Measurement of Electrical Conductivity. 233 
plant. It is only by immersion of the electrodes in the tissues that 
a good contact can in any way be assured, and many plant organs 
are too small to admit of any larger electrodes than platinum wire. 
It has moreover to he observed that in the case of immersion the 
larger the electrode the greater will be the quantity of wounded 
tissue. . . . 
The value of so-called unpolarisable electrodes is very douhtful 
in the case of living tissue as polarisation, effects are probably not 
only produced at the metallic electrodes, but everywhere in the 
plant where there is a surface of junction of two immiscible phases. 
Further in the case of the direct current there will take place 
electrolysis of substances inside the plant resulting in the formation 
of substances inside the cell. There will be also a probable increase 
in concentration of electrolytes about the electrodes; and not an 
increase in concentration of electrolytes only: it is probable that 
colloidal substances and other non-electrolytes will also be trans¬ 
ported to the electrodes (electrokinesis). 1 It is probably due to 
such changes as these that a continuous direct current as small as 
10 microamperes will often kill a plant in a few hours. 
It is possible however that the method of using a direct current 
may be of use in preliminary experiments, especially when the 
action under consideration produces an effect on the conductivity 
that is the reverse of that produced by the electrode and other 
effects of the direct current. Some preliminary experiments of the 
authors may serve to indicate this. 
The general result of the complications at the electrodes is to 
produce a rather regular and rapid increase in the resistance, which 
is slower the greater the E. M. F. used (provided of course the 
original resistance is the same). This is indicated by the following 
curves (Fig. I). 2 
When a stem with a direct current passing through it is 
chloroformed the result is a rise in conductivity as is indicated by 
the following curve (Fig. 2). There can be no doubt of the general 
result of the action under consideration as both the electrode effects 
and the presence of the non-electrolyte chloroform would favour a 
change of the conductivity in the opposite direction. 
It may also be possible to use the method if the E. M. F. used 
and the resistance are both large, when it is only necessary to use the 
current momentarily to take a galvanometer reading, as has been 
done by Stone. 
1 See, e.g., Bernstein (2). I 
* Cf. Poliacci (36), 
