GENESIS OF THE SOIL AND ITS POSSIBILITIES 203 



I have found that sugar canes grown in peat soils 

 contained a quantity of dark colored organic matter in 

 their sap which persisted even in the raw sugar made 

 therefrom. 



I further found that the quantity of amid nitrogen 

 in oats was greatly increased when grown on peaty soil. 



The chief functions of humus appear to be to mod- 

 ify the physical conditions of the soil with reference to 

 texture, moisture, absorption of heat and mineral mat- 

 ters useful to plants and especially to hold in suitable 

 form for progressive nitrification the partially decayed 

 nitrogenous principles of vegetable matters. 



SOIL AND SUBSOIL. 



Many subdivisions have been made of the above va- 

 rieties of soil, but they have little value for practical 

 purposes. For convenience in description for agricul- 

 tural purposes, the soil, however, is further divided 

 into soil and subsoil. In this sense the soil comprises 

 that portion of the surface of the ground, usually from 

 four to nine inches deep, containing most of the organic 

 remains of plants and animals and in which air circu- 

 lates more or less freely for the proper humification of 

 the organic matter, which usually gives a darker color to 

 the soil than to the subsoil. The subsoil proper lies 

 below this, and has usually more characteristic prop- 

 erties, especially in respect of color and texture, as it has 

 been less influenced by artificial conditions of cultiva- 

 tion and the remains of vegetation. 



The subsoil extends to an indefinite depth and is 

 limited usually by deposits of undecomposed or partly 

 decomposed rock matter, or by layers of clay, sand or 

 gravel. 



Hilgard regards as subsoil whatever lies beneath the 



