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Page:Popular Science Monthly Volume 19.djvu/376

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362
THE POPULAR SCIENCE MONTHLY.

plants are not contented simply to leave their seeds on the surface of the soil, but actually sow them in the ground.

Thus in Trifolium subterraneum, one of our rarer English clovers, only a few of the florets become perfect flowers, the others form a rigid, pointed head, which at first is turned upward, and, as their ends are close together, constitute a sort of spike. At first, I say, the flower-heads point upward like those of other clovers, but, as soon as the florets are fertilized, the flower-stalks bend over and grow downward, forcing the flower-head into the ground, an operation much facilitated by the peculiar construction and arrangement of the imperfect florets. The florets are, as Darwin has shown, no mere passive instruments. So soon as the flower-head is in the ground they begin, commencing from the outside, to bend themselves toward the peduncle, the result of which, of course, is to drag the flower-head farther and farther into the ground. In most clovers each floret produces a little pod. This

PSM V19 D376 Vicia amphicarpa.jpg
Fig. 18.—Vicia amphicarpa. a a, ordinary pods; b b, subterranean pods.

would in the present species be useless, or even injurious; many young plants growing in one place would jostle and starve one another. Hence we see another obvious advantage in the fact that only a few florets perfect their seeds.