352 Stiles and j0rgensen.—Studies in Permeability. /. 
tissue is used, as for example, potato tuber, if the tissue is immersed in 
a weak solution exosmosis takes place from the living cells, and so reduces 
the conductivity of the cell-sap, while in a strong solution we may expect 
absorption. Hence changes in conductivity of living tissue in such a case 
as this would depend very largely on the concentration of the external 
solution. 
Again, where higher plants are concerned, none of the methods in use 
have to do with the extremely dilute solutions such as one is concerned with 
in the actual soil solution absorbed by higher plants. Osterhout has sug¬ 
gested that calcium in the soil is useful to the plant in antagonizing the 
harmful effect of other salts ( 16 ), but, as he himself points out elsewhere ( 14 ), 
below a certain concentration none of the ordinary ‘ nutrient 5 ions are 
poisonous, and in the soil these ions are present in extremely dilute solution 
(Cameron, 4 ). 
In the present paper an account is given of a contribution towards 
an analysis of the action of salts on plant cells, in which we deal chiefly 
with the relations between the external solution and the exosmosis of 
electrolytes. 
We do not intend to apply the results obtained to any interpretation of 
the functions or the structure of the plasma membrane, but to give an idea 
of the complexity of the problems involved, and to advocate the use of the 
methods of physical chemistry. 
In using the methods of physical chemistry, one can get a better idea 
of the kinetics of the actions involved, than in the ordinary methods in 
general use in botanical and agricultural operations, and there is more hope 
of getting light shed on the complexity of the processes, but it is most 
necessary to beware of assuming results mechanically in all cases because 
a line of argument appears correct in one case. Examples of this we shall 
present in the part dealing with the results of experiments. 
Methods. 
We have attempted, in these experiments, to obtain some idea of the 
relations existing between plant tissue and a solution surrounding it, by 
examination of the changes in electrical conductivity of the latter. If 
a substance is absorbed from its solution by plant tissue without producing 
any change in the plasma membrane, it is to be expected that the electrical 
conductivity of the solution will be lowered, while if the plasma-membrane 
is altered by the substance in such a way that its permeability to electro¬ 
lytes is increased, a more rapid diffusion out from the cells into the solution 
may be expected, and if the concentration of the external solution is low, 
compared with that of the electrolytes in the cell-sap, the conductivity may 
be expected to rise. 
