190 CONCLUDING BEMAKKS. Ca^P. V. 



from branch to bramcli, and securely ramble over a 

 wide, sun-lit surface. 



Thediyisions containing twining plants, leaf-climbers, 

 and tendril-bearers graduate to a certain extent into 

 one another, and nearly all have the same remarkable 

 power of spontaneously revolving. Does this grada- 

 tion, it may be asked, indicate that plants belonging 

 to one subdivision have actually passed during the 

 lapse of ages, or can pass, from one state to the other ? 

 Has, for instance, any tendrU-bearing, plant assumed 

 its present structure without having previously existed 

 as a leaf-climber or a twiner ? If we consider leaf- 

 climbers alone, the idea that they were primordially 

 twiners is forcibly suggested. The internodes of 

 all, without exception, revolve in exactly the same 

 manner as twiners ; some few can still twine well, and 

 many others in an imperfect manner. Several leafr 

 climbing genera are closely allied. to other genera 

 which are simple twiners. It should also be observed, 

 that the possession of leaves with sensitive petioles, 

 and with the consequent power of clasping an object, 

 would be of comparatively little, use to a plant, 

 unless associated with revolving internodes, by which 

 the leaves are brought into contact with a support ; 

 although no doubt a scrambling plant would be apt, 

 as Professor Jaeger has remarked, to rest on other plants 

 by its leaves. On the other hand, revolving inter- 

 nodes, without any other aid, suffice to give the power 

 of climbing; so that it seems probable that leaf- 

 climbers were in most cases at first twiners, and subse- 



