In the first-described species, the tendrils
resemble in shape a bird's foot, and they are of no service to the
stem in spirally ascending a thin upright stick, but they can seize
firm hold of a twig or branch. When the stem twines round a somewhat
thick stick, a slight degree of sensitiveness possessed by the
petioles is brought into play, and the whole leaf together with the
tendril winds round it. In B. unguis the petioles are more
sensitive, and have greater power of movement than those of the last
species; they are able, together with the tendrils, to wind
inextricably round a thin upright stick; but the stem does not twine
so well. B. Tweedyana has similar powers, but in addition, emits
aerial roots which adhere to the wood. In B. venusta the tendrils
are converted into elongated three-pronged grapnels, which move
spontaneously in a conspicuous manner; the petioles, however, have
lost their sensitiveness. The stem of this species can twine round
an upright stick, and is aided in its ascent by the tendrils seizing
the stick alternately some way above and then contracting spirally.
In B. littoralis the tendrils, petioles, and internodes, all revolve
spontaneously.
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