PROPERTIES OP THE LEAF OP DIOMA. 
21 
whether the change produced by excitation, if any, is in relation with the excitatory 
process itself. 
The first observation on this subject was made in September, 1879, in the course of 
experiments made for other purposes. A leaf was led off as shown in the diagram 
(fig. 9)—that is, by opposite contacts, of which the internal corresponded to the space 
between the distal and proximal sensitive hairs, the surfaces of contact being as large as 
possible. The leaf was placed in the chamber at 38° C., and was kept there for an 
hour, at the end of which the two surfaces were nearly equipotential, there having 
been previously a difference of —(TOO7 D. During a period of 40 minutes the leaf 
was subjected to a series of 16 excitations, in the course of which the difference rose 
Pig. 10. 
Leading off: electrodes on rigid lobe. Exciting electrodes on left. 
from —}- 0*001 D. to + 0*0114 D. After a second series of 15 excitations it rose to 
+ 0*032 D. In another leaf, observed the following day by the same method, the 
difference increased during 14 excitations from +0*0084 D. to +0*046 D. In a 
third the initial difference was +0*0036 D. During the following two hours the leaf 
was excited 28 times at nearly equal intervals. At the end of the first half hour the 
difference was +0*0082 D. ; at the end of the second, +0*118 D.; of the third, 
+ 0*0178 D.; of the fourth, +0*024 D. In the first of these three observations the 
leaf was excited mechanically—that is, by touching the sensitive hairs of the opposite 
lobe. In the second and third, single opening induction currents were led through the 
opposite lobe by pointed electrodes which penetrated its external surface. 
It was not until the next year that the opportunity offered of further investigating 
this effect. A leaf was led off for the purpose, as in the previous experiment, by 
opposite contacts, the electrode being applied to the internal surface between the 
distal and proximal sensitive hairs. To ensure a more satisfactory initial determina¬ 
tion of the cross difference in the, unexcited leaf, it was introduced into the chamber 
(of which the temperature was 20° C.) the day before, in order that any accidental 
difference due to initial changes at the surface of contact might be got rid of. The 
