Origin of Species Variorum

→ Chapter . 1866 1869

Chapter .— 1859 1861

Chapter — . 1860

Chapter . 1872

→ arrived at 1869 1872

ever lived, have come to 1859 1860 1861 1866

→ to the action of 1869 1872

of 1859 1860 1861 1866

→ differences, generally of an unknown nature, 1869 1872

generally unknown differences 1859 1860 1861 1866

child to its parents are the same, whether the two parents differ

much

little

much

from each other,

namely,

namely

in the union of individuals of the same variety, or of different varieties, or of distinct species.

Laying aside

Independently of

the question of fertility and sterility, in all other respects there seems to be a general and close similarity in the offspring of crossed species, and of crossed varieties. If we look at species as having been specially created, and at varieties as having been produced by secondary laws, this similarity would be an astonishing fact. But it harmonises perfectly with the view that there is no essential distinction between species and varieties.

Summary

→ Chapter .

First crosses between

forms,

forms

sufficiently distinct to be ranked as species, and their hybrids, are very generally, but not universally, sterile. The sterility is of all degrees, and is often so slight that the

two

....

most careful experimentalists

who

....

have →arrived at diametrically opposite conclusions in ranking forms by this test. The sterility is innately variable in individuals of the same species, and is eminently susceptible →to the action of favourable and unfavourable conditions. The degree of sterility does not strictly follow systematic affinity, but is governed by several curious and complex laws. It is generally different, and sometimes widely different, in reciprocal crosses between the same two species. It is not always equal in degree in a first cross and in the

hybrid

hybrids

produced from this cross.

In the same manner as in grafting trees, the capacity of one species or variety to take on another, is incidental on →differences, generally of an unknown nature, in their vegetative systems, so in crossing, the greater or less facility