218 MISCELLANEOUS OBJECTIONS TO THE 



leaves or flowers, or these modified and converted into ten- 

 drils, are excited to bend round and clasp the touching 

 object. He who will read my memoir on these plants will, 

 I think, admit that all the many gradations in function and 

 structure between simple twiners and tendril-bearers are in 

 each case beneficial in a high degree to the species. For 

 instance, it is clearly a great advantage to a twining plant to 

 become a leaf-climber ; and it is probable that every twiner 

 which possessed leaves with long foot-stalks would have been 

 developed into a leaf-climber, if the foot-stalks had possessed 

 in any slight degree the requisite sensitiveness to a touch. 



As twining is the simplest means of ascending a support, 

 and forms the basis of our series, it may naturally be asked 

 how did plants acquire this power in an incipient degree, 

 afterward to be improved and increased through natural 

 selection. The power of twining depends, firstly, on the 

 stems while young being extremely flexible (but this is a 

 character common to many plants which are not climbers) ; 

 and, secondly, on their continually bending to all points of 

 the compass, one after the other in succession, in the same 

 order. By this movement the stems are inclined to all sides, 

 and are made to move round and round. As soon as the 

 lower part of a stem strikes against any object and is stopped, 

 the upper part still goes on bending and revolving, and 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 led to predict that some slight tendency to a 

 movement of this kind would be found to be far from uncom- 

 mon 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 afterward 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 



