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270. Economically or commercially, it has also been attempted to arrange the earth's surface into four great vegetable zones-the tropical, southern temperate, northern temperate, and arctic, each, no doubt, shading into the other, but still, on the whole, broadly made up of its own peculiar products. The first, for example, is characterised by and yields such produce as dates, bananas, cocoanuts, tamarinds, guavas; yams, melons, cassava, sago, maize, rice; sugar, coffee, cinnamon, cloves, nutmegs, pepper, ginger; vegetable butter, vegetable ivory, gutta-percha, caoutchouc; aromatic gums, vanilla, opium, betel; cotton, indigo, dye-woods, sandal-wood, mahogany, teak, &c.: the second by the date, orange, lemon, fig, pomegranate, olive, vine; rice, maize, millet, wheat, barley; the potato; tea, Paraguay tea; cotton in the northern part, and flax and tobacco throughout; walnut, chestnut, cork, mimosa, birch, &c.: the third by the apple, pear, cherry, plum, gooseberry, currant, strawberry, cranberry; wheat, barley, oats, buckwheat; tobacco, hops, flax, hemp; beet, turnip, cabbage; oak, ash, beech, birch, maple, lime, elm, alder, pine, larch, &c.: and the fourth by the gooseberry, currant, strawberry, cranberry; Iceland and reindeer moss; Scotch fir, larch, birch, alder, willow, and juniper.

271. Such, in general terms, is the distribution of plants over the surface of the globe. Though many families have a very narrow range, and naturally are never found beyond it, yet others having greater facilities for the dispersion of their seeds, and being, moreover, of a more elastic constitution, have a tendency to increase their area, and this often at the expense of other families that are destroyed by their presence-nature exercising, as it were, a power of selection, by which some races are extinguished and others brought prominently forward to predominate for a period, and then to give way in turn to new and advancing species. Others, again, possessing this greater adaptability, are transferred for their utility or ornament from region to region, and are now found acclimatised and growing luxuriantly in many countries to which they naturally would never have found their way. In general, however, the great natural laws of distribution are supreme, and the majority of plants attain their perfection only in the habitats to which they originally belong. In denselypeopled and cultivated countries man is ever destroying, transferring, and acclimatising; but, knowing the limit to which this power can be profitably exercised, he will cease to rear in one region what can be more abundantly and cheaply procured from another. It is thus that a knowledge of the geographical distribution of plants, and the laws on which that distribution depends,

becomes a subject not only of scientific interest, but of true economic importance.

272. The great question-How the globe has been clothed with its present vegetation? is one that belongs more to the domain of botany than that of geography; and yet on this point we cannot refrain from transcribing the very cautious and temperate views of the authority above quoted. "From all that has been said on this interesting subject," he remarks, "we are led to the conclusion that many plants must have originated primitively over the whole extent of their natural distribution; that certain species have been confined to definite localities, and have not spread to any great distance from a common centre; while others have been generally diffused, and appear to have been created at the same time in different and often far-distant localities; that migration has taken place to a certain extent, under the agency of various natural causes; that geological changes may, in some instances, have caused interruptions in the continuity of floras, and may have left isolated outposts in various parts of the globe; and, finally, that social plants were probably created in masses, that being the natural arrangement suited to their habits."

XIV.

LIFE-ITS DISTRIBUTION AND FUNCTION.

Animal Life--its Distribution and Governing Conditions.

273. BEING influenced by climate, food, and other external conditions, animals, like plants, are necessarily less or more restricted to certain geographical regions. Endowed with greater powers of dispersion and locomotion, their limits are, perhaps, less precise than those of plants; but in the main there is a similar horizontal and vertical arrangement of animal forms-from the equator to the poles, and from the sea-level to the loftiest heights of land, or to the greatest depths of ocean. The fauna of the tropics, taken in general terms, is more exuberant in kind, in size, strength, and beauty, than that of the temperate zones; and this, again, more abundant than that of the arctic and antarctic regions. The more luxuriant and sheltered lowlands are peopled by races differing from those that inhabit the mountain-slopes, and those that affect the mountain-sides are distinct from those that find subsistence among the higher and colder elevations. In like manner, the creatures that throng the shallow shore are specifically different from those that are scattered through the deeper ocean. In the great stratum of life every plant and animal has its own natural horizon, and in that horizon it takes some particular spot better fitted for its growth and development than another—and this spot in the case of a plant is known as its station, and in the case of an animal as its habitat.

