The Caledonian. [volume] (St. Johnsbury, Vt.) 1837-1867, 1848-04-01

From the Horiculiurst.
Popular Errors about the "Rise
and Fall" of Sap.

RY PROF. LISDLEY, UNIVERSITY OF LONDON.
What curious hallucination is that which
Supposes the sap of trees TO fan, or settle, in the
winter into the roots! One would have
thought that the notorious difficulty Of cram
ming quart ofwater into Il pint measure
might have suggested the improbabliiy of
such phenomenon. For II certainly does
require very large amount of crednity to
believe that the fluids Of the trunk and head
of tree, cGn 10y any natural force OF COM
preston, he compelled 10 enter so narrow n
lodging as tl!e root. The idea, however, hus
established itself in some persons minds,and,
we presume, in connection with that old vul-
gar error, that the sap is la rapid motion in
the spring time, in the roots ofa tree, before
il begins to flow in the branches. These
WITNESSES took their origin in days when the
world was contenlcd to accept assertions up
on trust, and when hypotheses and vain i'm
aginings formed the debased paper curren-
cy of science. But now men hive found out
she value of II golden standard both for mon
ey aud for knowledge; they call for facts be-
fore theories; aud The result, alrcndy, is II
wonderful disturbance in the crowded runks
of scientific as well as historical legends.
We shall assume the word sap 10 signify
she fluids, of whatever nature, which are
contained in the interior OF IL tree. In the
spring, the sap runs out of the trunk when il
TER, il docs not, unless exceptionally, make
sts appearance. But in truth the SAP is al
why's ia motion, ut all seasons, and under all
circumstances except in the presence of ln-
tense cold. The difference is, that there is
great deal of il in the spring and much less
AT other seasons
When tree fulls 10 rest AT the approach
Ofwinter, its leaves have carried of so much
snore fluid than the roots have been able 10
81, ,rV tgt
stnie ofconparalive dryness; and n large por
zion fIhat sap which was once fluid, has be-
come solid, in consequence of the various
chemical changes IL has undergone. Between
simple evaporation on the one hand, and
chemical qualification on the other, the
sap is, in the autumn, so much diminish
ed in quantity as to be no longer discOvera-
ale by mere incisions. The power that Il
plant Inay possess of resisting cold,is in pro-
E0rIioH to the completeness Of this drying
process.
&VLen the leaves have fallen of, the tree
IS no longer subject to mnch loss of fluid by
perspiration, nor 10 extensive chemical chang |
es by assimilation, for the leaves are the prin- |
cipal organs of perspiraiion ~ assimilation.
But the absorbing power of the roots IS not
arrested; they, Oh the contrary, 60 OH sucking
slud from the soil, and driving it upwards in
20 the system. The effect of thslis, that af
der some months ofsuch an action, that loss
of fluid which the tree had sustained in at-
Iumn 10y its leaves, is made good, and the
whole plant is disfended with watery part- |
Giles. This is a most wise provision, in order
no insure abundant food TO the new born
seares and branches, when warmth aud light |
stimulate them into growth.
During all the winter period, the sap APP |
pears indeed TO be at rest, for the refiling |
s,roccss is very gradual one. But NJ. Blot,
many years ago, proved, by an ingenious APP |
H)aratus, shat the rate of motion Of the sap
saav be measured at all seasons, and he as- |
ceriained il to be in state of considerable |
nctiviiy in mid winter. Among other things
he found that frost had considerable influence
sIpon the direction in which the sap moves. |
in mid weather the sap was constantly rising, |
but when frost was experienced the sap flow
ed i'ack again;-a phenomenon which he re- |
1erred 10 the contracting power fcold on
abe vessels of the trunk aud branches, the |
effect of which was 10 force the sap down !
Awards into the roots lying in warmer me-
dunn; then, aguin, when the frost reached the
FoOIs themselves and began acting on them, |
abe sap was forced back into sthe trunk; but
MS soon as thaw came on, and the ground re- |
covered it's heat, the rOots,O of which part
OF the sap had been forced upwards, were u
gain filled by the fluids above them, and the
sap was forced 20 fall A large poplar in the
aatter state, having been cut across at the
ground line, the surface of the stump was
found to he dry, but the end of the trunk it.
selfdrpped with sap. Sap, then, is always
an nfotiou; aud If i; settles 10 tue root in
:, visible manner, that is owing to temporary
causes, The removal Of which causes its in
slant re ascent.
As to the idea that The bleeding Of tree
begius first at the root, and la connection
with this suppoSiion, that what is called the
rise of abe sap is the cause of the expansion
of buds, and leaves and branches, moth
sng can well be more destitute of nny real
formulation. Ifin the spring, when the buds
are Just swelling, tree is cut across at the
ground line, no bleeding will take place, nei-
Hher will the sap flow for some distance up
wards; but among the branches the bleeding
will be found TO have commenced. This
was observed some years age by MIR Temp
son, at that time the Duke of Portand's
gardener, who thought he had discovered
that the sap of trees descends in the spring,
instead of ascending a strange speculation
enough, it must be confessed. The fact is,
that the sap is driven into accelerated motion
first al the extremities of tree, because it is
sbere that light and warmth first tell upon the
cxcitabe buds. The moment The buds are
excited they begin 10 suck sap from the parts
with which they are in contact TO supply
the waste SO produced, the adjacent sap
pushes upwards; as the expansion of the
leaves proceeds, the demand upon the sap
near them becomes greater a quicker mo-
dion sill is necessary on the part of the sap