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that the soil contains soluble nitrogen compounds (see 

 page 103). We now know the use of this nitrogen. 



Uses of food. You know that to live you must have 

 food. You know, too, that this food must be digested 

 and taken to all parts of your body. There it must 

 be changed from non-living into living material to be 

 used for growth, repair, or oxidation to produce 

 heat and energy. In order to make this possible, you 

 need air as well as food. In connection with the 

 changes which take place in the wearing out and the 

 building up of parts of the body and in the formation 

 of energy, certain waste substances are formed. These 

 are harmful to the body and must be gotten rid of. 

 The entire process necessary to keep you alive is known 

 as the process of nutrition. 



A plant, likewise, must carry on this process of 

 nutrition. From carbon dioxide from the air, water, 

 and solutes from the soil, and energy from the sun, 

 the plants make their own food. After they have 

 manufactured their food they are then ready to take 

 up the processes of nutrition just where we do after 

 food is eaten. Their food must be digested. By that 

 we mean that it must be transformed into soluble form 

 so that it can be transferred to all parts of the plant. 

 A wonderful process then takes place. This digested 

 food is made into protoplasm. The exact nature of the 

 chemical processes which this involves we do not know, 

 but in some way this non-living food material is made 

 into living protoplasm. Evidently this process can be 



