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TREES WORTH KNOWING
[Illustration: A BEND IN THE TRAIL]
_LITTLE NATURE LIBRARY_
TREES
WORTH KNOWING
BY JULIA ELLEN ROGERS
(_Author of_ _The Tree Book_, _The Tree Guide_, _Trees
Every Child Should Know_, _The Book of Useful
Plants_, _The Shell Book_, _etc., etc._)
[Illustration: "Fructus Quam Folia"]
_With forty-eight illustrations, sixteen being in color_
PUBLISHED BY
DOUBLEDAY, PAGE & COMPANY
FOR
NELSON DOUBLEDAY, INC.
1923
_Copyright, 1917, by_
DOUBLEDAY, PAGE & COMPANY
_All rights reserved, including that of
translation into foreign languages,
including the Scandinavian_
PRINTED IN THE UNITED STATES
AT
THE COUNTRY LIFE PRESS. GARDEN CITY, N. Y.
CONTENTS
PAGE
INTRODUCTION xi
PART I
THE LIFE OF THE TREES 3
PART II
THE NUT TREES 28
The Walnuts; The Hickories; The Beech; The Chestnuts;
The Oaks; The Horse-chestnuts; The Lindens
PART III
WATER-LOVING TREES 75
The Poplars; The Willows; The Hornbeams; The Birches;
The Alders; The Sycamores; The Gum Trees; The Osage Orange
PART IV
TREES WITH SHOWY FLOWERS AND FRUITS 101
The Magnolias; The Dogwoods; The Viburnums; The Mountain
Ashes; The Rhododendron; The Mountain Laurel; The MadroA+-a;
The Sorrel Tree; The Silver Bell Trees; The Sweet Leaf;
The Fringe Tree; The Laurel Family; The Witch Hazel;
The Burning Bush; The Sumachs; The Smoke Tree; The Hollies
PART V
WILD RELATIVES OF OUR ORCHARD TREES 147
The Apples; The Plums; The Cherries; The Hawthorns; The
Service-berries; The Hackberries; The Mulberries; The Figs;
The Papaws; The Pond Apples; The Persimmons
PART VI
THE POD-BEARING TREES 176
The Locusts; The Acacias; Miscellaneous Species
PART VII
DECIDUOUS TREES WITH WINGED SEEDS 193
The Maples; The Ashes; The Elms
PART VIII
THE CONE-BEARING EVERGREENS 217
The Pines; The Spruces; The Firs; The Douglas Spruce;
The Hemlocks; The Sequoias; The Arbor-vitaes; The Incense
Cedar; The Cypresses; The Junipers; The Larches
PART IX
THE PALMS 280
GENERAL INDEX 283
LIST OF COLORED ILLUSTRATIONS
PAGE
Canoe or Paper Birch _On Cover_
A Bend in the Trail _Frontispiece_
Shagbark Hickory 6
Mockernut Fruit and Leaves 7
A Grove of Beeches 22
Chestnut Tree 23
Weeping Beech 30
Black Walnut 31
White Oak 38
Bur or Mossy-cup Oak Leaves and Fruit 39
Horse-chestnut in Blossom 54
Weeping Willow 55
Tulip Tree, Flower and Leaves 103
Flowering Dogwood 118
American Elm 215
Eastern Red Cedars and Hickory 230
LIST OF OTHER ILLUSTRATIONS
PAGE
Black Walnut Shoots 70
Shagbark Hickory 71
American Linden Leaves and Fruit 86
Trembling Aspen Catkins and Leaves 86-87
Pussy Willow Flowers 86-87
American Hornbeam--A Fruiting Branch 87
The Tattered, Silky Bark of the Birches 102
Sycamore Bark and Seed-balls 102-103
Bark, Seeds, and Seed-balls of the Sweet Gum 102-103
Osage Orange Leaves, and Flowers 119
Dogwood Bark, Blossom, Fruit, and Buds 134
Mountain Ash Flowers and Leaves 135
Sassafras Flowers, Fruit, and Leaves 150
Foliage and Flowers of the Smooth Sumach 150-151
Buds, Leaves, and Fruit of the Wild Crabapple 150-151
Canada Plum--Flowers and Trunk 151
Wild Black Cherry--Flowers and Fruit 166
Fruiting Branch of Cockspur Thorn 167
Service-berry Tree in Blossom 182
Hackberry--Flowers, Fruit, and Leaves 183
Honey Locust's Trunk, and Black Locust's Flowers and Leaves 198
Sugar Maple 198-199
Red Maple Flowers 198-199
Seed Keys and New Leaves of Soft or Silver Maple 199
White Ash Buds and Flowers 214
A Group of White Pines 214-215
Shortleaf Pine Cones and Needles 214-215
The Sugar Pine 231
Leaves and Cones of Hemlock and of Norway Spruce 246
Black Spruce Cones and Needles 247
Spray of Arbor-vitae 262
American Larch Cones and Needles 263
INTRODUCTION
Occasionally I meet a person who says: "I know nothing at all about
trees." This modest disclaimer is generally sincere, but it has always
turned out to be untrue. "Oh, well, that old sugar maple, I've always
known that tree. We used to tap all the sugar maples on the place
every spring." Or again: "Everybody knows a white birch by its bark."
"Of course, anybody who has ever been chestnutting knows a chestnut
tree." Most people know Lombardy poplars, those green exclamation
points so commonly planted in long soldierly rows on roadsides and
boundary lines in many parts of the country. Willows, too, everybody
knows are willows. The best nut trees, the shagbark, chestnut, and
butternut, need no formal introduction. The honey locust has its
striking three-pronged thorns, and its purple pods dangling in winter
and skating off over the snow. The beech has its smooth, close bark of
Quaker gray, and nobody needs to look for further evidence to
determine this tree's name.
So it is easily proved that each person has a good nucleus of tree
knowledge around which to accumulate more. If people have the love of
nature in their hearts--if things out of doors call irresistibly, at
any season--it will not really matter if their lives are pinched and
circumscribed. Ways and means of studying trees are easily found, even
if the scant ends of busy days spent indoors are all the time at
command. If there is energy to begin the undertaking it will soon
furnish its own motive power. Tree students, like bird students,
become enthusiasts. To understand their enthusiasm one must follow
their examples.
The beginner doesn't know exactly how and where to begin. There are
great collections of trees here and there. The Arnold Arboretum in
Boston is the great dendrological Noah's Ark in this country. It
contains almost all the trees, American and foreign, which will grow
in that region. The Shaw Botanical Garden at St. Louis is the largest
midland assemblage of trees. Parks in various cities bring together as
large a variety of trees as possible, and these are often labelled
with their English and botanical names for the benefit of the public.
Yet the places for the beginner are his own dooryard, the streets he
travels four times a day to his work, and woods for his holiday,
though they need not be forests. Arboreta are for his delight when he
has gained some acquaintance with the tree families. But not at first.
