DISEASES OF SUGAR CANE 311 



marked off from the healthy outer tissue by a red line. The 

 young leaves are soft and reddened near their base and withered 

 towards their tips. In some cases the uppermost leaves are 

 distorted and fail to grow out properly. The result of this failure 

 of the top is that while further direct growth is stopped the eyes 

 are stimulated into growth and produce useless side shoots. 

 The decayed portion affords an easy means of access to stem- 

 rotting fungi. 



Bacteria are found in the degenerating tissues and some 

 gumming usually takes place. It has been fairly satisfactorily 

 established that the Australian disease is due to Bacterium 

 vascularum, and it is separately described on another page. 

 J. H. Wakker found in Java several kinds of bacteria present, 

 and that the condition is associated with abundant rain and high 

 atmospheric humidity. Wakker' s view is that some disorganiza- 

 tion is first produced by too rapid growth, which then renders 

 the tops susceptible to bacterial infection. 



In Porto Rico the condition described as top-rot usually 

 occurs in over-ripe cane, but it is observed that some varieties 

 rot back after maturity much more quickly than others. This 

 type of rot occurs particularly in dry weather. 



In the froghopper blight of Trinidad the cessation of growth 

 at the tip of immature shoots, brought about by excessive injuries 

 to the leaves, is followed by reddening of the region about the 

 growing point and watery degeneration and death of the soft 

 upper joints enclosed in the bud. This, and similar injury 

 arising from root disease or borers, has been called top-rot. 



Top-rot in general is obviously no more than a term for the 

 soft-rotting of the enclosed termination of the stem, and like the 

 similar bud-rot of the coconut palm includes conditions in 

 which similar symptoms arise from very different causes. 



Gumming Disease, Cobb's Disease. 



The disease of sugar-cane caused by Bacterium vascularum 

 (Cobb) E. F. S. has been recorded in the West Indies only from 

 Porto Rico (1920), and such accounts of top-rot as have appeared 

 do not suggest that it has so far occurred in the British islands. 



The disease was first adequately described by N. A. Cobb 

 in Australia, where it occurs in New South Wales and Queensland. 

 An affection with identical symptoms has been reported from 

 Brazil. It is also recorded from the Fiji Islands, Mauritius, 

 Java, Borneo and New Guinea, and is suspected to occur in the 

 Argentine. 



Symptoms. 



The specific symptom of the disease is the appearance in the 

 vascular bundles of a yellow slime and a red stain. When 

 infested stalks are cut across so as to leave a smooth surface. 



