C 197 ] 



The carbonic acid is probably absorbed by the 

 fluids in the cells of the green or parenchymatous part 

 of the leaf; and it is from this part that oxygene gas 

 is produced during the presence of light. M. Senne- 

 bier found that the leaf, from which the epidermis was 

 stripped off, continued to produce oxygene when 

 placed in water, containing carbonic acid gas, and the 

 globules of air rose from the denuded parenchyma; 

 and it is shewn both from the experiments of Senne- 

 bier and Woodhouse, that the leaves most abundant 

 in parenchymatous parts produce most oxygene in 

 water impregnated with carbonic acid. 



Some few plants * will vegetate in an artificial at- 

 mosphere, consisting principally of carbonic acid, and 

 many will grow for some time in air, containing from 

 one-half to one-third; but they are not so ^calthy as 

 when supplied with smaller quantities of this elastic 



substance. 



Plants exposed to light have been found to pro- 

 duce oxygene gas in an elastic medium and in wa- 

 ter, containing no carbonic acid gas; but in quantities 

 much smaller than when carbonic acid gas was pre- 

 sent. 



In the dark no oxygene gas is produced by 

 plants, whatever be the elastic medium to which they 

 are exposed; and no carbonic acid absorbed. In most 

 cases, on the contrary, oxygene gas, if it be present, is 

 absorbed, and carbonic acid gas is produced. 



* I found the Arenaria tenuifolia to produce oxygene in carbonic acid, which 

 was nearly pure. 



