Page:Researches on Irritability of Plants.djvu/106

Rh relaxation, not at first sight very different from the response-curve due to a single stimulus. There would nevertheless be an actual difference, inasmuch as the resulting contraction under tetanisation would, on account of additive effect, be greater than that caused by a single stimulus. After the apparent recovery, due to fatigue-reversal under tetanisation, however, the excitability, as already shown, is temporarily abolished; whereas after the normal recovery from a single stimulus, excitability is fully restored.

The typical case, the detailed consideration of which led us to these conclusions, was that of a plant which was in a somewhat sub-tonic condition. Had the plant been in the optimum condition to start with, then following the same line of reasoning we should expect that the curve of tetanisation would be modified in a definite way. Referring back to fig. 35, which gives successive records of a highly excitable specimen, we find in this instance that the very first stimulus evoked the maximum response, and that the subsequent responses exhibited fatigue. There is not here, to begin with, any staircase effect, nor are the contractions additive, the initial response being the greatest possible. On increasing the frequency of stimulation we should, after the first maximum response, obtain the phasic variation due to fatigue. The successive contractile responses would thus appear smaller and smaller, their respective recoveries being Rh