DISEASES OF BANANA 255 



or any wound expose them to infection, and where the disease 

 is prevalent a protective coating of Bordeaux mixture should 

 be applied as soon as possible after the severance is made. 



Otlier forms of blackhead disease are caused by the invasion 

 of the rootstock by Diplodia or b}^ a species of Pythium, in 

 association with a rot of the deeper roots in undrained or imper- 

 fectly drained heavy soUs, but apparently the most frequent form 

 of ail the blackheads is caused by the nematode, Tylenchus 

 similis, Cobb. (See Eelworm Black-rot.) 



Heart Leaf Disease. 



An affection occurs in Jamaica in which one or more of the 

 younger leaves are pale or yellow, and the youngest or heart leaf, 

 often almost white in hue, may be pushed up while still folded, 

 and fail to expand before beginning to wilt, turn brown in patches, 

 and rot. The condition of chlorosis may endure for a time, but 

 is frequently followed by a rapid fall of all the leaves at their 

 junction with the trunk, and a speedy brown rot of the latter 

 moving downwards from the top. 



The cause of the disease is uncertain. It is considered that 

 the condition of chlorosis may be induced by the depletion in the 

 sandy soil of one or more essential mineral elements through 

 washing with heavy and frequent rains, and that the rapid sappy 

 growth which ensues permits the rotting of the tissues by feeble 

 parasites. 



