MlX'HANlt - \ND USEFUL ARTS. 25 



ing of oui' laud ought to be regulated. In this dispute, however, you will not 

 expect me to take part, for it would be obviously improper. But I may be per- 

 mitted to remark, that whilst some points of difference between them still 

 remain open for further investigation, a much nearer correspondence of opi- 

 nion exists with respect to others, than the public in general, or even perhaps 

 the disputants themselves, are inclined to allow. In so far, indeed, as relates 

 to the relative advantages of mineral and ammoniacal manures, I presume 

 there is little room for controversy ; for although most soils may contain a suffi- 

 ciency of the inorganic constituents required by the crop, it by no means fol- 

 lows that the latter are always in an available condition ; and hence it may 

 well happen that hi most cases in which land has been long under cultivation, 

 the former class of manures becomes, as Baron Liebig asserts, a matter of para- 

 mount necessity. Now that the same necessity exists for the addition of 

 ammoniacal manures, can hardly be contended, when we reflect, that at the 

 first commencement of vegetable life, every existing species of plant must 

 have obtained its nourishment solely from the gaseous constituents of the 

 atmosphere, and from the mineral contents of the rock in which it vegetated. 

 The only divergence of opinion, therefore, that can arise, relates to the degree 

 of their respective utility in the existing state of our agriculture, and to the 

 soundness of Baron Liebig's position, that a plant rooted in a soil well charged 

 with all the requisite mineral ingredients, and in all other respects in a condi- 

 tion calculated to allow of healthy vegetation, may sooner or later be able to draw 

 from the atmosphere whatever else is required for its full development. And 

 does not, I would ask, this latter position derive some support from the luxu- 

 riant vegetation of the tropics, where art certainly contributes nothing towards 

 the result ? and is it not also favored by such experiments as those carried on 

 at Lois "Weedon in Northamptonshire, where the most luxuriant wheat crops 

 have been obtained for a number of consecutive years without manure of any 

 kind, simply by following out the Tullian system of stirring up and pulveriz- 

 ing the soil ? How, too, are we to explain that capacity of subsisting with- 

 out any artificial supply of ammonia, which Mr. Lawes is led by his experi- 

 ments to attribute to turnips, and other plants of similar organization, unless 

 we assume that the power residing in the leaves of absorbing ammonia from 

 the air may render plants, in some cases at least, independent of any extra- 

 neous aid ? Be this, however, as it may, there is at least a wide distinction 

 between this opinion and the one attributed to Baron Liebig by many, who 

 would seern to imagine, that according to Ms views, ammonia, if derived from 

 artificial sources, was in a manner useless to vegetation. As if it could be a 

 matter of any moment, whether the substance which hi both cases afforded the 

 supply of nitrogen, and which hi both cases also was primarily derived from 

 the decomposition of organic substances, had been assimilated by plants 

 directly upon its being thus generated, or had been received into their syste.ni 

 at a later period, after having been diffused through the atmosphere ? To 

 suppose that Baron Liebig should have attached any moment to this distinc- 

 tion seems inconsistent with many passages hi his work, in which, although 

 the paramount importance of mineral manures may be insisted upon, and the 

 success which had in certain cases attended the use of one compounded only 



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