CHAPTEE \1 



THE FOOD OF PLANTS 



54. Introductory. — All plants use the same kind of food, 

 but the AlgsB and Fungi suggest that they may have very 

 difEerent ways of obtaining it. The Algse can manufacture 

 food from raw material, while the Fungi must obtain it 

 already manufactured. Between these two extreme condi- 

 tions there are plants which can manufacture food, and at 

 the same time have formed the habit of supplementing this 

 by obtaining elsewhere more or less manufactured food. 

 Besides this, there are plants which have learned to work 

 together in the matter of food supply, entering into a con- 

 dition of symbiosis, as described under the Lichens. These 

 various habits will be presented here briefly. 



55. Green plants. — The presence of chlorophyll enables 

 plants to utilize carbon dioxide (C'Oj), a gas present in the 

 atmosphere and dissolved in waters, and one of the waste 

 products given off in the respiration of all living organisms. 

 This gas is absorbed by green plants, its constituent ele- 

 ments, carbon and oxygen, are dissociated, and with the ele- 

 ments obtained from absorbed water (HoO) are recombined to 

 form a carbohydrate (sugar, starch, etc.), which is an organ- 

 ized food. TVith this as a basis other foods are formed, 

 and so the plant can live without help from any other 

 organism. 



This process of utilizing carbon dioxide in the formation 

 of food is not only a wonderful one, but also very important. 

 It is wonderful, because carbon dioxide and water, both of 

 them very refractory substances, are broken up at ordinary 



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