320 L. A. GIDDINGS 



This was before temperature or wind velocity had reached a maxi- 

 mum and also be ''ore relative humidity was lowest. The third leaf 

 showed the greatest loss at the time when temperature was the 

 highest and relative humidity the lowest, but an hour before 

 wind velocity was highest. The leaves all became somewhat 

 wilted before the end of the experiment, but there was no appar- 

 ent wilting until 2.30 p.m., when No. II was slightly wilted. 

 Since these leaves came from the same plant at different heights 

 it is of interest to note how they compare with each other in the 

 amount of water lost. Taking the lowest leaf as the standard 

 or 100%, the loss per 100 sq. cm. of leaf surface for the other 

 leaves was 114.5%, 103.5%, and 86.5%, respectively. 



This experiment indicates that the upper leaves transpired 

 less actively than did the lower ones when placed under like 

 conditions. A tall plant is thus protected from the dangers of 

 greater loss of water at the greater heights, due to greater evap- 

 oration, not only by the diminished size of the leaf, but also 

 by the check upon transpiration which they are able to effect. 

 In the graphs for this experiment the leaves are numbered in 

 order from the lowest to the highest. The evaporimeters are 

 numbered in order from the ground up (fig. 5, fig. 6). 



In the experiment of August 21 (table 7) four SilpMum leaves 

 were used. No. I was taken from a height of 16 cm.. No, II 

 from a height of 50 cm., No. Ill from a height of 71 cm., and No. 

 IV from a height of 85 cm. 



Evaporimeter No. I was at a height of 25 cm., and evaporimeter 

 No. II at a height of 6 cm. above the ground. Here, as in the 

 other experiments where the evaporimeters were at different 

 heights, the one at the greater height Ijst the greater amount 

 of water. The anemometer was at a height of 54 cm. from the 

 ground. It will be noticed that both evaporimeters showed a 

 maximum l3ss at the time when relative humidity was the low- 

 est, but at a time prior to that of highest temperature and great- 

 est wind velocity. 



In this experiment the leaves showed the greatest loss from one 

 to three hours before the time of greatest evaporation. In this 

 experiment, as in practically all the rest of the series, the second 



