ROOTS AND THEIR WORK 



89 



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



C.s'. cell sap ; (^11", cell wall ; 

 iV, nucleus ; 5, soil particles. 



P, protoplasm ; 



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

 cell. The root hair 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 

 enough to be easily seen. 

 An egg with part of the 

 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 

 revoh'e the ^'ial so that an even film of celloidin 

 dries on the inside of tlie vial. This is removed, 

 filled with white of egg, and tied over the end of 

 a rubber cork in which a glass tulie has previously 

 been inserted, ^^llen placed in water, it gives a 

 very accurate picture of the root hair at work. 

 After a sliort time water begins to rise in the 

 tube, having jiassed through the film of cel- 

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

 stance which vnW 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 \\(^ must 

 remember that gases and liquids of ilifi'erent 

 densities, when sejiaiated liy a membrane (a 

 delicate porous lining ha\ing no holes visible to 

 the highest power microscdpe we possess), tend 

 to flow toward each other and mingle, the greatest flow a!wa>s 

 being in the direction of the den.ser medumi. The pmcfuf: hi/ irhich 

 two gases or fluids, separated by a invinbrune, pass Ihrouyli the iiiciii- 



An artificial root 

 hair, showing os- 

 mosis taking place. 



