igig] 



WEAVER &- MOGENSEN— TRANSPIRATION 



403 



power as spring advanced similar to that of the older pines in 

 the other battery. These plants were growing in a soil with an 

 average water content of 15.8 per cent (18.2 per cent maximum, 



TABLE III 



Total transpiration losses (in gm.) of 2-year-old yellow pines from 



October 18 to May 2 



14.6 per cent minimum), and an available water content varying 

 from 13 .5 to 10 per cent. 



Pinus Banksiana 



A battery of eight 3-year-old jack pines in containers 4 . 5 inches 

 in diameter and 10 inches deep was sealed and weighed on Sep- 

 tember 26. These trees were growing in a soil with an actual water 

 content ranging from 8.6 to 15.1 per cent, of which only 4 and 

 10.3 per cent respectively were available for growth. 



The leaf area, calculated in a manner similar to that already 

 described for the yellow pines, ranged from 2 . 141 to 4 .470 sq. dm. 

 The plants remained in good condition throughout the winter and 

 showed vigorous growth in the spring. In addition to the usual 

 brownish color of the leaves in winter, however, the tips of many 

 of the leaves died during January and February. Practically all 

 the leaves remained on the plants throughout the experiment. 

 Fig. 4 shows this battery as it appeared on February 28. 



The transpiration losses as determined for the several periods 

 are plotted in fig. 5. A glance at these graphs shows two things 

 which are at once apparent. First, the general parallelism of the 

 lines throughout (except from October 17 to 26, to be considered 

 later); that is, the plant which gave the highest or lowest losses 

 during the early periods continued this behavior throughout. The 



