CHAPTER XVII. 



Climbing Plants ; Power of Movement in Plants ; Insec- 

 tivorous Plants ; Kew Index of Plant Karnes. 



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 Ten- 

 drils 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 reference 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 pub- 

 lished 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 in- 

 ternodes, 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 harmoniously 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 Apocyneas with shoots 18 

 inches long (beyond the supporting stick), steadily search- 

 ing for something to climb up. When the shoot meets a 



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



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