242 Researches on the Action of Foliage. 
carbonic acid, they soon lose their decomposing power, 
and die from the impossibility of respiration—zze, are 
asphyxiated. 
Leaves confined in a limited portion of atmospheric or 
other air over mercury, lose the power of decomposing 
carbonic acid; and the experiments pretty clearly show 
that they lose it through the deleterious action of the 
vapour of mercury. It is thought remarkable that the 
leaf does not under these circumstances at all lose the 
power of transforming oxygen into carbonic acid; but 
that 1s what we should expect, for the carbonic acid so 
evolved (whether its evolution be called respiration or not) 
must be a product of decomposition of the leafs contents 
or substance. 
We owe to Boussingault and his assistant, Lewy, the 
idea of determining the composition of the air contained 
in a fertile soil, and the fact that this air in a strongly- 
manured soil contains a very large percentage of carbonic 
acid. Boussingault has now devised an experiment by 
which the air contained in the branch of an Oleander in 
full vegetation was extracted. It proved to be nitrogen 
88°01 per cent., oxygen 6°64, carbonic acid 5°35 per cent., 
—being about the composition of the air from a well- 
manured soil. This carbonic acid carried into the leaves 
with the sap, and also that which they may absorb directly 
from the atmosphere, decomposed along with water under 
sunlight, must be the source of the glucose (C,,H,,O,,) 
which it is the principal function of foliage to produce. 
This glucose, in fixing or abandoning the elements of 
water, becomes sugar, starch, cellulose, or other hydrates 
of carbon, which in whatever part of the plant accumu- 
lated or deposited, and however transformed or re-trans- 
formed, must always have originated from carbonic acid 
and water in the green part of plants. In closing his 
present paper with some illustrations of this now familiar 
view, Boussingault announces that his more recent experi- 
ments will enable him to demonstrate the direct formation 
of saccharine matter by the green parts of vegetables 
exposed to the light—A mer. Fourn. Sct. and Arts. 
