514 Science of Farmers. 
There are four other elementary bodies that enter into the 
growth and composition of plants, and it is from these that the 
greater part or bulk of plants and animals are composed. These 
four substances are oxygen, nitrogen, hydrogen and carbon. The 
three first of these are known to us only in a gaseous form. Car- 
bon is pure charcoal, and when burned, it combines with the 
oxygen of the air in certain and exact proportions forming car- 
bonic acid, These four are termed by chemists organic bodies, 
and they are susceptible among themselves (and with the inor- 
ganic constituents of plants,) of forming an infinity of chemical 
combinations, and yielding an endless variety of products. 
The atmosphere we breathe, and in which plants grow and 
live, is composed principally of a mixture of oxygen and nitro- 
gen gases, in the proportion, very nearly, of 21 of the former to 
79 of the latter. It also contains as a constituent necessary to 
the very existence of vegetable life, a small per centage of car- 
bonic acid, on an average of about one twenty-five hundredth 
part, and however incredible it may seem to those unacquainted 
with agricultural chemistry, yet it is a fact, that from this source 
is derived about one-half of the solid substance of all plants that 
grow upon the face of the whole globe. 
At the first view it would seem impossible that this apparently 
small amount of carbonic acid diffused through the atmosphere 
could supply to growing plants the carbon found in their solid parts, 
as it amounts to from 40 to 50 per cent of all trees, plants and vege- 
tables, in fact all the parts of plants which are cultivated for food 
of man or animals, and unquestionably most of this carbon is de- 
rived directly from the air, by the agency of the leaves of plants, 
although there can be no doubt but a small portion of it is taken 
up by the roots mixed with water, and some of the inorganic 
matters that are in solution, such as potash, lime, &c. 
When we reflect that the atmosphere not only entirely surrounds 
the earth, but extends in every direction about 45 miles, " and if 
the whole acid were collected in a stratum or bed occupying the 
lower part of the atmosphere, such a stratum would have a thick- 
ness of about thirteen feet," and this would be spread over the 
entire waters of the oceans, seas, lakes, rivers, the deserts of sand, 
the frozen regions of the poles, and in fact over every part and place 
of the globe, and by the wisdom of the Great Contriver, this gas 
is in innumerable ways, returned to the air as fast as abstracted 
by growing plants — here, then, our wonder ceases. 
We know, if we take a given quantity, by weight, of well- 
seasoned wood, and distil it in a close vessel, or burn it in heaps 
covered over so as to exclude the free access of air, wood char- 
coal is left behind. When this process is well performed, the 
charcoal will weigh from 40 to 50 per cent as much as the wood 
