58 



FOODS AITD NUTRITION 



which we call nutrients, are produced from the elements or 

 their inorganic compounds. A few simple experiments 

 with a seedling (see Ex. XIX.) demonstrate that a plant 

 grows well when its diet is restricted to water, certain min- 

 eral salts, and carbon dioxide. The roots take up the 

 salts and water as solutions, while the leaves absorb the 

 carbon dioxide from the air. When analyzed, the plant 

 thus restricted in diet is found to have produced proteid, 

 starch, sugars, and oils. Plant physiologists tell us that 

 the simple raw materials are broken up and recombined 

 chemically into what we call the nutrients, and that a plant 



is actually a sort 

 of manufacturing 

 chemical labora- 

 tory where these 

 reassemblings of 

 elements are con- 

 tinually taking 



mine soil 



A 



Fig. 22 — A, diagram illustrating the manufacture of nutrients ty the plant; -B, 

 cycle illustrating the relation of living forms and the mineral world in regard to 

 nutrient supply. 



place. Some of this manufactured nutrient the plant 

 uses for its own food and some it stores. The stored nu- 

 trients are in turn taken in by the animals, and by them 



