FORCE EXERTED BY TRANSPIRING SHOOTS 209 



a negative pressure existed was cut off under water at 12:45 

 P. M. and fastened to the apparatus at i P. M. After a few 

 minutes the following observations were made : 



1:27 P. M. Indicator bubble at o mg. Temp. 21.0 C. 



1:50 " 300 21.0 



2:05 " " 500 " 21.0 



2:14 " " 600 " 21.0 

 Readjusted. 



2:17 " " " o " 20.8 



2:28 " " " ioo " 20.7 



2:40 " " 200 " 20.5 



2:57 " " " 300 " 20.0 



This shoot was taken from the apparatus and placed in water. 

 The following day a small portion was cut from the excised end, 

 and it was refitted to the apparatus with the following results, 

 which show that the negative pressure had been equalized during 

 the first day : 



11:13:55 A.M. Indicator bubble at o mg. Temp. 20 o C. 



11:26 " " " ioo " 20.0 



11:39 " " " 20 " 20.1 



11:53 " " " 300 " 20.4 



12:05:5 " " " 400 " 20.7 



12:20 " " " 500 " 21.0 



12 = 33 " " " 60O ' 21.0 



The leaves showed a superficial extension of 300 sq. cm., in- 

 cluding the petioles ; area of stem surfaces, 40 sq. cm. This 

 apparatus is also convenient for obtaining the comparative trans- 

 piration of the stems and leaves. The leaves were stripped from 

 the shoot of the above tested plant, the base of which was trimmed 

 and refitted to the apparatus, and the following observations were 

 made : 



10:31 A.M. Indicator bubble at o mg. Temp. 17.5 C. 



11:12 



11:43 



12:13 P. M. 



1:23 " 



2:OO " 



IOO " 18.0 



200 " 18.8 



300 17.5 



500 " 16.0 



600 " 15.1 



280. Force Exerted by Transpiring Shoots. Cut off a branch 

 or stem of any woody plant and fit to the end of a glass tube of 



