opposed by an equivalent weight. We find that in these three cases there is very little difference in the time taken by the leaf to complete the fall (Fig. 34). [Illustration: FIG. 34.--Effect of weight on rapidity of fall. N, without action of weight; W, with weight helping; and A, with weight opposing.] It has been shown that the presence or absence of the 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. ACTION OF CHEMICAL AGENTS. 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. The chemical solution may be applied directly to the pulvinus, or it may be absorbed through the cut end, the absorption being hastened by hydrostatic pressure. The normal record is taken after observing precautions which have already been mentioned. The reaction of a given chemical agent is demonstrated by the changed character of the record. The effect of the drug is found to depend not merely on its chemical nature, but also on the dose. There is another very important factor--that of the tonic condition of the tissue--which is found to modify the result. The influence of this will be realised from the account of an experiment to be given presently, where an identical agent is shown to produce diametrically opposite effects on two specimens, one of which was in a normal, and the other in a sub-tonic, condition. The experiments described below relate to reactions of specimens in a normal condition. [Illustration: FIG. 35.--Stimulating action of hydrogen peroxide.] _Hydrogen Peroxide: Experiment 27._--This reagent in dilute solution exerts a stimulating action. Normal records, were taken after long-continued application of water on the pulvinus. The peroxide, as supplied by Messrs. Parke Davis & Co., was diluted to 1 per cent., and applied to the pulvinus; this gave rise to an enhancement of response. Re-application of water reduced the amplitude to the old normal value (Fig. 35). [Illustration: FIG. 36.--Incomplete recovery under the action BaCl_{2} and transient restoration under tetanisation at T.]