The Providence news. (Providence [R.I.]) 1891-1906, 1897-09-29
WHY AUTUMN LEAVES ARE COL
0RED.

The casting OF the leaf IL not "A sudden and
quick response 10 any single change in on
vironmsntal conditions, but il brought about
with "A complex interplay of processes begun
days. or perhaps weeks, before any external
changes are 60 be seen. The leaf Is rich in
two classes OF substances, one of which Is Of
no further benefit TO it, and another which IL
has constructed at great expense of energy
and which Is in a form of the highest possible
usefulness 10 the plant. To this class belong
the compound in the protoplasm, the green
color bodies, and whatever surplus food may
not have beoS previously conveyed away.
The substances which the plant must needs
discard are in the form of nearly insoiuble
crystals, ana by remaining In position in the
leaf drop with il TO the ground and pass
into that great complex laboratory of the soil
where by slow methods of disintegration use
ful clements are set free, and once again
may be taken up by the tree and trayel their
devious course through root hairs along the
sinuous 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 a loss 20 the plant II thrown away,
undergo quite different series Of changes.
These substances are in the EXTREMIST parts
Of the leaf. and TO pass into the plant body
just penetrate many hundreds Of membranes
by diffusing into the hong conducting cells
around the ribs or nerves, and then down
into the twigs and stems. The successful re.
treat Of tho great mass of valuable matter is
not a simple problem. These substances con.
tain nitrogen as IA part of their compounds,
and as a consequence are very readily broken
down when exposed TO the sunlight. In the
living normal leaf the green color forms
most offectual shield from the action of the
sun, but when the retreat Is begun, one of
the first steps results i'm the disintegration OF
the chlorophyll This would allow the fierce
rays of the September sun 10 strike directly
through the broad expanses of the leaf, de-
stroyng all within were not other means pro
vidod for protection. In the first place, when
the ohlorophyll breaks down, among the re
sulting substances formed is cyanophyli
(blue). which absorbs the suns rays III 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 tho chlorophyll, and Others
which are formed as decomposition products,
so that the leaf exhibits outwardly a gorgeous
panoply Of colors in reds, yellows and bronzes
that make up the autumnal display. From
the wild riot Of tints shown by clump of
trees or shrubs the erroneous impression
might be gained that the colors are acci
dental in their occurrence. This ~ far fron
the case, however. The keynote OF color In
any species is constant, with minor and local
variations. The birches are golden yellow;
oaks vary through yellow orange TO reddish
brown the red maple becomes a dark red /;
the tulip tree a blight yellow; hawthorn and
poison oak becomes violet, while the sumacs
and vines take flaming scarlet. These
colors exhibit some variation in accord with
the character Of the soil On which the plants
stand.-From Autumn Leaves by ID. L.
acDougal in Harpers Magazine for oc'
tober.