PROTOPLASMIC STREAMING 



291 



the cell-wall or magnet, and this does not appear to be exercised in the streaming 

 cell *. In addition, the direction and velocity of streaming are not directly affected 

 by the use of strong magnets 2 , so that the motor mechanism in the living cell can 

 hardly be of electro-magnetic origin, for the retarding effect produced after prolonged 

 exposure to intense magnetic action is probably of secondary origin 3 . 



Berthold considered that amoeboid movement was directly due to changes of 

 surface-tension, the movement always taking place towards the side of least surface- 

 tension 4 . The latter statement does not, however, apply to all cases, for a piece of 

 camphor floating on water moves towards the side where the surface-tension is greatest. 

 Streaming he considers to be due to changes of surface-tension in the vacuolar 



B 



l-dj 



FIG. 51. A. Diagram of section of Chara cell, showing rows of emulsion globules in endoplasm. The row of 

 arrows shows the relative velocities of different layers. B. Row of emulsion globules showing surface-tension 

 forces and resultant movement. (After Ewart.) 



membrane, and in support of this conclusion adduces the fact that the velocity of 

 streaming decreases from the vacuolar membrane towards the ectoplasm 5 . In cells 

 with a thick layer of endoplasm, by using minute floating particles of similar diameter 



1 Cf. Ewart, Protoplasmic Streaming in Plants, 1903, p. no seq. 



2 Becquerel, Compt. rend., 1837, T. v, p. 784 ; Dutrochet, Compt. rend., 1846, T. xxil, p. 619 ; 

 Reinke, Pfliiger's Archiv f. Physiol., 1882, Bd. xxvn, p. 140. [The orientation of suspended 

 streaming cells in a strong magnetic field, due mainly to the magnetic properties of the cell-wall, 

 would probably have led these observers to exactly the opposite conclusion had they not over- 

 looked it. Cf. Ewart, 1. c., p. 45 seq.] 3 Ewart, 1. c., p. 50. 



4 Berthold, Protoplasmamechanik, 1886, p. 115 seq. Cf. also Biitschli, I.e., p. 210. 



5 Berthold, I.e., p. 123; cf. also Wigand, I.e., p. 196. 



U 2 



