302 DISEASES OF CROP-PLANTS 



Symptoms. 



On the Bourbon cane the effects of the disease usually became 

 apparent during the last quarter of the year and increased, 

 often with startling rapidity, until the fields were reaped. The 

 mature leaves began to wither from the tip and edges inwards. 

 Some time later a brown patch appeared on one or more joints, 

 became wrinkled and sunken, and soon showed signs of secondary 

 infestation with Melanconimn Sacchari. At reaping time a 

 large proportion of the canes were dry and rotten, and others were 

 badly deteriorated. 



The symptom accepted as most typical of the disease is the 

 appearance, when a cane is split open, of a broad, irregular, 

 more or less central stripe of uneven red discoloration, broken 

 here and there by whitish patches. It is necessary to examine 

 stalks not far advanced in the disease to avoid the interference 

 of the more general discoloration produced by Melanconium. 

 The writer has seen an appearance very similar to that above 

 described produced in the lower joints apparently by Marasmius, 

 and certain diagnosis is only to be obtained from the recognition 

 of the fungus. 



The Fungus. 



The acervuli of Colletotrichum falcatum — tufts of black 

 bristles with the colourless conidia heaped about their base — 

 are produced in velvety patches on the surface of canes well 

 advanced with the disease, especially about the nodes, and on 

 dead or dying leaves or leaf-sheaths. The fruiting of the fungus 

 in the field is by no means abundant, and usually is decidedly 

 obscure, in striking contrast with the behaviour of Melanconium. 

 If a freshly diseased cane is split open and prevented from 

 drying out too rapidly or becoming mouldy from too much 

 moisture, the fructifications sometimes appear with great free- 

 dom on the cut surface. 



The conidia are hyaline, unicellular, more or less sickle- 

 shaped, with bluntly pointed ends, and measure about 25 x 4-5 

 microns. 



Injection. 



In the West Indies infection has been regarded as mainly 

 proceeding from borer holes and other wounds in the stem. 

 The studies of E. J. Butler in India have shown that while this 

 means, and the infection of exposed roots or root " eyes," prob- 

 ably account for the initial entry of the fungus, the infection of 

 standing canes is too small in amount to give rise to heavy 

 infestations. These, it has been shown, occur from the use of 

 infested canes as planting material, in which case the whole 

 stool, and not individual stalks, becomes infested. 



