Origin of Species Variorum

→ is, with reference to 1861 1869 1872

is, on 1859 1860

is with reference to 1866

→ first crossed, and the maximum produced 1869 1872

crossed and 1859 1860 1861 1866

→ parent-species 1859 1860 1866 1869 1872

parent species in 1861

→ serious error here intervene: a plant, 1872

error seems to me 1859 1860 1861 1866 1869

→ OMIT 1872

here introduced: a plant to be 1859 1860 1861

here introduced: a plant, to be 1866 1869

→ OMIT 1866 1869 1872

during several years 1859 1860 1861

→ some forms, such as the common red and blue pimpernels (Anagallis arvensis and cœrulea), which the best botanists rank as 1866 1869 1872

the primrose and cowslip, which we have such good reason to believe to be 1859 1860 1861

→ OMIT 1866 1869 1872

only once or twice succeeded in getting fertile seed; as he 1859 1860 1861

→ OMIT 1866 1869 1872

common red and blue pimpernels (Anagallis arvensis and cœrulea), which the best botanists rank as varieties, 1859 1860 1861

→ we may doubt whether many species are really so sterile, when intercrossed, 1869 1872

together; and 1859 1860 1861

we may doubt whether many other species are really so sterile, when intercrossed, 1866

→ OMIT 1866 1869 1872

came to the same concluson in several other analogous cases; it seems to me that we may well be permitted to doubt whether many other species are really so sterile, when intercrossed, as Gärtner 1859

came to the same conclusion in several other analogous cases; it seems to me that we may well be permitted to doubt whether many other species are really so sterile, when intercrossed, as Gärtner 1860

came to the same conclusion in several other analogous cases, it seems to me that we may well be permitted to doubt whether many other species are really so sterile, when intercrossed, as Gärtner 1861

two cases, has to be considered. The distinction

has probably

probably has

been slurred over, owing to the sterility in both cases being looked on as a special endowment, beyond the province of our reasoning powers.

The fertility of varieties, that is of the forms known or believed to

have

descended from common parents, when

intercrossed,

crossed,

and likewise the fertility of their mongrel offspring, →is, with reference to my theory, of equal importance with the sterility of species; for it seems to make a broad and clear distinction between varieties and species.

Degrees of Sterility .—

First, for the sterility of species when crossed and of their hybrid offspring. It is impossible to study the several memoirs and works of those two conscientious and admirable observers, Kölreuter and Gärtner, who almost devoted their lives to this subject, without being deeply impressed with the high generality of some degree of sterility. Kölreuter makes the rule universal; but then he cuts the knot, for in ten cases in which he found two forms, considered by most authors as distinct species, quite fertile together, he unhesitatingly ranks them as varieties. Gärtner, also, makes the rule equally universal; and he disputes the entire fertility of Kölreuter's ten cases. But in these and in many other cases, Gärtner is obliged carefully to count the seeds, in order to show that there is any degree of sterility. He always compares the maximum number of seeds produced by two species when →first crossed, and the maximum produced by their hybrid offspring, with the average number produced by both pure →parent-species

a state of nature. But

a serious

....

cause

causes

of →serious error here intervene: a plant, to be →OMIT

hybridised

hybridised,

must be castrated, and, what is often more important, must be secluded in order to prevent pollen being brought to it by insects from other plants. Nearly all the plants

experimentised

experimented

on by Gärtner were potted, and

apparently

....

were kept in a chamber in his house. That these processes are often injurious to the fertility of a plant cannot be doubted; for Gärtner gives in his table about a score of cases of plants which he castrated, and artificially fertilised with their own pollen, and (excluding all cases such as the Leguminosæ, in which there is an acknowledged difficulty in the manipulation) half of these twenty plants had their fertility in some degree impaired. Moreover, as Gärtner →OMIT repeatedly crossed →some forms, such as the common red and blue pimpernels (Anagallis arvensis and cœrulea), which the best botanists rank as varieties, and →OMIT found

the

them

→OMIT absolutely

sterile

sterile,

→we may doubt whether many species are really so sterile, when intercrossed, as he →OMIT

believes.

believed.

It is certain, on the one hand, that the sterility of various species when crossed is so different in degree and graduates away so

insensibly,

in- sensibly,