CH. VIl] EPICOTYLS. 183 



experiment. Gather 6 or 8 leaves and with a knife free 

 the lamina from the midrib', and cut off the apical third 

 of the midribs; now fix the basal | of the midribs 

 horizontally in an embankment of wet sand in the angle 

 of a tin box fitted with a close-fitting lid. Let half the 

 number of midribs be in the normal position, while the 

 remainder are reversed so that the upper surface of the 

 midrib is downwards. After 24 hours it will be found 

 that the latter, in which apogeotropism and epinasty 

 combine, are far more curved than the normally placed 

 midribs. 



(229) Nutation of epicotyls. 



An interesting feature in the curvature of the 

 epicotyls of some of the Leguminosse is the part played 

 by light in the phenomenon. Wortmann' has shown 

 that the epicotyls of Phaseolus multiflorus remain curved 

 in the dark and open when exposed to light. We use 

 the vetch {Vida sativa) in which the phenomenon is 

 particularly striking, the darkened epicotyl being often 

 curled into a complete loop. 



1 Note that the curvature of the midrib increases on being freed ; this 

 indicates a state of tension between the lamina and the midrib. See 

 H. de Vries in Sachs' Arbeiten, i. p. 241. 



2 Bot. Zeitung, 1882, p. 9l5. 



