CHAPTER XXVI 



NITROGEN AND ITS RELATION TO PLANTS 



244. Nitrogen. A substance which plays an important 

 part in animal and plant life is nitrogen. Soil and the ferti- 

 lizers which enrich it, the plants which grow on it, and the 

 animals which feed on these, all contain nitrogen or nitrog- 

 enous compounds. The atmosphere, which we ordinarily 

 think of as a storehouse of oxygen, contains far more nitrogen 

 than oxygen, since four fifths of its whole weight is made up 

 of this element. 



Nitrogen is colorless, odorless, and tasteless. Air is com- 

 posed chiefly of oxygen and nitrogen ; if, therefore, the oxy- 

 gen in a vessel filled with air can be made to unite with some 

 other substance or can be removed, there will be a residue of 

 nitrogen. This can be done by floating on water a light dish 

 containing phosphorus, then igniting the phosphorus, and 

 placing an inverted jar over the burning substance. The 

 phosphorus in burning unites with the oxygen of the air and 

 hence the gas that remains in the jar is chiefly nitrogen. It 

 has the characteristics mentioned above and, in addition, does 

 not combine readily with other substances. 



245. Plant Food. Food, is the source of energy in every 

 living thing and is essential to both animal and plant life. 

 Plants get their food from the lifeless matter which exists 

 in the air and in the soil ; while animals get their food 

 from plants. It is true that man and many other animals eat 



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