30 m.; I then turned the plant partly round, but
this made no change in the direction of the succeeding ellipse. The
next day I watched a plant similarly secured until the tendril (which
was highly sensitive) made an ellipse in a line exactly to and from
the light; the movement was so great that the tendril at the two ends
of its elliptical course bent itself a little beneath the horizon,
thus travelling more than 180 degrees; but the curvature was fully as
great towards the light as towards the dark side of the room. I
believe Dutrochet was misled by not having secured the internodes,
and by having observed a plant of which the internodes and tendrils
no longer curved in harmony together, owing to inequality of age.
Dutrochet made no observations on the sensitiveness of the tendrils.
These, whilst young and about an inch in length with the leaflets on
the petiole only partially expanded, are highly sensitive; a single
light touch with a twig on the inferior or concave surface near the
tip caused them to bend quickly, as did occasionally a loop of thread
weighing one-seventh of a grain (9.25 mg.). The upper or convex
surface is barely or not at all sensitive.
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