ABSORPTION AND TRANSMISSION OF SOLUTES 121 



phere makes this possible. Mechanical movements of the 

 plant, by wind, etc., probably hasten this diffusion by creat- 

 ing currents. 



Apart from this gaseous diffusion, all transmission of 

 solutes, whether gaseous, solid, or liquid, must take place in 

 the form of aqueous solution. Diffusion of solutes from cell 

 to cell takes place in accordance with the principles of 

 diffusion, the tendency being ever to equalize the diffusion 

 tension of all solutes throughout the extent of the solution. 



In order to emphasize the fact already referred to that 

 there is no relation between the turgidity produced by one 

 solute and the diffusion of another into or out of the same 

 turgid cell, the following example may be taken: Suppose 

 an artificial cell whose membrane is impermeable to dissolved 

 sugar but permeable to K and NO 3 ions. Such a membrane 

 may be made from copper ferrocyanid. Let this cell be 

 filled with a solution of sugar and potassium nitrate so made 

 up that the partial pressures of the two substances are equal 

 to each other, say five atmospheres. The total pressure of 

 the solution is then ten atmospheres. Now let this cell be 

 placed in distilled water. Since the membrane is permeable to 

 KNO 3 , this salt will immediately begin to diffuse outward, 

 and diffusion will continue until its diffusion tension is prac- 

 tically as great outside as it is within the cell. No osmotic 

 pressure will be manifested by the KNO 3 , excepting the 

 small amount due to friction in the membrane. But the 

 sugar cannot pass out of the cell, and must therefore exert 

 its full pressure upon the walls, making the cell turgid and 

 manifesting a stretching force of nearly five atmospheres. 

 Of course, as the cell becomes turgid a comparatively small 

 amount of water will enter from without, and thus dilute 

 the internal solution of sugar. 



So far the illustration shows that it is possible for turgidity 

 to be maintained while a substance is diffusing out of the 



