RUBBER (HEVEA) DISEASES 29 
serious disease. They will be further mentioned in the mycological 
section near the end of this bulletin. 
The most common disease which appeared to be of consequence as 
a result of the deep wounding of the tree with the ax was usually 
observed on trees in wet situations. Here the cuts frequently had 
made little progress in healing the wounds by the production of the 
usual callus. The removal of the bark around the wound fre- 
quently exposed discolored areas either in the form of small or large 
black patches, becoming confluent with similar neighboring areas or 
dark strips or streaks extended vertically and parallel to one an- 
other on the disorganized surface above and below the cut. These 
black bands appeared eventually to coalesce laterally, forming the 
larger diseased areas. These lines extended to a considerable depth 
in the wood (PL XIV. A) and also involved the renewing bark al 
lower edge of the cut and that which formed beneath the edge of the 
old bark above. The cambium of the affected area i- destro 
well as the viable parts above. The lines in the wood extend for 
several inches downward and upward from the cut and appear to 
be caused by infiltration substances from the diseased cambia*l area. 
A microscopic examination failed to disclose mycelia of any nature. 
The color was more intense in the medullary-ray cells. These dark 
lines were also discovered in the wood of old wounds which had 
overcome the disease and were completely occluded. 
The nature of the cut tends to obscure the presence of the di-' o ase. 
The coagulated latex following the first flow also hides all traces 
of the disea-e in early stages and is undoubtedly an effective protec- 
tion against a rapid spread of the disease. The first sign of the 
disease which could in most cases be relied upon was the discolora- 
tion of the bark and wood at the margin of the coagulated latex. 
This was apparently followed by a secondary exudation of latex, 
which when coagulated was of a much darker color than that of the 
original flow. The greatest area of infection found extended about 
6 inches above the cut and 3 inches below. In most cases it was 
less. The lateral extension of the disease was always less than the 
vertical. So far as could be determined the infections in most cases 
had eventually been overcome by the renewing growth. This, how- 
ever, evidently resulted in a very abnormal healing. It was noted 
that in wounds showing evidences of the disease having been present 
the callus was abnormally large and was arranged in vertical ] i 
This apparently resulted from the formation of the callus at the si.les 
of the vertically elongated diseased areas. In cases where the dis- 
ease had continued without healing, the infection had apparently 
been followed by other wound fungi and insects, resulting in large 
open canker- < PL VII. B). 
With the mean- at hand no organism was found in the diseased 
ti.-sues. The general character of the disease is similar to that 
commonly called "black-thread" in the Orient. This disease has 
been reported in practically all the rubber-growing countries of the 
East, and is the cause of considerable damage to the renewing bark, 
resulting in a reduction of yield. The causal organism wherever 
demonstrated ha> been found to be a Phytophthora. The identity 
of the species has not been satisfactorily determined. In Ceylon 
it has been shown that two species of Phytophthora are found on 
