174 FAEM-YAED MAXUEE. 



tlie composition of tlie effective constituents in tlie arable 

 soil. 



We have supposed our field to contain the ash-con- 

 stituents of the entke wheat plant in proper proportion 

 for the formation of straw, leaves, and grain. By leaving 

 the straw-constituents in the ground, while contmually 

 removing the grain-constituents, the former will accu- 

 mulate and grow out of due proportion to the remainder 

 of the grain-constituents still contained in the field. The 

 field retains its fertility for straw, but the conditions re- 

 quired for the production of grain are diminished. 



The consequence of this disproportion is an unequal 

 developement of the entu'e plant. As long as the soil 

 contained and supphed the right proportion of ash con- 

 stituents needful for the uniform growth of all parts of the 

 plant, so long the quality of the seed and the ratio between 

 straw and corn in the diminishing crops remained con- 

 stant and unaltered. But, in proportion as the conditions 

 for the production of leaves and straw became more 

 favourable, the quality of the grain deteriorated with its 

 decreasing quantity. The distinctive mark of this in- 

 equality in the soil, resulting fi^om cultivation, is a decrease 

 in the weight of the bushel of corn reaped fi'om the field. 

 At first a certain quantity of the constituents restored to 

 the soil in the straw (phosphoric acid, potash, magnesia), 

 was expended in the formation of grain ; but afterwards 

 the case is reversed, and the gTain-constituents (phosphoric 

 acid, potash, magnesia) are drawn upon for the production 

 of straw. The condition of a field is conceivable where 

 by reason of inequality in the relative conditions for pro- 

 ducing straw and grain, under temperature and moisture 

 favourable for the formation of leaves, a cereal plant 

 may yield an enormous crop of straw, with empty ears. 



The farmer, in cultivating his plants, can act upon the 



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