114 



CLARK— ON WATER CONTENT 

 TABLE IV (Results) 



It is seen from Table I that there is no definite time for maxima 

 and minima water contents. Fig. 1 shows however that, as a general 

 rule, in spite of numerous fluctuations, there is a gradual increase in 

 water content by night, and a gradual decrease by day. It shows 

 likewise that the curves of the two species of Populus, when compared 

 under similar conditions of habitat and atmosphere, follow each other 

 rather closely. This fact indicates the influence of a common factor. 

 By comparing Tables I, II, III and Figures I, II, it is evident that water 

 content is independent of both temperature and relative humidity. 



For both Populus tremuloides and Populus grandidentata under 

 similar atmospheric conditions, water content is greater under hydrophy- 

 tic than under xerophytic habitat. Under xerophytic cloudy conditions, 

 day readings only were obtained, and with this one exception, water 

 content for Populus tremuloides was found to be greater than for Populus 

 grandidentata. Day readings under both xerophytic and hydrophytic 

 situations were found for both species to be greater under clear than under 

 cloudy conditions. One exception to this was for Populus tremuloides 

 under xerophytic conditions. By night for both species, under hydro- 

 phytic situations, water content for clear was greater than for cloudy 

 conditions. Irregularities in general results occur only in P. tremuloides 

 under xerophytic conditions, and might probably be accounted for in 

 scarcity of moisture available in the dry soil. 



