Origin of Species Variorum

→ some of the 1872

the 1859 1860 1861 1866 1869

→ The 1872

but that the 1859 1860 1861 1866 1869

→ decreases greatly and suddenly. 1872

decreased. 1859 1860 1861

decreased greatly and suddenly. 1866 1869

↑ 1 blocks not present in 1859 1860 1861 1872; present in 1866 1869

With respect to this decrease, it may first be noticed that, when any deviation in structure or constitution is common to both parents, this is often transmitted in an augmented degree to the offspring; and both sexual elements in hybrid plants are already affected in some degree.

→ With respect to this decrease, it may first be noticed that when any deviation in structure or constitution is common to both parents, 1872

I do not doubt that 1859 1860 1861

→ often transmitted in an augmented degree to the offspring; and both sexual elements in hybrid plants are already affected in some degree. 1872

usually the case, and that the fertility often suddenly decreases in the first few generations. 1859 1860 1861

→ their 1872

in all these experiments the 1859 1860 1861

in nearly all these cases, that the 1866 1869

→ in nearly all these cases by 1872

by 1859 1860 1861 1866 1869

→ many experiments and collected so many 1872

large a body of 1859 1860 1861 1866 1869

→ OMIT 1866 1869 1872

that close interbreeding lessens fertility, and, 1859 1860 1861

→ the vigour and fertility of the offspring, and on the other hand that very close interbreeding lessens their vigour and fertility, 1866 1869 1872

fertility, 1859 1860 1861

→ conclusion. 1872

almost universal belief amongst breeders. 1859 1860 1861 1866 1869

→ if left to themselves, will 1872

will 1859 1860 1861 1866 1869

→ be 1859 1860 1861 1872

have to be 1866 1869

→ pollen from the same flower; and 1872

their own individual pollen; and I am convinced that 1859 1860 1861

their own individual pollen; and 1866 1869

and, on the other hand, that the fertility of pure species is so easily affected by various circumstances, that for all practical purposes it is most difficult to say where perfect fertility ends and sterility begins. I think no better evidence of this can be required than that the two most experienced observers who have ever lived,

namely,

namely

Kölreuter and Gärtner,

should have

....

arrived at diametrically opposite conclusions in regard to →some of the very same

species.

forms.

It is also most instructive to

compare—but

compare—

~~but~~

but

I have not space here to enter on

details—the

details—

~~the~~

the

evidence advanced by our best botanists on the question whether certain doubtful forms should be ranked as species or varieties, with the evidence from fertility adduced by different hybridisers, or by the same

author,

observer

from experiments made during different years. It can thus be shown that neither sterility nor fertility affords any

clear

certain

distinction between species and

varieties;

varieties.

→The evidence from this source graduates away, and is doubtful in the same degree as is the evidence derived from other constitutional and structural differences.

In regard to the sterility of hybrids in successive generations; though Gärtner was enabled to rear some hybrids, carefully guarding them from a cross with either pure parent, for six or seven, and in one case for ten generations, yet he asserts positively that their fertility never

increased,

increases,

but generally

greatly

....

→decreases greatly and suddenly. ↑ →With respect to this decrease, it may first be noticed that when any deviation in structure or constitution is common to both parents, this is →often transmitted in an augmented degree to the offspring; and both sexual elements in hybrid plants are already affected in some degree.

Nevertheless

But

I believe

~~that~~

that

→their fertility has been diminished →in nearly all these cases by an independent cause, namely,

from

by too

close interbreeding. I have

collected

made

so →many experiments and collected so many facts, showing →OMIT on the

other

one

hand,

hand

that an occasional cross with a distinct individual or variety increases →the vigour and fertility of the offspring, and on the other hand that very close interbreeding lessens their vigour and fertility, that I

must admit

cannot doubt

the correctness of this →conclusion. Hybrids are seldom raised by experimentalists in great numbers; and as the parent-species, or other allied hybrids, generally grow in the same garden, the visits of insects must be carefully prevented during the flowering

season:

season;

hence

hybrids

hybrids,

→if left to themselves, will generally →be fertilised during each generation by →pollen from the same flower; and this would

probably be

injurious to their fertility, already lessened by their hybrid origin. I am strengthened in this conviction by a remarkable statement repeatedly made by Gärtner, namely, that if even the less fertile hybrids be artificially

fertilised