300 DISEASES OF CROP-PLANTS 



themselves with undiminished intensity. In some remote dis- 

 tricts in Trinidad, and to a more considerable but rapidly dim- 

 inishing extent in British Guiana, the cultivation of the Bomrbon 

 is still continued. 



The statements of some writers that the breakdown of the 

 Bourbon was mainly due to root disease is not supported by the 

 evidence. Accounts agree that the crops grew well until they 

 were about 6 months old, and often for 9 or 10 months, and that 

 the attack then became general, while good soil, heavy manuring, 

 and efficient cultivation did nothing to reduce its severity. 

 This type of incidence is entirely different from that of root 

 disease. In the trials of Bourbon made from time to time by 

 planters, and in the plots maintained by experiment stations, 

 the failure is usually demonstrably due to Collet otrichum. 



At the same time the Bourbon cane is very susceptible to 

 root disease under adverse conditions, and no doubt the losses 

 occasioned in this way were indiscriminately set down to the 

 account of " rind disease." 



The question that remains most interesting is that of the 

 origin of the epidemic. Three explanations worth considering 

 have been offered : — 



(i) That a fungus previously occurring as a saprophyte 

 had evolved a strongly parasitic strain. 



(2) That the Bourbon cane, from long vegetative re- 

 production in the same soils, had degenerated and become 

 susceptible to parasites previously unable to attack it. 



(3) That a parasite previously absent had been introduced 

 from another region. 



A fourth idea held by some of the older school of planters, 

 that the disease resulted from the use of chemical manures, 

 was negatived by its prevalence in districts where these had not 

 been adopted. 



The first theory was mainly based on the belief that the disease 

 was due to Melanconium, which fungus was remembered to have 

 been noticed for many years. There is no evidence to show how 

 long the inconspicuous Colletotrichum had been present in the 

 West Indies, but it was described as a parasite with its present 

 characters in Java in 1893, and its distribution suggests that it 

 is indigenous to the Eastern Tropics. 



The theory most generally adopted was that of the breakdown 

 of the " constitution " of the Bourbon cane. It is in several 

 respects unconvincing. There was no progressive degeneration ; 

 the transition was a sudden one from a condition apparently as 

 good as had prevailed in the previous hundred years to a sudden 

 and almost complete failure. What seems at first sight conclusive 

 is that some other varieties are recorded as having shown little 

 or no more resistance. It is too much to assume that degeneration 