The trees may all be set out in tribes and families and labelled with
their scientific names. They will but confuse and discourage him.
There is not time to make their acquaintance. They overwhelm with the
mere number of kinds. Great arboreta and parks are very scarce. Trees
are everywhere. The acquaintance of trees is within the reach of all.
First make a plan of the yard, locating and naming the trees you
actually know. Extend it to include the street, and the neighbors'
yards, as you get ready for them. Be very careful about giving names
to trees. If you think you know a tree, ask yourself _how_ you know
it. Sift out all the guesses, and the hearsays, and begin on a solid
foundation, even if you are sure about only the sugar maple and the
white birch.
The characters to note in studying trees are: leaves, flowers, fruits,
bark, buds, bud arrangement, leaf scars, and tree form. The season of
the year determines which features are most prominent. Buds and leaf
scars are the most unvarying of tree characters. In winter these
traits and the tree frame are most plainly revealed. Winter often
exhibits tree fruits on or under the tree, and dead-leaf studies are
very satisfactory. Leaf arrangement may be made out at any season, for
leaf scars tell this story after the leaves fall.
Only three families of our large trees have opposite leaves. This fact
helps the beginner. Look first at the twigs. If the leaves, or (in
winter) the buds and leaf scars, stand opposite, the tree (if it is of
large size) belongs to the maple, ash, or horse-chestnut family. Our
native horse-chestnuts are buckeyes. If the leaves are simple the tree
is a maple; if pinnately compound, of several leaflets, it is an ash;
if palmately compound, of five to seven leaflets, it is a
horse-chestnut. In winter dead leaves under the trees furnish this
evidence. The winter buds of the horse-chestnut are large and waxy,
and the leaf scars look like prints of a horse's hoof. Maple buds are
small, and the leaf scar is a small, narrow crescent. Ash buds are
dull and blunt, with rough, leathery scales. Maple twigs are slender.
Ash and buckeye twigs are stout and clumsy.
Bark is a distinguishing character of many trees--of others it is
confusing. The sycamore, shedding bark in sheets from its limbs,
exposes pale, smooth under bark. The tree is recognizable by its
mottled appearance winter or summer. The corky ridges on limbs of
sweet gum and bur oak are easily remembered traits. The peculiar
horizontal peeling of bark on birches designates most of the genus.
The prussic-acid taste of a twig sets the cherry tribe apart. The
familiar aromatic taste of the green twigs of sassafras is its best
winter character; the mitten-shaped leaves distinguish it in summer.
It is necessary to get some book on the subject to discover the names
of trees one studies, and to act as teacher at times. A book makes a
good staff, but a poor crutch. The eyes and the judgment are the
dependable things. In spring the way in which the leaves open is
significant; so are the flowers. Every tree when it reaches proper age
bears flowers. Not all bear fruit, but blossoms come on every tree. In
summer the leaves and fruits are there to be examined. In autumn the
ripening fruits are the special features.
To know a tree's name is the beginning of acquaintance--not an end in
itself. There is all the rest of one's life in which to follow it up.
Tree friendships are very precious things. John Muir, writing among
his beloved trees of the Yosemite Valley, adjures his world-weary
fellow men to seek the companionship of trees.
* * * * *
"To learn how they live and behave in pure wildness, to see them in
their varying aspects through the seasons and weather, rejoicing in
the great storms, putting forth their new leaves and flowers, when all
the streams are in flood, and the birds singing, and sending away
their seeds in the thoughtful Indian summer, when all the landscape is
glowing in deep, calm enthusiasm--for this you must love them and live
with them, as free from schemes and care and time as the trees
themselves."
_Tree Names_
Two Latin words, written in italics, with a cabalistic abbreviation
set after them, are a stumbling block on the page to the reader
unaccustomed to scientific lore. He resents botanical names, and
demands to know the tree's name in "plain English." Trees have both
common and scientific names, and each has its use. Common names were
applied to important trees by people, the world over, before science
was born. Many trees were never noticed by anybody until botanists
discovered and named them. They may never get common names at all.
A name is a description reduced to its lowest terms. It consists
usually of a surname and a descriptive adjective: Mary Jones, white
oak, _Quercus alba_. Take the oaks, for example, and let us consider
how they got their names, common and scientific. All acorn-bearing
trees are oaks. They are found in Europe, Asia, and America. Their
usefulness and beauty have impressed people. The Britons called them
by a word which in our modern speech is _oak_, and as they came to
know the different kinds, they added a descriptive word to the name of
each. But "plain English" is not useful to the Frenchman. _ChAŠne_ is
his name for the acorn trees. The German has his _Eichenbaum_, the
Roman had his _Quercus_, and who knows what the Chinaman and the
Hindoo in far Cathay or the American Indian called these trees? Common
names made the trouble when the Tower of Babel was building.
Latin has always been the universal language of scholars. It is dead,
so that it can be depended upon to remain unchanged in its vocabulary
and in its forms and usages. Scientific names are exact, and remain
unchanged, though an article or a book using them may be translated
into all the modern languages. The word _Quercus_ clears away
difficulties. French, English, German hearers know what trees are
meant--or they know just where in books of their own language to find
them described.
The abbreviation that follows a scientific name tells who first gave
the name. "Linn." is frequently noticed, for Linnaeus is authority for
thousands of plant names.
Two sources of confusion make common names of trees unreliable: the
application of one name to several species, and the application of
several names to one species. To illustrate the first: There are a
dozen ironwoods in American forests. They belong, with two exceptions,
to different genera and to at least five different botanical families.
To illustrate the second: The familiar American elm is known by at
least seven local popular names. The bur oak has seven. Many of these
are applied to other species. Three of the five native elms are called
water elm; three are called red elm; three are called rock elm. There
are seven scrub oaks. Only by mentioning the scientific name can a
writer indicate with exactness which species he is talking about. The
unscientific reader can go to the botanical manual or cyclopedia and
under this name find the species described.
In California grows a tree called by three popular names: leatherwood,
slippery elm, and silver oak. Its name is _Fremontia_. It is as far
removed from elms and oaks as sheep are from cattle and horses. But
the names stick. It would be as easy to eradicate the trees, root and
branch, from a region as to persuade people to abandon names they are
accustomed to, though they may concede that you have proved these
names incorrect, or meaningless, or vulgar. Nicknames like nigger
pine, he huckleberry, she balsam, and bull bay ought to be dropped by
all people who lay claim to intelligence and taste.
With all their inaccuracies, common names have interesting histories,
and the good ones are full of helpful suggestion to the learner. Many
are literal translations of the Latin names. The first writers on
botany wrote in Latin. Plants were described under the common name, if
there was one; if not, the plant was named. The different species of
each group were distinguished by the descriptions and the drawings
that accompanied them. Linnaeus attempted to bring the work of
botanical scholars together, and to publish descriptions and names of
all known plants in a single volume. This he did, crediting each
botanist with his work. The "Species Plantarum," Linnaeus's monumental
work, became the foundation of the modern science of botany, for it
included all the plants known and named up to the time of its
publication. This was about the middle of the eighteenth century.
