177 
GARDENING AS A SCIENCE. 
No. VIII. 
The elementary constituents of the organic products of plants claim our imme- 
diate attention. Of late, a sort of conventional nomenclature has come into 
fashionable request. Everywhere we meet with chemical terms, and thus, the 
words oxygen, azote, carbon, and hydrogen, have become as familiar as blackberries : 
yet who correctly applies, and, still less, who philosophically explains them ? 
Our own professions are very unassuming ; but we hope to collect some 
materials, and to hazard a few conjectures, which, if they do not satisfy, may 
at least stimulate, the inquiring mind ; and, by leading to reflection, promote the 
research after truth. 
The elements — that is, those materials beyond which no power of analysis has 
produced a change — the elements of vegetable organization are very few ; two of 
them are discoverable in, nay, constitute the very essence of the air w^e breathe ; 
therefore, we select as our leading subject the air of the atmosphere. If we look 
at the dates of all the discoveries of real science, we shall be surprised how small is 
the portion of time that has elapsed since the science of chemistry became based 
upon philosophic truth. The experiments of Dr. Priestley, which paved the way 
to all subsequent researches in pneumatic chemistry, were not commenced till about 
the year 1768; he discovered oxygen in 1774, but previously, in 1771, he in- 
vestigated the subject of the purification or renovation of air contaminated by 
combustion and animal respiration. He ascertained that atmospheric air was not 
deteriorated by the growth of a sprig of mint, which he kept in it some months, 
and therefore presumed that, by the processes of vegetation, air spoiled by burning 
candles might be restored to its original purity. Accordingly, on the 17th August, 
1771, ^ sprig of mint was placed in a vessel containing air, in which a wax candle 
had burned out, and on the 27th of the same month, he found that another candle 
burned perfectly well in it. To confirm or disprove the conclusion to which he 
had arrived, the deteriorated air was divided. One half he merely suffered to 
remain over water ; into the other he put a sprig of mint ; the air in the latter 
was restored, but that in the first portion would not permit a candle to burn. 
Such is the account; and it remains to explain the causes of the several 
phenomena ; this we shall attempt to do, but, previously, quote a few lines from 
Dr. Priestley's own remarks. " This restoration of air," he observes, " I found 
depended upon the vegetating state of the plant ; for though I kept a good number 
of fresh leaves of mint in a small quantity of air in which candles had burned out, 
and changed them frequently for a long space of time, I could perceive no meliora- 
tion in the state of the air. This remarkable effect does not depend upon anything 
peculiar to mint^ for I found a quantity of this kind of air to be perfectly restored 
by sprigs of balm, groundsel, spinach, and some other plants." 
VOL. IX. NO. CIV. A A 
