I9I91 



WEAVER &- MOGENSEN— TRANSPIRATION 



405 



The midwinter losses, actual and relative, are just as marked as 

 they were in the case of the yellow pines. During the period 

 December 19 to February 7 the total average loss was only 2 .8 gm., 

 an amount which, compared on the daily basis, is only 1/169 of that 

 lost during the autumn period (September 26 to October 17). 



Abies grandis 



Two batteries of white firs were used. One consisted of eight 

 2-year-old seedlings in containers 3 . 5 inches in diameter by 6 . 5 

 inches deep, and the other of eight 4-year-old trees in containers 

 3 . 5 inches in diameter and 9 inches deep. 



Fig. 5. — Average daily losses in grams from eight 3-year-old jack pines; September 

 26 to December 19, 191 7. 



The younger plants were growing in soil with an available water 

 content ranging from 6 to 9.4 per cent. All were winter killed. 

 As this did not occur until January or February, the transpiration 

 losses up to that time are rehable. About January 15 the leaves 

 began to drop off badly, but the leaf area of several of the plants 

 was determined without removing the leaves, and before defoliation 

 had begun. This was accomplished by determining the number of 

 leaves, their lengths, and average diameters. Three of these 

 seedlings had leaf areas of 0.0972, 0.1641, and 0.0970 sq. dm. 

 respectively. These plants are shown in fig. 11. This picture 

 was taken late in February after many of the leaves had fallen. 

 Because of an accident to the top of one tree, it was discarded. 



