DISEASES OF SUGAR CANE 325 



in 1919 at three separate points, at one of which it was beUeved 

 to have been present for nearlj^ twenty years. In 1918 the disease 

 was found at many places in Santo Domingo, and it has been 

 discovered in St. Croix on plants from Porto Rico. 



A survey of the cane-growing districts of the United States, 

 made in consequence of the discovery of the disease on planting 

 material received in Porto Rico from Louisiana, has revealed 

 its wide distribution in Louisiana and Florida, and its occurrence 

 in the adjoining States. The river district of Louisiana was in 

 1919 already badly infested, the proportion of diseased plants 

 reaching 75 per cent, on some plantations. 



At the St. Augustine Experiment Station in Trinidad the 

 existence of a peculiar and abundant marking of the leaves on 

 the plot of D 3956 was noted by C. B. WiUiams in 1918 and 1919. 

 The adjacent plots appeared at this time to be practically free. 

 Early in 1920 the condition was recognised to be mosaic disease, 

 and a survey showed that it was then more or less present not 

 only throughout the Station but in the adjoining district for 

 several miles east and west, while many new centres of infection 

 had arisen on estates to which cuttings of selected varieties had 

 been sent. 



Early in 1920 the disease was found to be widely prevalent 

 in Jamaica in its typical form. It is now common in Barbados. 



In the Argentine Republic the disease is reported by G. L. 

 Fawcett to have been present for many years. It is common on 

 the Java canes there grown, which exhibit the S3anptoms to 

 varying degrees, but are not prevented from giving satisfactory 

 yields. Canes of the White Transparent type are uniformly 

 affected and have suffered deterioration, which is not, however, 

 attributed to the effects of mosaic disease. The Barbados and 

 Demerara seedlings are worst affected, except D 1135, which 

 is the only one suited to local conditions. 



Symptoms. 



The one marked and constant primary symptom of the disease 

 is the peculiar mottling of the leaves. 



This is difficult to describe, but is seldom difficult to recognize 

 after being once learned. Its commonest form is a general 

 longitudinal streakiness of the green colour, caused by the paling 

 of many small and ill-defined areas. It is hardly definite enough 

 to be called spotting, and a form of whitish or yellow spotting 

 is the appearance most frequently mistaken for it. It is often 

 best seen by transmitted light, and may be quite conspicuous 

 in the upper leaves as seen against the sky. In different cane 

 varieties and under various conditions the amount of the normal 

 green colour retained differs widely, in extreme cases being 

 present itself as patches on a lighter background. On certain 

 varieties in Trinidad the affected leaves as they grow old con- 



