The time of the falling of leaves has come again. Once more in our
morning walk we tread upon carpets of gold and crimson, of brown and
bronze, woven by the winds or the rains out of these delicate textures
while we slept.
How beautifully the leaves grow old! How full of light and color are
their last days! There are exceptions, of course. The leaves of most of
the fruit-trees fade and wither and fall ingloriously. They bequeath
their heritage of color to their fruit. Upon it they lavish the hues
which other trees lavish upon their leaves. The pear-tree is often an
exception. I have seen pear orchards in October painting a hillside in
hues of mingled bronze and gold. And well may the pear-tree do this, it
is so chary of color upon its fruit.
But in October what a feast to the eye our woods and groves present! The
whole body of the air seems enriched by their calm, slow radiance. They
are giving back the light they have been absorbing from the sun all
summer.
The carpet of the newly fallen leaves looks so clean and delicate when
it first covers the paths and the highways that one almost hesitates to
walk upon it. Was it the gallant Raleigh who threw down his cloak for
Queen Elizabeth to walk upon? See what a robe the maples have thrown
down for you and me to walk upon! How one hesitates to soil it! The
summer robes of the groves and the forests--more than robes, a vital
part of themselves, the myriad living nets with which they have
captured, and through which they have absorbed, the energy of the solar
rays. What a change when the leaves are gone, and what a change when
they come again! A naked tree may be a dead tree. The dry, inert bark,
the rough, wirelike twigs change but little from summer to winter. When
the leaves come, what a transformation, what mobility, what
sensitiveness, what expression! Ten thousand delicate veined hands
reaching forth and waving a greeting to the air and light, making a
union and compact with them, like a wedding ceremony. How young the old
trees suddenly become! what suppleness and grace invest their branches!
The leaves are a touch of immortal youth. As the cambium layer beneath
the bark is the girdle of perennial youth, so the leaves are the facial
expression of the same quality. The leaves have their day and die, but
the last leaf that comes to the branch is as young as the first. The
leaves and the blossom and the fruit of the tree come and go, yet they
age not; under the magic touch of spring the miracle is repeated over
and over.
The maples perhaps undergo the most complete transformation of all the
forest trees. Their leaves fairly become luminous, as if they glowed
with inward light. In October a maple-tree before your window lights up
your room like a great lamp. Even on cloudy days its presence helps to
dispel the gloom. The elm, the oak, the beech, possess in a much less
degree that quality of luminosity, though certain species of oak at
times are rich in shades of red and bronze. The leaves of the trees just
named for the most part turn brown before they fall. The great leaves of
the sycamore assume a rich tan-color like fine leather.
The spider weaves a net out of her own vitals with which to capture her
prey, but the net is not a part of herself as the leaf is a part of the
tree. The spider repairs her damaged net, but the tree never repairs its
leaves. It may put forth new leaves, but it never essays to patch up the
old ones. Every tree has such a superabundance of leaves that a few more
or less or a few torn and bruised ones do not seem to matter. When the
leaf surface is seriously curtailed, as it often is by some insect pest,
or some form of leaf-blight, or by the ravages of a hail-storm, the
growth of the tree and the maturing of its fruit is seriously checked.
To denude a tree of its foliage three years in succession usually
proves fatal. The vitality of the tree declines year by year till death
ensues.
To me nothing else about a tree is so remarkable as the extreme delicacy
of the mechanism by which it grows and lives, the fine hairlike rootlets
at the bottom and the microscopical cells of the leaves at the top. The
rootlets absorb the water charged with mineral salts from the soil, and
the leaves absorb the sunbeams from the air. So it looks as if the tree
were almost made of matter and spirit, like man; the ether with its
vibrations, on the one hand, and the earth with its inorganic compounds,
on the other--earth salts and sunlight. The sturdy oak, the gigantic
sequoia, are each equally finely organized in these parts that take hold
upon nature. We call certain plants gross feeders, and in a sense they
are; but all are delicate feeders in their mechanism of absorption from
the earth and air.
The tree touches the inorganic world at the two finest points of its
structure--the rootlets and the leaves. These attack the great crude
world of inorganic matter with weapons so fine that only the microscope
can fully reveal them to us. The animal world seizes its food in masses
little and big, and often gorges itself with it, but the vegetable,
through the agency of the solvent power of water, absorbs its
nourishment molecule by molecule.
A tree does not live by its big roots--these are mainly for strength
and to hold it to the ground. How they grip the rocks, fitting
themselves to them, as Lowell says, like molten metal! The tree's life
is in the fine hairlike rootlets that spring from the roots. Darwin says
those rootlets behave as if they had minute brains in their extremities.
They feel their way into the soil; they know the elements the plant
wants; some select more lime, others more potash, others more magnesia.
The wheat rootlets select more silica to make the stalk; the pea
rootlets select more lime: the pea does not need the silica. The
individuality of plants and trees in this respect is most remarkable.
The cells of each seem to know what particular elements they want from
the soil, as of course they do.
The vital activity of the tree goes on at three points--in the leaves,
in the rootlets, and in the cambium layer. The activity of the leaf and
rootlet furnishes the starchy deposit which forms this generative
layer--the milky, mucilaginous girdle of matter between the outer bark
and the wood through which the tree grows and increases in size.
