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 move- 

 ments 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 



