EVERGKEEN TEEES IN WINTER. 325 



V. Transpiration under Direct Insolation. 



For this experiment I used the pots prepared as has been 

 described above (p. 317). The pots were exposed all day to direct 

 sunlight on a stand in front of the laboratory. To keep them 

 free from rain, a glass roof was employed only during nights or 

 rainy days, while in fine weather it was always put aside from 

 morning till evening. Each pot was weighed once a day (4-5 p.m.), 

 but I omitted the weighing several times, since the loss of water 

 was too insignificant and the balance which I used was not 

 sufficiently accurate under 0.5 gram. 



In the beginning of each series of experiments a sufficient 

 amount of water was supplied to make the whole weight nearly 

 2 kilograms, at which weight the content of water might roughly 

 be equalized in each pot. The weighing began at the end of 

 December and lasted to the end of March, and in order to get 

 a correct comparison at different times during the winter I noted, 

 as far as possible, only the results of experiments in trans- 

 piration obtained on fine days, thereby omitting those obtained 

 on rainy or cloudy days. 



The materials employed were limited to the following 

 fourteen species of plants, of which five species were conifers, and 

 the others, foliage trees. Their characters and ages were as 

 follows : — 



