Climbing Plants 387 



His work on climbing plants was his first sustained piece of work 

 on the physiology of movement, and he remarks in 1864 : "This has 

 been new sort of work for me 1 ." He goes on to remark with some- 

 thing of surprise, " I have been pleased to find what a capital guide 

 for observations a full conviction of the change of species is." 



It was this point of view that enabled him to develop a broad 

 conception of the power of climbing as an adaptation by means of 

 which plants are enabled to reach the light. Instead of being com- 

 pelled to construct a stem of sufficient strength to stand alone, they 

 succeed in the struggle by making use of other plants as supports. 

 He showed that the great class of tendril- and root-climbers which 

 do not depend on twining round a pole, like a scarlet-runner, but 

 on attaching themselves as they grow upwards, effect an economy. 

 Thus a Phaseolus has to manufacture a stem three feet in length to 

 reach a height of two feet above the ground, whereas a pea " which 

 had ascended to the same height by the aid of its tendrils, was but 

 little longer than the height reached 2 ." 



Thus he was led on to the belief that twining is the more ancient 

 form of climbing, and that tendril-climbers have been developed 

 from twiners. In accordance with this view we find leaf-climbers, 

 which may be looked on as incipient tendril-bearers, occurring in 

 the same genera with simple twiners 3 . He called attention to the 

 case of Maurandia semperflorens in which the young flower-stalks 

 revolve spontaneously and are sensitive to a touch, but neither 

 of these qualities is of any perceptible value to the species. This 

 forced him to believe that in other young plants the rudiments of 

 the faculty needed for twining would be found — a prophecy which 

 he made good in his Power of Movement many years later. 



In Climbing Plants he did little more than point out the remark- 

 able fact that the habit of climbing is widely scattered through the 

 vegetable kingdom. Thus climbers are to be found in 35 out of the 

 59 Phanerogamic Alliances of Lindley, so that "the conclusion is 

 forced on our minds that the capacity of revolving 4 , on which most 



1 Life and Letters, in. p. 315. He had, however, made a beginning on the movements 

 of Drosera. 



2 Climbing Plants (2nd edit. 1875), p. 193. 

 ■ Loc. cit. p. 195. 



4 If a twining plant, e.g. a hop, is observed before it has begun to ascend a pole, it will 

 be noticed that, owing to the curvature of the stem, the tip is not vertical but hangs over 

 in a roughly horizontal position. If such a shoot is watched it will be found that if, for 

 instance, it points to the north at a given hour, it will be found after a short interval 

 pointing north-east, then east, and after about two hours it will once more be looking 

 northward. The curvature of the stem depends on one side growing quicker than the 

 opposite side, and the revolving movement, i.e. circumnutation, depends on the region of 

 quickest growth creeping gradually round the stem from south through west to south 

 again. Other plants, e.g. Phaseolus, revolve in the opposite direction. 



25—2 



