On any summer day, especially when the sun is shining brightly, we may see bees and butterflies flitting from flower to flower, busy as the proverbial bee. We already know enough about nature’s ways of doing things to be certain that these, and hundreds of other kinds of insects, do not come for nothing, and that the flower must have something to offer. Bees, especially, are thrifty creatures whose business demands exacting and prolonged toil. They would not waste five seconds upon idle flower calling if the blossoms did not yield a rich store. And thousands of flowers do yield the sweetest and richest kinds of stores of nectar or honey, which is, in fact, by the help of insects who alone can extract it, our sole source of honey. Many flowers which produce no nectar do have such plentiful stocks of pollen that the bees come for that alone. In the peony, for instance, over three million pollen grains are produced in each flower, only a minute fraction of which can ever fertilize an ovule. All the rest would be wasted were not pollen in itself a particularly nutritious food for young bees, and consequently much sought after by the careful bee mothers. They are the only insects that feed their young on pollen, or beebread, as it is called by the beekeepers, so that the enormous overproduction of this male fertilizing agent, from the point of view of the flower, is a decided attraction, one might almost call it a trap, to insure constant visitations from bees. For they are perhaps the most useful of all insects in the great game of securing cross-fertilization, as we shall presently see. Many other kinds of adult insects eat pollen directly and so add to the number of insect visitors. No one has ever been able to explain the beautiful coloring of flowers, except that it serves as an attraction for insects and small birds. Like the honey or nectar, it seems to play no real part in the home economy of the flower, to be of not the least use otherwise. While honey and the gorgeous colors of flowers are a delight to man, that would be no sufficient reason for the ability to produce them. Both of these attributes of flowers, as attractions for insect visitors, are, however, so absolutely essential to cross-fertilization that we must think of them as having grown up out of that demand. As we shall see a little later, even the structure of some insects has been modified so that they can reach the nectar or pollen only by automatically doing for the flower what it cannot do itself.