PHYSIOGNOMY OF PLANTS.
When the active curiosity of man is engaged in interrogating Nature, or when his imagination dwells on the wide fields of organic creation, among the multifarious impressions which his mind receives, perhaps none is so strong and profound as that of the universal profusion with which life is everywhere distributed. Even on the polar ice the air resounds with the cries or songs of birds, and with the hum of insects. Nor is it only the lower dense and vaporous strata of the atmosphere which are thus filled with life, but also the higher and more ethereal regions. Whenever Mont Blanc or the summits of the Cordilleras have been ascended, living creatures have been found there. On the Chimborazo,[1] eight thousand feet higher than Etna, we found butterflies and other winged insects, borne by ascending currents of air to those almost unapproachable solitudes, which man, led by a restless curiosity or unappeasable thirst of knowledge, treads with adventurous but cautious steps: like him strangers in those elevated regions, their presence shows us that the more flexible organization of animal creation can subsist far beyond the limits at which vegetation ceases. The condor,[2] the giant of the Vulture tribe, often soared over our heads above all the summits of the Andes, at an altitude higher than would be the Peak of Teneriffe if piled on the snow-covered crests of the Pyrenees. The rapacity of this powerful bird attracts him to these regions, whence his far-seeing eye may discern the objects of his pursuit, the soft-wooled Vicunas, which, wandering in herds, frequent, like the Chamois, the mountain pastures adjacent to the regions of perpetual snow.
But if the unassisted eye sees life distributed throughout the atmosphere, when armed with the microscope we discover far other marvels. Rotiferæ, Brachionæ, and a multitude of microscopic animalculæ, are carried up by the winds from the surface of evaporating waters. These minute creatures, motionless and apparently dead, are borne to and fro in the air until the falling dews bring them back to the surface of the earth, dissolve the film or envelope which encloses their transparent rotating bodies,[3] and, probably by means of the oxygen which all waters contain, breathe new irritability into their dormant organs.
According to Ehrenberg’s brilliant discovery, the yellow sand or dust which falls like rain on the Atlantic near the Cape de Verde Islands, and is occasionally carried even to Italy and Middle Europe, consists of a multitude of siliceous-shelled microscopic animals. Perhaps many of them float for years in the upper strata of the atmosphere, until they are brought down by vertical currents or in accompaniment with the superior current of the trade-winds, still susceptible of revivification, and multiplying their species by spontaneous division in conformity with the particular laws of their organisation.
But, besides creatures fully formed, the atmosphere contains innumerable germs of future life, such as the eggs of insects and the seeds of plants, the latter provided with light hairy or feathery appendages, by means of which they are wafted through the air during long autumnal wanderings. Even the fertilizing dust or pollen from the anthers of the male flowers, in species in which the sexes are separated, is carried over land and sea, by winds and by the agency of winged insects,[4] to the solitary female plant on other shores. Thus wherever the glance of the inquirer into Nature penetrates, he sees the continual dissemination of life, either fully formed or in the germ.
If the aereal ocean in which we are submerged, and above the surface of which we cannot rise, be indispensable to the existence of organised beings, they also require a more substantial aliment, which they can find only at the bottom of this gaseous ocean. This bottom is of two kinds; the smaller portion consisting of dry land in immediate contact with the external atmosphere, and the larger portion consisting of water, which may perhaps have been formed thousands of years ago by electric agencies from gaseous substances, and which is now incessantly undergoing decomposition in the laboratories of Nature, in the clouds and in the pulsating vessels of animals and plants. Organic forms also descend deep below the surface of the earth, wherever rain or surface water can percolate either by natural cavities or by mines or other excavations made by man: the subterranean cryptogamic Flora was an object of my scientific research in the early part of my life. Thermal springs of very high temperature nourish small Hydropores, Confervæ, and Oscillatoria. At Bear Lake, near the Arctic Circle, Richardson saw the ground, which continues frozen throughout the summer at a depth of twenty inches, covered with flowering plants.
We do not yet know where life is most abundant,—whether on continents or in the unfathomed depths of the ocean. Through the excellent work of Ehrenberg, “Über das Verhalten des kleinsten Lebens,” we have seen the sphere of organic life extend, and its horizon widen before our eyes, both in the tropical parts of the ocean and in the fixed or floating masses of ice of the Antarctic seas. Siliceous-shelled Polygastrica, and even Coscinodiscæ, with their green ovaries, have been found alive enveloped in masses of ice only twelve degrees from the Pole; the small black Glacier flea (Desoria glacialis) and Podurellæ inhabit the narrow tubular holes examined by Agassiz in the Swiss glaciers. Ehrenberg has shown that on several microscopic Infusoria (Synedra, Cocconeis) others live as parasites, and that in the Gallionellæ such is their prodigious power of development, or capability of division, that in the space of four days an animalcule invisible to the naked eye can form two cubic feet of the Bilin polishing slate. In the sea, gelatinous worms, living or dead, shine like stars,[5] and by their phosphoric light change the surface of the wide ocean into a sea of fire. Ineffaceable is the impression made on my mind by the calm nights of the torrid zone, on the waters of the Pacific. I still see the dark azure of the firmament, the constellation of the Ship near the zenith, and that of the Cross declining towards the horizon, shedding through the perfumed air their soft and planetary lustre; while bright furrows of flashing light marked the track of the dolphins through the midst of the foaming waves.
