264 DISEASES OF CROP-PLANTS 



Their absence from Barbados, and the comparative scarcity of the 

 green bug, make the disease of very Httle account in that island. 

 The fungoid form of the disease has not so far been reported from 

 other territories. 



Symptoms. 



There are no external symptoms on the infected bolls, save 

 in some cases a hardening perceptible to pressure ; the appear- 

 ance is that of a sound boll even when the contents are com- 

 pletely ruined. The shedding of young bolls is frequently due to 

 infection, but may also be induced by bug punctures alone, and 

 frequently occurs as a reaction of the plant to certain physical 

 conditions. Shedding from bug injury or infection extends to 

 bolls up to three weeks old and 20 mm. in diameter, whereas the 

 limits in natural shedding have been found to be about 8 or 9 

 days and a diameter of about 14 mm. 



In describing the symptoms displayed when green bolls are 

 cut open it is necessary to discriminate between the direct effects 

 of bug punctures (stigmonose) and of added infection (stigma- 

 tomycosis). Damage of the former nature is very heavy when 

 the bugs are present in large numbers and has been found in a 

 particular case spoiling 60 per cent, of the locks in a representa- 

 tive sample of bolls. Some or all of the seeds in a lock may be 

 killed outright or the embryo arrested in its development, the 

 immature lint soaking down into a discoloured film. In severe 

 cases the boll, if not more than half-grown, is usually shed. In 

 older bolls a large proportion of the uninfected punctures do not 

 reach the seed, and either have no recognisable effects, or the 

 effect is limited to a superficial patch of discoloration on the 

 lint beneath the puncture. The common pea chink {Edessa 

 medittabunda), which has relatively short mouth-parts, appears 

 to be limited on bolls of any age to the production of the latter 

 type of injury. Very little staining of the lint which reaches the 

 pickers' hands is attributable to direct bug injury. Much of the 

 loss from this cause goes disguised as shedding, and for the rest 

 the contents of heavily damaged locks when dry shrivel into a 

 hard mass which the pickers leave. When only part of the seeds 

 in a lock are attacked the remainder bear good unstained lint. 



The result of infection accompanying the punctures is greatly 

 to increase the amount and widen the range of damage. For a 

 lock to be destroyed by direct injury many punctures are re- 

 quired, for the same result from infection one early puncture 

 may suffice, since the fungus can spread from the lint of one seed 

 to that of all the rest. The effects vary with the age of the boU 

 attacked. Among young boUs a great deal of shedding results, 

 similar to that caused by direct injury. In bolls that reach 

 maturity the locks infected young are usually quite ruined. The 

 seeds are reduced to a pasty mass, with a black and yellow cover- 

 ing of rotting lint. Infections made later each produce a patch of 



