128 
the proportion diminished as the plant advanced in 
age*. These facts prove that the green parts of vegeta- 
bles contain saline compounds in great abundance : and 
since it has been shewn, that the colourable juices of 
leaves (369.), and the leaves themselves (375.), have 
their green colour improved, or are even changed 
from white to green, by the addition of alkaline mat- 
ter, the same chemical changes must occur in the li- 
ving leaf, if means can be found to decompose its sa- 
line compounds, and thus, by releasing their acid 
part, to occasion an excess or predominance of alka- 
line matter. 
378. Now the decomposition of carbonic acid in 
plants, by the agency of solar light, seems to be the 
mean employed by nature to accomplish this pur- 
pose ; for, by this mean, the acid is not only with- 
drawn from its combination and expelled, but the 
alkali is, at the same instant, rendered predominant, 
and exists in a state fitted to exert its specific action, 
on the colourable juices of the leaf; and this action, 
as we believe, it does exert, and the leaf, in conse- 
quence, exhibits a green colour. The colouration of 
the leaf, therefore, is not immediately owing to the 
expulsion of oxygen, nor even to the subtraction of 
carbonic acid, but to the predominance of alkaline 
matter which this subtraction of acid occasions ; 
consequently, the verdure succeeds to the decompo- 
sition of carbonic acid, and the evidence of that de- 
composition is the expulsion of oxygen gas. Hence, 
therefore, to speak correctly, we cannot so properly 
Recherches, p. 285. 