Not only the ocean, but also the waters of our marshes, hide from us an innumerable multitude of strange forms. The naked eye can with difficulty distinguish the Cyclidias, the Euglenes, and the host of Naids divisible by branches like the Lemna or Duckweed, of which they seek the shade. Other creatures inhabit receptacles where the light cannot penetrate, and an atmosphere variously composed, but differing from that which we breathe: such are the spotted Ascaris, which lives beneath the skin of the earthworm; the Leucophra, of a bright silvery colour, in the interior of the shore Naid; and a Pentastoma, which inhabits the large pulmonary cells of the rattlesnake of the tropics.[6] There are animalculæ in the blood of frogs and of salmon, and even, according to Nordmann, in the fluids of the eyes of fishes and in the gills of the Bleak. Thus the most hidden recesses of creation teem with life. We propose in these pages to direct our attention to the vegetable world, on the existence of which that of animals is dependent. Plants are incessantly engaged in disposing into order towards subsequent organization the raw materials of which the earth is composed: it is their office, by their vital forces or powers, to prepare those substances which, after undergoing a thousand modifications, are gradually converted to nobler purposes in the formation of nervous tissues. In directing our consideration towards the various families of plants, we shall at the same time glance at the multitude of animated beings to which they afford nutriment and protection.
The carpet of flowers and of verdure spread over the naked crust of our planet is unequally woven; it is thicker where the sun rises high in the ever cloudless heavens, and thinner towards the poles, in the less happy climes where returning frosts often destroy the opening buds of spring, or the ripening fruits of autumn. Everywhere, however, man finds some plants to minister to his support and enjoyment. If new lands are formed, the organic forces are ever ready to cover the naked rock with life. Sometimes, as at an early period among the Greek Islands, volcanic forces suddenly elevate above the surface of the boiling waves a rock covered with Scoriæ: sometimes, by a long-continued and more tranquil series of phenomena, the collective labours of united Lithophytes[7] raise their cellular dwellings on the crests of submarine mountains, until, after thousands of years, the structure reaches the level of the ocean, when the creatures which have formed it die, leaving a low flat coral island. How are the seeds of plants brought so immediately to these new shores? by wandering birds, or by the winds and waves of the ocean? The distance from other coasts makes it difficult to determine this question; but, no sooner is the rock of the newly raised islands in direct contact with the atmosphere, than there is formed on its surface, in our northern countries, a soft silky net-work, appearing to the naked eye as coloured spots and patches. Some of these patches are bordered by single or double raised lines running round their margins; other patches are crossed by similar lines traversing them in various directions. Gradually the light colour of the patches becomes darker, the bright yellow which was visible at a distance changes to brown, and the bluish gray of the Leprarias becomes a dusty black. The edges of neighbouring patches approach and run into each other; and on the dark ground thus formed there appear other lichens, of a circular shape and dazzling whiteness. Thus an organic film or covering establishes itself by successive layers; and as mankind, in forming settled communities, pass through different stages of civilisation, so is the gradual propagation and extension of plants connected with determinate physical laws. Lichens form the first covering of the naked rock, where afterwards lofty forest trees rear their airy summits. The successive growth of mosses, grasses, herbaceous plants, and shrubs or bushes, occupies the intervening period of long but undetermined duration. The part which lichens and mosses perform in the northern countries is effected within the tropics by Portulacas, Gomphrenas, and other low and succulent shore plants. The history of the vegetable covering of our planet, and its gradual propagation over the desert crust of the earth, has its epochs, as well as that of the migrations of the animal world.
