In Anguria the lower surface of the tendril, after it has
wound round a stick, forms a coarsely cellular layer, which closely
fits the wood, but is not adherent; whilst in Hanburya a similar
layer is adherent. The growth of these cellular out-growths depends,
(except in the case of the Haplolophium and of one species of
Ampelopsis,) on the stimulus from contact. It is a singular fact
that three families, so widely distinct as the Bignoniaceae,
Vitaceae, and Cucurbitaceae, should possess species with tendrils
having this remarkable power.
Sachs attributes all the movements of tendrils to rapid growth on the
side opposite to that which becomes concave. These movements consist
of revolving nutation, the bending to and from the light, and in
opposition to gravity, those caused by a touch, and spiral
contraction. It is rash to differ from so great an authority, but I
cannot believe that one at least of these movements--curvature from a
touch--is thus caused. {38} In the first place it may be remarked
that the movement of nutation differs from that due to a touch, in so
far that in some cases the two powers are acquired by the same
tendril at different periods of growth; and the sensitive part of the
tendril does not seem capable of nutation.
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