In all those plants that bear the different sexes in different flowers on the same plant, as in the hickory, or even on different plants, as in the willow, there must, of course, be some method arranged for cross-fertilization or they would promptly die out. So general is this cross-fertilization, so much a part of the economy of nature does it appear to be, that we can only think that there must be in the production of this vast horde of the cross-fertilized some advantage. Besides securing greater virility, which almost certainly results from this promiscuity, greater variability is promoted. If virility is the result, the price paid for it is tremendous, for the hindrances to self-fertilization are so many and so effective that most flowers would inevitably die as perfectly pure but ineffectual virgins if that fatality were not prevented. How they are saved from such a sterile fate, how they finally secure a mate by devices that outshine the most bewitching tricks of the daughters of Eve, is one of the most fascinating stories in all the history of the plant world. For, of course, flowers do secure a mate, and they are aided in this enterprise by the most formidable array of helpers, one might almost call them conspirators. The chief of these are insects, thousands of different kinds of which are constant flower visitors. Some of the smaller birds, and even snails, also help flowers to meet their mates. The wind, too, bears pollen through the air to some expectant bride-to-be. And, finally, in the water, by a series of acts the like of which no one could improve for cunning, the cross-fertilization of certain aquatic plants is consummated. It would take a book larger than the present one to give even the briefest account of how these different aids to maternity do their work and how the flower responds to this help. As that is quite out of the question, only some of the best-known examples of cross-fertilization will be given, and these will be grouped according to what agency the flower is indebted for its chance of doing that for which it is created. INSECTS AS FLOWER VISITORS