CHAPTER FIVE 



THE FOOD OF PLANTS 



There's magic done in plants. 

 O'er simple elements of earth and air, 

 A sun-beam wand is passed 

 And food is there ! 



NEVIN WOODSIDE 



WE live and grow on the food we eat, but a corn 

 plant lives and grows without eating. It sends its roots 

 out into the soil, spreads its leaves to the light and air, 

 and week by week increases in size. Finally the ear ap- 

 pears with the kernels swollen with a rich store of food. 

 The plant has lived, reached its full size, and at the end 

 of life has a surplus of food on hand. 



In our garden and field crops we find sugar, starch, oils, 

 and the other foods that we live on, and these are not in 

 the soil or air. Where do plants get them? What do 

 plants use for food? Only in comparatively recent years 

 have scientists been able to answer these questions. 



The food of plants. In your study of physiology 

 you learn that man and the lower animals use for food 

 proteins, fats, and starch and sugar. Plants use these 

 same foods. 1 The difference between the nourishment 

 of a green plant and the nourishment of an animal is 

 that the green plant makes its own foods from water, carbon 

 dioxid, and minerals, while an animal cannot do this 

 but must have its food already prepared for it. 



1 Sometimes carbon dioxid, water, and the various minerals used by 

 a plant are called "plant foods." Sometimes these are called the "raw 

 materials used in the making of food," or simply "food materials," and 

 the term "food" is used to mean the sugars, starches, fats, and proteins 

 that are built up from these substances. In this text the word is used 

 (as it is in animal physiology) to mean the complex, built-up substances 

 actually used in the nourishment and growth of the living matter of the 

 cells. 



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