PREFACE. 
1 
Tus 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 Miller, 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 move- 
ments of twining plants, by Dr. Hugo de Vries, have 
appeared in the ‘Arbeiten des Botanischen Instituts 
in Wiirzburg,’ 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 
