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, however, 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 colgur 
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. Petch, in 1905, investigated 
a blackening of fruits of Hevea in Ceylon and attributed it to a 
Phytophthora sp., now known as P. Faberi, 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. Petch examined this fungus in 1906 and described it as 
a new species, Nectria diversispora, which he regarded as a saprophyte. 
Subsequently Petch described some inoculation experiments with 
spores of the Phytophthora, at wounds made on the trunk of Iievea, 
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 Petch „ 
concludes that the “canker” of the stem and the blackening of the 
fruits is due to Phytophthora Faberi, the same fungus which causes 
the “canker” and “pod disease” of cacao. 
*A§ri. Bull. Straits and F. M. S., Vol, V. p. 39“. 
