604 RUBBER 



At the present time in Ceylon the general course of 

 the disease is less serious than in the cases just referred 

 to. In the great majority of cases the fungus does not 

 penetrate completely through the cortex, but stops after 

 advancing partly through, and the diseased tissue is then 

 cut off from the surrounding healthy cortex by a layer 

 of cork cells. The patch of diseased tissue dries up, and 

 forms a scale which can be easily detached. Underlying 

 this scale one finds healthy laticiferous cortex. The 

 scales are frequently lenticular, and if the fungus has 

 penetrated to the wood in the middle of the patch, they 

 leave a hole extending to the wood when they are 

 removed. 



This difference in the course of the disease is probably 

 to be attributed only to climatic conditions. There does 

 not appear to be any other reason why the disease should 

 cease to be active. In a very wet season the more serious 

 form of the disease would probably be the most common. 



Formerly it was advised that all cankered cortex should 

 be cut out. Owing to the damage caused by that treat- 

 ment on the exploitable part of the tree (canker most 

 often occurs within 4 ft. of the ground), it has now been 

 modified in imitation of what so frequently occurs 

 naturally. The diseased part is scraped or cut away so 

 as to remove most of the cankered bark, the cutting 

 being continued until latex begins to appear in minute 

 drops. This is a sign that the limit of the diseased part 

 is being reached, as the cankered cortex does not yield 

 latex. The remainder of the diseased cortex is then left 

 to dry up and scale out. Of course, if the disease has 

 penetrated to the wood the whole of the cankered cortex 

 is cut out. 



Old scales of canker, where the disease has not been 

 discovered prior to the scaling out, should be removed. 

 Canker often begins anew behind these scales. 



Spraying with Bordeaux mixture has been advised as 

 a preventive of canker, but hitherto the disease has not 

 been thought sufficiently serious to warrant its adoption. 

 Unfortunately, as is well known, the presence of copper 

 or copper salts in rubber tends to produce tackiness, and 

 it would therefore appear that Bordeaux mixture cannot 



