The verdant carpet which a luxuriant Flora spreads over the surface of the earth is not woven equally in all parts; for while it is most rich and full where, under an ever-cloudless sky, the sun attains its greatest height, it is thin and scanty near the torpid poles, where the quickly-recurring frosts too speedily blight the opening bud or destroy the ripening fruit. Yet everywhere man rejoices in the presence of nourishing plants. Even where from the depths of the sea, a volcano bursting through the boiling flood, upheaves a scoriaceous rock. (as once happened in the Greek Islands); or, to instance a more gradual phenomenon, where the united labours of the coral animal (Lithophytes)[[77]] have piled up their cellular dwellings, on the crests of submarine mountains, until after toiling for thousands of years their edifice reaches the level of the ocean, when its architects perish, and leave a coral island. Thus are organic forces ever ready to animate with living forms the naked rock. How seeds are so suddenly transported to these rocks, whether by birds, or by winds, or by the waves of ocean, is a question that cannot be decided, owing to the great distance of these islands from the coasts. But no sooner has the air greeted the naked rock, than, in our northern countries, it gradually acquires a covering of velvet-like fibres, which appear to the eye to be coloured spots. Some of these are bordered by single and others by double rows, while others again are traversed by furrows and divided into compartments. As they increase in age their colour darkens. The bright glittering yellow becomes brown, and gradually the bluish-grey mass of the Leprariæ changes to a dusty black. As the outlines of this vegetable surface merge into each other with increasing age, the dark ground acquires a new covering of fresh circular spots of dazzling whiteness. Thus one organic tissue rises, like strata, over the other; and as the human race in its development must pass through definite stages of civilization, so also is the gradual distribution of plants dependent on definite physical laws. In spots where lofty forest trees now rear their towering summits, the sole covering of the barren rock was once the tender lichen; the long and immeasurable interval was filled up by the growth of grasses, herbaceous plants, and shrubs. The place occupied in northern regions by mosses and lichens is supplied in the tropics by Portulacas, Gomphrenas, and other low and oleaginous marine plants. The history of the vegetable covering and of its gradual extension over the barren surface of the earth, has its epochs, as well as that of the migratory animal world.
But although life is everywhere diffused, and although the organic forces are incessantly at work in combining into new forms those elements which have been liberated by death; yet this fulness of life and its renovation differ according to difference of climate. Nature undergoes a periodic stagnation in the frigid zones; for fluidity is essential to life. Animals and plants, excepting indeed mosses and other Cryptogamia, here remain many months buried in a winter sleep. Over a great portion of the earth, therefore, only those organic forms are capable of full development, which have the property of resisting any considerable abstraction of heat, or those which, destitute of leaf-organs, can sustain a protracted interruption of their vital functions. Thus, the nearer we approach the tropics, the greater the increase in variety of structure, grace of form, and mixture of colours, as also in perpetual youth and vigour of organic life.
This increase may readily be doubted by those who have never quitted our own hemisphere, or who have neglected the study of physical geography. When in passing from our thickly foliated forests of oak, we cross the Alps or the Pyrenees and enter Italy or Spain, or when the traveller first directs his eye to some of the African coasts of the Mediterranean, he may easily be led to adopt the erroneous inference that absence of trees is a characteristic of hot climates. But they forget that Southern Europe wore a different aspect, when it was first colonised by Pelasgian or Carthaginian settlers; they forget too that an earlier civilization of the human race sets bounds to the increase of forests, and that nations, in their change-loving spirit, gradually destroy the decorations which rejoice our eye in the North, and which, more than the records of history, attest the youthfulness of our civilization. The great catastrophe by which the Mediterranean was formed, when the swollen waters of an inland sea burst their way through the Dardanelles and the Pillars of Hercules, appears to have stripped the contiguous lands of a large portion of their alluvial soil. The records of the Samothracian traditions[[78]] preserved by Greek writers seem to indicate the recent date of this great convulsion of nature. Moreover, in all the lands bathed by the Mediterranean, and which are characterised by the tertiary and cretaceous formations (Nummulites and Neocomian rocks), a great portion of the earth’s surface is naked rock. The picturesque beauty of Italian scenery depends mainly on the pleasing contrast between the bare and desolate rock and the luxuriant vegetation which, island-like, is scattered over its surface. Where the rock is less intersected by fissures, so that the water rests longer on its surface, and where it is covered with earth (as on the enchanting banks of Lake Albano), there even Italy has her oak-forests, as shady and verdant as could be desired by an inhabitant of the North.
