196 MISCELLANEOUS OBJECTIONS TO THE [Chap. VII 



to a highly complex pollinium, admirably adapted for transports! 

 by insects ; nor will he deny that all the gradations in the several 

 species are admirably adapted in relation to the general structure 

 of each flower for its fertilisation by different insects. In this, and 

 in almost every other case, the enquiry may be pushed further 

 backwards ; and it may be asked how did the stigma of an ordinary 

 flower become viscid, but as we do not know the full history of any 

 one group of beings, it is as useless to ask, as it is hopeless to 

 attempt answering, such questions. 



We will now turn to climbing plants. These can be arranged in 

 a long series, from those which simply twine round a support, to 

 those which I have called leaf-climbers, and to those provided with 

 tendrils. In these two latter classes the stems have generally, but 

 not always, lost the power of twining, though they retain the power 

 of revolving, which the tendrils likewise possess. The gradations 

 from leaf-climbers to tendril-bearers arc wonderfully close, and 

 certain plants may be indifferently placed in either class. But in 

 ascending the series from simple twiners to leaf-climbers, an impor- 

 tant quality is added, namely sensitiveness to a touch, by which 

 means the foot-stalks of the leaves or flowers, or these modified 

 and converted into tendrils, 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, afterwards to be 

 improved and increased through natural selection. The power of 

 twining depends, firstly, on the stems whilst young being extremely 

 flexible (but this is a character common to many plants which ar& 

 not climbers) ; and, secondly, on their continually bending to all 

 points cf 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 

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

 still goes on bending and revolving, and thus necessarily twines 

 round and up the support. The revolving movement jeases after 



