After
the tendrils have come into contact with a moderately thick
cylindrical stick or with rugged bark, the several branches may be
seen slowly to lift themselves up, change their positions, and again
come into contact with the supporting surface. The object of these
movements is to bring the double-hooks at the extremities of the
branches, which naturally face in all directions, into contact with
the wood. I have watched a tendril, half of which had bent itself at
right angles round the sharp corner of a square post, neatly bring
every single hook into contact with both rectangular surfaces. The
appearance suggested the belief, that though the whole tendril is not
sensitive to light, yet that the tips are so, and that they turn and
twist themselves towards any dark surface. Ultimately the branches
arrange themselves very neatly to all the irregularities of the most
rugged bark, so that they resemble in their irregular course a river
with its branches, as engraved on a map. But when a tendril has
wound round a rather thick stick, the subsequent spiral contraction
generally draws it away and spoils the neat arrangement. So it is,
but not in quite so marked a manner, when a tendril has spread itself
over a large, nearly flat surface of rugged bark.
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