made a circle of above 5 feet (or 62 inches) in diameter and 16 feet
in circumference, travelling at the rate of 32 or 33 inches per hour.
The weather being hot, the plant was allowed to stand on my study-
table; and it was an interesting spectacle to watch the long shoot
sweeping this grand circle, night and day, in search of some object
round which to twine.

If we take hold of a growing sapling, we can of course bend it to all
sides in succession, so as to make the tip describe a circle, like
that performed by the summit of a spontaneously revolving plant. By
this movement the sapling is not in the least twisted round its own
axis. I mention this because if a black point be painted on the
bark, on the side which is uppermost when the sapling is bent towards
the holder's body, as the circle is described, the black point
gradually turns round and sinks to the lower side, and comes up again
when the circle is completed; and this gives the false appearance of
twisting, which, in the case of spontaneously revolving plants,
deceived me for a time. The appearance is the more deceitful because
the axes of nearly all twining-plants are really twisted; and they
are twisted in the same direction with the spontaneous revolving
movement. To give an instance, the internode of the Hop of which the
history has been recorded, was at first, as could be seen by the
ridges on its surface, not in the least twisted; but when, after the
37th revolution, it had grown 9 inches long, and its revolving
movement had ceased, it had become twisted three times round its own
axis, in the line of the course of the sun; on the other hand, the
common Convolvulus, which revolves in an opposite course to the Hop,
becomes twisted in an opposite direction.

Hence it is not surprising that Hugo von Mohl (p. 105, 108, &c.)