Middlebury register. (Middlebury, Vt.) 1886-1937, 1888-04-06
FLOW OF SAP IN THE MAPLE.

|hpniX.
HE FLOW OF SAP IN THE MAPLE
In order to understand what really
appens when the sap flows from a maple
early spring, and why it happens, it is
ecessary to have a clear idea of the con-
tons existing in a tree at that time,
he trunk and branches of a tree, as is
ell known, consist of a multitude of
ny cells that is, minute cavities sur
Funded by a wall of woody substance.
t the close of the autumn there accum-
lates in these cavities of the sap-wood a
Prtain amour of sap, where, before, the
)aces were filled almost entirely with
r. This accumulation is rendered the
hsier as the cold weather lessons the
Fessure of the imprisoned air. During
pc winter complete inactivity reigns
hroughout the plant: and the mingled
and air remain practically unchang-
4. except that the sap may slowly dis
Plve a portion of the sugar and certain
her substances contained in the tissue
'ound it.
The warmth of early spring brings
bout the first change in conditions. A
Sc of temperature Don affects the air
nprisOned in the wood-cells. and causes
to expand, and exert a pressure on the
p. If, now, a hole is bored in the tree
unk, the sap in the cells around the
ble will be allowed to escape, and thus
lieve the pressure of the air in those
Ills. At the same time, sap in the cells
l%jacent to these is pressed on by the
kpanding air, and ooZes through the
ll-wall into the cells which have been
hrtially emptied: the contents of cells
FXt to these act in the same way, and
us the motion of sap from one cell to
lother extends throughout the length
the tree. This movement of the sap
ntinues as long as the air in the cells
Ferts sufficient pressure. At the sugar
mps it is found that the flow of sap
asses towards night, becoming slower
the temperature falls. Experiments
to show that, as the air in the cells
ses heat and contracts, there comes a
me when the pressure is reversed, and
ere is a suction at the hole.
From what has been said of the causes
operation, other facts familiar to those
10 have bored for maple sap may find
cir explanation. For example, it is
I'll known that the best flows of sap
e secured when a thawing day follows
freezing night. Such marked changes
temperature are, of course, best cal
lated to bring about the requisite
essure. The south side of the tree is
e one preferred for boring the hole
is side being the one which receives the
pst sunshine. the direct effect of tenn
nature is again to be observed. 1t has
ZEN found, however, that, after about
the sap that it will yield has been OBJ
ned from a hole on the south side. if a
lie be bored on the north side of the
me tree an additional quantity of sap
by be obtained.
The explanation of this lies in the fact
At water passes with much more ease
tn the grain of the wood than across
consequently a hole drains the sap
ncipally from the wood in the same
rtical line as itself.
The question is often asked, in what
lection does the cap of a tree flow in
Ply spring? The principal flow is, of
lrse, from above the hole down to it:
at the same time a small amount NAV
W from below, and probably a small
antity comes also from the sides.
ere is apparently no reason to believe
pit any flow would take place before
buds expand if no wound were in the
fe to allow a drainage which would re-
we the pressure. 1t is therefore inpor-
pit, as will be seen, to make a marked
ltinction between that flow of sap
hich may take place before the buds
|pand, and that normal flow of SAD
lich goes on while the plant is in active
e. Popular Science News.