The two
great classes of twiners and of plants with sensitive organs, namely,
leaf-climbers and tendril-bearers taken together, far exceed in
number and in the perfection of their mechanism the climbers of the
two first classes. Those which have the power of spontaneously
revolving and of grasping objects with which they come in contact,
easily pass 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
gradation, 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.
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