I0 PHYSICS OF STREAMING 



SECTION 3. The Influence of Osmotic Pressure, Percentage of 

 Water, and of Viscosity on Streaming. 



These three factors are all closely connected with one another. Thus 

 the removal of water from the cell increases the osmotic pressure of the 

 cell-sap, and also the viscosity of the protoplasm. A rise of osmotic 

 pressure caused by an increase in the percentage of salts in the cell-sap 

 will force the protoplasmic micellae closer together and squeeze out some 

 of its water of imbibition, thus increasing its viscosity and resistance to 

 flow. A decrease in the concentration of the cell-sap will permit the 

 protoplasm to imbibe more water, and hence will, ceteris paribus, decrease 

 the viscosity and increase the velocity of streaming. 



Osmotic pressure. Kohl l observed that the immersal of streaming cells 

 of Elodea and Tradescantia in weak solutions of asparagin was followed 

 by an increase in the rapidity of streaming, and considered this to be due 

 to the fact that the solution diminishes the pressure of the cell-sap against 

 the protoplasm and cell-wall, and hence decreases the friction between 

 these two. The suggestion is even made that changes in the internal 

 osmotic pressure may be the causes directly determining the cessation 

 or commencement of streaming. Strong solutions always retard rotation, 

 and the accelerating action of dilute solutions is not confined to asparagin, 

 but may be produced by a variety of substances such as KNO 3 (-5 to I per 

 cent), cane sugar (5 per cent), grape sugar (2 to 3 per cent.), and even 

 glycerine. Similarly, streaming may be caused to appear in the cells of 

 sections cut from seedlings of Brassica and Sinapis by immersing them 

 in -5 per cent. KNO 3 for a few hours and then placing them in water. 

 It is usually the case that the most active streaming is shown on returning 

 the cells to water, and frequently it is not until this has been done that the 

 velocity increases. Again, dilute glycerine rapidly penetrates most proto- 

 plasts, and hence cannot maintain any permanent plasmolytic action, 

 but nevertheless it may exercise the same effect as the other substances 

 mentioned in inducing and accelerating streaming. Dilute solutions of 

 KNO 3 (-5 to i per cent.) retard streaming very markedly in certain cases 2 

 (Char a, Nitella, Spirogyra), and -2 to -5 per cent, solutions of sodium 

 chloride exercise a similar action. Even more dilute solutions may 

 produce similar effects after prolonged immersal. Here, and in other cases 

 also, there is no immediate connexion between the action of the solution and 

 its osmotic concentration. Hence the action in question is undoubtedly an 

 obscure stimulating one, and differs in character according to the substance 



1 Bot. Centralbl., 1898, Bd. LXXIII, No. 5, p. 168 



plants. 



This is partly, though not entirely, the result of the low internal osmotic pressure in these 