Yet although organic life is everywhere diffused, and the organic powers are incessantly at work in reconnecting with each other the elements set free by death or dissolution, the abundance and variety of organised beings, and the rapidity with which they are renewed, differ in different climates. In the cold zones, the activity of organic life undergoes a temporary suspension during a portion of the year by frost; fluidity is an essential condition of life or vital action, and animals and plants, with the exception of mosses and other cryptogamia, are in those regions buried for several months of each year in winter sleep. Over a large part of the earth, therefore, there could only be developed organic forms capable of supporting either a considerable diminution of heat, or, being without leaves, a long interruption of the vital functions. Thus we see variety and grace of form, mixture of colours, and generally the perpetually youthful energy and vigour of organic life, increase as we approach the tropics. This increase can be denied only by those who have never quitted Europe, or who have neglected the study of physical geography. When, leaving our oak forests, we traverse the Alps or the Pyrenees, and enter Italy or Spain, or when we direct our attention to some of the African shores of the Mediterranean, we might easily be led to draw the erroneous inference that hot countries are marked by the absence of trees. But those who do so, forget that the South of Europe wore a different aspect on the first arrival of Pelasgian or Carthaginian colonies; they forget that an ancient civilisation causes the forests to recede more and more, and that the wants and restless activity of large communities of men gradually despoil the face of the earth of the refreshing shades which still rejoice the eye in Northern and Middle Europe, and which, even more than any historic documents, prove the recent date and youthful age of our civilization. The great catastrophe which occasioned the formation of the Mediterranean, when the swollen waters of what was previously an immense lake burst through the barriers of the Dardanelles and of the Pillars of Hercules, appears to have stripped the adjacent countries of a large portion of their coating of vegetable mould. The traditions of Samothrace,[8] handed down to us by Grecian writers, appear to indicate the recentness of the epoch of the ravages caused by this great change. In all the countries which surround the Mediterranean, and which are characterised by beds of the tertiary and cretaceous periods (nummulitic limestone and neocomian rocks), great part of the surface of the earth consists of naked rock. One especial cause of the picturesque beauty of Italian scenery is the contrast thus afforded between the bare rock, and the islands if I may so call them of luxuriant vegetation scattered over its surface. Wherever the rock is less intersected with fissures, so that it retains water at the surface, and where it is covered with vegetable mould, there, as on the enchanting shores of the Lake of Albano, Italy has her oak forests, with glades as deeply embowered and verdure as fresh as those which we admire in the North of Europe.
The deserts to the south of the Atlas, and the immense plains or steppes of South America, must be regarded as only local phenomena. The latter, the South American steppes, are clothed, in the rainy season at least, with grass, and with low-growing almost herbaceous mimosas. The African deserts are, indeed, at all seasons devoid of vegetation; seas of sand, surrounded by forest shores clothed with perpetual verdure. A few scattered fan-palms alone recall to the wanderer’s recollection that these awful solitudes belong to the domain of the same animated terrestrial creation which is elsewhere so rich and so varied. The fantastic play of the mirage, occasioned by the effects of radiant heat, sometimes causes these palm trees to appear divided from the ground and hovering above its surface, and sometimes shews their inverted image reflected in strata of air undulating like the waves of the sea. On the west of the great Peruvian chain of the Andes, on the coasts of the Pacific, I have passed entire weeks in traversing similar deserts destitute of water.
The origin of extensive arid tracts destitute of plants, in the midst of countries rich in luxuriant vegetation, is a geognostical problem which has hitherto been but little considered, but which has doubtless depended on ancient revolutions of nature, such as inundations or great volcanic changes. When once a region has lost the covering of plants with which it was invested, if the sands are loose and mobile and are destitute of springs, and if the heated atmosphere, forming constantly ascending currents, prevents precipitation taking place from clouds[9], thousands of years may elapse ere organic life can pass from the verdant shores to the interior of the sandy sea, and repossess itself of the domain from which it had been banished.
Those, therefore, who can view nature with a comprehensive glance and apart from local phenomena, may see from the poles to the equator organic life and vigour gradually augment with the augmentation of vivifying heat. But, in the course of this progressive increase there are reserved to each zone its own peculiar beauties; to the tropics, variety and grandeur of vegetable forms; to the north, the aspect of its meadows and green pastures, and the periodic reawakening of nature at the first breath of the mild air of spring. Each zone, besides its own peculiar advantages, has its own distinctive character. Primeval laws of organisation, notwithstanding a certain degree of freedom in the abnormal development of single parts, bind all animal and vegetable forms to fixed ever-recurring types. As we recognise in distinct organic beings a determinate physiognomy, and as descriptive botany and zoology, in the restricted sense of the terms, consist in a detailed analysis of animal and vegetable forms, so each region of the earth has a natural physiognomy peculiar to itself. The idea indicated by the painter by expressions such as “Swiss nature,” “Italian sky,” &c., rests on a partial perception of this local character in the aspect of nature. The azure of the sky, the lights and shadows, the haze resting on the distance, the forms of animals, the succulency of the plants and herbage, the brightness of the foliage, the outline of the mountains, are all elements which determine the total impression characteristic of each district or region. It is true that in every zone the same kinds of rocks, trachyte, basalt, porphyritic schists, and dolomite, form groups having the same physiognomy and aspect. The greenstone precipices of South America and Mexico resemble those of the Fichtel-Gebirge of Germany, just as among animals the form of the Allco, or native race of dogs of the New Continent, corresponds perfectly with that of the European race. For the inorganic crust of the globe shews itself independent of climatic influences; whether it be that differences of climate depending on differences of latitude were more recent than the formation of the rocks, or that the mass of the earth in solidifying and parting with its heat regulated its own temperature,[10] instead of receiving it from without. Thus all the kinds of rock with which we are acquainted may be met with in all parts of the globe, and everywhere affect the same characteristic forms. Everywhere basalt rises in twin mountains and truncated cones; everywhere the porphyritic trap appears in grotesquely arranged masses, and granite in rounded summits. Also similar forms of trees—pines and oaks—adorn the declivities of the mountains of Sweden, and those of the most southern part of Mexico.[11] Yet, notwithstanding these correspondences of form, and this similarity of outline in the component parts of the picture, their grouping gives to the whole the greatest difference of character.
