THE ELEMENTS THAT PLANTS USE 53 



destroyed, the elements that originally formed these sub- 

 stances enter into new combinations and go back either 

 to the soil or to the air (from where they came), there to 

 remain until called into service again by plants or animals 

 for some service of the world. 



Elements not in a pure state in the soil. Do not imag- 

 ine that the elements essential to plants are to be found 

 in a pure state in the soil, for they are not. You will 

 find only one or two in the entire list of chemical ele- 

 ments that are to be found in a pure state anywhere in 

 nature's storehouses. Of course, in the chemist's labora- 

 tory you will be able to find these, for it is his work to 

 separate the elements and to acquaint himself with their 

 characters that he may recognize them readily when freed 

 by him or held slave by some organized force, like a plant 

 or animal. 



These elements do not behave in just the same manner: 

 some are poisonous to us, others are food ; some may be 

 seen and felt and tasted, while others we can neither see 

 nor feel nor taste ; some are abundant, present in every 

 place ; others are so rare we may never see them at all. 



Plants use elements combined with others. When con- 

 sidering the elements that compose soils and plants and 

 animals, remember, therefore, that they are not in a free 

 and pure state such as the chemist in his laboratory may 

 force them to go ; they are combined always with other 

 elements, producing by their combination the innumer- 

 able products of the world. While we speak of elements 

 of plant food, we should remember that such are given to 

 the plant out of products which possess these elements, 

 but in combination with other kinds. To understand more 

 clearly these food substances which plants so greatly 

 fancy and need, a brief discussion of each will follow : 



Oxygen: our most important element. With every 



