where a small portion of carbonic acid was added to 
atmospheric air, it entered the vegetable in a propor- 
tion equal to that of oxygen ; but none entered, if 
she plant was confined in pure carbonic gas *. In the 
experiments also, which have been related (328. et 
seq.), not only oxygen, but hydrogen, nitrogen and 
carbonic gases obtained free admission into the vege- 
table body. The experiments likewise of Davy 
(500.), and of De Saussure (310.), prove the entrance 
of carbonic gas into the leaves of vegetables ; so that 
if the entrance of these gases be ascribed to chemical 
affinity, this affinity is not confined to one gas, but 
extends to many. It farther appears, that, though 
oxygen is generally converted into carbonic acid af- 
ter its entrance into the leaves, yet it is again com- 
pletely expelled in the state of oxygen gas, under ex- 
posure to the sun, and the other gases are often ex- 
pelled without any sensible change in their proper- 
ties, or any diminution in their quantity ; wherefore 
no part of them can have been appropriated by the 
plant ! 
342. Another curious circumstance, in the history 
of these phenomena, is, that various gases not only 
enter vegetables, without regard to their nature or 
composition, but they do so in a quantity, which, in 
many cases, considerably exceeds the bulk of the 
containing body. The leaves of the cactus, when 
confined through the night in atmospheric air, re- 
move a portion of its oxygen equal to three-fourths 
of their own volume ; and if the experiment be pro- 
Reche^ches, p 70. /- t Ibid. p. 82. et seq. 
