GARDENING AS A SCIENCE. 
VEGETABLE PHYSIOLOGY. — No. VI. 
Having proceeded so far into an inquiry concerning the structure of plants, it 
! will be now proper to consider the functions which may be assigned to each several 
jj part of the organization. 
1. Functions of the Root. — As the root is the part by which most plants 
i are attached to the soil, it has been supposed, and with reason, that it imbibes the 
! nutritive fluids of the ground, and conveys them to vessels, which transmit them 
to trunk, stem, branches and leaves. But all plants are not attached to soil ; some 
float in water, others derive their entire nutriment from the air. But apart from 
such anomalies, we can presume that all vegetables which grow and flourish in the 
' ground, must abstract from it some matters essential to their existence ; and this 
fact is proved to be such, by the certain and almost immediate effects which are 
observed when water is given to a potted plant, drooping in a dry and thirsty soil. 
Water theh is necessary — a pabulum of life, — -but is it taken up, pure , as such, or 
does it combine with other elements, extricated within the earth, and united to it 
by its solvent power ? 
Water , by analysis, is converted into hydrogen and oxygen gases, and these, in 
their turn, can be so made to combine, as to re-form fluid water ; but water alone 
can never produce carbon , — that is, the base of woody tissue ; and yet all plants 
abound with carbon. 
Physiological botanists instruct us, that carbon, however minute its particles, 
cannot be taken up by the root : Davy even found, that of the charcoal washed 
from gun-powder, not an individual particle could be traced in a vegetable grown 
for a considerable time in water mixed with the carbon, in a state so impalpable : 
therefore it is argued, that as carbon forms the bulk of vegetable matter, it 
can only be introduced when in the condition of carbonic acid dissolved in the 
water of the soil. 
Such carbonized water can be easily prepared in an apparatus containing 
powdered chalk, or marble dust, mixed with a quantity of water, and rendered 
effervescent by pouring on it small portions of muriatic or sulphuric acid. 
The gas thus generated ( carbonic acid ) being made to pass through a volume 
of pure water, will combine with that fluid to a considerable extent, and impart to 
it a slightly pungent, and rather acid flavour. 
Plants could absorb carbonic acid so dissolved in or blended with water ; but 
what proof do we possess that such a process is ever carried on in the vicinity of 
roots ? Let those answer the question who are possessed of demonstrative proof. 
The Sap — that is, the raw fluid absorbed directly from the earth by the soft, 
spongy tissue of the rootlets — can by no means hitherto known, be proved to con- 
tain any of the specific qualities or products of the perfect plant. Water, and 
VOL. xi. — no. cxxvi. 
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