10 



TWINING PLANTS. 



Chap. L 



generally and strongly with twining-plants than with 

 other plants, that there must be some connexion 

 between the capacity for twining and axial twisting. 

 The stem probably gains rigidity by being twisted 

 (on the same principle that a much twisted rope is 

 stiffer than a slackly twisted one), and is thus in- 

 directly benefited so as to be enabled to pass over 

 inequalities in its spiral ascent, and to carry its own 

 weight when allowed to revolve freely.* 



I have alluded to the twisting which necessarily 

 follows on mechanical principles from the spiral 

 ascent of a stem, namely, one twist for each spire 

 completed. This was well shown by painting straight 

 lines on living stems, and then allowing them to twine ; 

 but, as I shall have to recur to this subject under 

 Tendrils, it may be here passed over. 



The revolving movement of a twining plant has 

 been compared with that of the tip of a sapling, moved 

 round and round by the hand held some way down 

 the stem ; but there is one important difference. 

 Tbe upper part of the sapling when thus moved 



five were observed to be twisted 

 in an opposite direction. The 

 Spanish chestnut is often much 

 twisted : there is an interesting 

 article on this subject in the 

 ' Scottish Farmer,' 1865, p. 833. 



* It is well known that the 

 steins of many plants occasionally 

 become spirally twisted in a 

 monstrous manner ; and after my 

 paper was read before tbe Linnean 

 Society. Dr. Maxwell Masters re- 



marked to me in a letter that 

 "some of these cases, if not all, 

 are dependent upon some obstacle 

 or resistance to their upward 

 growth." This conclusion agrees 

 with what I have said about the 

 twisting of stems, which have 

 twined round rugged supports; 

 but does not preclude the twist- 

 ing being of service to the plant 

 by giving greater rigidity to th 

 stem. 



