PROPERTIES OP THE LEAP OP DIORAEA. 
23 
polar parts, affecting them in the same way as in nerve, so that whatever may be 
the nature of the action in the two cases, the phenomena scarcely admit ot being 
distinguished from each other, as may be seen from the following experiments made 
in the Kew Laboratory in July, 1878. 
A leaf was led off at the points / and m and/' m! in the diagram (fig. 11). The 
negativity of the attached to the free end of the leaf required O’Ol D. to compensate 
it, which was expressed by a deflection of 27 scale of the galvanometer. Between the 
two led off surfaces of the petiole there was a difference of 0'006 D., the leaf end 
being negative to the other. These measurements having been made, the contacts 
Pig. 11. 
Diagram of experiment as to extra polar-influence of voltaic currents. Tlie strong arrows 
indicate the direction of the derived current; the weak arrows that of the current deter¬ 
mined by it in the leaf. tEB.—The reverser should be turned the other way. 
f and m were led off to the galvanometer, while f' and m were connected with 
the compensator. The compensator was then reversed so as to conduct a current into 
the petiole opposite to that which would have been required to compensate it—in the 
same direction, therefore, as the natural difference—and the slide was pushed along 
until the needle of the galvanometer was brought to zero. The slide was then at a 
position indicating -f-0‘024 D. 
I have since endeavoured to determine the relation between the remarkable extra 
