PREFACE
This Essay first appeared in the ninth volume of the \'Journal of the
Linnean Society,\' published in 1865. It is here reproduced in a corrected
and, I hope, clearer form, with some additional facts. The illustrations
were drawn by my son, George Darwin. Fritz Muller, after the
publication of my paper, sent to the Linnean Society (Journal, vol. ix., p.
344) some interesting observations on the climbing plants of South Brazil,
to which I shall frequently refer. Recently two important memoirs, chiefly
on the difference in growth between the upper and lower sides of tendrils,
and on the mechanism of the movements of twining-plants, by Dr. Hugo
de Vries, have appeared in the \'Arbeiten des Botanischen Instituts in
Wurzburg,\' Heft. iii., 1873. These memoirs ought to be carefully studied
by every one interested in the subject, as I can here give only references to
the more important points. This excellent observer, as well as Professor
Sachs, {1} attributes all the movements of tendrils to rapid growth along
one side; but, from reasons assigned towards the close of my fourth
chapter, I cannot persuade myself that this holds good with respect to
those due to a touch. In order that the reader may know what points have
interested me most, I may call his attention to certain tendril-bearing
plants; for instance, Bignonia capreolata, Cobaea, Echinocystis, and
Hanburya, which display as beautiful adaptations as can be found in any
part of the kingdom of nature. It is, also, an interesting fact that
intermediate states between organs fitted for widely different functions,
may be observed on the same individual plant of Corydalis claviculata and
the common vine; and these cases illustrate in a striking manner the
principle of the gradual evolution of species.