250 
Sharpies .— The Laticiferous System of Hevea 
Heavy scraping of the bark, i. e. removal of the cork-cambium, exposes 
the outer old cortical cells. It is possible that in such tissues a cork- 
cambial layer does not form very readily, so that the outer cortical cells are 
exposed to the atmosphere for a comparatively long period. If this 
coincides with a period of wet weather, the exposed cells become water¬ 
logged and their activities interfered with. As a result, numerous ordinarily 
saprophytic fungi flourish on the exterior and grow inwards gradually, 
rotting the bark from the outside. Undoubtedly this is the method of 
attack in cases where there is not a direct attack by borers. The same 
applies to trees scraped so as to leave the cork-forming cambium intact. 
Such trees are not so readily attacked, due to the active cork-cambium 
quickly cutting off cork cells to the outside, forming a new protective layer. 
This rapid formation of cork prevents water-logging of the cells, and the 
danger of attack is considerably lessened thereby. But if the cork-cambium 
cells by any chance become water-logged, their activities are interfered with, 
and in such a case the bark is as liable to attack as that of the heavily 
scraped trees. 
During tapping operations the inner cortical tissues are opened up. In 
this connexion, the danger of bark affections similar to those observed in the 
experiment is slight. There is a considerable difference between exposing 
outer cortical tissues by scraping, and inner cortical tissues by paring, as in 
tapping. When tapping, the tissues down to the wood and bast-forming 
cambium are removed. Thus only very narrow strips of actively dividing 
cells are exposed at any one time. The coagulated latex along the tapping 
cuts protects these exposed strips to some extent, while the actively dividing 
cambium quickly cuts off layers of cells, one of which takes on the functions 
of a cork-forming cambium and the protective layer is soon replaced. 
The selective nature of the borer attack was a noticeable feature. On 
Block i A, two days after scraping, signs of borers could be observed on 
every tree. Later the insects appeared to concentrate in a vigorous attack 
upon one tree. Such selection is difficult to explain, but is probably asso¬ 
ciated with the fact that plantation conditions are fundamentally unhealthy. 
Our conception of a healthy tree is limited by a spreading crown of leaves 
and roots apparently unattacked by disease. This gives no indication of 
one tree being more susceptible to disease than another, yet such is the case. 
Under forest conditions the struggle for existence operates in a drastic 
manner, and susceptible individuals seldom enter the competition. Planta¬ 
tion conditions considerably modify the struggle, and there must be large 
numbers of apparently healthy trees surviving which under natural condi¬ 
tions could never reach maturity. 
Fickendy, in this application for patent rights, says that ‘ the bark 
should be scraped down to the cork-forming cambium ; leaving the latter 
intact \ The experimental results show that the trees carefully treated as 
