528 BOTANICAL GAZETTE [JUNE 
investigation at present available to analyze further the behavior 
of substances in passing through the various phases or across the 
boundaries between them. Hence, when we have used the term 
permeability in a quantitative sense we mean simply the capacity 
of a substance for entering the cell from the outside, or of passing 
out from the cell into the external medium, which are the 
phenomena with which we have so far mainly dealt. Generally 
we have not used the term permeability at all in a quantitative 
sense. Wherever possible it is much better to use the terms 
absorption or exosmosis, as the case may be, which have a definite 
unmistakable meaning and whose meaning does not depend upon 
an unproved and imperfect theory as does the term permeability 
as used by some writers. 
In a paper (14) which appeared three years ago, we published 
the results of some experiments from which we concluded that the 
relation between time and absorption of hydrogen ions by potato 
cells was a logarithmic one, and that the temperature coefficient 
of this absorption was about 2.2. From this result it was pointed 
out that “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.”’ When therefore OSTERHOUT 
(8) says “it is evident, therefore, that the temperature coefficient 
observed by STILES and JéRGENSEN may be that of a chemical 
process involving the union of hydrogen ions with some constituent 
of the cell other than the plasma membrane,” so far from contra- 
dicting our statement he is merely repeating our own conclusion in 
not very different words. When, however, he continues, ‘in 
which case it would have no bearing upon the problem of the nature 
of permeability,” it would appear that he uses the term per- 
meability, not in the general sense which we regard as the only 
legitimate one in which it can be used without qualification, but 
in a restricted sense, namely, the capacity of hydrogen ions for 
passing through “the plasma membrane (or other surface).”’ 
Against this restricted use of such a commonly used term as 
permeability we would enter a protest, as it rests upon a theory 
