OXIDS OF CARBON, CARBONATES, ETC. 



II 



PLANT FOOO FROM 



Vegetable foods and fuels are alike in chemcal com- 

 position, and serve somewhat the sa'me functions, 

 but in different ways. Food is used as fuel by the body, 

 and also for the renewal of old and the production of new 

 tissues. The heat produced from food is transformed 

 into muscular and other forms of energy ; the heat from 

 the 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 carbon 

 used by plants 



for the produc- 

 tion of the 

 various organic 

 compounds 

 found in vegeta- 

 ble substances, 

 and since about 

 50 per cent, of 

 the ash-free tis- 

 sue of plants is 

 carbon, it fol- 

 lows that the 

 carbon dioxid 

 of the air is an " SOURCES ofv PLANT FOOD \ 



Fig. 49. Production of organic compounds in plants, 

 tor in plant showing sources of plant food. 



growth. Hydrogen and oxygen are obtained from 

 the water of the soil which is received from the 

 air. The production of the various organic com- 