Mineralogy is not more distinct from geology than is the individual description of natural objects from a general description of the physiognomy of nature. George Forster, in the narrative of his voyages, and in his other publications,—Goethe, in the descriptions of nature which so many of his immortal works contain,—Buffon, Bernardin de St. Pierre, and Chateaubriand, have traced with inimitable truth of description the character of some of the zones into which the earth is divided. Not only do such descriptions afford us mental enjoyment of a high order, but the knowledge of the character which nature assumes in different regions is moreover intimately connected with the history of man, and of his civilisation. For although the commencement of this civilisation is not solely determined by physical relations, yet the direction which it takes, the national character, and the more grave or gay dispositions of men, are dependent in a very high degree on climatic influences. How powerfully have the skies of Greece acted on its inhabitants! The nations settled in the fair and happy regions bounded by the Euphrates, the Halys, and the Egean Sea, also early attained amenity of manners and delicacy of sentiment. When in the middle ages religious enthusiasm suddenly re-opened the sacred East to the nations of Europe who were sinking back into barbarism, our ancestors in returning to their homes brought with them gentler manners, acquired in those delightful valleys. The poetry of the Greeks, and the ruder songs of the primitive northern nations, owe great part of their peculiar character to the aspect of the plants and animals seen by the bard, to the mountains and valleys which surrounded him, and to the air which he breathed. And to recall more familiar objects, who does not feel himself differently affected in the dark shade of the beech, on hills crowned with scattered fir-trees, or on the turfy pasture, where the wind rustles in the trembling foliage of the birch? These trees of our native land have often suggested or recalled to our minds images and thoughts, either of a melancholy, of a grave and elevating, or of a cheerful character. The influence of the physical on the moral world,—that reciprocal and mysterious action and reaction of the material and the immaterial,—gives to the study of nature, when regarded from higher points of view, a peculiar charm, still too little recognised.
But if the characteristic aspect of different portions of the earth’s surface depends conjointly on all external phenomena,—if the contours of the mountains, the physiognomy of plants and animals, the azure of the sky, the form of the clouds, and the transparency of the atmosphere, all combine in forming that general impression which is the result of the whole, yet it cannot be denied that the vegetable covering with which the whole earth is adorned is the principal element in the impression. Animal forms are deficient in mass, and the individual power of motion which animals possess, as well as often the smallness of their size, withdraw them from our sight. The vegetable forms, on the contrary, produce a greater effect by their magnitude and by their constant presence. The age of trees is marked by their size, and the union of age with the manifestation of constantly renewed vigour is a charm peculiar to the vegetable kingdom. The gigantic Dragon-tree of Orotava,[12] (as sacred in the eyes of the inhabitants of the Canaries as the olive-tree in the Citadel of Athens, or the Elm of Ephesus), the diameter of which I found, when I visited those Islands, to be more than 16 feet, had the same colossal size, when the French adventurers, the Béthencourts, conquered these gardens of the Hesperides in the beginning of the fifteenth century; yet it still flourishes, as if in perpetual youth, bearing flowers and fruit. A tropical forest of Hymenæas and Cæsalpinieæ may perhaps present to us a monument of more than a thousand years’ standing.
If we embrace in one general view the different species of phænogamous plants at present contained in herbariums, the number of which may now be estimated at considerably above 80000,[13] we shall recognise in this prodigious multitude certain leading forms to which many others may be referred. In determining these leading forms or types, on the individual beauty, the distribution, and the grouping of which the physiognomy of the vegetation of a country depends, we must not follow the march of systems of botany, in which from other motives the parts chiefly regarded are the smaller organs of propagation, the flowers and the fruit; we must, on the contrary, consider solely that which by its mass stamps a peculiar character on the total impression produced, or on the aspect of the country. Among the leading forms of vegetation to which I allude, there are, indeed, some which coincide with families belonging to the “natural systems” of botanists. Such are the forms of Bananas, Palms, Casuarineæ, and Coniferæ. But the botanic systematist divides many groups which the physiognomist is obliged to unite. When plants or trees present themselves in masses, the outlines and distribution of the leaves and the form of the stems and of the branches are blended together. The painter (and here the artist’s delicate tact and appreciation of nature are demanded) can distinguish in the middle distance and background of a landscape groves of palms or pines from beech woods, but he cannot distinguish the latter from woods consisting of other deciduous forest trees.
