658 
narrow ones of less xerophytie structure. Only in Plot D does the 
distribution of these species overlap. Other trees with very xerophytic 
leaves, found in the upper plots and not represented in the lower ones, 
are Vaccinium jagori, V. cumingianum, Leptospermum amboinense, and 
Clethra lancifolia, all low, scraggy trees with leaves very suggestive of 
those of the heath family to which two of them belong. Indeed, ecolog- 
ically the forest of the ridge very much resembles the heath associations 
so common in dry, sandy soils or exposed windy places of the north 
temperate zone, except that here the plants are trees rather than shrubs. 
There is a striking difference in the relative humidity of the two 
situations. (See Table XXI.) Many visits to Plot A, when the weather 
was clear at this locality, showed Plot H to be bathed in dense fog. 
Often, an early morning journey from Station 3 to the top of the 
mountain demonstrated Plots A and D to be dry while above Plot D 
the vegetation would gradually become more and more wet, until near 
Plot H it would be reeking with moisture. While this relative humidity 
in itself tends to reduce the transpiration of the foliage of the trees and 
to conserve the moisture of the soil, so as to render more water available 
for absorption and thus to produce a less xerophytie condition, yet it 
is seen that the tree vegetation is more, rather than less, xerophytic. If, 
then, soil, moisture, and atmospheric humidity can not explain the 
ecological difference in the habitat for arboreal vegetation of the two 
places, then it must be due to the greater influence of the wind in the 
two situations. As one ascends the mountain, this becomes more and 
more pronounced, the trunks of trees become shorter (see Pl. XXXIV), 
until in many places near the top of the highest peaks the trail becomes a 
tunnel the top of which, composed of mingling branches of the trees, is so 
low that one often has to stoop in order to pass through it. The branches, 
also, in many cases, become more scraggy and crooked and the twigs 
shorter and stouter. Again, especially in the case of Leptospermum 
amboinense (see Pl. 1), the branches have an arrangement in one or more 
stiff, horizontal planes and known as the umbrella type, which, according 
to Schimper,** is an adaptation caleulated to resist the strong winds. 
This tree is invariably found on the most exposed places, where the 
erosion is sufficiently rapid to keep the bed rock at or near the surface, 
Its leaves are so reduced in size and so hard as to become almost lke 
coniferous ones in form and texture. On the whole, the effect of exposure 
on the arboreal vegetation on the ridge under consideration is such as to 
obtain here, so far as stunted growth and reduction in leaf size is con- 
cerned, the most xerophytic condition on the Reserve, not excepting the 
extremely xerophytie vegetation of the sea beach cliffs and the mangrove 
swamps, and this condition is brought about notwithstanding the fact 
Schimper, A. EF. W.: Pflanzengeographie auf physiologischer Grundlage 
(1898), English edition, translated by Fischer (1903), 348. 
