COKN AND STRAW CONSTITUENTS IN SOILS. 195 



This expression, therefore, means that the roots of 

 the cereal plant must have absorbed from the earthy 

 particles in contact with them a certain proportion of 

 nutritive substances for the production of leaves, roots, 

 and stalks, and after this an additional amount of sev- 

 eral of the same constituents for the formation of grain. 

 The total produce is, of course, dependent upon the sum 

 of the K and S constituents, which the soil is able to sup- 

 ply to the plants during the natural period of growth. 



The ratio between corn and straw results from a 

 division of the K and St constituents in the plant itself, 

 and depends upon the relative proportion of the K and 

 St constituents in the soil, as also upon the action of 

 external causes favouring the production of corn or 

 straw. 



When the quantity of K constituents in the ground 

 decreases, less grain will be produced ; but it is only in 

 certain cases that this will exercise any influence upon 

 the produce of straw. 



When the quantity of St constituents in a field is 

 increased, the enhanced conditions for the formation of 

 leaves, stalks, and roots, must injure the crop of grain, 

 if the amount of aK required for the additional forma- 

 tion of straw is taken from the store of K contained in 

 the soil. 



If one of two fields is poorer in K but richer in St 

 constituents than the other, the former may give the 

 same, perhaps even a larger, amount of straw, than the 

 latter, but its produce of corn will necessarily be less. 



A similar increase of straw, at the expense of grain, 

 takes place when the state of the weather is more fa- 

 vourable for the formation of leaves, stalks, and roots, 

 than for grain. The period of growth is thus pro- 

 longed, and the plant then takes up more of the St con- 

 stituents, which are usually in excess ; for the assimila- 

 tion of these, a certain additional quantity of the K 

 constituents is consumed, which would otherwise have 

 served to form seed. 



Let st represent the additional supply of St constitu- 

 ents afforded by the soil under these circumstances, and 



