84 
OF GARDENING AS A SCIENCE. 
But carbon, in the forni of woody fibre chiefly, and secondarily, as a constituent 
of every vegetable organic product, is obtained from some source or other ; and in 
conducting inquiry to trace that source, the writer displays much acumen, and 
power of original thought : for example, p. 16 — 
The Origin of Carbon in plants is intimately connected with that of the origin 
of humus. " It is universally admitted that humus arises from the decay of plants. 
No primitive humus, therefore, can have existed ; for plants must have preceded 
the humus. Now, whence did the first vegetables derive their carbon ? and in 
what form is the carbon contained in the atmosphere ? The answer to the last 
query is plain and definite — that it does, and can exist, only in the condition of 
carbonic acid ; a gas which, a few years past, was called Jlxed air, or aerial acid. 
" It is quite evident that the quantities of carbonic acid and oxygen in the 
atmosphere, which remain unchanged by lapse of time, must stand in some fixed 
relation to one another ; a cause must exist, which prevents the increase of carbonic 
acid, by removing that which is constantly forming ; and there must be some 
means of replacing the oxygen, which is removed from the air by the processes of 
combustion and putrefaction, as well as by the respiration of animals. Both these 
causes are united in the process of vegetable life \" (p. 18.) 
Here we quit our author till our next article, when we hope to adduce his 
authority, confirming our own observations, in proof that plants must derive their 
woody fibre from the atmosphere. 
Thus generalising now, we reserve our remarks on garden humus, as distinct 
from chemical humic acid, to another month. In the mean time, we suggest that 
the gardener may find his purest type of humus in the brown and black decayed 
vegetable matter of the earth ; first called ' bog-earth,' then peat, but more 
correctly, ' heath ' or ' moor soil,' 
We have heard of ferruginous bog, and that such a material is destructive of 
the fine hairy-rooted tribes. All soils contain some iron, and possibly, where the 
heath soil of a district approaches to true peat, and is digged from a bog, the iron 
may exist as a salt ; when, assuredly, it will be insalubrious. We have before us 
three analysed specimens of heath mould ; two from Wimbledon common, and one 
from Bagshot. One of the former was brown, fibrous, and light ; 15 grains lost 
at a red heat 5 grains, leaving 10 grains of dingy sand : the other weighed 26 
grains ; it was of a pale grey colour, very loose, and left 23 grains of sand. 
Bagshot soil, deep blackish grey, lost 4 grains of 24 : the sand of all, digested in 
weak sulphuric acid, yielded a colourless solution, till a drop of prussiate of potash 
was applied • when the fluid assumed an intense blue tint, owing to the separation 
of Prussian blue. This iron, not amounting to -^-^ of the whole, can do no injury 
to any of the heath tribes ; but every trial furnishes new evidence of the great 
variation of soils, both as respects their chemical constituents and texture. Our 
limits are attained, and we must defer other important remarks, which we had 
hoped to oficr at this time. 
