198 EPINASTY. [CH. VII 



(227) Epinasty\ 



This curvature (due to internal stimulus) may be 

 observed in a variety of plant-members. The strong 

 epinastic curvature of the leaves of Rayiunculus ficaria 

 has been made use of in exjD. 217, and similar curvatures 

 by which the leaves are pressed against the ground are to 

 be seen in Plantago media and in Pinguicula. 



(228) Combination of epinasty and geotropism'^. 



The leaves of the dock {Rumex) serve for this experi- 

 ment. 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 hori- 

 zontally in an embankment of wet sand, piled up in the 

 angle of a tin box which must have 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 



^ H. de Vries in Sachs' Arbeiten, i. p. 252; see also Vines, Annals of 

 Botany, 1889. 



2 H. de Vries in Sachs' Arbeiten, i. p. 255. 



5 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. 



