Little Nature Library TREES Fructus Quam Folia
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." 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. ChÊne 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 piÑon and madroÑa 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." 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. Starch contains carbon, hydrogen, and oxygen, the last two in the exact proportion that they bear to each other in water, H2O. The carbon comes in as carbon dioxide, CO2. 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, C6H10O5. 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 CO2 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. |