Page:Researches on Irritability of Plants.djvu/75

CHAPTER V

THE ADDITIVE EFFECT; INFLUENCE OF LOAD, TEMPERATURE, AND INTENSITY OF STIMULUS

Greater excitatory efficiency of the break-shock—Additive effect of stimulus—Quantitative relation of additive effect—Effect of load—Measurement of work under different loads—Rate of work—Thermal chamber—Effect of temperature—Effect of increasing intensity of stimulus on response.

Fig. 19.—The electric signal.

In exciting Mimosa by means of induction-currents we may employ either the make- or break-shock. It has already been stated that the break-shock is more efficient than the make-shock. That is to say, as we gradually push in the secondary nearer the primary, excitation is effected earlier with the break than with the make. I will now proceed to demonstrate this fact by experiments.

For obtaining the record I employed a writer which had a vibration-frequency of 20 times per second. The make and break of the primary current was

effected by a metronome. In the primary circuit an electrical signal (fig. 19) was also included, which marked at the base of the figure the moments when the current was made and broken. When the current is made, an up-line is described by the writer attached to the

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