This section is from the book "The Standard Cyclopedia Of Horticulture Vol2", by L. H. Bailey. See also: Western Garden Book: More than 8,000 Plants - The Right Plants for Your Climate - Tips from Western Garden Experts.
The very strict limitation of range in flower-colors demands careful study if it would be thoroughly understood. Augustin Pyramus de Candolle divided flower-colors into two classes, which he named xanthic (red, scarlet, orange, gold-orange, yellow, and green-yellow), and cyanic (green-blue, blue, ultramarine-violet, violet, purple, and red). Further, he explained, flowers of the yellow (xanthic) series could pass into red or white but never into blue, and those of the blue (cyanic) series could pass into red or white but never into yellow. The theory is correct but it requires both modification and revision. Gold-orange must evidently displace yellow, and ultramarine-violet displace blue as series names; furthermore, the passage into red should not exceed scarlet-red in the xanthic series, or crimson-red in the cyanic series. Pure red logically should be the zero point between the two divisions, and not be included in either unless connected by analogous hues.
Gold-orange and ultramarine-violet are respectively the type-colors of the two series because each occupies a median position with equal influence on either hand. Red, occupying the median position between the two series, should and does exercise an equal influence on both; a casual glance at the chromatic scale demonstrates the fact. Neither the xanthic nor the cyanic series can exclusively claim the respective yellow and blue in absolute purity, for the cogent reason that among flowers yellow is associated with both these divisions, and a true blue scarcely appears at all. Further, if pure red is the zero point between the two series, then the consistent red of the xanthic order is scarlet-red, and that of the cyanic order is crimson-red; a pure red or pure yellow flower, therefore, consistently belongs to either order according to its xanthic or cyanic congeners.
The best proofs of the above statements are to be found among the flowers themselves. Asters belong to the cyanic group, but there is no blue aster. Tropaeo-lums belong to the xanthic group, but there is no pure yellow nasturtium; there are, however, ultramarine-violet asters and gold-yellow nasturtiums. There is a pure yellow, a golden orange, but no white marigold (Tagetes); the species is xanthic. The family Cru-ciferae is cyanic; it includes pure yellow, deeper yellow, and magenta flowers. The genus Hyacinthus is cyanic; it includes no blue flower, but many which are purple, violet, cyanic red, and modified yellow. Viola tricolor is cyanic; it includes a strong yellow along with intense purple and violet-ultramarihe flowers. The genus Zinnia is xanthic, it includes no true yellow flower but many which range through all reds into cyanic crimson. The genus Rosa is cyanic; its flowers range from pure red to magenta-crimson, develop a strong, modified yellow, fuse yellow with crimson, but never approach the xanthic gold-orange. The genus Chrysanthemum is xanthic; its flowers include all yellows, skip pure orange and scarlet, and range from scarlet-red to cyanic red-crimson.
Species belonging to the cyanic group invariably produce white flowers which have an albino origin. Species of the xanthic order produce white flowers which are not albinos but which invariably displace flowers of some strong, pure xanthic hue. For example, geraniums are white, red,.scarlet, and pink, but never gold-orange or golden yellow. Carnations are white, red, and cardinal-red, but never scarlet, or orange. Chrysanthemums are yellow, white, and pink, but never orange or scarlet. Dahlias are scarlet, red, crimson-red, and even pure yellow, but never pure gold-orange, or orange.
It is perfectly evident from the foregoing examples that the range in a given genus, or species, is limited to what may be termed the swing of a pendulum upon the chromatic scale (Fig. 1038). The swing may extend over a quarter of the dial, rarely it does more. If it happens that two colors are developed, like violet and yellow, it will still be found that there is but one pendulum-swing and not two. Violet will be associated with contiguous hues, but yellow will be developed quite alone.
Fig. 1038. The circle of 360° in colors.
This, it is reasonable to believe, is direct evidence of a dual or treble origin of color in a flower group. Yellow cannot be evolved from violet, or vice versa. Necessarily, if white appears in a xanthic group, it must have evolved alone and independent of any color-range in that group. Undoubtedly the range of contiguous colors itself has evolved from a median hue which has spread out, fanlike, in graded variations within strict limits. Naturally, such statements conflict with the old theory that all flowers were originally yellow, but they are not inimical to the idea that the earlier ones might have been yellow, and later ones magenta, violent ultramarine, scarlet, and gold-orange. It is important to keep in mind the fact that a steamboat is not evolved from a locomotive.
It is further evident that yellow belongs quite as little to the xanthic as it does to the cyanic series, or, to put it more strongly, it belongs to neither. Its origin, independent of any "range," was undoubtedly the elimination of blue from chlorophyll. Hence, it is not surprising to find it in some modified form associated with both series, and in the cyanic series isolated. The flora of the northeastern United States is essentially cyanic. Twenty-one per cent is yellow, 21 per cent magenta and 22 per cent white; the remainder is 8 per cent xanthic and 28 per cent cyanic-the last mostly pink and light violet. The record is significant and points directly either to an arrested color development, or to a depauperate color condition in an inclement region; the former seems the more likely. An aggregation of cyanic-flowered plants are found in the north temperate zone, and of xanthic-flowered plants in the torrid zone.
Color results from a play of light upon a surface which rejects or absorbs certain rays. It is a significant fact that the red end of the spectrum comprehends those hues which are produced by the caloric rays of the sun, and the violet end those hues which are produced by the actinic rays. It is not surprising therefore that the coloring of vegetation is intense, and that xanthic flowers predominate under the equator. A separation of cyanic and xanthic flowers follows almost identically the thermal lines which band the great continents of the northern hemisphere, cyanic color prevailing north, and xanthic color south of the line marking 80° F. In a word, xanthic flowers belong to a very warm, and cyanic flowers to a temperate or cold climate. That they should become mixed in a narrow zone between the extremes is only natural; the rule, therefore, is in no way compromised thereby. That yellow, too, should appear in both cyanic and xanthic groups is not at all surprising. In the spectrum it holds a median position between the red and the violet ends; it is neither a hot nor a cold color, and has consequently evolved from its primitive condition as a constituent of the green in chlorophyll under any and all temperatures.
That is the only way to account for its isolation when connected with cyanic groups.
It would appear, then, that magenta, violet, and ultramarines, together with gold-orange, orange, and red, are primitive colors quite as well as yellow and white. In what order they appeared upon the earth in the petals of flowers, it would be difficult to determine, but it is reasonable to think they appeared as original colors, in weak, perhaps, but absolute purity. Otherwise, the remarkable limitation of color-range must be accounted for by a less logical theory. Upset this limitation, and attempts to produce a blue rose, yellow aster, white nasturtium, or green carnation, should prove successful. Recognize the limitation, and the futility of such attempts becomes at once apparent, and the possibility of improving existing "strains" of color is illimitable. At some time or other in the distant past the law of limitations fixed the range of flower-colors; no new law of elasticity has since developed to remove the boundaries and thus aid the floriculturist in his ambition to produce what would prove to be a mere novelty.
See Standards of Color.
F. Schuyler Mathews.