Origin of Species Variorum

→ his 1866 1869 1872

the production of the most distinct 1859 1860 1861

→ such varieties not having been exposed for a very long period to uniform conditions of life;—from 1869

not wishing or being able to produce recondite and functional differences in the reproductive system; from 1859 1860 1861

not wishing or being able to produce recondite and functional differences in their reproductive systems; from 1866

such varieties not having been exposed for very long periods to uniform conditions of life;— from 1872

→ we may conclude that fertility does not constitute 1869 1872

and facts, I do not think that the very general fertility of varieties can be proved to be of universal occurrence, or to form 1859 1860

and facts, I do not think that the very general fertility of varieties can be proved either to be of universal occurrence, or to form 1861

and facts, I do not think that the fertility of varieties can be proved either to be of universal occurrence, or to form 1866

→ species when crossed. 1869 1872

species. 1859 1860 1861 1866

→ crossed species may safely be looked at not as 1869

varieties does not seem to me sufficient to overthrow the view which I have taken with respect to the very general, but not invariable, sterility of first crosses and of hybrids, namely, that it is not 1859 1860

varieties, considering how entirely ignorant we are on the causes of both fertility and sterility, does not seem to me sufficient to overthrow the view taken with respect to the very general, but not invariable, sterility of first crosses between species and of their hybrids, namely, that it is not 1861 1866

crossed species may safely be looked at, not as 1872

→ acquirement or endowment, but as 1869 1872

endowment, but is 1859 1860 1861 1866

→ changes of an unknown nature in their sexual elements. 1869 1872

slowly acquired modifications, more especially in the reproductive systems of the forms which are crossed. 1859 1860 1861

modifications, slowly impressed, by unknown means, on the reproductive systems of the parent-forms. 1866

→ compared, 1866 1869

compared, 1859 1860

compared , 1861

compared , 1872

to external

external

characters in →his domestic varieties, and from →such varieties not having been exposed for a very long period to uniform conditions of life;—from these several considerations →we may conclude that fertility does not constitute a fundamental distinction between

them

varieties

and →species when crossed. The general

fertility

sterility

of →crossed species may safely be looked at not as a special →acquirement or endowment, but as incidental on →changes of an unknown nature in their sexual elements.

Hybrids

and

Mongrels

→ compared,

independently

their

fertility .—

fertility .

Independently of the question of fertility, the offspring of species

~~when crossed~~

when crossed

and of varieties when crossed may be compared in several other respects. Gärtner, whose strong wish

was

it was

to draw a

marked

distinct

line

of distinction

....

between species and varieties, could find very

few

few,

and, as it seems to me, quite unimportant differences between the so-called hybrid offspring of species, and the so-called mongrel offspring of varieties. And, on the other hand, they agree most closely in

very

....

many important respects.

I shall here discuss this subject with extreme brevity. The most important distinction is, that in the first generation mongrels are more variable than hybrids; but Gärtner admits that hybrids from species which have long been cultivated are often variable in the first generation; and I have myself seen striking instances of this fact. Gärtner further admits that hybrids between very closely allied species are more variable than those from very distinct species; and this shows that the difference in the degree of variability graduates away. When mongrels and the more fertile hybrids are propagated for several

generations

generations,

an extreme amount of