HOW SOILS ARE MADE AND MIXED 



11 



carbon. It is the only element which they do not take 

 from the soil. 



Hydrogen and oxygen are odorless, invisible gases. 

 They are not at all alike, but will unite with each other, 

 the compound formed being water, 

 H2O. Plants of course draw a great 

 deal of water from the soil, and from 

 this water they take the hydrogen 

 and oxygen which they must have in 

 order to live. 



Nitrogen, too, is an invisible gas, 

 but it differs greatly from both 

 hydrogen and oxygen. It com- 

 prises nearly four fifths of the at- 

 mosphere ; yet plants, whose leaves 

 are held aloft in it, can take none 

 whatever from the air. Instead, 



B C 13 



- Plants growing in water cultures. 



A, plant receives all the essential elements; B, plant receives all 

 essential elements except nitrogen ; C, plant receives all essential 

 elements except phosphorus ; D, plant receives all essential elements 

 except potassium. 



it combines with other elements ; and the compounds 

 so formed, which are found in the soil, are dissolved 

 and carried upward into the plant by the soil water. 



Sulfur is commonly seen as a yellow powder, which 

 produces suffocating fumes when burned. Phosphorus is 



