They then still retain their sensitiveness,
and can clasp a support placed BEHIND the stem. Owing to this power,
the plant is able to ascend a thin upright stick. Ultimately the two
tendrils belonging to the same petiole, if they do not come into
contact with any object, loosely cross each other behind the stem, as
at B, in fig. 7. This movement of the tendrils towards and round the
stem is, to a certain extent, guided by their avoidance of the light;
for when a plant stood so that one of the two tendrils was compelled
in thus slowly moving to travel towards the light, and the other from
the light, the latter always moved, as I repeatedly observed, more
quickly than its fellow. The tendrils do not contract spirally in
any case. Their chance of finding a support depends on the growth of
the plant, on the wind, and on their own slow backward and downward
movement, which, as we have just seen, is guided, to a certain
extent, by the avoidance of the light; for neither the internodes nor
the tendrils have any proper revolving movement. From this latter
circumstance, from the slow movements of the tendrils after contact
(though their sensitiveness is retained for an unusual length of
time), from their simple structure and shortness, this plant is a
less perfect climber than any other tendril-bearing species observed
by me.
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