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XXVI. 



ON THE EFFECTS OF STIMULATIVE AND ANESTHETIC 

 GASES ON TRANSPIRATION. (PRELIMINARY NOTE.) 

 By HENRY H. DIXON, D.Sc, Assistant to the Professor of 

 Botany, Trinity College, Dublin. 



(cOilMITNICATED BY E. P. WRIGHT, M.D.) 



[ReadJANUAKY 10, 1898.] 



It has been pointed out' that experimental data do not allow us to 

 decide whether the energy which raises the sap in tall trees during 

 transpiration is directly derived from the inflow of heat at the evapo- 

 rating surfaces in the leaves, or whether the energy is, at least in 

 part, derived from the potential energy stored in the form of various 

 oxidisable substances in the leaf. In other words, whether transpira- 

 tion is a purely physical process, or whether it is complicated by 

 phenomena which biologists describe as vital processes. 



This investigation is an attempt to elucidate this point. It was 

 hoped that, by observing the effects of stimulative and anaesthetic 

 gases on transpiration, we might obtain a clue as to the nature of the 

 process. Thus, if it was noted that a gas like oxygen, which stimu- 

 lates the vital actions of protoplasm, caused the rate of transpiration 

 to increase markedly, this observation would tend to show that tran- 

 spiration might with probability be referred to vital action. Again, if 

 the action of anresthctics tended to retard transpiration, we would have 

 in this fact additional evidence pointing in the same direction ; whereas ; 

 if these gases were without special effects on the process, other than 

 their simple physical properties would exert on evaporatian we might 

 conclude that so far transpiration was similar to evaporation. 



The direct effects of the stimulating and ansestheticising gases are, 

 however, complicated by other attending phenomena ; so that the 

 results, so far as I have been able to proceed, are neither easily 

 obtained nor are they of unequivocal interpretation. 



The method of experiment was as follows : — The rate of transpi- 

 ration of a branch enclosed in a large receiver, and supplied with a 



' " Eeport of a Discussion on the Ascent of "Water in Trees," Ann. Bot., 

 Dec. 1896, and "On tlie Physics of the Transpiration Current, p. 34. 



