One of the tendrils which thus became bent in
31 seconds, had been touched two hours previously and had coiled into
a helix; so that in this interval it had straightened itself and had
perfectly recovered its irritability.
To ascertain how often the same tendril would become curved when
touched, I kept a plant in my study, which from being cooler than the
hot-house was not very favourable for the experiment. The extremity
was gently rubbed four or five times with a thin stick, and this was
done as often as it was observed to have become nearly straight again
after having been in action; and in the course of 54 hrs. it answered
to the stimulus 21 times, becoming each time hooked or spiral. On
the last occasion, however, the movement was very slight, and soon
afterwards permanent spiral contraction commenced. No trials were
made during the night, so that the tendril would perhaps have
answered a greater number of times to the stimulus; though, on the
other hand, from having no rest it might have become exhausted from
so many quickly repeated efforts.
I repeated the experiment made on the Echinocystis, and placed
several plants of this Passiflora so close together, that their
tendrils were repeatedly dragged over each other; but no curvature
ensued.
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