"Let us not underrate the value of a fact; it will one day flower in a truth." The defects in Sprengel's work were, after all, not actual defects. The error lay simply in his interpretation of his carefully noted facts. As Hermann Müller has said, "Sprengel's investigations afford an example of how even work that is rich in acute observation and happy interpretation may remain inoperative if the idea at its foundation is defective." What, then, was the flaw in Sprengel's work? Simply that he had seen but half the "secret" which he claimed to have "discovered." Starting to prove that insects fertilize the flowers, his carefully observed facts only served to demonstrate in many cases the reverse-that insects could not fertilize flowers in the manner he had declared. He was met at every hand, for instance, by floral problems such as are shown at E and F, where the pollen and the stigma in the same flower matured at different periods; and even though he recognized and admitted that the pollen must in many cases be transferred from one flower to another, he failed to divine that such was actually the common vital plan involved. It may readily be imagined that his great work precipitated an intense and prolonged controversy, and incited emulous investigation by the botanists of his time. Though a few of the more advanced of his followers, among them Andrew Knight (1799), Köhlreuter (1811), Herbert (1837), Gärtner (1844), clearly recognized the principle and foreshadowed the later theory of cross-fertilization, it was not until the inspired insight of Darwin, as voiced in his "Origin of Species," contemplated these strange facts and inconsistencies of Sprengel that their full significance and actual value were discovered and demonstrated, and his remarkable book, forgotten for seventy years, at last appreciated for its true worth. Alas for the irony of fate! Under Darwin's interpretation the very "defects" which had rendered Sprengel's work a failure now became the absolute witness of a deeper truth which Sprengel had failed to discern. One more short step and he had reached the goal. But this last step was reserved for the later seer. He took the fatal double problem of Sprengel-as shown at E and F, to express the consummation pictorially-and by the simple drawing of a line, as it were, as indicated between G and H, instantly reconciled all the previous perplexities and inconsistencies, thus demonstrating the fundamental plan involved in floral construction to be not merely "insect fertilization," the fatal postulate assumed by Sprengel, but cross -fertilization-a fact which, singularly enough, the latter's own pages proved without his suspicion.

Thus we see the four successive steps in progressive knowledge, from Grew in 1682, Linnæus, 1735, Sprengel, 1787, to Darwin, 1857-1858, and realize with astonishment that it has taken over one hundred and seventy-five years for humanity to learn this apparently simple lesson, which for untold centuries has been noised abroad on the murmuring wings of every bee in the meadow, and demonstrated in almost every flower.

This infinite field now open before him, Darwin began his investigations, and the whole world knows his triumphs. He has been followed by a host of disciples, to whom his books have come as an inspiration and ennobling impulse. Hildebrand, Delpino, Axell, Lubbock, and, latest and perhaps most conspicuous, Hermann Müller, to whom the American reader is especially referred. "The Fertilization of Flowers," by this most scholarly and indefatigable chronicler, presents the most complete compendium and bibliography of the literature on the subject that have yet appeared. Even to the unscientific reader it will prove full of revelations of this awe-inspiring interassociation and interdependence of the flower and the insect.

Many years ago the grangers of Australia determined to introduce our red clover into that country, the plant not being native there. They imported American seed, and sowed it, with the result of a crop luxuriant in foliage and bloom, but not a seed for future sowing! Why? Because the American bumblebee had not been consulted in the transaction. The clover and the bee are inseparable counterparts, and the plant refuses to become reconciled to the separation. Upon the introduction and naturalization of the American bumblebee, however, the transported clover became reconciled to its new habitat, and now flourishes in fruition as well as bloom.

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