Page:Life Movements in Plants.djvu/134

104 specimen is precisely the opposite, namely, an enhancement of conductivity. I give below accounts of two typical experiments carried out with petiole-pulvinus preparation of Mimosa. Excessive stimulation in these cases was caused by injury.

Action of Injury on Normal Specimens: Experiment 36.—A cut stem with entire leaf was taken, and stimulus applied at a distance of 15 mm. from the pulvinus. From the normal record (1) in Fig. 42 the velocity of transmission was

42.—Effect of injury, depressing rate of conduction in normal specimen: (1) record before, and (2) after injury. (Dot-intervals, 0.1 sec).

found to be 18.7 mm. per sec. The end of the petiole beyond the point of application of the testing stimulus was now cut off, and record of velocity of transmission taken once more. It will be seen from record (2) that the excessive stimulus caused by injury had induced a depression in the conducting power, the velocity being reduced to 10.7 mm. per sec. Excessive stimulation of normal specimens is thus seen to depress temporarily the conducting power.

Action of Injury on Sub-tonic Specimens: Experiment 37.—I will now describe a very interesting experiment which shows how an identical agent may, on account of difference