Li eee ee EG a 
420 
have an opportunity to develop horizontally as well as vertically, the 
buttresses are correspondingly large. This horizontal growth is especially 
marked in the Bambusia-Parkia formation, where the dicotyledinous 
trees overtop the bamboo. Here Parkia itself shows strong buttresses. 
In the formation higher up the mountain the buttress habit is present, 
but not so prevalent; it disappears altogether on the exposed ridges of 
the mountain. 
It will be seen that the same causes which operate to produce short, 
thick boles in open places in temperate regions are possibly also present 
here, with the difference that the buttresses, which take the place and 
perform the function of the uniformly thick trunks, appear later in the 
life of the tree. This means that the tree in youth, while it is 
crowded in the forest, develops a regular bole, but that when it reaches 
above the surrounding vegetation, in response to the increasing heaviness 
of the top, the buttresses appear at the base, enabling the tree to withstand 
the extra strain. It is possible that this of itself is the stimulus causing 
the development. It is known that the presence of heavy limbs often 
produces extra growth in the trunk at a point just beneath the insertion 
of the branches, and the fluted appearance so commonly observed in such 
cases is the result. The cause for this growth is ascribed to the stimulus 
due to the extra strain, although why such a stimulus should produce this 
result is not known. A transference of the strain to the base of the trunk 
would likewise cause prolific growth at the point or points where its in- 
fluence is felt the strongest; this point would be at the attachment of the 
roots, and especially of the larger ones, and thus would cause the develop- 
ment of board roots or plank buttresses. So long as the tree top is pro- 
tected on all sides by others, the strain will not be very great for two 
reasons, i. e., the top will not have a chance to broaden out and it will not 
be exposed to strong winds, but so soon as it emerges above the tops of 
other trees, the exposure and the increasing heaviness above will produce 
a strain sufficiently great to cause a stimulus of growth at the base and 
thus produce the buttresses. However, whatever may be the cause, there 
is no doubt that the abundance and size of buttresses in many instances is 
associated with the dominance of certain trees over others, and thus the 
irregular profile of the forest results. This is strongly emphasized by 
the fact that in places where the trees reach a more uniform diameter 
and height and where they are set sufficiently close to produce a class 
with an intermediate crown, or, to express it in another way, to form 
a regular profile, the buttress habit is not so pronounced. Such is the 
case in places in the Anisoptera-Strombosia formation and it is more 
prevalent in the Dipterocarpus-Shorea one which is to be discussed below. 
Trunks.—The shape of the bole of the tree is of the greatest impor- 
tance to the forester. Other things being equal, the more nearly the 
bole reaches a true cylinder throughout its entire length, the more 
lumber will it produce. In other words, the more nearly the form factor 
