The enhancement of the rate of growth on irrigation with cold water took place after seventy seconds. The interval will obviously depend on the distance between the root by which the water is absorbed and the region of growth. It will further depend on the activity of the process of the ascent of sap. The time interval is greatly reduced when this activity is in any way increased. Thus the responsive growth elongation after application of warm water was very much quicker; in the case described it was less than 20 seconds. With regard to application of warm water, the variation of temperature should not be too sudden; it should commence with tepid, and end with warm water. _Sudden_ application of hot water brings about certain complications due to excitatory effect. As regards the persistence of after-effect of a single application of warm water, it should be remembered that the absorbed water gradually cools down. In an experiment with a peduncle of _Zephyranthes_ the growth under partial drought was found to be 0.04 µ per second; application of warm water increased the growth rate to 0.20 µ per second. After 15 minutes the growth rate fell to 0.13 µ per second; and after an hour to 0.08 µ per second. It will be noted that even then the rate was twice the initial rate before irrigation. TABLE XII.--EFFECT OF IRRIGATION. +---------------+---------------------------+------------------+ | Specimen. | Condition of Experiment. | Rate of growth. | +---------------+---------------------------+------------------+ |_Kysoor_ |Dry soil |0.21 µ per second.| | |Irrigation with cold water |0.30 µ " " | | |Irrigation with warm water |1.33 µ " " | |Peduncle of |Dry soil |0.04 µ " " | |_Zephyranthes_ |Irrigation with warm water |0.20 µ " " | +---------------+---------------------------+------------------+ EFFECT OF ARTIFICIAL INCREASE OF INTERNAL HYDROSTATIC PRESSURE. Increased turgor was, next, artificially induced by increase of internal hydrostatic pressure. _Experiment 71._--The plant was mounted water-tight in the short limb of an U-tube, and subjected to increased hydrostatic pressure by increasing the height of the water in the longer limb. Table XIII shows how increasing pressure enhances the rate of growth till a critical point is reached, beyond which there is a depression. This critical point varies in different plants. TABLE XIII.--EFFECT OF INCREASED INTERNAL HYDROSTATIC PRESSURE (_Kysoor_).