Page:Researches on Irritability of Plants.djvu/79

56 specimen, but using the reduced stimulus-intensity of ·2. The result given in fig. 25 shows that the stimulus had to be repeated five times to become effective. We see once more in this experiment that the additive effect is strictly quantitative, and that the effective stimulation is constant under varying intensity of stimulus, being equal to the individual intensity multiplied by the number of repetition. In the

Rh

two cases here given we have a strict reaffirmation of this quantitative relation—namely, ·5 X 2 = ·2 X 5 = constant.

In the response of muscle it is found that the muscle-curve is modified by the effect of the load which it has to raise during contraction. With an increasing load the height of response undergoes a progressive diminution, but the period of recovery is at the same time correspondingly shortened. In the contractile response of Mimosa a similar phenomenon is observed. In carrying out this experiment a load was placed on the arm of the horizontal lever opposite to that of the leaf-attachment, and at an equal distance from the fulcrum. The leaf, during its contractile movement, has to lift this weight. In the first experiment of the series a load of 100 milligrammes was employed. In the second this was increased to 500 mgrms.,