Page:Popular Science Monthly Volume 5.djvu/146

134 anther is turned outward away from the stigma. This arrangement will be seen in Fig. 4, which presents a longitudinal section of the flower after the petals have been removed. It is as if you apply powder to the surface of one sheet of paper and mucus to the surface of another, and, intending that the powder should be brought into contact with the mucus, place the two sheets together, surface to surface,

but turn the powdered surface out. What a seeming design, and yet, seemingly, what a fatal blunder! But this is nature as manifested in the iris. Pollen and stigma, so close together, are separated by the blade of the stamen. But for insects which, attracted by the color, light, and search the flower for its nectar, and push, now against an anther and now against a stigma, the iris could never set a seed.

Flowers, as Dr. Gray has said, seem to be made on the principle, "how not to do it." By traps, and pits, and springs, insects are made to do by indirection what it would seem could be better done directly by the flower itself. For many flowers the service can be rendered as well by one nectar-loving insect as another. But in some species the parts are so modified that only a single species of insect, correspondingly modified, can reach the organs of fructification. In the northern part of the United States the yucca (Fig. 5) has never been known to set seeds.

An entomologist has lately discovered a small moth with white head and thorax and wings, and legs of dingy yellow. To this moth he has given the name Pronuba yuccasella—yucca's go between. The structure of this moth will be seen in Fig. 6. In Fig. 7 the larva and the moth are drawn in the natural size. The peculiarity of this moth is, that in the female the basal joint of one of the maxillary palpi (Fig. 6, 5) is modified in a most wonderful manner into a long prehensile