164 TENDRIL-BEARERS. Cuar. IV. 
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 pro- 
tects 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 along range of cable ahead to serve 
as a spring as she surges to the storm. 
When an unattached tendril contracts spirally, the 
spire always runs in the same direction from tip to 
base. A tendril, on the other hand, which has caught 
a support by its extremity, although the same side is 
concave from end to end, invariably becomes twisted 
in one part in one direction, and in another part in the 
opposite direction; the oppositely turned spires being’ 
separated by a short straight portion. This curious 
