AGRICULTURE 



plant can use are dissolved in the films of water which, as you 

 learned, surround soil particles. 



Osmosis. But the roots have no mouths or openings through 

 which to take in food. How, then, do they get it ? The root hairs 

 take it in by os mo'sis. That is the scientific name for the passing 

 of substances through a membrane, or layer of covering tissue. 

 By a simple experiment you can observe the working of this force. 



Fill a small bottle with 

 a sirup made of sugar 

 and water, and tie over 

 the mouth a piece of 

 softened bladder or the 

 membrane of the while 

 of an egg. Invert this 

 bottle in a glass con- 



The bottle on the left and the glass on the right contain taining clear Water. In 

 sirup; observe how the membrane covering the bottle is ^ little while the Water 

 pushed out on the left and in on the right by osmosis. -111 11 



will be sweetened by 



the sirup which osmosis causes to pass through the membrane. 

 Reverse the experiment, putting clear water in the bottle and 

 sirup in the glass; again the sirup is drawn through the bladder 

 into the water. So, by osmosis, the water containing the dissolved 

 elements passes through the membranes of the root hairs. 



Do you think that the hungry roots feed at once upon this sap, 

 as it is called ? No, it is not yet ready for them. It must be pre- 

 pared for plant use, as our food must be prepared to nourish our 

 bodies. The leaves are often called the stomach of the plant, 

 because it is in them that the sap is prepared for plant food. 



How Sap Rises. Do you wonder how the sap gets from the 

 roots to the leaves? Osmosis, capillarity, and transpiration all 

 aid in pumping it up. You can observe for yourself the working 



