Page:Researches on Irritability of Plants.djvu/103

80 large, and the difference between the pairs in the series goes on increasing. The sum of heights of pairs of successive responses remains however approximately the same. The odd numbers in the series decline continuously (1) 18·5, (3) 16, (5) 11, (7) 6; whereas the responses in the even series grow in amplitude (2) 25·5 (4) 30, (6) 33.

If the Mimosa leaf be subjected to continuous stimulation it has been found that, after the preliminary fall, it re-erects itself in spite of the stimuli which are still acting upon it. This at first sight would appear to be very perplexing, but the apparent anomaly would however disappear when we recognise the essential unity of response in the plant and the animal. A frog's muscle, under continued tetanising electric shocks, at first exhibits the normal contraction, but afterwards relaxes, in spite of the excitation to which it is being subjected (fig. 41). The difference between the normal relaxation of recovery (expansion) and this fatigue-relaxation induced under continuous stimulation, lies in the fact that in the former case response takes place on renewed stimulation, while in the latter the tissue has become