31 



Imt small. The former flourishes even 011 "poor, sandy " soils, whilst the latter suc- 

 ceeds, and is naturally found on "rich, heavy "ones only, although the absolute 

 amount of plant food taken from the soil may be the same in either case. 



It is obvious that without a knowledge of the respective depths and penetrability of 

 two soils a comparison of the percentages of their plant constituents will be useless. 

 The surface soil, with its processes of nitrification, oxidation, carbonic acid solution, 

 <fcc., in full progress, must always be distinguished from the subsoil in which these 

 processes are but feebly developed, and where the store of plant food, in which it is 

 generally richer than the surface soil, is comparatively inrrt. Hence the obvious im- 

 portance of samples correctly taken, and the necessity of intelligent and accurate 

 observations on the spot. 



The concentration of the available portion of the plant food of soils in their finest 

 portions has become a maxim. A " strong soil " is invariably one containing within 

 reach of the plant the large amount of impalpable matter ; although the reverse is by 

 no means generally true. 



A comparison of tbe composition of soils of known productiveness, and character- 

 ized in their natural state by certain in variable features of plant growth, soou reveals 

 the existence of definite relations, not only to the absolute amounts of certain ingre- 

 dients present in the soil, but also to their relative proportions. No ingredient exerts 

 in these respects a more decided influence than lime, its ad vent in relatively large pro- 

 portion, other things remaining equal, changing at once the whole character of vege- 

 tation, so as to be a matter of popular remark everywhere. Only it is not popularly 

 known, nor has it been definitely recognized by agricultural chemists thus far, that it 

 is the lime that brings the change. 



The amount of the different soil constituents which may he con- 

 sidered the minimum consistent with fertility has already been given. 



