hrasiliensis and its Protective Function. 
249 
scraped. The control trees in Block 1 C and the remaining untreated trees 
in the surrounding area were unaffected. The unscraped areas of the 
treated trees showed no sign of beetle attack. 
The trees were affected in two different ways : One tree in Block 1 A, 
one in Block 1 B, and one in Block 2 A, suffered from a direct attack from 
boring beetles. The bark of the remaining two trees affected in Block 2 A 
were attacked by a fungus, which progressed rapidly in one case, killing the 
bark over a large area, but in the other only small areas of bark were 
attacked, and this tree now showed signs of recovery. The tree with cracks 
in the bark and latex exuding in Block 2 B was not affected further. A 
striking feature was the rapidity of the attack, borers being active on the 
first affected tree within four days. 
The results show that removal of the outer corky layers increases the 
susceptibility of the trees to attack by fungi and insects. They show also 
that if the green cork-cambium is left intact the susceptibility to attack 
is less than it is when this layer is scraped away. This experiment 
indicates that the corky integument is the important protective layer against 
insect and fungus attacks and not the laticiferous layer. The activity of 
the borers on the trees in Block 1 A and 2 A, within a week of scraping the 
bark caused exudation of the latex in streams down the scraped areas. 
Dozens of beetles were caught in the streaming latex, but this did not prevent 
others getting through the bark into the wood. It may be emphasized 
here, that the experimental plot is clear of timber, is fairly widely planted, 
24 ft. by 12 ft., and more or less isolated from the rest of the plantations, so 
that conditions are not favourable for the insects. The rapid nature of the 
attack prevents the assumption of a fungus preceding and killing the tissue 
in advance of the borers. 
The results obtained confirm field observations. The years 1915-16 
have been noteworthy for a very heavy wintering of the trees on the planta¬ 
tions during the months January, February, and March. The wintering 
period in both cases coincided with a spell of dry weather and numerous 
cases of leaf fires occurred, the thick carpet of leaves on the ground burning 
furiously. The trunks of the trees in the area through which the fires 
passed were scorched up to a height of ten feet, and borers were quickly at 
work on the scorched portions of the trees. In every case a copious exuda¬ 
tion of latex was noticeable from the bore-holes, but this did not prevent the 
entry of the insects. One estate was visited four days after the fires had been 
put out, and the boring beetles were actively working on half a dozen trees 
not badly scorched and from which there was a good flow of latex beneath 
the scorched areas. The laticiferous system was obviously healthy at the time 
of the attack, but the flowing latex did not prevent the insects penetrating 
into the wood. If the outer corky, protective layers of Hevea br 'asiliensis are 
removed or injured the tree is liable to a direct attack from boring beetles. 
