather Sea Island cotton during its 

 vegetative period may take on an abnormal form of growth to 

 which the names above have been applied. It most frequently 



