Page:Life Movements in Plants.djvu/119

RESPONSE OF PETIOLE-PULVIN US PREPARATION 89 were taken after long-continued application of water on the pulvinus. The peroxide, as supplied by Messrs. Parke Davis & Co., was diluted to 1 per cent., and applied to the pulvinus; this gave rise to an enhancement of response. Re-application of water reduced the amplitude to the old normal value (Fig. 35). Barium Chloride : Eacperiment 28.-The action of this agent is very characteristic, inducing great sluggishness in recovery. The preparation had been kept in 1-per cent. solution of this substance for two hours. After this the first response to a given test-stimulus was taken ; the response was only moderate, and the recovery incomplete. The sluggishness was so great that the next stimulation, represented by a thick dot (Fig. 36), was ineffective. Tetanising electric shock at T, not only brought about FIG. 36.-Incomplete recovery under the action of BaCl, and transient restoration under tetanisation at T. response, but removed for the time being the induced sluggishness. This is seen in the next two records, which were taken under the old test-stimulus. There is now an enhanced response and a complete recovery. Beneficial effect of tetanisation disappeared, however, on the cessation