SECT. V. ELABORATION OF CARBONIC ACID. 151 



seven cubic inches of nitrogene. Several plants 

 of the same species were made to vegetate in a 

 similar apparatus, at the same time and in the same 

 exposure, in pure atmospheric air. Their atmos- 

 phere was not altered either in purity or volume, 

 but their carbon instead of augmenting had rather 

 diminished ; whilst the carbon of the others, as 

 was found by comparative analysis had augmented 

 very considerably. Experiments of the same Of which 

 kind were made upon Mentlia aquatica, Lythrum Js 

 Salicaria, Pinus genevensis, and Cactus Opuntia ; a part * 

 and the results were always similar, from which it 

 follows also that plants decomposing carbonic acid 

 gas assimilate at least a part of the oxygene which 

 it contains. 



Such are the several results obtained from expe- 

 riments, concerning the accuracy of which there 

 can be no doubt. The decomposition of carbonic 

 acid gas takes place only during the light of day, 

 though Saussure has made it also probable that 

 plants decompose a part of the carbonic acid gas 

 which they form with the surrounding oxygene 

 even in the dark. But of this there does not yet 

 exist any satisfactory proof; how the light acts is 

 not certainly known. But the effect is operated 

 chiefly by means of the leaves and other green parts 

 of vegetables, that is, chiefly by the parenchyma ; 

 the wood, roots, petals, and leaves that have lost 

 their green colour not being found to exhale oxy- 



