THE NATURE OF TRANSPIRATION 



r 5 



In order to form some idea of this effect, I suspended a 

 shallow dish containing water in the receiver, previously 

 occupied by the transpiring branch; and in connection 

 with the train of apparatus previously described, successive 

 weighings gave approximately the loss of water by evapora- 

 tion from this dish. During the experiment a stream of 

 gas, dried as before described, was kept up through the 

 apparatus. The rate of evaporation, when this current 

 was composed of air, oxygen, carbon dioxide, and largely 

 of ether and chloroform, was observed. 



Again denoting the loss of weight of a vessel of water 

 in air as 100, the loss in the other gases was found to be 

 as follows : 



Table 2. 



From these observations it would appear that the rate 

 of transpiration is diminished when the leaves are sur- 

 rounded by carbon dioxide, ether vapour, or chloroform, 

 much in the same degree as the rate of evaporation would 

 be diminished by the presence of these gases ; and this 

 diminution is in the inverse order of their densities. In 

 the case of oxygen, however, the rate of transpiration is 

 increased much more than the rate of evaporation would 

 be from a liquid surface. 



It must be understood that these numbers only apply 

 to the first effects of carbon dioxide, ether, and chloro- 

 form ; for when these gases begin to exercise a lethal 

 action on the cells, the rate of transpiration is very 



