BOTANICAL GARDENS. The term botanical garden is used to designate a limited area of ground on which is grown a collection of plants including a large number of species brought together to subserve scientific, educa tional, esthetic or economic purposes. In the broadest sense, it is a museum of plants and one of its chief ends is to represent, by means of living specimens so far as possible, the prin cipal types of vegetation of the earth. It is impossible to cultivate more than a few thou sand species on any given area under the nat ural conditions of soil and climate, and the open-air plantations are generally supplemented by collections grown under shelter, in glass houses and in specially prepared soils. It has been found practicable to grow in this manner as many as 12,000 or 15,000 species of the higher plants in the botanical gardens at Saint Louis and New York, at Kew, near London, England, and at Berlin, Germany. A proper selection of this number may be made to rep resent somewhat fairly the principal forms of plants,. which include about 250,000 species. That is to say, it is possible to grow in one place about. one species out of every 17 in existence.
Living plants cultivated in the open air are most suitably arranged in plantations according to their general habit and in such manner as to show their general relationships. Then special groups are often made of certain families, such as the conifers, the willows and poplars, the grasses, ferns or mosses. The most common arrangement of plantations includes the her baceous grounds, the aquatic plants, alpinum, viticetum, fruticetum, arboretum and economic plantations. Some institutions bring together collections for the purpose of illustrating the local flora or the flora of any given geographi cal district.
The herbaceous plantations are intended to include the representatives of small soft-bodied plants which die down to the soil during the winter or resting season, and which may or may not have a perennial underground stem formation of some kind. Many of the species are annuals and must be grown from seeds every year.
The pools for aquatic plants are arranged to afford suitable means for the culture of forms which float or root in ponds and streams of fresh water, and include a wide variety, such as the water-lily, pondweeds, Philotria, water hyacinth, etc.
An alpinum is a special plantation generally arranged to afford means of cultivation of species from cold climates on mountain-tops or in higher latitudes. Plantations of this kind are often termed rockeries, and are in the form of a ridge or hill covered with boulders. In such plantations precautions must be taken to give lime-loving plants a place among limestone rocks, and with the necessary low temperatures.
The viticetum is a plantation devoted to the cultivation of climbing and trailing vines, and may take almost any form demanded by the exigencies of practical gardening. Among the necessary features are trellises or supports for twining and tendril climbing forms.
The fruticetum includes all woody perennial plants which do not form a central trunk six feet in height, and which are therefore not trees. These are most effectively grouped when the individuals of the separate species are placed in the ground separately in a scheme of general arrangement by which every plant may be in spected from all sides and is unshaded by its neighbors.
The arboretum includes trees, and these may be variously arranged, singly or in groups, al ways with respect to their mutual relationship. On account of their great size and compara tively slow growth and greater permanency, the placing of trees in any given landscape scheme in a garden is attended to with the greatest care.
The economic plantations may include useful plants arranged according to their relationships, and grouped according to the use or nature of the derivative. Thus a division may be made in which only species used for medicine, foods or clothing are included, or a division may be made to include plants which yield starches, oils, gums and resins.