45 
262. To the experiments of Dr Woodhouse on 
the vegetation of plants in atmospheric air, we have 
already referred (30.), and have stated their general 
agreement with those which have now been related, 
He found that plants, confined either in atmospheric 
air or in oxygen gas, previously washed in lime wa- 
ter, rendered it impure, by forming carbonic acid, 
He farther asserts, that growing vegetables do hot 
purify the air, but that the same effects are produced 
in the air by the growth of plants, as by the germi* 
nation of seeds, and from the same causes. He sup- 
posed, indeed, that the carbon, which united with the 
oxygen, was afforded, not by the living plant, but 
by a dead portion of the leaves *. The facts, how- 
ever, which have been so fully stated, sufficiently e- 
vince that this acid may be formed by the living, as 
well as by the dead, vegetable substance. 
263. From the series of experiments and opinions 
which has now been delivered, we see that all the 
more distinguished philosophers, who have applied 
themselves to the investigation of this subject, with 
the single exception of Dr Priestley, agree in the fol- 
lowing general facts : That oxygen gas is, at all 
times, necessary to vegetation ; that, in the shade, or 
in perfect darkness, this gas constantly disappears, 
and is replaced by carbonic acid ; and that, when the 
atmosphere contains no oxygen gas, vegetation no 
longer goes on. Even the experiments of Dr Priest- 
ley cannot be considered as opposing any serious ob- 
jection to these conclusions ; for though it were grant- 
* Nicholson's Journal, vol. ii. p. 152- 
