Studies in Permeability. 
IV. The Action of Various Organic Substances on the Per- 
meability of the Plant Cell, and its Bearing on Czapek’s 
Theory of the Plasma Membrane. 
BY 
WALTER STILES 
AND 
INGVAR J0RGENSEN. 
With fifteen Figures in the Text. 
Introduction. 
W HEN plant tissue is immersed in aqueous solutions of various sub- 
stances part of the contents of the cells diffuses out into the external 
liquid as a result of changes produced in the permeability of the cell. 
Czapek (1, 2, 3) in an investigation of the question comes to the conclusion 
that an important relation exists between the surface tension of aqueous 
solutions in contact with air and their power of producing exosmosis of the 
cell contents, and from his conclusions in this respect builds up a theory of 
the plasma membrane. He alleges that a solution will not produce 
exosmosis from a plant cell unless its surface tension against air is reduced to 
a certain definite value. Czapek determined the limiting concentration 
which is just capable of producing exosmosis from plant cells of certain cell 
substances whose presence can be easily demonstrated. The solution in this 
limiting concentration should have the same critical surface tension in- 
dependent of the substance, and in most of Czapek’s experiments he con- 
cluded that this was the case. He says, ‘ Surface active substances do not alter • 
the diosmotic properties of the plasma membrane before they act injuriously 
on the cell on account of their surface tension ’ (Czapek 3, p. i). 
Several authors have already subjected Czapek’s work to considerable 
criticism, and indeed it seems strange to attempt to explain the properties 
of a highly complex organization like the plasma membrane in terms of one 
physical property. 
A very brief consideration is required to make it clear that in the 
system produced by immersing plant tissue in an aqueous solution of 
a substance several factors must necessarily come into play. For instance, 
if we make the assumption that the change in permeability of the cell is due 
[Annals of Botany, Vol. XXXI. No. CXXI. January, 1917.] 
