418 
Agricultural Chemistry. 
(luce of the soil, without any effort to increase it, and in time abandonins; it 
for a soil as yet undisturbed. If Licbig had sufliciently considered this dis- 
tinction, he would not have assumed that certain substances employed as 
manures are of little value, because plants and trees, in their natural state, are 
capable of obtaining them in sufficient quantity for their nse." — Journal of 
the Punjal Afjricidtnral Society of England, vol. viii. part i. p. 227-8, 
" The atmosphere and the virgin soil being originally the exclusive sources, 
the former of the '■ onjanic,^ Tmi the latter of the '■ ■inorganic'' or ^ mineral'' 
constituents of plants, it has been supposed that the amount of produce 
which a given space of gi'ound would yield must depend upon its richness in 
those substances proper to itself, namely, the mineral constituents ; and that 
these being supplied in full quantity, according to the indications of the 
analyses of the ashes of the crops it is wished to grow, the atmosphere would 
always prove an ample available resource for the more peculiarly vegetable 
matters. It will be readily understood that on such a view as this, economy 
in agriculture would be attained by a very different course of practice from 
that required were it to be shown that cultivation should effect an artificial 
accumulation in the soil of those constituents primarily derived from the 
atmosphere, rather than [of such as more especially belong to its own con- 
stitution. 
" The theory referred to has led to the analysis of the ashes of a great 
many agricultural crops, and upon the data thus obtained (rather than upon 
a consideration of the requirements actually induced by an artificially 
enhanced vegetation, or of the real source and destination of the constituents 
under a course of practical agriculture), recommendations to the agriculturist 
have been founded, the validity of which it was desirable should be tested 
by actual experiment, as well as by the presumed dictates of experience." — Ih. 
vol. viii. part ii. p. 535. 
" It is true that, in the case of vegetation in a native soil, unaided by art, 
the mineral constituents of the plants being furnished from the soil, the 
atmosphere is found to be a sufficient source of the nitrogen- and carbon ; and 
it is tlie supposition that these circumstances of natural vegetation apply 
equally to the various crops when grown under cultivation that has led 
Baron Liebig to suggest that, if by artificial means we accumulate within the 
soil itself a sufficiently liberal supply of those constituents fotmd in the ashes 
of the plant, essentially soil constituents, we shall by this means be able in 
all cases to increase thereby the assimilation of the vegetable or atmospheric 
constituents in a degree sufficient for agricultural purposes. But agriculture 
is itself an artificial process ; and it will be found that, as regards the produc- 
tion of wheat more especially, it is only by the accumulation within the soil 
itself of nitrogen, naturally derived from the atmosphere, rather than of the 
peculiarly soil-constituents, that our crops of it can be increased. Mineral 
substances will indeed materially develop the accumulation of vegetable or 
atmospheric constituents when applied to smne of the crops of rotation ; 
and it is thus chiefly that these crops become subservient to the growth of the 
cereal grains ; but even in these cases it is not the constituents, as found 
collectively in the ashes of tJie plants to he groxvn, that are the most efficient in 
this respect ; nor can the demand which we find thus made for the production 
of crops in agricidturcd quantify be accounted for by the mere idea of snjiply- 
ing the actual constituents of the crop. It would seem, therefore, that we can 
only arrive at correct ideas in agriculture by a close examination of the actual 
circumstances of growth of each particular crop when grown under cultivation." 
— B). vol. xii. part i. p. G, 7. 
But there is another sentence in one of our Papers in which we 
have sought to indicate Baron Liebig's views, against which ho 
strongly protests. It is as follows : — 
