1902.] 



Influence of Carton Dioxide on Leaves, etc. 



397 



monas producing a brown rot (not to be confused with P. campestris, 

 E. F. Smith), which I am at present studying, works in a totally 

 different manner ; its action is very much slower, and the rapid 

 swelling of the cell-wall, as described above, is not a conspicuous 

 feature. 



" The Influence of Varying Amounts of Carbon Dioxide in the Air 

 on the Photosynthetic Process of Leaves and on the Mode of 

 Growth of Plants." By Horace T. Brown, LL.D., F.E.S., 

 and F. Escombe. B.Sc, F.L.S. Eeceived April 28, — Eead 

 May 29 ; 1902. 



[Plates 5—10.] 



In a paper recently laid before this Society dealing with the physical 

 processes which regulate the entry of atmospheric carbon dioxide into 

 the leaves of plants,* we incidentally described a series of experiments 

 relating to the rate of absorption of dilute gaseous carbon dioxide by 

 surfaces of solutions of caustic alkali, when air containing definite 

 small amounts of this gas is drawn over the liquid. Contrary to what 

 might be expected from the perfect absorbing nature of the solution, 

 and the known laws of gaseous diffusion, the amount of C0 2 absorbed 

 by unit area of the liquid surface in unit time ceases sensibly to 

 increase when a comparatively low velocity of the moving air current 

 has been reached. This, however, only holds good when the propor- 

 tion of C0 2 in the air stream is maintained quite constant, any slight 

 variation in the amount at once affecting the rate of absorption. On 

 investigation it was found that for dilutions of carbon dioxide lying 

 between 0-6 part and 6 parts per 10,000 of air, the rate of absorption 

 of the carbon dioxide is strictly proportional to its partial pressure.^ 



In determining the rates of gaseous diffusion of atmospheric carbon 

 dioxide through multiperforate diaphragms extended over chambers 

 containing perfect absorbents, the same relations between partial 

 pressure of the gas and its absorption were found to hold good : under 

 these conditions the amount of carbon dioxide passing through the 



* * Phil. Trans.,' B, 1900, vol. 193, p. 278. 



f So accurately is this the case that the process, which is described in detail in 

 the above-mentioned communication, may be used for determining the varying 

 amounts of C0 2 in air without the necessity of measuring the volume of air which 

 passes through the apparatus. It is merely necessary to pass the air over the 

 absorbing surface at a sufficient rate to ensure maximum absorption, and to compare 

 this amount of absorption in a given time with that produced from air of a known 

 content of carbon dioxide, a process of standardisation which is done once for all 

 with the apparatus. The ratios of the absorptions giye at once the ratios of the 

 partial pressures of the C0 2 in the two cases. 



2 E 2 



