' 
on Experiments on Vegetation. 355 
*< ln genéral the experiments of this year were unfavourable to 
my former hypothesis; for whether I made the experiments with 
air injured by respiration, burning of candles, or any other phlo- 
gistic process, it did not grow better, but worse ; and the longer 
the plants continued in the air the more phlogisticated it was. 
{ also tried a great variety of plants with no better success.” 
From this one would imagine that W.H. G. thought the Doctor 
was about to abandon his old opinion: but if he had taken the 
trouble of turning over one leaf, he would have found the Doctor 
still firmly maintaining his “ old story,” for he says, “ Upon the 
whole | s¢z// thought it probable, from the experiments of ¢his 
year, that the vegetation of healthy plants, growing in situations 
natural to them, has a salutary effect on the air in which they 
grow ;—for one clear instance of the melioration of air in these 
circumstances should weigh against a hundred cases in which the 
air is made worse by it.” 
Is there here any reason to concltide that the Doctor was ‘‘ aware 
of the inaccuracy of his conclusions ?”” Does not the above prove 
that, so far from altering his opinion, he was determined to sup- 
port“ his old story” in the strongest possible language? 
Your correspondent has seen fit to class Dr. Ingenhousz as 
well as Sir Humphry Davy aniong the half dozen authors “ who 
experimentally contradict the above opinion.” Now, as W.H.G. 
accuses me of ** unpardonable ignorance,” surely we ouglit not 
to expect him to betray any in his criticisms on me. But let 
us see what were the experimental opinions which Dr. Ingen- 
housz promulgated in p. 23 of his prefatory remarks. He says, | 
** The discovery of Dr. Priestley, that plants thrive better in foul 
air than in common and in dephlogisticated air, and that plants 
have a power of correcting bad air, has thrown a new and im- 
portant light upon the arrangement of this world. It shows, even 
to a demonstration, that the vegetable kingdom is subservient to 
the animal, and vice versd, that the air spoiled and rendered 
noxious to animals by their breathing it, serves to plants as a 
kind of nourishment.” And at section 16, he says, ‘* In order to 
put my conjecture to the trial, I placed at eleven o’clock, in a 
warm sunshine, two jars of an equal size, each containing ar 
equal quantity of sprigs of peppermint in pump-water. In one 
of these was let up a certain quantity of common air. In the 
other jar was let up the same quantity of air fouled by respiration: 
at two o'clock the air of both jars was found much improved ; 
and at four o’clock the common air was still more improved.” 
I shall not make any remarks on the manner in which these ex- 
periments were conducted; I merely quote the above to prove 
that your correspondent has erred (I will not suppose wilfully) 
in representing Dr, Ingenhousz as “ one of the half dozen id 
Z2 thors 
