34 AMERICAN AGRICULTURE. 



ficial modern reader, is wholly untenable. Some agricul- 

 turists of the present day, however, while they scout Tull's 

 theory, (who was, nevertheless, a very shrewd man for his 

 time), will yet claim as essential to successful vegetation, 

 the existence in the soil, of but a part only of the food of 

 plants. Thus, one asserts that the salts alone will secure 

 good crops ; others maintain that the nitrogenous substances 

 are the true source of fertility ; while still another class refer 

 to the presence of humus or geine, (the available product of 

 vegetable and animal decay in the soil), as the only valuable 

 foundation of vegetable nutriment in all manures. Truth 

 and sound practice lie between, or rather in the combination 

 of all these opinions. 



It has been shown in a preceding page (17th), that all 

 fertile soils must have not less than fifteen, and more pro- 

 bably sixteen, different simple or elementary substances, in 

 various combinations with each other. All of the ordinary 

 cultivated plants, contain potash, soda, lime, magnesia, 

 alumina, silica, oxide of iron, oxide of manganese, sul- 

 phuric acid, phosphoric acid, chlorine, and frequently 

 iodine ; each of which, excepting the two last, are in com- 

 bination with oxygen. In addition to these, they also have 

 carbon, oxygen, nitrogen and hydrogen. Other substances 

 or ultimate principles may possibly exist in plants, which 

 analysis may hereafter detect, but which have hitherto elu- 

 ded the closest investigation. 



It is therefore obvious, that such principles as all fertile 

 soils furnish to vegetables, must be contained in manures. 

 It is no satisfactory answer to this position, to assert, that 

 numerous experiments have apparently been successful, of 

 growing plants in pure sand and water ; or with charcoal 

 and the salts added ; or even that there are some atmosphe- 

 ric plants, that fulfill their zoophytic existence in air. 

 Growth may continue for a long time under such circum- 

 stances ; but full maturity never arrives, and probably 

 never can, without the available presence in the soil, of 

 every element which enters into the composition of plants. 



Profitable farming requires, that manures embodying all 

 these elements, should be added in sufficient quantities to the 

 soil, to develope fully and rapidly, such crops as are sought 

 from it. It becomes then, a matter of the highest consequence 

 to the farmer, to understand not only what substances may be 

 useful as manures ; but also, how to apply them in the best 



