360 The Philippine Journal of Science 
The failure of a large proportion of the forms examined to make an 
accelerated or exaggerated growth when freed from the influence of 
light, even when provided with an adequate food supply, shows that light 
has no invariable or universal relation to increase in length, or thickness, 
or to the multiplication or increase in volume of separate cells. 
Oestrum nocturnum is one of the most rapidly growing of 
all cultivated plants in Manila; it branches profusely and in a 
very short time grows into a large shrub. It seems to grow 
very much better when fully exposed to the sun than it does 
in the shade. It is interesting to note that this plant is so 
apparently adversely affected by the very conditions that seem 
to be necessary for its rapid growth. However, while it is not 
elongating, it may be accumulating food to be used in elongation 
at night, and it is doubtful whether or not the apparently 
adverse effect of high transpiration during the day has any 
considerable influence on the total rate of growth of the plant 
for a day and night period. 
The shortening of the shoot during the day is apparently a 
very similar process to the decrease in the diameter of fruits 
and stems, the decrease in area of leaves, and the lessened 
water-content of leaves. It thus appears that perhaps all aerial 
parts of mesophytic plants may decrease in size as the result 
of excessive water loss. 
SUMMARY 
Shoots of Oestrum nocturnum wilt regularly on every com- 
paratively dry day during the time they are exposed to direct 
sunlight. During such days they may decrease in length; and 
late in the afternoon or early at night, when they again become 
turgid, return to their original length. At night they elon- 
gate rapidly, while during most of the day they may show no 
elongation except insofar as, in the late afternoon, they return 
to their original length. Absence of growth and actual shrink- 
age during the day are apparently connected with excessive 
transpiration, which causes the plants to lose more water than 
they absorb. 
