424 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1914. 
one arm of a lever, V; the other is loaded with a small weight, which 
acts as a counterpoise. A long wire, W, bent at the tip, is placed at 
right angles to the lever, and serves as a writer. The tip of this 
writer touches a smoked-glass plate, which is allowed by means of a 
clockwork to fall at a definite rate. (Fig. 1.) An instantaneous 
electric shock is applied on the leaf stalk at A. The excitation will, 
after a time, be prop- 
(+) Vv agated from A to the 
responding pulvinus 
at B, inducing the 
responsive fall of the 
leaf. After a definite 
period the leaf recoy- 
ers from excitations 
and is reerected. <A 
complete curve of 
response is thus ob- 
tained in which the 
ordinate a b repre- 
sents the intensity of 
excitation, and the 
abscissa ac the period 
of complete recovery. 
(Fig.2.) Any condi- 
tion which increases 
excitability will also 
enhance the ampli- 
tude of response. 
Depression, on the 
other hand, is at- 
tended by a diminu- 
Fia. 1.—Diagrammatic representation of plant recorder. Respond- tion of response. At 
ing leaf attached to one arm of lever V, at the fulerum of which is 
attached W, the writer. G, sliding smoked glass plate for record. death the response Is 
Recording plate is lifted and allowed to drop. Ata definite position alto g ether abolished. 
during fall, R makes momentary electric contact with R’, giving 
rise to instantaneous electric shock at A. Moment of application of Thus ) by means of 
stimulus marked on recording plate by arrow a; arrival of excita- : 
tion at B causes fall of leaf, which pulls the writer toleft, describing bc. testing blows, WiCrATe 
For determination of latent period, stimulus is applied on the pul- able to make the 
annie plant itself reveal 
those invisible internal changes which would otherwise have entirely 
escaped us. 
The above is a description of the theoretical method of obtaining 
response of the plant. In practice numerous difficulties have to be 
overcome. In the case of muscle-contraction, the pull exerted 
is considerable and the friction offered by the recording surface 
constitutes no essential difficulty. In the case of plants, however, the 
