i 4 PHYSICS OF STREAMING 



That the presence of a certain percentage of water varying within 

 wide limits is an essential condition for streaming is certain, but this is 

 neither the cause of streaming nor an explanation of it. The percentage 

 of water not only affects the viscosity of the protoplasm and the osmotic 

 pressure of the cell-sap, but may also modify the respiratory activity and 

 amount of chemical change occurring in the cell, in virtue of the influence 

 of relative mass, and hence of dilution and concentration upon chemical 

 action. Bastit and Jumelle (Lichens and Mosses) and Aubert (Crassulaceae) * 

 have shown that in the case of plants which can withstand partial or 

 complete dessication, the activity of respiration steadily increases as the 

 plants are allowed to imbibe water, although above a certain optimal limit 

 further saturation with water causes a secondary decrease in the respiratory 

 activity. Hence it is possible that in certain cases a decrease in the 

 percentage of water might increase the supply of kinetic energy available 

 for rotation, and that this might more than counterbalance the retarding 

 effect of the concomitantly increased viscosity. These facts also suffice 

 to show the inadequacy of Kohl's supposition that the vacuolar pressure 

 determines the presence or absence of rotation, and that a diminution 

 of the vacuolar pressure acts as a direct physical cause, like the removal 

 of a brake, increasing the activity of streaming or rendering it possible. 



The mechanical and physical effects produced by an osmotic solution 

 must always be distinguished from its indirect stimulating action. The 

 indirect acceleration of streaming which may be caused by the stimulating 

 action of weak solutions of many substances is usually only temporary ; 

 but if after prolonged immersal the velocity becomes the same, or even 

 less than it was at first, this is partly due to a direct physical action. 

 Moderately strong osmotic solutions always decrease the activity of 

 streaming, the direct physical action preponderating, but irregular varia- 

 tions may occur at first, and these are probably the result of some indirect 

 stimulating action. Very strong plasmolytic solutions such as 8 to 10 

 per cent. KNO 3 ; 6 to 8 per cent. NaCl ; 40 to 50 per cent, cane sugar, 

 and 25 per cent, glucose always cause an immediate stoppage if suddenly 

 applied, whereas if the concentration is gradually raised, streaming slowly 

 and progressively decreases to nil. If the immersal has not been too 

 prolonged, streaming may recommence in water, either after a short 

 interval, or after one extending to several hours in some cases. That the 

 effect produced is not due to the plasmolysis, but to the withdrawal of 

 water from the protoplasm, is shown by placing streaming cells in solutions 

 of glycerine of gradually increasing strength, when streaming is gradually 

 retarded, and ultimately ceases without any plasmolysis being produced. 



1 Bastit, Rev. ge*n. de Bot, 1891, T. in, p. 476 ; Aubert, ibid., 1892, T. I. iv, p. 379 ; Jumelle, 

 ibid., 1892, T. iv, p. 169. 