The vast body of information which the "Species Plantarum" contained
was systematically arranged. All the different species in one genus
were brought together. They were described, each under a number; and
an adjective word, usually descriptive of some marked characteristic,
was written in as a marginal index.
After Linnaeus's time botanists found that the genus name in
combination with this marginal word made a convenient and exact means
of designating the plant. Thus Linnaeus became the acknowledged
originator of the binomial (two-name) system of nomenclature now in
use in all sciences. It is a delightful coincidence that while
Linnaeus was engaged on his great work, North America, that vast new
field of botanical exploration, was being traversed by another Swedish
scientist. Peter Kalm sent his specimens and his descriptive notes to
Linnaeus, who described and named the new plants in his book. The
specimens swelled the great herbarium at the University of Upsala.
Among trees unknown to science before are the Magnolia, named in honor
of the great French botanist, Magnol. Robinia, the locust, honors
another French botanist, Robin, and his son. Kalmia, the beautiful
mountain laurel, immortalizes the name of the devoted explorer who
discovered it.
Inevitably, duplication of names attended the work of the early
scientists, isolated from each other, and far from libraries and
herbaria. Any one discovering a plant he believed to be unknown to
science published a description of it in some scientific journal. If
some one else had described it at an earlier date, the fact became
known in the course of time. The name earliest published is retained,
and the later one is dropped to the rank of a _synonym_. If the _name_
has been used before to describe some other species in the same genus,
a new name must be supplied. In the "Cyclopedia of Horticulture" the
sugar maple is written: "_Acer saccharum_, Marsh. (_Acer saccharinum_,
Wang. _Acer barbatum_, Michx.)" This means that the earliest name
given this tree by a botanist was that of Marshall. Wangheimer and
Michaux are therefore thrown out; the names given by them are among
the synonyms.
Our cork elm was until recently called "_Ulmus racemosa_, Thomas." The
discovery that the name _racemosa_ was given long ago to the cork elm
of Europe discredited it for the American tree. Mr. Sargent
substituted the name of the author, and it now stands "_Ulmus
Thomasi_, Sarg." Occasionally a generic name is changed. The old
generic name becomes the specific name. Box elder was formerly known
as "_Negundo aceroides_, Moench." It is changed back to "_Acer
Negundo_, Linn." On the other hand, the tan-bark oak, which is
intermediate in character between oaks and chestnuts, has been taken
by Professor Sargent in his Manual, 1905, out of the genus _Quercus_
and set in a genus by itself. From "_Quercus densiflora_, Hook. and
Arn." it is called "_Pasania densiflora_, Sarg.," the specific name
being carried over to the new genus.
About one hundred thousand species of plants have been named by
botanists. They believe that one half of the world's flora is covered.
Trees are better known than less conspicuous plants. Fungi and
bacteria are just coming into notice. Yet even among trees new species
are constantly being described. Professor Sargent described 567 native
species in his "Silva of North America," published 1892-1900. His
Manual, 1905, contains 630. Both books exclude Mexico. The silva of
the tropics contains many unknown trees, for there are still
impenetrable tracts of forest.
The origin of local names of trees is interesting. History and
romance, music and hard common sense are in these names--likewise much
pure foolishness. The nearness to Mexico brought in the musical
_piA+-on_ and _madroA+-a_ in the southwest. _Pecanier_ and _bois d'arc_
came with many other French names with the Acadians to Louisiana. The
Indians had many trees named, and we wisely kept hickory, wahoo,
catalpa, persimmon, and a few others of them.
Woodsmen have generally chosen descriptive names which are based on
fact and are helpful to learners. Botanists have done this, too. Bark
gives the names to shagbark hickory, striped maple, and naked wood.
The color names white birch, black locust, blue beech. Wood names red
oak, yellow-wood, and white-heart hickory. The texture names rock elm,
punk oak, and soft pine. The uses name post oak, canoe birch, and
lodge-pole pine.
The tree habit is described by dwarf juniper and weeping spruce. The
habitat by swamp maple, desert willow, and seaside alder. The range by
California white oak and Georgia pine. Sap is characterized in sugar
maple, sweet gum, balsam fir, and sweet birch. Twigs are indicated in
clammy locust, cotton gum, winged elm. Leaf linings are referred to in
silver maple, white poplar, and white basswood. Color of foliage, in
gray pine, blue oak, and golden fir. Shape of leaves, in heart-leaved
cucumber tree and ear-leaved umbrella. Resemblance of leaves to other
species, in willow oak and parsley haw. The flowers of trees give
names to tulip tree, silver-bell tree, and fringe tree. The fruit is
described in big-cone pine, butternut, mossy-cup oak, and mock orange.
Many trees retain their classical names, which have become the generic
botanical ones, as acacia, ailanthus, and viburnum. Others modify
these slightly, as pine from _Pinus_, and poplar from _Populus_. The
number of local names a species has depends upon the notice it
attracts and the range it has. The loblolly pine, important as a
lumber tree, extends along the coast from New Jersey to Texas. It has
twenty-two nicknames.
The scientific name is for use when accurate designation of a species
is required; the common name for ordinary speech. "What a beautiful
_Quercus alba_!" sounds very silly and pedantic, even if it falls on
scientific ears. Only persons of very shallow scientific learning use
it on such informal occasions.
Let us keep the most beautiful and fitting among common names, and
work for their general adoption. There are no hard names once they
become familiar ones. Nobody hesitates or stumbles over chrysanthemum
and rhododendron, though these sonorous Greek derivatives have four
syllables. Nobody asks what these names are "in plain English."
TREES WORTH KNOWING
TREES
PART I
THE LIFE OF THE TREES
The swift unfolding of the leaves in spring is always a miracle. One
day the budded twigs are still wrapped in the deep sleep of winter. A
trace of green appears about the edges of the bud scales--they loosen
and fall, and the tender green shoot looks timidly out and begins to
unfold its crumpled leaves. Soon the delicate blade broadens and takes
on the texture and familiar appearance of the grown-up leaf. Behold!
while we watched the single shoot the bare tree has clothed itself in
the green canopy of summer.
How can this miracle take place? How does the tree come into full
leaf, sometimes within a fraction of a week? It could never happen
except for the store of concentrated food that the sap dissolves in
spring and carries to the buds, and for the remarkable activity of the
cambium cells within the buds.
What is a bud? It is a shoot in miniature--its leaves or flowers, or
both, formed with wondrous completeness in the previous summer. About
its base are crowded leaves so hardened and overlapped as to cover and
protect the tender shoot. All the tree can ever express of beauty or
of energy comes out of these precious little "growing points," wrapped
up all winter, but impatient, as spring approaches, to accept the
invitation of the south wind and sun.
The protective scale leaves fall when they are no longer needed. This
vernal leaf fall makes little show on the forest floor, but it greatly
exceeds in number of leaves the autumnal defoliation.
