178 DIAGEOTROPISM. [CH. VII 



is desired to keep a permanent record' of the experiment 

 the roots should be traced on the outside of the glass with 

 a paint brush filled with white paint or some clearly 

 visible bright colour, such as vermilion. One end of 

 the trough must now be raised on a wooden block, so that 

 the edge of the trough makes an angle of about 45° or 50° 

 with the horizon, and the curvature of the secondary 

 roots, by which they return to their original position with 

 regard to the horizontal, must be noted. We find that a 

 downward curvature is more rapidly and perfectly effected 

 than a corresponding movement upwards ^ 



(222) Growth of secondary roots in light. 



If the trough is left exposed to light instead of being 

 kept in the dark room the secondary roots grow more 

 obliquely downwards*. The same thing may, according to 

 Stahl, be observed in the runners of Adoxa moschatellina. 

 This is not due to a directive influence of light, it is 

 rather that light influences the mode of reaction to the 

 gravitation-stimulus. A somewhat similar state of things 

 is described in exp. 229. 



(223) Biageotropic flowers. 



The horizontal position assumed by the corolla-tube of 

 various species of Narcissus is due to diageotropism*. 

 The movement may be easily observed in Narcissus 



' Blfving (Sachs' Arbeiten, ii. p. 489) used the runners of Eleocharis, 

 Sparganium and Scirpus maritimwi for similar experiments on diageo- 

 tropism. 



2 Stahl, Berichte d. deut. hot, Gesellseh. 1884. 



•' Vochting, Bewegungen der BlUthen und Friichte, 1882. 



