CHAPTER TWO 



Learning 

 about plant 

 food male- 

 rials 

 through 

 chemistry 



Elements 



and 



compounds 



Elements 

 that any 

 plant must 

 have 



THE FOOD OF PLANTS 



Out of its little hill faithfully rise the potato's dark green leaves, 

 Out of its little hill rises the yellow maize stalk. 



WALT WHITMAN 



To have an intelligent understanding of the soil and 

 the sources of plant food, we must learn some of the 

 things that chemists can tell us, for it is their business 

 to study the composition of substances and the changes 

 that take place in them. Chemists have found out 

 that all things in the world are made up of only about 

 eighty-five different elements. 



An element is a substance that cannot be separated 

 into any two or more things, for it is made of one 

 thing only. Thus, hydrogen is an element but water 

 is not, for water is made of two things, hydrogen 

 and oxygen. (Exp. i.) Iron, also, is an element, 

 for it is made of only one thing, iron. Iron rust is 

 composed of iron and oxygen. (Exp. 2.) It is a com- 

 pound. A compound is a substance made of two or 

 more elements united. Thus, water is a compound, 

 and nearly all other substances, as stones, soil, fer- 

 tilizers, wood, food, and even our own bodies, are made 

 up of compounds. 



Plant food materials ; sources of supply. There are 

 only ten elements that all ordinary farm plants must 

 have in order to make leaves, stems, roots, seeds, and 

 everything that the plant produces. These are as 

 follows : potassium, calcium, iron, and magnesium ; 

 nitrogen, phosphorus, sulfur, and carbon; hydrogen 



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