of Science to Agriculture. 143 



age, living at a period indeed at which the treatment of diseases 

 was empirical, but at least possessing the means of conveying to 

 others, by the aid of a precise system of nosology, a knowledge 

 of the nature of the disorder for which a certain class of remedies 

 had been found beneficial. 



But the adoption of a precise nomenclature, though an im- 

 portant preliminary step, carries us after all but a small way 

 towards that goal which the agriculturist should aim at attaining ; 

 and he who is content with knowing what manures will suit his 

 land, without troubling himself to ascertain the principle on 

 which they act, is as far removed from a system of perfect hus- 

 bandry, as the empiric of a former age is from the more enlightened 

 practice of the present day. Why, for example, a method of 

 culture, which has succeeded to admiration on one kind of land, 

 appears inapplicable to another ; why a manure, which has pro- 

 duced great crops the first year, seems to lose its effect on the 

 next; or why the fertilising influence which it exerted when 

 applied originally should be succeeded by the opposite effect at a 

 later period ; w^hy a difference of season should cause an entire 

 change in its effects upon the same land : these, and many other 

 problems of the same description, we can only be said to be on 

 the way to solve, when we have first settled amongst ourselves the 

 principle upon which the substances applied to our land operate 

 in improving it. 



At present the agricultural world seems divided on this point 

 between two theories, both of them probably applicable to cer- 

 tain cases, but nevertheless carefully to be distinguished as lead- 

 ing to the greatest discrepancies in practice. The first of these 

 considers manure as serving for food to plants : the latter regards 

 them in some sense as stimulants to their vegetation. 



Here, however, as in the former instance, much confusion has 

 arisen, in consequence of the term manure being applied to desig- 

 nate two classes of agents essentially distinct. Thus some of the 

 substances alluded to, such as quicklime, or its carbonate, act by 

 improving the mechanical or chemical qualities of the soil and 

 humus to which they are applied ; and to this operation the French 

 term amendment of the soil would seem to be appropriate. 

 Other manures, on the contrary, such as the dung of animals, 

 exert a more direct influence upon the plants themselves ; and it 

 is to these latter alone that either of the two theories alluded to 

 can be considered applicable. 



Thus whilst the former class of manures communicates to the 

 soil those qualities upon w^iich vigorous and active vegetation 

 depends, the other may be supposed to supply the means for car- 

 rying it on ; both of them conditions equally essential to the 

 growth of plants, though each one perfectly distinct from the 



