That the
movements of leaves and cotyledons which do not sleep come within the class
of circumnutating movements cannot be doubted, for they are closely similar
to those of hypocotyls, epicotyls, the stems of mature plants, and of
various other organs. Now, if we take the simplest
[page 410]
case of a sleeping leaf, we see that it makes a single ellipse in the
twenty-four hours, which resembles one described by a non-sleeping leaf in
every respect, except that it is much larger. In both cases the course
pursued is often zigzag. As all non-sleeping leaves are incessantly
circumnutating, we must conclude that a part at least of the upward and
downward movement of one that sleeps, is due to ordinary circumnutation;
and it seems altogether gratuitous to rank the remainder of the movement
under a wholly different head. With a multitude of climbing plants the
ellipses which they describe have been greatly increased for another
purpose, namely, catching hold of a support. With these climbing plants,
the various circumnutating organs have been so far modified in relation to
light that, differently from all ordinary plants, they do not bend towards
it.
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