184 MISCELLANEOUS OBJECTIONS TO THE [CHAP. VH 



thus necessarily twines round and up the support. The revolving 

 movement ceases after the early growth of each shoot. As in 

 many widely separated families of plants, single species and 

 single genera possess the power of revolving, and have thus 

 become twiners, they must have independently acquired it, and 

 cannot have inherited it from a common progenitor. Hence I was 

 ied to predict that some slight tendency to a movement of this 

 kind would be found to be far from uncommon with plants which 

 did not climb ; and that this had afforded the basis for natural 

 selection to work on and improve. When I made this prediction, 

 I knew of only one imperfect case, namely of the young flower- 

 peduncles of a Maurandia which revolved slightly and irregularly, 

 like the stems of twining plants, but without making any use of 

 this habit. Soon afterwards Fritz Miiller discovered that the 

 young stems of an Alisma and of a Linum, plants which do not 

 climb and are widely separated in the natural system, revolved 

 plainly, though irregularly ; and he states that he has reason to 

 suspect that this occurs with some other plants. These slight 

 movements appear to be of no service to the plants in question ; 

 anyhow, they are not of the least use in the way of climbing, 

 which is the point that concerns us. Nevertheless we can see that 

 if the stems of these plants had been flexible, and if under the con- 

 ditions to which they are exposed it had profited them to ascend 

 to a height, then the habit of slightly and irregularly revolving 

 might have been increased and utilised through natural selection, 

 until they had become converted into well-developed twiningspecies. 

 With respect to the sensitiveness of the foot-stalks of the leaves 

 and flowers, and of tendrils, nearly the same remarks are applicable 

 as in the case of the revolving movements of twining plants. As 

 a vast number of species, belonging to widely distinct groups, are 

 endowed with this kind of sensitiveness, it ought to be found in 

 a nascent condition in many plants which have not become 

 climbers. This is the case: I observed that the young flower- 

 peduncles of the above Maurandia curved themselves a little 

 towards the side which was touched. Morren found in several 

 species of Oxalis that the leaves and their foot-stalks moved, 

 especially after exposure to a hot sun, when they were gently and 

 repeatedly touched, or when the plant was shaken. I repeated 

 these observations on some other species of Oxalis with the same 

 result ; in some of them the movement was distinct, but was best 

 seen in the young leaves ; in others it was extremely slight. It is 

 a more important fact that according to the high authority of 

 Hofmeister, the young shoots and leaves of all plants move after 

 being shaken ; and with climbing plants it is, as we know, only 

 during the early stages of growth that the foot-stalks and tendrils 

 are sensitive. 



