308 Delf. — Studies of Protoplasmic Permeability by 
whereas the curves from o° to i6° C. are well separated by temperature effect, 
the curves for 20°, 25 0 , and 30° C. are practically identical. This van 
Rysselberghe regards as a true index of the temperature effect. While this 
physiological view is entirely different from that substantiated in this paper, 
it is interesting that an appearance of the same result can be got for 
dandelion scapes by our method, but only by using very strong plasmoly sing 
solutions . The interpretation of this phenomenon seems to be that there is 
an absolute upper limit to the rate at which the mechanical tissue-system of 
cell-walls can collapse and shrink. If so, then however fast and suddenly 
the protoplasts are crushed by the strong osmotic pressure of 25 per cent, 
cane-sugar, the cell-wall reticulum — which is what is measured — cannot 
follow at a rate above a certain limit. In van Rysselberghe’s experiments that 
limit seems to be reached with 0-731 grm. M. cane-sugar at 20° C. A great 
part of each contraction curve must consist of the ‘ settling down ’ phase, 
and over this permeability of protoplasm has no control. 
The moral to be drawn from these considerations is that, for demon- 
strating the full accelerating effect of temperature, it is essential to employ 
plasmolysing solutions which are subtonic , so that the force exerted 
on the cell is slight. At low temperatures the absolute rate of contraction 
will be very slow, but it will then be possible to demonstrate the continued 
accelerating effect of high temperatures without the records being cut 
off by some mechanical limiting factor which has nothing to do with 
permeability of protoplasm. 
Section VIII. Summary and Conclusions. 
The method of following the rate of shrinkage of strips of tissue bathed 
in solutions that tend to plasmolyse them has been developed as a means of 
measuring the permeability of protoplasm to water. 
Hollow leaves of onion and hollow scapes of dandelion have been 
selected for investigation because they present on their inside a natural 
surface of uncuticularized thin-walled cells. 
Apparatus has been employed by which a current of liquid flows 
continuously through a short cylinder (30 mm.) of the material under 
investigation. By suitable arrangements a solution of sugar can be instan- 
taneously substituted for the water-current and vice versa without any 
alteration of temperature. 
An ‘ optical lever ’ is connected to the upper end of the tissue cylinder 
and alterations in length of 0-003 mm. (one part in ten thousand) are made 
evident. 
The change of protoplasmic permeability with temperature between 
5 0 C. and 42 0 C. has been carefully studied by this technique. 
Such experiments cannot be satisfactorily carried out with strong 
plasmolysing solutions, as the shrinkage is then very quick at even moderate 
