86 DISEASES OF TROPICAL PLANTS CH . 



but Lyon has more recently proved it to be due to a 

 fungus which attacks the young shoots, "binding the 

 leaf-bases into a tight, unyielding, jacket about the 

 stem." The outer leaves become dry and the entire 

 shoot eventually dies. The dead leaf-sheaths are always 

 pinkish-brown, and the rind of the developing stalk a 

 deep bluish-gray. The fungus has two stages, the 

 perfect stage known as Gnomonia iliau, which is not 

 common, and the Melanconium stage which is very 

 abundant, especially in cool damp weather. The spores 

 of the perfect stage are carried by the wind and those 

 of the latter stage are probably carried by water. The 

 disease can be controlled to some extent by early 

 planting and by good cultivation. 



In addition to the preceding diseases which may be 

 considered the most important stem diseases of this 

 very important crop, we also find a number of diseases 

 which, although doing only a slight amount of damage, 

 may develop into serious pests at any time. They 

 are is follows : 



Cytospora sacchari, Butler, is a fungus causing 

 a stem disease which occurs in Bengal and Madras. It 

 is very similar to and very easily mistaken for the 

 Melanconium stage of Tricosphaeria sacchari. 



Black Rot (Sphaeronaema adiposum, Butler). 

 Occurs in Bengal and causes dusky red streaks in the 

 interior of the stems. 



Schizophyllum lobatum is a wound-parasite in Java. 

 S. commune, Fries, has been reported on stems of sugar- 

 cane in the West Indies. It is also said to be a parasite 

 on the mulberry tree. 



The Sooty Mould (Capnodium sp.). This is not a 

 disease but is mentioned in this connection because it 

 is frequently mistaken for one. It is a black fungus 

 growing superficially in the honey-dew which is exuded 

 by mealy bugs (Aleyrodes). It does not penetrate the 

 plant, but when abundant it does interfere with the 

 physiological function of the plant by shutting off the 

 light, although not so severe on the cane as on some 



