78 VEGETABLE RESPIRATION. 
evidently must have taken place, as the deep green colo 
of their leaves, and the general healthy character of their 
functions sufficiently testify. 
273. He also found that when plants were supplied with 
a greater quantity of carbonic acid than existed in the natu-— 
ral condition of the atmosphere, they displayed a more 
luxuriant vegetation than under ordinary circumstances: 
Among numerous other experiments, Senebier mentions — 
that the branch of a tree which did not cause the disengage 
ment of any gas in distilled water, in common water disen- 
gaged a volume of gas equal to that of 108 grains of water 
and when the water was artificially saturated with carbome 
acid, the volume of the gas then equalled 1664 grains of 
water. : : 
274. It would appear, if we attempt to draw any conclu- 
sion from the experiments at present known, that, in clear 
sunshine, plants decompose carbonic acid derived from the 
sap or from that in the air, retain the carbon, and give out 
the oxygen; that in diffuse daylight or cloudy weather. 
they sometimes perform this process, and sometimes giv? 
out carbon, which unites with the oxygen of the air, and 
forms carbonic acid ; and that during the complete absence 
of light, they mostly perform the latter process. This, how — 
ever, is such an obscure and unsatisfactory view of vegetable 
respiration, that we must pause before we put implicit faith 
on the accuracy of the experiments on which it rests.* 
cluded, and the plant is made to act ona limited quantity of air. The actio? 
of light, which is supposed to be the stimulus to the expulsion of oxyge™ 
must be weakened. It isnot improbable that the heat which accompanie 
