124 Dr. H. T. Brown and Mr. F. Escoml-e. 



than when it was saturated with moisture. The following are the 

 limits between which the coefficients of diffusion of ions, produced by 

 point discharges, were found to vary : 



Positive ions in dry air 0*0247 0*02 1 6 



Negative ions in dry air 0-037 0*032 



Positive ions in moist air 0*028 0-027 



Negative ions in moist air 0*039 0*037 



" Static Diffusion of Gases and Liquids in Relation to the Assimi- 

 lation of Carbon and Translocation in Plants."* By HORACE 

 T. BROWN, F.R.S., LL.D., and F. ESCOMBE, B.Sc., F.LS. Re- 

 ceived May 31, Read June 14, 1900. 



(Abstract.) 



This paper is intended to be the first of a series descriptive of the 

 work carried out by the authors in the Jodrell laboratory on the 

 fixation of carbon by green plants, and deals mainly with the purely 

 physical processes by which atmospheric carbon dioxide gains access to 

 the active centres of assimilation. 



The new evidence which F. F. Blackman brought forward in 1895 

 in favour of the gaseous exchanges of leaves taking place exclusively 

 through the stomatic openings, presents at first sight certain difficul- 

 ties of a physical nature, which have led to an examination of the 

 whole question of the free diffusion of carbon dioxide at very low 

 tension, and under a set of conditions very different from those under 

 which the previous determinations of the coefficient of diffusion of 

 carbon dioxide and air have been made by Loschmidt and others, 

 where the gases were initially of equal tension, and the ratios of 

 mixture departed widely from those of ordinary atmospheric air. The 

 inquiry has led to the discovery of some new facts connected with the 

 static diffusion of gases and liquids, which are of considerable interest, 

 not only from the physical point of view, but from the explanations 

 they suggest of certain natural processes which are primarily dependent 

 on diffusivity. 



The method employed in the first instance for the determination of 

 the diffusivity of atmospheric carbon dioxide was one of static diffusion 

 down a column of air of a definite length, towards an absorptive 

 surface at the bottom of the column. When a static condition has 

 been established, there is a steady flux of the carbon dioxide down the 



* The title of the .paper as communicated to the Society was " Some New 

 Observations on the Static Diffusion of Gases and Liquids, and their Significance 

 in certain Natural Processes occurring in Plants." 



