Experiments on Vegetation. 207 
periments which have been detailed in half a dozen professed 
. treatises, and otherwise promulgated in every possible way, he 
surely betrays a most unpardonable ignorance, The corre- 
spondent to whom I allude is Mr. Tatum, who has favoured 
you with a paper in a late Number, wherein he alludes to the 
old story of the purification of the atmosphere by vegetable re- 
spiration, of which, he says, few or none doubt the correctness. 
Mr. Tatum however could net rest satisfied with the general 
adoption of this opinion, and in the true spirit of philosophic 
research he determined to try the matter himself. Accordingly 
his experiments teach him that seeds, when confined under a jar, 
evolve during germination only carbonic acid; and he moreover 
discovers that plants in common with animals consume the oxy- 
gen of the air, which is accounted for in the formation of car- 
bonic acid. ‘These facts no doubt would be very interesting dis 
coveries, had they not been discoveries of twenty years pausing, 
I have said that Mr. Tatum’s observations have Leen anticipated 
by half a dozen authors, and I think I shall be able to make good 
the assertion. The opinion that plants purify the air originated, 
as is well known, with Dr. Priestley; but even he seems afterwards 
to have been aware of the inaccuracy of his conclusions ;—“ for,” 
says he, in vol. iii. p.273, “in general, the experiments of this year 
were unfavourable to my for mer hypothesis,—for whether I made 
the experiments with air injured by respiration, the burning of 
candles or any other phlogistic process, it did not grow better, 
but worse ; and the longer the plants continued in air the more 
phlogisticated it was. 1 also tried a great variety of plants with 
no better success.” The first author that eaperimentally con- 
tradicted this opinion was Scheele ; and to avoid prolonging this 
letter, I shall content myself with referring to his work on Fire 
and Air, p.160. After Scheele came Ingenhousz and Sennebier, 
one of whom wrote three volumes of experiments on this sub- 
ject; the other, five. That Mr. Tatum may lose no time in 
looking over the ill-digested works of these authors, I refer him 
to Ingenhousz’s book, vol. i. p. 255 ; and again, vol. ii. p. 758, 
and to vol. iii. p. 114, of Sennebier’s publication, Physiolog. 
Veget. at which references he will find an explicit declaration 
of what I have said. At present we have still living M. Saus- 
sure junior, who has written a most interesting, ingenious, and 
luminous work on the Chemical Functions of Vegetables, and 
his experiments entirely corroborate what had been done by 
Scheele, Jugenhousz and Sennebier. Vide Annales de Chimie, 
tom. xxiy. p. 139, and his work entitled Expérience sur la 
Vegétation. Before the appearance of Saussure’s work the at- 
tention of the public was called to this question by the first 
volume of Mr, Ellis’s treatise on the Respiration of Plants and 
Animals, 
