222 
of acid gas *. Thus, then, we see, that lime, which 
is considered to destroy plants by abstracting the car- 
bonic acid from their atmosphere in sunshine, is ac- 
tually favourable to vegetation when that process is 
conducted in the shade. In what way, then, does 
lime, in these different experiments, affect the vege- 
tation of plants, and from what cause does tfiis re- 
markable difference in its action proceed ? 
502. It appears, that, in the experiments made in 
sunshine (500.), the carbonic acid was entirely attract- 
ed by the lime; but in the shade (501.), the atmosphere 
still contained ^ of that gas. Did then the plants 
die in sunshine, because their atmosphere contained 
no carbonic acid ? and did they live in the shade, be- 
cause a small portion of carbonic acid was present in 
it ? If the first of these positions were true, then ve- 
getation should cease in air deprived of carbonic acid 
(499.), which is not the fact; and, contrarily, if 
the second were true, then plants should not grow in 
air deprived of this acid gas, which nevertheless they 
are found to do. Consequently, the presence of car- 
bonic acid is not essential to the vegetation of plants, 
even in sunshine, neither is it injurious to those which 
grow in the shade ; and since, therefore, neither the 
presence nor the absence of this gas materially affect- 
ed the vegetative process in these experiments, we 
must seek out for some other cause of the contrariety 
in result which they afford. 
503. Now this cause must be connected with some 
circumstances arising out of accidental situation ; for 
* Recherches Chim. p. 36. 
