Trees Worth Knowing Part 2

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 h.o.r.n.y 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 coa.r.s.e-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. Ba.s.swood whose fibres are tough is excellent for ill.u.s.tration.

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 s.h.i.+ps, 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 advent.i.tious 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 s.h.i.+ne 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 sa.s.safras 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 s.h.i.+ning 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 antic.i.p.ates 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 quant.i.ty 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 pa.s.ses over the woodlands. No weed or gra.s.s 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 alb.u.minous 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; alt.i.tude and lat.i.tude 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, a.s.sume 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 dest.i.tute 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 reenacts 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 trans.m.u.te 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 s.p.a.ce 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 a.n.a.logies 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.

[Ill.u.s.tration: _See page 42_

A GROVE OF BEECHES]

[Ill.u.s.tration: _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 quant.i.ty 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 pa.s.sages. 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 antic.i.p.ated. 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 cl.u.s.ter 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 a.n.a.logy 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 ma.s.ses 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 s.p.a.ces 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.