TREE, the name given to those plants which live for many years, and have woody stems and branches, the stem being generally single, and beating a head of branches and twigs; whereas shrubs (q.v.) have generally a number of stems springing from one root. The terms tree and shrub are not, however, of very exactly defined signification; and many shrubs, under certain circumstances, assume the form of trees, either naturally or by the help of art; while trees are, in other circumstances, converted into shrubs. common hawthorn, for example, is very often a mere shrub, but sometimes appears as a tree, with stem and head as perfect as the greatest monarch of • the forest. The goose berry bush is usually trained in our gardens in a tree-like habit, notwithstanding its small size, and the shortness of its stem; this, however, is entirely artificial, its natural habit being that of a shrub, to which, but for the gardener's knife, it would almost certainly relapse in a single year. The greater number of trees are exogenous. Palms are almost the only endogenous plants to which this name can be given. Very different from the ordinary exogenous trees are the gymnogens (q.v.) of Lindley—firs, pines, yews, etc. Trees are found in all climates except the coldest, but the number of species, as well as the luxuriance of the forests, is greatest in the tropics. As we advance toward the
polar regions, or ascend high mountains, trees 'disappear before other forms of vegeta tion. The different characters of trees affect very much the landscape of the countries in which they grow; some countries, and particularly in northern parts of the world, being covered with somber pine forests, while others abound in ash, beech, and similar trees of verdant foliage. Every kind of tree has its peculiar character, not only in its foliage, but in its general form and its mode of branching. An ash is as easily distin guished from an elm, by a practiced eye, in winter, when destitute of leaves, as in the full foliage of summer. Some trees attain a very great age, but the ordinary duration of life is very different in different species. There are trees in England which arc sup posed to be more than a thousand years old, and are still healthful and flourishing. Oaks and yews are among the trees of longest life. The baobab of Africa is also regarded as a very long-lived tree.
No acotyledonous plant assumes the character of a tree, except a few ferns, known as tree ferns. See ARBORICULTURE.