10 SOILS AND PLANT LIFE 



accumulation was an inch in every five years. The im- 

 portance of the worms, both as mellowers of the soil and 

 as levelers of inequalities is therefore very great." 



7. Elements in the Soil an(f Air which Plants must 

 have in Order to make a Healthy Growth. — In this 

 brief lesson, we have learned that soil is made up of pow- 

 dered rock and decaying vegetable and animal matter. 

 We have learned how they are mixed by various agents. 

 The soil contains a large number of distinct substances 

 called elements. Only ten of them, however, are essential 

 to plant growth. Their names together with their chemi- 

 cal symbols are given below : 



Carbon (C) Nitrogen (N) Potassimn (K) 



Hydrogen (H) Sulfur (S) Calcium (Ca) 



Oxygen (0) Phosphorus (P) Magnesium (Mg) 



Iron (Fe) 



We shall learn in chemistry of the various ways in 

 which these elements combine in the soil to form plant 

 food. It is enough here for us to know that without any 

 one of them a plant can not make healthy growth. 



Carbon, as usually seen, is a black solid. Coal and 

 charcoal owe their black color to the fact that they are 

 nearly pure carbon. This element comprises about a 

 half of the dry matter of all plants, that which is present 

 in coal and charcoal coming from plants that have Uved 

 in the past. All of our foods likewise contain carbon, 

 which accounts for their turning black, or charring, when 

 burned. Under certain conditions, carbon will unite 

 with oxygen, forming carbon dioxide, a gas which is 

 found in the atmosphere. The leaves of plants take this 

 gas from the air, and in this way, plants get all their 



