XX. straw. The joints of the bamboo contain crystallizations BOOK of pure silex.* There are, however, other plants which are as much impregnated with calcareous earth, such as the Charavulgaris. the Hypnum crista castrensis, the Neckera dendroides, and several cryptogamic plants. Other plants, such as the Salsola kali, the salicornia, the mesembry-anthemum, float almost in a solution of alkali. All the substances which chemistry procures from vegetables are reducible into four elements, namely, oxygen, hydrogen, azote, and carbon. The alkali which is extracted from several vegetables, probably owes its origin to the azote. Tannin, the principle of astringency which is found in the bark, the roots, and the leaves of some trees, seems to be carbon in a particular state. Vegetable physiology is full of uncertainty, and can furnish the geography of plants only with a very limited number of principles. The empire of vegetation embraces the globe from pole Extent of to pole, and from the summit of the Andes, where the lichen vegetation. creeps over the hardest rocks, to the bosom of the ocean, from which floating fields of algæ and fuci rise unseen. Cold and heat, light and shade, fertile lands and pathless. deserts, every place and every temperature has its own kind of vegetation, which thrives and prospers there.‡ Plants of the cryptogamic class even ramify upon the dark vaults of mines, and upon the walls of the deepest caverns. The course which vegetation pursues in its conquests over Progress of inorganic matter, presents remarkable gradations. "Let a volcano," says M. Humboldt, "raise up from the bottom of the sea, all at once above the boiling waves, a rock covered with scoria; or, to refer to a less dreadful phenomenon, suppose the nereides, with united industry, continue to elevate their cellular abodes for thousands of years, till, finding themselves above the level of the sea, they die, after having in this way formed a flattened isle of coral; organic force * Lampadius, Samlung praktischer Abhaudl., iii., p. 187. Davy, Nicholson, vol. ii. No. 27, p. 56. Macie and Russel, Philosoph. Transact. pol. lxxx. and lxxxi. + Humboldt, Aphorism, p. 105, 106. Linneus, Amoenitat, acad. vol. iv. p. 64. vegetation. XX. BOOK is instantly ready to produce vegetation upon this rock: yet who can have brought there so suddenly the seeds of plants? Is it the birds, or the winds, or the waves of the sea? It is the great distance from the coasts which renders it difficult to decide this question. But scarcely has the air come in contact with the naked rock, when in the northern climates there is formed upon its surface a net-work of tufted threads, which appear to the unassisted eye like coloured spots. Some of them are bordered by lines bending outwards, sometimes single, sometimes double; others are cut by furrows which cross each other. As they grow older, their bright colour darkens; the yellow, which shone even to a great distance, changes into brown, and the bluish gray of the lepraria insensibly acquires a tint of dusty black. The extremities of the older coverings approach and mingle together; and upon this dark ground are formed new lichens of a circular form, and of a dazzling whiteness. It is thus that an organic net-work is wrought in successive layers. Where the majestic oak now raises its ærial head, slender lichens once covered the bare rock. Moss, grasses, herbaceous and shrubby plants, fill up this long interval, the duration of which cannot be calculated: In the torrid zone, the portulaca, the gomphrena, and other low plants inhabiting the shores, supply the place, and produce the effects of the lichens and mosses in the northern climates.” This interesting observation tends to establish certain epochs in the history of the successive propagation of the plants which now cover the earth: Without doubt, where vegetation had already thrown her verdant mantle over the primary and secondary mountains, the ternary lands might still be seen scarcely dried, covered with muddy slime, and sown with some languishing plants, rushes, mosses, and thick bushes of osier and willows. The Greeks alleged, that men, animals, and plants, inhabited the mountains long before they spread themselves over the plains, and along the coasts.* * Plat. de Leg. iii. Oper. ii. p. 677. Edit. Serran. Aristot. Méteorol. ii. 13, Strabo. Geog. i, and iii. 407, ed Cas. Rudbeck XX. Tacitus describes Germany as full of inaccessible marsh- BOOK es, which are now in a great measure dried up. himself admits, that according to the tradition of the counEpochs in try, the low parts of Scandinavia presented the same as the propapect. Thus, history appears to confirm the hypothesis so gation of plants. ingeniously developed by Lacepede and Ramond; according to which, we ought to look upon the great chains of mountains as so many centres, whence vegetable, as well as animal population, was scattered over the rest of the globe. In truth, the chains of the Alps of Mount Atlas and Mount Taurus, the central upland plain of Asia, that of Southern Africa, the Andes, the Allegany mountains, seem to be the native land of the vegetables which cover the countries lying at their base. To these grand centres of Primitive the vegetable kingdom, the progress of discovery will, ere