VEGETABLE RESPIRATION. “TE 
ygen than they give out, and add to the carbonic acid in 
the atmosphere; and that they do not derive carbon from 
@ action of the leaf on the air. Subsequently, Sir Hum- 
phrey Davy was led from some experiments to adopt Priest- 
ley’s opinion, that plants purify, or add to the oxygen of the 
atmosphere, gaining carbon from that source. There is 
ill wanting a series of experiments sufficiently varied and 
accurate to enable us to pronounce upon this point. 
270. Numerous experiments have been made to show the 
ect of the green parts of the plant in decomposing the 
rbonic acid. Decandolle arranged one experiment in the 
following manner: On the stand of a pneumatic trough, 
which was filled with distilled water, he placed two inverted 
jars, one of these was also filled with distilled water, and 
ntained a plant of the Mentha aquatica—the other in- 
erted jar only contained carbonic acid an The vessels 
were then exposed to the action of the sun’s rays, to prevent 
y errors, the surface of the water in the trough being pre- 
viously protected from the action of the air by a deep stra- 
tum of oil. In the glass where the plant was, the water 
gradually descended, its place being supplied by an equiva- 
lent bulk of oxygen, while in the other glass, the water 
ascended, an equivalent proportion of carbonic acid having 
mn removed. 
271. If distilled water only, or oxygen gas only be em- 
oyed, there is no apparent result, and the plant speosy 
becomes sickly. 
(272. It is further to be noticed, that in the experiments 
zs shila to: effect in dneckapiaition of tha.cechuale mall zs 
all the experiments the transmission of the direct solar 
; was essential to effect this end; but in 
1 conditions of plants, in the shade under he zes, 
s other positions, where there is no ossibility 
sun's rays reaching them, these cha 
formed by De Candolle and others, it was found that the — ae 
shtest diffuse day-light, or the strongest lamp-light, was ge 
