Trees are a chief material in landscape gardening. Trees and shrubs are of different shapes, colours, and growths.

"The varieties in their shapes," says Mr. Whateley, "may be reduced to the following heads. Some thick with branches and foliage have almost an appearance of solidity, as the beach, the elm, the lilac, and seringa. Others thin of boughs and of leaves, seem light and airy, as the ash, and the arbele,the common arbor vitae, and the tamarisk.

"There is a mean betwixt the two extremes, very distinguishable from both, as in the bladder-nut, and the ashen-leaved maple. They may again be divided into those whose branches begin from the ground, and those which shoot up in a stem before their branches begin. Trees which have some, and not much clear stem, as several of the firs, belong to the former class; but a very short stem will rank as a shrub, such as the althaea in the latter.

"Of those whose branches begin from the ground, some rise in a conical figure, as the larch, the cedar of Lebanon, and the holly. Some swell out in the middle of their growth, and diminish at both ends, as the Weymouth pine, the mountain ash, and the lilac; and some are irregular and bushy from the top to the bottom, as the evergreen oak, the Virginian cedar, and Guelder rose. There is a great difference between one whose base is very large, and another whose base is very small, in proportion to its height; the cedar of Lebanon and the cypress, are instances of such a difference, yet in both the branches begin from the ground.

"The heads of those which shoot up into a stem, before their branches begin, sometimes are slender cones, as of many firs, sometimes are broad cones, as of the horse-chestnut, sometimes they are round, as of the stone pine, and most sorts of fruit trees; and sometimes irregular, as of the elm. Of this last kind there are many considerable varieties.

"The branches of some grow horizontally, as of the oak. In others they tend upwards, as in the almond, and in several sorts of broom, and of willows. In others they fall, as in the lime and the acacia; and in some of these last they incline obliquely, as in many of the firs; in some they hang directly down, as in the weeping willow.

" These are the most obvious great distinctions in the shapes of trees and shrubs. The difference between shades of green cannot be so considerable, but these also will be found well deserving of attention.

"Some are of a dark green, as the horse-chestnut and the yew. Some of a light green, as the lime and the laurel. Some of a green tinged with brown, as the Virginian cedar. Some of a green tinged with white, as the arbele and the sage tree. And some of a green tinged with yellow, as the ashen-leaved maple and the Chinese arbor vita;. The variegated plants also are generally entitled to be classed with the white or the yellow, by the strong tincture of the one or the other of those colours on their leaves.

"The fall of the leaf is the time to learn the species, the order, and the proportion of tints, which blended, will form beautiful masses; and,on the other hand, to distinguish those which are incompatible near together.

"The peculiar beauty of the tints of red, cannot then escape observation, and the want of them throughout the summer months must be regretted ; but the want, though it cannot perfectly, may partially be supplied, for plants have a permanent and an accidental colour. The permanent is always some shade of green, but any other may be the accidental colour; and there is none which so many circumstances concur to produce as a red. It is assumed in succession by the bud, the blossom, the berry, the bark, and the leaf. Sometimes it profusely overspreads, at other times it dimly tinges the plant, and a reddish-green is generally the hue of those plants on which it lasts long or frequently returns.

"Admitting this, at least for many months in the year, among the characteristic distinctions, a large piece of red-green, with a narrow edging of dark green, along the further side of it, and beyond that, a piece of light green, still larger than the first, will be found to compose a beautiful mass. Another, not less beautiful, is a yellow green, nearest to the eye, beyond that a light green, then a brown green, and lastly a dark green. The dark green must be the largest, the light green the next in extent, and the yellow green the least of all.

"From those combinations, the agreements between particular tints may be known. A light green may be next either to a yellow or a brown green, and a brown to a dark green; all in considerable quantities, and a little rim of dark green may border on a red or a light green.

"Further observations will show, that the yellow and the white greens connect easily; but that large quantities of the light, the yellow, or the white greens, do not mix well with a large quantity also of the dark green; and that to form a pleasing mass, either the dark green must be reduced to a mere edging, or a brown or an intermediate green must be interposed ; that the red, the brown, and the intermediate greens agree among themselves, and that either of them may be joined to any other tint; but that the red green will bear a larger quantity of the light than of the dark green near it; nor does it seem so proper a mixture with the white green as with the rest. In massing these tints, an attention must be constantly kept up to their forms, that they do not lie in large stripes one beyond another; but that either they be quite intermingled, or, which is generally more pleasing, that considerable pieces of different tints, each a beautiful figure, be in different proportions placed near together.

"Exactness in the shapes must not be attempted, for it cannot be preserved ; but if the great outlines be well drawn, little variations afterwards occasioned by the growth of the plants, will not spoil them. Another effect attainable by the aid of the different tints, is founded on the first principles of perspective; objects grow faint as they retire from the eye; a detached clump or a single tree of the lighter green will, therefore, seem farther off than one equidistant of a darker hue, and a regular gradation from one tint to another will alter the apparent length of a continued plantation, according as the dark or the light greens begin the graduation.

"Single trees scattered about a lawn, cast it into an agreeable shape, and to produce that shape, each must be placed with an attention to the rest; they may stand in particular directions, and collectively form agreeable figures, or between several straggling trees, little glades may open full of variety and beauty. The lines they trace are fainter than those which larger plantations describe, but then their forms are their own; they are therefore absolutely free from all appearance of art; any disposition of them, if it be but irregular, is sure to be natural.

"The situations of single trees, is the first consideration, and differences in the distances between them, their greatest variety. In shape, they admit of no choice but that which their species afford: greatness often, beauty often, sometimes mere solidity, and now and then peculiarity alone, recommends them. Their situations will also frequently determine the species; if they are placed before a continued line of wood only to break it, they should commonly be similar to the trees in that wood, they will else lose their connection, and not affect the outline which they are intended to vary; but if they are designed to be independent objects, they are as such more discernible, when distinguished both in their shapes and their greens, from any plantations about them. After all, the choice, especially in large scenes, is much confined to the trees on the spot; young clumps from the first have some, and soon produce a considerable effect; but a young single tree for many years has none at all, and it is often more judicious to preserve one already growing, though not exactly such as might be wished, either in itself or in its situation, than to plant in its stead another, which may be a finer object, and better placed, in a distant futurity." See Clump, Avenue, Grove and Wood.