Sometimes these bud scales lengthen before the shoot spares them. The
silky, brown scales of the beech buds sometimes add twice their
length, thus protecting the lengthening shoot which seems more
delicate than most kinds, less ready to encounter unguarded the wind
and the sun. The hickories, shagbark, and mockernut, show scales more
than three inches long.
Many leaves are rosy, or lilac tinted, when they open--the waxy
granules of their precious "leaf green" screened by these colored
pigments from the full glare of the sun. Some leaves have wool or silk
growing like the pile of velvet on their surfaces. These hairs are
protective also. They shrivel or blow away when the leaf comes to its
full development. Occasionally a species retains the down on the lower
surface of its leaves, or, oftener, merely in the angles of its veins.
The folding and plaiting of the leaves bring the ribs and veins into
prominence. The delicate green web sinks into folds between and is
therefore protected from the weather. Young leaves hang limp, never
presenting their perpendicular surfaces to the sun.
Another protection to the infant leaf is the pair of stipules at its
base. Such stipules enclose the leaves of tulip and magnolia trees.
The beech leaf has two long strap-like stipules. Linden stipules are
green and red--two concave, oblong leaves, like the two valves of a
pea pod. Elm stipules are conspicuous. The black willow has large,
leaf-like, heart-shaped stipules, green as the leaf and saw-toothed.
Most stipules shield the tender leaf during the hours of its
helplessness, and fall away as the leaf matures. Others persist, as is
often seen in the black willows.
With this second vernal leaf fall (for stipules are leaves) the leaves
assume independence, and take up their serious work. They are ready to
make the living for the whole tree. Nothing contributed by soil or
atmosphere--no matter how rich it is--can become available for the
tree's use until the leaves receive and prepare it.
Every leaf that spreads its green blade to the sun is a laboratory,
devoted to the manufacture of starch. It is, in fact, an outward
extension of the living cambium, thrust out beyond the thick,
hampering bark, and specialized to do its specific work rapidly and
effectively.
The structure of the leaves must be studied with a microscope. This
laboratory has a delicate, transparent, enclosing wall, with doors,
called stomates, scattered over the lower surface. The "leaf pulp" is
inside, so is the framework of ribs and veins, that not only supports
the soft tissues but furnishes the vascular system by which an
incoming and outgoing current of sap is kept in constant circulation.
In the upper half of the leaf, facing the sun, the pulp is in
"palisade cells," regular, oblong, crowded together, and perpendicular
to the flat surface. There are sometimes more than one layer of these
cells.
In the lower half of the leaf's thickness, between the palisade cells
and the under surface, the tissue is spongy. There is no crowding of
cells here. They are irregularly spherical, and cohere loosely, being
separated by ample air spaces, which communicate with the outside
world by the doorways mentioned above. An ordinary apple leaf has
about one hundred thousand of these stomates to each square inch of
its under surface. So the ventilation of the leaf is provided for.
The food of trees comes from two sources--the air and the soil. Dry a
stick of wood, and the water leaves it. Burn it now, and ashes remain.
The water and the ashes came from the soil. That which came from the
air passed off in gaseous form with the burning. Some elements from
the soil also were converted by the heat into gases, and escaped by
the chimneys.
Take that same stick of wood, and, instead of burning it in an open
fireplace or stove, smother it in a pit and burn it slowly, and it
comes out a stick of charcoal, having its shape and size and grain
preserved. It is carbon, its only impurity being a trace of ashes.
What would have escaped up a chimney as carbonic-acid gas is confined
here as a solid, and fire can yet liberate it.
The vast amount of carbon which the body of a tree contains came into
its leaves as a gas, carbon dioxide. The soil furnished various
minerals, which were brought up in the "crude sap." Most of these
remain as ashes when the wood is burned. Water comes from the soil. So
the list of raw materials of tree food is complete, and the next
question is: How are they prepared for the tree's use?
The ascent of the sap from roots to leaves brings water with mineral
salts dissolved in it. Thus potassium, calcium, magnesium, iron,
sulphur, nitrogen, and phosphorus are brought to the leaf
laboratories--some are useful, some useless. The stream of water
contributes of itself to the laboratory whatever the leaf cells demand
to keep their own substance sufficiently moist, and those molecules
that are necessary to furnish hydrogen and oxygen for the making of
starch. Water is needed also to keep full the channels of the
returning streams, but the great bulk of water that the roots send up
escapes by evaporation through the curtained doorways of the leaves.
[Illustration: _See page 37_
SHAGBARK HICKORY]
[Illustration: _See page 40_
MOCKERNUT FRUIT AND LEAVES]
Starch contains carbon, hydrogen, and oxygen, the last two in the
exact proportion that they bear to each other in water, H^{2}O. The
carbon comes in as carbon dioxide, CO^{2}. There is no lack of this
familiar gas in the air. It is exhaled constantly from the lungs of
every animal, from chimneys, and from all decaying substances. It is
diffused through the air, and, entering the leaves by the stomates,
comes in contact with other food elements in the palisade cells.
The power that runs this starch factory is the sun. The chlorophyll,
or leaf green, which colors the clear protoplasm of the cells, is able
to absorb in daylight (and especially on warm, sunny days) some of the
energy of sunlight, and to enable the protoplasm to use the energy
thus captured to the chemical breaking down of water and carbon
dioxide, and the reuniting of their free atoms into new and more
complex molecules. These are molecules of starch, C^{6}H^{10}O^{5}.
The new product in soluble form makes its way into the current of
nutritious sap that sets back into the tree. This is the one product
of the factory--the source of all the tree's growth--for it is the
elaborated sap, the food which nourishes every living cell from leaf
to root tip. It builds new wood layers, extends both twigs and roots,
and perfects the buds for the coming year.
Sunset puts a stop to starch making. The power is turned off till
another day. The distribution of starch goes on. The surplus is
unloaded, and the way is cleared for work next day. On a sunless day
less starch is made than on a bright one.
Excess of water and of free oxygen is noticeable in this making of
starch. Both escape in invisible gaseous form through the stomates. No
carbon escapes, for it is all used up, and a continual supply of CO^2
sets in from outside. We find it at last in the form of solid wood
fibres. So it is the leaf's high calling to take the crude elements
brought to it, and convert them into food ready for assimilation.
There are little elastic curtains on the doors of leaves, and in dry
weather they are closely drawn. This is to prevent the free escape of
water, which might debilitate the starch-making cells. In a moist
atmosphere the doors stand wide open. Evaporation does not draw water
so hard in such weather, and there is no danger of excessive loss.
"The average oak tree in its five active months evaporates about
28,000 gallons of water"--an average of about 187 gallons a day.
In the making of starch there is oxygen left over--just the amount
there is left of the carbon dioxide when the carbon is seized for
starch making. This accumulating gas passes into the air as free
oxygen, "purifying" it for the use of all animal life, even as the
absorption of carbon dioxide does.
