ELECTRIC PULSATION IN DESMODIUM GYRANS. 415 
direction as before, and the usual recovery took place once more 
on the return of the tissue to the condition of rest. It will 
be thus seen that (i) the electric response takes place during 
the mechanical movement of the plant; (ii) that the sign of 
electrical response is independent of the direction of motion; and 
(iii) that the intensity of response depends on the rate of 
motion. 
In Desmodium gyrans, starting from the uppermost position, 
the leaflet moves down, and having attained its maximum swing 
stops in that position for a while. The first or principal wave 
of electric response attains its height during this movement, 
and recovery takes place while the leaflet is undergoing its 
temporary rest. The latter now commences an upward move- 
ment, and the subsidiary wave of response is similarly obtained 
during this process. The mutual relation which thus exists 
between the mechanical wave and the concomitant double 
electric wave will be clearly seen from the inspection of two 
records taken simultaneously, to be given presently. 
Apparatus for taking the Record of 
Mechanical Response. 
The difficulty of the mechanical record lies in the extreme 
slenderness of the leaflets, in consequence of which the attacb- 
ment of an index is apt to produce a great constraint on their 
natural movement. This difficulty has been overcome in the 
following manner, by which it is possible to obtain the 
mechanical record with ease and accuracy. 
A lever having two unequal arms, OA and OB, is made of 
aluminium wire. It is balanced about the pivot PP’, which 
rests on frictionless bearings. The long arm has a slight 
overweight, which makes it tilt somewhat downwards. One end 
of a single cocoon-thread is attached to the tip of the leaflet by 
means of a small quantity of shellac varnish, the other end of 
the thread being fixed to the long arm of the lever. A light con- 
cave mirror C is attached to the prolongation of the pivot (fig. 8). 
From the perfect balance of the arrangement, it will be seen 
that the slightest movement of the leaflet causes a corresponding 
tilt in the lever, the pull exserted by it being negligible. A spot 
of light reflected from the mirror C gives a record of the move- 
ment of the leaflet on a magnified scale. The magnification 
