TWINING PLANTS 41 



exercised by the support having long ago been shown to be erroneous 

 by Mohl. 



Torsion. Circumnutation does not involve torsion, but the latter 

 is usually shown very strongly by the older internodes of stems which 

 have not twined. The torsion is indicated by the twisting of ridges on 

 the stem and by the displacement of the phyllotaxis, and follows the same 

 direction as the circumnutation and twining. It arises, however, from 

 internal causes and hence persists when circumnutation and twining are 

 arrested by rotation on a klinostat *. 



Stems twined around a support usually show antidromous torsion 

 resulting from the twining, and which, owing to the fixation of the coils 

 to the support, has been incapable of removal by the plant's tendency to 

 homodromous torsion. If portions of the support are cut away the latter 

 comes into play over these regions and the antidromous torsion is wholly 

 or partly removed. The same takes place when the coils are loose or 

 unattached, and hence it is hardly surprising that the torsions observed 

 in a climbing stem should vary considerably, and even be in some cases 

 antidromous, in others homodromous 2 . 



Mohl supposed that circumnutation and twining were produced by the torsion 

 of the stem, but Palm and, more especially, Darwin and de Vries have shown that 

 this was an error. The two latter authors recognized the dissimilar origins of anti- 

 dromous and homodromous torsions, and their mode of action. Schwendener, and 

 at a later date Baranetzsky, Ambronn, and Kolkwitz, showed in detail how the anti- 

 dromous torsion was the mechanical result of coiling. If an india-rubber tube bearing 

 a longitudinal stripe is coiled around a support without hindering its tendency to 

 twist around its own longitudinal axis, the spiral twisting of the stripe will show the 

 antidromous torsion resulting from coiling. To keep the stripe on the convex side 

 the tube must be twisted during coiling, and if the end is partially freed the tube 

 will tend to twist back to the original condition. In a stem capable of growth the 

 forcible torsion might become partially or entirely fixed 3 , just as is the antidromous 

 torsion produced by twining when tight coils are formed. The homodromous torsion 

 attempted in the attached coils has the effect of fixing the stem more firmly to the 

 support by tightening up loose coils 4 . 



Heliotropism and twining. According to Mohl, Dutrochet, Darwin, and 

 Baranetzsky 5 the circumnutating shoots of climbers are usually positively heliotropic, 

 but this irritability is so weak as merely to somewhat accelerate circumnutation when 



1 Baranetzsky, 1. c., p. 31. 



2 For details see Kolkwitz, Ber. d. bot. Ges., 1895, p. 497; Schwendener (1881), Gesammelte 

 hot. Mitth., p. 420; Ambronn, Zur Mechanik d. Windens, 1884, I ; 1885, II (Repr. from Sitzungsb. 

 d. sachs. Ges. d. Wiss.) ; Baranetzsky, Die kreisformige Nutation und das Winden d. Stengel, 1883, 

 p. 66; De Vries, Arb. d. bot. Inst. in Wiirzburg, 1873, Bd. I, p. 330; Darwin, Climbing Plants, 



1875- 



3 Cf. Kolkwitz, 1. c., p. 505. * Cf. Id., p. 512. 

 5 Darwin, The Power of Movement in Plants, 1880, p. 449. 



