Page:Researches on Irritability of Plants.djvu/59

36 point, we shall call the Apex Time. The pulvinus remains for a short time in its contracted condition.

Third and lastly, recovery of the pulvinus from the effect of stimulus begins to take place, with consequent re-erection of the leaf. This process of recovery is very much slower than the responsive fall. While the responsive fall is a matter of a few seconds only, the re-erection or recovery requires several minutes. This recovery, again, is at first rapid and at the end relatively slow.

Quantitative measurements of these different phases may, as we shall see, be derived from the response-curve itself. In obtaining these, there are two elements to be measured—namely, the extent and the rate of movement. The amplitude or height of the curve gives a measure of the amount of movement. Magnification or reduction of the record results, as we have seen, from two elements of adjustment—namely, the ratio between the horizontal arm of the lever and the length of the recorder, and the ratio between the distance of thread-attachment from the pulvinus and the entire length of the leaf.

In the record given in fig. 12 the length of the vibrating recorder was 10 cm. and the thread-attachment with the leaf was made with the horizontal arm of the lever at a distance of 5 cm. from the fulcrum rod. The magnification of the writing-lever was therefore 2. The total length of the responding leaf was 9 cm. But the thread-attachment to the horizontal lever was made at a point on the petiole 3 cm. from the pulvinus. The responsive movement of that particular point on the petiole was therefore reduced to one-third the movement of the tip of the leaf. Thus we have a reduction to one-third brought about by the selection of the point of attachment on the petiole, and a magnification of two, due to the writing-lever. The record obtained represents in this case the actual movement of the tip of the leaf, reduced to two-thirds.

As regards the time-measurements of the responsive