CHAPTER VI 

 THE ELEMENTS THAT PLANTS USE 



We have considered heretofore the physical side of 

 soils: the components that make them, the size, the ar- 

 rangement, and the behavior of the soil particles, the 

 work of air and water how each is influenced by the 

 texture of the soil. 



Our knowledge of these things has been given to us 

 largely by the soil physicist, who, either in the field or in 

 his laboratory, has sought to discover those laws that are 

 concerned with the mechanical conformation. Now we 

 are ready to learn of some of the findings of the chemist, 

 for in his laboratory are revealed many hidden secrets, but 

 none of more interest than those having to do with soils 

 and plants. 



A word about the element itself. We must not mis- 

 understand the nature of an element: it is a single thing 

 altogether, standing by itself and alone. Water is not an 

 element, because it is composed of two elements oxygen 

 and hydrogen. Table salt is not an element, for sodium 

 and chlorine two elements themselves have united and 

 salt has resulted. Wheat is not an element, nor is the air 

 we breathe ; neither are the clothes we wear, the coal we 

 burn, the food we eat: these are compound substances, 

 made of two or more single elements. 



An element from its very nature is indestructible. You 

 can destroy plants, and animals, and wooden things, all 

 made of many elements, but you cannot destroy the ele- 

 ments that compose them. When plants or animals die, 

 when substances decay and disintegrate, or otherwise are 



