356 T fle Philippine Journal of Science im 



had decreased still further in length. Between 11 o'clock and 

 noon, when they were exposed to diffused light, three of them 

 elongated 0.5 millimeter, while the other one remained station- 

 ary. This latter, however, had elongated 0.5 millimeter during 

 the preceding hour. After this all of the shoots were in the 

 shade and there was a gradual elongation until 8 o'clock in the 

 evening, when all of the stems were again curved upward. 

 From the table it will be seen that, as they increased in length, 

 they gradually became less wilted. However, at 8 o'clock in 

 the evening, when all of the shoots were apparently turgid and 

 curved upward, the length was in every case exactly the same 

 as at 8 o'clock in the morning, which would indicate that they 

 made absolutely no growth during the intervening period. This 

 result would, of course, be expected from the wilted condition 

 of the shoots which was noticeable throughout the day. The 

 elongation during the first afternoon, as the shoots became more 

 turgid, was very probably also due simply to their regaining 

 the length they had possessed in the morning. If the evapor- 

 ating power of air is compared with the measurements of the 

 shoots and the condition of the plants, as shown in their 

 respective columns, it will be seen that the period of greatest 

 decrease in length and greatest degree of wilting did not coin- 

 cide with the time when the evaporating power of air was 

 greatest ; but that, when the evaporating power of air was great- 

 est, the plants were elongating and recovering from wilting. 

 Had measurements of evaporation been made with a radio- 

 atmometer instead of with a white atmometer, the records 

 would in all probability have shown greater coincidence between 

 the period of greatest evaporation and that of greatest wilting. 

 From the figures in Table I it would appear that the action of 

 sunlight on the leaves had a greater effect in producing wilting 

 than had the evaporating power of the air, as measured by the 

 white atmometer. That the plants did not grow during the day 

 but made a fairly rapid growth at night would seem to be related 

 to the amount of water contained in them. When the wilting of 

 the plants indicated that they were giving off more water than 

 they were absorbing, they made no growth. 



Two shoots on the second plant were selected for measure- 

 ment. The results for these are presented in Table II in the 

 same form as are those in Table I. The evaporation given in 

 this table was measured by the atmometer placed near the 

 first plant and, as the atmometer was not illuminated in the 

 same manner as the second plant, it could not be expected to 



