Page:Researches on Irritability of Plants.djvu/107

84 correspondingly larger and larger. This is clearly seen in fig. 42, where the successive stimulations are applied at intervals of seven minutes.

Thus on subjecting a specimen in an optimum condition to continuous stimulation, we should expect to find that the extent of contraction due to tetanisation was but little different from that due to a single stimulus. This is verified by the following pair of records (fig. 43) showing the response of a plant near optimum condition, under single stimulus and under tetanisation.

The contractile response of the pulvinus of Mimosa exhibits characteristics similar to those of the response of muscle.

Under normal conditions of the plant, and with sufficient intervening periods of rest, the responses are found to be uniform.

The responses exhibit fatigue under conditions of incomplete recovery.

The excitability of the plant in a sub-tonic condition is enhanced by the action of the stimulus itself. Under such conditions the responses exhibit a staircase increase.

The anomalous erection, after a preliminary fall of the leaf of Mimosa under continuous stimulation, is explicable on the common characteristics of response in plant and animal tissues. In both, contraction is reversed to relaxation under fatigue.