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The facts now given on dimorphic and trimorphic plants are important, because they show us, first, that the physiological test of lessened fertility, both in first crosses and in hybrids, is no safe criterion of specific distinction; secondly, because we may conclude that there is some unknown bond which connects the infertility of illegitimate unions with that of their illegitimate offspring, and we are led to extend the same view to first crosses and hybrids; thirdly, because we find, and this seems to me of especial importance, that two or three forms of the same species may exist and may differ in no respect whatever, either in structure or in constitution, relatively to external conditions, and yet be sterile when united in certain ways.
Girou de Buzareingues crossed three varieties of gourd, which like the maize has separated sexes, and he asserts that their mutual fertilisation is by so much the less easy as their differences are greater. How far these experiments may be trusted, I know not; but the forms experimentised on, are ranked by Sagaret, who mainly founds his classification by the test of infertility, as varieties.
Most of us can remember the school maps of our own youth, showing a vast region marked, vaguely, "The Great American Desert," which was considered hopeless for any human industry, but much of which has since proved as rich as any land anywhere on the globe. Perhaps it was the treeless nature of the vast Plains which carried the first idea of their infertility.
We fully agree with the general tenor of this weighty passage; but forcible as are these arguments, and little as the value of fertility or infertility as a test of species may be, it must not be forgotten that the really important fact, so far as the inquiry into the origin of species goes, is, that there are such things in Nature as groups of animals and of plants, the members of which are incapable of fertile union with those of other groups; and that there are such things as hybrids, which are absolutely sterile when crossed with other hybrids.
But those who are disposed to believe in this doctrine should study the evidence brought forward in its support by M. Broca, its latest and ablest advocate, and compare this evidence with that which the botanists, as represented by a Gaertner, or by a Darwin, think it indispensable to obtain before they will admit the infertility of crosses between two allied kinds of plants.
It was called "a sunny land," and, notwithstanding the infertility of its soil, it was full of picturesque beauty.
But why, in the case of distinct species, the sexual elements should so generally have become more or less modified, leading to their mutual infertility, we do not know; but it seems to stand in some close relation to species having been exposed for long periods of time to nearly uniform conditions of life.
It is at the same time warning and execration, the startled solitary's outburst of uncontrolled rage at the abhorred sight of a fellow-being in his woodland haunt. Small birds were numerous at that spot, as if for them also its wildness and infertility had an attraction.
Every rain brings the light soil down the ravine and lays it like a hand of infertility upon my farm. It had always bothered me, this wastage; and as I looked across my fence I thought to myself: "I must have that hill. I will buy it. I will set the fence farther up. I will plant the slope. It is no age of tonsures either in religion or agriculture."
Those people who profess belief in the inherent superiority of a particular race naturally look upon the tendency towards race-blending as a perverse proclivity, while those who think that all men are potentially equal regard it as a wholesome instinct provided by nature to counteract the feebleness and infertility which cause the dying-out of the race that becomes too pure.
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