CHAPTER IV 



THE FOOD OF PLANTS 



Need of Abundance of Food. If a plant has no food or 

 has too little food, it starves to death, just as we should 

 do. But the least quantity of food which will keep a 

 plant alive is not enough to make it grow, and if a plant 

 does not grow, it is of no value to agriculture. Nor is 

 mere growth all that is needed. Agriculture is not 

 profitable unless the plants raised grow thriftily and 

 rapidly. They cannot do this unless they have a great 

 deal more food than would keep them alive and let them 

 grow a very little. Hungry plants, like hungry men, are 

 poor workers. 



Importance of Variety of Food. Plants are also like ani- 

 mals in needing several kinds of food. Men need to eat 

 some salt; if they did not get salt, by itself or in other 

 food, they would die. But if they got salt and no other 

 food, they would still more quickly starve to death. 



Rice is the principal food of nearly all Filipinos, but 

 all Filipinos know that they cannot live on rice alone. 

 Plants have many foods which are so absolutely neces- 

 sary that if any one is entirely wanting, the plant must 

 die. 



CHEMICAL ELEMENTS 



Composition of Substances. Nearly all the substances 

 we see in the world are combinations of simpler sub- 



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