The boundless plains or steppes of South America, and the deserts beyond the Atlas range of mountains, can only be regarded as mere local phenomena. The former are found to be covered, at least in the rainy season, with grasses and low almost herbaceous Mimosæ; while the latter are seas of sand in the interior of the Old Continent,—vast arid tracts surrounded by borders of evergreen forests. Here and there only a few isolated fan-palms remind the wanderer that these dreary solitudes are a portion of animated nature. Amid the optical delusions occasioned by the radiation of heat, we see the bases of these trees at one moment hovering in the air, at the next their inverted image reflected in the undulating strata of the atmosphere. To the west of the Peruvian Andes, on the shores of the Pacific, I have passed weeks in traversing these waterless deserts.
The origin of this absence of plants over large tracts of land, in regions characterised on every side by the most exuberant vegetation, is a geological phenomenon which has hitherto received but little attention; it undoubtedly arises from former revolutions of nature, such as inundations, or from volcanic convulsions of the earth’s surface. When once a region loses its vegetable covering, if the sand is loose and devoid of springs, and if vertically ascending currents of heated air prevent the precipitation of vapour[[79]], thousands of years may elapse before organic life can penetrate from the green shores to the interior of the dreary waste.
Those who are capable of surveying nature with a comprehensive glance, and abstract their attention from local phenomena, cannot fail to observe that organic development and abundance of vitality gradually increase from the poles towards the equator, in proportion to the increase of animating heat. But in this distribution every different climate has allotted to it some beauty peculiar to itself: to the Tropics belong variety and magnitude in vegetable forms; to the North the aspect of its meadows and the periodical renovation of nature at the first genial breath of spring. Every zone, besides its own peculiar advantages, has its own distinctive character. The primeval force of organization, notwithstanding a certain independence in the abnormal development of individual parts, binds all animal and vegetable structures to fixed ever-recurring types. For as in some individual organic beings we recognise a definite physiognomy, and as descriptive botany and zoology are, strictly speaking, analyses of animal and vegetable forms, so also there is a certain natural physiognomy peculiar to every region of the earth.
That which the painter designates by the expressions “Swiss scenery” or “Italian sky” is based on a vague feeling of the local natural character. The azure of the sky, the effects of light and shade, the haze floating on the distant horizon, the forms of animals, the succulence of plants, the bright glossy surface of the leaves, the outlines of mountains, all combine to produce the elements on which depends the impression of any one region. It must be admitted, however, that in all latitudes the same kind of rocks, as trachyte, basalt, porphyritic schist, and dolomite, form mountain groups of exactly similar physiognomy. Thus the greenstone cliffs of South America and Mexico resemble those of the Fichtel mountains of Germany, in like manner as among animals, the form of the Allco, or the original canine race of the New Continent, is analogous to that of the European race. The inorganic crust of the earth is as it were independent of climatic influences; perhaps, because diversity of climate arising from difference of latitude is of more recent date than the formations of the earth, or that the hardening crust, in solidifying and discharging its caloric, acquired its temperature from internal and not from external causes[[80]]. All formations are, therefore, common to every quarter of the globe and assume the like forms. Everywhere basalt rises in twin mountains and truncated cones; everywhere trap-porphyry presents itself to the eye under the form of grotesquely-shaped masses of rock, while granite terminates in gently rounded summits. Thus, too, similar vegetable forms, as pines and oaks, alike crown the mountain declivities of Sweden and those of the most southern portion of Mexico[[81]]. But notwithstanding all this coincidence of form, and resemblance of the outlines of individual portions, the grouping of the mass, as a whole, presents the greatest diversity of character.
