388 The Movements of Plants 



climbers depend, is inherent, though undeveloped, in almost every 

 plant in the vegetable kingdom 1 ." 



In the Origin 2 Darwin speaks of the "apparent paradox, that 

 the very same characters are analogical when one class or order is 

 compared with another, but give true affinities when the members of 

 the same class or order are compared one with another." In this 

 way we might perhaps say that the climbing of an ivy and a hop are 

 analogical ; the resemblance depending on the adaptive result rather 

 than on community of blood ; whereas the relation between a leaf- 

 climber and a true tendril-bearer reveals descent. This particular 

 resemblance was one in which my father took especial delight. He 

 has described an interesting case occurring in the Fumariaceae 3 . 

 "The terminal leaflets of the leaf-climbing Fumaria officinalis are 

 not smaller than the other leaflets ; those of the leaf-climbing 

 AcUumia cirrhosa are greatly reduced ; those of Corydalis clavicu- 

 lata (a plant which may be indifferently called a leaf-climber or a 

 tendril-bearer) are either reduced to microscopical dimensions or 

 have their blades wholly aborted, so that this plant is actually in a 

 state of transition ; and finally in the Dicentra the tendrils are 

 perfectly characterized." 



It is a remarkable fact that the quality which, broadly speaking, 

 forms the basis of the climbing habit (namely revolving nutation, 

 otherwise known as circumnutation) subserves two distinct ends. 

 One of these is the finding of a support, and this is common to 

 twiners and tendrils. Here the value ends as far as tendril-climbers 

 are concerned, but in twiners Darwin believed that the act of 

 climbing round a support is a continuation of the revolving move- 

 ment (circumnutation). If we imagine a man swinging a rope round 

 his head and if we suppose the rope to strike a vertical post, the free 

 end will twine round it. This may serve as a rough model of twining 

 as explained in the Movements and Habits of Climbing Plants. 

 It is on these points — the nature of revolving nutation and the 

 mechanism of twining — that modern physiologists 4 differ from 

 Darwin. 



Their criticism originated in observations made on a revolving 

 shoot which is removed from the action of gravity by keeping the 

 plant slowly rotating about a horizontal axis by means of the instru- 

 ment known as a klinostat. Under these conditions circumnutation 

 becomes irregular or ceases altogether. When the same experiment 

 is made with a plant which has twined spirally up a stick, the process 



1 Climbing Plants, p. 205. 



2 Ed. I. p. 427, Ed. vi. p. 374. 3 Climbing Plants, p. 195. 



4 See the discussion in Pfeffer's The Physiology of Plants, Eng. Tr. (Oxford, 1906), 

 in. p. 84, where the literature is given. Also Jost, Vorlesungen fiber Pfianzenphysiologie, 

 p. 562, Jena, 1904. 



