78 



SOIL AND ITS RELATION TO ROOTS 



tell us that once upon a time at least a part of the earth was molten. 



Later, it cooled into solid rock. Soil making began when the ice 



and frost, working al- 

 ternately with the heat, 

 chipped off pieces of 

 rock. These pieces in 

 time became ground in- 

 to fragments by action 

 of ice, glaciers, running 

 water, or the atmos- 

 phere. This process 

 is called weathering. 

 Weathering is aided by 

 oxidation. A glance 

 at almost any crum- 

 bling stones will con- 

 vince you of this, 

 because of the yellow 

 oxide of iron (rust) 

 disclosed. So by slow 

 degrees this earth be- 

 came covered 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 the 



so-called rich soil and poor 



soil. The dark soil con- 

 tains more dead plant and 



animal matter, which 



forms the portion called 



humus. 



Humus contains Or- 



Apparatus tor testing the capacity of soils 



ganic Matter. - It IS an to take m and retain moisture. 



This picture shows how the forests help to cover 

 the inorganic soil with an organic coating. 

 Explain how. 



