Measurement of Rate of Shrinkage of Ttirgid Tissues. /. 305 
out by taking a common relative value of unity for their permeability at the 
middle point 25 0 C. We then have the appended series of values : 
..o 
5 . 10. 
1 5 °. 
20°. 
25° 
30°. 
35 ° 
40°. 
Onion 
0-36 0*44 
0*50 
o-66 
1-0 
i -7 
2-9 
5 *° 
Dandelion 
— 0*22 
0-30 
0-5° 
1*0 
1-9 
3-0 
5 '° 
Section VII. 
Critical 
Consideration 
OF 
THE 
Relation 
between Permeability and Temperature put forward by 
F. van Rysselberghe. 
The only other known published results on the exact relation between 
permeability of protoplasm to water and temperature are those brought 
forward by F. van Rysselberghe 1 in 1901. As these results differ com- 
pletely as to the effect of temperatures above 20° C. they must now be care- 
fully examined. Studies were made of the time taken to plasmolyse and to 
deplasmolyse different kinds of material, such as cylinders of elder pith, 
epidermal cells of Tradescantia , and Spirogyra. Each kind was examined 
at the temperatures set out below, and harmonious ratios for the relative 
rates of the observed processes at different temperatures were obtained. 
The ratios are appended, the rate at o° C. being taken as unity (van Ryssel- 
berghe, p. 189) : 
Temperature o°C. 6° C. 12 0 C. 16 0 C. 20° C. 25 0 C. 30° C. 
Rate 1 i*9 4-5 6-25 7*15 7-5 8 
It will be seen that above 20° C. there is practically no further increase in 
permeability, and the graphic record Fig. 1 6 copied from van Rysselberghes 
paper shows how this curve agrees broadly with our present results up to 20°, 
but differs completely in type afterwards. 
Many of his types of measurement must have been difficult to carry 
out with precision ; such as the exact time for complete plasmolysis of 
a cell, and still more so the exact time taken by such a cell to recover its 
normal state. The data provided for this type of observation do not lend 
themselves to critical analysis, but the measurements of the shortening of 
pith are recorded at several successive points of time, and it is proposed to 
consider them carefully. Long cylinders of elder pith were plasmolysed in 
strong sugar solution. The procedure was as follows : the cylinders were 
freshly cut from the plant, freed from traces of wood, and soaked for six 
hours in water at 16 0 C., during which time they expanded from 100 mm. to 
1 14 mm. The cylinders were then cut longitudinally into two half-cylinders, 
as equal as possible. One half was placed in sugar solution at o° C. as 
a control, and the other kept in sugar solution at one of the temperatures 
specified above. The cane-sugar solution used for plasmolysis was 25 per 
cent. (0-731 grm. M.). At all temperatures the half-cylinders shrank 
1 F. van Rysselberghe : Influence de la temperature sur la perm^abilite du protoplasme vivant 
pour l’eau et les substances dissoutes. Bull. Acad. Roy. de Belgique, 1901, pp. 175-221. 