vegetation. long, add the upland plains or chains of mountains which are supposed to occupy the interior of New Holland and the north-west parts of America. centres of It would, we conceive, be extremely unwarrantable to reduce these centres of vegetable and animal life to one single centre, as has been attempted by several philosophers, led away by an undue regard to mythological traditions, or to their own interpretation of the sacred records. Could the organic energy by which matter was animated, have acted originally only upon one point of the globe? Would not nature, upon the banks of Senegal, have exercised the same power as upon the shores of the Ganges? Why should corn have sprung up in Tartary before it grew in Europe? Why have not Spain and Italy produced wild olives, when Persia, which is much colder, is covered with them? The Migration pretended migrations of plants are very much exaggerated. of plants. We are willing to suppose, for example, that Europe has received wheat and barley from Tartary, the walnut tree from Persia, the olive from Syria, the vine from the borders of the Caspian Sea; in short, we accumulate histori Rudbeck, Atlantica, i. p. 45. Torfæi. Hist. Norweg. i. p. 111. † Memoires de l'Institut et Annales du Museum, XX. BOOK cal proofs, to shew that all our useful plants come from Asia; but all these observations of the ancients relate only to the cultivation of a plant, and not to its origin. Lucullus, without doubt, was the first who brought from Cerasus, in Pontus, the cherry trees since cultivated in Italy; but, in relating this fact, Pliny tells us that the cherries of Lusitania were the most esteemed in Belgic Gaul, and that Macedonia produced a particular kind. Would he have spoken in this manner, had the cherry trees of Macedonia and Lusitania been propagated from those of Pontus? The same author, however, seems to allow that the vine was indigenous to Gaul. Ancient traditions concur in ascribing the first cultivation of wheat to Sicily or to Attica, a cultivation contemporary with the first attempts at legislation. A kind of rye, known under the Celtic name of Arinca, from which the term used in Dauphiny, "Riguet," is derived, was a native of Gaul. These examples, which it were easy to multiply, prove that the farinaceous plants, and in general the vegetables of Europe, may dispense with the honour of a foreign origin. On the other hand, we cannot deny that the migrations of man have a singular influence upon the geographical extension of plants. Not only has man intentionally carried the coffee-tree from Arabia to the West Indies, and the potato from America to the shores of Europe, but even the accidental introduction of a foreign grain into a bale of merchandize, has propagated many plants from the Brazils to the environs of Lisbon, and some of these, in their turn, from Portugal to the coasts in the neighbourhood of Falmouth and Plymouth in England. * Heyne, Opusc. Acad. vol. i. p. 380-383. Linné, Coloniæ Plantarum, &c. Sprengel, cité par Humboldt, Tableaux de la Nature, i. Dureau de la Malle, Aperçu de l'Origine des Plantes Céréales, Annales des Voyages, x. 321, $29. † Plin. lib. xv. cap. 25. Id. Plin. xiv. 3, 9. Pausan. in Arcad. Plin, xviii. 8. Callim. Hymn. in Cerer. Plin. vii. 56. Sociable There are in the dissemination of plants several singula- BOOK rities difficult to account for and even to define. Some plants XX. appear to live in society, and occupy exclusively large tracts of ground, from which they banish all other vegetables. plants. We can trace through Jutland, Holstein, Hanover, Westphalia, and Holland, a long chain of hills, entirely covered with common heath, and the Erica tetralix. The farmers have opposed for centuries, but with little success, the inroads of these vegetable hosts.* It is singular that the genus called Erica, is found only upon one side of our planet. Of the 137 species of heaths at present known, there is not even one to be met with in the new continent, from Pennsylvania, and the coast of Labrador, to Nootka and Alashka. They appear even very rare in Asia. We see, at other times, very singular leaps or intervals in the distribution of plants. Most of the forest trees of Europe, and even those which are the hardiest, disappear towards the Uralian mountains, and particularly towards the banks of the Tobolsk and the Irtych; they do not grow in Siberia, although under the same climate. The oak, the nut tree, and the wild apple, are subject to this common law. In vain should we search for one plant of them from the Tobol to the Daouria. The two first of these trees, however, reappear suddenly upon the banks of the Argoun and the Amur; the last occurs anew in the Aleutian Islands.+ These remarks will have shown how difficult it is to mark with exactness the regions of botanical geography, a subject which, besides, appears to belong to that part of our work which contains a particular description of the different countries. We must here confine ourselves to a brief sketch of the general appearance and the advantages of vegetation in the different zones of the globe. * Humboldt, Tableaux de la Nature, ii. 47. There are upwards of four hundred sorts or varieties. T. f Georgi, Description de la Russie, iiie tome, 4e partie, p. 1015, et se partic. p. 1301, 1305, |