In short, we have given to the
string the regular spiral arrangement of a tendril caught at both
ends. The spiral contraction generally begins at the extremity which
has clasped a support; and these first-formed spires give a twist to
the axis of the tendril, which necessarily inclines the basal part
into an opposite spiral curvature. I cannot resist giving one other
illustration, though superfluous: when a haberdasher winds up ribbon
for a customer, he does not wind it into a single coil; for, if he
did, the ribbon would twist itself as many times as there were coils;
but he winds it into a figure of eight on his thumb and little
finger, so that he alternately takes turns in opposite directions,
and thus the ribbon is not twisted. So it is with tendrils, with
this sole difference, that they take several consecutive turns in one
direction and then the same number in an opposite direction; but in
both cases the self-twisting is avoided.
Summary on the Nature and Action of Tendrils.
With the majority of tendril-bearing plants the young internodes
revolve in more or less broad ellipses, like those made by twining
plants; but the figures described, when carefully traced, generally
form irregular ellipsoidal spires.
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