COLORS. The colors of flowers are primarily due to nutrition. The parti-colored spots and streaks leading down into the bottoms of flowers, called 'guides' and 'pathfinders.' invariably lead to the nectaries. and these effects seem directly due to the visits of insects. "The guides," says Henslow, "like obstructing tangles of hair and neetaries, are always exactly where the irritation would be set up, I take to be one result of a more localized flow of nutriment to the posi tions in question. Instead, therefore, of a flower having first painted a petal a golden streak to invite the insect, and to show it the right way of entering, the first insect. visitors thentsel•es induced the flower to do it. and so benefited all future comers." The facts and theories suggested by the colors of flowers are further borne out by the geological history of fossil flowering plants and of those orders of insects containing flower-visiting forms. In the Paleozoic age there were, so far as yet, known, no ill /Werti, III //' any moths, flies, ants, or bees. The first flowering plant, the screw-pine, appeared in the Permian, but its flowers were greenish and inconspicuous. Early in the Mesozoic age more modern plants appeared, and by this time the most primitive beetles, moths, and hymenopterans probably arose, although the traces discovered are very scanty.
But at the opening of the Upper Cretaceous vast forests of deciduous trees clothed the uplands, while in the jungles, in the plains, and in the openings of the forests true flowers abounded, since fossil composite blossoms, like the sun flower, occur in the Upper Cretaceous clays of New Jersey. Now, the remains of moths, butter flies, many flies, ants, and bees abound in the Middle Tertiary, and undoubtedly their forerun ners existed in the Cretaceous, so that we are justified in assuming that flowers and the insects which visit them were nearly simultaneously brought into existence, and from all that has been said it is a reasonable theory to advance that the forms of flower-visiting insects were the result of the presence of flowers, and that flowers have been modified from small greenish forms of inflorescence into the beautiful creations which now deck the fields and adorn our gardens.
BIBLIOGRAPHY. Darwin, Pornis of Powers Bibliography. Darwin, Pornis of Powers (London, 1877) ; Kerner, Flowers and Their l'n bidden Guests (London, 1878) ; IL Midler, The Fertilization of Powers, translation by Thomp son (London, 1883) : Ifenslow. The Origin of Floral Structures, Through Insert and Other Agencies (2d ed.. New York, 1893) ; Coulter, Plant Relations (New York, 1899).