oy a ee Vere eee ee es “ a ~seo™ wb) tte 8 SSS ee 
ra ae ? ro eee F -) ? + a i 
380 
rain the surface layers of the soil are dry and the ground water level 
is low, yet, it is believed, a sufficiently high chresard exists to prevent the 
most pronounced deciduous habit from prevailing and vegetative activity 
from being altogether inhibited. ‘The table shows that with an increase 
in altitude there isa decided increase in the rainfall. This, among other 
things, will account for a chresard which would be sufficiently high to 
assist in maintaining a nearly evergreen forest on the upper part of the 
mountain, although here, as well as at the base, there is a response to the 
xerophytic conditions of the dry season. On account of its deciduous 
element, the vegetation at the foot of the mountain can not be regarded 
as the best expression of Schimper’s tropical rain forest, neither can it 
be classed with the monsoon forests, for the evergreen element is nearly 
absent in the latter. 
Next to the rainfall, and especially to the precipitation as conserved 
in the shape of a chresard, the relative humidity (or its complement, the 
saturation deficit) is the most important factor in explaining ecological 
distribution, for just as the chresard controls the absorption, so does 
the saturation deficit regulate the transpiration. 
Taste I1.—Monthly and annual averages of the saturation deficit for Manila, 
1IS83—-1902. 
; eesti Paes 2: - 
May. | June. | July. Aug. Sept. Oct. Lor. | Dec. 
29,3 23.3 | .18.6 15, 2 15, 2 14.5 17.3 oh ae 
PP SOS 
As would be expected, these data show a high saturation deficit during 
the dry and a low one during the wet season. When compared with those 
for some regions in temperate zones, these figures are not exceptionally 
low even during the rainy-season. Attempts have been made by Haber- 
landt,'* Holtermann, and others to compare the transpiration in the 
damp Tropics with that in temperate zones. The general conclusion 
seems to be that in the shade the transpiration in the Tropics is much 
less than it is under the same condition in the temperate zone, while 
in open places it is greater. Holtermann draws the conclusion that 
for the entire twenty-four hours of an average day it is less in the 
Tropics than in Europe. In the region under consideration, especially 
during the month of July, there is almost continuous rain for two 
and even three weeks, yet these rains are usually accompanied by high 
winds and the periods between the showers show a comparatively high 
saturation deficit. Considering all factors, it is not believed that the 
lack of transpiration has any deleterious effect on the vegetation as a 
“See Burgerstein A. Die Transpiration der Pflanzen (1904) 160 to 174, for a 
review of the subject of the condition of transpiration in damp warm tropical 
regions, and for a citation of the literature. 
i <a 
