THE 
■ f 
NEW PHYTOLOGIST 
Vol. XXII 5 No. i 
February 20, 1923 
PERMEABILITY 
By WALTER STILES 
CHAPTER XI 
THE DETERMINATION OF THE PERMEABILITY OF PLANT 
CELLS TO DISSOLVED SUBSTANCES 
he passage of dissolved substances into living cells takes place 
X for the most part independently of the absorption of water. Just 
as the latter enters the cell in order to bring about equilibrium on the 
two sides of the cell membranes, so the passage of a dissolved sub¬ 
stance into the cell can only proceed until the distribution of the sub¬ 
stance within and without the cell fulfils the conditions of equilibrium. 
Of course, if the passage of water into, or out from, the cell should 
alter the conditions of equilibrium with regard to dissolved substances, 
passage of dissolved substance across the cell membranes may take 
place, but there appears no reason for supposing there is any closer 
connexion between the entrance of water and solutes into plant cells. 
The entrance of any solute into a cell depends therefore not only 
on the permeability of the cell membranes to the substance, but also 
on how far the distribution of the substance on the two sides of the 
membrane is removed from the equilibrium conditions. For this 
reason, although the passage of a substance into the cell can be taken 
as evidence of the permeability of the cell to the substance, the non¬ 
entrance of it need not necessarily indicate that the cell is imper¬ 
meable to the substance. Similarly the rate at which a substance 
enters a cell cannot be taken as a measure of the permeability of the 
cell. If a dissolved substance were able to penetrate the protoplasm 
and combine with some constituent of the cell, it would obviously 
enter the cell to a much greater extent and at a greater rate, than if 
it did not combine with any constituent. In the latter case it might 
Phyt. XXII. I. I 
