226 
moisture, both from the plant itself, and probably 
from the atmosphere in which it was confined. 
507. But farther, according to M. de Saussure, 
plants in the shade grow better in vessels which 
contain lime, than in those in which this substance is 
not present. The carbonic acid, which they then 
form, is, in great part, attracted j but we are not 
able, says he, to judge of the effect of a total privation 
of this acid, because it is formed in too great quantity 
to be entirely removed ; the effect, however, of a 
partial privation, he adds, is to favour vegetation *. 
We have, however, given examples (44.) of the total 
privation of this acid gas from plants vegetating in 
the shade, without ita producing any apparent change 
in their vegetative powers ; and, on the contrary, we 
have related other experiments, in which the carbonic 
acid, formed in vegetation, was allowed to remain, 
without apparently producing any suspension of that 
process, except in so far as the oxygen gas of the air 
suffered diminution ; so that, in the ordinary vege- 
tation of plants in a given portion of atmospheric 
air, neither the presence nor the absence of the car- 
bonic acid which they form seems materially to in- 
fluence the process. This inference is still more cer- 
tain with regard to plants which grow naturally in 
the open atmosphere, where the proportion of car- 
bonic acid is always nearly uniform, and seldom or 
never exceeds 1000 ficr cent. 
508. In certain circumstances, however, lime is so 
far from promoting vegetation, even in the shade, that 
it altogether arrests that process, as appears from the 
* Recherches Chim. p. 37. 
