424 Stiles and j0rgensen. — Studies in Permeability . V. 
It is not advisable to enter into a discussion of the meaning of these 
temperature coefficients while our analysis of the processes involved is so 
incomplete. As the rate of swelling is dependent not only on the perme- 
ability of the protoplasm to water, but also on the elasticity of the cell wall 
and probably on other factors also, as for instance permeability to substances 
dissolved in the cell sap, it is clear that at present we can do no more than 
record the fact that temperature increases the rate of swelling in the manner 
indicated. Moreover, it does not follow that tissue in which the inherited 
factors are different or which has previously been subjected to different 
external conditions will give the same values for the temperature coefficient 
of swelling as recorded here. 
(c) The Influence of Dissolved Substances on the 
Swelling of Potato . 
1 . Sodium chloride . 
It was shown by de Vries that above a certain concentration of solute, 
solutions of various substances brought about a contraction of the proto- 
plasm of the cell away from the wall. This was explained by de Vries and 
Pfeffer as due to the outer layer of the protoplast acting as a semi-perme- 
able membrane which allowed water to pass through, but which prevented 
the passage of the dissolved substance. A solution of the same osmotic 
concentration as the cell sap should produce no effect whatever, but above 
that concentration it should bring about plasmolysis. Thus, the terms 
hypotonic, isotonic, and hypertonic were introduced to describe solutions re- 
spectively lower, equal, or higher in osmotic concentration than the cell sap. 
If in the case of hypertonic solutions the cell wall should shrink to some 
extent along with the protoplast, water should be exuded and the tissue 
should lose weight. As in distilled water the cell wall stretches, so it is 
reasonable to expect it to be capable also of shrinkage, and the experiments 
of Miss Delf (6), in which the rate of shrinkage in length of tissues in such 
solutions is measured, show that this is the case. 
The following table shows the swelling and shrinkage of potato tissue 
in various strengths of sodium chloride solution. The values are given in 
terms of percentages of the original weight of the tissue : 
Table VIII. 
Swelling and Shrinkage of Potato in Sodium Chloride Solutions. 
Distilled Water. 
N 
12 
NaCl. 
N 
10 
NaCl. 
N 
8 
NaCl. 
N 
7 
NaCl. 
N 
6 
NaCl. 
Time. 
Swelling. 
Time. 
Swelling. 
Time. 
Swelling. 
Time. 
Swelling. 
Time. 
Swelling. 
Time. 
Swelling. 
hrs. 
per cent. 
hrs. 
per cent. 
his. 
per cent. 
hrs. 
per cent. 
hrs. 
per cent. 
hrs. 
per cent. 
o *57 
6*4 
4.0 
o *75 
i*8 
0*92 
o*6 
1*72 
-i*6 
1*62 
- 4-6 
3*12 
13.6 
3-28 
3.6 
3* 1 8 
i*8 
3-25 
1*2 
2*42 
- 3 *o 
2*42 
- 5-6 
6*8o 
21*80 
17.2 
22*4 
7*12 
22*03 
2*6 
2*8 
6*92 
1*2 
5-83 
7.00 
6 6 
3*25 
- 3*0 
3*20 
-6*8 
