Repetition of the same arrangement of plants of various kinds, and of course distinct to view, contributes greatly to prolong the extent either of an alley or of a mass; a similar general effect repeated a certain number of times becomes a standard, by means of which the eye judges the space to be greater than if it were bordered with individuals of the same species or variety equal in number to the former. This effect is carried to the utmost extent when the arrangement is composed of a certain number of tufts—five, for instance—placed between two trees, which rise above them, but not too high. Repetition and distinctness of view concur in producing an agreeable effect. 583. _Variety_, like every other principle, should never be carried too far, and it is a great mistake to suppose that plantations made without design, and which thus it might seem must be extremely diversified, produce in this respect more effect than those which have been arranged according to the principles of distinct view, contrast, and repetition. Whenever objects must have a certain superficial extent, we gain nothing by multiplying varieties of them. Thus, the repetition of an arrangement of three colours, including white or black, will generally be more agreeable than that of an arrangement of five colours. Diversity of colours, pushed to the extreme, can only be permitted in a continuous border, or a bed of different varieties of the same species of flowers, as a border of larkspur, china aster, or anemones; but, for flowering shrubs, we shall gain everything by not indefinitely multiplying their colour, in a view which the eye can embrace at once. And as with colours so with forms, which must not be too diversified in the same arrangement. _Symmetry._ 584. We should deceive ourselves very much if we supposed the principle of symmetry to be excluded from landscape gardening. But, in order to perceive it or to put in practice, it is necessary to distinguish the _symmetry of similar parts_, and _the symmetry of parts merely corresponding_. The former is that of two equal parts of one whole, as the two halves of a circle, of a square, of an equilateral or isosoceles triangle, &c.; while _Symmetry of parts merely corresponding_, is that of two parts of the same whole, which, without being equal, have the same form, or nearly so; such are the two triangular parts of the Mass 3, Plate 18. Or, that of two separate parts, more or less analogous in form, extent, or nature, which have a correspondence of position relatively to an intermediate object. Or, that of two masses or groups of trees, or of a mass and a group of trees which are presented, the one to the left, the other to the right. _General Harmony._