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assert that it is wholly absorbed, in the form of carbonic acid, 
from the atmosphere; others imagine that its chief portion is 
taken up by the roots ; again, others believe that the entire 
surface of plants is absorbent, and that carbonic acid gas is taken 
in both from the atmosphere, and from the earth in which the 
plant grows. The latter opinion is by far the most probable, 
and no contradiction can be given it, merely because a plant 
has grown in earth and water, both of which were believed not 
to possess it. This is an uncertain criterion, for carbonic acid 
is more or less every where present; it is, as Dr. Lindley 
truly says, "A kind of air, compounded of carbon and oxygen, 
found in the atmosphere, incessantly expelled from the lungs of 
animals, and produced by the decay of vegetable and animal 
bodies. On this invisible, untouchable, substance plants feed; 
out of this they help themselves to the charcoal, returning the 
oxygen to the air. And thus the vast forests of the earth, and 
all the herbage at their feet, are gradually built up, and 
fashioned into the beautiful green mantle of our planet.” 
The evidence in support of the beneficial influence of Char- 
coal, as a manure to plants, is so convincing that we cannot for 
a moment doubt its validity. It is natural enough that the 
zealous advocates of any novelty should sometimes over-rate 
its advantages. We are always prepared to meet this, but, 
from the statements of respectable persons, and from our 
own experience, we are convinced that Charcoal, independently 
of its mechanical action in keeping composts light and per- 
vious, is an active stimulant to vegetation ; and when kept in 
contact with the roots of growing plants, it has been found to 
lose thereby a portion of its weight, which is tolerably clear 
evidence that the plant must have appropriated some of its 
ingredients to its own use. Still, whether it be from its own 
decomposition, or by its attraction of certain gases from the 
atmosphere, as stated by Liebeg, is to the practical man of little 
importance. In some respects it is superior to other manures 
which have been of late brought prominently under notice; 
for it is not likely to prove unsuitable to any variety of soil; 
nor is it likely that it can be used in excess, since it can, as 
previously shown in the experiments of Mr. Lucas, be used 
advantageously by itself. On the contrary, Guana and Salt 
have been used incautiously, and proved injurious, and the 
234. AOCTIBIDM. 
