Colors of flowers, we may believe, were evolved somewhat in this way: A flower, hitherto white or green, showed by chance a bit of red or yellow, blue or pink, perhaps only a streak or dot. Insects were attracted to that flower, and it was pollinated, while others lacking the color may have been neglected. The tendency of both plants and animals to reproduce marked traits of their parents is well known. The young plant springing from the marked flower would probably reproduce the color rather more strongly, and its offspring more strongly still. In time, perhaps after many generations, a perfectly colored flower would be the result.
We therefore judge that those flowers which have evolved color are high in rank. By the rank of a plant is meant the place it holds in the ascending series from simplest and lowest to the most complex, the most highly organized, and the most successful in securing its own dissemination and propagation.
Flowerless plants, the algae, mosses, and ferns, appeared first on the earth. These were succeeded by "wind lovers," flowers like those of pines and hemlocks, which are pollinated by the wind. The wind blows impartially, caring not at all for the fair spread of the lily bell or the soft scent of the violet. No color has, therefore, appeared in flowers which are pollinated by the wind.
"Insect lovers" alone are colored and fragrant. Sometimes dull flowers are surrounded by red or yellow bracts, as in the painted cup (Castilleja coccinca). Night-blooming flowers, adapted to night-flying moths, sometimes keep their petals shut in the daytime; for the right insect is wanted by a flower. Insects too large or too slim, or in any way unsuited to the shape of the flower, do not make good pollen-carriers, and the methods for keeping them away make an interesting chapter. Flowers adapted to flies often evolve fetid odors such as flies like. Bees generally avoid the ill-odored flowers, and turn to the honeysuckle or clown-blossom.
We may, then, think of bright colors and odors of flowers as banners hung out to inform the insect army that the feast is ready. Since most flowers have not yet attained to their highest condition, white and greenish colors are predominant, while next follow yellows, pinks, blues, and purples. There are few really red blossoms. Dark crimson, magenta, and crimson purple are generally counted as red. A thousand years hence, when evolution has made greater progress among the plants, a white flower may be rare.
The influence of surroundings is especially noticeable in the plant world. A plant born to wet soil will not flourish in dry. One adapted to open fields will not bury itself in the shade of deep woods. If it is transplanted to new environments, it may vary its normal type in the endeavor to adapt itself to its new dwelling-place. For this reason, if the soil be changed, as when marshes are drained or fields cultivated, new plants will spring up. Weeds follow the farmer's plow. When the forest disappears, the forest flora will also go. Build a road and see the typical roadside plants spring up along its borders. Certain "fireweeds" cover burnt-over districts as if by magic. Whence come the new plants? Do their seeds always lie in the soil waiting for favorable conditions? The "alternation of crops" which farmers find so useful to their soil and harvests may have its suggestive prototype in nature.
The season for blossoming remains unchanged for every plant, forming a never-failing flower calendar. Thoreau says that if he were waked up from a long winter's nap and placed in the woods or fields, by seeing what flowers were in bloom around him he could tell almost the day of the month. Not more surely does the first robin announce the coming of spring than do the bloodroot and hepatica peeping from under the dead leaves of the woods. The spring flowers fade and are succeeded by those that like the hot sun of July and August. Asters and hawkweeds tell of the coming of autumn, the end of the flower season, and the approach of winter.