Page:Popular Science Monthly Volume 22.djvu/691

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THE PEDIGREE OF WHEAT.

rical, for the outer one is simple and convex, while the inner one is apparently double, being made up of two pieces rolled into one, and still possessing two green midribs, which show distinctly like ribs on its flat outer surface. Here, it will immediately be apparent, the traces of the original trinary arrangement are very slight indeed.

But when we come to inquire into the rationale and genesis of these curiously one sided flowers, it is not difficult to see that they have been ultimately derived from trinary blossoms of the rush-like type. The first and most marked divergence from that type, for which the analogy of the sedges has already prepared us, is the reduction of the ovary to a single one-seeded cell, whose ripe, fruity form is known as a grain. At one time, we may feel pretty sure, there must have existed a group of nascent grasses, which only differed from the wood-rush genus in having a single-celled ovary instead of a three celled pistil with one seed in each cell; and even the ovary of this primitive grass must have retained one mark of its trinary origin in its possession of three styles to its one grain, thus pointing back (as most sedges still do) to its earlier rush-like origin. That hypothetical form must have had three sepals, three petals, six stamens, and one three-styled ovary. But the peculiar shape of modern grass-flowers is clearly due to their very spiky arrangement along the edge of the axis. In the wood-rushes and the sedges, we see some approach to this condition; but in the grasses, the crowding is far more marked, and the one-sidedness has accordingly become far more conspicuous. Suppose we begin to crowd a number of wind-fertilized lily-like flowers along an axis in this manner, taking care that the stamens and the sensitive feathery styles are always turned outward to catch the breeze (for otherwise they will die out at once), what sort of result shall we finally get?

In the first place, the calyx, consisting of three pieces, will stand toward the crowded stem or axis in such a fashion that one piece will be free and exterior, while two pieces will be interior and next the stem, thus:

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Now, the effect of constant crushing in this direction will be that the two inner calyx-pieces will be slowly dwarfed, and will tend to coalesce with one another; and this is what has actually happened with the inner pale of wheat and of other grasses, though the midribs of the two originally separate pieces still show on the compound pale, like dark-green lines down its center. Thus, in the fully developed grasses, in place of a trinary calyx, we get two chaffy scales or pales, the outer one representing a single sepal, and the inner one, which has been dwarfed by pressure against the stem, representing two sepals rolled