«276 DISEASES OF CROP-PLANTS 



1916 became acquainted with the fungus as the apparent cause 

 of a brown rot of bolls, to which his attention was called by S. C. 

 Harland at the St. Vincent Experiment Station. Some further 

 notes were made at the same place under the drier conditions 

 of 1917, when the affection was almost confined to one perennial 

 plant. Certain perennial types appear to be specially susceptible. 

 In 1919 more Sea Islands bolls than usual were seen to be affected. 

 These are so far the only records of Diplodia disease in the 

 Lesser Antilles. 



Nature of the Attack. 



The earliest external sign of attack as seen on the St. Vincent 

 bolls is a brown patch of discoloration of somewhat indefinite 

 form which rapidly extends over a great part or the whole of the 

 boll. The surface soon becomes dry and hard, and is roughened 

 by the appearance all over it of slight projections marking the 

 developing pycnidia. The contents are by this time fully in- 

 fested with the dark slaty-grey mycelium. The pycnidia dis- 

 charge at first whitish tendrils of hyaline one-celled spores, and 

 later the more mature black two-celled spores are produced in 

 such quantity as to cover the whole boll in a soot-like layer. 

 The boll is completely ruined. 



These notes agree with Edgerton's account of the disease in 

 Louisiana. 



Mode of Infection. 



According to Edgerton, the fungus gains entrance through an 

 insect puncture or other wound, and infests the contents of the 

 boll before it is able to attack the outer wall. The fungus is 

 found on dead stems and other parts of the cotton plant, but is 

 regarded as saprophytic in these situations. 



The most significant function of the fungus in these islands 

 is judged to be that of the infection and complete destruction of 

 bolls already attacked by other diseases. 



Control. 



The inability of the fungus to penetrate the uninjured epider- 

 mis suggests that measures taken to preserve the bolls from injury 

 offer the best means of protection against this disease. An 

 additional reason, if one were needed; is thus given for efforts 

 to keep down the numbers of bugs infesting the cotton 

 plant. 



Prevention of the damage resulting from its function as a 

 secondary parasite likewise depends on the control of other ex- 

 ternal boll diseases which cause the formation of spots on the boll 

 and thus give it access to the lint and seed. 



