64 



ROOTS 



microscope, we find considerable water clinging to the soil particles 

 and forming a delicate film around each particle. 



Under the microscope, also, most soils are seen to contain par- 

 ticles of different kinds. Some are tiny pieces of rock, like those 

 still being formed where solid rock is exposed to the weather. 

 Rain, cold, and ice, working alternately with heat, chip off pieces 

 of rock. These pieces in time may be worn smaller b}' the action 

 of ^4nds, running water, and in some places by glaciers. These 

 processes of soil making are aided by oxidation. A glance at crum- 

 bling stones will give you an example of this, in the yellow oxide of 

 iron (rust) disclosed. So by slow degrees the earth became covered 



Inorganic soil is being formed b\ 

 weatliering. 



Forests help to cover inorganic soil -^dth 

 an organic coating. 



with a coating of what we call inorganic soil. Later, generation 

 after generation of tiny plants and animals which lived in the soil 

 died, and their remains formed the first organic materials of the soil. 



You are all familiar with the difference between so-called rich 

 soil and poor soil. The dark soil contains more dead plant and 

 animal matter, which forms the portion called humus. 



Humus contains Organic Matter. — It is eas}^ to prove that 

 black soil contains organic matter, for if equal weights of care- 

 full}^ dried humus and of soil from a sandy road are heated red- 

 hot for some time and then reweighed, the humus will be found to 

 have lost considerably in weight, and the sandy soil to have lost 

 very little. The material left after heating is inorganic materiaL 

 the organic matter having been burned out. 



