_Experiment 76._--In this experiment, I took a peduncle of _Zephyranthes_, which had a normal rate of growth of 0.18 µ 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 µ per second, or three-fifths 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 minutes the rate became 0.14 µ per second; after an hour the recovery was complete, the rate being now 0.18 µ per second, the normal rate before stimulation (Fig 74_a_). We shall presently see that not only is the growth rate greatly depressed under intense stimulation, but the period of recovery also becomes very much protracted. I have often been puzzled by the fact, that specimens apparently vigorous exhibited little or no growth, after attachment to the recorder. After waiting in vain for an hour, I had to discard them for others with equally unsatisfactory results. One of these specimens happened to be left attached to the recorder overnight, and I was surprised to find that the specimen, which had shown no growth the previous evening, was now exhibiting vigorous growth after being left to itself for 12 hours. I then realised that the temporary abolition of growth must have been due to the irritation of somewhat rough handling during the process of mounting and attachment of the specimen to the recorder. In the matter of mechanical stimulation, some specimens are more irritable than others. The persistence of after-effect of irritation in retardation of growth will be demonstrated in the following experiments, where the stimulus employed was more intense. EFFECT OF WOUND. A prick causes an intense excitation in _Mimosa_. I tried the effect of this form of stimulation on responsive variation in growth.