Permeability 237 
of the initial length. Although greater contractions were obtained 
in the stronger sucrose solutions, it was found almost impossible 
to decide how much of this was to be attributed to plasmolysis, 
and how much to the after-shrinkage of the cell walls. On this 
account weaker solutions, “ subtonic,” that is, diluter than isotonic, 
were used for the crucial experiments, the actual concentrations 
chosen being such that the contractions produced after the tissue 
had been allowed to swell to equilibrium in pure water were suffi¬ 
ciently large to be measured satisfactorily with the apparatus em¬ 
ployed, while a definite end-point was reached in about two hours. 
The solutions which fulfilled these conditions were 0-18 M sucrose 
for onion leaves and 0-3 M for dandelion scapes. 
With the subtonic solutions employed the shrinkage was found 
to follow an approximately logarithmic course. Miss Delf states 
that ‘'with great care in the choice of material and in repeating the 
same experimental conditions, there was a certain amount of varia¬ 
tion in the rate of plasmolysis at the same temperature. At medium 
temperatures, therefore, it was usual to perform several experiments 
under the same conditions, and to select the ones which gave the 
curve of approximately logarithmic form.” This selection of certain 
curves appears a weakness in Miss Delf’s work, for as the rejected 
experiments were conducted with the same care and under the same 
conditions as the selected experiments, the form of the time-shrink¬ 
age curves does not seem an adequate ground for selecting some and 
rejecting others. 
At ‘ temperatures above that of the laboratory complications 
occur. These are (1) a contraction resulting from the effect of pro¬ 
longed high temperature, probably on account of the escape of water 
from the cells as a result of increased exosmosis of solutes from the 
cell sap at high temperatures, and (2) an expansion resulting probably 
from the entry of sucrose into the cell. Up to 35 0 C. in the case of 
the dandelion scape, and up to 36° C. in the onion leaf, it was found 
to be unnecessary to apply any correction on account of these 
complications, but above this temperature the shrinkage drte simply 
to the presence of the sub tonic solution at the higher temperature was 
obtained by subtracting the shrinkage resulting in distilled water 
at the higher temperature from the total shrinkage actually observed. 
From the shrinkage-time curves obtained by Miss Delf the rates 
of contraction at 30, 50 and 70 per cent, of the total contraction 
were calculated for the temperatures employed in the experiments, 
and the rates for temperatures between 5 0 and 40° C. found by inter- 
