324 DISEASES OF CROP-PLANTS 



may be only slightly attacked, that from the first replanting 

 much more severely, and the second replanting may be so badly 

 affected that a whole field looks Hke a cultivation of lemon grass, 

 with here and there a cane stalk rising out of the low grass-like 

 clusters. Ratooned fields are almost invariably badly attacked. 



No parasitic organism has been shown to be connected with 

 the causation of the disease, and it is now usually regarded as 

 coming within the class of virus diseases. 



It will be seen from the foregoing description that the actual 

 symptoms of Sereh may be somewhat indefinite, and as a matter 

 of fact the appearances described by Went can all be found 

 exactly reproduced, including the reddening of the vascular 

 bundles in the nodes, in stools affected by froghopper in Trinidad, 

 and are more or less simulated by the results of other affections 

 elsewhere. In no such case, however, has there been developed 

 the progressive degeneration which is the essential character 

 of the disease. 



Control. 



The system by means of which the disease is avoided consists 

 in the use of cuttings raised in hill nurseries, which are not 

 subject to the disease. The canes from these are reproduced 

 in the plains for only two or three vegetative generations before 

 they are again replaced with plants from the hills. 



Mosaic Disease, Mottling Disease, Yellow Stripe Disease. 



History and Distribution. 



About 1916 the existence of a serious epidemic disease on 

 sugar-cane was noticed in the north-western quarter of Porto 

 Rico. The affection was described by J. A. Stevenson under the 

 name of mottling disease. Later it was found to be identical 

 with the " gele strepenziekte " (yellow stripe disease) of Java, 

 in which island it was described by J. H. Wakker in i8g6. 



The disease was known in Java in 1890, and circumstances 

 point to its having then been present for many years. It was 

 regarded there as due to recurrent bud variation. Elimination 

 methods, and its operation as a factor in selection have restricted 

 its prevalence. It occurs in Java on all types of soil and, with 

 greater or less severity, on all kinds of sugar-cane except the 

 wild species. 



When attention was first attracted to the disease in Porto 

 Rico, it was restricted to a single district, but it had then 

 assumed epidemic form, and its spread was so rapid that in 

 1919 more than three-fourths of the cane-growing area was 

 invaded. 



E. W. Brandes reports the finding of the disease in Cuba 



