34 



MOVEMENTS IN CURVATURE 



not only shown by twiners but also by the apices of many tendril-climbers 

 and by the tendrils themselves. Furthermore the periodic daily movements 

 of leaves bearing tendrils may aid the latter in reaching a support l . 



SECTION 9. The Twining of Stems. 



The obliquely ascending coils formed by a twining stem around a 

 support do not result from the tip being closely applied to it and growing 

 along a continuous spiral path. They are instead the result of complicated 

 movements of the free circumnutating tip, which is pressed closely against 

 the support at one part of its revolution but stands out away from it 



in 



FlG. 6. Twining stem of 

 Convolvulus arvensts. 



FlG. 7 a b c. Twining stem-apex of Humulus Lupulus in 

 successive phases (a, b, c) of movement. 



at another 2 (Figs. 6 and 7). It appears that the coiling is not the result 

 of a contact stimulus as in tendrils, but that the support merely acts as 



1 As in the case of Mutisia Clematis quoted by Darwin (1. c., p. 90). 



8 For details see Darwin, Climbing Plants; de Vries, Arb. d, bot. Inst. in Wiirzburg, 1873, 

 Bd. Ij p. 326 ; Schwendener (1881), Gesammelte bot. Mitth., Bd. I, p. 405 ; Baranetzsky, Die kreis- 

 .formige Nutation und das Winden der Stengel, 1883, p. 54; Schenck, Beitrage z. Biol. u. Anat. d. 

 .Lianen, 1892, p. 115. 



