12 TRANSPIRATION AND ASCENT OF SAP ch. 



When the rate of transpiration in air was compared 

 with that in oxygen, it was found that when a branch 

 was surrounded with the latter gas, transpiration was 

 slightly more rapid. The index for the branch in air 

 moved 1 cm. in 36 sec. ; for the same branch in oxygen 

 it moved 1 cm. in 33 sec. 



If, while a current of air was passing through the receiver, 

 a piece of cotton wool soaked in chloroform was intro- 

 duced, a much more marked difference in the rate of 

 transpiration became apparent in a short time. Thus the 

 index was traversing 10 cm. in 50 - 8 sec. before chloroform 

 was introduced. Thirty minutes later the index took 

 516 sec. to traverse the same distance. The chloroform 

 was then removed, and the air current maintained for 

 60 minutes. At the end of this time the index moved 

 10 cm. in 120 sec. This result is the mean of a number 

 of experiments made with a small branch of Acer macro- 

 phyllum. 



With another branch in air the motion of the index 

 was 10 cm. in 127 sec. When surrounded with chloroform 

 vapour for 45 minutes the index took 642 sec. to traverse 

 the same distance. 



A similar diminution in the rate of transpiration is 

 observed when the branch is surrounded by ether vapour. 

 Thus, with a branch of Acer macrophyllum in air, the 

 index moved 10 cm. in 205 sec. ; with the same in ether 

 vapour it moved 10 cm. in 265 sec. 



These experiments indicate a large difference in the rate 

 of transpiration in the different gases. The figures given 

 here will serve only as examples of the results of such 

 experiments, for, although they were the means of a 

 number of observations, the latter are made so precarious 

 by various circumstances, that they can only be taken as 

 indicating a difference, and not as giving a measure of it. 

 The sticking of the index in the capillary tube, and the 

 opening of the receiver to introduce the anaesthetics, bring 



