207 
Forest Reserve ” (Phil, Journ, of Sci. I. p. 419) treats the subject 
more in detail and states that his observations lead him to 
conclude that buttresses are only developed by trees reaching 
a dominant position, and thereby enabled to develop wide 
crowns, and that the extent to which the buttress is developed 
is in proportion to the spread of the crown. 
The majority of trees able to assume dominant positions in 
the tropical Rain Forests always appear to develop buttresses ; 
and trees that do not attain to such positions do not exhibit 
any tendency to do so. Whilst normally trees that develop 
buttresses have no tap roots, information supplied by Dr. F. 
Foxworthy from his work on Dracontomelon dao in the Philippines 
provides an instance of trees developing buttresses in addition 
to a marked taproot. As it is usual for the same species and 
genera to attain dominant positions in the forest, and as the 
size of the buttresses varies considerably for the same species 
of tree in different or the same locality, observations were made 
to see if there was any factor in connection with the buttresses 
that was more or less constant. 
It was found that the presence, absence or the style of the 
buttress enabled the trees to be considered under four headings. 
the first are grouped those cases of stilt roots or hollow 
buttresses, where a growth arises some distance above the 
ground and curves downwards, when it may remain more or 
less cylindrical (as in the Mangrove and Ficus spp.) or a thickening 
may occur in the upper angle of the root and stem (Musanga 
Smithii P. Beauv.) or this thickening may extend downwards 
so as to form a more or less complete plank buttress (Tarrietia 
utilis Sprague). 
A second group comprises those cases where the buttress is 
a thickening in the angle formed by the stem and the main roots 
arising at the collar and spreading laterally along the surface 
of the ground. Here the buttress is solid and plank-like, as in 
the majority of the big forest trees. we 
In a third group no distinct buttress is formed but the bottom 
part of the stem is grooved or fluted, the folds passing at the 
base into the main lateral roots. ee 
The four thgroup includes a very few trees of dominant position 
where the bole is cylindrical to the ground (Mimusops). 
A further consideration of the specimens that are included in 
the third group, namely those that exhibit solid, plank buttresses, 
revealed another point in that the shape of the buttress is constant 
for the species or genus, regardless of its size. 
If the buttress be considered to be a right angled triangle 
with the right angle at the base of the tree, it will be seen that the 
side of the triangle representing the height to which the buttress 
reaches on the tree, bears a definite relation to the base of the 
triangle, or the length the base of the buttress stretches along 
the root from the tree. The hypotenuse of the triangle, that 
is the outside edge of the buttress is straight, concave or convex, 
