Page:Life Movements in Plants.djvu/218



The movements of leaves of: sensitive plants are caused by variation of turgor in the pulvinus induced by stimulus. The down movement or negative reSponse of .llinmm is caused by a diminution or negative variation of turgor, while the erection or positive response is brought about by an increase, or positive. variation of turgor.

We shall now investigate the change induced in a growing organ in the rate of growth by variation of turgor. 'l‘urgor may be increased by enhancing the rate of ascent of sap or by an artificial increase of internal hydrostatic pressure. A diminution of turgor may, on the other hand, he produced by withdrawal of water through plasmolysis. In order to maintain a constant terminology I shall desig- nate an increase, as the positive, and a diminution, the, negative variation of turgor.

lu experimenting with Jlinmsa. the plant was subjected to the eoudition of drought,. water being withheld for a day. On supplying water, the leaf. after a short period, exhibited a nesitive or erectile movement (Expt. 12). The delay was evidently due to the time taken by the water absorbed by root to reach the responding organ.

Method «gl'II'I'I'gttttoii : h‘.r1n'rinzent 70.—-—Iu order to investigate the etl'eet et' enhancint turgor on growth, I took a Specimen 0f