54 AGRICULTURE 



PLANT FOOD 



Plants' Need of Food. You know that an animal must have 

 food; did you ever consider that food is as necessary to a plant as 

 to an animal ? Every living thing needs food to keep it alive and 

 to make it grow. But, you say, we did not feed the cotton plant. 

 We did so indirectly. We planted the seed and cared for the young 

 plant so that it could get food from its two great storehouses, the 

 soil and the air. Sometimes, however, we have to do more than 

 this. We have to supply to our crop-plants elements that they 

 need, and in order to do this we ought to know what these ele- 

 ments are. 



Chemists have analyzed plants and separated them into the 

 elements of which they are composed. Thus they have learned 

 what is needed to make them grow and develop. All of the elements 

 which exist in the soil are not necessary to plants. 



Necessary Elements. There are ten which are necessary for 

 plant growth. These are oxygen, hydrogen, carbon, nitrogen, iron, 

 phosphorus, sulphur, calcium, magnesium, and potassium. We 

 cannot say that any one of these is more important than another. 

 If the plant be deprived of any one, it will die. 



Air-derived Elements. The elements oxygen, hydrogen, car- 

 bon, and nitrogen are derived directly or indirectly from the air. 

 They form about ninety-five per cent of the plant's body. 



The oxygen and hydrogen are taken in chiefly in the form of 

 water. It dissolves solids, liquids, and gases, and carries food 

 to plant roots. 



Carbon composes about half the solid matter of a plant. It 

 forms a small quantity of the air, only about one part in 

 twenty-five thousand, but the amount in the whole volume of 