When daylight is gone, the exchange of these two gases ceases. There
is no excess of oxygen nor demand for carbon dioxide until business
begins in the morning. But now a process is detected that the day's
activities had obscured.
The living tree breathes--inhales oxygen and exhales carbonic-acid
gas. Because the leaves exercise the function of respiration, they
may properly be called the lungs of trees, for the respiration of
animals differs in no essential from that of plants.
The bulk of the work of the leaves is accomplished before midsummer.
They are damaged by whipping in the wind, by the ravages of fungi and
insects of many kinds. Soot and dust clog the stomates. Mineral
deposits cumber the working cells. Finally they become sere and russet
or "die like the dolphin," passing in all the splendor of sunset skies
to oblivion on the leaf mould under the trees.
_The Growth of a Tree_
The great chestnut tree on the hillside has cast its burden of ripe
nuts, flung down the empty burs, and given its yellow leaves to the
autumn winds. Now the owner has cut down its twin, which was too near
a neighbor for the well-being of either, and is converting it into
lumber. The lopped limbs have gone to the woodpile, and the boards
will be dressed and polished and used for the woodwork of the new
house. Here is our opportunity to see what the bark of the living tree
conceals--to study the anatomy of the tree--to learn something of
grain and wood rings and knots.
The most amazing fact is that this "too, too solid flesh" of the tree
body was all made of dirty water and carbonic-acid gas. Well may we
feel a kind of awe and reverence for the leaves and the cambium--the
builders of this wooden structure we call a tree. The bark, or outer
garment, covers the tree completely, from tip of farthest root to tip
of highest twig. Under the bark is the slimy, colorless living layer,
the _cambium_, which we may define as the separation between wood and
bark. It seems to have no perceptible diameter, though it impregnates
with its substance the wood and bark next to it. This cambium is a
continuous undergarment, lining the bark everywhere, covering the wood
of every root and every twig as well as of the trunk and all its
larger divisions.
Under the cambium is the wood, which forms the real body of the tree.
It is a hard and fibrous substance, which in cross section of root or
trunk or limb or twig is seen to be in fine, but distinctly marked,
concentric rings about a central pith. This pith is most conspicuous
in the twigs.
Now, what does the chestnut tree accomplish in a single growing
season? We have seen its buds open in early spring and watched the
leafy shoots unfold. Many of these bore clusters of blossoms in
midsummer, long yellow spikes, shaking out a mist of pollen, and
falling away at length, while the inconspicuous green flowers
developed into spiny, velvet-lined burs that gave up in their own good
time the nuts which are the seeds of the tree.
The new shoots, having formed buds in the angles of their leaves, rest
from their labors. The tree had added to the height and breadth of its
crown the exact measure of its new shoots. There has been no
lengthening of limb or trunk. But underground the roots have made a
season's growth by extending their tips. These fresh rootlets clothed
with the velvety root hairs are new, just as the shoots are new that
bear the leaves on the ends of the branches.
There is a general popular impression that trees grow in height by the
gradual lengthening of trunk and limbs. If this were true, nails
driven into the trunk in a vertical line would gradually become
farther apart. They do not, as observation proves. Fence wires
stapled to growing trees are not spread apart nor carried upward,
though the trees may serve as posts for years, and the growth in
diameter may swallow up staple and wire in a short time. Normal wood
fibres are inert and do not lengthen. Only the season's rootlets and
leafy shoots are soft and alive and capable of lengthening by cell
division.
The work of the leaves has already been described. The return current,
bearing starch in soluble form, flows freely among the cells of the
cambium. Oxygen is there also. The cambium cell in the growing season
fulfills its life mission by absorbing food and dividing. This is
growth--and the power to grow comes only to the cell attacked by
oxygen. The rebuilding of its tissues multiplies the substance of the
cambium at a rapid rate. A cell divides, producing two "daughter
cells." Each is soon as large as its parent, and ready to divide in
the same way. A cambium cell is a microscopic object, but in a tree
there are millions upon millions of them. Consider how large an area
of cambium a large tree has. It is exactly equivalent to the total
area of its bark. Two cells by dividing make four. The next division
produces eight, then sixteen, thirty-two, sixty-four, in geometric
proportion. The cell's power and disposition to divide seems limited
only by the food and oxygen supply. The cambium layer itself remains a
very narrow zone of the newest, most active cells. The margins of the
cambium are crowded with cells whose walls are thickened and whose
protoplasm is no longer active. The accumulation of these worn-out
cells forms the total of the season's growth, the annual ring of wood
on one side of the cambium and the annual layer of bark on the other.
What was once a delicate cell now becomes a hollow wood fibre, thin
walled, but becoming thickened as it gets older. For a few years the
superannuated cell is a part of the sap wood and is used as a tube in
the system through which the crude sap mounts to the leaves. Later it
may be stored full of starch, and the sap will flow up through newer
tubes. At last the walls of the old cell harden and darken with
mineral deposits. Many annual rings lie between it and the cambium. It
has become a part of the heart wood of the tree.
The cells of its own generation that were crowded in the other
direction made part of an annual layer of bark. As new layers formed
beneath them, and the bark stretched and cracked, they lost their
moisture by contact with the outer air. Finally they became thin,
loose fibres, and scaled off.
The years of a tree's life are recorded with fair accuracy in the
rings of its wood. The bark tells the same story, but the record is
lost by its habit of sloughing off the outer layers. Occasionally a
tree makes two layers of wood in a single season, but this is
exceptional. Sometimes, as in a year of drought, the wood ring is so
small as to be hardly distinguishable.
Each annual ring in the chestnut stump is distinct from its
neighboring ring. The wood gradually merges from a dark band full of
large pores to one paler in color and of denser texture. It is very
distinct in oak and ash. The coarser belt was formed first. The spring
wood, being so open, discolors by the accumulation of dust when
exposed to the air. The closer summer wood is paler in color and
harder, the pores almost invisible to the unaided eye. The best timber
has the highest percentage of summer wood.
If a tree had no limbs, and merely laid on each year a layer of wood
made of parallel fibres fitted on each other like pencils in a box,
wood splitting would be child's play and carpenters would have less
care to look after their tools. But woods differ in structure, and all
fall short of the woodworker's ideal. The fibres of oak vary in shape
and size. They taper and overlap their ends, making the wood less
easily split than soft pine, for instance, whose fibres are regular
cylinders, which lie parallel, and meet end to end without "breaking
joints."
Fibres of oak are also bound together by flattened bundles of
horizontal fibres that extend from pith to cambium, insinuated between
the vertical fibres. These are seen on a cross-section of a log as
narrow, radiating lines starting from the pith and cutting straight
through heart wood and sap wood to the bark. A tangential section of a
log (the surface exposed by the removal of a slab on any side) shows
these "pith rays," or "medullary rays" as long, tapering streaks. A
longitudinal section made from bark to centre, as when a log is
"quarter-sawed," shows a full side view of the "medullary rays." They
are often an inch wide or more in oak; these wavy, irregular, gleaming
fibre bands are known in the furniture trade as the "mirrors" of oak.
