56 
therefore, additional evidence of the power of the 
vegetable to produce this specific change in the air, 
and shew that, with respect to these parts at least, it 
is the natural effect of vegetation. As, however, 
carbonic acid is thus, at all times, produced by these 
several parts of plants ; and as all the green parts 
have likewise been shown to produce a similar effect 
in the shade -, it is evident, that, if a contrary effect 
arise when the green parts are exposed to the rays of 
the sun, it must proceed from the peculiar agency of 
the sun upon those parts alone. We proceed there- 
fore, in the next place, to investigate the changes in- 
duced on the air by the leaves and green parts of 
living vegetables, when exposed to the direct agency 
of the solar rays. 
SECT. II. Of the Vegetation of Plants in Sunshine. 

280. IN our former publication we were led, by 
the results of our own experiments, to consider the 
consumption of oxygen gas, by living plants, as the 
natural and necessary effect of vegetation ; and this 
conclusion has, we presume, been abundantly con- 
firmed by the additional facts and circumstances which 
have just passed under our review. But the opinion^ 
which maintained the production of this gas by grow- 
ing vegetables exposed to the sun, appeared so di- 
rectly opposed to these views, that we were induced 
to question the accuracy of the facts, and to combat 
the correctness of the reasoning on which it rested y 
