Sap ; how obtained and supplied. 123 



1 1 7. All of you have seen an apple tree, and 

 know the various forms of food into which its 

 fruit can be made; but do you know where 

 and how the tree gets the food which it lives 

 upon ? Let us talk about this. 



1 1 8. The substances which supply it with its 

 food or nourishment are in the ground and the 

 air. 



119. The principal substances are called carbon, 

 hydrogen, and oxygen. 



120. Many thousands of little mouths in the 

 roots are ever on the alert for these substances, 

 which go to make wood, leaves, and fruit ; 

 taking them in with the water in the soil, and 

 sending sap upward to every branch, twig, and 

 leaf. 



121. The leaves, too, are at work all day long, 

 breathing in through their countless pores, or 

 mouths, moisture from the atmosphere, and, 

 with the aid of sunlight, changing and prepar- 

 ing the sap. Then the sap returns toward the 

 roots, supplying on its way what is needed for 

 every part of the tree. 



122! The roots, trunk, and branches, contain 

 multitudes of little tubes or pipes, through 

 which the sap flows ; one set for the rising sap, 

 and another set for the returning sap. The sap 