274. In this way terrestrial animals may be broadly arranged into a tropical, a temperate, and an arctic fauna-each shading to a certain extent into the other, but still, in the main, characterised by genera and species that do not naturally occur in the other sections. Thus, the Tropics are the great headquarters of the apes and monkeys; of the lion, tiger, panther, hyena, and larger carnivora; of the giraffe and zebra; the elephant, rhinoceros,

hippopotamus, and tapir; the crocodile, turtle, boa, and larger reptiles; the ostrich, flamingo, peacock, parrots, humming-birds, and generally of birds remarkable for their brilliant and variegated plumage. Insect life is also much more varied and exuberant in tropical than in colder latitudes-attaining its maximum in variety, in size, activity, and brilliancy of hue, within the luxuriant regions of Brazil, Guinea, and the Indian Archipelago, and gradually declining towards either temperate zone. This declension does not take place, of course, everywhere in the same ratio, for wherever there is abundance of plant-life, there certain insects increase in corresponding numbers; and variety in plant-life is also attended by a greater variety of insect-life-each genus, and often each species, being limited to its own peculiar vegetation.

275. The Temperate zones, on the other hand, though marked on their warmer limits by the presence of such tropical forms as the tiger, jackal, hyena, crocodile, &c., are, on the whole, the headquarters of such ruminants as the ox, bison, buffalo, goat, sheep, stag, and elk. The useful animals—that is, those more especially fitted for domestication, like the horse, ox, sheep, dog, &c.-increase in the milder zones, while the larger carnivora decrease not only in species, but in power and numbers. Peculiar to them also are the Bactrian camel, the wild boar, wolf, fox, and beaver; the opossum in the northern hemisphere and the kangaroo in the southern; the eagle and falcon, turkey, goose, grouse, and pheasant, among birds; while reptiles become fewer and smaller the nearer we approach the arctic zone. Insects also, with the exception of beetles, decrease in species, size, and brillianey-the beetles being specifically more abundant in temperate than in tropical climes, though inferior in size and brilliancy of colouring. 276. The Arctic zone (for the Antarctic is almost exclusively occupied by the ocean) is characterised by greater uniformity in its fauna, by few species but by numerous individuals, and generally by the quiet and sombre colouring both of its birds and quadrupeds. The reindeer, musk-ox, brown bear, polar bear, wolf, arctic fox, and sable, are peculiar to this region; the sea-fowl that frequent its summer seas are chiefly migrants from the waters of the colder-temperate zone; and reptile life is unknown. And here it may be observed that as the land in the northern hemisphere lies in great contiguous or all but contiguous masses, while in the southern it consists of far-separated spurs and patches, so there is a greater similarity between the fauna and flora of northern than of southern zones. The Life of the Antarctic zone occurs in dissimilar and far-scattered specks and patches, while in the Arctic, the musk-ox, reindeer, polar bear, Esquimaux

dog, and arctic fox occur in uninterrupted continuity wherever they can find a habitable locality.

277. Still more minutely than these great thermal zones, it has been attempted to arrange the earth's surface into certain zoological kingdoms and provinces, but, it must be confessed, with much less precision and certainty than in the case of the vegetable world. The following epitome of this arrangement, by the late Edward Forbes, may be sufficient for the student at this stage of his progress :-The first kingdom embraces Europe, which is again subdivided into northern, middle, and southern provinces. The limit between the northern and central provinces falls about lat. 60° north, or, more accurately, it corresponds with the curve of 41° of mean annual temperature. The separation between the central and southern provinces is formed by the chains of the Pyrenees and Alps. The peninsulas of Spain, Italy, and Greece, with the islands of the Mediterranean, form the southern province, which in the east is divided by the Ural Mountains from the second kingdom, which comprises Asia. At the junction of Europe and Asia, on the coasts of the Black Sea and the Caucasus, the European and Asiatic forms of animals are mixed, and pass into each other. There is here a peculiar zoological district-country of Anterior Asia, or the countries of the Caucasus, Asia Minor, Syria, and the table-lands of Persia-which may be designated the "European-Asiatic Transition province," in which are also found specimens of the zoological characters of Africa. Asia is divided also into three provinces, the northern, middle, and southern. The northern province extends from the Volga in the west to the mountain-range of the Altai, with a mean temperature of 42°; and eastward to the shores of the Pacific, where it is bounded by the isotherm of 32°, which marks the limit of permanently frozen ground. This province embraces the whole of Siberia, Kamtchatka, &c. The central province is limited on the south by the Himalayan Mountains, consequently it comprises all Asia from the Caspian Sea to the Pacific Ocean, including the islands of Japan, &c. Beyond the Himalaya begins the southern province, or the Indian world, comprising both peninsulas, a part of the southern province of China, and the whole of the Archipelago. The south-eastern extremity of the zoological region of Asia is so strictly defined by the Moluccas and Timor, that whilst in these islands there is a great abundance of carnivora and other orders of animals, in New Guinea (separated only by a small arm of the sea) they appear to be almost or wholly wanting. We have now reached the oceanic province, which is characterised by a great deficiency of carnivorous animals; southward from it lies the third

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