CH. VII] 



DIAGEOTROPISM. 



195 



in the dark) in a position so that the corolla-tube is 45 

 below the horizon. The curvature of the flower-scape will 

 begin to diminish and the corolla-tube will, in about 24 

 hours, become once more horizontal, as shown in the figure, 



FIG. 39. Exp. 223. 



in which the dotted line D gives the position from which 

 the flower has risen. The angle made by the corolla with 

 the horizon may be roughly measured, as shown in the 

 figure, by means of a graduated semicircle of cardboard Q 

 to the centre of which a plummet P is suspended. The 

 zero should be in the centre of the arc and the graduations 

 should run from to 90 in either direction. 



It is of interest to note that although the curvature is 

 diageotropic, yet that light has a directive influence on 

 the flower 1 . 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- 



1 Yochting, loc. cit. 



132 



