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