The rate
does not seem governed by the thickness of the shoots: those of the
Sollya are as thin and flexible as string, but move more slowly than
the thick and fleshy shoots of the Ruscus, which seem little fitted
for movement of any kind. The shoots of the Wistaria, which become
woody, move faster than those of the herbaceous Ipomoea or
Thunbergia.
We know that the internodes, whilst still very young, do not acquire
their proper rate of movement; hence the several shoots on the same
plant may sometimes be seen revolving at different rates. The two or
three, or even more, internodes which are first formed above the
cotyledons, or above the root-stock of a perennial plant, do not
move; they can support themselves, and nothing superfluous is
granted.
A greater number of twiners revolve in a course opposed to that of
the sun, or to the hands of a watch, than in the reversed course,
and, consequently, the majority, as is well known, ascend their
supports from left to right. Occasionally, though rarely, plants of
the same order twine in opposite directions, of which Mohl (p. 125)
gives a case in the Leguminosae, and we have in the table another in
the Acanthaceae.
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