Miscellaneous. 343 
compose carbonic acid and water, CO°, HO=CO, H, O*: the O° 
being liberated, CO, H expresses the relation under which carbon is 
united with the elements of water in cellulose, starch, sugar, &c., 7. e. 
in the important principles elaborated by the leaves, the composition 
of which is represented by carbon and water. He goes on to prove 
that a leaf which has been decomposing carbonic acid and water all 
day long is capable of doing the same work the next day, if not 
allowed to dry; but the losing of a certain amount of water annihi- 
lates this faculty, and irremediably destroys the life of the cells of a 
leaf, vegetable life in this state being far less tenacious than that of 
some of the lower animals (Tardigrades, Notipes, &c.), which bear 
wonderful desiccation. 
The third instalment of the investigation is given in Nos. 16 and 
17 of the same volume (Oct. 16 and 23,1865). It appears that de- 
tached leaves, kept in shade for many days, with the cut end of the 
petiole in water to prevent desiccation, preserve the power of decom- 
posing carbonic acid whenever brought into sunshine. But for this 
they must be kept in an atmosphere containing a supply of oxygen ; 
without this they soon die, as Boussingault thinks, from asphyxia. 
This oxygen in darkness is slowly transformed into carbonic acid, 
through an operation which is presumed to go on continually, whether 
in light or darkness, and to answer to respiration. Of course a healthy 
and active leaf decomposes far more carbonic acid in the light than 
it forms in darkness. In eighteen experiments with oleander-leaves 
exposed to the sun from 8 a.m. to 5 p.m. in an atmosphere rich in 
carbonic acid, a square metre of foliage decomposed on the average 
over a litre of carbonic acid per hour, while in darkness only >> of 
a litre of carbonic acid was produced per hour. In air which con- 
tains oxygen and carbonic acid, leaves will go on indefinitely pro- 
ducing oxygen in the presence of carbonic acid, and carbonic acid in 
the presence of oxygen. But the latter, though relatively small in 
amount, seems to be necessary to the preservation of their vitality. 
In hydrogen, carburetted hydrogen, or nitrogen, as well as in pure 
carbonic acid, they soon lose their decomposing power, and die from 
the impossibility of respiration, 7. e. are asphyxiated. 
Leaves confined in a limited portion of atmospheric or other air 
over mercury Jose the power of decomposing carbonic acid; and the 
experiments pretty clearly show that they lose it through the dele- 
terious 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 is what we 
should expect; for the carbonic acid so evolved (whether its evolu- 
tion be called respiration or not) must be a product of decomposition 
of the leaf’s contents or substance. 
We owe to Boussingault and his assistant Lewy the idea of deter- 
mining 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 ex- 
periment by which the air contained in a branch of an oleander in 
full vegetation was extracted. It proved to be, nitrogen 88°01 per 
