DISEASES OF ROOT CROPS 335 



These plants continued in an active state of growth when normal 

 plants had ripened. 



The affection produces an attenuated condition of the 

 rhizomes, which develop long internodes and abundant roots. 

 The yield of starch is small and difficult to extract. 



Microscopic examination showed that the cells contained few 

 normal starch grains in the older parts, but many corroded 

 grains m all stages of disintegration. Preliminary studies sug- 

 gested that the active agent in this was a filamentous bacterium 

 which was found to be abundant in the slime deposited by the 

 mill water. 



Cassava. 



Cassava is very widely grown in the Lesser Antilles, but sel- 

 dom on a very large scale. It is grown for starch manufacture in 

 St. Vincent and is used to some extent as a rotation crop on sugar 

 estates in Barbados ; a few years ago attempts were made to 

 extend its cultivation in Trinidad. 



Apart from injuries due to insects and mites no disease of 

 serious importance has been met with on this plant. 



WiTHER-TlP. 



A wither-tip and dieback disease apparently due to a Gloeo- 

 sporium occurs occasionally in Barbados, on plants with reduced 

 vigour, and has been seen to follow on defoliation by caterpillars. 

 The fungus is probably Gloeosporium manihot Earle. known as 

 the cause of a similar disease in the United States and Porto 

 Rico. 



Leaf-Spots. 



A bacterial leaf disease occurs in Barbados in which a distinct 

 varmsh-like deposit of bacteria appears on the surface of the 

 angular leaf-spots produced. 



Two leaf-spot diseases unidentified are reported to be 

 prevalent m Trinidad. A leaf-spot due to Cercospora henninRsii, 

 All. is common in Porto Rico. 



1 -11^"?^^ appropriate circumstances cassava is liable to be 

 killed by Rosellinia root disease. 



Onion. 



Bacterial Soft-Rot. 

 Onions in the West Indies as in North America are liable under 

 certain cu-cumstances to a soft-rot of the bulb scales caused by 

 bacteria of the Bacillus cawtovorus t3'pe. Very heavy losses 

 were experienced on some estates in Barbados after a wet season in 

 1904, and m the islands where onions are now grown on a large 



