QUANTITATIVE MEASUREMENT OF PERMEABILITY 
WALTER STILES AND INGVAR JORGENSEN 
OsTERHOUT (8) has recently sought to explain the divergent 
results of some of his experiments and some of our own, on the basis 
of our confusion of permeability with absorption. It seems to us 
that any confusion that may have arisen is due largely to the 
different interpretations placed by different workers on such 
expressions as permeability in relation to complex systems like the 
cell. In this paper we discuss especially the meaning of the term 
permeability when it is used in a quantitative sense, and at the 
same time we take the opportunity of dealing with the points raised 
by OsTERHOUT in regard to the relation of his results and conclusions 
with our own. The term permeability may be classed with those 
expressions in current use in plant physiology which BARNES and 
LivincsTon (4) have described as cloaks for our ignorance. We 
may vaguely understand what is meant by the permeability of a 
membrane in regard to a particular substance, that is, its capacity 
for allowing the substance to pass through the membrane, although 
we may have no very clear idea as to how this takes place. In 
the case of the living cell, however, the matter is not so simple. 
The nomenclature used in regard to the passage of substances 
into and out of the living cell has largely resulted from the work of 
De Vries on plasmolysis, and the theory derived from his results. 
It is a matter of common knowledge that as a result of the researches 
of DE VRIEs (17, 18) and PFEFFER (9, 10), the plant cell came to be 
practically universally regarded as an osmotic cell, a solution sur- 
rounded by a semipermeable membrane, the plasma membrane, 
constituting the outer layer of the protoplast. On this view the 
permeability of the plasma membrane obviously means its capacity 
for allowing a substance to pass through the membrane. As plant 
physiology has developed, however, the realization of the com- 
plexity of the systems with which the plant physiologist has to deal 
has become more and more general, and it must be admitted that 
such a simple theory as that of DE Vries will not afford a complete 
Botanical Gazette, vol. 65] [526 
