754 
REVIEW—ORGANIC CHEMISTRY. 
“ Is the quantity of carbonic acid in the atmosphere, which scarcely amounts 
to one-tenth per cent, sufficient for the wants of the whole vegetation on the 
surface of the earth,—is it possible that the carbon of plants has its origin from 
the air alone ? This question is very easily answered. It is known that a column 
of air of 2216.66 lbs. weight, Hessian measure, rests upon every square Hes¬ 
sian foot of the surface of the earth ; the diameter of the earth and its super¬ 
ficies are likewise known, so that the weight of the atmosphere can be calcu¬ 
lated with the greatest exactness. The thousandth part of this is carbonic 
acid, which contains upwards of 27 per cent, of carbon. By this calculation it 
can be shewn, that the atmosphere contains 3000 billion Hessian lbs. of carbon; 
a quantit}'^ which amounts to more than the w^eight of all the plants, and of all 
the strata of minerals and hroem coal, which exist upon the earth. This 
carbon is, therefore, more than adequate to all the purposes for which it is 
required.” 
The opinion, certainly, is not new, that the carbonic acid of the 
air serves for the nutriment of plants, and that the carbon is assi¬ 
milated by them—the leaves and the roots being the organs by which 
it is taken up; in the former, the change so necessary to the well¬ 
being of organic nature taking place. This has been admitted, de¬ 
fended, and argued for by the soundest, most intelligent natural phi¬ 
losophers. Some, however, have disputed it; and others think the 
theory quite refuted, because plants placed in sulphur, canara, 
marble, or sulphate of barytes, and sprinkled with water containing 
carbonic acid, did not grow : but many conditions are necessary for 
the growth of plants as well as animals, and although the essential 
elements of plants are hydrogen, oxygen, and carbon, yet they ap¬ 
pear to want certain metallic compounds, so as to continue in health, 
as animals do common salt 
“ If we knew with certainty that there existed a substance capable, alone, 
of nourishing a plant, and of bringing it to maturity, we might be led to a 
knowledge of the conditions necessary to the life of all plants, by studying its 
characters and composition. If humus were such a substance, it would have 
precisely the same value as the only single food which nature has produced 
for animal organization, namely milk. (Provf)." 
Our author next proceeds to the consideration of the origin and 
action of humus, and shews that this is not indispensable for plants. 
No primitive humus could have existed, since it is universally ad¬ 
mitted, that this principle arises from the decay of woody fibre; 
and plants must, then, have preceded it. 
The sources and assimilation of hydrogen and nitrogen are next 
dwelt upon, and the necessity of certain inorganic constituents in 
plants pointed out. 
“ Carbonic acid, water, and ammonia, are necessary for the existence of 
plants, because they contain the elements from which their organs are formed; 
but other substances are likewise requisite for the formation of certain organs 
destined for special functions peculiar to each family of plants. Plants obtain 
these substances from inorganic nature. Many of these consti¬ 
tuents vary according to the soil in which plants grow, but a certain number 
of them are indispensable to their development. It is quite impos¬ 
sible to mature a plant of the family of Grandnccc^ or of the Eqmsetacece, the 
