1 52 TRANSPIRATION AND ASCENT OF SAP ch. 



already used in A and E were observed. Consequently 

 they had already been exposed for some time to carbon 

 dioxide. 



At the end of experiment D, when the pressure had 

 been reduced to normal for about 10 min., the margins 

 of the leaves unrolled and their usual appearance was 

 reassumed. 



Table 18. 

 Tilia americana in Air. 



Experiment C in Table 18 is subject to a correction 

 for the elasticity of the branches' conduits. In deter- 

 mining the amount of the water transpired, the vessel 

 beneath was placed in position before the pressure was 

 raised in the glass cylinder and removed for its second 

 weighing, while the pressure was still maintained. Con- 

 sequently, some water was squeezed back from the con- 

 duits, owing to their elastic yield, and remained in 

 the vessel, diminishing the amount of transpiration 

 observed. In order to estimate how much ought to 

 be allowed for this, an experiment was made in which 

 the same branch was raised to a pressure of 6 atmos- 

 pheres for ten minutes. While this was maintained, a 



