On Paring and Burninf/. 345 



there are soils which, like many very fertile clays, hardly con- 

 tain any humus, and yet are highly productive. These incon- 

 sistencies have compelled the adherents of the humus theory 

 to assume a number of such terms as dead, inert matter, sweet 

 and sour humus — terms which, in the sense in which they are 

 generally used even now are meaningless, and which for this 

 reason might with much benefit be subjected, to the process of 

 burning. 



The humus theory has retarded rather than promoted agricul- 

 tural improvements. Happily it may be regarded at present as 

 fully exploded. Had Liebig done nothing else for agriculture 

 but to give the coup de cjrace to the humus theory, by means of 

 his irresistible argumentative writings, the agricultural com- 

 munity would still be highly indebted to the great German 

 chemist ; for as long as this theory found favour with practical 

 men, much to their disadvantage, the importance of the mineral 

 constituents, so necessary for every description of agricultural 

 produce, was altogether overlooked. It was reserved for Liebig 

 to give general recognition to the fact, that the mineral matters 

 which enter into the composition of plants are not merely acci- 

 dental, but essential, constituents, without which plants cannot 

 live ; and to point out in a clear and convincing manner the 

 necessity of the presence in the soil of those mineral matters 

 which are found in the ashes of the plants we intend to cultivate. 

 The influence of Baron Liebig's writings on this subject upon 

 agricultural improvements can hardly be over-estimated. It is 

 not saying too much that Liebig's writings have given a new 

 impulse to agricultural pursuits, and created a new branch of 

 industry, viz. the manufacture of artificial manures. Though 

 unsuccessful in the first attempt to manufacture efficient artificial 

 manures, Liebig has nevertheless opened the way to the manu- 

 facture and general application of artificial manures. 



The failure of Liebig's mineral manures, to whatever it may 

 have been due, however, does not prove the unsoundness of the 

 principle so clearly announced in Liebig's writings, namely, the 

 principle that plants cannot grow vigorously if the mineral con- 

 stituents found in their ashes are deficient in the soil or in the 

 manure applied to it. Liebig's position in enforcing this truth 

 is unassailable ; nor has it indeed been assailed by any one who 

 can lay claim to the title of a man of science. It is, in reality, 

 not in principle but in practice that Liebig has failed. And. 

 this need not excite surprise ; for, however true a principle 

 may be in the abstract, such a principle, if applied to a subject 

 upon which it can have no bearing, is evidently misapplied, and 

 likely to lead to errors in practice. Thus it is unquestionably 

 necessary upon a purely sandy soil, containing very little besides 



