ROOTS AND THEIR WORK 



89 



material, formed by the activity of the living substance of the 

 cell. The rootjhair is a living plant cell with a wall so delicate that 

 water and mineral sub- 

 stances 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 Diagram of a root hair: CM, cell membrane; 



enough to be easily seen. cs > cel1 ^P; cw > cel1 wall; P, protoplasm; 



An egg with part of the 



N, nucleus; S, soil particles. 



outer shell removed so as to expose the soft membrane under- 

 neath is an example. Better, a root hair may be made in the 

 following way : Pour some soft celloidin into a tube vial ; carefully 

 revolve the vial so that an even film of celloidin 

 dries on the inside of the vial. This 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 cel- 

 loidin. If grape sugar, salt, or some other sub- 

 stance 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 

 An artificial root densities, when separated by a membrane (a 

 hair, showing os- Delicate porous lining having no holes visible to 



mosis taking place. .,,._. 



the highest power microscope we possess), tend 

 to flow toward each other and mingle, the greatest flow always 

 being in the direction of the denser medium. The process by which 

 two gases or fluids, separated by a membrane, pass through the mem- 



