It became straight again
in rather above one hour. A loop of soft thread weighing one-seventh
of a grain (9.25 mg.) was thrice tried, and each time caused the
tendril to become curved in 30 or 40 m. Half this weight produced no
effect. The long foot-stalk is much less sensitive, for a slight
rubbing produced no effect, although prolonged contact with a stick
caused it to bend. The two branches are sensitive on all sides, so
that they converge if touched on their inner sides, and diverge if
touched on their outer sides. If a branch be touched at the same
time with equal force on opposite sides, both sides are equally
stimulated and there is no movement. Before examining this plant, I
had observed only tendrils which are sensitive on one side alone, and
these when lightly pressed between the finger and thumb become
curved; but on thus pinching many times the tendrils of the Cissus no
curvature ensued, and I falsely inferred at first that they were not
at all sensitive.
Cissus antarcticus.--The tendrils on a young plant were thick and
straight, with the tips a little curved. When their concave surfaces
were rubbed, and it was necessary to do this with some force, they
very slowly became curved, and subsequently straight again.
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