Measurement of Rate of Shrinkage of Turgid Tissues. /. 309 
temperatures, and there seem to be mechanical limitations to a quicker 
shrinkage being manifested at higher temperatures. With the weak 
subtonic solutions adopted, 0-18 grm. M. for onion and 03 grm. M. for 
dandelion, plasmolysis is not reached, contraction is comparatively slow, 
and the experimentation is confined to the strictly normal state of falling 
turgor, without actual separation of the protoplast from the cell-wall. 
A large number of records with such subtonic sugar solutions have 
been made at different temperatures. The agreement between individual 
records at the same temperature is generally good, though the absolute 
shrinkage dealt with is only o-ia mm. Fig. 13 illustrates the most extreme 
divergence observed at any one temperature. Sufficient records have been 
taken to establish that the most regular curves follow a nearly logarithmic 
course. 
The most regular medium curve of each temperature group has been 
selected as representative, and these are charted together — onion, Fig. 11, 
dandelion, Fig. 14 — all the contractions being brought to the uniform scale 
of 100 units. 
These curves show a continuously increasing rapidity of shrinkage with 
rise of temperature over the whole scale. 
Up to 35 0 C. it is found that, when perfused with water alone, the 
tissue length remains constant for a long period of time. Above 35 0 C. 
some shrinkage takes place in water alone, so that the further shrinkage 
when perfused with sugar is not quite a simple effect. The curves charted 
for these high temperatures represent sugar-shrinkage less the amount 
of water-shrinkage during the corresponding time. Such a corrected curve 
errs, if at all, on the side of being not steep enough. 
To obtain the true measure of temperature-effect from these curves in 
the charts, it must be remembered that the rate of shrinkage, as expressed 
by the slope of the curve at any point, is a product of two factors. Of these, 
one is the compressing force acting on the protoplast and causing exudation 
of water (the osmotic force of the perfused solution, plus the elastic pressure 
of the cell-wall, less the osmotic pressure of the cell-sap) ; and the other, the 
permeability of the protoplast for water at the temperature prevailing. 
The influence of the permeability factor can only be obtained from 
a set of temperature shrinkage-curves by comparing them at really 
corresponding points, that is at points where the compressing force is 
equal throughout the set. Such corresponding points are those lying 
on any one horizontal line on the chart, parallel to the abscissa-axis. 
For the three lines corresponding to 30 per cent., 30 per cent., and 
70 per cent, of the total contraction, respectively, the exact slope of every 
curve has been ascertained by measuring the values of the tangents at 
these points on a large-scale diagram. The values of these tangents, repre- 
senting the relative rates of contraction, are set out for the three series 
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