Page:Life Movements in Plants.djvu/105

Rh These difficulties were ultimately overcome from knowledge derived through systematic investigation on the relative importance of the different parts of the motor apparatus, on the immediate and after-effect of section on the excitability of the leaf, and on the rate of decay of this excitability on isolation from the plant. The experience thus gained enabled me to secure long-continued and uniform sensibility under normal conditions. It was thus possible to study the physiological effects of changing external conditions by observing the responsive variation in the isolated petiole-pulvinus preparation. I propose to deal with the different aspects of the investigation in the following order:—


 * 1) The effect of wound or section in modification of normal excitability.
 * 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