a similar delay of ·1 second being again due, as in the previous case, to the latent period. Thus we see that while the stimulus of the feebler intensity of ·75 was effective at 'break,' it took the stronger stimulus of 1 to induce response at 'make.'
Additive Effect of Stimulus
In the responsive tissue of the animal a single stimulus, by itself ineffective, is found to become effective on repetition. In order to test whether this holds good in the case of the plant also, I carried out the experiments which I
Fig. 22.—Stimulus of intensity ·5 became effective on being repeated four times.
shall now describe. With a given specimen I found that a single make-and-break shock of intensity ·75 was ineffective in inducing excitation. I then adjusted the secondary for intensity of ·5, and made a reed-interrupter interposed in the primary circuit give a series of make-and-break shocks till the leaf responded by a fall. The interrupting reed was adjusted to vibrate five times per second and the number of interruptions is recorded below in the usual manner. It will be seen in the record given in fig. 22 that the make-and-break stimulus, which singly was ineffective, here became effective on being repeated four times.
Desiring next to observe the effect of still further reducing the intensity of stimulus with the same specimen, I adjusted the secondary for an intensity of ·1. It must be remembered that this is the intensity of tetanisation, which
