Part 10

RELATIONS OF TREES TO THE ATMOSPHERE.

I have not much faith in the science of ignorant men; for the foundations of all knowledge are laid in books; and those only who have read and studied much can possess any considerable store of wisdom. But there are philosophers among laboring swains, whose quaint observations and solutions of nature’s problems are sometimes worthy of record. With these men of untutored genius I have had considerable intercourse, and hence I oftener quote them than the learned and distinguished, whom I have rarely met. The ignorant, from want of knowledge, are always theorists; but genius affords its possessor, how small soever his acquisitions, some glimpses of truth which may be entirely hidden from the mere pedant in science. My philosophic friend, a man of genius born to the plough, entertained a theory in regard to the atmosphere, which, though not strictly philosophical, is so ingenious and suggestive that I have thought an account of it a good introduction to this essay.

My friend, when explaining his views, alluded to the well-known fact that plants growing in an aquarium keep the water supplied with atmospheric air—not with simple oxygen, but with oxygen chemically combined with nitrogen—by some vital process that takes place in the leaves of plants. As the lungs of animals decompose the air which they inspire, and breathe out carbonic-acid gas, plants in their turn decompose this deleterious gas, and breathe out pure atmospheric air. His theory is that the atmosphere is entirely the product of vegetation, and that nature has no other means of composing it; that it is not simply a chemical, but a vital product; and that its production, like its preservation, depends entirely on plants, and would be impossible without their agency. But as all plants united are not equal in bulk to the trees, it may be truly averred that any series of operations or accidents that should deprive the earth entirely of its forests would leave the atmosphere without a source for its regeneration.

The use of the foliage of trees in renovating the atmosphere is not, I believe, denied by any man of science. This theory has been proved to be true by experiments in vital chemistry. The same chemical appropriation of gases and transpiration of oxygen is performed by all classes of vegetables; but any work in the economy of nature assigned to vegetation is the most effectually accomplished by trees. The property of foliage that requires carbonic-acid gas for its breathing purposes, and causes it to give out oxygen, is of vital importance; and it is hardly to be doubted that a close room well lighted by the sun would sustain its healthful atmosphere a longer time, if it were filled with plants in leaf, but not in flower, and occupied by breathing animals, than if the animals occupied it without the plants.

But there is another function performed by the foliage of trees and herbs in which no chemical process is involved,—that of exhaling moisture into the atmosphere after it has been absorbed by the roots. Hence the humidity of this element is greatly dependent on foliage. A few simple experiments will show how much more rapidly and abundantly this evaporation takes place when the soil is covered with growing plants than when the surface is bare. Take two teacups of equal size and fill them with water. Place them on a table, and insert into one of them cuttings of growing plants with their leaves, and let the other stand with water only. In a few hours the water will disappear from the cup containing the plants, while that in the other cup will not be sensibly diminished. Indeed, there is reason to believe that gallons of water might be evaporated into the air by keeping the cup containing the cuttings always full, before the single gill contained in the other cup would disappear. If a few cuttings will evaporate a half-pint of water in twelve hours, we can imagine the vast quantity constantly exhaled into the atmosphere by a single tree. The largest steam-boiler in use, kept constantly boiling, would not probably evaporate more water than one large elm in the same time.

We may judge, from our experiment with the cuttings, that a vastly greater proportion of moisture would be exhaled into the atmosphere from any given surface of ground when covered with vegetation, than from the same amount of uncovered surface, or even of standing water. Plants are indeed the most important existing agents of nature for conveying the moisture of the earth into the air. The quantity of transpiring foliage from a dense assemblage of trees must be immense. The evaporation of water from the vast ocean itself is probably small compared with that from the land which it surrounds. And there is reason to believe that the water evaporated from the ocean would not produce rain enough to sustain vegetation, if by any accident every continent and island were deprived of its trees. The whole earth would soon become a desert. I would remark, in this place, that trees are the agents by which the superfluous waters of the ocean, as they are supplied by rivers emptying into it, are restored to the atmosphere and thence again to the surface of the earth. Trees pump up from great depths the waters as they ooze into the soil from millions of subterranean ducts ramifying in all directions from the bed of the ocean.

THE HOLLY.

As the hawthorn is consecrated to vernal festivities, the Holly is sacred to those of winter, and the yew to those attending the burial of the dead. In Europe, from the earliest ages, the Holly has been employed for the decoration of churches during Christmas. The poets have made it a symbol of forethought, because its leaves are saved from the browsing of animals by the thorns that surround them; and the berries, concealed by its prickly foliage, are preserved for the use of the winter birds. The Holly is found only in the southern parts of New England. In Connecticut it is common, and in the Middle and Southern States it is a tree of third magnitude. The leaves of the Holly are slightly sinuate or scalloped, and furnished at each point with short spines. It not only retains its foliage in the winter, but it loses none of that brilliancy of verdure that distinguishes it at other seasons.

