312 DISEASES OF CROP-PLANTS 



a yellowish gummy ooze collects in droplets on the ends of the 

 severed bundles. This material dries to a bright yellow stain. 

 The disease is primarily one of the vascular system, but in 

 advanced stages the parenchyma is attacked, especially just 

 below the terminal bud, and cavities are formed which are filled 

 with the yellow bacterial slime ; this may also ooze from the sto- 

 mata of the inner surface of the leaf-sheath. 



The external signs of the disease are various degrees of 

 dwarfing, striping of the leaves, dr5dng of tops, and decay of the 

 terminal bud (top-rot). 



Inoculations which demonstrated the causative connection 

 of B. vascularum with the disease have been described by E. F. 

 Smith. Wilbrink has recently investigated bacterial vascular 

 disease as it occurs in Java, where it is characterised by external 

 and internal symptoms similar to those of Cobb's disease, with 

 the important exception that no gum nor slime is produced by 

 it in the canes. The bacterium does not develop gum in pure 

 cultures, but resembles B. vascularum in other physiological 

 characters. 



Incidence. 



Condition of soil, other than lack of drainage, is said not to 

 influence the prevalence of the disease. Canes rich in sugar, 

 grown on good land, are subject to it. The evidence suggests 

 that infection in any way from stool to stool is not very active, 

 but that the extension of the disease mainly comes from the 

 planting of diseased sets. Both in Brazil and in Australia the 

 disease proved exceedingly destructive on susceptible varieties. 



Control. 



The means of control consist in the planting of resistant 

 varieties, some of which are nearly or quite immune, or, where 

 the cultivation of susceptible canes is continued, the careful 

 selection of healthy sets, rotation of crops, and provision for 

 good drainage. 



Smut. 



The Smut disease, due to Ustilago Sacchari, Rab., is common 

 in the East on the thin canes of the Indian type. C. K. Bancroft 

 reports its presence in British Guiana, stating that little damage 

 has been attributed to it. It is often quoted as occurring in 

 Trinidad, but the reference usually given, to 0. W. Barrett's 

 record that " a leaf rust, probably Ustilago sacchari, was very 

 common " is obviously worthless. No other record in the West 

 Indies is known to the writer. 



The disease is at once recognisable by the occurrence of a 

 long, curved, whip-like shoot, often several feet in length, at the 

 apex of the cane. This abnormal growth, which probably 



