Report of Experiments on the Growth of Wheat. 
95 
value of manure was to a great extent measurable by the amount 
of nitrogen it contained. 
In Liebig's first work on 'Organic Chemistry in its appli- 
cations to Agriculture and Physiology,' published in 1840, he 
illustrated, more pointedly than Roussingault had done, the 
importance of the incombustible or ash-constituents ; which, to 
distinguish them from carbonic acid, water, and ammonia, 
from which the organs of plants were in great part formed, he 
designated as " inorganic ". substances. He, at the same time, 
also insisted strongly upon the importance of the nitrogen, or 
ammonia-yielding matter, of manures. 
Soon after the appearance of Liebig's work, Boussingault 
published, much more fully, the results of his own agricultural 
investigations, and the conclusions deducible from them, bring- 
ing out more prominently his views as to the importance, in a 
practical point of view, of the nitrogen in manures. 
Liebig followed with a new edition in 1843, in which he criti- 
cised Boussingault's experiments ; condemned his notion of the 
relative importance of the nitrogen of manures ; maintained (in 
direct opposition to the view put forward in his former edition) 
that the atmosphere afforded a sufficient supply of nitrogen for 
cultivated as well as for uncultivated plants ; argued that this 
supply was sufficient for the cereals as well as for the Legu- 
minous plants ; that it was not necessary to supply nitrogen to 
the former ; and insisted very much more strongly than formerly 
on the relative importance of the incombustible, or, as he desig- 
nated them, the " inorganic " or " mineral " constituents. He 
even went so far as to say : — 
" Is fertility not quite independent of the ammonia conveyed 
to the soil ? If we evaporated urine, dried and burned the solid 
excrements, and supplied to our land the salts of the urine, and 
the ashes of the solid excrements, would not the cultivated plants 
grown on it — the graminea; and leguminosae — obtain their carbon 
and nitrogen from the same sources whence they are obtained by 
the gramineaj and leguminosae of our meadows ? 
" There can scarcely be a doubt with regard to these questions, 
when we unite the information furnished by science to that 
supplied by the practice of agriculture." — 3rd Ed., p. 204. 
Again — 
" The crops on a field diminish or increase in exact proportion 
to the diminution or increase of the mineral substances conveyed 
to it in manure." — 3rd Ed., p. 211. 
Somewhat later, he said — 
" It has been demonstrated that ammonia is a constituent part 
of the atmosphere, and that as such it is directly accessible and 
absorbable by all plants. If, then, the other conditions necessary 
