deeper down even than that, since both belong to the same colony at the same period of failing growth, the impulse to fresh effort afforded by such a union would appear to be less; indeed, in some cases it is quite inoperative; whereas, when each comes from a separate plant, not only are the chances of diversity in constitution greater, but the constitutional fillip or stimulus to growth is more distinctly marked. Birth is a result of the union of unlikenesses.
Hence, while among the lowest and least developed flowers self-fertilization (or, to speak more correctly, fertilization of each ovary by its brother-stamens) is very common, among the higher and more specially adapted plants devices for promoting crossfertilization, either by wind or insects, are almost universal. In some instances, indeed, the ovary can not be impregnated by pollen coming from the same flower—the fillip does not seem sufficient to promote growth, and the ovary touched only with pollen of a neighboring stamen remains to the end perfectly sterile. Truly distinct pollen is needed to quicken it. In other cases, though such incapacity does not exist, special arrangements have been made to prevent self-fertilization—the stamens and pistils do not mature together, or else they are so arranged in the blossom that contact of the pollen with the stigma is almost impossible. And in some of the very highest plants of all, the stamen-bearing and ovary-bearing flowers are distributed on totally distinct trees or bushes, thus affording the most perfect known development of the sexual principle—a sort of automatic compulsory exogamy, whereby each blossom must needs intermarry with a member of an entirely different colony.
For the same reason it will now, I hope, at once be clear why the offspring in every case resembles on the whole both parents equally. The various leaves which each rose-tree puts forth are exactly alike, and we don't expect them to be at all otherwise, because they are all similar products of the self-same active and formative energy. However much we may subdivide the parts of a plant, we look forward to finding its manifestations remain unchanged, as in the familiar case of cuttings, grafts, layers, suckers, bulbs, and runners. The different leaves, made of the same ultimate stuff, the new material of the species, resemble one another exactly as two parts of the same lump of clay or putty have similar characters; or exactly as the two halves of the same crystal rebuild their lost parts and renew their original shape alike when immersed in a mass of the same mother-liquid. So, too, we may well believe the undeveloped embryo or unfertilized seed potentially resembles in all things (as far as it goes) the mother-plant; but, as soon as it is fertilized by the pollen from its neighbor, it becomes in every portion of itself part and parcel of two previous
