If we inquire how a petiole, a branch or flower-peduncle first became
sensitive to a touch, and acquired the power of bending towards the
touched side, we get no certain answer. Nevertheless an observation
by Hofmeister {44} well deserves attention, namely, that the shoots
and leaves of all plants, whilst young, move after being shaken.
Kerner also finds, as we have seen, that the flower-peduncles of a
large number of plants, if shaken or gently rubbed bend to this side.
And it is young petioles and tendrils, whatever their homological
nature may be, which move on being touched. It thus appears that
climbing plants have utilized and perfected a widely distributed and
incipient capacity, which capacity, as far as we can see, is of no
service to ordinary plants. If we further inquire how the stems,
petioles, tendrils, and flower-peduncles of climbing plants first
acquired their power of spontaneously revolving, or, to speak more
accurately, of successively bending to all points of the compass, we
are again silenced, or at most can only remark that the power of
moving, both spontaneously and from various stimulants, is far more
common with plants, than is generally supposed to be the case by
those who have not attended to the subject.
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