Page:Researches on Irritability of Plants.djvu/102

Rh was then effective in evoking a feeble response. The most striking fact, however, is that on the completion of recovery the specimen actually exhibited a growing contraction as an after-effect of stimulus. Thus, while at the beginning a growing condition of a-tonicity gave rise to increasing relaxation, afterwards in consequence of stimulation this state of things became reversed, and we have a growing condition of tonic contraction appearing as the after-effect of stimulus. That the tonic condition in fact became improved is shown by the large response evoked as the immediate effect of the usual stimulation.

This after-effect of a single stimulus in inducing a second contraction is signiﬁcant as showing the possibility of holding incident stimulus latent for a time, to find expression later. It heralds the phenomenon of Multiple Response, which we shall consider in a subsequent chapter.

The curious phenomenon of alternation sometimes observed in a highly excitable specimen has already been noticed (fig. 36). The characteristic peculiarity observed there was a large response followed by a small one, such alternation continuing for a time. The difference between successive responses, however, vanished after a time. With plants in a sub-tonic condition the phenomenon of alternation is also found occasionally. The characteristics here exhibited (fig. 40) are in sharp contrast to those seen in fig. 36. Here the first response is small, and the second