190 CONCLUDING REMARKS. Cuap. V. 
from branch to branch, and securely ramble over a 
wide, sun-lit surface. 
The divisions 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 tendril-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 leaf- 
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- 
