2Q4 
Delf.- — Studies of Protoplasmic Permeability by 
It will be seen that there is a much greater shrinkage with strong 
than with weak solutions, but that the contraction is easily measurable 
with the weakest solution employed. 
In dealing with plasmolysis rates at different temperatures, it is 
necessary to have some definite standard of comparison. The length of 
the pieces used varied from 28 to 30 mm. — being usually nearer 29 mm. ; 
the absolute contraction, therefore, was necessarily also variable. It 
seemed best to relate the total linear contraction observed in each ex- 
periment, therefore, to a fixed length which was taken as 100, the observed 
contractions at any point being thus expressed as percentages of the total 
contraction. The ordinates in Figs. 11, 13, 14, are of this type. 
Fig. 8. Curves comparing effect of 018 and 0-731 grm. M. concentration of sugar on the plasmo- 
ly lie contraction of onion leaves, plotted to same scale. Ordinates are divisions of scale. 
For this method it was necessary to know when the plasmolytic 
contraction in any solution had ceased, a thing almost impossible to 
judge in the case of strong solutions which gave a continuous slow con- 
traction towards the end, for many hours. In Fig. 8 the actual course 
of contraction is shown of dandelion scapes under identical conditions at 
34° C. but at different concentrations of sugar ; curve B shows part of this 
slow final shrinkage, and curve A on the same scale the slight but definitely 
ending contraction with a subtonic solution. In addition to this difficulty, 
with strong solutions there is often a slower rate of plasmolysis at the 
beginning of an experiment than after the first half-hour. This can only 
be due to some secondary factor disturbing the normal course of contrac- 
