I now pass to a subject, a full consideration of which would 

 involve the whole science of agriculture, properly so called, 

 but which is nevertheless in its main points capable of concise 

 statement. I refer to the rotation of crops. To begin with 

 the simplest proposition, it is self-evident, that, besides the 

 elements of growth contained in air and water, a vegetable 

 substance is made u]) from constituents of the soil. Chem- 

 htry shows us what these elements are, and in what propor- 

 tion they occur in different forms of vegetable life. It re- 

 mains then to ascertain what elements a given soil contains, 

 and in what proportion, and we are ready to apply our prin- 

 ciple. Let the elements of fertility contained in a given soil 

 be represented by the letters A, B, C We plant, for in- 

 •stance, a vegetable which contains the same elements as arc 

 represented by C. The original soil contains A, plus B, plus 

 C. At the end of the year a certain amount of C is appro- 

 j)riated ; and by the same process repeated a i'cw successive 

 years C becomes exhausted. 



It is evident, as the vegetable produced contains only C, 

 that A and B still remain in the soil. Then take another 

 vegetable, the constituents of which are represented by B. 

 That the })roduct which called for the elements of fertility 

 denoted by C can no longer be grown is no reason why a croj) 

 irequiring B will not turn out as well as did the former the 

 first season. And so we might go on until the sum total of 

 the fertilizing elements denoted by A, B and C is exhausted, 

 and the soil is, in common phrase, run out. It is thus seen 

 that under the conditions here supposed, a succession of equal- 

 ly good crops is grown upon the same land, without any ad- 

 dition of fertility. 



The vast economy effected in the productiveness of a given 

 piece of ground, by the observance of this rule, becomes ap- 

 parent upon the most cursory view. Old time farming saw 

 the necessity of fallowing where soil had ceased to be produc- 

 tive of a given crop ; and this constant lying idle of some 

 part of tlie land is in reality just to what the neglect of the 



