36 
PROFESSOR B. SANDERSON ON THE ELECTROMOTIVE 
propagation ; for such inequality would not account for the effect produced by changing 
the seat of excitation. We must suppose that, independently of any difference in 
physiological activity which may exist between the lobes, the electrical disturbance is 
more intense in those parts of the leaf which are nearest to the seat of excitation than 
in those which are more distant from it. This being admitted, and account being 
taken of the complicated arrangement of the electromotive structures concerned, the 
incongruity of the results need no longer surprise us. 
Symmetrical contacts on the under surface , opposite the space between the sensitive 
hairs (fig. 13).—The same considerations apply to this case as to that in which the leaf 
is led off from the upper surface; but inasmuch as the under surface presents no 
appreciable difference of structure, whereas in the upper we have to do with the 
sensitive hairs, the prospect of obtaining congruous results is not so hopeless. It will 
be sufficient to refer to one or two experiments made during the autumn of 1880, 
in which the galvanometer and rheotome were used for comparison of the excitatory 
effects. 
Fig. 13. 
Leaf led off by symmetrical contacts on under surface of lobes. 
The first leaf used for the purpose was one in which symmetrical results could 
hardly be expected. It was a large well-grown leaf which contained the remains of a 
digested fly; and when, after having been excited an equal number of times on either 
side, it was allowed to close, the incurvature of the left lobe was much greater than 
that of the right. This leaf was excited electrically (the exciting contacts, x, being on 
the internal surface) and led off symmetrically, the electrodes touching the external 
surface exactly opposite the trigone on either side, the fixed electrode being on the 
right side. The rheotome gave the following result, the period of closure being 
0 * 2 " 
x On left lobe. 
x On right lobe. 
M. 
F. 
At 0-4”. 
-37-5 
+ 50 
At 0-6" .. 
- 9-0 
-*-41 
At 0-8". 
+ 33’0 
+ 40 
