PLANTS. 61 



evident that plants appeared first upon the earth, 

 and animals afterwards. Animals cannot exist 

 without previous plant life. It is true that some 

 animals eat nothing but flesh, or other animals; 

 but all animal life would soon disappear from the 

 face of the earth if there were no plants from 

 which they could get the organic material. 



The leaves of plants get most of the material for 

 plant structure from the atmosphere, and only a 

 small amount from the soil. It would appear, 

 then, that the farmer need care little about the soil 

 in which plants are grown; but the substances in 

 the soil are absolutely necessary. Besides, the soil 

 costs money, while the air is free to all. In the 

 burning of a stove two things are necessary fuel, 

 and oxygen of the air. The fuel costs money, 

 but the oxygen comes floating in without price. 

 Nearly twice as much oxygen as fuel is used in the 

 act of combustion. If it had to be paid for at the 

 same rate as fuel, modern house heating would be 

 very expensive. It is likewise true of ourselves, 

 and the animals we raise the food costs labor and 

 money, but the large amount of oxygen costs noth- 

 ing. So it is with plants carbonic acid gas comes 

 free, but land is scarce and high-priced. Besides, 

 the air can never be exhausted of its supply, for all 

 burning and decay constantly return enormous 

 quantities of this gas to the atmosphere, to be used 

 over and over again. 



