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XXXIV. 



CRYOSCOPIO DETERMINATION OF THE OSMOTIC PRESSURES 

 OF SOME PLANT ORGANS. 



By W. R. GELSTON ATKINS, M.A., 

 Demonstrator in Botany, Trinity College, Dublin. 



[communicated by professor H. H. DIXON, SC.D., F.R.S.] 

 [Read April 26; Ordered for Publication May 10; Published June 30, 1910.] 



In every living cell movements and reactions are progressing which involve 

 an expenditure or transformation of energy. Accordingly the amount of 

 energy which is available sets a limit to all the phenomena of life. This 

 total energy is the osmotic pressure exerted by all the dissolved substances 

 present together with the chemical energy of these bodies, as measured by 

 the liberation of energy by their complete oxidation. 



It is well known that a cell placed in a chemically harmless solution will 

 not continue to live normally in it unless this solution has an osmotic pressure 

 approximately the same as that of the cell. If the solution is hypertonic, the 

 cell decreases in size through diffusion of water outwards, and may thus, if the 

 hypertonicity is not too great, arrive again at a state of equilibrium by raising 

 the concentration of its vacuole solutes. If the medium in which the cell is 

 placed is markedly hypotonic, the cell takes up water, its vacuoles increase in 

 size, and the cell ultimately bursts, unless, as in most plant-cells, there is a 

 wall which imposes a limit upon this distention. As the earliest organisms 

 were water-dwellers, this question of the adjustment to varying osmotic 

 pressure has had to be faced by every living creature. Moreover, it still lias 

 to be faced; for those animals which now live on land are water-dwellers 

 when considered cell by cell. In the ease of plants this problem has been 

 solved for a hypotonic solution by the production of a limiting membrane ; 

 for hypertonic solutions the answer has not been fully given, adjustment by 

 the contraction of the whole distended cell, wall and all, being possible over 

 a limited range only, after which plasmolysis ensues. Besides this regula- 

 tion there may be a physiological regulation by the production of soluble 

 substances from reserve materials to restore osmotic equilibrium. 



From these considerations it may be seen how important a part in the 

 life of a cell is played by the osmotic pressure. 



This paper forms one of a series in which by systematic measurements an 



SOIENT. PKOO. E.D.S., VOL. XII., NO. XXXIV. 3 T 



