The tip is
slightly and permanently curved, so as to act to a limited extent as
a hook. The concave side of the tip is highly sensitive to a touch;
but not so the convex side, as was likewise observed to be the case
with other species of the family by Mohl (p. 65). I repeatedly
proved this difference by lightly rubbing four or five times the
convex side of one tendril, and only once or twice the concave side
of another tendril, and the latter alone curled inwards. In a few
hours afterwards, when the tendrils which had been rubbed on the
concave side had straightened themselves, I reversed the process of
rubbing, and always with the same result. After touching the concave
side, the tip becomes sensibly curved in one or two minutes; and
subsequently, if the touch has been at all rough, it coils itself
into a helix. But the helix will, after a time, straighten itself,
and be again ready to act. A loop of thin thread only one-sixteenth
of a grain in weight caused a temporary flexure. The lower part was
repeatedly rubbed rather roughly, but no curvature ensued; yet this
part is sensitive to prolonged pressure, for when it came into
contact with a stick, it would slowly wind round it.
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