Stiles and J0rgensen.—Studies in Permeability . I. 365 
ment of the ions in the reverse direction. When strong solutions are used, 
an excess of endosmosis is to be expected. This we have observed our- 
chloride and calcium chloride and of mixtures of the two. 
Although in dilute solutions of equal strength the relative amount 
of exosmosis might be regarded as a measure of toxicity, it cannot be 
assumed that the curves of conductivity of the external solution can so be 
considered. However suggestive they may be in this respect, it is necessary 
to remember the complexity of action possible in the solution. The 
different rates of absorption of different ions and the diffusing out of 
substances from the plant which react with the external solution are both 
possible phenomena. As regards the second of these we may cite the case 
of ferric chloride, in which there results in the external solution conditions 
which cause the precipitation of ferric hydroxide, while in the control 
solutions of the same composition no such precipitation takes place. 
In solutions containing ferric chloride also, the rapid absorption of the 
hydrogen ions present no doubt influences the conductivity curve exceed¬ 
ingly. It is possible that the same explanation may account for the 
apparent antagonism between copper and aluminium indicated by the con¬ 
ductivity curves of solutions containing both these ions. No such explana¬ 
tion seems possible of the results in the case of mixtures of lithium with 
potassium and calcium, but in view of the facts of the case of copper and 
iron mixtures, we feel that some other reason may account for the form of 
the curves rather than the apparent one of an antagonism between the two 
metallic ions. 
Nevertheless we feel the results obtained by the method here used 
suggest a means of obtaining much information relative to the relations 
between the electrolytes in the cell, the cell membranes, and the external 
solution. Having regard to the different results obtained in different cases, 
it is evident that each case will have to be worked out separately. It seems, 
moreover, quite probable that the different cases of antagonism so far 
recorded are due in many instances to different underlying causes. 
As far as our experiments go, there appears to be no qualitative 
difference between the behaviour, in respect to permeability to electrolytes, 
of slices of potato tuber and the roots of uninjured bean plants. This 
suggests that the methods are suitable for general use, and that general 
permeability phenomena are being dealt with. 
It becomes clear from the experiments here described that the 
processes involved when plant tissue is immersed in a solution of one salt or 
a mixture of salts are complex. It thus seems to us that many of the 
generalizations that have been made by earlier writers, often from single 
cases, are premature. For example, Osterhout finds that when tissue 
