THE POWER OR ENERGY OF THE PLANT 183 



pounds which it absorbs from the soil, and also 

 makes use of the physical energy exhibited by cer- 

 tain substances. 



220. Sunlight as a source of energy. — The por- 

 tion of sunlight absorbed by leaves is used as a 

 means of separating compounds in such manner 

 that the parts of these compounds will form new 

 and more powerful unions. It is as if one had two 

 magnets, to each of which was adhering a small bar 

 of iron. By the use of a small amount of force 

 the magnets and the iron may be separated, and 

 then the magnets will mutually attract each other 

 with greater force. Sunlight tears away some of 

 the oxygen united with the magnet hydrogen to 

 form water, and some of the oxygen united with 

 the magnet carbon in carbon dioxide, leaving the 

 carbon and hydrogen to rush together, forming a 

 stronger chemical union and carrying with them 

 a portion of the oxygen. 



221. Chemical compounds as a source of energy. — • 

 Animals get all their energy from chemical com- 

 pounds used as food. The foods of the plant are 

 very simple compounds, but they gain some energy 

 in this manner. 



