204 



Cessation of the flow of latex is, however, by no means always a 

 sign of "canker". Trees may cease to give latex through over- 

 tapping or during periods of drought ; but it is not uncommon to find 

 trees, here and there, which have stopped yielding from other causes, 

 the nature of which it is not easy to determine. Sometimes these 

 trees are poor in foliage and are unhealthy in appearance, but in 

 many cases the cause of the cessation of the flow of latex is obscure. 

 Such trees commence to yield again after some months or even, 

 perhaps, a year. It is, hov/ever, desirable that tapping coolies should 

 be made to report at once such trees as cease to yield, in order that 

 an examination may be made for the purpose of determining whether 

 the effect is pathological. 



The presence of a black border or rim to the diseased tissues, as 

 mentioned above, requires some consideration. The normal colour 

 of the outer tissues of the older bark of Hevea is either white, yellowish 

 or light or deep red. In barks which possess a light colour it is not 

 uncommon to find a dark brown layer just external to the latex layer; 

 this layer may be 1/15 of an inch in width. The presence of this 

 layer has been repeatedly put forward as a symptom of " canker " by 

 some who have read or heard of the disease. An examination has, 

 however, shown that the cells composing this layer are in a normal 

 condition of health and that the colour is due to the presence of 

 brown colouring matter in the cell-walls. 



It has been mentioned above that the disease has not yet been 

 recorded in this country. Ridley has, however, reported a blackening 

 and decay of fruits of Hevea in the Federated Malay States'^ which 

 he attributed to a species of Phytophthora. Fetch, in 1905, investigated 

 a blackening of fruits of Hevea in Ceylon and attributed it to a 

 Phytophthora sp., now known as P. Faheri, Maubl., a fungus which is 

 regarded in the light of recent work by Rorert as the cause of the 

 "canker," and "pod disease" of cacao. The blackening and decay 

 of Hevea fruits was previously recorded by Carruthers in Ceylon in 

 1903-4 and was attributed to a new species of Nectria, with the spores 

 of which Carruthers claims to have reproduced the "canker" disease 

 of the stem. Fetch examined this fungus in 1906 and described it as 

 a new species, Nectria diversispora, which he regarded as a saprophyte. 

 Subsequently Fetch described some inoculation experiments with 

 spores of the Phytophthora, at wounds made on the trunk of Hevea, 

 both by excising a small piece of bark down to the laticiferous tissue 

 without drawing latex and by a slanting cut which did not extend so 

 deep as to cause a flow of latex. Distinct infection was observed after 

 24 days in three out of five of the first series ; but none of the second 

 series showed any signs of infection. The spread of the disease was 

 said to be much slower than on cacao. From these results Fetch 

 concludes that the "canker" of the stem and the blackening of the 

 fruits is due to Phytophthora FaberU the same fungus which causes 

 the " canker " and " pod disease " of cacao. 



* Agri. Bull. Straits and F. M. S., Vol. V. p. 39". 



