A collection of trees, shrubs, bushes, and underwood, is called a _grove_; when it consists only of trees, it is termed _a group of trees_. There are _thickets_ of shrubs, bushes, underwood, and of flowering herbaceous plants. There are _thickets_ formed of a single species of plants, and thickets formed of several species. The first are called _homogeneous_, and the second _heterogeneous_, or _varied_. There are _isolated masses_, and _masses subordinated together_. A small mass of flowers or shrubs, isolated, and of a circular or elliptical form, is called a _bed_. CHAPTER I. _Of Lines of Plants._ 567. I call a _line of plants_, plants placed at equal distances from each other, in straight or curved lines: these plants may be trees, shrubs, bushes, underwood, or flowering herbaceous plants. 568. A _line of plants_ of sufficient extent, and of which the plants are close enough to conceal from view objects placed behind them, is called a _screen_. All masses planted according to my method are composed of lines of plants parallel to each other; in other words, there is between two similar lines an equal distance throughout. But the distance between the first and the second may differ from the distance between the second and the third, and so of the others. The result would be the same if the lines were closed curves, as, for instance, circles or ovals. The lines of plants are the elements of the masses. ARTICLE I. _Of the Lines of Plants called Screens._ 569. When we desire to conceal any object of considerable extent, we have recourse to a _screen of plants_. Whenever the extent of the land will not permit of the planting of several lines, constituting a mass, evergreens, such as thujas, almond-laurels, &c., are those to be preferred, succeeded by the hornbeam, lilac, privet, &c. The most homogeneous screens, that is to say, those which are formed of a single species of plant, are preferable to all others for the object they are intended to fulfil; and to avoid the monotony of a single species, we must have recourse to one which offers varieties. For example, a screen composed of violet and white lilacs, will possess at the same time the advantage of homogeneity for concealing what is behind it, and the advantage of variety of foliage; the leaves of the violet-lilac being of a less yellow-green than those of the white lilac. We may alternate one or more plants of violet-lilac with one plant of white lilac. _Of Lines of Plants considered as Elements of Masses._ 570. 1st. If the plants in the same line are not of the same species, it is essential that they do not differ too much from each other in respect to height. 2nd. Where a line happens to be entirely seen, the same species must be placed alternately. 3rd. We must avoid placing the same species in two neighbouring lines, when we would employ varied masses which are composed of several lines only.