Page:Life Movements in Plants.djvu/232

202 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 irritahle than others. The persistence of after- etl'ect of irritation in retardation of growth will he demon- strated in the following experiments, where the stimulus employed was more intense.

A prick causes an intense. excitation in Jlimosa. I tried the ell'ect of this form of stimulation on responsive varia- tion in growth.

Experiment 77.——'l‘he specimen was the same as had been employed in the last. experiment. After moderate stimula- tion due to friction it had, in the course of an hour, com- pletely recovered its normal rate of growth of 0'18 )1; per second. I now applied the stimulus of pin prick; the aetual injury to the tiss'ie due to this was relatively slight; but the retardation of growth induced by this more intense mode of stimulation was very great. With mode -ate mechanical friction the rate havl fallen from 0'18 p. to 0'11 a per second, i.c., to three-fifths the normal rate: in consequence of prick the depression was from 0°18 ,u to 0‘05 ,1; per Second, 5.9., to less than a third of the normal etc. After 15 minutes the rate recovered from 0'05 )1; to 0'07 p. per second. After mode 'ate. friction the recovery was complete after an hour; but in this :ase the. recovery after an equal interval was only three-fourths of the original, the rate being new 0'12. a per second (Fig. 331)). I next applied the more. intense stimulus caused by a longitudinal cut.