8 PHYSICS OF STREAMING 



opposite direction to that of streaming, but the phenomenon may not 

 be directly connected with the reappearance of streaming, since it might 

 be caused by localized changes of surface-tension, by the diosmosis of 

 liquid, or by a displacement of the centre of gravity due to localized 

 contractions or change of shape. 



It becomes a question of considerable interest as to what effect will 

 be produced by removing the supporting cell-wall from the ectoplasm 

 of a cell exhibiting rotation, and by separating the protoplasmic contents 

 into two or more distinct masses. If strong induction shocks are passed 

 through a cell, the protoplasm often separates into a number of balls, 

 in which streaming may recommence, lasting either until they reunite 

 or ceasing again if the cell ultimately dies. Velten 1 states that the 

 periphery of such balls is always at rest, but this might be due to their 

 bases adhering to the cell-wall beneath them. That this is so can easily 

 be shown by inclining the preparations and noting that they usually 

 retain their original positions although denser than the cell-sap. 



If, however, fragmentation is induced by immersal in a plasmolyzing 

 solution (3 to 5 per cent. KNO 3 , 15 to 25 per cent. C 12 H 22 O U , 8 to 12 per cent. 

 C C H ]0 O 5 ) which is subsequently slightly diluted, or if cells are opened in an 

 isosmotic solution of sugar, balls of plasma are sometimes obtained which 

 float freely and may exhibit streaming for hours 2 , but the ball as a whole 

 exhibits no tendency to roll round in the opposite direction to that of 

 streaming, even when streaming is active. On more than one occasion, 

 however, spheres exhibiting streaming during or shortly after their forma- 

 tion remained temporarily connected to the main mass of plasma by a 

 protoplasmic thread, which was drawn out until it broke in such a fashion 

 as though the ball as a whole was slowly rotating in the same direction as 

 that of streaming (Fig. 2). In another case, however, the reverse was the 

 case, so that this peculiar phenomenon may be safely ascribed to causes 

 unconnected with the internal streaming movements. 



If only partial plasmolysis is produced, the velocity of streaming 

 in regions where the ectoplasm is free can be compared with that in 

 regions where it is still adherent to the cell-wall. Chloroplastids floating 

 in the peripheral endoplasm are often distinctly retarded at such points 

 as at A, Fig. 3, and may be caught up by those behind them. This may, 

 however, be simply due to the inward bulging at A, producing a tendency 

 to eddy currents and hence causing a loss of momentum. When crossing 

 the curved region, a chloroplastid may often be seen, if floating near to the 

 internal limit of the endoplasm, to have a slight aggregation of protoplasm 



1 Flora, 1873, p. loi. 



3 Chara and Nitella are unsuitable. Cells of Elodea, Vallisneria, Aristolochia, Sagittaria, as 

 well as hairs of Trianea and Cucurbita may be used. For methods of determining isosmotic values 

 cf. Pfeffer's Physiol. Vol. i (Clar. Pr ss). p. 145. 



