8 ON CHEMISTRY. 
fluid must be perpetually, and without intermission, proceeding 
during the progress of vegetable vital action. 
Let a glass globe be filled with water, and a sprig or two of mint, 
or the green leaves of almost any tree, or a growing entire plant, be 
then introduced. The globe is next to be inverted, and placed in a 
vessel of water with its neck downward, so that no air may enter, 
nor water escape. 
The plant or leaves are thus immersed ; and in this situation, the 
vessel being exposed to the direct light of the sun, the foliage is 
acted upon by the rays of light passing through the media of glass 
and water. Bubbles of air are formed on the leaves, which increase 
in bulk, till they rise to the top of the globe, and displace some of 
the water. The gas thus developed, is found to be oxygen, for it 
supports combustion in a very eminent degree. Chemists sav that 
the hydrogen of the water combines with the plant; they consider 
that it contributes to its nourishment; and that, in proportion as 
the hydrogen is taken up by the leaves, the oxygen gas is liberated. 
The fact is decisive of the agency of light upon vegetables; but I 
am apt to doubt the accuracy of the deduction. [ think it quite as 
probable that the water is taken up by the vegetable, and the decom¬ 
position effected within the cells, by the agency of the solar light, 
the gas set free, being propelled through the oscular pores of the 
leaves, as that the leaves merely attract the hydrogen, and thus cause 
the liberation of the other component. Be this as it may, the result 
is one of great interest; and it is connected with another, which 
will be noticed in a future paper, on the course of the vegetable 
fluids. 
Every one knows that water is essential to the life and growth of 
plants; but a real mystery is involved in the consideration of the 
mode in which it acts upon them. Is water taken up in its simple, 
entire state, into the vegetable vessels ; or is it decomposed in the 
soil, and assumed under the form of gas ? Does it act simply as a 
solvent of the nutritive matters contained in the soil, thus enabling 
the processes of the roots to take up the essential qualities of those 
matters which otherwise could not find a passage through orifices of 
such infinite minuteness as those with which the rootlets are fur¬ 
nished ? 
These enquiries lead to the consideration of the following facts:_ 
Many plants will strike root very freely in water, whether that be 
pure from the clouds, or the more compound fluid from rivers and 
wells, which usually contains vegetable matter, and some chemical 
solution of chalk. These rooted plants will live for a considerable 
