Stiles and Jergensen.—Shi dies in Permeability. II. 617 
But it has been shown by van’t Hoff and subsequent workers that the 
rate of many chemical reactions is doubled or trebled by a rise of io°C. 
In the realm of plant physiology such a rise has been shown by F. F. 
Blackman in the case of carbon-assimilation in the leaf. The study of 
the effect of temperature on the absorption of the hydrogen ion would 
seem to indicate that this absorption is controlled by some chemical action 
in the cell, and is not the result of simple diffusion through the plasma- 
membrane, or of mere adsorption by the cell protoplasm. 
That the numbers obtained experimentally show that the rate of the 
reaction depends merely on the temperature coefficient k , and the con- 
lime in hoars 
Fig. 4. For explanation see text. 
centration of the acid indicates that the quantity of the substance with 
which the acid reacts, presumably the plasma-membrane, or some part 
of it, remains constant during the first few hours of the reaction, as it does 
not influence the rate of reaction. This suggests that either the absorbing 
substance is present in such large quantity as compared with the acid that 
the amount changed is small in comparison with the total amount, or 
that the substance formed as a result of the absorption is broken down 
again almost as soon as formed. Such a view of the plasma-membrane is 
held by Pauli and Sziics who regard the entrance of ions into the cell 
as due to the reversibility of such a reaction between ions and the plasma- 
S s 3 
