XV.—EFFECT OF MECHANICAL STIMULUS ON GROWTH
By
Sir J. C. Bose.
Amongst tho various stimuli which induce excitation in .llimusa may be mentioned the irritation caused by rough contact, by prick, or wound. Friction causes mode 'atc stimu- lation, from which the oxcitated pulvinus recovers within a short limo. But. a prick or a cut induces a far more in- it‘IlHt‘ and persistent excitation; the recovery becomes pro- t'acicd, and the wounded pulvinus remains Contracted for a long period.
I shall now describe the eti'ect of mechanical irritation on growth. For moderate stimulus, I employ rough con- tact. or friction; more intense stimulation is caused by a prick or a cut.
EFFECT OF MECHANICAL IRRITATION.
[drpminmzl 76.—~In this experiment, I took a peduncle ul' Zuphgfltnlhm, which had a normal rate of growth of 0'18 it per second. I then caused mechanical irritation by rubbing the surface with a piece of card-board. The mechanical stimulation was found to have caused a retardation of growth, the depressed rate being 0'11 ,1. per second, or three-tit'ths the normal rate. As this particular mode of stimulation was very moderate, the normal of rate growth was found to be restored after a short period of rest. After 15
