Dixon — On the Effects of Gases on Transpiration. 619 



constant current of dried air, was observed. This rate was then com- 

 pared with the rate of transpiration, when a similar current of some 

 other dried gas, or dried air, carrying with it some anaesthetieising 

 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 hermetically to the cut end of 

 the branch, or by directly weighing the amount of water transpired. 

 In the latter case, which was found to be the more satisfactory, the 

 branch, inserted through a caoutchouc cork into a test-tube containing 

 water, was hung from one arm of a balance. The arrangement is 

 shown in the figure. In this figure h is a ' tower ' containing calcium 



Fig. 1. 

 chloride, aud c is a sulphuric acid bulb for drying the gas supplied. 

 Before passing through the drying materials, the gas entering at e is 

 led into an inverted flask d, which is provided, in addition to the 

 tubes of entry and exit, with a U -tube, /, filled with oil. The supply 

 of gas is adjusted until the oil in the longer arm of the tube/ is 

 brought to a certain level. By this means the pressure, and con- 

 sequently the flow, of gas through the apparatus can be adjusted and 

 compared. "When vapours are to be supplied, the liquid from which 

 the vapour is derived is placed in a sulphuric acid bulb, like that in the 

 figure, but inserted in the train between the air supply and the flask d. 



The first experiments made were with the index method of esti- 

 mating the rate of transpiration. A modification of the apparatus, as 

 figured, which is readily understood, was then used. The branch, 

 sealed hermetically to a capillary tube containing the index, was then 

 inserted from below into the receiver.. 



"With these arrangements there soon appeared to be a marked differ- 

 ence in the rate of transpiration in oxygen and CO2. Thus, to quote 



