From the series of results that have been given above, it will be seen that employing very different methods of turgor variation, the rate of growth, within limits, is enhanced by an increase of turgor. A diminution or negative variation of turgor, on the other hand, brings about a retardation or negative variation in the rate of growth. We should, in this connection, bear in mind the fact that, growth is dependent on protoplasmic activity, and the variation of turgor itself is also determined by that activity.
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 " " |