They take a beautiful polish, and are highly esteemed in cabinet work.
The best white oak has 20 per cent. to 25 per cent. of its substance
made up of these pith rays. The horny texture of its wood, together
with its strength and durability, give white oak an enviable place
among timber trees, while the beauty of its pith rays ranks it high
among ornamental woods.
The grain of wood is its texture. Wide annual rings with large pores
mark coarse-grained woods. They need "filling" with varnish or other
substance before they can be satisfactorily polished. Fine-grained
woods, if hard, polish best. Trees of slow growth usually have
fine-grained wood, though the rule is not universal.
Ordinarily wood fibres are parallel with their pith. They are straight
grained. Exceptions to this rule are constantly encountered. The chief
cause of variation is the fact that tree trunks branch. Limbs have
their origin in the pith of the stems that bear them. Any stem is
normally one year older than the branch it bears. So the base of any
branch is a cone quite buried in the parent stem. A cross-section of
this cone in a board sawed from the trunk is a _knot_. Its size and
number of rings indicate its age. If the knot is diseased and loose,
it will fall out, leaving a _knot hole_. The fibres of the wood of a
branch are extensions of those just below it on the main stem. They
spread out so as to meet around the twig and continue in parallel
lines to its extremity. The fibres contiguous to those which were
diverted from the main stem to clothe the branch must spread so as to
meet above the branch, else the parent stem would be bare in this
quarter. The union of stem and branch is weak above, as is shown by
the clean break made above a twig when it is torn off, and the
stubborn tearing of the fibres below down into the older stem. A half
hour spent at the woodpile or among the trees with a jack-knife will
demonstrate the laws by which the straight grain of wood is diverted
by the insertion of limbs. The careful picking up and tearing back of
the fibres of bark and wood will answer all our questions. Basswood
whose fibres are tough is excellent for illustration.
When a twig breaks off, the bark heals the wound and the grain becomes
straight over the place. Trees crowded in a forest early divest
themselves of their lower branches. These die for lack of sun and air,
and the trunk covers their stubs with layers of straight-grained wood.
Such timbers are the masts of ships, telegraph poles, and the best
bridge timbers. Yet buried in their heart wood are the roots of every
twig, great or small, that started out to grow when the tree was
young. These knots are mostly small and sound, so they do not detract
from the value of the lumber. It is a pleasure to work upon such a
"stick of timber."
A tree that grows in the open is clothed to the ground with branches,
and its grain is found to be warped by hundreds of knots when it
reaches the sawmill. Such a tree is an ornament to the landscape, but
it makes inferior, unreliable lumber. The carpenter and the wood
chopper despise it, for it ruins tools and tempers.
Besides the natural diversion of straight grain by knots, there are
some abnormal forms to notice. Wood sometimes shows wavy grain under
its bark. Certain trees twist in growing, so as to throw the grain
into spiral lines. Cypresses and gum trees often exhibit in old stumps
a veering of the grain to the left for a few years, then suddenly to
the right, producing a "cross grain" that defies attempts to split it.
"Bird's-eye" and "curly maple" are prizes for the furniture maker.
Occasionally a tree of swamp or sugar maple keeps alive the crowded
twigs of its sapling for years, and forms adventitious buds as well.
These dwarfed shoots persist, never getting ahead further than a few
inches outside the bark. Each is the centre of a wood swelling on the
tree body. The annual layers preserve all the inequalities. Dots
surrounded by wavy rings are scattered over the boards when the tree
is sawed. This is bird's-eye grain, beautiful in pattern and in sheen
and coloring when polished. It is cut thin for veneer work. Extreme
irregularity of grain adds to the value of woods, if they are capable
of a high polish. The fine texture and coloring, combined with the
beautiful patterns they display, give woods a place in the decorative
arts that can be taken by no other material.
_The Fall of the Leaves_
It is November, and the glory of the woods is departed. Dull browns
and purples show where oaks still hold their leaves. Beech trees in
sheltered places are still dressed in pale yellow. The elfin flowers
of the witch hazel shine like threads of gold against the dull leaves
that still cling. The trees lapse into their winter sleep.
Last week a strange thing happened. The wind tore the red robes from
our swamp maples and sassafras and scattered them in tatters over the
lawn. But the horse-chestnut, decked out in yellow and green, lost
scarcely a leaf. Three days later, in the hush of early morning, when
there was not a whiff of a breeze perceptible, the signal, "Let go!"
came, and with one accord the leaves of the horse-chestnut fell. In an
hour the tree stood knee deep in a stack of yellow leaves; the few
that still clung had considerable traces of green in them. Gradually
these are dropping, and the shining buds remain as a pledge that the
summer story just ended will be told again next year.
Perhaps such a sight is more impressive if one realizes the vast
importance of the work the leaves of a summer accomplish for the tree
before their surrender.
The shedding of leaves is a habit broad-leaved trees have learned by
experience in contact with cold winters. The swamp magnolia is a
beautiful evergreen tree in Florida. In Virginia the leaves shrivel,
but they cling throughout the season. In New Jersey and north as far
as Gloucester, where the tree occurs sparingly, it is frankly
deciduous. Certain oaks in the Northern states have a stubborn way of
clinging to their dead leaves all winter. Farther south some of these
species grow and their leaves do not die in fall, but are practically
evergreen, lasting till next year's shoots push them off. The same
gradual change in habit is seen as a species is followed up a mountain
side.
The horse-chestnut will serve as a type of deciduous trees. Its leaves
are large, and they write out, as if in capital letters, the story of
the fall of the leaf. It is a serial, whose chapters run from July
until November. The tree anticipates the coming of winter. Its buds
are well formed by midsummer. Even then signs of preparation for the
leaf fall appear. A line around the base of the leaf stem indicates
where the break will be. Corky cells form on each side of this joint,
replacing tissues which in the growing season can be parted only by
breaking or tearing them forcibly. A clean-cut zone of separation
weakens the hold of the leaf upon its twig, and when the moment
arrives the lightest breath of wind--even the weight of the withered
leaf itself--causes the natural separation. And the leaflets
simultaneously fall away from their common petiole.
There are more important things happening in leaves in late summer
than the formation of corky cells. The plump green blades are full of
valuable substance that the tree can ill afford to spare. In fact, a
leaf is a layer of the precious cambium spread out on a framework of
veins and covered with a delicate, transparent skin--a sort of
etherealized bark. What a vast quantity of leaf pulp is in the foliage
of a large tree!
As summer wanes, and the upward tide of sap begins to fail, starch
making in the leaf laboratories declines proportionately. Usually
before midsummer the fresh green is dimmed. Dust and heat and insect
injuries impair the leaf's capacity for work. The thrifty tree
undertakes to withdraw the leaf pulp before winter comes.
