116 THE ROYAL SOCIETY OF CANADA 



in the upper soil they increase the osmotic pressure of these solutions. 

 This may cause an osmotic rise of moisture from greater depths than 

 would take place if the surface soils had not been made rich in soluble 

 salts by fallowing. 



Other suggestions. 



Does the increase in temperature of the soil in summer bring about an 

 upward movement of moisture by osmotic pressure? 



If the rise of moisture in soil is all brought by capillary action, 

 then the supply in summer should be less than that in spring or fall, 

 because the surface tension of water decreases with an increase in 

 temperature. That is, the supply of moisture to plants should be 

 least when they most need it. It is true that the decrease in surface 

 tension is offset to some extent in two ways: by the increase in con- 

 centration by evaporation of the solutions near the surface, which 

 increases the surface tension, and by the increase in fluidity of the 

 water at higher temperatures. 



If, however, the rise of water is due partly to osmotic pressure, 

 the supply of water would be increased by an increase in temperature 

 in a number of ways: 



(1) If the increased evaporation increases the concentration, 

 and therefore the osmotic pressure of the solution near the sur- 

 face, it should increase the amount of water raised through the 

 subsoil. 



(2) The increased bacterial action, at higher temperatures, 

 should increase the concentration and osmotic pressure of the soil 

 solutions. This should increase the amount of water raised through 

 the subsoil. 



(3) With increase of temperature more soluble salts would be 

 dissolved in the soil solution, and their osmotic pressure should there- 

 by be increased. This again should increase the amount of water 

 raised through the subsoil. 



(4) The osmotic pressure of any solution is increased by an 

 increase of temperature. This should be the case with the soil 

 solution. 



We see then that the osmotic pressure of the soil solutions near 

 the surface should be increased in a number of ways by an in- 

 crease of temperature. This should increase the amount of water 

 raised from below through the subsoil. That is, in summer when 

 the plants need more water, they should receive it by osmotic 

 pressure. 