Above sixteen different forms of vegetation are principally concerned in determining the aspect or physiognomy of Nature. I mention only those which I have observed in the course of my travels both in the New and Old Continents, where during many years I have attentively examined the vegetation of the regions comprised between the 60th degree of North and the 12th degree of South latitude. The number of these forms will no doubt be considerably augmented when travellers shall have penetrated farther into the interior of Continents, and discovered new genera of plants. In the South-eastern part of Asia, the interior of Africa and of New Holland, and in South America from the river of the Amazons to the province of Chiquitos, the vegetation is still entirely unknown to us. How if at some future time a country should be discovered in which ligneous fungi, Cenomyce rangiferina, or mosses, should form tall trees? The Neckera dendroides, a German species of moss, is in fact arborescent; and bamboos (which are arborescent grasses) and the tree ferns of the tropics, which are often higher than our lime-trees and alders, now present to the European a sight as surprising as would be that of a forest of tree mosses to its discoverer. The absolute size and the degree of development attained by organic forms of the same family (whether plants or animals), depend on laws which are still unknown to us. In each of the great divisions of the animal kingdom, insects, crustacea, reptiles, birds, fishes, or mammalia, the size of the body oscillates between certain extreme limits. But these limits, which have been established by observation as far as it has yet gone, may be corrected by the discovery of species with which we are still unacquainted.
In land animals the higher temperatures of the low latitudes appear to have favoured organic development. The small and slender form of our lizards is exchanged in the south for the gigantic, heavy, and cuirassed bodies of crocodiles. In the formidable tiger, lion, and jaguar, we see repeated, on a larger scale, the form of the common cat, one of the smallest of our domestic animals. If we penetrate into the interior of the earth, and search the cemeteries in which the plants and animals of the ancient world lie entombed, the fossil remains which we discover not only announce a distribution inconsistent with our present climates,—they also disclose to us gigantic forms that contrast no less with those which now surround us, than does the simple heroism of the Greeks with the character of human greatness in modern times. Has the temperature of our planet undergone considerable changes,—possibly of periodical recurrence? If the proportion between land and sea, and even the height of the aerial ocean and its pressure,[14] have not always been the same, the physiognomy of nature, and the dimensions and forms of organised beings, must also have been subjected to various alterations. Huge Pachydermata, Mastodons, Owen’s Mylodon robustus, and the Colossochelys, a land-tortoise above six feet high, have existed, and in the vegetable kingdom there have been forests composed of gigantic Lepidodendra, cactus-like Stigmarias, and numerous kinds of Cycadeæ. Unable to depict fully according to its present features the physiognomy of our planet in this its later age, I will only venture to attempt to indicate the characters which principally distinguish those vegetable groups which appear to me to be most strongly marked by physiognomic differences. However favoured by the richness and flexibility of our native language, it is still an arduous and hazardous undertaking when we attempt to trace in words that which belongs rather to the imitative art of the painter. I feel also the necessity of avoiding as much as possible the wearisome impression almost inseparable from all lengthened enumerations.
We will begin with palms,[15] the loftiest and noblest of all vegetable forms, that to which the prize of beauty has been assigned by the concurrent voice of nations in all ages; for the earliest civilisation of mankind belonged to countries bordering on the region of palms, and to parts of Asia where they abound. Their lofty, slender, ringed, and, in some cases, prickly stems, terminate in aspiring and shining either fanlike or pinnated foliage. The leaves are frequently curled, like those of some gramineæ. Smooth polished stems of palms carefully measured by me had attained 192 English feet in height. In receding from the equator and approaching the temperate zone, palms diminish in height and beauty. The indigenous vegetation of Europe only comprises a single representative of this form of plants, the sea-coast Dwarf-palm or Chamærops, which, in Spain and Italy, extends as far north as the 44th parallel of latitude. The true climate of palms has a mean annual temperature of 20°.5-22° Reaumur (78°.2-81°.5 Fahr). The Date, which is much inferior in beauty to several other genera, has been brought from Africa to the south of Europe, where it lives, but can scarcely be said to flourish, in a mean temperature not exceeding 12°-13°.5 Reaumur (59°-62°.4 Fahr). Stems of palms and fossil bones of elephants are found buried beneath the surface of the earth in northern countries, in positions which make it appear probable that their presence is not to be accounted for by their having been drifted thither from the tropics, and we are led to infer that in the course of the great revolutions which our planet has undergone, great changes of climate, and of the physiognomy of nature as dependent on climate, have taken place.
