Restoration in Nature 147 



It thus comes to pass that plants lock up in their body- 

 substance enormous amounts of carbon combined with 

 other elements, chiefly oxygen, hydrogen, and, to a 

 smaller extent, nitrogen. When the plants die and 

 mingle with the soil, their carbon becomes a part of 

 the latter as soil-humus. Hence, soil-humus, the decay- 

 ing remains of plants, owes its existence to the carbon 

 and nitrogen of the air, as well as to the hydrogen and 

 oxygen' derived from the water-vapor of the atmosphere. 



But if the vegetation of forests, meadows, and 

 prairies continued indefinitely to draw upon the com- 

 paratively small amount of carbon dioxid in the air for 

 their carbon, the time would come when the atmosphere 

 would have but little left. The surface of the earth 

 would become covered with vast accumulations of fallen 

 trees and tangled herbs, and, in time, plant and animal 

 life would cease because of the exhaustion of the carbon 

 dioxid in the atmosphere. 



Fortunately, however, there is provision in nature 

 for the restoration of this carbon dioxid. In the burning 

 of wood and of coal, the carbon of these materials is 

 changed again into carbon dioxid; in the respiration of 

 animals the carbon of their food is changed to carbon 

 dioxid, and, more important still, in all the processes 

 of decay and putrefaction carbon dioxid is formed. 

 Indeed, .life could not persist without decay. The dead 

 tissues must be* resolved into simple substances that 

 new life may arise and find expression in an almost 

 endless variety of material forms. 



The vastly important processes of decay and putre- 

 faction are biological in character. They would not take 



