of this curve gives the amplitude of the movement, and the horizontal distance measures the corresponding time. The up-line here, a b, indicates the responsive fall, and the descending line, b c, the gradual erection, due to recovery. The responsive movement was initiated within an exceedingly short time after the application of stimulus—in this case an electrical shock—and the fall was completed also within a relatively short period. In a record which will be given later, taken on a faster-moving plate, these characteristics will be seen better. The recovery, however, is a slow process, the earlier part being comparatively quick and becoming slower towards the end. The entire recovery is here seen to require 12 minutes.
If we were able to apply a stimulus of exactly identical intensity at regular and suitable intervals, and if the physiological condition of the responding tissue remained constant, then we should obtain a series of responsive twitches which would be practically identical. But if the physiological condition were to undergo any change, under environmental conditions, then the record would give us indications of that internal change, otherwise entirely beyond our power of scrutiny. Thus if the plant were to become depressed, the amplitude of the pulse would undergo a diminution. If on the other hand its excitability should be enhanced, that fact would be indicated by an increase in the amplitude of the response.
The mere amplitude of the twitch, however, affords only a broad indication of the physiological condition of the tissue. There are many factors the effects of which find expression in subtler changes of the response-curve. One agency, for instance, will make the plant more alert. This is at once reflected at that part of the curve which corresponds to the Latent Period. This becomes shorter. The ascent of the curve will also be more abrupt. Another agency will induce, let us say, a contrary change. Different agencies, similarly, will bring about definite changes in the contracting and relaxing portions of the curve. The
