PLANT GROWTH WITHOUT FERTILIZERS 5 



Absorption of Water by the Plant. The water needed 

 by plants is absorbed by the roots in very nearly every case 

 of plant life. The absorption of water, indeed, constitutes 

 one of the most important of the root functions and is depen- 

 dent upon the molecular concentration of plant sap in relation- 

 ship to that of the water in the soil. The laws which govern 

 diffusion follow those of the laws of diffuse matter which are 

 best known in the form of the gas laws. If we imagine 10 

 grammes of cane sugar existing in the form of a gas, and 

 occupying one litre of space, at a temperature of 14 C., 

 and a pressure of 760 mm., it would be easy to calculate by 

 the ordinary gas laws what pressure it would exert. The 

 molecular weight of cane sugar is 342. That amount of cane 

 sugar would occupy 22^4 litres, at 760 mm. pressure, o C., 

 from which we can calculate that 10 grammes of cane sugar 

 occupying i litre would exert a pressure of 521 mm. at 

 14 C. Actual measurements of the osmotic pressure exerted 

 in a porous pot by a solution of cane sugar in water of the 

 above strength, gave figures from 508 to 535 mm., showing 

 that the agreement with theory is very close. 



It is the pressure caused in the above manner that forces 

 sap to rise in plants, and to give to plants the great force 

 of suction by which they absorb water from a soil. Since 

 sodium chloride in weak solution ionizes almost completely, 

 it will exert a pressure double that of the amount that sodium 

 chloride would exert if the molecule remained intact. That 

 is to say, a solution of 0-086 % of sodium chloride would 

 exert the same osmotic pressure as i % of cane sugar. It is 

 thus easy to perceive why salt will upset the general course 

 of plant life by interfering with, and even possibly reversing, 

 the osmotic pressure normally developed. When water 

 is drawn out of a living plant by soluble salts, plasmolysis 

 sets in, and the protoplasm shrinks. Excessive amounts 

 of very soluble fertilizers can do harm by setting up such an 

 interference with normal conditions of growth. 



The Soil Conditions Suited to the Growth of Plants.- 

 Plants need a soil which is sufficiently open to admit of root 

 penetration and a ready movement of air. and water. If the 



