CHAPTER X 

 PLANT FOODS AND PLANT GROWTH 



WE HAVE learned something about the important substances 

 found in plants, the starches, sugar, oils and proteids which make 

 them valuable for food. We have also learned that they con- 

 tain many other substances of more or less value in commerce. 

 We also know that many plants are grown for their fibre which 

 is used in many manufacturing industries, and we also use the 

 wood of many of the larger plants for many purposes. There- 

 fore, it is very evident that the plant kingdom produces a very 

 large number of useful plants. Let us now study the source of 

 these products and the processes by which they are formed. 



Plants are unlike animals in that they use comparatively 

 simple compounds which are obtained from the soil and air and 

 transformed into true food materials for their own growth; 

 animals cannot use such simple compounds, but are compelled 

 to feed upon plants from which they secure already manufac- 

 tured or true foods, carbohydrates and proteids. Therefore, all 

 animal life is dependent either directly or indirectly on plant 

 life for its existence. The most important raw foods or com- 

 pounds that the plant gets from the earth are water (H 2 O), 

 ammonia compounds (NH 3 ), sulphur, potassium and phos- 

 phorus, and various salts. The most important raw foods from 

 the air are carbonic acid gas or carbon dioxide (CO 2 ) and very 

 small amounts of oxygen (O). 



The energy with which these raw materials are transformed 

 into true foods comes from the sun in the form of heat and light. 

 Therefore, all life (both plant and animal) upon the earth is 

 dependent upon the sun for its existence. These raw foods are 

 transformed into true foods in the plant before they can be 



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