422 
Agricultural Cliemistrij. 
donhf. until rexjard to these questions, ii;?ien we unite the mformation furnished 
hy science to that s^ipplied hy the pTactice of agriculture,'''' — p. 203. 
These then are Baron Liebig's opinions, in his later editions, 
as to the equal independence of plants, — wild or cultivated, — 
graminaceous or leguminous — of assimilable nitrogen provided 
within the soil. We do not mean to say, that there are not both 
facts and opinions recorded in Baron Liebig's writings, totally in- 
compatible with the series of sentences which we have quoted. 
But we leave the inconsistency to be explained by Baron Licbig 
himself. 
We must here beg the reader's attentive recognition of the fact, 
that the subject of which both Baron Liebig and ourselves are 
speaking is agriculture, not normal vegetation — that we treat of 
" cultivated " land, not a mere sand-pit, or other circumstances 
{agriciilturalhf speaking abnormal), under which every mineral 
constituent of the plant has to be artificially provided. It must 
not be forgotten that there are here certain "preliminary condi- 
tions" namely, a cultivated soil — one, therefore, which is supposed 
to contain a certain amount of the necessary food of plants : but 
in a more or less actively fertile condition, according to the 
original composition of the soil itself — its state of mechanical 
and chemical degradation — and the home-manuring and cropping 
to which it has been subject. What then are the circumstances, 
with these ''^preliminary conditions,'''' under which produce in 
agricultural quantity is to be obtained ? Baron Liebig says : — 
" The ammonia of animal excrements exerts a favourable influence ordy 
ieeause it is accompanied by other substances necessary for its conversion into 
the constituents of the blood. When these conditions are furnished with am- 
monia, the latter becomes assimilated. JBut when the ammonia is absent from 
themanure, the pjlants extract their nitroyen from the ammonia of the air; to 
which it is again restored the decay and putrefaction of dead animal and 
vegetable remains." — p. 210, 211. 
" But, at the same time, it is of great importance for agriculture, to know 
with certainty that the supply of ammonia is unnecessary for most ol our cul- 
tivated plants, and that it may be even superfluous, if only the soil contain a 
sufficient supply of the mineral food of plants, mhen the ammonia required for 
their development luill he furnislied by the atrnosphere." — p. 212. 
Referring to the mineral elements of the soil, Baron Liebig 
says : — 
" If these elements are present in suflicient quantity, and in appropriate 
proportions, the soil contains the conditions which render the plant capable of 
absorbing carbonic acid and ammonia /ro7?i the air, which is an inexhaustible 
store-house for them, and renders their elements capable of being assimilated 
by their organism. The agi'iculturist must, therefore, confine himself to giving 
to the field the composition necessary to the development of tlie plants which 
he intends to grow ; it must be his principal task to supply and restore all the 
elements required in the soil, and not only one, as is so frequently done ; the 
ingredients of the air, carbonic acid, and ammonia, the plants can, in most 
cases, procure without man's interference ; he must take care to give to his 