Generation and regeneration take place through this layer. I have called
it the girdle of perpetual youth. It never grows old. It is annually
renewed. The heart of the old apple-tree may decay and disappear, indeed
the tree may be reduced to a mere shell and many of its branches may die
and fall, but the few apples which it still bears attest the fact that
its cambium layer, at least over a part of its surface, is still
youthful and doing its work. It is this layer that the yellow-bellied
woodpecker, known as the sapsucker, drills into and devours, thus
drawing directly upon the vitality of the tree. But his ravages are
rarely serious. Only in two instances have I seen dead branches on an
apple-tree that appeared to be the result of his drilling.
What we call the heart of a tree is in no sense the heart; it has no
vital function, but only the mechanical one of strength and support. It
adds to the tree's inertia and power to resist storms. The trunk of a
tree is like a community where only one generation at a time is engaged
in active business, the great mass of the population being retired and
adding solidity and permanence to the social organism. The rootlets of a
plant or a tree are like the laborers in the field that produce for us
the raw material of our food, while the leaves are like our many devices
for rendering it edible and nourishing. The rootlets continue their
activity in the fall, after the leaves have fallen, and thus gorge the
tree with fluid against the needs of the spring. In the growing tree or
vine the sap, charged with nourishment, flows down from the top to the
roots. In the spring it evidently flows upward, seeking the air through
the leaves. Or rather, we may say that the crude sap always flows
upward, while the nutritive sap flows downward, thus giving the tree a
kind of double circulation.
A tree may be no more beautiful and wonderful when we have come to a
knowledge of all its hidden processes, but it certainly is no less so.
We do not think of the function of the leaves, nor of the bark, nor of
the roots and rootlets, when we gaze upon a noble oak or an elm; we
admire it for its form, its sturdiness, or its grace; it is akin to
ourselves; it is the work of a vast community of cells like those that
build up our own bodies; it is a fountain of living matter rising up out
of the earth and splitting up and spreading out at its top in a spray of
leaves and flowers; and if we could see its hidden processes we should
realize how truly like a fountain it is. While in full leaf a current of
water is constantly flowing through it, and flowing upward against
gravity. This stream of water is truly its life current; it enters at
the rootlets under the ground and escapes at the top through the leaves
by a process called transpiration. All the mineral salts with which the
tree builds up its woody tissues,--its osseous system, so to speak,--the
instruments with which it imprisons and consolidates the carbon which it
obtains from the air, are borne in solution in this stream of water. Its
function is analogous to that of the rivers which bring the produce and
other material to the great cities situated upon their banks. A cloud of
invisible vapor rises from the top of every tree and a thousand
invisible rills enter it through its myriad hairlike rootlets. The trees
are thus conduits in the circuit of the waters from the earth to the
clouds. Our own bodies and the bodies of all living things perform a
similar function. Life cannot go on without water, but water is not a
food; it makes the processes of metabolism possible; assimilation and
elimination go on through its agency. Water and air are the two ties
between the organic and the inorganic. The function of the one is mainly
mechanical, that of the other is mainly chemical.
As the water is drawn in at the roots, it flows out at the top, to which
point it rises by capillary attraction and a process called osmosis.
Neither of them is a strictly vital process, since both are found in the
inorganic world; but they are in the service of what we call a vital
principle. Some physicists and biochemists laugh at the idea of a vital
principle. Huxley thought we might as well talk about the principle of
aqueosity in water. We are the victims of words. The sun does not shoot
out beams or rays, though the eye reports such; but it certainly sends
forth energy; and it is as certain that there is a new activity in
matter--some matter--that we call vital.
Matter behaves in a new manner; builds up new compounds and begets
myriads of new forms not found in the inorganic world, till it finally
builds up the body and mind of man. Death puts an end to this activity
alike in man and tree, and a new kind of activity sets in--a
disorganizing activity, still with the aid of water and air and living
organisms. It is like the compositor distributing his type after the
book is printed. The micro-organisms answer to the compositor, but they
are of a different kind from those which build up the body in the first
instance. But the living body as a whole, with its complex of
coördinating organs and functions--what attended to that? The cells
build the parts, but what builds the whole?
How many things we have in common with the trees! The same mysterious
gift of life, to begin with; the same primary elements--carbon,
nitrogen, oxygen, and so on--in our bodies; and many of the same vital
functions--respiration, circulation, absorption, assimilation,
reproduction. Protoplasm is the basis of life in both, and the cell is
the architect that builds up the bodies of both. Trees are rooted men
and men are walking trees. The tree absorbs its earth materials through
the minute hairs on its rootlets, called fibrillæ, and the animal body
absorbs its nutriment through analogous organs in the intestines, called
lacteals.
Whitman's expression "the slumbering and liquid trees" often comes to my
mind. They are the words of a poet who sees hidden relations and
meanings everywhere. He knows how fluid and adaptive all animate nature
is. The trees are wrapped in a kind of slumber in winter, and they are
reservoirs of living currents in summer. If all living bodies came
originally out of the sea, they brought a big dower of the sea with
them. The human body is mainly a few pinches of earth salts held in
solution by several gallons of water. The ashes of the living tree bulk
small in comparison with the amount of water it holds. Yes, "the
slumbering and liquid trees." They awaken from their slumber in the
spring, the scales fall from their buds, the fountains within them are
unsealed, and they again become streams of living energy, breaking into
leaf and bloom and fruit under the magic of the sun's rays.