62 Dr. D. P. Gardner on the 
37. Some observations made by me in the summer of 1844, 
also serve to verify the position, that the gases exhaled by plants 
are not constant, but depend upon the atmosphere in which they — 
are plunged. Specimens of the Conferva mucosa were placed in 
pump-water, which is their natural medium, and others in dis- 
tilled water impregnated with carbonic acid gas, and exposed to 
sunlight. In six hours the gases produced in the receivers were 
entirely separated, and the arrangement left for twenty-four hours 
without any fresh water; the gases were again withdrawn, and 
thus for four and five days, no fresh water being added throughout. 
It is evident that the gas of the water was constantly changing — 
in its composition, and therefore the experiments were the same 
as if made in‘a number of different artificial mixtures of gases: 
The plants in pump-water gave in the first six hours an expired 
gas, consisting of oxygen 73, nitrogen 27 per cent.; im twenty- 
four hours, oxygen 53, nitrogen 47 per cent.; in forty-eight 
hours, oxygen 18-6, nitrogen 81-4 per cent. The specimens in 
carbonated water produced in six hours, gas consisting of oxygen _ 
68, nitrogen 32 per cent.; in twenty-four hours, oxygen 63, ni- 
trogen 37 per cent. ; in forty-eight hours, oxygen 12, nitrogen 
88 per cent. ; in pines pane hours, oxygen 3:5, nitrogen 965 
per cent. These latter were in no way injured at this time, for 
upon adding a little fresh fluid they yielded at ninety-six hours, 
agas consisting of oxygen 15, nitrogen 85 per cent. The ali- — 
ment of these plants was not changed, for they continued healthy, 
the different gases expired were merely the result of physical 
necessity, the aériform matter of the water being continually 
changed. I do not assert that all the nitrogen in the foregoing 
measures was thrown out from the interior of the plants, because 
as we have already shown in section 24, the physical disturbance 
of the water gas will be attended with the evolution of nitrogen, — 
and although distilled water was used, there is no process - 
which all its gas can be driven out. 
38. Conclusion.—From the preceding evidence I infer that 
plants are a simple porous system, so far as they are related to 
the air and the gases of fluids in the soily leaving out of consid- 
eration the internal phenomena of penetration. 'The advantages 
resulting from the adoption of this philosophical view of veget® 
tion, both. in assimilating facts hitherto insulated and criticising 
. -) t tia physiology, form its great 
