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. [Illustration: FIG. 70.--Effect of irrigation: D. record of growth under drought, C. acceleration after irrigation with cold water, H. enhanced acceleration on irrigation with warm water. (_S. Kysoor_)] _Method of Irrigation: Experiment 70._--In order to investigate the effect of enhanced turgor on growth, I took a specimen of _Kysoor_ which had been dug up with an attached quantity of soil; this latter was enclosed in a small bag. The plant was then securely clamped and fixed on a stand. This precaution was taken to prevent upward displacement by the swelling of the soil in flower pot of the plant under irrigation. The specimen was then subjected to a condition of drought, water being withheld for a day. The depressed rate of growth is seen in record (Fig. 70). Ordinary cold water was now applied at the root, the effect of which is seen in record C. Finally the record (H) was obtained after irrigation with tepid water. It will be seen that the spaces between successive dots, representing magnified growth at intervals of ten seconds, are very different. While a given elongation took place under drought in 19 × 10 seconds, a similar lengthening took place, after irrigation with cold water, in 13 × 10 seconds, and after irrigation with warm water in 3 × 10 seconds. Irrigation with warm water is thus seen to increase the rate of growth more than six times.