366 Stiles and j0rgensen.—Studies in Permeability . /. 
of Laminaria saccharina is placed in a solution of 0*52 N NaCl, which has 
a conductivity equal to that of sea-water, the conductivity of the tissue rises 
with time approximately according to a simple exponential relation. 
From this he concludes that the change in permeability is due to a change 
of some substance in the protoplasm, either by a catalytic action of the 
sodium chloride, or by a reaction with sodium chloride in which very little 
of the salt is used. He states that a study of the temperature coefficient 
(a rise of io° C. more than doubles the rate of reaction) shows that diffusion 
of sodium chloride inwards and other salts outwards is not the determining 
cause of the progress of the reaction. But, as our experiments show, with an 
increase in permeability there is necessarily an increased rate of diffusion 
through the cell-membrane, which will of itself produce conductivity 
changes in the tissues. Moreover, when we are dealing with a complex 
system such as this, the results obtained at different temperatures require 
careful analysis, before conclusions as to the nature of the processes taking 
place can be drawn from them. 
Because the plant cell is able to absorb inorganic salts Osterhout holds 
with Loeb and Pauli that the plasma membrane is protein in nature rather 
than lipoid, and that the Quincke-Overton theory is untenable. But while 
it is now generally realized that the plasma membrane cannot be wholly 
composed of lipoid substances, there is not at present evidence justifying the 
assumption that it is protein. The cell membrane is one of the most 
important structures of the cell in regard to its life, and it seems reasonable 
to suppose that its structure is correspondingly complex. In any case a great 
deal more experimental work in regard to the permeability of the cell to 
substances necessary for the ordinary life of the plant is required, before the 
materials will be obtained for putting forward any satisfactory theory as to 
the nature of the cell membranes. 
Summary. 
The exosmosis of electrolytes from plant tissue has been examined 
in relation to the composition of different external solutions by means of 
physical chemistry methods. Within certain limits it seems reasonable to 
conclude that the rate of exosmosis is a measure of toxicity. A decrease in 
this rate when certain ions are added to solutions containing undoubtedly 
poisonous ions might be due to the same cause that produces what other 
investigators have called antagonism. In some instances we have shown 
that the phenomena are more complex than are generally assumed. We 
have emphasized the necessity of examining and analysing each case 
separately. The use of the methods of physical chemistry indicate the 
possibility of obtaining more definite information of the laws governing the 
exchange of substances between the interior and exterior of the cell. 
Botany Department, 
The University, Leeds, 
February 27, 1915. 
