Dr Gilby on the Respiration of Plants. 105 
to the arguments in his treatise, which I think are as conclusive as 
possible. If this statement be correct, it shews clearly the absur- 
dity of supposing, that the amelioration of the atmosphere can be 
maintained, on the opinion above stated, as it imagines the dis- 
continuance of a part of the natural economy of vegetation. In 
rejecting this opinion, we must conclude, that the formation of 
carbonic acid continues even during sunshine. If so, it becomes 
a matter of interest, with regard to the question in view, whe- 
ther the carbonic acid is formed without or within the leaf. In 
the former case, the conclusion is unavoidable, that the air is al- 
ways vitiated by vegetable respiration ; for if the carbon is ex- 
haled from the leaf, and exterior to it unites with the oxygen 
of the air, as soon as the carbonic acid is formed, it immediately 
mixes with the atmosphere, and is altogether withdrawn, both 
from the influence of the sun and plant. If, on the other hand, 
the carbonic acid have its origin in the leaf, it will, indeed, du- 
ring sunshine, be decomposed ; but only so much oxygen will 
be given out, as was necessary for its preparation, and of course 
the air will receive no improvement from this cause ; so that in 
whatever way we view the respiration of plants, we shall And, 
that it is impossible to ascribe to them any beneficial effect in 
maintaining the uniform purity of the atmosphere. 
It is the opinion of some, that the vegetable kingdom has 
the power of decomposing the water which they imbibe. It 
may be so. But we have no proof of it by experiment, that I 
am aware of. On the contrary, it appears, in all the experi- 
ments of Sennebier, Saussure, and in numerous trials of mine, 
that no more oxygen was given out, than what could most cor- 
rectly be accounted for from the carbonic acid employed. And 
even when plants have been allowed to vegetate for a number 
of days and nights in a confined portion of atmospheric air, as in 
an experiment of Ingenhousz, and as also (if I remember right) 
in one mentioned in Sir H. Davy’s Agricultural Chemistry, its 
constitution at the close had suffered no change, the carbonic 
acid which had been elaborated during the night, being, during 
sunshine, again resolved into its original elements. 
Some, again, have supposed, that the decomposition of the 
carbonic acid which is contained in the water imbibed in the 
plant, is another source by which oxygen is supplied to the at- 
