Page:Life Movements in Plants.djvu/218

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XIII.—EFFECT OF VARIATION OF TURGOR AND OF TENSION ON GROWTH


By


Sir J. C. Bose.


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 Mimosa 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. Turgor 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, be produced by withdrawal of water through plasmolysis. In order to maintain a constant terminology I shall designate an increase, as the positive, and a diminution, the negative variation of turgor.

RESPONSE TO POSITIVE VARIATION OF TURGOR.

In experimenting with Mimosa the plant was subjected to the condition of drought, water being withheld for a day. On supplying water, the leaf, after a short period, exhibited a positive 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 of Irrigation: Experiment 70.—In order to investigate the effect of enhanced turgor on growth, I took a specimen of

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