406 PROF. J. C. BOSE ON THE 
a periodic up-and-down or elliptical movement, the period varying 
from about two to four minutes. 
The excitation produced in ordinary plants by external 
stimulus was evidenced by electric responses. I was desirous 
to find out whether these automatic periodic movements, due to 
the action of internal stimuli, were attended by concomitant 
electric pulsations. 
Experimental Arrangements. 
I have shown in my previous paper (Journ. Linn. Soc., 
Bot. xxxv. (1902) p. 278) that stimulus gives rise to electric 
changes in the plant, and that an electromotive force is thereby 
induced between the excited and unexcited portions of a tissue. 
The direction of the current of response in the tissue is, normally 
speaking, from the more excited to the less excited point. If 
the plant-tissue is in the same physico-chemical condition 
throughout, the surface is iso-electric, local excitation giving rise 
to electromotive variations. If the tissue is not in the same 
physico-chemical condition, there will be a more or less per- 
manent current—the current of rest. This, however, does not 
alter the general result ; the electromotive changes due to excita- 
tion are simply superposed on the existing electromotive force. 
In order, then, to get the responsive electromotive changes 
which accompany the automatic movements of the leaflets, it 
was necessary to make one of the electric contacts at a point 
of tissue which was in a relatively resting condition ; the second 
contact being made at the place where the excitatory movement 
was atits maximum. It is to be borne in mind that the internal 
changes, to which the movement is due, take place in the 
slender petiolules to which the leaflets are attached, the latter 
serving merely as indicating flags. Acting on the considerations 
referred to above, I made one contact with the slender stalk of the 
lateral leaflet, the other being made with the common petiole. 
The contacts are securely made by means of cotton threads 
moistened with normal saline solution and connected with 
non-polarisable electrodes not shown in the figure. The 
electrodes lead to a sensitive and dead-beat galvanometer. 
The electromotive variations produced in the plant cause corre- 
sponding deflections in the galvanometer. The excursions of the 
spot of light are recorded by means of the response-recorder, 
fully described in my previous paper. We have thus contacts 
