CHAPTER IX 

 CONSTRUCTION OF THE PLANT'S FOOD 



The Source and Uses of Food. — It is the business of the 

 green plants, known also as the autophytes, or independent 

 plants, to make the food that is consumed by themselves as 

 well as by other plants and animals. This they do by com- 

 pounding carbon, which they get from the carbon dioxide of 

 the atmosphere, hydrogen and oxygen from water, and nitro- 

 gen, phosphorus and sulphur from the soil, into sugars, starches, 

 oils, proteids, and some other less common forms of food. These 

 are the food of plants, made by the green plants for their own 

 use, but consumed also by parasitic plants and by animals, all 

 of which are directly or indirectly parasitic on green plants. 



It is sometimes said that plants live on inorganic matter, 

 animals on organic. This, however, is not an exact statement. 

 The food of plants and animals is the same. The difference is, 

 rather, in this, that green plants make their food from inorganic 

 matter, namely, from carbon dioxide, etc., as above stated, 

 while animals cannot make their food, but must take that pro- 

 vided by plants. A bean plant, a corn plant, an oak plant, all 

 green plants, so long as the leaves are green, are making food 

 while the sun shines and furnishes them the energy with which 

 to work. 



The food has two distinct uses: It provides materials for the 

 construction of the body, and energy for carrying on the vital 

 functions. The living protoplasm and the cell-wall, — every 

 part of the plant body in all its details, are made from materials 

 that first appeared as food in the form of sugar, starch, oil, 

 proteid, etc., and practically everything that plants do, aside 

 from food-construction where the sun supplies the needed energy 



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