Movements and Habits of Climbing Plants | Page 5

the more rapid movements,
after the performance of the third revolution, lasted during three days
and twenty hours. The regular revolutions, from the ninth to thirty-sixth
inclusive, were effected at the average rate of 2 hrs. 31 m.; but the
weather was cold, and this affected the temperature of the room,
especially during the night, and consequently retarded the rate of
movement a little. There was only one irregular movement, which
consisted in the stem rapidly making, after an unusually slow
revolution, only the segment of a circle. After the seventeenth
revolution the internode had grown from 1.75 to 6 inches in length, and
carried an internode 1.875 inch long, which was just perceptibly
moving; and this carried a very minute ultimate internode. After the
twenty-first revolution, the penultimate internode was 2.5 inches long,
and probably revolved in a period of about three hours. At the

twenty-seventh revolution the lower and still moving internode was
8.375, the penultimate 3.5, and the ultimate 2.5 inches in length; and
the inclination of the whole shoot was such, that a circle 19 inches in
diameter was swept by it. When the movement ceased, the lower
internode was 9 inches, and the penultimate 6 inches in length; so that,
from the twenty-seventh to thirty-seventh revolutions inclusive, three
internodes were at the same time revolving.
The lower internode, when it ceased revolving, became upright and
rigid; but as the whole shoot was left to grow unsupported, it became
after a time bent into a nearly horizontal position, the uppermost and
growing internodes still revolving at the extremity, but of course no
longer round the old central point of the supporting stick. From the
changed position of the centre of gravity of the extremity, as it revolved,
a slight and slow swaying movement was given to the long horizontally
projecting shoot; and this movement I at first thought was a
spontaneous one. As the shoot grew, it hung down more and more,
whilst the growing and revolving extremity turned itself up more and
more.
With the Hop we have seen that three internodes were at the same time
revolving; and this was the case with most of the plants observed by me.
With all, if in full health, two internodes revolved; so that by the time
the lower one ceased to revolve, the one above was in full action, with
a terminal internode just commencing to move. With Hoya carnosa, on
the other hand, a depending shoot, without any developed leaves, 32
inches in length, and consisting of seven internodes (a minute terminal
one, an inch in length, being counted), continually, but slowly, swayed
from side to side in a semicircular course, with the extreme internodes
making complete revolutions. This swaying movement was certainly
due to the movement of the lower internodes, which, however, had not
force sufficient to swing the whole shoot round the central supporting
stick. The case of another Asclepiadaceous plant, viz., Ceropegia
Gardnerii, is worth briefly giving. I allowed the top to grow out almost
horizontally to the length of 31 inches; this now consisted of three long
internodes, terminated by two short ones. The whole revolved in a
course opposed to the sun (the reverse of that of the Hop), at rates
between 5 hrs. 15 m. and 6 hrs. 45 m. for each revolution. The extreme
tip thus 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