237 
there is no just reason for supposing that it ever takes 
place. 
521. As farther arguments against the decompo- 
sition of water, M. de Saussure observes, that he 
could never find in the atmosphere of confined plants, 
which grew many months in sunshine, any additional 
quantity of oxygen, which, however, might have 
been expected if they had directly decomposed wa- 
ter ; but the air, in general, suffered no sensible 
change *. Whenever plants afforded oxygen gas in 
sunshine, it proceeded not from the decomposition of 
water, but of the carbonic acid contained in the sub- 
stance of the leaff; for when solution of potassa 
was placed in the vessel to attract the carbonic acid, 
the leaves then afforded no oxygen gas J. From 
these and other facts, M. de Saussure concludes, 
that living plants do not, in any case, directly decom- 
pose water, by assimilating its hydrogen, and expel- 
ling its oxygen in a gaseous form ; nor do they ever 
afford oxygen gas, but by the immediate decomposi- 
tion of carbonic acid . This conclusion seems to be 
fully warranted by the facts above stated, and per- 
fectly accords with the opinion delivered (317.) in a 
former section. 
522. But though the preceding experiments (518.) 
afford no support to the opinion that water is decom- 
posed by growing vegetables, or even combined and 
fixed in them during vegetation, yet M. de Saussure 
believes this fixation to be prevented by the deficien- 
* Recherches Chim. p> 230. f Ibid. p. 233. 
J Ibid, p. 23^. Ibid, p, 237. 
