24 MOVEMENTS OF CURVATURE 



The torsions of the stems of climbers and many forms of loose winding 

 are autonomic in origin. The same applies to the contortion of the flower- 

 bud of Convolvulus^ the bending of the apex of the peduncle of Cyclamen, 

 and of the labellum of Himantoglossum, the twisting of the internodes of 

 Char a and of the peristome of Barbula \ the coiling of the stalk of the 

 female flower of Vallisneria, of the pods of Medicago, and of tendrils which 

 have failed to reach a support. 



Although many of the movements taking place during development are the result 

 of external stimuli, an equally large number are autogenic in origin. Among these 

 are most of the movements of the sexual organs, which ensure proper pollination. 

 In addition to Ruta, similar movements of the stamens are shown by Dictamnus, 

 Parnassia, and Saxifraga, of the style by Saxifraga and Nigella, and of the stigmas 

 by Mtmulus, Martynia, Epilobium, and Compositae 2 . 



Historical. The remarkable movements of the basal leaflets of Desmoditim 

 gyrans attracted attention two centuries ago, and Hales also mentioned a few 

 ephemeral nutation curvatures 3 . At a later date the circumnutation of twiners was 

 investigated by Palm and by Mohl, that of tendrils by Dutrochet *. After a number 

 of pronounced periodic and ephemeral movements had been recognized, Darwin 

 showed that all growing organs perform spontaneous periodic movements, which in 

 many cases are only perceptible when magnified 5 , but in others have been increased 

 in amplitude by adaptive modification. This applies to the circumnutation of twiners 

 and tendrils, while Darwin considers that the pronounced curving nutation of subter- 

 ranean stolons makes it easier for them to pass between obstacles in the soil. The 

 same result may, however, be produced by the mechanical displacement of the growing 

 tip, so that roots grow equally well through soil, although they usually perform only very 

 slight autonomic oscillations 6 . The pronounced periodic curvatures of Zygnemaceae 

 may aid in movement, or in escaping from deposited layers of mud. This may also 

 apply to the movements of Oscillaria, but the exact importance of periodic variation 



1 A few instances are given by Wichura, Flora, 1852, p. 39; Jahrb. f. wiss. Bot, 1860, Bd. n, 

 p. 201. On forced torsion cf. de Vries, Jahrb. f. wiss. Bot., 1892, Bd. xxni, p. 13; Dingier, Flora, 

 1897, Erg.-bd., p. 289. 



2 Beyer, Die spontane Bewegung d. Staubgefasse u. Stempel, 1888; Hansgirg, 1895, I.e., and 

 the literature here quoted. Cf. also A. P. de Candolle, Pflanzenphysiol., 1835, Bd. II, p. 71; 

 Schulz, I.e., 1902. 



3 Meyen, Pflanzenphysiol., 1839, Bd. ill, p. 553. 



* Palm, Ueber das Winden d. Pflanzen, 1827, p. 16 ; Mohl, Ueber den Bau u. d. Winden d. 

 Ranken- u. Schlingpfknzen, 1837, PP- IO 5j IJ 2 ; Dutrochet, Ann. d. sci. nat., 1844, 3 e se"r., T. xn, 

 p. 156. 



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



6 Pfeffer, Druck- und Arbeitsleistungen, 1893, p. 362. [This may under normal conditions be 

 due to the geotropic irritability suppressing any pronounced oscillations. At any rate the radicles 

 of Maize, Pea and Bean show more pronounced oscillations (two to six times greater) when rotated 

 horizontally on a klinostat, than when at rest or rotated with the apex downwards. In each case 

 the observations were made every few hours by comparing the position of the radicle by means of 

 a horizontal microscope with a triangular framework of glass threads attached to the seed but not 

 touching the root. The rotation was too rapid (twelve revolutions per hour) to permit of the 

 result being due to the inductive action of gravity.] 



