38 THE PLANT. 



Caiibon. — III the f(fim of carhonic acid from tliG 

 atmosphere, and from that contained 

 in the sap, the oxygen being returned 

 to the air. 



c ^ ) From the elements of the water con- 

 IIydrogen. ) stitnting the sap. 



KiTEOGEX. — From the soil (chiefly in form of am- 

 monia). It is carried into the plant 

 through the roots in solution in water. 

 Earthy \ From the soil, and only in solution in 

 MATfER. ) water. 



Many of the chemical changes wliicli take place 

 in the interior of the plant are v.-ell, and some but 

 imperfectly understood, but they require too much 

 knowledge of chemistry to be easily comprehended 

 by the young learner, and it is not absolutely essen- 

 tial that they should be understood by the scholar 

 who is merely learning the elements of the science. 



It is sufficient to say that the food taken up by 

 the plant undergoes such changes as are required for 

 its growth ; as in animals, where the food taken into 

 the stomach is digested, and is afterward formed 

 into bone, muscle, fat, hair, etc., so in the plant the 

 nutritive portions of the sap are resolved into wood, 

 bark, grain, or other necessary parts. 



Tlie results of these changes are of the greatest 

 importance in agriculture, and no person ought to 

 be called a thoroughly practical farmer who does 

 not understand them. 



