CHAPTER IX 



THE INTAKE OF CARBON AND THE MAKING 

 OF ORGANIC FOOD 



ORGANIC matter constitutes the predominant part of the 

 solid constituents of plants. As organic matter so-called, 

 this element is linked chiefly with hydrogen ; with hydro- 

 gen and oxygen; with hydrogen, oxygen, and nitrogen; 

 or with the preceding and one or more of the essential 

 mineral elements. Nevertheless, carbon may be regarded 

 as the significant element of organic compounds. The 

 number of such organic compounds in plants and animals 

 and their products is almost beyond count. It is the 

 special province of organic chemistry to deal chemically 

 with these carbon series, but some account of the origin, 

 nature, and role of certain of these substances in the living 

 organism is a most important part of physiology, whether 

 elementary or advanced. 



104. The amount of carbon in the plant. We have 

 noted the relatively small amount of mineral or ash ele- 

 ments in plants, constituting usually from 1 to 5 per cent 

 of the total weight of the water-free substance. Nitrogen 

 adds a further fraction, seldom more than 5 percent, 

 and the remainder, that is, more than 90 per cent of 

 the dry matter, is made up of carbon, hydrogen, and oxy- 



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