659 
that, on the whole, the relative humidity and the rainfall are greater 
and the average temperature is lower, all factors which are favorable to 
mesophytic vegetation. 
In the above discussion, two areas presenting approximately the same 
soil conditions have been compared. It now is in order to discuss situa- 
tions in which the altitude and exposure are the same, but in which the 
soil conditions differ. In this respect Plots A and B offer admirable 
examples. ‘The former has already been described. Plot B is separated 
from it by a ridge-saddle only. It is a large rock (Pl. XXXV) on three 
sides standing 4 to 6 meters above the ridge on which it is situated. on 
the fourth grading more perceptibly into the ridge itself, although here 
also it rises slightly above it. The upper surface is covered with a very 
thin soil most of which owes its origin to vegetable decay. On this rock 
the arboreal vegetation has established itself only because its fissures offer 
opportunity for the former to maintain a foothold. Both the dwarfed 
condition and leaf surface of the trees which are present show this situa- 
tion to be a more xerophytic one than that of Plot A. The species are 
almost entirely different. Hugenia acuminatissima, represented by 32 
individuals on Plot A, here has only four and these are at the end of the 
rock where the soil is deepest. Acronychia laurifolia, Decaspermum 
blancot, D. paniculatum, Ligustrum cumingianum, Leucosyke capitellata 
var. celtidifolia, found in Plot B, are not represented in Plot A, although 
nearly all of them occupy places in a similar situation in Plot D, which 
is on a rock cliff distant some 2 kilometers, at an altitude 150 meters 
higher. Acronychia laurifolia and Decasperum paniculatum are good 
illustrations of the deciduous habit in trees on the mountain and em- 
phasize the xerophytic nature of the ridge habitat. Both these trees, 
like the other species, have hard, xerophytic leaves. During the latter 
portion of March and first part of April they are almost destitute of 
foliage. The leaves of cronychia, before they are shed, fold or half 
shut on the midrib, thus considerably reducing the transpiring surface. 
Many other trees also show a more diminished leaf display during a por- 
tion of the dry season than they do during the rainy one. Indeed, almost 
without exception, as is true of the formation at the base and in more 
xerophytic situations on the higher slopes, there is an interval of time 
between the beginning of the shedding of the old leaves and the appear- 
ance of the new ones. his, in the aggregate, makes the forest canopy 
much thinner during the dry months and is undoubtedly an adaptation 
to prevent rapid transpiration. 
On ascending from the slopes of the Shorea-Plectronia formation to 
the first prominent ridge peaks, one finds a very sudden transformation 
from the tall trees to the dwarfish arboreal growth of the ridge (see 
Pl. XXXIV and contrast it with Pl. XXII), and apparently in confor- 
mity with this change there is a still greater variation in the multiplicity 
of the species and the individuals of the epiphytic vegetation. This 
Oh Of kee ee ed 
