The Soil 



into humus, and also the leaves that fall from 

 the trees and rot on the ground. The vege- 

 table generations of to-day are nourished by 

 the humus formed by the remains of their 

 predecessors ; and they, in their turn, will 

 become the soil which will give birth to their 

 successors. It is thus that plant life is sup- 

 ported in portions of the earth that are not 

 cultivated by man. Humus is the natural 

 manure and where it is formed uninter- 

 ruptedly the plant life remains vigorous, 

 transmitting the same substance from one 

 generation to the next, alternately plant and 

 soil. But the hay from the meadow is taken 

 to the hay-loft and the harvest of the corn- 

 field is stored in the barn ; so that the ground 

 is deprived of the humus which would be 

 naturally formed by the corruption of the 

 hay or wheat. We must therefore restore 

 to the ground in some way the soil that has 

 been removed, or it will gradually become 

 poorer and finally barren. This is done by 

 supplying it with manure ; for the dung of 

 animals is a kind of humus, produced by the 

 work of digestion instead of by natural 

 corruption. 



Humus fulfils a double office. In the first 

 place it makes the earth lighter, so that it is 



7 1 



