Physical Structure of Plants. as AQ 
and seeds perfected. To enter this organism, gases must penes 
trate the bounding tissue, and whatever elastic products are form- 
ed by chemical dition must find exit. But however 
readily some might admit the-porosity of this inferior vegetable, 
most botanists are disposed to look to a recondite principle, a 
vitality, for the solution of physiological points. ‘The influence 
of ordinary penetration in plants has never been proved, although 
conjectured by Liebig, Dumas, and the more speculative chemists, 
on the contrary the only direct series of experiments made on 
the subject by Messrs. Ferrand and Calvert, (Ann. de Chim. 
&e., August, 1844,) led those gentlemen to the opposite conclu- 
sion, They assert, at page 485 of their memoir, that “the blad- 
ders of Colutea arborescens are not permeable to the air except in 
the most limited degree.” In the case of Clorococcunt the pene- 
tration of gases is not only an essential point but nearly the only 
physical phenomenon, the other processes of growth and decom- 
position of carbonic acid, éc., being effects of this in a great de- 
gree. Now there is little doubt that the organic forces of this 
plant are those of the whole vegetable kingdom ; hence to prove 
that the structures of other plants is identical with this, is to Show 
all are reducible in their essential functions to a system, 
subject to physical penetration, and this is the object before me. 
I propose to discuss this position under the following heads :— 7 
~ Ast. The bounding membrane of plants is porous. 
+ 2d. The nature of the internal gas of plants. 
~ 3d. The action of roots on the gases of the soil fluid. res 
Ath. The- Sh cha of oe by page is a result a 
porosity. ‘ 
— The action of slants upon sesiiziol Seconegheects 
L The bounding Membrane of Plants is porous. 
, 3, "Phe object here is to show that the epidermis is not merely 
capable of transmitting a gas of particular composition, but that 
it obeys the theoretical requisitions of a porous membrane. ‘This 
is not indeed asserted of other plants than those employed, al- 
though I believe it to be a general law of the vegetable kingdom, 
the exceptions being inconsiderable. 'The bounding membrane 
of leaves is taken for experiment, because there exists no doubt 
of the. free. intercommuhication within plants by the cellular 
other channels, and ‘because it is obvious that if any 
/ Szcoxp aes, Vol. 4,1 No. tote 1846. 7 
