THE MOTIVE-FOKCE OF PLANTS. 395 



heat, or into magnetic force, or, as in the case of the decom- 

 position of water, into chemical force. In no case is there a 

 diminution or increase of force. If, according to the materi- 

 alist, matter is indestructible, the same holds good with regard 

 to force. It is not extinguished ; its apparent annihilation, 

 its disappearance, is only a conversion into some other form. 



We know now the origin of the heat and light which 

 warm and illuminate our dwellings, of the heat and power 

 generated in our bodies by the vital process. Plants are the 

 one source of all materials used for the production of heat 

 and light, and of that nourishment which must be daily taken 

 to maintain the phenomena of vitality. The elements of 

 plants are earthy in their nature, and are obtained from 

 water, earth, and air. In plants, certain inorganic com- 

 pounds carbonic acid, water, and ammonia-r-are decom- 

 posed. The carbon of the carbonic acid, the hydrogen of 

 the water, and the nitrogen of the ammonia, are retained as 

 constituents of their organs, but the oxygen of the carbonic 

 acid and of the water are returned as gas to the air. With 

 out light, however, plants cannot grow. 



The vital process in plants exhibits itself as directly oppo- 

 site in its character to the chemical process in the formation 

 of salts. f 



Carbonic acid, water, and zinc, when brought together pro- 

 duce a certain effect on each other. In virtue of chemical 

 affinity there is formed a white powdery compound, contain- 

 ing carbonic acid, zinc, and oxygen from the water, and 

 hydrogen is at the same time evolved. 



In plants, the living bud or part of the plant takes the 

 place of the zinc. By their growth are formed, from carbonic 

 acid and water, compounds containing carbon and hydrogen, 

 or carbon and the elements of water, and oxygen is at the 

 same time evolved. Sunlight acts in living plants like elec- 

 tricity, which arrests the natural attraction of the elements of 

 water, and separates them from each other. 



