When a tendril has caught a yielding object, this is sometimes
enveloped and still further secured by the spiral folds, as I have
seen with Passiflora quadrangularis; but this action is of little
importance.
A far more important service rendered by the spiral contraction of
the tendrils is that they are thus made highly elastic. As before
remarked under Ampelopsis, the strain is thus distributed equally
between the several attached branches; and this renders the whole far
stronger than it otherwise would be, as the branches cannot break
separately. It is this elasticity which protects both branched and
simple tendrils from being torn away from their supports during
stormy weather. I have more than once gone on purpose during a gale
to watch a Bryony growing in an exposed hedge, with its tendrils
attached to the surrounding bushes; and as the thick and thin
branches were tossed to and fro by the wind, the tendrils, had they
not been excessively elastic, would instantly have been torn off and
the plant thrown prostrate. But as it was, the Bryony safely rode
out the gale, like a ship with two anchors down, and with a long
range of cable ahead to serve as a spring as she surges to the storm.
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