There are some other flowers that hold visiting insects in a trap until cross-fertilization has been completed, and all of them by no means furnish their visitors such a snug little heated chamber as the magnolia. One vine from the eastern United States, known as the Dutchman’s-pipe, or sometimes as the pipevine (Figure 71), is singularly ruthless in this respect. Its flowers are of such evil odor that only carrion-loving insects, such as certain kinds of flies and gnats, ever visit them. The flower is of very peculiar structure, being formed of a hollow tube bent from its stalk first downward, and then upward. The upper part ends at the opening which is provided with a three-lobed lip or doorway. Through this the insects crawl, and they finally reach the bottom of the curved part of the flower. Behind and above them is the entrance through which they have just come. And above them, in the other curved part of the flower, is the stigma. As in the magnolia, this matures several days before the pollen from its surrounding stamens is ripe, so that self-fertilization is never possible. What is now the [Illustration: FIG. 71.--THE DUTCHMAN’S-PIPE A vine producing evil-smelling flowers, which trap insects sometimes for days, thus insuring cross-fertilization.] plight of the insect at the bottom of the upward-pointing tubes, one leading to the organs of reproduction, the other to the exit? By an almost diabolical cunning the inside of this flower is so smooth that no insect can crawl up its slippery sides. It takes some time for the prisoner to find this out, and, in the meantime, it has explored every nook and corner of the flower by flying. In the course of this exploration it reaches and covers the stigma with pollen, for as we shall see presently, it always comes _into_ the flower pollen-laden. Evidently becoming panicky about getting out, the insect then flies with very considerable force in every direction. Toward the true exit it naturally flies the most, and by a refinement of cruelty this is the lighter end of the flower, and therefore the obvious mode of escape for it. But the three lips and the entrance they cover are not flat across the flower, as the cover of a lunch box would normally be, but turned at such an angle as the lunch box would be if set on end. The insect, in flying toward the light, invariably hits the smooth surface just inside the three lips and falls to the bottom of the flower because there is nothing rough enough for it to cling to. Throughout most of the day, and sometimes for several days, the insect will keep up this ceaseless struggle to escape, flying first up one tube and then the other. These frantic efforts would end in exhaustion if kept up too long, and before that happens, but after the impregnated ovules have no further use for the flies, the anthers give forth plentiful supplies of pollen. Of course, the insect can scarcely avoid becoming covered with this, and