79 
every twelve hours, lest their vegetation might lan- 
guish, yet they produced no oxygen gas, but aug- 
mented their atmosphere, by a quantity of carbonic 
acid *. 
313. Even in perfect darkness, continues M. de 
Saussure, some plants would seem to possess the power 
of decomposing carbonic acid. He confined plants 
of peas and of salicaria, in two equal recipients of at- 
mospheric air, and set them aside in a place perfect- 
ly dark. One of the recipients contained a portion 
of lime or potassa, while the other held the plants on- 
ly : in both vessels, the plants were daily renewed. 
At the end of four or five days, the air, in both reci- 
pients, was vitiated ; and in several repetitions of the 
experiments, he constantly found that the air of the 
vessel, which held the lime or potassa, contained less 
oxygen gas, than that of the vessel which had no al- 
kali. This difference, it is added, may be presumed 
to arise from less acid being present for decomposi- 
tion in the vessels, which contained the alkali, than 
existed in the recipients which held no alkaline sub- 
stance f. 
314. We have already stated (25.) that artificial 
light changes the colour of plants in a manner simit 
lar to that of the sun. M. Decandolie found, that 
various plants, raised from seeds in a vault lighted 
by lamps, became green both in their stems and 
leaves, nearly like those which grew in the open air. 
He confined also the leaves of various plants in in^ 
verted glass vessels of water, and placed them in a 
* Recherches, p. 199. 201, t l bid * P 55. 
