CHAPTER IV. 

 CHEMISTET OF THE GAKDEH. 



The chemistry of the garden is that science which 

 attempts to define the action of plants upon the chemi- 

 ical constituents of the soil and air; consequently 

 includes the studies of garden geology, the nature of 

 minerals composing the soil, vegetable physiology and 

 plant nutrition, each indicating how the chemical sub- 

 stances are made use of by the vegetable world. The 

 subject of agricultural chemistry is a voluminous and 

 intricate one, and only a very brief reference can be 

 made to it here. Nothing more can be here attempted, 

 than to lead the reader to desire for further information, 

 obtainable from the writings and reports of men like 

 Lawes and Gilbert, of England, Samuel W. Johnson, 

 and others, of this country. All garden and farm plants 

 may, as respects their food, be divided into three classes : 



First: Those requiring an excess of potash, as 

 peas, beans, potatoes, clover, flax. 



Second: Those requiring much nitrogen, as beets, 

 cabbage, oats, wheat, barley and hemp. 



Third: Those requiring large amounts of phos- 

 phoric acid, as radish, turnip and corn. 



Plants draw some food from the air by their leaves, 

 but most from the earth by their roots. The composition 

 of the air is quite constant, but the character of the soil is 

 exceedingly variable, and crops grown continuously upon 

 a soil draw out one or more of its nutritive principles ; 

 consequently, it can only be reinvigorated by returning 

 to it those elements removed in the crops. 



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