200 THE SYSTEM OF FARM-YARD MANURING. 



This expression, therefore, means that the roots of the 

 cereal plant mnst 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 several of the 

 same constituents for the formation of o-rain. The total 

 produce is, of course, dependent upon the sum of the K 

 and S^ constituents, which the soil is able to supply to the 

 plants during the natural period of growth. 



The ratio between corn and straw results from a divi- 

 sion of the K and S^ 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. 



Wlien the quantity of S^ 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 formation 

 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 S^ con- 

 stituents 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 straAv, at the expense of grain, 

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

 able for the formation of leaves, stalks, and roots, than 

 for grain. The period of growth is thus prolonged, and 

 the plant then takes up more of the St constituents, which 

 are usually in excess; for the assimilation of these, a 



