While on this subject we may say a few words on the arrangement of colours, as on that alone depends the success of the system of massing flowering and foliage plants. Though not of so much importance in the mixed border, it should be one of the first considerations.

It is necessary to bear in mind that there are only three simple or primary colours, from which all the others are derived, namely, red, yellow, and blue; and that their complete fusion in certain determined proportions produces a sensation of white to the eye. These colours combined in pairs give birth to the composite colours. Orange, to wit, is the result of the union of red and yellow, green comes from the blending of yellow and blue, and violet is a combination of blue and red. The tint of these mixed colours varies according to the relative proportion, of the two elements which enter into its composition; and as there is no limit to the variations of the proportions themselves, the result is an infinite number of intermediate shades between the two composing colours. A complementary colour is that which when added to a combination of colours, or a simple colour, will reconstitute the triad of elementary colours. Thus, green - composed of blue and yellow - is the complementary of red; violet - proceeding from red and blue - is the complementary of yellow; orange - composed of red and yellow - is the complementary of blue; and reciprocally, blue, yellow, and red are complementary to orange, violet, and green. The fusion of a colour with its complementary would naturally produce white. Black is merely the absence, or total extinction of the three elementary colours.

The association of these colours and their numerous shades in twos or threes, or in a greater number, produce a very-different effect upon the eye, according to the combinations adopted. There are certain tints that mutually set off each other by approximation, and are pleasing to the eye; and there are others which lose by association, producing a very poor effect, and are even unpleasant and offensive to the eye. In the arrangement of colours we cannot choose a better guide than the eminent Professor Chevreuil, who has deeply studied the subject as applied to art, dyeing of fabrics, and the dispo-stion of flowers in a parterre. We give the substance of the essential parts of his instructions.

1. The three simple colours, blue, red, and yellow, when pure, or nearly pure, contrast agreeably together; but in close contiguity each of them absorbs, as it were, something of the shade which would result from a proper combination with the complementary colours of its neighbours. For instance, red by the side of yellow assumes a slight tinge of violet, which is the complementary of yellow, and the yellow a shade of green, which is the complementary of red.

2. The colours complementary to one another contrast advantageously. This is sufficiently evident by the approximation of yellow and violet - composed of red and blue; red and green - composed of yellow and blue; or blue and orange - composed of red and yellow.

3. The binary association of composite colours will also produce pleasing results, because in each group all three of the elementary colours will be found reunited. That the contrasts will be strong and effective maybe judged by bringing together violet (red and blue), and orange (red and yellow), or the former with green (yellow and blue).

4. But the results are poor or bad when simple colours are associated with mixed colours into whose composition they enter, as in this case only two of the primary colours are represented. Hence red contrasts badly with orange - yellow and red, and with violet - red and blue; blue with violet-red and blue, or with green - blue and yellow. Yet if the simple colour form but a small proportion of the mixed colour with which it is associated, the contrast will be sufficiently strong to please the eye. Thus a lively blue produces a good effect by the side of a bright or yellowish green, and bright yellow by the side of a deep green - in which the blue element predominates. But these two cases, as will be seen, come within the preceding rules, which show that, in a general sense, contrasts are agreeable in the same proportion as they are decided.

5. All colours, simple or compound, are brightened by the vicinity of white, and moreover, contrast with it in a most agreeable manner. White has the additional advantage of improving bad combinations, by being placed between the colours that do not look well together, as, for instance, between red and orange, red and violet, or violet and blue, etc. Hence, this colour, so freely lavished in nature, plays an important role in decorative culture.

6. With the exception of white, all colours are weakened by the neighbourhood of black, which deprives them to a certain extent of their brilliancy. Dull or deep tints suffer especially when associated with black - resulting, of course, from the feebleness of the contrasts. But as black, broadly speaking, does not exist in the Vegetable Kingdom,1 such contrasts could not be effected, except between the plants and the soil, and then the latter is never truly black. In the absence of this colour it is replaced to a certain degree by the dull purple foliage of such plants as Perilla Nankinensis, or by the very deep purple-violet flowers of the Sweet Scabious, some Dahlias and Hollyhocks.

1 The black spot on the flower of the Horse Bean (Faba vulgaris) is perhaps the only instance of pure black in flowers.

The combinations of colours in the flower-garden are com-monly binary or ternary, rarely quaternary, unless the green of the foliage be considered as taking rank in these combinations.