In all parts of the globe the palm form is accompanied by that of Plantains or Bananas; the Scitamineæ and Musaceæ of botanists, Heliconia, Amomum, and Strelitzia. In this form, the stems, which are low, succulent, and almost herbaceous, are surmounted by long, silky, delicately-veined leaves of a thin loose texture, and bright and beautiful verdure. Groves of plantains and bananas form the ornament of moist places in the equatorial regions. It is on their fruits that the subsistence of a large part of the inhabitants of the torrid zone chiefly depends, and, like the farinaceous cereals of the north, they have followed man from the infancy of his civilisation[16]. The aboriginal site of this nutritious plant is placed by some Asiatic fables or traditions on the banks of the Euphrates, and by others, with more probability, at the foot of the Himalaya. Grecian fables named the fields of Enna as the happy native land of the cereals; and if in northern climes, where corn is cultivated in immense unbroken fields, their monotonous aspect adds but little to the beauty of the landscape, the inhabitant of the tropics, on the other hand, in rearing groves of plantains wherever he fixes his habitation, contributes to the adornment of the earth’s surface by the extension of one of the most noble and beautiful forms of the vegetable world.
The form of Malvaceæ[17] and Bombaceæ, represented by Ceiba, Cavanillesia, and the Mexican hand-tree Cheirostemon, has enormously thick trunks; large, soft, woolly leaves, either heart-shaped or indented; and superb flowers frequently of a purple or crimson hue. It is to this group of plants that the Baobab, or monkey bread-tree, (Adansonia digitata), belongs, which, with a very moderate elevation, has a diameter of 32 English feet, and is probably the largest and most ancient organic monument on our planet. In Italy the Malvaceæ already begin to impart to the vegetation a peculiar southern character.
The delicately pinnated foliage of the Mimosa form[18], of which Acacia, Desmanthus, Gleditschia, Porleria, and Tamarindus are important members, is entirely wanting in our temperate zone in the old continent, though found in the United States, where, in corresponding latitudes, vegetation is more varied and more vigorous than in Europe. The umbrella-like arrangement of the branches, resembling that seen in the stone pine of Italy, is very frequent among the Mimosas. The deep blue of the tropic sky seen through their finely divided foliage has an extremely picturesque effect.
The Heath form[19] belongs more especially to the old world, and particularly to the African continent and islands: taking for our guides physiognomic character and general aspect, we may class under it the Epacrideæ and Diosmeæ, many Proteaceæ, and those Australian Acacias which have mere leaf-stalks instead of leaves (phyllodias). This form has some points of similarity with that of needle trees, and the partial resemblance enhances the effect of the pleasing contrast which, when these two are placed together, is afforded by the abundant bell-shaped blossoms of the heaths. Arborescent heaths, like some other African plants, extend to the northern shores of the Mediterranean: they adorn Italy, and the cistus-covered grounds of the south of Spain. The declivity of the Peak of Teneriffe is the locality where I have seen them growing with the greatest luxuriance. In the countries adjoining the Baltic, and farther to the north, the aspect of this form of plants is unwelcome, as announcing sterility. Our heaths, Erica (Calluna) vulgaris, Erica tetralix, E. carnea, and E. cinerea, are social plants, and for centuries agricultural nations have combated their advance with little success. It is remarkable that the extensive genus which is the leading representative of this form appears to be almost limited to one side of our planet. Of the 300 known species of Erica only one has been discovered across the whole extent of the New Continent, from Pensylvania and Labrador to Nootka and Alashka.
The Cactus form,[20], on the other hand, is almost exclusively American. Sometimes spherical, sometimes articulated or jointed, and sometimes assuming the shape of tall upright polygonal columns resembling the pipes of an organ, this group presents the most striking contrast to those of Liliaceæ and Bananas. It comprises some of the plants to which Bernardin de St. Pierre has applied the term of “vegetable fountains in the desert.” In the waterless plains of South America the animals suffering from thirst seek the melon-cactus, a spherical plant half buried in the dry sand, and encased in formidable prickles, but of which the interior abounds in refreshing juice. The stems of the columnar cactus rise to a height of 30 or 32 feet; they are often covered with lichens, and, dividing into candelabra-like branches, resemble, in physiognomy, some of the Euphorbias of Africa.
While the above-mentioned plants flourish in deserts almost devoid of other vegetation, the Orchideæ[21] enliven the clefts of the wildest rocks, and the trunks of tropical trees blackened by excess of heat. This form (to which the Vanilla belongs) is distinguished by its bright green succulent leaves, and by its flowers of many colours and strange and curious shape, sometimes resembling that of winged insects, and sometimes that of the birds which are attracted by the perfume of the honey vessels. Such is their number and variety that, to mention only a limited district, the entire life of a painter would be too short for the delineation of all the magnificent Orchideæ which adorn the recesses of the deep valleys of the Andes of Peru.
