The chemistry of plant and animal life . y in the chap-ters relating to the chemistry of foods. OXIDS OF CARBON, CARBONATES, ETC. 117 Vegetable foods and fuels are alike in chemcal com-position, and serve somewhat the same functions,but in different ways. Food is used as fuel by the body,and also for the renewal of old and the production of newtissues. The heat produced from food is transformedinto muscular and other forms of energy ; the heat fromthe combustion of fuel is converted into chemical energy,which is utilized for mechanical purposes. 145. Production of Organic Compounds in Plants.—
The chemistry of plant and animal life . y in the chap-ters relating to the chemistry of foods. OXIDS OF CARBON, CARBONATES, ETC. 117 Vegetable foods and fuels are alike in chemcal com-position, and serve somewhat the same functions,but in different ways. Food is used as fuel by the body,and also for the renewal of old and the production of newtissues. The heat produced from food is transformedinto muscular and other forms of energy ; the heat fromthe combustion of fuel is converted into chemical energy,which is utilized for mechanical purposes. 145. Production of Organic Compounds in Plants.—The carbon dioxid of the air is the source of the carbonused by plantsfor the produc-tion of thevarious organiccompoundsfound in vegeta-ble substances,and since about50 per cent, ofthe ash-free tis-sue of plants iscarbon, it fol-lows that thecarbon dioxidof the air is animportant fac-tor in plantgrowth. Hydrogen and oxygen are obtained fromthe water of the soil which is received from theair. The production of the various organic corn-. Fig. 49.—Production of organic compounds in plants,showing sources of plant food. Il8 AGRICULTURAI, CHEMISTRY pounds of plants takes place in the cells of theleaves, and is the result of chemical changes induced bylife processes. In order to promote cell activity, sun-light and a suitable temperature are necessary. Thesuns rays take an important part in promoting chemicalchanges in the leaves of plants. In addition to carbondioxid, water, heat, and sunlight, various mineral ele-ments in the form of compounds of potassium, calcium,phosphorus, nitrogen, iron, magnesia, sulfur, and pos-sibly of a iew others are required as plant food. Withoutthese essential elements and requisite conditions, thegrowth of crops cannot take place. It often happens thatsoils are unproductive because of the absence, in availableform, of some of the elements essential for plant production in the leaves of plants of the various or-ganic compounds, as cellulos
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