The advocate., 1897-10-06
WhH Autumn Leaves Are ColOred.

Why Autumn Leaves Are Uolored'
The casting of the leaf is not sud-
den and quick response to any single
change in enVirOnmental conditions, but
is brought about with complex inter-
play 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 fur
ther benefit to it, and another which 1t
has constructed at great expense Of en-
ergy and which is in form Of the high
est possible usefulness to the plant. To
this class belong the compounds in the
protOplasm, the green color 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 in
soluble crystals, and by remaining in pO-
sltion in the leaf, drop with it to the
ground, and pass into that great complex
laboratory of the soil where by slow
methods OF disintegratiOn useful ele-
ments are set free, and once again may
be taken up by the tree and travel
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 to the plant If
tnrown 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 diffu-
sion into the long conducting cells
around the ribs or nerves, and then down
into the twigS and stems. The success
Iul retreat OF this great mass OF valuaDle
matter is not simple problem. These
substances contain nitrogen as a part
Of their CON pounds, and as COnse-
Quence are very readily broken down
when exposed to the sunlight. In the
living normal leaf the green color forms
a most effectual shield from the action
of the sun, but when the retreat is be-
gun, one of the first steps results in the
disintegratiOr Of the chlOrOphyll. This
would allow the fierce rays Of the Sep
tember sun to strike directly through
the broad eXpanses Of the leaf, destroy
ing all within were not other means pro-
Vided for protection. In the first place,
when the ChlOrOphyll breaks down,
among the resulting substances formed
is cyanOphyll (blue), which absorbs the
SUMS 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 chlOrophyll, and
others which are formed as dec0mpOsi-
tiOn. products, SO that the leaf exhibits
outwardly gorgeous panOply Of cOlOrs
in reds, yellcws and brOnZes that make
up the autumnal display. From the wild
riot Of tints shown by a clump Of trees
or shrubs, the erroneous impression
might be gaired that the cOlOrs are ac-
in their occurrence. This is far
from the case, however. The keynote
of color in any species Is constant, with
minor and local variations. The birChes
are q golden yellow; oaks vary through
yellOw-orange to reddish-brOwn; the red
maple becomes dark red; the tulip-tree
a light yellow; hawthorn and poisOn-oak
become violet; while the sumacs and
vines take on flaming scarlet. These
colors exhibit some variation In accord
with the character of the soil on which
the plants stand.-FrOm Autumn
Leaves" by D. T. MacDOugal, in Har-
per's Magazine for October.