This section is from the book "Landscape Gardening", by Andrew Jackson Downing. Also available from Amazon: Landscape Gardening.
* This reference to the rolling prairies looks like easy prophecy. In modern times several able men have attempted to define and to create a "prairie style" in Landscape Gardening. — F. A. W.
Besides the beauties of form and expression in the different modes of laying out grounds, there are certain universal and inherent beauties common to all styles, and, indeed, to every composition in the fine arts. Of these, we shall especially point out those growing out of the principles of unity, harmony, and variety.
Unity, or the production of a whole, is a leading principle of the highest importance, in every art of taste or design, without which no satisfactory result can be realized. This arises from the fact, that the mind can only attend, with pleasure and satisfaction, to one object, or one composite sensation, at the same time. If two distinct objects, or classes of objects, present themselves at once to us, we can only attend satisfactorily to one, by withdrawing our attention for the time from the other. Hence the necessity of a reference to this leading principle of unity.
To illustrate the subject, let us suppose a building, partially built of wood, with square windows, and the remainder of brick or stone, with long and narrow windows. I low-ever well such a building may be constructed, or however nicely the different proportions of the edifice may be adjusted, it is evident it can never form a satisfactory whole. The mind can only account for such an absurdity, by supposing it to have been built by two individuals, or at two different times, as there is nothing indicating unity of mind in its composition.
In Landscape Gardening, violations of the principle of unity are often to be met with, and they are always indicative of the absence of correct taste in art. Looking upon a landscape from the windows of a villa residence, we sometimes see a considerable portion of the view embraced by the eye, laid out in natural groups of trees and shrubs, and upon one side, or perhaps in the middle of the same scene, a formal avenue leading directly up to the house. Such a view can never appear a satisfactory whole, because we experience a confusion of sensations in contemplating it. There is an evident incongruity in bringing two modes of arranging plantations, so totally different, under the eye at one moment, which distracts, rather than pleases the mind. In this example, the avenue, taken by itself, may be a beautiful object, and the groups and connected masses may, in themselves, be elegant; yet if the two portions are seen together, they will not form a whole, because they cannot make a composite idea. For the same reason, there is something unpleasing in the introduction of fruit trees among elegant ornamental trees on a lawn, or even in assembling together, in the same beds, flowering plants and culinary vegetables — one class of vegetation suggesting the useful and homely alone to the mind, and the other, avowedly, only the ornamental.
In the arrangement of a large extent of surface, where a great many objects are necessarily presented to the eye at once, the principle of unity will suggest that there should be some grand or leading features to which the others should be merely subordinate. Thus, in grouping trees, there should be some large and striking masses to which the others appear to belong, however distant, instead of scattered groups, all of the same size. Even in arranging walks, a whole will more readily be recognized, if there are one or two of large size, with which the others appear connected as branches, than if all are equal in breadth, and present the same appearance to the eye in passing.
In all works of art which command universal admiration we discover unity of conception and composition, with unity of taste and execution. To assemble in a single composition forms which are discordant, and portions dissimilar in plan, can only afford pleasure for a short time to tasteless minds, or those fond of trifling and puerile conceits. The production of an accordant whole is, on the contrary, capable of affording the most permanent enjoyment to educated minds, everywhere, and at all periods of time.
After unity, the principle of variety is worthy of consideration, as a fertile source of beauty in Landscape Gardening. Variety must be considered as belonging more to the details than to the production of a whole, and it may be attained by disposing trees and shrubs in numerous different ways; and by the introduction of a great number of different species of vegetation, or kinds of walks, ornamental objects, buildings, and seats. By producing intricacy, it creates in scenery a thousand points of interest, and elicits new beauties, through different arrangements and combinations of forms and colors, light and shades. In pleasure-grounds, while the whole should exhibit a general plan, the different scenes presented to the eye, one after the other, should possess sufficient variety in the detail to keep alive the interest of the spectator, and awaken further curiosity.
Harmony may be considered the principle presiding over variety, and preventing it from becoming discordant. It, indeed, always supposes contrasts, but neither so strong nor so frequent as to produce discord; and variety, but not so great as to destroy a leading expression. In plantations, we seek it in a combination of qualities, opposite in some respects, as in the color of the foliage, and similar in others more important, as the form. In embellishments, by a great variety of objects of interest, as sculptured vases, sun dials, or rustic seats, baskets, and arbors, of different forms, but all in accordance, or keeping with the spirit of the scene.
To illustrate the three principles, with reference to Landscape Gardening, we may remark, that, if unity only were consulted, a scene might be planted with but one kind of tree, the effect of which would be sameness; on the other hand, variety might be carried so far as to have every tree of a different kind, which would produce a confused effect. Harmony, however, introduces contrast and variety, but keeps them subordinate to unity, and to the leading expression; and is, thus, the highest principle of the three.
In this brief abstract of the nature of imitation in Landscape Gardening and the kinds of beauty which it is possible to produce by means of the art, we have endeavored to elucidate its leading principles, clearly, to the reader. These grand principles we shall here succinctly recapitulate, premising that a familiarity with them is of the very first importance in the successful practice of this elegant art. viz.:
The imitation of the beauty of expression, derived from a refined perception of the sentiment of nature: The recognition of art, founded on the immutability of the true, as well as the beautiful: and the production of unity, harmony, and variety, in order to render complete and continuous, our enjoyment of any artistical work.
Neither the professional Landscape Gardener, nor the amateur, can hope for much success in realizing the nobler effects of the art, unless he first make himself master of the natural character or prevailing expression of the place to be improved. In this nice perception, at a glance, of the natural expression, as well as the capabilities of a residence, lies the secret of the superior results produced even by the improver, who, to use the words of Horace Walpole, " is proud of no other art than that of softening nature's harshness, and copying her graceful touch." When we discover the picturesque indicated in the grounds of the residence to be treated, let us take advantage of it; and while all harshness incompatible with scenery near the house is removed, the original expression may in most cases be heightened, in all rendered more elegant and appropriate, without lowering it in force or spirit. In like manner good taste will direct us to embellish scenery expressive of the beautiful, by the addition of forms, whether in trees, buildings, or other objects, harmonious in character, as well as in color and outline.
 
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