240 Walter Stiles and Ingvar Jorgensen. 
Pig. 5 will give an idea of the general arrangement. The frequency 
of the waves was of the order 10 6 -10 7 . By comparing this damping 
effect with that produced by electrolytes of various concentrations, 
Hober determines the internal conductivity of the cell. 
In later experiments better results were obtained by measuring 
the damping effect when the electrolyte or cell-suspension was 
introduced into the capacity or into a small capacity in parallel 
with the main one. In the latest development of the method the 
damping electrolyte was placed in parallel with the self-induction, 
and was contained in a glass tube with platinum electrodes. 
Hober’s measurements indicate that the internal conductivity 
of the cells examined is much greater than the conductivity 
measured by Kohlrausch’s method. The internal conductivity is 
not altered by the addition of the non-electrolyte saponin, whereas 
the addition of this substance increases the conductivity as 
measured by Kohlrausch’s method. This indicates that the cell- 
surface must constitute an obstacle to the diffusion of the ions, i.e., 
there must be a plasma-membrane, which before the addition of the 
saponin is only to a certain extent permeable to the ions. 
Hober’s work has been done with suspensions of blood 
corpuscles and with animal tissues. It would be interesting to see 
what would be the result of the application of his methods to plant 
physiology. 
Conclusion. 
Prom these pages it will be seen that the use of ele«trical 
conductivity methods in plant physiology is still only in its 
preliminary experimental stage. Having regard to the results 
which have so far been obtained by its means it seems likely that 
with further development of methods, electrical conductivity will 
afford a convenient and comparatively simple means of investigating 
certain classes of problems in plant physiology. 
The University. 
Leeds. 
25th February , 1914. 
