SECTION VI. HOW PLANTS GET FOOD FROM 

 SOIL AND AIR 



No solid matter can enter a plant. The living matter 

 that lines the inside of each cell-wall will not let even the 

 finest solid particles pass, though they be as fine as those 

 of flour or of phosphate. No part of the soil can act as 

 food until it has been dissolved. 



Sugar and salt, as you know, dissolve in water, and just 

 so do certain substances in the soil dissolve in the water. 

 In ordinary soil this solution is very weak, so weak that 

 it will usually take several thousand pounds of water to 

 carry to the plant one pound of lime, phosphate, or any 

 other single plant-food. In later chapters, you will learn 

 what food certain plants require and also how the farmer 

 adds this to any soil that is too poor to supply to the plant 

 the needed nourishment. 



Plants are made largely from the air. Fortunately for 

 the farmer and for the food supply of the world, the plant 

 obtains more material for its solid substance from the 

 air than from the soil. In every hundred pounds of dry 

 plants there are usually less than three pounds that come 

 from the soil. The grains of wheat, corn, and rice consist 

 chiefly of starch. Other plants are rich in sugar, while 

 the seeds of still others contain much oil or fat. Starch, 

 sugar, oil, and many other substances in plants are made 



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