580. _After tracing the lines of plantations, and putting in the stakes to mark out the centre of the holes to be dug, we must draw upon grey paper lines representing those of the masses we intend to plant, taking as many equidistant points as there are stakes in the corresponding lines of plantation; we then fasten on these points wafers, or little circles of paper, of the colour of the flowers or the foliage of the plants, according to the desired effect._ By this means we can judge of the harmony of the colours of flowers with the different hues of green composing the mass, and thus rectify any defect in the plan before we begin to plant. The principles on which the preceding rules are founded are those of height, form, variety, facility of development, and distinctness of view. Harmonious arrangement, with reference to these points, not being so exclusively the object of this work as the subject of colour, must be passed with this indication. _Contrast of Colours._ 581. This principle, regarded generally, is included in the preceding, since a difference in colour will render plants distinct which have numerous analogies; but viewed specially, it produces among perfectly dissimilar plants, effects which can only be obtained from colour; and it is then that the principle of contrast is to be taken into consideration. In the application of the law of contrast to the arrangement of flowers, we must never forget the difference between an assemblage forming a line of plants, and an assemblage of flowers belonging to plants of various heights, standing on different planes, so as to produce the effect of a picture. I have alluded to this before (551); for in a linear arrangement, for example, there is nothing more unpleasant than the blue flowers of the German iris, associated with the light violet of the lilac. But if we add to this association large tufts of _alyssum saxatile_, Persian iris, and red tulips, so that the golden yellow, white, and deep red, appear on one plane, and the deep blue and the light violets on a more distant plane, we shall obtain general effects of a most agreeable kind. _Repetition._ 582. When a line of plants exhibits the repetition of the same species, and presents them regularly at the same intervals, an effect is produced which, although very agreeable, is but little appreciated—for it is very rarely met with in gardens. It is especially the repetition of a similar arrangement of colours that is agreeable, and which recommends the observance of this principle.