or newly-grown parts act in climbing, the climbing and the growth are
entirely distinct. To this there is one exception--an instructive one, as
showing how one action passes into another, and how the same result may be
brought about in different ways--that of stems which climb by rootlets, such
as of ivy and trumpet-creeper. Here the stem ascends by growth alone,
taking upward direction, and is fixed by root-lets as it grows. There is no
better way of climbing walls, precipices, and large tree-trunks.

But small stems and similar supports are best ascended by twining; and this
calls out powers of another and higher order. The twining stem does not
grow around its support, but winds around it, and it does this by a
movement the nature of which is best observed in stems which have not yet
reached their support, or have overtopped it and stretched out beyond it.
Then it may be seen that the extending summit, reaching farther and farther
as it grows, is making free circular sweeps, by night as well as by day, and
irrespective of external circumstances, except that warmth accelerates the
movement, and that the general tendency of young stems to bend toward the
light may, in case of lateral illumination, accelerate one-half the circuit
while it equally retards the other. The arrest of the revolution where the
supporting body is struck, while the portion beyond continues its movement,
brings about the twining. As to the proximate cause of this sweeping
motion, a few simple experiments prove that it results from the bowing or
bending of the free summit of the stem into a more or less horizontal
position (this bending being successively to every point of the compass,
through an action which circulates around the stem in the direction of the
sweep), and of the consequent twining, i.e., "with the sun," or with the
movement of the hands of a watch, in the hop, or in the opposite direction
in pole-beans and most twiners. Twining plants, therefore, ascend trees or
other stems by an action and a movement of their own, from which they derive
advantage. To plants liable to be overshadowed by more robust companions,