Their outer surfaces
are highly sensitive; for when lightly rubbed with a twig, they
became perceptibly curved in 4 m. and greatly curved in 7 m. In 7
hrs. they became straight again and were ready to re-act. The
tarsus, for the space of one inch close to the toes, is sensitive,
but in a rather less degree than the toes; for the latter after a
slight rubbing, became curved in about half the time. Even the
middle part of the tarsus is sensitive to prolonged contact, as soon
as the tendril has arrived at maturity. After it has grown old, the
sensitiveness is confined to the toes, and these are only able to
curl very slowly round a stick. A tendril is perfectly ready to act,
as soon as the three toes have diverged, and at this period their
outer surfaces first become irritable. The irritability spreads but
little from one part when excited to another: thus, when a stick was
caught by the part immediately beneath the three toes, these seldom
clasped it, but remained sticking straight out.
The tendrils revolve spontaneously. The movement begins before the
tendril is converted into a three-pronged grapnel by the divergence
of the toes, and before any part has become sensitive; so that the
revolving movement is useless at this early period.
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