Vermont farmer. [volume] (Newport, Orleans County, Vt.) 1870-1877, 1876-04-28
The Circulation of Sap.

President Clark who has made a special
study with elaborate experiments, of the
circulation Of sap, says:
The circumstances which affect the flow
Of sap from the sugar maple, the daily and
hourly flow correspond with the weather.
The most unlavorable weather is that which
is either steadily and severely cold, or uai.
formly warm and foggy, while the best sap
days are such as are bright and warm at
midday but preceded by freezing nights.
Such varieties Of temperature as affect the
flow ofmaple sap are most likely to occur when
the ground is covered with snow, because the
heat of the sun during the day cannot then
accumulate to moderate the cooling influence
Of the night. The most probable explana-
tion Of the effect Of these alterations, appears
to be that the outer tissues of the trees are
partially emptied Of their contents by the
contracting influence of cold, the sap being
driven into the heart-wood of the trunk and
large roots Meanwhile absorption goes on
as usual underground and thus when relief
is afforded by the heat Of the sun, the sap
rushes back to the surface and flows abun-
dainty.
Experiments also prove that spring sap
enters and fills the heart-wood as well as the
sap-wood. Trees tapped on the north side
yield twice as mnch sap as those tapped on
the south side, and flow two weeks longer.
Sap flows most freely within twelve feet of
the earth, and flows from both ends of cut
root The average yield of ordinary trees
in a sugar orchard is sixty pounds Of sap
aud two pounds Of sugar, but a tree in Lev
erett is reported to have produced l. ,40C
pounds of sap-probably about. forty pound:
Of sugar.
1t only remains to state in few words
some Of the surprising results obtained by the
application of mercurial gauges to the sugar
maple, the black birch and the grape vine
| Observations were made on one or more
gauges several times daily and occasionally
every hour of the day and night, from the
] st Of April to the Goth Of July.
A guage was attached to sugar maple
March 3lst, which was three days after the
maximum flow Of sap for this species, Sc
that further observations are required earl
in the season to complete the record anC
determine with certainty the maximum pres
!
record made, the following facts are special
interesting. First the mercury was subjec
to constant and singular oscillations, stand
ing usually in the morning below zero, ST
that there was indicated a powerful suction
into the tree, and rising rapidly with tn,
sun until the force indicated was sufiicien
to sustain column of water many feet il
height. Thus at a. m, April 2l, ther
was suction into the tree sufficient to rails
a column of water 25.95 feet. As soon a
the morning sun shone upon the tree the
mercury suddenly began to rise, so that a
S.l5 a. M, the pressure outward was enougl
to sustain q column of water l9.47 feet II
height change represented by more thar
A feet of water. On the morning of Apri
% the change was still greater, requiring
for representation Al ~ feet of water. Thes
extraordinary fluctuations were not attende,
by any peculiar state Of weather, and hap
peued twelve days before there were an,
indications of growth to be detected in tn
buds. These observations are quite new an,
as yet wholly inexplicable, but will receiv
further attention another spring.