These are but a dozen of the millions of similar challenges, riddles, puzzles, which the commonest flowers of field and garden present to us; and yet we claim to "know" our nasturtium, our pink, our monk's-hood larkspur, our daisy, and violet! No; we must be _more_ than "botanists" before we can hope to understand the flowers, with their endless, infinite variety of form, color, and fragrance. It was not until the flowers were studied in connection with the insects which visit them that the true secret of these puzzling features became suspected. We all know, or should know, that the anther in flowers secretes and releases the pollen. For years even the utility of this pollen was a mystery. Not until the year 1682 was its purpose guessed, when Nehemias Grew, an English botanist, discovered that unless its grains reached the stigma in the flower no seed would be produced (Diagram A). But the people refused to believe this, and it was not until fifty years later that Grew's statement was fully accepted, and then only because the great Linnæus assured the world that it _was_ true. But about fifty years later another botanist in Germany, Sprengel, made the discovery that the flower could not be fertilized as these botanists had claimed, that in many blossoms the pollen could not fall on the stigma. [Illustration: A] [Illustration: B] Sprengel knew that this pollen must reach the stigma, but showed that in most flowers it could not do so by _itself_. He saw that insects were always working in the flowers, and that their hairy bodies were generally covered with pollen, and in this way pollen grains _were_ continually carried to the stigma, as they could easily be in these two blossoms shown at Diagram B. Sprengel then announced to the world his theory--the dawn of discovery, the beginning of the solution of all these floral riddles. The _insect_ explained it all. The bright colors and fragrance were intended to attract him, and the nectar to reward him, and while thus sipping he conveyed the pollen to the stigma and fertilized the flower. [Illustration: C] [Illustration: D] But now Sprengel himself was met with most discouraging opposition to his theory, showing that he had guessed but half the secret after all. Flowers by the hundreds were brought to his notice, like that shown in Diagram C, in which the insect could _not_ transfer the pollen from anther to stigma, as the stigma is closed when the pollen is ripe, and like that in Diagram D, which does not open until the pollen is shed. For seventy years this astonishing fact puzzled the world, and was at last solved by the great Darwin, who showed that nearly all flowers shun their own pollen, and are so constructed, by thousands of singular devices, that the _insect_ shall bring to each the _pollen of another flower_ of the same species, and thus effect what is known as _cross-fertilization_.