As the oryctognostic knowledge of minerals differs from geology, so also does the general study of the physiognomy of nature differ from the individual branches of the natural sciences. The character of certain portions of the earth’s surface has been described with inimitable truthfulness by George Forster in his travels and smaller works, by Goethe in the descriptive passages which so frequently occur in his immortal writings, by Buffon, Bernardin de St. Pierre, and Chateaubriand. Such descriptions are not only calculated to yield an enjoyment of the noblest kind, but the knowledge of the character of nature in different regions is also most intimately associated with the history of the human race and its mental culture. For although the dawn of this culture cannot have been determined solely by physical influence, climatic relations have at any rate to a great extent influenced its direction, as well as the character of nations, and the degree of gloom or cheerfulness in the dispositions of men. How powerfully did the skies of Greece act on its inhabitants! Was it not among the nations who settled in the beautiful and happy region between the Euphrates, the Halys, and the Ægean Sea, that social polish and gentler feelings were first awakened? and was it not from these genial climes that our forefathers, when religious enthusiasm had suddenly opened to them the Holy Lands of the East, brought back to Europe, then relapsing into barbarism, the seeds of a gentler civilization? The poetical works of the Greeks and the ruder songs of the primitive northern races owe much of their peculiar character to the forms of plants and animals, to the mountain-valleys in which their poets dwelt, and to the air which surrounded them. To revert to more familiar objects, who is there that does not feel himself differently affected beneath the embowering shade of the beechen grove, or on hills crowned with a few scattered pines, or in the flowering meadow where the breeze murmurs through the trembling foliage of the birch? A feeling of melancholy, or solemnity, or of light buoyant animation is in turn awakened by the contemplation of our native trees. This influence of the physical on the moral world—this mysterious reaction of the sensuous on the ideal, gives to the study of nature, when considered from a higher point of view, a peculiar charm which has not hitherto been sufficiently recognised.
However much the character of different regions of the earth may depend upon a combination of all these external phenomena, and however much the total impression may be influenced by the outline of mountains and hills, the physiognomy of plants and animals, the azure of the sky, the form of the clouds, and the transparency of the atmosphere, still it cannot be denied that it is the vegetable covering of the earth’s surface which chiefly conduces to the effect. The animal organism is deficient in mass, while the mobility of its individual members and often their diminutiveness remove them from the sphere of our observation. Vegetable forms, on the other hand, act on the imagination by their enduring magnitude—for here massive size is indicative of age, and in the vegetable kingdom alone are age and the manifestation of an ever-renewed vigour linked together. The colossal Dragon Tree[[82]], which I saw in the Canary Isles, and which measured more than sixteen feet in diameter, still bears, as it then did, the blossoms and fruit of perpetual youth. When the French adventurers, the Béthencourts, conquered these Fortunate Isles in the beginning of the fifteenth century, the Dragon Tree of Orotava, regarded by the natives with a veneration equal to that bestowed on the olive tree of the Acropolis at Athens, or the elm at Ephesus, was of the same colossal magnitude as at present. In the tropics a grove of Hymeneæ and Cesalpiniæ is probably a memorial of more than a thousand years.
On taking one general view of the different phanerogamic species which have already been collected into our herbariums[[83]], and which may now be estimated at considerably more than 80,000, we find that this prodigious quantity presents some few forms to which most of the others may be referred. In determining those forms, on whose individual beauty, distribution, and grouping, the physiognomy of a country’s vegetation depends, we must not ground our opinion (as from other causes is necessarily the case in botanical systems) on the smaller organs of propagation, that is, the blossoms and fruit; but must be guided solely by those elements of magnitude and mass from which the total impression of a district receives its character of individuality. Among the principal forms of vegetation there are, indeed, some which constitute entire families, according to the so-called “natural system” of botanists. Bananas and Palms, Casuarineæ and Coniferæ, form distinct species in this mode of arrangement. The systematising botanist, however, separates into different groups many plants which the student of the physiognomy of nature is compelled to associate together. Where vegetable forms occur in large masses, the outlines and distribution of the leaves, and the form of the stems and branches lose their individuality and become blended together. The painter—and here his delicate artistical appreciation of nature comes especially into play—distinguishes between pines or palms and beeches in the background of a landscape, but not between forests of beech and other thickly foliated trees.