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. 



Cestrum 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 Cestrum 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. 



