58 Dr. D. P. Gardner on the 
28. But that there might be no doubt on the action of a porous 
vegetable tissue, such as envelops every part of plants, when 
containing an atmosphere similar to that called the plant gas, an 
surrounded by a mixture resembling the water gas, the experi- 
ments detailed in section 7 were contrived. The results in these 
eases were directly coincident with theory. If it be admitted 
that the epidermis employed resembles the tissue of the roots, 
the consequences must also be admitted. ‘That the tissues are 
analogous and would act in the same way may be inferred from 
the observations of M. Payen, who maintains that the enveloping 
cellular tissue of all parts of plants (ced/ulose) has a definite com- 
position; and if the chemical nature be the same, the affinity for 
different gases and fluids will be identical. There is but one 
other disturbing cause, which we cannot enter upon in this place, 
—the affinity of the gases and fluids stored within cellules and 
closed vessels. Now the bounding membrane of a cell may ex- 
ert an attractive force towards a given gas or fluid, which, not- 
withstanding, never penetrates to the interior because of the an- 
tagonism of the included substance, which does not combine with 
it, and therefore the passage is arrested at the internal limit of the 
‘membrane. Whatever effect may arise from this or any other 
cause in the complex processes of the higher vegetation are not 
before us now ; the absorption and evolution of certain gases by 
plants is the resultant of all the internal actions, and with these 
only are we concerned. 
29. If we consider the action of leaves on ccidiieaens air, the : 
theory of physical penetration is more certainly established. In 
this case we find oxygen and carbonic acid absorbed and nitro- 
gen liberated in the same way as ‘in the experiments in section 7, 
where the plant gas, nitrogen 87-0, oxygen 13-0 per cent., was 
brought in contact by a piece of epidermis with a mixture of 
common air and ten per cent. carbonic acid. With living plants 
the experiment has been made by the most skillful observers, 2S 
, Davy, Daubeny, and others. In Saussure’s researches 
nitrogen was always evolved, whilst carbonic acid and’ oxygen 
were absorbed. It is not indeed admitted by all vegetable phys 
jologists that oxygen is uniformly absorbed and nitrogen thrown 
out during the growth of the green parts, but upon examining 
ine facts will be found abundantly con- 
aR a 
