Cuar. I. TWINING PLANTS. 7 
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 foratime. 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.) thought that the twisting of the 
axis caused the revolving movement; but it is not 
