RUBBER (HEVEA) DISEASES 63 
persons familiar with the previous history of the trees, but the evi- 
dence of old wound tissue blackened by oxidation (wound rot), 
canker, or superficial molds can be observed in cross sections of 
felled trunks. The complete healing over of the wounds naturally 
depends upon their number. A few cuts here and there or a few 
rows properly spaced around the trunk would in time be covered 
over more rapidly with fewer callous warts than when the entire 
surface had been hacked up. The latter condition stimulates such 
surface abnormalities with subsequent changes in the uninjured 
wood that the tendency of the affected tissues to return to the normal 
is lost entirely, resulting in continuous hypertrophies. 
Whether the cuts are healed over and buried beneath new layers 
of wood or the abnormalities continue, the zone of dead blackened 
wood, almost continuous around the entire circumference, introduces 
an element of weakness in the mechanical strength of the trunk. 
This is due to the fact that the surface of the wound wood is not 
anatomically connected with the new wood formed over it. This in- 
troduces a line of friction, and the two sides may split or separate, 
causing the tree to be more easily broken under the stress of high 
winds. On old dead trunks these concentric zones of wood may be 
split out like troughs. 
In this connection it is interesting to note that Cross, in his report 
to the Indian Office in 1898, makes mention that in the region of Para 
he found large trees in a state of decay and that up to a height of 
10 or 20 feet from the ground the trunk was one swollen mass of 
warty protuberances and knots covered with thick scales and flakes 
of hard dry bark. He then describes the system of tapping and 
concludes that it is the injury done the wood and not overlapping 
which lessens the flow of the latex and ultimately causes the death 
of the tree. 
The earliest account of the collection of rubber and its effects on 
the tree appears to be that of Condamine in 1751. This author pre- 
sents a picture which may be considered to represent the response of 
the tree to excessive wounding. 
Pruning. — On some of the plantations visited and along roadways 
where Hevea was planted the trees in some cases had produced 
lateral branches low down on the stem, and these had been cut off. 
For the sake of improving the form of the trunk it may be found 
desirable to prune such living branches. It must be remembered, 
however, that the removal of large living branches is attended with 
considerable danger to the health of the tree. Not only is there a 
retardation of growth due to the loss of the assimilatory surface, 
but the making of wounds on the trunk may result in serious in- 
fections unless the operation is properly performed. 
The pruning of large lateral branches should be done by triple 
sawing. First, at some little distance from the trunk, saw one- 
third or one-half through the branch from the under side. A few 
inches beyond on the upper side, saw the branch until it splits to 
the first cut and falls. The weight of the branch now being re- 
moved, the stub may be cut off through the bulge at its base and 
flush or parallel with the trunk. This method prevents splitting and 
bruising the lower side of the wound, which often occurs when the 
branch is cut off from above at one operation. 
