Page:Life Movements in Plants.djvu/177

This page has been proofread, but needs to be validated.
MODIFYING INFLUENCE OF TONIC CONDITION
147

3 minutes. Figure 54 shows how the functional activity of the sub-tonic specimen is enhanced by stimulus, the successive responses thus exhibiting the staircase effect.


Fig. 54.
Fig. 55.

Fig. 54.—Staircase response in sub-tonic Mimosa.

Fig. 55.—Positive, diphasic and negative response under successive stimulation.

POSITIVE RESPONSE IN SUB-TONIC SPECIMEN.

Experiment 50.—A still lower degree of sub-tonicity was ensured by keeping the specimen in an isolated condition for 12 hours. Stimulus of light for 20 seconds' duration was applied at intervals of 2 minutes. In the record (Fig. 55) the first two responses, not shown, were purely positive. The third exhibited a positive A-effect, followed by the negative response D-effect. The A-effect is thus seen fully unmasked. In subsequent responses the A-effect became more and more overshadowed by the D-effect. At the third response the masking is complete and the excitatory negative response is at its maximum. The record of staircase effect (Fig. 54) also exhibits a preliminary positive twitch at the beginning of the series, which disappeared after the second response.

This article is issued from Wikisource. The text is available under Creative Commons Attribution-Share Alike 4.0 unless otherwise noted. Additional terms may apply for the media files.