The Pickens sentinel. [volume] (Pickens, S.C.) 1871-1903, 1882-11-23


have been asked whether the state
ment now going the rounds of the pa
pers THAT "a dead branch on O. tree
makes almost as great o strain on the
mann plant Tor moisture as does q living
one" is accurate or not. The statement
Is coupled with another referring to its
practical application in tree culture, the
conclusion being that every dead
branch 'should he at once cut away.n
Brlety IT might be answered that the
hrst statement is true in the main, and
that, without any doubt at all, the con-
cluslon is a wise one and ought to he
followed in practice. TO explain this
matter Will take considerable more
space, and in order to understand it we
must go to vegetable physiology and in
qulre into the nature of the evaporation
of water from plants. 1t was long sup
posed to be physiological process, and
was considered to be entirely different
from ordinary physical evaporation. AS
long as this view was held the process
was called Transportation, to distinguish
it from the physical process. Tho
breathing pores, the stomata, which oc-
cur in the epidermis of all leaves in
great numbers, were supposed to be
organs OF Transportation, which was con-
sidered to be one of the most important
functions of the leaf,
Within few years, however, our
knowledge of these matters has been
greatly increased and we now know that
the escape OF water from the leaf does
not dltleC in any way from the evapOra-
tlon OF water from any other moist sur
face. A leaf is q mass of cells, cvery
one OF which is gorged with watcry mat
ter, which in dry atmosphere, as q
matter vi course, tends to escape. The
epidermis, composed of dryish, impervi-
Gus cells, which entirely surrounds the
watery cells of the leaf, would prevent
almost completely the evaporation of
water from the latter were it not for the
breathing pores before mentioned.
These pores are for permitting the free
ingress and egress of gases, particular
~ oxygen, carbonic acid and probably,
also, ammonia. Now, when the pores
are open for their legitimate purpose it
happens that more or less water es-
capes, if the air is dry. If the air hap
pens to be very moist the loss of water
through the breathing pores is very lit
tie or even none at all.
We may put it in this way: the leaf
loses water simply because it is watery
ellucIulci ltS cplleTnlS Is ucSlSncu TO
prevent this loss, and the breathing
pores with their power of opening and
closing arc for the same purpose. A
leaf instead of being an organ Of evap-
Grafton is actually u structure in which
evaporation is quite u.cessfully
checked. Careful experiments made
under my supervision in the Iowa Agri-
cultural College in 1880 by Miss Ida
Twitchcll, graduate student, demon
stratcd that the evaporation from q
moist piece of dead wood was exactly
i like that from q living leaf. Now when
n dead branch is large enough to keep
continually moist in the interior it will
in dry air constantly lose water by evap-
Grafton from its surface. This water so
lost is taken from the tree, and must
have been supplied directly or Indirect
ly by the living portions. Moreover, it
must be remembered that q living
branch is well protected against loss OF
water through evaporation, by the cpl
! dermis which covers all its surface when
young, or the imper> ious corky bark
which is always found on it when older.
When branch dies, these protecting
! de- ices soon fall into decay and the wa,
ter, 50 carefully guarded by the living
parts of the plant, is wasted by evapo,
ration-Prot. BeSScU, IN N. Y. TriJ1t11G