430 Stiles and J 0 rgensen.— Studies in Permeability. V. 
However, as we hope to deal on a later occasion both with the 
question of the action of dilute solutions and with the general behaviour of 
plant tissue towards acids, we do not propose to enter into a detailed dis- 
cussion of these results here. 
Concluding Remarks. 
In the preceding pages we have recorded the results of some pre- 
liminary experiments on the exchange of water between the plant cell and 
the surrounding medium. The chief difference between these experiments 
and most of the earlier ones on the same subject lies in the fact that the 
method employed is quantitative and the reaction is followed with time. In 
work with such complex systems as the plant physiologist has to deal with, it 
is extremely easy to draw incorrect conclusions and to refer observed effects 
to wrong causes, and this is especially the case where the course of the 
reaction with time is not followed. It is only necessary for us to refer to 
the conclusions drawn by van Rysselberghe (18) from his experiments on 
our subject, as an example of this. Thus, Miss Delf (6) has recently shown 
that van Rysselberghe’s conclusions are false, and that it would have been 
impossible for him to have drawn them if he had made measurements in his 
experiments from time to time. Again, it is only by quantitative work that 
an analysis of complex processes will ever be made and the laws under- 
lying the processes discovered. The whole history of physics and chemistry 
exemplifies this. 
By far the most important work on the subject here dealt with which 
has appeared since PfefifePs fundamental researches, is that of Miss Delf (6) 
on the effect of temperature on the passage of water out of the cell when 
slightly plasmolysed, in which the method employed was quantitative and 
sensitive and in which the change with time was followed. Her conclusion 
that the rate of passage of water out of the cell is greatly increased by rise 
of temperature agrees well with the results of the authors’ experiments, 
which show a similar effect of temperature on the rate of intake of 
water by the cell surrounded by distilled water. 
As regards the magnitude of the coefficient, it is impossible to make 
any definite statement. The actual rate of swelling depends on the previous 
history (environmental and genetic) of the tissue employed, and it is at 
least not improbable that the temperature coefficient of swelling may show 
similar variations with the previous history. For there are at least four 
different processes concerned, namely, the absorption of water by the cell 
wall, the absorption of water by the protoplasm, the passage of water into 
the vacuole, and the stretching of the cell wall, and if these are differently 
affected by temperature and also by the factors to which they are subjected 
by previous history, the temperature coefficient of swelling will depend on 
the previous history. 