But how?
It is not a simple process nor is it fully understood. The tubes that
carried the products of the laboratory away are bound up with the
fibres of the leaf's skeleton. Through the transparent leaf wall the
migration of the pulp may be watched. It leaves the margins and the
net veins, and settles around the ribs and mid vein, exactly as we
should expect. Dried and shriveled horse-chestnut leaves are still
able to show various stages in this marvellous retreat of the cambium.
If moisture fails, the leaf bears some of its green substance with it
to the earth. The "breaking down of the chlorophyll" is a chemical
change that attends the ripening of a leaf. (Leaf ripening is as
natural as the ripening of fruit.) The waxy granules disintegrate, and
a yellow liquid shows its colors through the delicate leaf walls. Now
other pigments, some curtained from view by the chlorophyll, others
the products of decomposition, show themselves. Iron and other
minerals the sap brought from the soil contribute reds and yellows and
purples to the color scheme. As drainage proceeds, with the chemical
changes that accompany it, the pageant of autumn colors passes over
the woodlands. No weed or grass stem but joins in the carnival of the
year.
Crisp and dry the leaves fall. Among the crystals and granules that
remain in their empty chambers there is little but waste that the tree
can well afford to be rid of--substances that have clogged the leaf
and impeded its work.
We have been mistaken in attributing the gay colors of autumnal
foliage to the action of frost. The ripening of the leaves occurs in
the season of warm days and frosty nights, but it does not follow that
the two phenomena belong together as cause and effect. Frost no doubt
hastens the process. But the chemical changes that attend the
migration of the carbohydrates and albuminous materials from the leaf
back into twig and trunk and root for safe keeping go on no matter
what the weather.
In countries having a moist atmosphere autumn colors are less vivid.
England and our own Pacific Coast have nothing to compare with the
glory of the foliage in the forests of Canada and the Northeastern
states, and with those on the wooded slopes of the Swiss Alps, and
along the Rhine and the Danube. Long, dry autumns produce the finest
succession of colors. The most brilliant reds and yellows often appear
long before the first frost. Cold rains of long duration wash the
colors out of the landscape, sometimes spoiling everything before
October. A sharp freeze before the leaves expect it often cuts them
off before they are ripe. They stiffen and fall, and are wet and limp
next day, as if they had been scalded; all their rich cell substance
lost to the tree, except as they form a mulch about its roots. But no
tree can afford so expensive a fertilizer, and happily they are not
often caught unawares.
Under the trees the dead leaves lie, forming with the snow a
protective blanket for the roots. In spring the rains will leach out
their mineral substance and add it to the soil. The abundant lime in
dead leaves is active in the formation of _humus_, which is decayed
vegetable matter. We call it "leaf mould." So even the waste portions
have their effectual work to do for the tree's good.
The leaves of certain trees in regions of mild winters persist until
they are pushed off by the swelling buds in spring. Others cling a
year longer, in sorry contrast with the new foliage. We may believe
that this is an indolent habit induced by climatic conditions.
Leaves of evergreens cling from three to five years. Families and
individuals differ; altitude and latitude produce variations. An
evergreen in winter is a dull-looking object, if we could compare it
with its summer foliage. Its chlorophyll granules withdraw from the
surface of the leaf.
They seek the lower ends of the palisade cells, as far as they can get
from the leaf surface, assume a dull reddish brown or brownish yellow
color, huddle in clumps, their water content greatly reduced, and thus
hibernate, much as the cells of the cambium are doing under the bark.
In this condition, alternate freezing and thawing seem to do no harm,
and the leaves are ready in spring to resume the starch-making
function if they are still young. Naturally, the oldest leaves are
least capable of this work, and least is expected of them. Gradually
they die and drop as new ones come on. As among broad-leaved trees,
the zone of foliage in evergreens is an outer dome of newest shoots;
the framework of large limbs is practically destitute of leaves.
_How Trees Spend the Winter_
Nine out of every ten intelligent people will see nothing of interest
in a row of bare trees. They casually state that buds are made in the
early spring. They miss seeing the strength and beauty of tree
architecture which the foliage conceals in summertime. The close-knit,
alive-looking bark of a living tree they do not distinguish from the
dull, loose-hung garment worn by the dead tree in the row. All trees
look alike to them in winter.
Yet there is so much to see if only one will take time to look. Even
the most heedless are struck at times with the mystery of the winter
trance of the trees. They know that each spring reA"nacts the vernal
miracle. Thoughtful people have put questions to these sphinx-like
trees. Secrets the bark and bud scales hide have been revealed to
those who have patiently and importunately inquired. A keen pair of
eyes used upon a single elm in the dooryard for a whole year will
surprise and inform the observer. It will be indeed the year of
miracle.
A tree has no centre of life, no vital organs corresponding to those
of animals. It is made up, from twig to root, of annual, concentric
layers of wood around a central pith.
It is completely covered with a close garment of bark, also made of
annual layers. Between bark and wood is the delicate undergarment of
living tissue called _cambium_. This is disappointing when one comes
to look for it, for all there is of it is a colorless, slimy substance
that moistens the youngest layers of wood and bark, and forms the
layer of separation between them. This cambium is the life of the
tree. A hollow trunk seems scarcely a disability. The loss of limbs a
tree can survive and start afresh. But girdle its trunk, exposing a
ring of the cambium to the air, and the tree dies. The vital
connection of leaves and roots is destroyed by the girdling; nothing
can save the tree's life. Girdle a limb or a twig and all above the
injury suffers practical amputation.
The bark protects the cambium, and the cambium is the tissue which by
cell multiplication in the growing season produces the yearly
additions of wood and bark. Buds are growing points set along the
twigs. They produce leafy shoots, as a rule. Some are specialized to
produce flowers and subsequently fruits. Leaves are extensions of
cambium spread in the sun and air in the season when there is no
danger from frosts. The leaves have been called the stomachs of a
tree. They receive crude materials from the soil and the air and
transmute them into starch under the action of sunlight. This
elaborated sap supplies the hungry cambium cells during the growing
season, and the excess of starch made in the leaf laboratories is
stored away in empty wood cells and in every available space from bud
to root tip, from bark to pith.
The tree's period of greatest activity is the early summer. It is the
time of growth and of preparation for the coming winter and for the
spring that follows it. Winter is the time of rest--of sleep, or
hibernation. A bear digs a hollow under the tree's roots and sleeps in
it all winter, waking in the spring. In many ways the tree imitates
the bear. Dangerous as are analogies between plants and animals, it is
literally true that the sleeping bear and the dormant tree have each
ceased to feed. The sole activity of each seems to be the quiet
breathing.
Do trees really breathe? As truly and as incessantly as you do, but
not as actively. Other processes are intermittent, but breathing must
go on, day and night, winter and summer, as long as life lasts.
Breathing is low in winter. The tree is not growing. There is only the
necessity of keeping it alive.
