in this case, supplied to the plant ; but Ingenhousz 
asserts, that oxygengas is likewise produced by plants 
immersed in water, from which all the air has been 
previously expelled by boiling *. Nay, the experi- 
ments of Priestley, Senebier and Woodhouse demon- 
strate, that the production of oxygen by vegetables 
takes place not in proportion to the quantity of that 
gas which the water may contain, but to that of the 
carbonic acid which exists in it. It is a fact, how- 
ever, that boiled and distilled waters, deprived of air, 
do not support the vegetation, even of aquatic plants, 
and water fully saturated with carbonic acid is still 
more destructive ; for the conferva rwularls and 
potagmogeton crisptim, says Dr Ingenhousz, were 
soon destroyed in it t ; and yet from such water, so 
impregnated in a slighter degree, he often obtained, 
by means of plants, a great quantity of air of exquisite 
purity J. 
335. Nor is it only when they are thus secluded 
from air, or immersed in water deprived of air, or in 
that which is impregnated with carbonic acid, that 
this operation of yielding oxygen gas is performed by 
the leaves of vegetables ; for the experiments of Da- 
vy (300.) shew, that these leaves, when confined in 
pure carbonic acid, equally afford oxygen gas, and 
those of De Saussure prove the same thing to happen 
in vessels of hydrogen or nitrogen gas ||, although it 
is universally admitted that these gases are incapable 
* Exper. torn. ii. p. 321. 
t Exper. torn. ii. p, 270. J Ibid. p. 283. 
j| Recherches Chim. p. 84. et seq. 