The Casuarina form[22], leafless, like almost all species of Cactus, consists of trees with branches resembling the stalks of our Equisetums. It is found only in the islands of the Pacific and in India, but traces of the same singular rather than beautiful type are seen in other parts of the world. Plumier’s Equisetum altissimum, Forskäl’s Ephedra aphylla from the north of Africa, the Peruvian Colletias, and the Siberian Calligonum pallasia, are nearly allied to the Casuarina form.
As the Banana form shews the greatest expansion, so the greatest contraction of the leaf-vessels is shewn in Casuarinas, and in the form of Needle trees[23] (Coniferæ). Pines, Thuias, and Cypresses, belong to this form, which prevails in northern regions, and is comparatively rare within the tropics: in Dammara and Salisburia the leaves, though they may still be termed needle-shaped, are broader. In the colder latitudes the never-failing verdure of this form of trees cheers the desolate winter landscape, and tells to the inhabitants of those regions that when snow and ice cover the ground the inward life of plants, like the Promethean fire, is never extinct upon our planet.
Like mosses and lichens in our latitudes, and like orchideæ in the tropical zone, plants of the Pothos form[24] clothe parasitically the trunks of aged and decaying forest trees: succulent herbaceous stalks support large leaves, sometimes sagittate, sometimes either digitate or elongate, but always with thick veins. The flowers of the Aroideæ are cased in hooded spathes or sheaths, and in some of them when they expand a sensible increase of vital heat is perceived. Stemless, they put forth aerial roots. Pothos, Dracontium, Caladium, and Arum, all belong to this form, which prevails chiefly in the tropical world. On the Spanish and Italian shores of the Mediterranean, Arums combine with the succulent Tussilago, the Acanthus, and Thistles which are almost arborescent, to indicate the increasing luxuriance of southern vegetation.
Next to the last-mentioned form of which the Pothos and Arum are representatives, I place a form with which, in the hottest parts of South America, it is frequently associated,—that of the tropical twining rope-plants, or Lianes,[25] which display in those regions, in Paullinias, Banisterias, Bignonias, and Passifloras, the utmost vigour of vegetation. It is represented to us in the temperate latitudes by our twining hops, and by our grape vines. On the banks of the Orinoco the leafless branches of the Bauhinias are often between 40 and 50 feet long: sometimes they hang down perpendicularly from the high top of the Swietenia, and sometimes they are stretched obliquely like the cordage of a ship: the tiger-cats climb up and descend by them with wonderful agility.
In strong contrast with the extreme flexibility and fresh light-coloured verdure of the climbing plants, of which we have just been speaking, are the rigid self-supporting growth and bluish hue of the form of Aloes,[26] which, instead of pliant stems and branches of enormous length, are either without stems altogether, or have branchless stems. The leaves, which are succulent, thick, and fleshy, and terminate in long points, radiate from a centre and form a closely crowded tuft. The tall-stemmed aloes are not found in close clusters or thickets like other social or gregarious plants or trees; they stand singly in arid plains, and impart thereby to the tropical regions in which they are found a peculiar, melancholy, and I would almost venture to call it, African character. Taking for our guides resemblance in physiognomy, and influence on the impression produced by the landscape, we place together under the head of the Aloe form, (from among the Bromeliaceæ) the Pitcairnias, which in the chain of the Andes grow out of clefts in the rocks; the great Pournetia pyramidata, (the Atschupalla of the elevated plains of New Granada); the American Aloe, (Agave); Bromelia aranas and B. karatas; from among the Euphorbiaceæ the rare species which have thick short candelabra-like divided stems; from the family of Asphodeleæ the African Aloe and the Dragon tree, (Dracæna draco); and lastly, from among the Liliaceæ, the tall flowering Yucca.
If the Aloe form is characterised by an almost mournful repose and immobility, the form of Gramineæ,[27] especially the physiognomy of arborescent grasses, is characterised, on the contrary, by an expression of cheerfulness and of airy grace and tremulous lightness, combined with lofty stature. Both in the East and West Indies groves of Bamboo form shaded over-arching walks or avenues. The smooth polished and often lightly-waving and bending stems of these tropical grasses are taller than our alders and oaks. The form of Gramineæ begins even in Italy, in the Arundo donax, to rise from the ground, and to determine by height as well as mass the natural character and aspect of the country.
