Page:Researches on Irritability of Plants.djvu/7

viii ideal methods of attacking problems in the life of plants, the realisation of which would make a great advance in physiological investigation.

It would also be desirable to discard, if possible, the troublesome method of obtaining record by photography, which necessitates work in a dark room; in this connection it should be remembered that subjection of the plant to darkness introduces complications by modifying its normal excitability. For these reasons, another requirement which it is necessary to fulfil is the devising of some simple and direct method of obtaining the record. And in order that the results obtained should not be influenced by any personal factor, it would be further desirable that the plant attached to the recording apparatus should be automatically excited by stimulus absolutely constant, should make its own responsive record, going through its own period of recovery, and embarking on the same cycle over again without assistance at any point on the part of the observer.

The difficulties encountered in realising these ideal requirements appeared at first to be insurmountable. In the records of response serious errors occurred as regards amplitude and time-relations, owing to the friction of the writing lever against the recording surface. As an extreme instance of this, in recording the rhythmic movement of the leaflets of Desmodium the very slight friction which the smoked-glass surface offered was enough to stop the pulse-record.

After many attempts, I was at last successful in overcoming all obstacles by the device of the Resonant and Oscillating Recorders. Taking the very difficult test of direct record of the rhythmic movements of Desmodium leaflets, it will be found that the pulsations recorded in this book not only gave accurate measure of the amplitude and period, but also the absolute rate of movement during any phase of their autonomous response. Again, in the matter of accurate measurement of short intervals of time required for the determination of the latent period and velocity of transmission of excitation, I have shown the possibility