A more remarkable case of leaving one final chance for self-fertilization is the gas plant. It exhales such a strong and peculiar odor that only certain kinds of insects will visit it. In fact, the odor is so strong and is so heavily charged that a lighted match held near it has been known to slightly ignite--hence the plant’s name. The flower bears a low, squat stigma, profusely covered with honey, which is perfectly accessible to any insect visitor. It has ten stamens, which at first are quite out of the way of insects, two being folded back in each of the five yellow petals. First one stamen begins moving gently from the shelter of its petal, and the anther, pollen-coated, hovers over the stigma, which would inevitably lead to self-fertilization if the stigma were only ready. It never is, and, as though realizing this, the stamen gently moves back out of the way, still, in most cases, retaining some of its pollen. Then another tries and, again, as though realizing the futility of impregnating the unreceptive stigma, it also moves back. So it goes with all the other eight stamens, each of which moves gently out over the stigma, and gently back again, all of them failing to fertilize the laggard stigma. But there has been during all this time a constant procession of insects coming for the honey, and never for a moment have the stamens been off guard, so that each visitor goes off with at least some pollen clinging to it. Finally the stigma, after all the faithful ten are folded back among the petals, comes into its period, and is cross-fertilized by the insects which come from other flowers laden with pollen, as we now know. But if, by one of those accidents of nature, such as bad weather or what not, no insect ever does come, what then is to be the fate of the stigma? Has it staked all only to lose out in the end? It would almost seem that to ignore the steady attentions of the willing ten might make barren sterility a fitting punishment. But, in spite of what has happened, the stamens come to the rescue, if all insects fail, and this time, in a body, they rise up and shed upon the stigma from the half-withered anthers their few remaining pollen grains. There could be no finer example of having an anchor to windward. One of the largest families of flowering plants is the pea family (Figure 72), with over five thousand members, practically all of which rely on bees for cross-fertilization. In some kinds, where bees occasionally fail them, the flowers wither without self-fertilization and, of course, no seed are then produced. In such a large family of plants there are [Illustration: FIG. 72.--THE EVERLASTING OR PERENNIAL PEA A member of the Papilionaceæ or pea family which rely almost entirely on bees for fertilization.]