It is probable that these slight movements of the roots are
due to the quicker growth of the side exposed to the light, in
comparison with the other side, and not because the roots are
sensitive to contact in the same manner as true tendrils. According
to Mohl, the rootlets of certain species of Lycopodium act as
tendrils. {43}
Concluding Remarks on Climbing Plants.
Plants become climbers, in order, as it may be presumed, to reach the
light, and to expose a large surface of their leaves to its action
and to that of the free air. This is effected by climbers with
wonderfully little expenditure of organized matter, in comparison
with trees, which have to support a load of heavy branches by a
massive trunk. Hence, no doubt, it arises that there are so many
climbing plants in all quarters of the world, belonging to so many
different orders. These plants have been arranged under four
classes, disregarding those which merely scramble over bushes without
any special aid. Hook-climbers are the least efficient of all, at
least in our temperate countries, and can climb only in the midst of
an entangled mass of vegetation. Root-climbers are excellently
adapted to ascend naked faces of rock or trunks of trees; when,
however, they climb trunks they are compelled to keep much in the
shade; they cannot pass from branch to branch and thus cover the
whole summit of a tree, for their rootlets require long-continued and
close contact with a steady surface in order to adhere.
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