RESPONSE OF MOTILE AND GROWING ORGANS TO VARIATION OF TURGOR. I have already described (p. 40) the effects of variation of turgor on the motile pulvinus of _Mimosa_. There is a strict correspondence between the responsive movement of the leaf of _Mimosa_ and the movement due to growth, which is summarized as follows:-- (1) _An increase or positive variation of turgor induces an erection or positive response of the leaf of_ Mimosa, _and a positive variation or enhancement of the rate of growth_. (2) _A diminution or negative variation of turgor induces a fall or negative response of the leaf of_ Mimosa, _and a negative variation or retardation of the rate of growth_. EFFECT OF EXTERNAL TENSION. _Experiment 73._--The recording levers are at first so balanced that very little tension is exerted on the plant. Record of normal growth is taken of a specimen of _Crinum_. The tension is gradually increased from one gram to ten grams. The table given below shows how growth-rate increases with the tension till a limit is reached, after which there is a retardation. TABLE XV.--EFFECT OF TENSION ON GROWTH. +--------------+--------------------+ | Tension. | Rate of growth. | +--------------+--------------------+ | 0 (Normal) | 0.41 µ per second. | | 4 grams | 0.44 µ " " | | 6 " | 0.48 µ " " | | 8 " | 0.52 µ " " | | 10 " | 0.40 µ " " | +--------------+--------------------+ SUMMARY. Increase of turgor induced by irrigation enhances the rate of growth. Irrigation with warm water induces a further augmentation of the rate of growth. The latent period for enhancement of growth depends on the distance of growing region from the root. The latent period is reduced when the plant is irrigated with warm water. Artificial increase of internal hydrostatic pressure, up to a critical degree, enhances the rate of growth. A diminution or negative variation of turgor depresses the rate of growth. There is a strict correspondence between the responsive movement of the leaf of _Mimosa_, and the movement due to growth. An increase or positive variation of turgor induces an erection of positive response of the leaf of _Mimosa_, and a positive variation or enhancement of the rate of growth. A diminution or negative variation of turgor induces a fall or negative response of the leaf of _Mimosa_, and a negative variation or retardation of the rate of growth. External tension within limits, enhances the rate of growth. XIV.--EFFECT OF ELECTRIC STIMULUS ON GROWTH _By_ SIR J. C. BOSE, _Assisted by_ GURUPRASANNA DAS.