Page:Researches on Irritability of Plants.djvu/61

38 shows in a striking manner how the speed first accelerates and then slows down.

The maximum movement is generally attained about ·5 second after the shock. The actual rate of the maximum responsive fall is here 40 mm. per second. The rate of the responsive fall is modified by various conditions:—

(1) The speed is greater under stronger stimulus. This is well seen in fig. 12, where the lower one was taken under stimulus intensity of 1, and the upper one under stimulus intensity of 4. The gentler slope of the lower curve, and

more abrupt rise of the upper, clearly show the greater speed and vigour of the responsive movement under the stronger stimulus. The curves show moreover that the amount of this responsive movement is greater under stronger stimulation.

(2) In a fatigued condition the rate of the responsive fall under constant stimulus is relatively slow. Thus in a certain experiment, where the maximum rate of fall, when fresh, was 30 mm. per second, the rate was slowed down to 20 mm. per second in consequence of fatigue. In another case the rate when fresh was 50 mm. per