Now that it's fall, I'm noticing a lot of questions about the
leaves. Namely, what makes the colors change and why do trees
lose their leaves?
THE COLOR CHANGE
Inside the leaves of trees are many phytochemicals. Most of the
year, green chlorophyll is the most prominent one. But there
are others, and these come in many colors! They are actually
always there, but in the main growing season, they are simply
drowned out by the chlorophyll.
When the weather cools and days shorten, the chlorophyll begins
to break down as the tree starts to enter dormancy. This is what
causes the change in color. Once the chlorophyll isn't covering
up the colors of the other phytochemicals (natural plant
chemicals), they shine out, sometimes with great beauty! How
beautiful? That depends on what species of tree, and on the
weather. Rainfall, or lack of it (depending on which weatherman
is talking) can cause the other colors to end up kind of drab.
I personally notice that the display is lackluster if there has
been a lot of drizzle and humidity.
Between each leaf's stem and the woody stalk it is attached to,
is what is called an ABCISSION LAYER. This is a barrier of cells.
During the main growing season, this functions like part of the
leaf stem, allowing nutrients and water to pass much like the
stem itself. But, in response to the same changes that trigger
the change in leaf color, the cells of the abcission layer
begin to die. When most of them are dead, they can no longer
hold the leaf to the tree, and it falls. This layer is what you
see when you look at the place where the leaf just fell from
in the fall. You will see a shape on the woody stem (where the
leaf was) which is the shape of the end of the leaf stalk. This
"leaf scar" is what's left of the abcission layer. The layer's
continued presence on the tree helps to keep infection from the
tree by preventing an open wound from resulting from the leaf's
fall. It's like an immediate, natural band-aid.
HA! HA! Just joking! Give 'em a few passes with the mower and
they'll go away, no work at all if you have a riding mower, and
even if you don't, it beats raking!!!
ENJOY the colors!
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