io TRANSPIRATION AND ASCENT OF SAP ch. 



reduced when its activities were depressed. Starting 

 from this idea an endeavour was made to test the effect 

 on transpiration of an application of chloroform vapour, 

 ether vapour, and carbon dioxide gas. Although each of 

 these three agents, when they were brought round the 

 transpiring leaves, led to a marked falling off in the amount 

 transpired, consideration showed that their actions are so 

 manifold that the effect observed cannot with certainty 

 be attributed entirely to their direct action in checking the 

 vital actions of the protoplasm. At the same time, experi- 

 ments were made to test the effect of an increased supply 

 of oxygen on transpiration ; the marked acceleration pro- 



FlG. 1. 



duced by this gas possibly is due to its stimulating effect 

 on the secretion, but in any case is of considerable interest 

 in this discussion. 



The method of experiment was as follows : The rate of 

 transpiration of a branch enclosed in a large receiver, and 

 supplied with a constant current of dried air, was observed. 

 This rate was then compared with the rate of transpiration, 

 when a similar current of some other dried gas, or dried 

 air, carrying with it some anaesthetising vapour, was 

 passed through the receiver. 



The rate of transpiration was estimated, either by the 

 motion of an index moving in a capillary tube sealed 



