The petioles of the perfect leaves of
Tropaeolum tricolorum, as well as the tendril-like filaments of the
plants whilst young, ultimately move towards the stem or the
supporting stick, which they then clasp. These petioles and
filaments also show some tendency to contract spirally. The tips of
the uncaught leaves of the Gloriosa, as they grow old, contract into
a flat spire or helix. These several facts are interesting in
relation to true tendrils.
With leaf climbers, as with twining plants, the first internodes
which rise from the ground do not, at least in the cases observed by
me, spontaneously revolve; nor are the petioles or tips of the first-
formed leaves sensitive. In certain species of Clematis, the large
size of the leaves, together with their habit of revolving, and the
extreme sensitiveness of their petioles, appear to render the
revolving movement of the internodes superfluous; and this latter
power has consequently become much enfeebled. In certain species of
Tropaeolum, both the spontaneous movements of the internodes and the
sensitiveness of the petioles have become much enfeebled, and in one
species have been completely lost.
CHAPTER III.
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