17 



principles of rotation leads to-day, IMany a farmer, year 

 after year, by preparing the same land for the same crop with 

 an occasional fallowing, goes on piling up wealth of fertilizing 

 power, perhaps only to be utilized by his more enlightened 



successor. 



Simple, however, as is this underlying principle of the ro- 

 tation of crops, it suggests problems most difficult of solution. 

 It is easy to say, given the relative amount of fertilizing 

 agents contained in a certain soil, determine the kind of pro- 

 duction to which it is adapted ; but it is not so easy to ascer- 

 tain either the elements contained, or the best combination of 

 those elements, to forward as well as to insure vegetable 

 "•rowth. We all know that diiferent forms of food which 

 contain about the same elements of nutrition, are different in 

 their effects upon the luuuan system, and the same seems to 

 •obtain of vegetable life, especially Avith regard to the stimu- 

 lating qualities of certain manures. And it is upon this 

 ground alone, as f have before hinted, that the efficacy of the 

 manures of commerce may be established as affording that 

 ■concentration with which is associated stimulating power. 



Again it is found that a stated crop does not follow in ro- 

 tation, with the same result, all crops to which it bears the 

 same chemical relation. 



But to turn from the complexities which the refinements of 

 agriculture open to our view, the most mai'ked effects of the 

 workings of this great principle are to be observed in the 

 crudest attempts at tilling the soil, and it is to nature herself 

 that we look to behold the most striking instance of the law, 

 that when there is no artificial renewal of fertility change 

 becomes a necessity of long continued growth. Witness the 

 ever-green forest, which once leveled by the Avoodman's ax, 

 turns, or may it not be, returns to a deciduous growth. 



The estimation in which any pursuit has been held in dif- 

 ferent countries at diflferent eras, has been founded not neces- 

 sarily upon its usefulness, nor even upon the kind or quality 

 of labor or ex^ertaon demaji-ded in its prosecution, but has been 

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