Page:Life Movements in Plants.djvu/232
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 he 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.
Experiment 77.—The specimen was the same as had been employed in the last. experiment. After moderate stimulation due to friction it had, in the course of an hour, completely recovered its normal rate of growth of 0.18 μ per second. I now applied the stimulus of pin prick; the actual injury to the tissue due to this was relatively slight; but the retardation of growth induced by this more intense mode of stimulation was very great. With moderate mechanical friction the rate had fallen from 0.18 μ to 0.11 μ per second, i.e., to three-fifths the normal rate; in consequence of prick the depression was from 0.18 μ to 0.05 μ per second, i.e., to less than a third of the normal rate. After 15 minutes the rate recovered from 0.05 μ to 0.07 μ per second. After moderate friction the recovery was complete after an hour; but in this case the recovery after an equal interval was only three-fourths of the original, the rate being now 0.12 μ per second (Fig. 33b). I next applied the more intense stimulus caused by a longitudinal cut.