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bles suitable to the temperature of the localities, provided they be frequently watered by rain.
The circumstances which subject sand to the power of vegetation do not everywhere exist; there are even vast countries where the earth appears condemned to present to its inhabitants nothing but a dry and burnt surface. Such are those immense plains of Africa, those dreadful deserts, the countries of silence and of death, which man traverses only with fear, but which Nature may yet, by means of certain local circumstances, bring to a state of life, as she has done in many other places. The most efficacious, in fact the only means of doing this, is the presence of water. We already know, that several great rivers carry their waters through them, such as the Nile in Egypt, and the Niger in a part of the Sahara. The springs which feed them, enlarged by the rains, occasion, every year, considerable overflowings. These superabundant waters deposit, upon the lands which have been inundated by them, a mud which, by being mingled with sand, acquires a great degree of fertility; in other places they form seas, lakes, and pools, which carry the principles of life into those countries of death.
A new order of plants meets us upon the edges, and at the surface of these lakes. We can easily imagine, that those which have established vegetation upon the sandy or stony soils could not here fulfil the same object, and we shall see this all-powerful Nature overcoming with time, the obstacles which oppose themselves to its operation. When the waters have covered a piece of ground, plants almost immediately begin to appear; they are more or less abundant, according to circumstances If these waters are running like those of rivers, or agitated like those of great lakes, vegetation only exists upon their edges ; but if they be tranquil, stagnant, and of little depth, plants grow in them more numerously, and with more rapidity; they at first cover the surface of the waters, and occupy, from the simplicity of their organisation, the same order as those which grow upon rocks; they are merely very delicate, interwoven filaments, without roots, and without apparent fructification. They precede the growth of more perfect vegetables, and prepare the soil which is to receive them,--an operation which we may equally observe without leaving our houses. If we examine neglected or abandoned basins of water, we find them covered with a greenish scum, which, for a long time, was considered as consisting of impurities thrown out to the surface of the water, but which, if observed with more attention, we shall easily be convinced, belongs to the vegetable kingdom. The substances of which this scum consists are designated by the names of conferva and byssi. Duckweeds (lemnæ) and callitriches accompany or succeed them. These plants, which are destitute of roots, form, by their interlacement, a sort of floating sward, the remains of which are precipitated to the bottom of the water, and constitute the soil destined to receive plants of a superior rank. After this potamogetons, charæ, and myriophylla line the interior of basins and lakes, extend themselves into meadows constantly covered with water, and reserved for the nourishment of a great number of aquatic animals.
In proportion as the bottom is raised, more vigorous species appear above the water, and develope those beautiful corollas, the brilliancy of which vies with that of the flowers of our gardens. The liquid plain is converted into a parterre embellished with tufts of floating ranunculi, naiads, hydrocharides, val. lisneriæ, surmounted by the ample calices of silver, gold or azure of the nelumbos, and nuphars, with broad and varnished leaves, while the sagittariæ, flowering junci, menyantheses, huttoniæ, &c. form upon their edges an elegant and varied border, to which are joined beautiful veronicæ, ænanthæ, phyllandræ, surmounted by salicariæ, bidentes, eupatoriæ, &c.
Thus the waters, as well as the bare and stony part of the globe, are peopled with vegetables, which convert into marshes those liquid plains upon which have formerly floated the barks of fishermen. These waters gain in surface what they lose in depth, and carry fertility to all the surrounding grounds. In proportion as they are lowered, we see beginning to grow those species which in some measure hold an intermediate place between aquatic and terrestrial plants, such as large gramineæ, reeds, poas, carices, scirpi, rushes, typhæ, &c., but no plant contributes more to the conversion of these marshes into pasture grounds, than the prevalence of certain species of mosses, especially sphagna, which rise in yearly layers above one another, and daily increase in thickness as well as in extent. If these waters, absorbed by the power of vegetation, are not fed by springs in proportion to their loss, this marshy soil will by de grees be dried up, and will be covered in time with fertile meadows and trees of all sorts, and will then be fit for cultivation.
What I have here said with respect to the gradual progress of vegetation is in no degree conjectural: we find its proof at almost every step, as well in the bosom of the earth as at its surface, especially in soil which has not been overturned by recent revolutions. In how many places do we not meet, beneath the bed of vegetable or argillaceous earth, ancient peat-bogs extended over strata of sand or heaps of rolled stones; an evident proof that this soil has formerly been traversed by the waters of rivers, or occupied by those of lakes. The vast marshes of the Somme furnish us with one example among a thousand. The soil is often covered, as M. Girard has observed, with a layer of earth adapted for vegetation, about two feet in its greatest thickness; the height of the bed of peat on which it rests is from six to ten feet thick between Amiens and Pecquigny; it increases to thirty feet opposite the villages of L'Etoile and Long, beyond which it gradually diminishes. The low part of the city of Amiens, according to the observations of M. Sellier, is built upon a bed of peat, which is sometimes more than twelve feet thick ; it rests upon a bed of marl, which is itself supported by a bed of sand and pebbles, mixed with marine shells. This vast formation has therefore been long occupied by great lakes, as is proved by the discovery which has been made of several boats and Roman arms preserved in the peat at different depths.
