io$ 
D. Thoday 
ON TURGESCENCE AND THE ABSORPTION OH 
WATER BY THE CELLS OF PLANTS. 
By D. Thoday, M.A. (Cambridge). 
[With One Figure in the Text.] 
S O much has been written concerning osmosis in plant that it 
would appear at first sight superfluous to discuss in any 
detail the conditions which govern osmotic equilibrium in turges- 
cent cells and tissues. Nevertheless the full significance and 
implications of the elementary treatment of this subject appear 
to be by no means generally understood. Lepeschkin 1 has dealt in 
some detail with the equilibrium relations of cells to water and 
solutions in connection with his interesting researches with 
Pilobolus and Spirogyra, but his papers are not as well known as 
they deserve to be. Renner’s 3 admirable papers on transpiration 
from the point of view of the cohesion theory contain thoroughly 
sound discussions of the relation of suction force to osmotic 
pressure. But with few exceptions those who have worked in this 
field either have not fully understood the subject or have regarded 
it as too elementary to need dealing with in detail. Even in 
Livingston’s “ Role of Diffusion and Osmotic Pressure in Plants ” 
there is no perfectly clear and explicit treatment of the equilibrium 
of a cell with solutions or. other cells in contact with it; and his 
reservation of the term turgor “ to express the osmotic pressure of 
the internal fluid ” seems to the writer particularly unfortunate. 
These problems are fundamental to the whole question of 
the water relations of plants ; yet the inadequate or even mis¬ 
leading treatment of them in existing text-books makes this 
important subject one of special difficulty to the student. The 
discovery, to which reference has been made in an earlier paper, 3 
that workers like Stiles and Jorgensen, who have shown them¬ 
selves clear sighted and critical in other directions, have not 
succeeded in freeing their minds from the misconception that a 
solution in which a turgescent tissue shows no gain or loss of 
water is isotonic with the cell-sap, 4 forces the writer to the con- 
conclusion that inadequate views are still widely prevalent. 
That such a use of the term isotonic is unjustifiable is obvious 
when one considers that submerged fresh water algae are normally 
in an essentially similar condition of equilibrium which could not 
be described by saying that their sap is isotonic with water 1 
It is however not sufficient merely to realise an error of this 
1 Bot. Centralblatt, Beihefte XIX, 1, 1906, pp. 425 et seq; Berichte d.d. 
but. Ges., XXVla, 1909, p. 198 , etc. 
3 Flora, 103, 1911, p. 171. 3 Nkw Phytologist, 1918, p. 57. 
4 “Studies in Pcrmability,” Ann of Bot., 1917, pp. 425, 426, 
