With none of the above-described species,
cultivated in pots and carefully observed, was there any permanent
bending of the petioles without the stimulus of contact. In winter,
the blades of the leaves of C. vitalba drop off; but the petioles (as
was observed by Mohl) remain attached to the branches, sometimes
during two seasons; and, being convoluted, they curiously resemble
true tendrils, such as those possessed by the allied genus Naravelia.
The petioles which have clasped some object become much more stiff,
hard, and polished than those which have failed in this their proper
function.
TROPAEOLUM.--I observed T. tricolorum, T. azureum, T. pentaphyllum,
T. peregrinum, T. elegans, T. tuberosum, and a dwarf variety of, as I
believe, T. minus.
Tropaeolum tricolorum, var. grandiflorum.--The flexible shoots, which
first rise from the tubers, are as thin as fine twine. One such
shoot revolved in a course opposed to the sun, at an average rate,
judging from three revolutions, of 1 hr. 23 m.; but no doubt the
direction of the revolving movement is variable. When the plants
have grown tall and are branched, all the many lateral shoots
revolve. The stem, whilst young, twines regularly round a thin
vertical stick, and in one case I counted eight spiral turns in the
same direction; but when grown older, the stem often runs straight up
for a space, and, being arrested by the clasping petioles, makes one
or two spires in a reversed direction.
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