330 Mr F. Darwin and Mr R W. Phillips, [Nov. 23, 



supposed that the strength of a mixture is equal to the sum 



of strengths of its constituents, i.e. according to the formula 



H.N 

 M = (Ty ^T A.o TT » where M is the pressure of the mixture, H and 



N pressures of hydrogen and nitrogen. It seems that calculated 

 and observed pressures disagree more than it could be explained 

 by the imperfection of the proportionality of strength and pressure 

 of gases and by errors of experiments. 



(3) On the mutual action of oscillatory twists in a vibrating 

 medium. By A. H. Leahy, M.A. 



This paper is being printed in the Transactions of the Society. 



(4) On the transpiration-stream in cut branches. By Fkancis 

 Darwin, M.A., Trinity College, and Reginald W. Phillips, 

 B.A., St John's College. 



CONTENTS. 



PAGE 



§ 1. Object of Experiments 330 



§ 2. Method - 331 



§ 3. On Dufour's experiments ......... 337 



§4. Estimation of the effect of 'double sawing*' on the flow of water in 



transpiring branches .......... 338 



§ 5. Estimation of the effect of double-sawing on branches through which a 



stream of water is drawn by means of an air-pump .... 353 

 § 6. Discussion on a point of difference between the results given in § 4 and § 5. 356 

 § 7. Experiments with solution of eosin, and with colour held in suspension 



in water ............ 358 



§ 8. Conclusions as to Dufour's double-sawing experiments — and general 



discussion of results 359 



§9. Experiments on bending and compressing the tissues of transpiring 



branches ........... . . 364 



§ 1. Object of the Experiments. 



The series of experiments here recorded was commenced in 

 the spring of 1884, and was in large part completed in that 

 year. We have been forestalled in some of our results since the 

 work was begun, nevertheless we think it best to publish them, 

 since the amount of evidence available on the subject is by no 

 means large. 



It is not necessary to refer in detail to the views held by different 

 botanists as to the way in which the transpiration-stream passes 

 through wood. The subject has been recently discussed in an 

 admirable paper by Elfving+, and more recently in Godlewski'sj 

 paper on the same subject. 



* i. e. Branches sawn half through on opposite sides at points near each other. 

 + Ueber den Transpirationstrom in den Pflanzen. Acta Soc. Scient. Fennicce. 

 Tom. xiv, 1884. 



X Pringsheim's Jahrbuch. 1884. Bd. xv, Heft 4. 