There seems to be no very notable difference between the American and European Holly. Selby says of the latter: “The size which the Holly frequently attains in a state of nature, as well as when under cultivation, its beauty and importance in forest and woodland scenery, either as a secondary tree or merely as an underwood shrub, justify our placing it among the British forest trees of the second rank.” He adds: “As an ornamental evergreen, whether in the form of a tree or as an undergrowth, the Holly is one of the most beautiful we possess. The deep green glittering foliage contrasts admirably with the rich coral hue of its berries.”

THE SPIRÆA.

In the month of July the wooded pastures are variegated with little groups of shrubbery full of delicate white blossoms in compound pyramidal clusters, attracting more attention from a certain downy softness in their appearance than from their beauty. These plants have received the name of Spiræa from the spiry arrangement of their flowers. The larger species among our wild plants, commonly known as the Meadow-Sweet, in some places as Bridewort, is very frequent on little tussocks and elevations rising out of wet soil. It is a slender branching shrub, bearing a profusion of small, finely serrate and elegant leaves, extending down almost to the roots, and a compound panicle of white impurpled flowers at the ends of the branches. It is well known to all who are familiar with the wood-scenery of New England, and is seen growing abundantly in whortleberry pastures, in company with the small kalmia and the swamp rose. It is a very free bloomer, lasting from June till September, often blending a few solitary spikes of delicate flowers with the tinted foliage of autumn.

THE HARDHACK.

The flowers of the purple Spiræa, or Hardhack, are conspicuous by roadsides, especially where they pass over wet grounds. It delights in the borders of rustic wood-paths, in lanes that conduct from the enclosures of some farm cottage to the pasture, growing all along under the loose stone-wall, where its crimson spikes may be seen waving in the wind with the nodding plumes of the golden-rod and the blue spikes of the vervain, well known as the “Simpler’s Joy.” The Hardhack affords no less pleasure to the simpler, who has used its flowers from immemorial time as an astringent anodyne. There is no beauty in any part of this plant, except its pale crimson flowers, which are always partially faded at the extremity or unopened at the base, so that a perfect cluster cannot be found. The leaves are of a pale imperfect green on the upper surface and almost white beneath, and without any beauty. The uprightness of this plant, and the spiry form of its floral clusters, has gained it the name of “Steeplebush,” from our church-going ancestors.

THE HAWTHORN.

Few trees have received a greater tribute of praise from poets and poetical writers than the Hawthorn, which in England especially is consecrated to the pastoral muse and to all lovers of rural life. The Hawthorn is also a tree of classical celebrity. Its flowers and branches were used by the ancient Greeks at wedding festivities, and laid upon the altar of Hymen in the floral games of May, with which from the earliest times it has been associated. In England it is almost as celebrated as the rose, and constitutes the most admired hedge plant of that country. It is, indeed, the beauty of this shrub that forms the chief attraction of the English hedge-rows, which are not generally clipped, but allowed to run up and bear flowers. These are the principal beauties of the plant; for its leaves are neither luxuriant nor flowing.

The Hawthorn in this country is not associated with hedge-rows, which with us are only matters of pride and fancy, not of necessity, and their formal clipping causes them to resemble nature only as a wooden post resembles a tree. Our admiration of the Hawthorn, therefore, comes from a pleasant tradition derived from England, through the literature of that country, where it is known by the name of May-bush, from its connection with the floral festivities of May. The May-pole of the south of England is always garlanded with its flowers, as crosses are with holly at Christmas. The Hawthorn is well known in this country, though unassociated with any of our rural customs. Many of its species are indigenous in America, and surpass those of Europe in the beauty of their flowers and fruit. They are considered the most ornamental of the small trees in English gardens.

The flowers of the Hawthorn are mostly white, varying in different species through all the shades of pink, from a delicate blush-color to a pale crimson. The fruit varies from yellow to scarlet. The leaves are slightly cleft, like those of the oak and the holly. The flowers are produced in great abundance, and emit an agreeable odor, which is supposed by the peasants of Europe to be an antidote to poison.

SUMMER WOOD-SCENERY.

I have alluded to a beneficent law of Nature, that causes her to waste no displays of sublimity or beauty by making them either lasting or common. Before the light of morn is sufficient to make any objects distinctly visible, it displays a beauty of its own, beginning with a faint violet, and melting through a succession of hues into the splendor of meridian day. It remains through the day mere white transparent light, disclosing the infinite forms and colors of the landscape, being itself only the cause that renders everything visible. When at the decline of day it fades, just in the same ratio as substantial objects grow dim and undiscernible, this unsubstantial light once more becomes beautiful, painting itself in soft, tender, and glowing tints upon the clouds and the atmosphere. Similar phenomena attend both the opening and the decline of the year. Morning is the spring, with its pale and delicate tints that gradually change into the universal green that marks the landscape in summer, when the characterless brilliancy of noonday is represented on the face of the land. Autumn is emblemized by the departing tints of sunset; and thus the day and the year equally display the beneficence of Nature in the gradual approach and decline of the beauty and the splendor that distinguish them.

