I9I9] 



WEAVER &- MOGENSEN— TRANSPIRATION 



417 



accompanying the unfolding of the buds. Six plants were winter 

 killed, and no losses were recorded for them after January i. 



Quercus macrocarpa 



A number of bur oak seedlings were grown from acorns obtained 

 from an Illinois nursery in May 191 7. Seven of the lot were finally 

 selected for experimental work. These were repotted in containers 

 5 inches in diameter and 7 inches deep. They may be seen in the 

 foreground in fig. i. The initial available water content of the 

 soil ranged from 11 .3 to 15 .2 per cent, but the soil moisture was 

 reduced by evaporation from the surface of the several containers 



TABLE VIII 



Average daily losses (in gm.) of bur oak seedlings from September 24 to 



January 4 



Plant 



I. 

 2. 

 3- 

 4- 

 5- 

 6. 



7- 



September 24- 



October 3 



(9 days) 



October 3-10 

 (7 days) 



October 10-18 

 (8 days) 



9.0 



10. 2 



15-5 

 7.2 



45 



15-2 



7.0 

 II .0 

 6.4 

 9 9 

 3-4 

 2.6 

 12.9 



2 . 1 

 4 9 



4-3 

 I . I 

 0.4 



0-5 

 8.0 



November 1-16* 

 (15 days) 



25 

 55 

 22 

 26 

 21 

 28 



1.89 



December 7- 

 January 4 

 (28 days) 



* At this time all the leaves had fallen, and the losses are not calculated on the average daily basis, 

 but on the total loss for the entire period. 



to a minimum of 4 . 4 and a maximum of 9 . 6 per cent respec- 

 tively from October 18 to November i. After this the seals were 

 again replaced and half of the containers brought back to the 

 original water content. The transpiration losses are shown in 

 table VIII. 



The gradual falling off in the transpiration rate without any 

 increase, as in the case of the elms and maples, may be explained 

 by an examination of the dates, which show that the first loss was 

 not recorded until a time (October 3) when all the trees show a 

 steady decrease. By November i all of the leaves had fallen 

 (or the dried leaves were removed). Following this the losses are 

 extremely small. The stem areas of the oaks were only 0.039- 

 0.088 sq. dm. 



