It will be observed that black does not figure in the table of the classification of colors given above. Absolute black, in fact, does not exist in any flower. If some parts appear black, it is only because their tint is excessively dark. The black of the petals of Pelargonium triste and of the bean is yellow, and that of the Orchis nigra is a brown. Apparent blacks are, moreover, extremely rare.
The gamut of the reds is much more varied than that of other colors. The reds of the xanthic series are generally more lively-hued, carnation or flame-colored; those of the cyanic series present tints more nearly approaching violet. These two reds may furthermore give rose-colors, but a little skill will divine their origin. The rose of the hydrangea inclines to blue, while that of the rose tends rather toward yellow. Blue colors are the most variable, and readily pass to violet and red, but most frequently to white. The most tenacious hues are those of yellow, and we might affirm that the bright and glistening yellow of the buttercup may be said never to change. The paler yellows change more easily, but rarely pass to anything but white. Green flowers, not being readily distinguished from the foliage around them, need not be specially mentioned. They are believed to be much rarer than they really are.
Horticulturists are able, by cultivation, selection, and hybridization, to cause the colors of flowers to vary in considerable proportions. Not much is known of the laws of these variations, chiefly because gardeners who might tell botanists of them if they would have not the scientific spirit. We cite here what MM. Decaisne and Naudin[7] say respecting the variations of the color of flowers:
"Change in this respect is effected in two ways: sometimes there is a simple discoloration, drawing the red, yellow, or blue tints of the corolla toward a more or less pure white; sometimes there is a radical substitution of one color for another. Flowers in which red or blue are the dominant tints are most subject to turn white, but the change may also be observed on some flowers that are naturally yellow, such as the disk of the daisy, the dahlia, and the chrysanthemum when those flowers suffer ligular transformation. Nothing, on the other hand, is more common in our gardens than white varieties of pink or of red roses, lilac, scarlet runners, larkspur, purple digitalis, Canterbury bells, etc.—in fact, nearly all plants with lilac, rose, red, purple, blue, or violet flowers. There are some flowers, however, in these categories the coloration of which is very persistent, and rarely fades perceptibly—as may be seen in the purple petunias, the hue of which does not lose its vivacity even when it is crossed with the white variety.
"The radical substitution of one color for another, whether over the whole corolla or only on some of its parts, in the form of spots, stripes, or variegations, is also of frequent occurrence, and is one of the sorts of modifications which horticulturists have used with great advantage. A considerable number of 'fancy' plants derive almost all their importance from the facility with which the liveliest colors replace one another, blend, and intermix in a thousand ways and in relative proportions of which nothing is fixed, so that we can not find in these collections, when they are well chosen, two plants out of a hundred that are exactly alike in the tone and distribution of their colors. These multicolored varieties, all the offspring of cultivation, are generally perpetuated true by cuttings, while the seedlings compensate for the uncertainty of what they will produce by the certainty that they will give rise to new combinations of colors. This is not the case with single-colored varieties, which, unless they are crossed with others, tend to perpetuate themselves through their seedlings. The yellow, white, and purple varieties of the four-o'clock, for example, when they are pure, reproduce themselves constantly; when crossed with one another they give rise to intermediately colored flowers, and more frequently to variegated ones."
Mr. Hughes Gibb observed, in the mild winter of 1897-'98, that flowers blooming out of season were liable not to have the same color as regularly blooming ones.
The cactus dahlia, usually red, has put out flowers almost orange and with exterior florets sometimes nearly yellow. On the other hand, these dahlias have often shown a marked tendency to return to the simpler form.
A species of nasturtium, habitually of a bright scarlet-red, has given in the cold frame late flowers of a bright yellow, a red band near the center of the petals remaining the only vestige of the normal color. In both cases the change of color began on the edges of the petals. The flower of the myosotis, normally bright blue, has become almost clear rose, without the slightest trace of blue; and a pure blue phlox has shown a tendency toward greenish-yellow.—Translated for the Popular Science Monthly from La Nature.