SOIL AND ITS RELATION TO ROOTS 



75 



Diagram of a root hair; CS, cell sap; CW, cell 

 wall ; P, protoplasm ; A^, nucleus ; S, particles 

 of soil. 



called cell sap. Forming a part of the living protoplasm of the 



root hair, sometimes in the hairlike prolongation and sometimes 



in that part of the cell which forms the epidermis, is found a 



nucleus. The protoplasm and nucleus are alive ; the cell wall 



formed by the living matter in the cell is dead. The root hair is a 



living plant cell with a wall 



so delicate that water and 



mineral substances from 



the soil can pass through 



it into the interior of the 



root. 



How the Root absorbs 

 Water. — The process by 

 which the root hair takes 

 up soil water can better 

 be understood if we make 

 an artificial root hair large enough to be easily seen. An egg with 

 part of the outer shell removed so as to expose the soft skinlike 

 membrane underneath is an example. Better, an artificial root 

 hair may be fnade in the following way. Pour some soft celloidin 

 into a test tube ; carefully revolve the test tube so that an even 

 film of celloidin dries on the inside. This membrane is removed, 

 filled with white of egg, and tied over the end of a rubber cork in 

 which a glass tube has previously been inserted. When placed 

 in water, it gives a very accurate picture of the root hair at 

 work. After a short time water begins to rise in the tube, having 

 passed through the film of celloidin. If grape sugar, salt, or some 

 other substance which will dissolve in water were placed in the 

 water outside the artificial root hair, it could soon be proved by 

 test to pass through the wall and into the liquid inside. 



Osmosis. — To explain this process we must remember that 

 gases and liquids of different densities, when separated by a mem- 

 brane, tend to flow toward each other and mingle, the greater flow 

 always being in the direction of the denser medium. The process 

 hy which two gases or fluids, separated by a membrane, tend to pass 

 through the membrane and mingle with each other, is called osmosis. 

 The method by which the root hairs take up soil water is exactly 



