Burlington weekly free press. [volume] (Burlington, Vt.) 1866-1928, 1911-05-18
WHAT WAY DOES SAP flow
An Easily Constructed Gauge i""' ~
of Use to sugar Makers.


Ask mamie sugar workers which way
,he manic Juice flows; one will answer,
prom the roots" the second, From the
branches" and the third II do not
troc," writes w. s. G.. Russell Of Rut
land cou,tv. Vermont, in the American
Cultivator. The first two are guesses and
rort,v right Many are like the third
nerson who has never given 1t
thought. Sufficient for his purpose is
the knowledge that If the tree is pune
tured the sap will flow.
The principle underlying the transmits
sion of sap from cell to cell is technical
~ termed osmosis. II two cells are in
contact, one OF which contains n fluid
less dense than the other. then the con-
tents Of the cell containing tho less
dense fluid will soak or osmose into the
cell containing the more dense fluid.
This has frequently been shown in the
laboratory by immersing a porous cup,
closed at the top and connected with
gauge. In distilled water in second
cup. The first cup contains a dilute solu-
ton Of saltpeter or sugar. After lit
tie the pure water will work It's way
through the wall of the inner cup faster
than the sugar solution can work out
the inner cup which is measured by the
rise Of mercury In the gauge.
Plants and trees gather most of their
fluids IN the same way. A tree Is but an
infinite number of cells. more delicate
than the artificial ones Of the expert
mentcr. with those near the circumfer-
ence in perfect condition. The myriad
roots are absorbing moisture. in fact,
hn 0,,f
is pushed upward from cell to cell with
irresistible force, which fills the tree to
saturation on many days. and pressure
is exerted which can be measured
have devised simple gauge which
any boy can construct. Select a four
ounce bottle. with a two-holed rubber
stopper to It, MI the bottle two-thirds
full of mercury, and pass through the
holes heavy walled glass tubes, one of
which is bent at right angles four Inches
from the end and carrying three
fourths-inch. one-hole rubber stopper to
be inserted tightly in the tree. The tube
from the tree to the bottle should be
two feet long, and the other should be
continued up the tree five feet by join
ing the glass tubing end to end with
short, stout rubber tubing. Set the
gauge thus made on a block, and strong
ly wire the stopper down to the block,
and wire the other stopper into the tree.
The tendency of the sap TO escape from
the wounded tree exerts n downward
pressure on the mercury, and the con-
| sequent rise OF the mercury In the long
open tube measures this force. The
gauge is a sap neter-it Is subject to
| sudden and great changes of level. which
correspond exactly with the volume of
flow of sap from the neighboring trees.
A sudden and continued rise Of the mer
curry foretells an immediate flow of sap.
| Every sugar maker should At one tree
early in the season with such a gauge,
| as it will tell the time to tap.
The tree undergoing examination by
my botany class at this writing has reg
| istered % inches of mercury. Since mer-
curry Is 1886 times as heavy as water
| 1--WE will assume the density OF sap to be
one in the calculation). we have the
| following proportion by changing inches
| to feet; x. 68S ia. 1851. in which equals
Sc, 24s feet This shows that the tendency
| Of sap in this tree to flow through the
| opening is equal to the pressure of &c, o45
| feet OF water. This corresponds quite
| closely to the height OF the tree and
leads logically to the inference that on
a good sap day We may regard tree
as a hollow cylinder filled with sap: this
conclusion is strengthened by the read
| ing OF the gauge placed many feet above
the ground in the same tree for the
readings Of the two Conforned to the
law that pressure in liquids varies direct
/ ly the depth.
From two to four weeks hence the
birches will transmit their sap, and the
flow Is much greater than in the maple
especially in the case Of the black and
yellow birch. and the gauge set In one Of
these trees can be proftably read daily
till about the time the leaves are full
grown.
The birch and maple absorb water Wig
orously by osmosis at the rootets and
the cell, as the prime agent in this Won
derful and silent force, We learn thst
the protoplasm of cells is covered by a
transparent. delicate membrane which
possesses the remarkable property of be-
ing previous to water only, but as the
water is carried upward by these power
full force pumps, 1t passes into cells that
are ruptured. into the ducts and sap
ways dissolTng portions OF tho cell con-
| tents. The entire tree is under n pres
sure varying with its height, and when
the tree is tapped the MUD flows from
both root and limb. from the limb as
flows water from a leaky pail, from the
roots as the original source, and more
freely; from them rs the bit breaks the
column and cuts off much OF the pres
sure.