The form of Ferns,[28] as well as that of Grasses, becomes ennobled in the hotter parts of the globe. Arborescent ferns, when they reach a height of above 40 feet, have something of a palm-like appearance; but their stems are less slender, shorter, and more rough and scaly than those of palms. Their foliage is more delicate, of a thinner and more translucent texture, and the minutely indented margins of the fronds are finely and sharply cut. Tree ferns belong almost entirely to the tropical zone, but in that zone they seek by preference the more tempered heat of a moderate elevation above the level of the sea, and mountains two or three thousand feet high may be regarded as their principal seat. In South America the arborescent ferns are usually found associated will the tree which has conferred such benefits on mankind by its fever-healing bark. Both indicate by their presence the happy region where reigns a soft perpetual spring.
I will next name the form of Liliaceeous plants,[29] (Amaryllis, Ixia, Gladiolus, Pancratium) with their flag-like leaves and superb blossoms, of which Southern Africa is the principal country; also the Willow form[30], which is indigenous in all parts of the globe, and is represented in the elevated plains of Quito, (not in the shape of the leaves but in that of the ramification), by Schinus Molle; Myrtaceæ[31], (Metrosideros, Eucalyptus, Escallonia myrtilloides); Melastomaceæ[32], and the Laurel form[33].
It would be an enterprise worthy of a great artist to study the aspect and character of all these vegetable groups, not merely in hot-houses or in the descriptions of botanists, but in their native grandeur in the tropical zone. How interesting and instructive to the landscape painter[34] would be a work which should present to the eye, first separately and then in combination and contrast, the leading forms which have been here enumerated! How picturesque is the aspect of tree-ferns spreading their delicate fronds above the laurel-oaks of Mexico; or groups of plantains over-shadowed by arborescent grasses (Guaduas and Bamboos)! It is the artist’s privilege, having studied these groups, to analyse them: and thus in his hands the grand and beautiful form of nature which he would pourtray resolves itself, (if I may venture on the expression) like the written works of men, into a few simple elements.
It is under the burning rays of a tropical sun that vegetation displays its most majestic forms. In the cold north the bark of trees is covered with lichens and mosses, whilst between the tropics the Cymbidium and fragrant Vanilla enliven the trunks of the Anacardias, and of the gigantic fig trees. The fresh verdure of the Pothos leaves, and of the Dracontias, contrasts with the many-coloured flowers of the Orchideæ. Climbing Bauhinias, Passifloras, and yellow flowering Banisterias, twine round the trunks of the forest trees. Delicate blossoms spring from the roots of the Theobroma, and from the thick and rough bark of the Crescentias and the Gustavia.[35] In the midst of this profusion of flowers and fruits, and in the luxuriant intertwinings of the climbing plants, the naturalist often finds it difficult to discover to which stem the different leaves and flowers really belong. A single tree adorned with Paullinias, Bignonias, and Dendrobium, forms a group of plants which, if disentangled and separated from each other, would cover a considerable space of ground.
In the tropics vegetation is generally of a fresher verdure, more luxuriant and succulent, and adorned with larger and more shining leaves than in our northern climates. The “social” plants, which often impart so uniform and monotonous a character to European countries, are almost entirely absent in the Equatorial regions. Trees almost as lofty as our oaks are adorned with flowers as large and as beautiful as our lilies. On the shady banks of the Rio Magdalena in South America, there grows a climbing Aristolochia bearing flowers four feet in circumference, which the Indian boys draw over their heads in sport, and wear as hats or helmets.[36] In the islands of the Indian Archipelago the flower of the Rafflesia is nearly three feet in diameter, and weighs above fourteen pounds.
The great elevation attained in several tropical countries not only by single mountains but even by extensive districts, enables the inhabitants of the torrid zone—surrounded by palms, bananas, and the other beautiful forms proper to those latitudes—to behold also those vegetable forms which, demanding a cooler temperature, would seem to belong to other zones. Elevation above the level of the sea gives this cooler temperature even in the hottest parts of the earth; and Cypresses, Pines, Oaks, Berberries and Alders, (nearly allied to our own) cover the mountainous districts and elevated plains of Southern Mexico and the chain of the Andes at the Equator. Thus it is given to man in those regions to behold without quitting his native land all the forms of vegetation dispersed over the globe, and all the shining worlds which stud the heavenly vault from pole to pole.[37]
These and many other of the enjoyments which Nature affords are wanting to the nations of the North. Many constellations, and many vegetable forms,—and of the latter, those which are most beautiful, (palms, tree ferns, plantains, arborescent grasses, and the finely-divided feathery foliage of the Mimosas),—remain for ever unknown to them. Individual plants languishing in our hot-houses can give but a very faint idea of the majestic vegetation of the tropical zone. But the high cultivation of our languages, the glowing fancy of the poet, and the imitative art of the painter, open to us sources whence flow abundant compensations, and from whence our imagination can derive the living image of that more vigorous nature which other climes display. In the frigid North, in the midst of the barren heath, the solitary student can appropriate mentally all that has been discovered in the most distant regions, and can create within himself a world free and imperishable as the spirit by which it is conceived.