Page:Researches on Irritability of Plants.djvu/45

22 for the excitation of the plant tissue, perfect methods of stimulation, the intensity of which can either be maintained constant or varied in a perfectly known manner. We have moreover to render the successive stimulations, and consequent scripts of the plant, a perfectly automatic process; so that the experimenter may be comparatively relieved of personal participation in the securing of the records. This will have the incomparable advantage of having no element of personal error in the results so obtained. The question of the effects of the various forms of stimulus will be dealt with in the next chapter.

In the response-records of plants, errors are introduced on account of friction of the writing-point against the recording-surface.

These errors are eliminated by the method of intermittent instead of continuous contact for the record. By employing the principle of resonance, the writer is made to vibrate to and fro at a known and definite rate. The record consists of series of dots giving deﬁnite time-intervals. The record is thus its own chronogram.