50 ; Dr, D.P. Gardner on the ™ 
vital force or antagonism existed to the operation of the phyisical 
laws of penetration it would be situated at the threshold ; over the 
exterior and not in the interior of plants. 
4. The experiments were planned with the twofold doje of 
showing that carbonic acid would penetrate into a vessel contain- 
ing common air, notwithstanding the opposition of a barrier of ; 
vegetable epidermis, and-secondly that an enclosed atmosphere _ 
of theoretical composition would solicit the passage of both car- — 
bonic acid and oxygen towards it, and at the same time throw 
out nitrogen gas. ‘There was some difficulty in obtaining perfect 
specimens of epidermis from most leaves and the observations 
were limited to those plants which furnished it readily and were ve) 
accessible. 
5. The experiments. August 6th, 1845, a tube five inna 
long and one third of an inch in bore was aabeatedl and one ex- 
tremity softened and pressed until-it presented a thick”ring of ~ 
glass, this was next ground toa plane surface. This tube was _ 
depressed in a mercurial vessel to within an inch of the mouth, a _ 
portion of the, fresh epidermis of the Madeira vine (Bassilla 
lucida) was then adapted to the ground surface by means of soft 
wax. ‘The portion of membrane lying over the bore of the tube - : 
was circular and nearly a third of an inch im diameter. The 
tube was now raised up three inches from the trough and_sus- 
pended by a wire ; the membrane sustained the pressure of three 4 
inches of mercury without leakage. In about ten minutes suf-_ aL 
ficient clear limewater was introduced through the column of 
mercury to reduce its level to that in the vessel, so that the tube 
contained one inch of atmospheric air at the same pressure aS 
that without, and three inches of limewater, and was closed 
above by vegetable membrane and below by mercury. Over this 
arrangement a small bell ‘jar was placed containing atmospheric | 
air with 10 per cent. carbonic acid. The experiment commenced “4 
_at 1 o’clock p. m., temperature 81° Fah., and at 6 o’clock p. ™ 
the limewater exhibited a distinct allies of carbonate of lime. 
Be The carbonic acid therefore penetrated the epidermis. 
experiment was made with slight modifications with the 
upper and lower epidermis of the Madeira vine, the epidermis of 
the cabbage leaf, the Alanthus alata, Chenopodium album, and 
seramhauean Sedum which anes covered with a i : 
; 
Impatiens ba 
is ee Mi i eh ee 8 OE oe ee 
