Edgefield advertiser. [volume] (Edgefield, S.C.) 1836-current, 1840-06-18

pant ~ neiQ III Souliol ny W;lteT anu III t'iu'
slate, enters the spongiole by sort Of affinity
which, in chemical philosophy, is called capilla-
! ry attraction; but from the well known fact
that the action of this principle is confined with
in very narrow limits, the ascent of the sap from
the eStrcmelics Of the roots, throug b the trunk,
TO The eXtrcmetics of the branches, and into the
leaves, cannot be accounted Tor, but upon some
other principle less hbvious, and more difficult to
be comprchcnded Aware ofthis difficulty ,physi.
ologisls attempted to account for the plcnolne.
non. by ascribing il to the pressure Of the at
mosriere upon the spongioles; thus forcing the
sap through The vessels of the plant, upon the
same principle that column of water is made
to ascend in Il tube by the pressure of The at
mosplerc upon the external surface OF tile
water. This notion prevailed until it was en-
ploded by DR.. Hales, who ascer;;!incd by an in
geninus experiment; tlatihe sap ofthe plant as
cends with velocity sufficient TO overcome the
pressure OF column Of wafer AZ feet in per
pendcular height; which is nearly one third
greater than tho force cxcrted by'the atinos-
pherc. that being sufficient 10 overcome the
pressure of column Of wafer Of only 32 feet
in perpendicular height. The opinion now
generally received is. that The circulation ofthe
sap is effected by the alternate contraction and
.dilatation Of the sap vessels; but how this con-
traction and di'ata,on take place. so long as
Vegetables are denied the functions of sensibilily
and rri'abi1itv must anprchcrd ever remain
Il profound mystery. That the san does ascend,
however. and with the force ascrbcd 10 it by
Dr:TIales, has been proved by ocl,ardemons,r;l-
iion funded on experiment; and il is pretty
well ascertained that il ascends, in the infancy
Of the plant, through The pih, and in its more
advanced.sate, throngh'tlIc alburrllm or white
wood. or in common phrasc6logy, the sap of
the tree, in contradistinclion to The heart. Tile
Sap, in lis ascent, undergncs little or no change,
until it reaches tie leaves fthc plant. Here,
by means of the porosty of the leaves, i, is cx-
posed to the action of the atmosphere, and is
said To have new property impaired to il by
tie oxygen of tic atmosphere; and thus, after
undergoing certain chemical changes aud COM
binatonsin in Tic leaves, precisely astIlevcnorrs
blood of animals, by being brought in contact
with the air in the lungs becomes oxygenatcd
and purified, the sap is fitted for giving nour-
islmcnt TO, and being assimiatcd with, the
propcr-substance ofthr plaht. But the analogy
between these animal und vegetable functions
does not stop here; for as the venous blood of
the animal, thus purified hy being brought i'll
contact with air i'll the lungs, is, by means Of
a different set of vessels, conductei,buck TO the
heart, thence TO be difliuscd through the sys-
tom; so the returning sap or peculiar juice of
the plant as it is now calfeSS, dcsccnds not in
the same vessels through which il ascendcd, bul
returns through the liber or inner bark, deposit.
ing in lis descent, portion of its nuiritve pro-
pertles wherever it is most needed foi the pre-
sent growth of the plant, and also laying up in
store certain portions. to be used dusing the
winter and following spring, before vegetation
commences. But tie leaves have yet other i'm
portant functions 10 perform. They not only
elaborate the crude sap absorbed by the roots,
and prepare it for beSg nssimila,cd and incor
pomlcd into the substance of the plant, butihcy
decomposc portion of the carboliic acid gas
of the atmosphere, and retain The carbon n.
food, whist the oxygen is disengaged and
tbro'Tn of, TO be employed in purifying the at
noSpherc which has been derioracd BY the
respiration of animals, aud the combustion and
decomposition Of vegetable end animal SUBJ
stances. The process Of absorbing carbon and
emitting oxygen is known TO take place only in
the day, or when light is prescul-a fact from
which Psychologists conjrclured That this lunc.
ton of the leaves is suspended during the
night; bm upon investigating the subject by
repealed experiments, Ingcuhousz and others
ascerlaincd that the process which goes on dur
ing the day, is reversed at night, oxygen being
absorbed, and cafbopc acid gas being evolved
by the plant.
|, is obvious lrcm the analogy which it bears
10 Il similar function in animals, that this pro-
cess NAV be called tho respiration of vegetables
Carbonaceous matter whether il bc derived
from the soil throueh the medium of the sap
vessels, Or from The atmosphere, is The appro-
pirate food Of vegetables; and physiSlogisls at
tempt TO account for the phenomena ofvcgetn-
bic respiration, by supposing that carbon is
generally unfit for the purposes of nutrition,
until it has been combined with oxygen in such
proportion as to form carbonic acid gas in the
plant an: that this intricate process Of cabora
ton and purifca,on is completed by the car
bonic acid gas being dccomposed by the leaves,
during tue day, throwing OF the oxygen and
retaining the carbon precisely in that state of
disinlegralioH which fits it for bcing readily as
simulated and Incorporated into the vegetable.