Leaf-climbers are, moreover, intermediate in many respects between
twiners and tendril-bearers. Eight species of Clematis and seven of
Tropaeolum were observed, in order to see what amount of difference
in the manner of climbing existed within the same genus; and the
differences are considerable.
CLEMATIS.--C. glandulosa.--The thin upper internodes revolve, moving
against the course of the sun, precisely like those of a true twiner,
at an average rate, judging from three revolutions, of 3 hrs. 48 m.
The leading shoot immediately twined round a stick placed near it;
but, after making an open spire of only one turn and a half, it
ascended for a short space straight, and then reversed its course and
wound two turns in an opposite direction. This was rendered possible
by the straight piece between the opposed spires having become rigid.
The simple, broad, ovate leaves of this tropical species, with their
short thick petioles, seem but ill-fitted for any movement; and
whilst twining up a vertical stick, no use is made of them.
Nevertheless, if the footstalk of a young leaf be rubbed with a thin
twig a few times on any side, it will in the course of a few hours
bend to that side; afterwards becoming straight again.
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