CH. VIl] 



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 0° 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\ 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 Vochting, loc. cit. 



13—2 