The flowering of the forest is the conclusion of the beautiful phenomena of spring, and summer cannot be said to begin until we witness the full expansion of its foliage. In the early part of the season each tree displays modifications of verdure peculiar, not only to the species, but to the individual and the situation, and hardly two trees in the wood are shaded alike. As the foliage ripens, the different shades of green become more thoroughly blended into one universal hue; and this uniformity, when perfected, distinguishes the true summer phase of vegetation. As summer advances, this monotony increases until near its close. The only trees that variegate the prospect are the evergreens, by their darker and more imperfect verdure, and one or two rare species, like the catalpa and ailantus, which display a lighter and more lively green, resembling the verdure of early summer.

It may be said, however, in behalf of summer, that no other season affords so good an opportunity to note the different effects of sun and shade in the foliage of the woods and fields. The leaves of the trees and grass are never so beautiful in their summer dress as they appear during the hour preceding sunset, when we view them with the sun shining obliquely toward us. All foliage is more or less transparent, and the rays of the sun, made slightly golden by the refraction of the atmosphere, communicate a brilliant yellow tinge to the leaves, as they shine through them. The same effects are not produced by reflection; for if we look away from the sun, the foliage and grass present a much less attractive appearance. A few hours after noonday, before the sunlight is yellowed by refraction, we may study these phenomena more minutely. When we look in the direction of the light, as I have just remarked, we see the least variety of light and shade; for as every leaf is an imperfect mirror, the surface of the forest presents a glitter that throws a glazed and whitish appearance over the green of the foliage. The whole is a mere glare, so that the landscape is almost without expression when viewed in this manner, and all the tiresome uniformity of summer verdure is aggravated. The only relief for the eye comes from the shadows of isolated trees and small forest groups as they are cast upon the ground.

Now let us turn our eyes in an opposite direction. To obtain the best view, we should look obliquely toward the sun. Then do we behold a magnificent blending of light and shade; for every mass of foliage has a dark shadow beneath it, forming a more appreciable contrast on account of the intense brilliancy, without glitter, caused by the illumination of every leaf by the sunlight shining through it. Under these circumstances we can once more distinguish species, to some extent, by their colors. We shall soon discover that trees which have a thin corrugated leaf, without gloss, make the most brilliant spectacle when viewed in this manner. Nothing can surpass the foliage of the elm, the lime, the maple, and the birch in this peculiar splendor. But trees like the poplar, the tulip-tree, the oak, and the willow, having a leaf of a firmer texture and less diaphanous, look comparatively dull under the same circumstances.

I would repeat that the true summer phase of wood-scenery is that which succeeds the flowering of the forest, when all the different greens have faded into one dark shade of verdure. There is no longer that marked and beautiful variety which is displayed before the maturity of the leaves. Summer is not, therefore, the painter’s season. It is dull and tame compared even with winter, when regarded as a subject for the brush or the pencil, and especially when compared with spring and autumn. Summer is the time for the observations of the botanist, not for those of the picturesque rambler; for beneath this sylvan mass of monotonous verdure the sods are covered with an endless variety of herbs and flowers, surpassing in beauty those of any other season.

THE OAK.

If the willow be the most poetical of trees, the Oak is certainly the most useful; though, indeed, it is far from being unattended with poetic interest, since the ancient superstitions associated with it have given it an important place in legendary lore. It is not surprising, when we remember the numerous benefits conferred on mankind by the Oak, that this tree has always been regarded with veneration, that the ancients held it sacred to Jupiter, and that divine honors were paid to it by our Celtic ancestors. The Romans, who crowned their heroes with green Oak leaves, entitled the “Civic Crown,” and the Druids, who offered sacrifice under this tree, were actuated by the same estimation of its pre-eminent utility to the human race. When we consider the sturdy form of the Oak, the wide spread of its lower branches, that symbolize protection; the value of its fruit for the sustenance of certain animals; and the many purposes to which the bark, the wood, and even the excrescences of this tree may be applied,—we can easily understand why it is called the emblem of hospitality. The ancient Romans planted it to overshadow the temple of Jupiter; and in the adjoining grove of oaks,—the sacred grove of Dodona,—they sought those oracular responses which were prophetic of the result of any important adventure.

To American eyes, the Oak is far less familiar than the elm as a wayside tree; but in England, where many

“... a cottage chimney smokes From betwixt two aged oaks,”

this tree, formerly associated with the principal religious ceremonies of that country, is now hardly less sacred in the eyes of the inhabitants from their experience of its shelter and its shade, and their ideas of its usefulness in all the arts. The history of the British Isles is closely interwoven with incidents connected with it, and the poetry of Great Britain has derived from it many a theme of inspiration.