Conical or oblong-headed trees, when carefully employed, are very effective for purposes of contrast, in conjunction with horizontal lines of buildings such as we see in Grecian or Italian architecture. Near such edifices, sparingly introduced, and mingled in small proportion with round-headed trees, they contrast advantageously with the long cornices, flat roofs, and horizontal lines that predominate in their exteriors. Lombardy poplars are often thus introduced in pictures of Italian scenery, where they sometimes break the formality of a long line of wall in the happiest manner. Nevertheless, if they should be indiscriminately employed, or even used in any considerable portion in the decoration of the ground immediately adjoining a building of any pretensions, they would inevitably defeat this purpose, and by their tall and formal growth diminish the apparent magnitude, as well as the elegance of the house.
Drooping trees, though often classed with oblong-headed trees, differ from them in so many particulars, that they deserve to be ranked under a separate head. To this class belong the weeping willow, the weeping birch, the drooping elm, etc. Their prominent characteristics are gracefulness and elegance; and we consider them as unfit, therefore, to be employed to any extent in scenes where it is desirable to keep up the expression of a wild or highly picturesque character. As single objects, or tastefully grouped in beautiful landscape, they are in excellent keeping, and contribute much to give value to the leading expression.
When drooping trees are mixed indiscriminately with other round-headed trees in the composition of groups or masses, much of their individual character is lost, as it depends not so much on the top (as in oblong and spiry trees) as upon the side branches, which are of course concealed by those of the adjoining trees. Drooping trees, therefore, as elms, birches, etc., are shown to the best advantage on the borders of groups or the boundaries of plantations. It must not be forgotten, but constantly kept in mind, that all strongly marked trees, like bright colors in pictures, only admit of occasional employment; and that the very object aimed at in introducing them will be defeated if they are brought into the lawn and park in masses, and distributed heedlessly on every side. An English author very justly remarks, therefore, that the poplar, the willow, and the drooping birch, are "most dangerous trees in the hands of a planter who has not considerable knowledge and good taste in the composition of a landscape." Some of them, as the native elm, from their abounding in our own woods, may appear oftener; while others which have a peculiar and exotic look, as the weeping willow, should only be seen in situations where they either do not disturb the prevailing expression, or (which is better) where they are evidently in good keeping. "The weeping willow," says Gilpin, with his usual good taste, "is not adapted to sublime objects. We wish it not to screen the broken buttress and Gothic windows of an abbey, or to overshadow the battlements of a ruined castle. These offices it resigns to the oak, whose dignity can support them. The weeping willow seeks an humble scene — some romantic footpath bridge, which it half conceals, or some grassy pool over which it hangs its streaming foliage, -'And dips Its pendent boughs, as if to drink.'"
* In America the Lombardy poplar has now come to be a sort of shibboleth. The critical naturalists refuse it because of its exotic character, while the architects and formalists use it with dangerous frequency. There is some criticism, too, of the Lombardy poplar as being a "cheap" tree, i.e., quickly grown and quickly lost. — F. A. W.
Having now described the peculiar characteristics of these different classes of round-headed, spiry-topped oblong, and drooping trees, we should consider the proper method by which a harmonious combination of the different forms composing them may be made so as not to violate correct principles of taste. An indiscriminate mixture of their different forms would, it is evident, produce anything but an agreeable effect. For example, let a person plant together in a group, three trees of totally opposite forms and expressions, viz., a weeping willow, an oak, and a poplar; and the expression of the whole would be destroyed by the confusion resulting from their discordant forms. On the other hand, the mixture of trees that exactly corresponds in their forms, if these forms, as in oblong or drooping trees, are similar, will infallibly create sameness. In order then to produce beautiful variety which shall neither on the one side run into confusion, nor on the other verge into monotony, it is requisite to give some little attention to the harmony of form and color in the composition of trees in artificial plantations.
The only rules which we can suggest to govern the planter are these: First, if a certain leading expression is desired in a group of trees, together with as great a variety as possible, such species must be chosen as harmonize with each other in certain leading points. And, secondly, in occasionally intermingling trees of opposite characters, discordance may be prevented, and harmonious expression promoted, by interposing other trees of an intermediate character.
In the first case, suppose it is desired to form a group of trees, in which gracefulness must be the leading expression. The willow alone would have the effect; but in groups, willows alone produce sameness: in order therefore, to give variety, we must choose other trees which, while they differ from the willow in some particulars, agree in others. The elm has much larger and darker foliage, while it has also a drooping spray; the weeping birch differs in its leaves, but agrees in the pensile flow of its branches; the common birch has few pendent boughs, but resembles in the airy lightness of its leaves; and the three-thorned acacia, though its branches are horizontal, has delicate foliage of nearly the same hue and floating lightness as the willow.