106 
OF GARDENING AS A SCIENCE. 
of oxygen in the atmosphere is thus invariably the same? Carbon and the elements 
of water form the principal constituents of vegetables ; the quantity of substances 
which do not possess this composition being in very small proportion. It is there- 
fore certain that plants must possess the power of decomposing carbonic acid, 
since they appropriate its carbon for their own use. The formation of their prin- 
cipal component substances must necessarily be attended with the separation of 
the car])on of the carbonic acid from the oxygen, which must he returned to the 
atmosphere^ whilst the carbon enters into combination with water or its elements. 
" The atmosphere must thus receive a volume of oxygen for every similar 
volume of carbonic acid which has been decomposed." 
Thus reasons our author ; but upon this great miracle of nature he advances no 
novel idea ; he only brings us back to the observations of Dr. Priestley, Sennebier, 
De Saussure, and others ; but his modes of proof, his deductions from calculation, 
are his own. That many have doubted the grand facts w^hich he now confirms, is 
true as it is lamentable ; for there is not in all creation one other traceable agency 
by which the destructive increase of carbonic acid could be prevented, if we deny 
it to vegetable vitality ! " The life of plants is closely connected with that of 
animals in a most simple manner, and for a wise and sublime purpose. The 
presence of a rich and luxuriant vegetation may be conceived without the concur- 
rence of animal life ; but the existence of animals is undoubtedly dependent upon 
the life and development of plants. 
" Plants not only afford the means of nutrition for the growth and continuance 
of animal organization, but they likewise furnish that which is essential for the 
support of the important vital process of respiration ; for, besides separating all 
noxious matters from the atmosphere, they are an inexhaustible source of pure 
oxygen, which supplies the loss which the air is constantly sustaining. Animals, 
on the other hand, expire carbon, which plants inspire ; and thus the composition 
of the medium in which both exist, namely the atmosphere, is maintained con- 
stantly unchanged." 
This beautiful reciprocity speaks volumes : it sets aside that weak appeal to 
tlie agency of humus which has of late years been so imperiously urged. The 
presence of manuring matter in the soil, and the important changes which it operates, 
have doubtless tended to blind us to the more important agency of the atmosphere ; 
but why decaying vegetable matter — whose decomposition is effected by the agency 
of air and moisture — should be identified with the artificial humus of the labo- 
ratory, is a mystery. If such be the results of the application of chemistry to the 
theory of agriculture, we are free to confess that we should prefer the ignorant 
routine of our forefathers. They pay a poor compliment to science, who thus mis- 
apply its discoveries ! 
