300 BOTANICAL GAZETTE [APRIL 
is brought about by either opening or closing shocks from an induc- 
tion coil, but the former are much more effective than the latter. 
The feeble effect of closing shocks is shown by the fact that when as 
many as 100 of these were applied to leaves at intervals of 15 seconds, 
the coil being at position o (see table I), the leaves showed no sign 
of response. When the closing shocks were followed by opening 
shocks, the leaves responded to two of the latter as if nothing had 
preceded them. In another case two dry cells were used in the 
primary circuit, and the leaf closed on the 21st closing shock. Con- 
tinuous current from a dry cell failed to cause closure. 
EFFECT OF COMBINING STIMULI OF TWO FoRMs.—As has been 
shown, leaves kept at 15°C. usually respond to two marked bend- 
ings of the sensitive hairs. A series of such plants was stimulated first 
by a single contact and then by an electric shock of such strength that 
two of these would be required to cause closure if used alone. These 
plants usually responded on the first electrical stimulus, while in two 
control series, in one of which only contact stimuli were used and in 
the other only electrical stimuli, they usually responded on the second 
stimulus. Table IV represents these three series. 
TABLE IV 
STIMULATION OF SENSITIVE HAIR BY MECHANICAL AND ELECTRICAL STIMULI 
SERIES II SERIES I 
SERIES HAre STIMULATED ONLY | Harr STIMULATED = 
Har spies BY ONE MECHANICAL CONTACT BY OPENING SHOCKS OF | BY MECHANICAL CO 2 
OLLOWED BY OPENING SHOCKS THE SAME INTENSITY AS TACTS SIM T : 
THOSE OF SERIES I THOSE OF SERIES 
Crehalesee carro 
Number of shocks required for No. Bil No. of 
i lete cl shoc ‘ contacts re- 
Experiment complete closure Experiment Experiment quired for for 
ee number iy number 
— ‘lectri ae 
ical) Electrical Total clos — 
bh ae aerate at I I 2 . ; : 2 
Riki oes ss I I 2 fe “ = 2 
Sore was I I 2 3 3 3 2 
eee G es 1 2 3 4 : 4 2 
5 PUES he ara rr i I 2 5 Fi 5 3 
eee aon eee wr 1 ieee 
The results given in table IV seem to show that stimuli of different 
forms produce a similar internal effect, and that the leaves respone, 
as has already been pointed out, only with the accumulation of @ 
certain amount of this effect. 
