Chap. 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 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.) thought that the twisting of the 

 axis caused the revolving movement ; but it is not 



