Evening times-Republican. [volume] (Marshalltown, Iowa) 1890-1923, 1916-10-17
COOL WEATHER DOES NOT CAUSE THE FALL
OR COLORING OF LEAVES; WHY THEY FALL
BY ARTHUR r.. GERHART
Agriculture Marshalown High School

1t is generally known that the leaves
are the breathing organs Of the tree. l.
is less widely understood that they are
its digestive organs also. The latter
may be less exact than the former, but
mineral matter from the soil, together
with the carbon dioxide OF the air, is
changed into form in which it will be
useful to the tree, in the leaf This
work Is performed in the leaf rather
than In the interior of the tree because
the leaf Is the part which Is most
readily exposed to the sunlight, the
motor force or energy for the whole
operation.
Accordingly during the growing sea-
son we find various mineral matters
in solution passing from the soil int"
the roots and hence into the leaves for
manufacture into plant food. The wa
ter which is the carrier Of this raw
material rs, evaporated from the pores
of the leaf. OF these pores there are
thousands to every square inch Of leaf
surface. They may be likened to the
pores of the skin of the human body.
And altho their primary function Is to
facilitate an interchange Of oxygen and
carbon dioXide between the inside and
the outside of the plant, the amount
Of water which is constantly evaporat-
ing from them is enormous. 1t has been
estimated that birch tree 10 years
old in one summer transpired approx
imately $3.50 gallons of water; and
that an oak tree with 100000 leaves
transpired about $50 gallons Of water
daily.
In the winter the ground will be
frozen hard and the roots will be un-
able to secure any water to sustain the
leavesaand keep them alive. Therefore,
In order to check this, evaporation the
tree sheds its leaves in the fall. thus
greatly reducing the evaporating sur.
face. Were evaporation to take place
very long without renewal Of the wa
ter supply, the death Of the tree would
quickly ensue. Indeed, the winter kill
ing of the tree would quickly ensue.
Indeed. the winter killing of many
trees during prolonged periods Of very
cold weather is due in most cases. not
to the freezing OF the trees. but to
their being dried out as is shown by
the shriveled appearance Of their twigs
and smaller branches.
Now it must be borne in mind that
tree is a living thing. 1t has no abil-
ity to reason Of course, no state OF feel-
ing or consciousness, but still 1t has
life; and it has become habitual with
the tree, as a living organism, to re"
spond to the conditions Of climatic
change by shedding its leaves. 1t does
this in much the same way that an
animal produces heavier coat OF hair
in the fall. Both the tree and the ami
NAL are equally unconscious OF the
change but both adapt themselves just
as surely, to Withstand the approaching
winter.
Long before the leaves fall the tree
is preparing dor the separation. Growth
has been steadily declining since tho
last OF June. The valuable pulp OF ac-
lively growing cells of which the lear
at first is full is being gradually with
drawn into the stem, until finally moth
ing remains but the mere framework,
A separation tissue or layer Of cells.
called the absciss-layer is formed at
the base of the leaf stem. The cells OF
which this layer is composed difter
from the other cells Of the leaf ana
soon become mucilaginous along the
plane Of separation.
They soon disintegrate and the
slightest movement Of wind or even the
weight Of the leaf itself may cause the
break.
Meanwhile, the chlorophyll. the high
" complex and little understood green
material which is the active agent in
food making, is broken up into blush
green and yellow pigment. This, to-
gether with the red and orange pig
ments, previously existing in the leaf
but obscured by the presence of the
superabundant chlor6phyll. are now
disclosed.
An increase in the amount OF red
pigment is also brought about by the
cooler weather. It Is an interesting
fact that In cooler weather the leaves
Of the tree manufacture more sugar
than ordinarily and that an abundance
Of sugar tends to increase the amour!
Of red pigment. The truth of this can
readily be demonstrated by growing
plant in a strong sugar solution.
At last, filled with unusable minera.
matter, its pores clogged and choked
with dust, hardened and calloused by
drouth, withered by frost and dtsns-