Page:Researches on Irritability of Plants.djvu/138

Rh All this takes place during the continuance of one pressure of the handle. During the descent of the plate, stimulation due to instantaneous break-shock takes place at the definite moment corresponding to the stimulation mark.

Electric connections are appropriately made with the plant by means of threads moistened in dilute saline solution. One electrode of the secondary coil is thus connected with the stem of the specimen: the moistened thread in connection with the other electrode is lightly wound round the pulvinus. It is sometimes preferable, for reasons previously explained, to make this contact with

glycerin. The connections are so made that the current of the break-shock enters by the stem and leaves by the pulvinus, the latter being thus the kathode. We shall understand later the reason of this, in as much as the kathode is the point of excitation.

I now describe the record of an experiment (fig. 67) carried out in summer for the purpose of determining the latent period in a specimen of Mimosa. Stimulus was applied at the point marked by the vertical line, and the upper of the two records was the first taken. The vibrating-recorder employed had been tuned to exactly 100 vibrations per second; successive dots therefore represent intervals of