180 TWISTED INTEENODES. [CH. VII 



It is of interest to note that although the curvature is 

 diageotropic, yet that light has a directive influence on 

 the flower. The flower buds of Narcissus are at first 

 directed vertically upwards, and the direction in which 

 they bend, in assuming the horizontal position, is de- 

 tenAined by light, although the a/movnt of such movement 

 is regulated by the gravitation stimulus. 



(224) Horizontal branches. 



The horizontal position assumed by some branches 

 is according to Frank' due to diageotropism. The 

 following observations are worth making although they 

 leave it undecided whether the horizontal position is due 

 to light- or gravitation-stimulus. 



In the spring the developing buds of the hazel (Corylus), 

 hornbeam (Carpinus), elm (Ulmus), and lime (Tilia) are 

 curved so as to point downwards, and as further develop- 

 ment proceeds they move up into a horizontal position. 

 Select a horizontal branch of one of the above plants 

 in which the terminal bud is directed vertically downwards, 

 and fix it vertically upwards so that the bud is horizontal. 

 It will be found that in this case the curvature of the bud 

 remains unchanged, so that the branch into which it 

 develops is at right angles to the older part of the branch 

 with which it is continuous. 



(225) Torsion of internodes. 



In many plants, as Frank has shown^ the arrangement 



^ Frank, Die natiirliche wagerechte Richtung, etc., 1870. 



