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A STUDY OF THE PROBLEM OF WATER 
ABSORPTION. 
BY LOUIS OTTO KUNKEL. 
I. INTRODUCTION. 
When we observe under the microscope a piece of plant 
tissue, an algal filament, or the spores of a fungus, in that 
condition that we are pleased to call normal, we find that in 
each case the cells are quite rigid. This rigidity, or turgidity, 
as it is generally termed, is due to the fact that the protoplast 
exerts a certain amount of pressure on its cell wall. When 
a cell becomes plasmolysed the protoplasm ceases to exert any 
pressure on the cell wall, and we say that such a cell has lost 
its turgor. 
It is a difficult problem to explain the origin of the force 
from which results turgidity in living cells. The explana- 
tion most generally given is based on the assumption that a 
semi-permeable membrane or, at least, a membrane pos- 
sessing only limited permeability for dissolved substances 
surrounds each cell. When such a membrane is interposed 
between two solutions of different concentrations, the major 
current of the solvent is toward the more concentrated solu- 
tion, and osmotic pressure becomes manifest. In this way is 
explained the entrance of water into cells. If we assume that 
a semi-permeable membrane surrounds the living cell, we may 
account for the pressure observed in turgid cells by saying 
that it is due to osmotic pressure resulting from a difference 
in concentration between the solutions inside and outside of 
the cell. The purpose of this paper is to give the results of 
some experiments that bear upon this problem and to con- 
sider to what extent we are justified in assuming the existence 
of a semi-permeable living membrane. 
This assumption that the cell is an osmotic system carries 
with it certain conclusions, for osmotic pressureis known to 
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