THE CAUSES OF AUTONOMIC MOVEMENT 27 



shown by the movement of swarm-cells to and from a constant source 

 of illumination, owing to the alteration of their phototactic irritability, 

 according to the intensity of illumination. Similar movements have also 

 been observed as the result of autogenic changes in both the phototactic 

 and chemotactic irritability of micro-organisms. 



The curvatures of the peduncles of Papaver t Tnssilago, and of many- 

 other plants are due to changes of geotropic irritability, whereas the 

 autogenic movements of the pedicels of Asphodelus luteus and the peduncles 

 of Allium controversnm appear to be produced without the aid of any 

 external agency *. Similarly the movements of many stamens, styles, and 

 stigmas appear to be purely autotropic in character, whereas in the flowers 

 of Dictammis, Aesciilus, and Epilobiuni the movements of the sexual organs 

 are due to changes of geotropic irritability 2 . The curvatures of the 

 hypocotyl of Helianthns and of the epicotyl of Faba and Pisnm are 

 produced when the seedlings are revolved on a klinostat 3 , whereas the 

 bending of the apex of the stem of Avipclopsis and of other plants is due 

 to a geotropic reaction 4 , the straightening of the older growing zones 

 being the result of a change in the geotropic irritability co-operating with 

 the autogenic orthotropism of the stem. 



Since the curvatures result from the joint action of gravity with internal 

 factors, it is hardly surprising that in some cases they should not entirely 

 disappear when gravity is eliminated. Plants grown on a revolving klinostat 

 in fact perform a variety of movements, and the torsions in the internodes 

 of Char a and in the peristome of Barbnla are produced independently 

 of gravity. Whether the same applies to the coiling and uncoiling of the 

 peduncle of Vallisneria has yet to be determined. 



The pronounced movements of the leaflets of Desmodiinn gyrans and 

 of Trifolium, as well as those of the gynandrophore of Stylidium appear 

 to be independent of the action of gravity, but direct proof is wanting. 

 The movements of cilia continue, however, even when the rotation of a 



1 Vochting, Bewegtmgen d. Blvithen u. Friichte, 1882, p. 192 ; Scholtz, Cohn's Beitrage z. Biol., 

 1893, Bd. VI, p. 306 ; Hansgirg, Photod-ynam. Unters., 1889, p. 250 (Repr. from Sitzungsb. d. bohm. 

 Ges. d. AViss.) ; Physiolog. u. phycophytol. Unters., 1893, Neue Unters. iiber d. Gamo- u. Karpo- 

 tropismus, 1896 (Repr. from Sitzungsb. d. bohm. Ges. d. Wiss.). According to Vochting (I.e., 

 P- J 37) the bending of the stem of Viola is due to geotropism, a statement which Schwendener u. 

 Krabbe (Gesamm. Abhandl. von Schwendener, 1892, Bd. II, p. 336) contradict. 



2 Dufour, Arch. d. sci. phys. et nat., 1885, III, T. xiv, p. 418 ; Vochting, Jahrb. f. wiss. Bot., 

 1886, Bd. xvil, p. 340; J. af Klercker, Die Bewegungserschein. der FmwzVa-Bliithen, 1892 (Repr. 

 from Bihang till Svenska Vet.-Akad. Handlingar, Bd. xvm). 



s Vochting, Bewegungen d. Bluthen u. Friichte, 1882, p. 186 ; Darwin, The Power of Movement 

 in Plants, 1880, pp. 45, 553 ; Sachs, Arbeit, d. bot. Inst. in \Yiirzburg, 1873, Bd. I, p. 403; Lehrbuch, 

 3. Aufl., p. 75. That these and other curvatures are not the direct result of the weight supported, as 

 supposed, has been shown by Vochting, 1. c., and Scholtz, Cohn's Beitrage z. Biologic, 1892, Bd. V, 

 p. 400. Cf. also Rothert, Cohn's Beitrage z. Biologic, 1896, Bd. vn, p. 141. 



4 Scholtz, 1. c., 1892, p. 401. 



