Popular Science Monthly/Volume 55/July 1899/The Colors of Flowers

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MUCH might be said, from an artistic and poetic point of view, concerning the colors of flowers. It is in the corolla that they reveal themselves in their most minute delicacy. The tints so widely diffused among animals, even those of butterflies, are coarse as compared with them, and the painter's palette is powerless to reproduce them. They run through the whole gamut of the solar spectrum, even to its most minute details. Some naturalists have striven to establish a classification of them, and it will be convenient to be acquainted with their efforts, though they are not decisive and are somewhat artificial, like all classifications. We give one of the most ingenious of them:

Cyanic series. Greenish-blue. Yellow-green Xanthic series.
Blue. Yellow.
Blue-violet. Yellow-orange.
Violet. Orange.
Violet-red. Orange-red.

The type of the cyanic series is blue, and that of the xanthic series yellow. The first is sometimes denominated the deoxidized series, and the second the oxidized, but these designations have hardly solid enough foundations to be preserved. De Candolle, who publishes the table in his Vegetable Physiology, appends some interesting remarks to it.

It will be noticed by the inspection of the table that nearly all the flowers susceptible of changes of color, as a rule, simply go up or down the scale of shades of the series to which they belong. Thus, in the xanthic series the flowers of the Nyctago jalapa may be yellow, yellow-orange, or red; those of Rosa eglantina yellow-orange or orange-red; those of nasturtium from yellow to orange; the flowers of Ranunculus asiaticus present all the colors of red up to green; those of the Hieracium staticefolium, and of some other yellow Chicoraceæ and of some Leguminosæ like the lotus, become greenish-yellow when dried, etc. In the cyanic series the flowers of many Boraginaceæ, especially of Lithospermum purpureo-œeruleum, vary from blue to violet-red; those of hortensia from rose to blue; the ligulate flowers of the asters from blue to red or violet; those of the hyacinths from blue to red, etc.

There are, however, a few apparent exceptions to this rule. Thus, although the hyacinths usually vary only in the blues, reds, or white, yellowish varieties, indicating an approach to the xanthic series, are sometimes found in gardens. The auricula, which is originally yellow, passes to reddish-brown, to green, and to a sort of violet, but never reaches pure blue; and single petals occasionally give suggestions of both series in distinct parts of their surfaces.

Some surprise may be felt that white does not figure in De Candolle's table. This is because an absolutely white color does not seem to exist in any flower. The fact may be shown by placing some flowers supposed to be of the purest white, like the lily, the white campanula, or the wood anemone, on a leaf of clear white paper. It will be found that the white of the corolla is really washed with yellow, blue, or orange, according to what flower is taken. If the tint does not appear distinct, infusions of the corollas in alcohol will present tones unmistakably yellow or red, etc. White flowers are therefore flowers with tints appertaining to one of De Candolle's series, but albinized, as if they were etiolated. A small number of flowers begin white, and are subsequently colored under the action of light. The Cheiranthus chameleo passes from white to citron-yellow and a slightly violet-red; the Ænothera tetraptera, at first white, becomes rose and then almost red; the petals of the Indian tamarind are white the first day and yellow the second; and the corolla of the Cobea scandens comes out greenish-white and turns to violet the second day. The most remarkable plant in this respect is Hibiscus mutabilis, which Rumph calls the hourly flower, because it starts white, turns flesh-color toward noon, and becomes red at sunset.

In his recent work on Plants and their Cosmic Media, M. Costantin has some remarks concerning the precocity of various races and the tint of their flowers. Hoffmann made observations on this point for several years. He remarked, as the result of eight years' observation, that the common lilac with white flowers blooms on an average six days earlier than the normal form with purple flowers. This might be a curious anomaly with no bearing, but the more we advance in the study of Nature the more we perceive that all phenomena, even the most insignificant, deserve to be examined. Similar results have been observed in varieties of radish (Raphanus raphanistrum) and of saffron (Crocus vernus); in the former the white flowers expand on an average of sixteen days earlier than the yellow ones (twelve years of observation), and in the latter plant the difference is four days.

These changes of tint sometimes appear to depend on the temperature. Thus, the white lilac was obtained by horticulturists under the influence of a temperature of between 30° and 35° C. We can not, however, affirm that spontaneous races with white flowers originated in the same way as the white lilac. It will be enough to point out a few facts that may contribute to the guidance of persons who are seeking to learn the origin of these colored varieties. The Papava alpinum has a very stable variety with yellow flowers, which, according to Focke, has been observed in the polar regions, while the white varieties have been seen in Switzerland. The cultivation of the same species at Giessen, Germany, has made it possible to obtain specimens with white flowers by metamorphosis from specimens with yellow flowers, but it is impossible to say whether or not heat is the agent that produces the changes in these cases. The experiments of MM. Schübela and Bonnier have shown that flowers become darker without changing their color in high regions and in those near the pole; but this phenomenon is one of light and not of color. Be their origin what it may, these white and colored forms have remarkable fixedness.

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[1] 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 flower's 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.

  1. Manuel de l'amateur des jardins.