60 Dr. D. P. Gardner on the e 
position resulting from the continued absorption of oxygen and 
carbonic acid during daylight. The deficiency thus caused as 
the first effect of the sun’s rays, brings into operation the laws of 
diffusion. From the common atmosphere, carbonic acid and ox- 
ygen enter through the epidermis of the leaves, whilst the spon- 
gioles give passage only to such a gaseous mixture as is required 
by the sap. The gases thus finding entrance to equilibrate a 
deficiency, are in their turn decomposed or appropriated, at first 
by a decomposition of carbonic acid an excess of oxygen is pro- 
duced, but a portion being evolved, the per-centage within is 
gradually. diminished until it becomes less than that of the at- 
mosphere. The same changes continuing during daylight, a 
stream of carbonic acid sets into the plant, whilst portions of its 
oxygen with nitrogen are liberated; oxygen with carbon being 
continually fixed by the plant. It is the unsatisfied equilibrium 
of the internal gases which ae and. maintains the current. 
V. The effects of Artificial Atmospheres upon Plants. 
33. But to show more distinctly the mere physical porosity of 
vegetable tissues, we may examine the interesting observations 
of M. Marcet, which like many other similar facts remain unas- 
similated. This observer found (Ann. de Chim., &c., t. lviii, p. 
407 ) that the same Species of fungi exposed to different atmos- 
pheres, as common air, pure oxygen, or pure nitrogen, gave off 
dissimilar gases. If we investigate these results, it will be seen 
that in each case the theoretical indications of a porous system ~ 
are satisfied. The table gives a synopsis of the action of the 
same living fungi on the three atmospheres; in each case 100 
volumes of the gas were used, and after the plants had been im- 
mersed therein eight to ten hours its composition was ascertained 
and found— 
Atmospheres. . 
Common air. Oxygen. Nitrogen. 
a WXVRen, . ‘ 20 313 * Ae 
_ Nitrogen, . 5 77:0 24-0 96-1 
Carbonic ace... 210 44-7 39 
100° 100° 
From the a of a ees gas, it is apparent that 
the plant “isare se hese fungi contained a high per-centage 
of nitrogen and ros acid with a deficiency of oxygen, 
adopting this speculation enact. seam: the three atmospheres 
