Considering the group with reference to total structure we shall see that the unit group in the smaller works may constitute the entire paragraph. In other words, to develop a small garden in good paragraphic structure it may prove best to use only one group to each paragraph. Or certain paragraphs may have only the one group in each. In larger works there will usually be several or many groups to each paragraph. In short, the group will be a smaller unit than the paragraph.
When several groups are used in any one paragraph they must obviously be much alike. This follows from the fact that they must all present the leading motive in a consistent manner, because it is the purpose of each paragraph to make a perfectly clear and unified presentation of some one phase of the leading motive.
It will occur to all that any feeling of rhythm which our landscape compositions may possess is likely to be given through the appearance and reappearance of similar forms in successive groups—is likely to be a matter of grouping. Now the correspondence between music and landscape is very close; and since rhythm plays so great a role in music we might expect it to be equally important in landscape composition. But this expectation is not wholly fulfilled. Repetition of similar elements— lines, forms, colors, species,—is indeed a very valuable practice in landscape composition, and this repetition may be fairly regular and rhythmic. It is easy, too, to cite the great rhythms of Nature, particularly the round of the hours, of day and night, and of the seasons. Yet when we come to practical problems of grouping plants in informal composition it must be confessed that Nature's rhythms are too subtle for easy imitation. The landscape designer, sitting at his drawing board, with his nurseryman's catalog in his left hand, can not make much headway in his planting plans upon any rhythmic formula. Rhythm in the formal garden is a much simpler matter, for the formal garden is essentially rhythmic in its structure, like poetry.
It is fairly evident that each group must have some character—some individuality. Otherwise it ceases to be a unit—it loses its unity. On the other hand it must not stand out with such prominence as to break the unity of the paragraph of which it is a part, or of the whole larger composition. Some artistic skill will be required, therefore, to balance these two tendencies. No rules can be made for matters like this. They are questions of taste pure and simple, and if a man has not the needful taste, he is not a safe designer.
This much can be said, however, that, in order to give any group any individuality whatever, or any intelligible meaning of any sort, it will always be necessary to follow the law of dominance. Each group must be commanded by some one species, all the other members being plainly subordinate. Thus one plant each of Philadelphus coronarius, Forsythia suspensa, Lonicera tartarica, Weigelia rosea, Rhodotypos Kerrioides, Viburnum lentago, Cornus florida, Spirea callosa, Cydoma japonica and Deutzia gracilis do not constitute a group in any artistic sense. Equal dabs of color out of several different paint tubes mixed on the palette do not make a color, but only a characterless gray..
The only possible way to compose groups in landscape gardening is to select one species for the dominating element in each group, and then to build the other material on to this controlling quantity. Naturally the dominating element will be the main factor in relating the group to its paragraphic control and to the leading motive of the entire composition.
No survey of Nature's methods of grouping would be complete without mention of a landscape form which classifies with difficulty into our poor human categories. This is the scattered distribution which presents individuals, yet presents them in such constantly obvious relationship that the usual effect is not that of the individual, neither is it the effect of the mass. The most striking examples of this are to be found in the scattered oaks along the hills which follow the Mississippi river from St. Paul to Cairo, and in the widely spaced pines on the pine barrens of central Florida. There are, however, hundreds of good examples of this scattering habit in the natural distribution of wild species.
Usually this arrangement is wholly pleasing to the eye. The spiritual effect is characteristic and agreeable. It is unfortunate, therefore, that this method should have been quite generally overlooked by the men who make planting plans. It would seem to be a method capable of considerable service in informal designing.
Old time debates about questions of grouping used to turn usually upon the shapes of groups, meaning their horizontal projection or plan. Some planters, whatever their theoretical principles, plainly made all their groups in a monotonously oval form. Hundreds of gardeners—and not all of them amateurs—still speak of "clumps of bushes" or of trees. Quite recently I visited a city park where the designing was professedly naturalistic yet in which the margin of an informal lake was' decorated with successive, equally spaced perfectly circular "clumps" of shrubs, each "clump" of a single species, but each one different from all the others.
Earlier in this chapter reference has been made to the equilateral triangle which so easily becomes a conventionalized group form. An examination of any large number of planting plans will indicate how easy it is to fall into some set form of grouping and how very, very hard it is to learn that infinite variety which so bountifully blesses the works of Nature. I have often been especially impressed with the structural stupidity of the ordinary plan for an herbaceous border. It consists of a crazy patchwork of irregular spots of approximately the same size. The finished border cannot be anything except a sample book of the nurseryman's materials.
Now the remedies for this are three. Simplification—changing to a much simpler geometric pattern; dominance—the selecting of one or two species which shall be placed in so large a majority as to control the whole; pictorial instead of horticultural treatment—making of the border a unified picture instead of a collection of miscellaneous garden plants, however pretty and pleasing they may be.