Page:Life Movements in Plants.djvu/117

Rh little difference in the time taken by the leaf to complete the fall (Fig. 34).

It has been shown that the presence or absence of the

34.—Effect of weight on rapidity of fall. N, without action of weight; W, with weight helping; and A, with weight opposing.

upper half of the pulvinus makes practically no difference in the period of fall; it is now seen that the weight exerts comparatively little effect. We are thus led to conclude that in determining the rapidity of fall, the factors of expansive force of the upper half of the pulvinus and the weight of the leaf are negligible compared to the active force of contraction exerted by the lower half of the pulvinus.

In connection with this subject it need hardly be said that the various experiments which I had previously carried out with the intact plant can also be repeated with the isolated preparation. I will only give here accounts of experiments which are entirely new.