COMPOSITION OF PLANTS. 101 



plants may appear trifling, as shown by the an- 

 alyses ; but its value is startling when we con- 

 sider it in the crops removed from an acre of 

 land. The following case, given by Professor 

 Johnson, will illustrate this in a striking man- 

 ner : 



In a four years' course of cropping, in which 

 the crops gathered amounted per acre to 



1st year, turnips, 20 tons bulbs, and 6^ tons tops ; 

 2nd year, barley, 40 bushels, and 1 ton of straw; 

 3rd year, wheat, 25 bushels, and If tons of straw ; 

 4th year, clover and rye grass, 1J tons each of straw ; 



the quantity of inorganic matter carried off in 

 the four crops, supposing none to be consumed 

 on the land, is a follows : 



Silica 356 Ibs. 



Phosphoric Acid 116 " 



Sulphuric Acid 108 " 



Lime 193 



Magnesia 55 " 



Oxide of Iron 15 " 



Potash 317 " 



Soda 54 " 



Chlorine . . . 70 " 



Total 1284 Ibs. 



Now, if the entire produce be carried from the 

 land, and no manures be applied in the meantime, 

 it will be necessary, to restore the land to its 

 original condition, to add to each acre : 



