It thus
dragged the shoot which bore the tendril towards the stick; and as
the tendril continually tried to revolve, a fourth branch was brought
into contact. And lastly, from the spiral contraction travelling
down both the main stem and the branches, all of them, one after
another, were ultimately brought into contact with the stick. They
then wound themselves round it and round one another, until the whole
tendril was tied together in an inextricable knot. The tendrils,
though at first quite flexible, after having clasped a support for a
time, become more rigid and stronger than they were at first. Thus
the plant is secured to its support in a perfect manner.
LEGUMINOSAE.--Pisum sativum.--The common pea was the subject of a
valuable memoir by Dutrochet, {27} who discovered that the internodes
and tendrils revolve in ellipses. The ellipses are generally very
narrow, but sometimes approach to circles. I several times observed
that the longer axis slowly changed its direction, which is of
importance, as the tendril thus sweeps a wider space. Owing to this
change of direction, and likewise to the movement of the stem towards
the light, the successive irregular ellipses generally form an
irregular spire.
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