It is remarkable that the two extremes of climate are distinguished by the predominance of evergreens in their vegetation.  Thus, the acicular-leaved trees, consisting of Pines and their congeners, mark the cold-temperate and sub-arctic zones, in north latitude,—­while Myrtles, Magnolias, and other broad-leaved evergreens, mark the equatorial and tropical regions.  The deciduous trees belong properly to the temperate zones, and constitute, indeed, the most interesting of all arborescent vegetation.

With regard to the age of forests, it may be affirmed that there are some undoubtedly in existence which are coeval with the earliest history of nations; but no individual trees are of such antiquity.  Like nations, the assemblage may be perpetual, while the members that compose it are constantly perishing, and leaving their places to be supplied by others of more recent origin.  Probably the earth does not contain forests in which any tree exceeds a thousand years of age, though the oldest forest extant may be as ancient as the Chinese Empire; for the oldest trees are not found in dense assemblages, but are probably such as have grown singly in isolated situations.  As soon as a tree in a forest begins to feel the infirmities of age, its place is usurped by some young and more vigorous neighbor, and it is gradually deprived of subsistence in this unequal contest.  The tempests and tornadoes, it may be added, which occasionally sweep over a country, commonly make the oldest and tallest trees their victims; for events seem to follow the same course in a forest as in human society.  The most vigorous growers at any period continue to flourish a certain length of time at the expense of others; but when they have risen above the common level, they become marks for destruction,—­they fall before certain inimical forces that do not reach their more humble companions.

It was the opinion of Humboldt, that, if any tract of wooded country deserves to be considered a part of the great “primeval forest”, it is “that boundless district which, in the torrid zone of South America, connects the river-basins of the Amazon and the Orinoco.”  This tract, unequalled in extent by any other forest in the world, occupies an area of more than a thousand miles square.  In this vast chaos of teeming vegetation, trees of the largest dimensions are connected by an undergrowth of vines and shrubbery which is almost impenetrable.  Immense rivers and their tributaries intersect the forest in all directions, and constitute the only avenues of commercial intercourse.  This impervious thicket is like a huge wall, separating near neighbors, rendering them, as it were, inhabitants of distant regions, and obliging them to make long and circuitous river journeys before they can hold communication.