38 THE PLANT. 



CARBON. In the form of carbonic acid from the 



atmosphere, and from that contained 



in the sap, the oxygen being returned 



to the air. 



OXYGEN j p rom t j ie elements of the water con- 



UVDROGEN. ) stituting the sap. 



N ITKOGEN. 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 

 HATTER. ) water. 



Many of the chemical changes which take place 

 in the interior of the plant are well, 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. 



The 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. 