We are not permitted to follow the establishment of vegetation in the depths of the ocean ; but if marine plants, like land or fresh-water ones, required to be implanted in an earthy or muddy soil, we should scarcely conceive how they could re: sist the destructive action of those roaring waves which incessantly overturn and drive before them every obstacle that comes in their way, sweeps the bottom of the seas, and heaps upon the shores the debris of rocks. To struggle with impediments so powerful, marine plants would require a peculiar mode of existence : nature has therefore awarded them a more solid base than that of a mobile sand, continually tossed about by the impetuous movements of the waters; it has fixed their abode upon the hardest bodies, upon stones and rocks, to which they adhere by a base of great tenacity, or rather are cramped by means of a sort of branched claw, very different from a root, although having its appearance. These claws are not destined to draw from a soil which they cannot penetrate, alimentary juices which are to be carried to the upper parts of these vegetables ; for these parts, being entirely immersed in the same medium, equally absorb, by the whole of their surface, the principles of their nutrition, and we have not as yet been able to discover the ascent of any liquid, such as sap, &c. Marine plants have, besides a foliage which is plane or divided into filaments, of a pliant texture, a coriaceous or membranaceous structure, susceptible of accommodating itself to all the motions of the water. in which it is immersed, without receiving any injury.
Although their mode of fructification is still little known, it appears that their seeds, or what they have in place of them, are very glutinous ; that they attach themselves indifferently to all solid bodies, and cover the rocks with a vegetation equally abundant, and not less agreeable than that of the swards which carpet our mountains. It is true they do not expand brilliant corollæ, nor fill the air with their perfumes, but they often present, in the form, variety and mixture of the colours of their foliage, an aspect not less seducing.
It would be difficult to say what are the circumstances favourable or hurtful to their multiplication ; but if we examine the rocks which it is permitted us to approach, we shall find them covered with a rich vegetation. It is to be supposed that these plants, although placed in the same general medium, are, equally with terrestrial plants, subjected to the influence of localities, depths and temperature, since there are some which only shew themselves in certain seas, which are met with, for instance in the Atlantic, while they are not to be seen in the Mediterranean, which occur in the Indian Ocean, while they are denied to the frozen seas of the north, &c. Others grow at such depths that we are only acquainted with them by means of their fragments.
I shall not follow further in her great works, Nature inces santly occupied in laying everywhere the foundations of vegetation. What I have said will suffice to present an idea of all the
resources which she employs to overcome obstacles, and diffuse motion and life throughout. We have followed her in the plains, upon the mountains, in the moving sands, and in the very
bosom of the waters. If we now descend into the cavities where the light never penetrates, we shall there find peculiar plants, destined to dwell in darkness, such as certain species of rhizomorphæ, byssi, &c. In short there are no substances, whether contained in the open air, or in the waters, laid open to the light, or concealed in the most obscure recesses, exposed to humidity or to dryness, which are not occupied by plants adapted for these different localities. The moulds attack all our alimentary provisions, when they are left undisturbed and kept in damp places; numerous fungi, enormous boleti, grow in the shade upon plants in a state of putrefaction ; lichens and mosses penetrate the wrinkled bark of trees; a multitude of animals of a very inferior order, such as larvæ of insects, worms, mollusca, whether naked or testaceous, crustacea, arachnida, establish their abode in the midst of this growing vegetation; they deposit their offspring there, live in abundance, like our herds in the pastures, enjoy the coolness and the shade, like the great animals in their forests. In this manner is propagated the sublime work of creation in those organic beings which contribute, during their life, by their secretions, and after their death by their spoils, to the augmentation of vegetable earth, and of many other inorganic substances.
Observations made during a Visit to Madeira, and a Residence
in the Canary Islands. By Baron LEOPOLD Von Buch.
(Continued from former volume, p. 380.) At this we were much surprised. We did not imagine we had climbed to such a height, and we thought that it was impossible to ascend so high in Madeira. The accounts of the height of Pico Ruivo, which is by far the highest mountain on the island, stood far below our calculation of the height of Toringas. Dr Thomas Heberden (a brother of Dr William Heberden, to whom we are indebted for the remarkable obser