( 313 ) 



CHAPTER XVII. 



Climbing Plants; Power of Movement in Plants; Insec- 

 tivorous Plants ; Kew Index of Plant Names. 



My father mentions in his Autobiography (p. 45) that he was 

 led to take up the subject of climbing plants by reading 

 Dr. Gray's paper, "Note on the Coiling of the Tendrils of 

 Plants." * This essay seems to have been read in 1862, but I 

 am only able to guess at the date of the letter in which he asks 

 for a referonce to it, so that the precise date of his beginning 

 this work cannot be determined. 



In June 1863, he was certainly at work, and wrote to Sir 

 J. D. Hooker for information as to previous publications on the 

 subject, being then in ignorance of Palm's and H. v. Mohl's 

 works on climbing plants, both of which were published in 

 1827. 



C. Darwin to Asa Gray. Down, August 4 [1863]. 



My present hobby-horse I owe to you, viz. the tendrils : 

 their irritability is beautiful, as beautiful in all its modifica- 

 tions as anything in Orchids. About the spontaneous move- 

 ment (independent of touch) of the tendrils and upper inter- 

 nodes, I am rather taken aback by your saying, " is it not well 

 known ? " I can find nothing in any book which I have. . . . 

 The spontaneous movement of the tendrils is independent of 

 the movement of the upper internodes, but both work har- 

 moniously together in sweeping a circle for the tendrils to 

 grasp a stick. So with all climbing plants (without tendrils) 

 as yet examined, the upper internodes go on night and day 

 sweeping a circle in one fixed direction. It is surprising to 

 watch the Apocyne® with shoots 18 inches long (beyond the 

 supporting stick), steadily searching for something to climb up. 

 Wnen the shoot meets a stick, the motion at that point is 

 arrested, but in the upper part is continued; so that the 

 climbing of all plants yet examined is the simple result of the 

 * Proc. Amer. Acad, of Arts and Sciences, 1858. 



