130 
OF GARDENING AS A SCIENCE. 
This " burning," which is a word of common parlance, is false in application, 
though correct in its apparent effects. Plant an Azalea in fresh bog, and in a few 
days the points, then the half of the leaves, become brown, the shrub ceases to grow, 
the leaves fall, and it perishes. But keep that individual soil during two seasons 
exposed to the weather, turning it occasionally, and the same species which would 
perish in it while fresh, now grow, and thrive luxuriantly. 
This burning, then, is the effect of gaseous developments, produced by progressive 
decomposition of the redundant vegetable matter. In farm-yard dung, ammoniacal 
gas is copiously extricated ; but in moor or heath-soil we are inclined to think that 
some neutral salt of iron exists, (the sulphate, perhaps, in many instances,) which is 
gradually decomposed, loses its acid, and becomes an innocuous oxide. 
But this is a digression, though one which involves many curious phenomena — 
it is our object to show that, simple as is this soil of our heaths, consisting of little 
else than sand and a small portion of laborated humiis^ a heath, azalea, andromeda, 
or rhododendron, may grow in a pot of it for years, and never exhaust it of any 
portion of its black vegetable matter. If any discernible alteration take place, so 
far from it becoming more pale or sandy, the tint becomes darker, as if finely 
powdered charcoal had been added to it. We will readily admit that the plant 
will require fresh aliment and more space, but the change wrought in the old soil, 
whereby it is rendered improper for the plant, is not one of exhaustion. The 
vegetable adds to the soil, or rather it ejects into it substances which are f^cal and 
excrementitious, and which, consequently, cannot with impunity be taken up a 
second time into its organic tissue. 
Now, if this weakest of soils lose nothing of its humus, is not the theory 
of Liebig substantiated by a fact which any gardener has it at command to observe 
and adduce ? 
Liebig has been accused of self-contradiction, and that too so recently as in the 
June number of the Quarterly Journal of Agriculture, page 105 : it is said there 
is "a strange inconsistency between his various statements upon this subject" 
(Jimnus) " as they occur in different parts of his work " — thus, at p. 19, " we are 
expressly told that plants derive their carbon excluswely from the atmosphere," and 
then at p. 47, " that the roots absorb, as their proper nourishment, the carbonic 
acid generated in the soil by the humus!' 
These apparent contradictions exist ; but the critic has overlooked one primal 
fact of the hypothesis, namely, that the humus becomes the source of aliment to all 
germinating seeds and young plants during their first developments, prior to the 
expansion of leaves ; but that subsequently, when the foliage expands, the leaves 
absorb the carbonic acid of the air, from which acid the woody fibre and all the 
peculiarly-organized products of the vegetable are formed, and that henceforward 
plants yield more carbon or humus to the soil than tliey take up from it. 
Here is no contradiction, though we may admit that the author, as is but too 
commonly the case, has written too discursively ; and it every day becomes more 
