RULE.—_When two lines of vegetation are planted to constitute a mass, in planting the first or exterior line, we must follow the rule indicated above_ (570), _then go on planting the second line, in the same manner as the first, except that the stakes indicating the centre of vegetation must be placed chequer-wise relatively to the centre of vegetation of the first line._ I will cite an example of a plantation of two lines intended to conceal a wall. 1st _Line_. 1. Almond-laurel. 2. Violet-lilac. 3. Laburnum. 4. Violet-lilac. 1_a_. Almond-laurel, &c. 2nd _Line_. 1. Clump of _prunus mahaleb_. 2. _Idem_, &c. The distance between the clumps of the first line is four or five feet. We may plant the first line in _screen_, and the second with trees larger than in the first; we may also plant the second line with roots of _prunus mahaleb_, comprehending between two roots three or five clumps of the same species. _Of Homogeneous Masses._ 571. The _homogeneous mass_ includes only a single species of plant, because the intention of the gardener in forming it, is to produce an effect of _individuality_. In the large French garden, designed by Le Notre, where the trees combine so effectually with the elements established by the architect, to prolong, so to speak, a similar work, the symmetrical plantations are identical, and generally composed of trees of a single species. 572. Although homogeneous masses of trees have a good effect in a large composition, it is not so with those which are composed of a single species, or of a single variety of flower. They almost always present a monotonous aspect, especially if the latter have a definite extent; and if the species of plant of which they are composed is in flower only a part of the year, the defect of monotony will be greatly increased. Homogeneous masses of shrubs or of flowers are only suitable when they are in leaf or in flower during a great portion of the year; as their extent is small, and they serve simply as a bond of union between different parts more or less distant from each other. _Of Heterogeneous or Varied Masses._ 573. I shall distinguish two cases—one where it is a _heterogeneous_ or _varied_ mass, isolated, intended to serve as an individual composed of distinct parts; and the other where it consists of many varied masses, allied together, and separated by paths, at least in some parts. _Isolated Masses._ If each line consists of only a single species, we must arrange the lines according to their size. For example—1. Lilacs. 2. Laburnum. 3. Judas trees. 574. _Heterogeneous or varied masses_ placed together so as to form a whole, are generally separated from each other by glades, or unplanted intervals, but cultivated or sown in grass, or by paths. To make what follows thoroughly understood, I must point out the essential difference that exists between landscape gardening and French (geometrical) gardening.