RUBBER (HEVEA) DISEASES 57 
eter and were usually confined to the areas between the calluses. 
On the surface immediately beyond the tapping cuts, the scales were 
larger. By shaving off the exposed tissues, grayish yellow spots or 
reddish brown streaks were exposed. These discolored spots were 
of varying depth in the cortex and were rarely united to form a 
continuous brown line. This brown zone when present was next the 
cambium and was usually separated from it by a narrow laticiferous 
layer (PI. XXX, C). This layer was separable from the cortex 
along the brown line. In the worst cases examined the isolated dis- 
colored areas external to the brown line had become confluent in one 
plane, so that the cortex in radial sections gave a banded or zoned 
appearance. Later, these bands became fused, so that the entire cor- 
tex was uniformly torown. This occurred only in patches varying 
from half an inch to 3 inches in diameter and was especially marked 
in the cortex covering the callous nodules. By shaving off the surface 
dead cortex these reddish brown areas were exposed. In late stages 
the tissues of these areas become hard and brittle and separate from 
the rest of the cortex. They may be removed, exposing the white 
laticiferous layer beneath. The latter may be normal or not, ac- 
cording to thickness. A fact of interest was noted in that occa- 
sionally small elongated nodules had developed beneath these scales 
or at tne margin of the depression. These nodules had developed a 
new cortex and were entirely separated from the surrounding 
tissues (PI. XXX, B). 
The disease was not found on untapped trees and was by no means 
common on the tapped ones. Only on those that had been exces- 
sively mutilated could the disease be expected to occur. In one 
such case the disease was present from the ground level and for 3 
feet above the last tapping cut, a total distance of about 15 feet. 
In all cases the vigor of the trees appeared to be in nowise im- 
paired. The cambium in every tree examined appeared to be healthy. 
The failure of the cortex on some of the large callous nodules, leaving 
the wood exposed so that it had become hard and weathered, was 
apparently the only permanent form of injury aside from the general 
mutilations by the ax that the trees had suffered. 
Although the cause of brown-bast has not been discovered, it 
would appear from the investigations that have been made by Rands, 
Bobilioff, and others that it is a physiological degeneration of the 
tissues resulting from tapping and the extraction of the latex. 
From the fact that the disease is very widely spread in the East 
it is believed that it may become more pronounced in the American 
Tropics when the eastern tapping methods are employed. There 
is no reason to think that the tree has undergone any physiological 
change from being planted in the East that would make it more 
susceptible to the disease in that region. 
One very interesting and important fact must be considered in 
judging the presence of brown-bast in the Amazon Valley, viz, the 
great variation in the normal color of the tissues of the cortex. 
Several varieties of rubber trees based on the color of the bark are 
recognized. These are the black (preta), the white (branca), the 
red (vermilha), the barriguda (Ilevea spruceana), and the Itapuru 
(Hevea guyanensis). On the basis of resiliency the rubber of these 
several varieties is rated differently commercially. That from the 
