172 FAEM-YAED MANUEE. 



composition of the effective constituents in the arable 

 soil. 



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

 tituents of the entire wheat plant in proper proportion 

 for the formation of straw, leaves, and grain. By leav- 

 ing the straw-constituents in the ground while continu- 

 ally removing the grain-constituents, the former will 

 accumulate 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 required for the production of grain are 

 diminished. 



The consequence of this disproportion is an unequal 

 developement of the entire plant. As long as the soil 

 contained and supplied 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 re- 

 mained constant and unaltered. But, in proportion as 

 the conditions for the production of leaves and straw 

 became more favourable, the quality of the grain dete- 

 riorated with its decreasing quantity. The distinctive 

 mark of this inequality in the soil, resulting from cul- 

 tivation, is a decrease in the weight of the bushel of 

 corn reaped from 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 re- 

 versed, and the grain-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 

 producing 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 direction of the vegetative force only through the 

 soil, i. e. by supplying his field with nutritive sub- 

 stances, in the right proportions. For the production 



