Page:Popular Science Monthly Volume 22.djvu/692

674 into one, with two midribs still remaining as evidence of their original distinctness.

Next, in the case of the petals, which alternate with the sepals of the calyx, the relation to the stem is exactly reversed; for we have here two petals free and exterior, with one interior petal crowded closely against the axis, thus:

Here, then, the two external petals will be saved, exactly as the one external sepal was saved in the case of the calyx; and these two petals are represented by the very small white lodicules under the outer pale in our existing wheats and grasses. On the other hand, the inner petal, jammed in between the grain and the inner pale (with the stem at its back), has been utterly crushed out of existence, partly because of its very small size, partly because of its functional uselessness, and partly because it had no other part with which to coalesce, and so to save itself as the inner sepals had managed to do. Moreover, it must be remembered that the sepals do still perform a useful service in protecting the young flower before it opens, and in keeping out noxious insects during the kerning or swelling of the grain; whereas the lodicules or rudimentary petals are now apparently quite functionless; and so we may congratulate ourselves that they are there at all, to preserve for us the true ground-plan of the floral architecture in grasses. Indeed, they have not survived by any means in all grasses; among the smaller and more degraded kinds they are often wholly wanting, having been quite crushed out between the calyx and the grain. It is only the larger and more primitive types that still exhibit them in any great perfection. On the other hand, one group of very large exotic grasses, the bamboos, has three regular petals, thus clearly showing the descent of the family as a whole from rush-like ancestors, and also obviously suggesting that the obsolescence of the inner petal in the other grasses is due to their small size and their closely packed minute flowers.

Among the stamens, one-sidedness has not notably established itself, for in wind-fertilized plants they must necessarily hang out freely to the breeze, and therefore they do not get much crowded between the other parts. A few grasses still even retain their double row of stamens, having six to each floret; but most of them have only one whorl of three. In some of the lower and more degraded forms, however, even the stamens have lost their trinary order, and only two now survive. This is the case in our own very degenerate little sweet vernal-grass, the plant which imparts its delicious fragrance to new mown hay. But in the cereals and in most other large species the three stamens still remain in undiminished effectiveness to the present day.