St. Johnsbury Caledonian. [volume] (St. Johnsbury, Vt.) 1867-1919, 1897-10-01
Why Autumn Leaves Are Colored.

The casting OF the leaf is not a sud-
den and quick response to any single
change in environmental conditions,
but is brought about with complex
interplay of processes begun days or
perhaps weeks before any external
changes are to be seen. The leaf is
rich in two classes of substances, one
of which is of no further benefit to it,
and another which it has constructed
at great expense ofenergy, and which
is in form of the highest possible
usefulness to the plant. To this class
belong the compounds in the proto-
plasm, the green colored bodies, and
whatever surplus food may not have
been previously conveyed away. The
substances which the plant must
needs discard are in the form Of
nearly soluble crystals, and by re.
naming in position in the leaf, drop
with it to the ground, and pass into
that great complex laboratory OF
the soil where by slow methods OF
disntegration useful elements are
set tree, and once again may be taken
up by the tree and travel their devi-
Gus course through root hairs along
the slnuous roots. and up through
million-celled columns OF the trunk,
out through the twigs to the leaves
once more.
The plastic substances within the
leaf, which would be loss to the
plant it thrown away, undergo quite
a different series of changes. These
substances are in the EXTREMIST parts
OF the leaf, and to pass into the plant
body must penetrate many hundreds
of membranes by diffusion into the
long conducting cells around the ribs
or nerves, and then down into the
tw,gs and stems. The successful
retreat OF this great mass of valuable
matter is not a simple problem.
These substances contain nitrogen
as a part OF their compounds, and
as consequence are very readily
broken down when exposed to the
sunlight. In the living normal Leaf
the green color forms most tffectua
shield from the action OF the sun, but
when the retreat is begun, one of
the tlrst steps results in the disinte
grafton of the chlorophyl. This
would allow the fierce RAYS of the
September sun to strike directly
through the broad expanses of the
leaf, destroying all within were not
other means provided for protection.
In the first place, when the chloro.
phyl! breaks down, among the result
ing substances formed is cyanophyll
(blut J, which absorbs the suns rays
IN the same general manner as the
chlorophyll. In addition, the outer
layers of cells of the leaf contain
other pigments, some of which have
been masked by the chlorophvIl,
and Others which are formed
, as decomposition products so that
the leaf exhibits outwardlv a
: gorgeous panoply of colors in reds.
,, yellows and bronzes that make up
the autumnal display. From the
wild riot of tints shown bv a
I clump OF trees or shrubs, the CHROME.
r Gus impression might be gained that
t the colors are accidental in their oc.
currence. This is tar from the case
however. The keynote of color in
any species is constant, with minor
and local variations. The birches
:, are a golden yellow; oaks vary
e through yellow-orange to reddish
: brown; the tulip-tree light yellow :
, hawthorn and poison oak become
y violet; while the sumacs and vines
take on flaming scarlet. These
colors exhibit some variation in ac.
. cord with the character of the soil on
= which the plants stand. -TFrom
r Autumn Leaves" bv ID. T Mac.
Dougal. in Harper's Magazine for
d October.