[Illustration: _See page 42_
A GROVE OF BEECHES]
[Illustration: _See page 44_
THE CHESTNUT]
Leaves are the lungs of plants. In the growing season respiration goes
on at a vigorous rate. The leaves also throw off in insensible vapor a
vast quantity of water. This is called _transpiration_ in plants; in
animals the term used is _perspiration_. They are one and the same
process. An average white oak tree throws off 150 gallons of water in
a single summer day. With the cutting off of the water supply at the
roots in late fall, transpiration is also cut off.
The skin is the efficient "third lung" of animals. The closing of its
pores causes immediate suffocation. The bark of trees carries on the
work of respiration in the absence of the leaves. Bark is porous, even
where it is thickest.
Look at the twigs of half a dozen kinds of trees, and find the little
raised dots on the smooth surface. They usually vary in color from the
bark. These are _lenticels_, or breathing pores--not holes, likely to
become clogged with dust, but porous, corky tissue that filters the
air as it comes in. In most trees the smooth epidermis of twigs is
shed as the bark thickens and breaks into furrows. This obscures,
though it does not obliterate, the air passages. Cherry and birch
trees retain the silky epidermal bark on limbs, and in patches, at
least, on the trunks of old trees. Here the lenticels are seen as
parallel, horizontal slits, open sometimes, but usually filled with
the characteristic corky substance. They admit air to the cambium.
There is a popular fallacy that trees have no buds until spring. Some
trees have very small buds. But there is no tree in our winter woods
that will not freely show its buds to any one who wishes to see them.
A very important part of the summer work of a tree is the forming of
buds for next spring. Even when the leaves are just unfolding on the
tender shoots a bud will be found in each angle between leaf and stem.
All summer long its bud is the especial charge of each particular
leaf. If accident destroy the leaf, the bud dies of neglect. When
midsummer comes the bud is full grown, or nearly so, and the fall of
the leaf is anticipated. The thrifty tree withdraws as much as
possible of the rich green leaf pulp, and stores it in the twig to
feed the opening buds in spring.
What is there inside the wrappings of a winter bud? "A leaf," is the
usual reply--and it is not a true one. A bud is an embryo shoot--one
would better say, a shoot in miniature. It has very little length or
diameter when the scales are stripped off. But with care the leaves
can be spread open, and their shape and venation seen. The exact
number the shoot was to bear are there to be counted. Take a
horse-chestnut bud--one of the biggest ones--and you will unpack a
cluster of flowers distinct in number and in parts. The bud of the
tulip tree is smaller, but it holds a single blossom, and petals,
stamens, and pistil are easily recognizable. Some buds contain flowers
and no leaves. Some have shoots with both upon them. If we know the
tree, we may guess accurately about its buds.
There is another popular notion, very pretty and sentimental, but
untrue, that study of buds is bound to overthrow. It is the belief
that the woolly and silky linings of bud scales, and the scales
themselves, and the wax that seals up many buds are all for the
purpose of keeping the bud warm through the cold winter. The bark,
according to the same notion, is to keep the tree warm. This idea is
equally untenable. There is but feeble analogy between a warm-blooded
animal wrapped in fur, its bodily heat kept up by fires within (the
rapid oxidation of fats and carbohydrates in the tissues), and the
winter condition of a tree. Hardy plants are of all things the most
cold blooded. They are defended against injuries from cold in an
effective but entirely different way.
Exposure to the air and consequent loss of its moisture by evaporation
is the death of the cambium--that which lies under the thick bark and
in the tender tissues of the bud, sealed up in its layers of
protecting scales.
The cells of the cambium are plump little masses of protoplasm,
semi-fluid in consistency in the growing season. They have plenty of
room for expansion and division. Freezing would rupture their walls,
and this would mean disintegration and death. Nature prepares the
cells to be frozen without any harm. The water of the protoplasm is
withdrawn by osmosis into the spaces between the cells. The
mucilaginous substance left behind is loosely enclosed by the crumpled
cell wall. Thus we see that a tree has about as much water in it in
winter as in summer. Green wood cut in winter burns slowly and oozes
water at the ends in the same discouraging way as it does in
summertime.
A tree takes on in winter the temperature of the surrounding air. In
cold weather the water in buds and trunk and cambium freezes solid.
Ice crystals form in the intercellular spaces where they have ample
room, and so they do no damage in their alternate freezing and
thawing. The protoplasm stiffens in excessive cold, but when the
thermometer rises, life stirs again. Motion, breathing, and feeding
are essential to cell life.
It is hard to believe that buds freeze solid. But cut one open in a
freezing cold room, and before you breathe upon it take a good look
with a magnifier, and you should make out the ice crystals. The bark
is actually frozen upon a stick of green stovewood. The sap that oozes
out of the pith and heart wood was frozen, and dripped not at all
until it was brought indoors.
What is meant by the freezing of fruit buds in winter, by which the
peach crop is so often lost in Northern states? When spring opens, the
warmth of the air wakes the sleeping buds. It thaws the ice in the
intercellular spaces, and the cells are quick to absorb the water they
gave up when winter approached. The thawing of the ground surrounds
the roots with moisture. Sap rises and flows into the utmost twig.
Warm days in January or February are able to deceive the tree to this
extent. The sudden change back to winter again catches them. The plump
cells are ruptured and killed by the "frost bite."
It is a bad plan to plant a tender kind of tree on the south side of a
house or a wall. The direct and the reflected warmth of the sun forces
its buds out too soon, and the late frosts cut them off. There is
rarely a good yield on a tree so situated.
There is no miracle like "the burst of spring." Who has watched a tree
by the window as its twigs began to shine in early March, and the buds
to swell and show edges of green as their scales lengthened? Then the
little shoot struggled out, casting off the hindering scales with the
scandalous ingratitude characteristic of infancy. Feeble and very
appealing are the limp baby leaves on the shoot, as tender and pale
green as asparagus tips. But all that store of rich nutritive material
is backing the enterprise. The palms are lifted into the air; they
broaden and take on the texture of the perfect, mature leaf. Scarcely
a day is required to outgrow the hesitation and inexperience of
youth. The tree stands decked in its canopy of leaves, every one of
which is ready and eager to assume the responsibilities it faces. The
season of starch making has opened.
Cut some twigs of convenient trees in winter. Let them be good ones,
with vigorous buds, and have them at least two feet long. You may test
this statement I have made about the storing of food in the twigs, and
the one about the unfolding of the leafy shoots. Get a number of them
from the orchard--samples from cherry, plum, and apple trees; from
maple and elm and any other familiar tree. Put them in jars of water
and set them where they get the sun on a convenient window shelf. Give
them plenty of water, and do not crowd them. It is not necessary to
change the water, but cutting the ends slanting and under water every
few days insures the unimpeded flow of the water up the stems and the
more rapid development of the buds you are watching. When spring comes
there are too many things that demand attention. The forcing of winter
buds while yet it is winter is the ideal way to discover the trees'
most precious secrets.