2. The change of excitability after immersion in water. 3. Quantitative determination of the rate of decay of excitability in an isolated preparation. 4. Effect of amputation of the upper half of pulvinus. 5. Effect of removal of the lower half. 6. Influence of the weight of leaf on rapidity of responsive fall. 7. The action of chemical agents. 8. Effect of “fatigue” on response. 9. The influence of constant electric current on recovery. 10. The action of light and darkness on excitability. The isolated petiole-pulvinus preparation is made by cutting out a portion of the stem bearing a single lateral leaf. The four diverging sub-petioles may also be cut off. In order to prevent rapid drying the specimen has to be kept in water. Preparations made in this way often appeared to have lost their sensibility. I was, however, able to trace this loss to two different factors: first, to the physiological depression due to injury caused by section, and, second, to the sudden increase of turgor brought on by excessive absorption of water. I shall now proceed to show that the loss of sensibility is not permanent, but is capable of restoration. EFFECT OF WOUND OR SECTION IN MODIFICATION OF NORMAL EXCITABILITY. In connection with the question of effect of injury, it is to be borne in mind that after each excitation the plant becomes temporarily irresponsive and that the excitability is fully restored after the completion of protoplasmic recovery. A cut or a section acts as a very intense stimulus, from the effect of which the recovery is very slow. If the stem be cut very near the leaf, the excitation of the pulvinus is very intense, and the consequent loss of excitability becomes more or less persistent. But if the stem be cut at a greater distance, the transmitted excitation is less intense, and the cut specimen recovers its excitability within a moderate time. I have also succeeded in reducing the excitatory depression by previously benumbing the tissue by physiological means. The isolated specimen can be made still more compact by cutting off the sub-petioles bearing the leaflets; the preparation now consists of a short length of stem of about 2 cm. and an equally short length of primary petiole, the motile pulvinus being at the junction of the two. [Illustration: FIG. 30--The Resonant Recorder, with petiole-pulvinus preparation. (From a photograph.)]