During
these movements a coloured line, painted along the convex surface,
appeared after a time on one side, then on the concave side, then on
the opposite side, and lastly again on the convex side. The two
branches of the same tendril have independent movements. After a
tendril has spontaneously revolved for a time, it bends from the
light towards the dark: I do not state this on my own authority, but
on that of Mohl and Dutrochet. Mohl (p. 77) says that in a vine
planted against a wall the tendrils point towards it, and in a
vineyard generally more or less to the north.
The young internodes revolve spontaneously; but the movement is
unusually slight. A shoot faced a window, and I traced its course on
the glass during two perfectly calm and hot days. On one of these
days it described, in the course of ten hours, a spire, representing
two and a half ellipses. I also placed a bell-glass over a young
Muscat grape in the hot-house, and it made each day three or four
very small oval revolutions; the shoot moving less than half an inch
from side to side. Had it not made at least three revolutions whilst
the sky was uniformly overcast, I should have attributed this slight
degree of movement to the varying action of the light.
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