38 
PROFESSOR B. SANDERSON ON THE ELECTROMOTIVE 
the neighbourhood of the seat of excitation than at a distance from it. No other 
explanation would account for the results. 
Rate of propagation of the excitatory disturbance. —The only certain method of 
determining the rate of transmission of the excitatory change in Dionsea consists in 
measuring the interval of time after excitation at which the electrical effect first 
becomes appreciable, by a series of observations in which a leaf, led off as in the funda¬ 
mental experiment, is excited alternately in the neighbourhood of the leading off 
electrodes, and at a corresponding part of the opposite lobe. In such an experiment 
the interval of time between excitation and effect in the one case will be greater than 
in the other by a fraction of a second. That fraction, multiplied by the distance 
in millims, will give the rate per second in millims. 
In our former paper we attempted to arrive at a conclusion on the subject by a 
method which we now know to be inapplicable. I will first refer to certain experi¬ 
ments which were made on this principle in the Kew Laboratory in 1878, for the 
purpose of confirming the statements contained in our former paper (1876). A 
plant was placed in the chamber at 30° C., and led off as above stated. The 
excitatory variation on the electrometer scale was — 12 followed by -J- 10. The leaf 
was excited by touching the sensitive hairs, alternately on opposite sides, the time of 
excitation and that of response being determined by the method referred to in Part II. 
During the period of observation the temperature rose to 37° C. The observations 
were made in four series, in which the means of the time-intervals between excitation 
and response were as follows :— 
1. Excitation of the hairs of the same side.0*08^ 
2. „ „ „ „ opposite side .... 0‘28" 
3. „ ,, „ „ same side.0T16" 
4. ,, ,, „ „ opposite side .... (T243" 
In another leaf the experiment was made first at the temperature of the room, 
afterwards at that of the chamber 32° C. Six observations gave 
1. 
Excitation of the hairs of the same side 
temp. 18° . 
. 0T0 
2. 
>> 
33 
33 
,, opposite side. 
„ 18° • 
. 0-27 
3 . 
33 
>3 
„ same side 
„ 32° . 
. 0‘05 
4. 
)? 
3) 
33 
„ opposite side 
„ 32 ° . 
. 0'12 
5. 
>> 
S3 
33 
„ same side 
o 
QO 
i— i 
. 0’43 
6 . 
y 3 
„ opposite side 
3, 18° . 
. 078 
Here the excitation was by induction shocks, the external surface being punctured 
by fine electrodes for the purpose. This observation shows the combined effect of 
temperature and local diminution of excitability. The influence of the latter is still 
more strikingly shown in the following series, the temperature throughout being 
i8° a 
