196 CHARLES DARWIN. 



production of "an abundant supply of seeds with 

 little expenditure." 



" Climbing Plants." The subject of this volume 

 was published as .a paper before the Linnean Society 

 in 1864. After being corrected, the material was 

 brought out as a volume in 1875. Darwin, as he 

 tells us in the Autobiography, was first led to study 

 the subject by a paper by Asa Gray, which appeared 

 in 1858 (Proc. Amer. Acad. of Arts and Sciences). 

 Writing to Asa Gray, August 4th, 1863, he said, " My 

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

 One of the most interesting results brought forward 

 in this work is the fact that the upper growing part 

 of a twining stem bends to one side and then travels 

 slowly round, between two and three hours being 

 required for each revolution, in the case of the 

 hop growing in a room and observed at the period 

 of most active movement. The circle swept at the 

 27th revolution was 19 inches in diameter. In the 

 case of this plant the three youngest internodes (or 

 joints), and never less than two of them, were con- 

 cerned in the movement ; " by the time the lower one 

 ceased to revolve, the one above was in full action, 

 with a terminal internode just commencing to move." 

 The object of this movement is to strike some object 

 round which the plant may twine. A much grander 

 example was seen in Ceropegia Gardnerii, in which 

 three long internodes and two short ones swept a 

 circle over 5 feet in diameter, " at the rate of 32 

 or 33 inches per hour, in search of some object 



