which they avoid attachment to, or winding themselves upon, the ascending
summit of the stem that bears them. This they would inevitably do if they
continued their sweep horizontally. But when in its course it nears the
parent

stem the tendril moves slowly, as if to gather strength, then C.~ stiffens
and rises into an erect position parallel with it, and C so passes by the
dangerous point; after which it comes rapidly down to the horizontal
position, in which it moves until it again approaches and again avoids the
impending obstacle.

Climbing plants are distributed throughout almost all the natural orders.
In some orders climbing is the rule, in most it is the exception, occurring
only in certain genera. The tendency of stems to move in circuits--upon
which climbing more commonly depends, and out of which it is conceived to
have been educed--is manifested incipiently by many a plant which does not
climb. Of those that do there are all degrees, from the feeblest to the
most efficient, from those which have no special adaptation to those which
have exquisitely-endowed special organs for climbing. The conclusion reached
is, that the power "is inherent, though undeveloped, in almost every
plant;" "that climbing plants have utilized and perfected a
widely-distributed and incipient capacity, which, as far as we can see, is
of no service to ordinary plants."

Inherent powers and incipient manifestations, useless to their possessors
but useful to their successors--this, doubtless, is according to the order
of Nature; but it seems to need something more than natural selection to
account for it.