Origin of Species Variorum

Comparison with 1869

find that the seedlings were miserably dwarfed and utterly sterile, and that they behaved in all other respects like ordinary hybrids. He might then maintain that he had actually proved, in accordance with the common view, that his two varieties were as good and as distinct species as any in the world; but he would be completely mistaken.

The facts now given on dimorphic and trimorphic plants are of importance, because they show us, firstly, that the physiological test of lessened fertility, both in first crosses and in hybrids, is no safe criterion of specific distinction; secondly, because we are thus led to infer, as previously remarked, that there must be some unknown law or bond connecting the infertility both of illegitimate unions and of first crosses, with the infertility of their illegitimate and hybrid offspring; thirdly, because we find, and this seems to me of especial im- portance, that two or three forms of the same species may exist and may differ in no respect, except in their reproductive organs, and yet be sterile when united in certain ways. With, dimorphic plants, the unions between the two distinct forms are alone quite fertile, and produce quite fertile offspring, whilst unions between individuals belonging to the same form are more or less sterile; so that the result is exactly the reverse of what occurs with distinct species. With dimorphic plants the resultant sterility is quite independent of any difference in general structure or constitution, for it arises from the union of individuals belonging not only to the same species, but to the same form. It must, therefore, depend on the nature of the sexual elements, which are so adapted to each other, that the male and female elements occurring in the same form do not suit each other, whilst those occurring in the two distinct forms are mutually suited to each other. From these considerations, it seems probable that the sterility of distinct species when crossed, and of their hybrid progeny, depends exclusively on the nature of their sexual elements, and not on any general difference in structure or constitution. ↑ ↑ ↑ We are indeed led to his same conclusion from considering reciprocal crosses between the same two species, in which the male of one cannot be united, or can be united with great difficulty, with the female of the other species, whilst the converse cross can be effected with perfect facility; for this difference in the facility of making reciprocal crosses and in the fertility of their offspring must be attributed either to the male or to the female element in the first species having been differentiated, with reference to the .. sexual elements of the second species in a higher degree than in the converse case. That excellent observer, Gärtner, likewise came to this same conclusion, namely, that species when crossed are sterile owing to differences confined to their reproductive systems. ↑

Fertility of Varieties when Crossed, and of their Mongrel Offspring .

It may be urged, as a most forcible argu- ment, that there must be some essential distinction between species and varieties, and that there must be some error in all the foregoing remarks, inasmuch as varieties, however much they may differ

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. ↑ For we must remember that it is the union of the sexual elements of individuals of the same form, for instance, of two long-styled forms, which results in sterility; whilst it is the union of the sexual elements proper to two distinct forms which is fertile. Hence the case appears at first sight exactly the reverse of what occurs, in the ordinary unions of the individuals of the same species and with crosses between distinct species. It is, however, doubtful whether this is really so; but I will not enlarge on this obscure subject. ↑ We may, however, infer as probable from the consideration of dimorphic and trimorphic plants, that the sterility of distinct species when crossed and of their hybrid progeny, depends exclusively on the nature of their sexual elements, and not on any difference in their structure or general constitution. We are also led to this same conclusion by considering reciprocal crosses, ... in which the male of one species cannot be united, or can be united with great difficulty, with the female of a second species, whilst the converse cross can be effected with perfect facility. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. That excellent observer, Gärtner, likewise concluded that species when crossed are sterile owing to differences confined to their reproductive systems. ↑

Fertility of Varieties when Crossed , and of their Mongrel Offspring , not universal .

It may be urged, as an overwhelming argument, that there must be some essential distinction between species and varieties, ... inasmuch as the latter, however much they may differ