Considered vaguely it is simply a collection of indigenous and exotic trees, disposed according to the proprietor's taste, and congregated upon a small superficies of ground, or scattered over an estate of twenty or thirty acres. This acceptation of the term is not, however, the general one. In all modern arboretums, every genua or tribe of plants is grouped together more or less densely, and the whole collection arranged with order and regularity; so that the connecting link of natural affinity may be at once discovered between immediate neighbors. In very large estates, or in botanical or other public gardens, these departments create a variation, and this is frequently a very pleasing one. They also furnish the beholder, at one glance, with a knowledge of the hardy ligneous species of every genus, tribe, or order of plants, and the position they occupy in the natural system of botany.

Arboretums are thus of great advantage to the scientific student, or to any one really desirous of acquiring a thorough knowledge of the aspect, habits, varieties, and affinities of arboreous plants. By this arrangement, too, a more specific and discriminate cultivation can be afforded, with greater certainty and convenience. Nor is there any other mode whereby a complete assortment may be conserved, which is desirable in many respects. Yet, when we have said this, there remains nothing more to be said in their favor. For they are entirely incompatible with beauty, with ornament, and with the proper development or exhibition of the character of a plant. Indeed, they are nothing more than living descriptive catalogues, experimental and observative departments - and not at all to be thought of for limited pleasure grounds, whether public or private.

Now, if it be desirable to exhibit the charms and beauties of vegetation, we must avoid arranging plants of any description according to affinity, or their position in any system of classification; for in landscape gardening there are two extremes to be deprecated - dull monotony, and a slovenly, displeasing irregularity. This may seem rather paradoxical, but it is nevertheless true. Local uniformity differs widely from a comprehensive unity, and is confined to the particular beds or plots occupied by the species of certain genera or tribes. These frequently assimilate so closely in appearance, that in one place a bed of trees will be seen all evergreen; close by, a cluster of dwarf shrubs, all flowering at the same time; and equally near, in another direction, a group of the largest deciduous trees. In themselves all these are monotonous and present a total lack of congruity, if viewed in connection and comparison with each other.

Nothing then can be more adverse to the genuine principles of landscape disposition, than the system above described. There must be diversity of outline, form, color, season, and the duration of foliage and flowers, as absolute essentials to the beauty of any scenery. Without them it appears dull, formal and constrained; in fact, unnatural: and much as theorists may affect to despise imitating Nature, it is after all the correct system, and the only successful one.

But we are to remember that a garden is the medium which associates natural with artificial objects - the mansion with the surrounding country. Its arrangement and appearance should therefore be in precise accordance with this design. To plant trees, then, en masse, or even in arboretums, without regard to size, appearance, or their general character, is not only inadmissable, but intolerable, where all is required to be conformable and harmonious.

In planting ornamental trees and shrubs, (and no others should be allowed a place in the pleasure garden,) they should be so arranged as to stand quite distinct from each other, so that each one may he witnessed and examined separately, without suffering any detraction from its entire exposure. They must also he so blended, associated, and intermingled, that a distant view may present the appearance of an agreeable and diversified mass of verdure. These two objects apparently so remote, may nevertheless be concurrently accomplished. In shrubberies or parterres, whether large or small, a due regard to the known character or habits of the plants selected, will enable the gardener (if sufficiently intelligent) to place them at such distances as will allow room for their full and complete extension, without becoming entangled with other plants. Again : If the plot of ground be small, or the diminutive size of the plants oppose this arrangement at first, they may be so planted as to admit of any subsequent thinning to the required extent, without in the least detracting from the general appearance of the group.

Judgment and taste will overcome obstacles, and sooner or later there will appear a harmonious development.

The shrubbery thus planted with exotic trees, would in itself be an arboretum; and if that charming variety be consulted which can alone please the eye, none of the objections against those departments would in such a case apply. Species and genera would certainly be separated and scattered about, and their associations lost; but then, pleasure gardens are not botanical nurseries; and we are of an opinion, that few, if any, proprietors would follow out any such idea, at the expense of everything that renders them picturesque and attractive. If information be desired, that can be readily obtained from books; and the attempt to illustrate it, or to facilitate its acquirement by the disposing of plants according to any other system than that dictated by taste, sense, and nature, is neither more nor less than an outrage on all the principles of beauty, and a thorough perversion of the science of landscape gardening.

In planting trees and shrubs, no method is so well calculated to display the perfection of their character, as that of singly placing them in conspicuous situations in the center of small parterres, or on lawns. It is, however, rather unfortunate, that this system must be limited to certain portions of the pleasure ground; for if carried to too great an extent, its effect would not be pleasing. For this purpose, then, we are to select the most rare, beautiful, and symmetrical kinds. We have thus the advantage of examining the plants on every side. Being perfectly isolated, air and light are freely admitted to all their surface, and from the operation of these agents, they alone can attain that graceful symmetry of form which all plants should exhibit in such situations.

We have thus given our opinion of the different modes of planting and arranging ornamental hardy shrubs and trees. The subject admits of a much greater scope of language and development of detail than is here presented to the reader, yet enough is said to give a right direction to the thoughts of the inexperienced, and to lead them, as we think, properly, in the laying out of their pleasure grounds. In very extensive domains, there is no doubt that arboretums may in some degree be rendered ornamental, but the extension of the system is by no means to be desired, for it is not only defective in principle, but in practice these defects are glaringly manifest.

Let every man, then, who loves his garden and his pleasure grounds, and who seeks to embellish and adorn them - who would heighten rather than mar their natural beauties, and steer with precision between the rules of art and nature, avoiding the defects of either, yet rising superior to both, let him so plant his trees and shrubs as to present individually and collectively the greatest diversity, combined with the most delightful and harmonious arrangement.