2 Mil. DARWIN ON CLIMBING PLANTS. 



memoirs by Dutrochet*. Nevertheless I believe that my obseiv 

 rations, founded on the close examination of above a hundred 

 widely distinct living plants, contain sufficient novelty to justify 

 me in laying them before the Society. 



Climbing plants may be conveniently divided into those which 

 spirally twine round a support, those which ascend by the move- 

 ment of the foot-stalks or tips of their leaves, and those which 

 ascend by true tendrils, — these tendrils being either modified 

 leaves or flower-peduncles, or perhaps branches. But these sub- 

 divisions, as we shall see, nearly all graduate into eacli other. 

 There are two other distinct classes of climbing-plants, namely 

 those furnished with hooks and those with rootlets ; but, as such 

 plants exhibit no special movements, we are but little concerned 

 with them ; and generally, when I speak of climbing plants, I refer 

 exclusively to the first great class. 



Part I. — Spirally twining Plants. 



This is the largest subdivision, and is apparently the primor- 

 dial and simplest condition of the class. My observations will be 

 best given by taking a few special cases. When the shoot of a 

 Hop (llwmdtis Lwpulus) rises from the ground, the two or three 

 first-formed internodes are straight and remain stationary ; but 

 the next-formed, whilst very young, may be seen to bend to one 

 side and to travel slowly round towards all points of the compass, 

 moving, like the hands of a watch, with the sun. The movement: 

 very soon acquires its full ordinary velocity. From seven obser- 

 vations made during August on shoots proceeding from a plant 

 which had been cut down, and on another plant during April, the 

 average rate during hot weather and during the day was 2h. 8 m. 

 for each revolution ; and none of the revolutions varied much 

 from this rate. The revolving movement continues as long as 

 the plant continues to grow ; but each separate internode, as it 

 grows old, ceases to move. 



To ascertain more precisely what amount of movement each in- 

 ternode underwent, I kept a potted plant in a well-warmed room 

 to which I was confined during the night and day. A long in- 

 clined shoot projected bey on d the upper end of the supporting 



Treatise was published only a few weeks before Mold's. See also ' The Vege- 

 table Cell' (translated by Henfroy), by H. von Mohl, p. 147 to end. 



* "Des Mouvenients n'volutil's spontanea," &c\, ' Coinptes Rendus,' torn. xvii. 

 (1843) p. 989 ; "E^cherches sur la Volubility des Tiges," &c, torn. xix. (1844) 

 p. 295. 



