Origin of Species Variorum

→ though they rarely 1866 1869 1872

generally 1859 1860 1861

→ external characters, yet generally differ in fertility 1866 1869 1872

fertility 1859 1860 1861

→ fertility in the hybrid is 1859 1860 1861 1866 1869

the fertility of a hybrid may be 1872

→ cross. 1859 1860 1861 1866 1869

cross; that the fertility of hybrids is not related to the degree in which they resemble in external appearance either parent; and lastly, 1872

→ hybrids 1859 1860 1861 1866 1869

making a first cross between any two species 1872

→ related to the degree in which they resemble in external appearance either parent. 1859 1860 1861 1866 1869

always governed by their systematic affinity or degree of resemblance to each other. 1872

one species having first been used as the father and then as the mother, →though they rarely differ in →external characters, yet generally differ in fertility in a small, and occasionally in a high degree.

Several other singular rules could be given from Gärtner: for instance, some species have a remarkable power of crossing with other species; other species of the same genus have a remarkable power of impressing their likeness on their hybrid offspring; but these two powers do not at all necessarily go together. There are certain hybrids

which

which,

instead of having, as is usual, an intermediate character between their two parents, always closely resemble one of them; and such hybrids, though externally so like one of their pure parent-species, are with rare exceptions extremely sterile. So again amongst hybrids which are usually intermediate in structure between their parents, exceptional and abnormal individuals sometimes are born, which closely resemble one of their pure parents; and these hybrids are almost always utterly sterile, even when the other hybrids raised from seed from the same capsule have a considerable degree of fertility. These facts show how completely →fertility in the hybrid is independent of its external resemblance to either pure parent.

Considering the several rules now given, which govern the fertility of first crosses and of hybrids, we see that when forms, which must be considered as good and distinct species, are united, their fertility graduates from zero to perfect fertility, or even to fertility under certain conditions in

excess;

excess.

that

That

their fertility, besides being eminently susceptible to favourable and unfavourable conditions, is innately

variable;

variable.

that

That

it is by no means always the same in degree in the first cross and in the hybrids produced from this →cross.

that

That

the

facility

fertility

of →hybrids is not →related to the degree in which they resemble in external appearance either parent.