50 



obtain any material to work on for all the afPected trees had been 

 subjected to treatment. In February again, through the kind 

 permission of the manager, I was able to visit another estate 

 200 miles away from the first where apparently a disease of a similar 

 nature had occurred. Sharpies, the Government Mycologist, was 

 visiting this estate and he isolated the fungus Phytophthora from 

 the diseased bark. Within a day or two I visited an estate which it 

 is my privilege to visit regularly and there found a considerable 

 number of trees with this same disease. I have now isolated the 

 fungus from material collected. From evidence collected it appears 

 that the fungus is not Phytophthora Faberi but another species of 

 the same genus. 



The disease is undoubtedly the same as that known as " bark 

 rot " in Ceylon, " black thread disease of Hevea " in Burma, and one 

 form of canker (vertical black line) in Java. Infection only takes 

 place on the most recently tapped surface and, therefoi'e, the fungus 

 appears to be a wound parasite. Essentially the disease is a decay 

 of the tapped surface. The most recently tapped bark immediately 

 above the tapping cut shows vertical black lines varying in 

 length up to one inch or more, and these on removal of the bark 

 are shown to continue into the wood. This " bark rot " may spread 

 and several " lines " of decay may coalesce to form small 

 blackened or sometimes greyish, roughly rectangular areas of dead 

 bark. Further, as the fungus develops several areas may coalesce, 

 producing a decayed area of bark just above the tapping cut and 

 right across the tapped area. Superficially the lines often appear 

 as slits or vertical depressions some little distance above the tapping 

 cut, but frequently, at an early stage, the lines may only be 

 discovered by removing the thin outer-layer. As Dastur has pointed 

 out the depressions may be due to the collapse of the cell walls of 

 the outer tissues. Rutgers in Java, Dastur in Burma, and Macrae in 

 India have proved that the decay of the tapped surface or " bark rot " 

 is due to an infection of Phytojjhthora. That a species of this 

 fungus is the actual cause of the decay is beyond all doubt since 

 these three independent workers obtained positive results by infection 

 experiments. That work has also been done in this country by 

 Messrs. Belgrave and Norris in the Agricultural Department. 



In Ceylon, Fetch has shown that there are four different diseases 

 caused by Phytophthora Faberi — namely, stem canker, " bark rot " of 

 the tapping surface, abnormal leaf fall and pod disease, but recent 

 evidence goes to show that more than one species of Phytophthora 

 is responsible for these diseases. 



Until January last I had not seen any sign of a disease caused 

 by Phytophthora on any of the estates I visit regularly but I am 

 inclined to think that the " bark rot " of the tapping surface is now 

 extremely common in the country. 



