SPIBATj TWI5ETIS. 5 



speciadc to watcli the long slioot sweeping, night and day, tbia 

 grand circle in search of some object round which to twine. 



If we take hold of a growing sapling, we can of course bend it 

 so as to malie its tip describe a circle, like that performed by the 

 tip of a spontaneously revolving j^lant. 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 

 Avhich is iippermost 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 op- 

 posite course to the Hop, becomes t^visted in an opposite direction. 



Hence it is not surprising that Hugo von Mohl (S. 105, 108, 

 &c.) thought that the twisting of the axis caused the revolving 

 movement, I cannot fully understand how the one movement is 

 supposed to cause the other; but it is scarcely possible that the 

 twisting of the axis of the Hop three times could have caused 

 thirty-seven revolutions. Moreover, the revolving movement 

 commenced in the young internode before any twisting of the 

 axis could be detected ; and the internode of a yotmg Siphomeria 

 or Lecontea revolved during several days, and became twisted 

 only once on its own axis. But the best evidence that the 

 twisting does not cause the revolving movement is afforded by 

 many leaf-climbing and tendril-bearing plants (as Pisum sativum^ 

 Uchinocj/sfis lobata^Bignonia capreolata^ Eccrcmocmyus «ca5er, and 

 with the leaf-climbers, Solanum jasminoides and various species 

 of Clematis), of which the internodes are not regularly twisted, 

 but which regularly perform, as we shall hereafter see, revolving 

 movements like those of true twining-plants. Moreover, accord- 

 ing to Palm (S. 30,95) and Mohl (S. 149), and Ldon*, internodes 

 may occasionally, and even not very rarely, be found which are 



* Bull. Bot. Soc. de France, torn. v. 1858, p. 356, 



