292 LOCOMOTORY AND PROTOPLASMIC MOVEMENTS 



as indicators, it can usually be distinctly seen that the velocity of streaming increases 

 slightly from the vacuolar membrane to a point lying a variable distance beneath 

 the ectoplasm, and thence rapidly decreases to nil outwardly *. (Cf. Fig. 51.) This 

 distribution of velocity affords definite proof that the energy of movement is liberated 

 not at the boundary of the cell-sap but throughout the substance of the streaming 

 endoplasm. If we assume that the bipolar paramagnetic and diamagnetic particles of 

 protoplasm in the endoplasmic emulsion are definitely arranged in regard to the para- 

 magnetic cell-membrane, it is easy to see how continuous rotation might be brought 

 about if electrical currents are produced by the differences of potential at the internal 

 and external boundaries of the feebly-conducting protoplasm 2 , and are maintained 

 by the chemical actions in the latter. For these currents traversing the endoplasm 

 and producing definite changes of surface-tension in the regularly-arranged particles 

 of the emulsion might in this way cause a movement of the whole protoplasm 3 . 

 Where the regular arrangement is not maintained, circulatory movements, or a cessa- 

 tion of streaming, may ensue. 



Although this hypothesis coincides more exactly with the facts observed in 

 dermatoplasts than that of Berthold, it may ultimately prove to be as far from the 

 truth as Quincke's conclusion that the movement was due to surface-tension actions 

 exercised by the non-moving ectoplasm 4 . 



The influence of the shape of the cell and of the union in tissues. The typical 

 rotation in elongated cells takes place parallel to the long axis of the cell 5 , the 

 plane of rotation being parallel to the surface of the leaf in Vallisneria and at right 

 angles to the surface in the cortical cells of Chara 6 . The plane of rotation can, 

 however, be altered by injuries, by the death of neighbouring cells and by exposure 

 to strong light after prolonged darkening 7 . According to Velten, in rotating around 

 the longitudinal axis of the cell the plasma follows the path of least resistance 8 . In 

 Chara, however, as was observed by Braun 9 , spiral streaming appears when the inter- 

 nodes undergo torsion, and then Hermann 10 considers the streaming to be along the 

 path of absolutely greatest resistance, while, according to Rhumbler n , the arrangement 

 of the chloroplastids is due to the spiral streaming instead of inducing it. Neither 

 Velten nor Hormann brings forward any experimental evidence or theoretical calcula- 

 tion in support of his statements, and as a matter of fact the resistance to flow in 

 cylindrical cells with rounded ends is not affected by the direction of flow. Naturally 

 in cells showing circulation the total resistance to flow increases as the number of 

 threads increases and their diameter decreases, but the path of least resistance is 

 that in which the passage across a definite space requires the least expenditure of 



Ewart, Protoplasmic Streaming in Plants, 1903, p. 113. 2 Id., p. 123. 



Id., p. 116. * Pfeffer, Plasmahaut und Vacuolen, 1896, p. 277. 



Nageli, Beitrage zur wiss. Bot., 1860, Heft ii, p. 62. See also A. Braun, Ber. liber d. Ver- 

 hand g. d. Berliner Akad., 1852, p. 214 ; Hofmeister, Pflanzenzelle, 1867, p. 36. 



Berthold, 1. c., p. 122. 7 Ewart, 1. c., p. 34. 



Velten, Flora, 1873, p. 86; Berthold, 1. c., p. 120. 



A. Braun, I.e., p. 225. See also Berthold, I.e., p. 121; Meyen, Pfianzenphysiol., 1838, 

 Bd. n, p. 236 ; Velten, 1. c., p. 85. 



10 Hormann, Studien ii. d. Protoplasmastromung b. d. Characeen, 1898, p. 16. 



11 Rhnmbler, Zeitschrift f. allgem. Physiologic, 1902, Bd. I, p. 300. 



