Origin of Species Variorum

→ them becoming inarched 1859 1860 1861 1866

their inarching 1869 1872

→ and of their hybrid progeny has not, as far as we can judge, been increased through natural selection so as to attain that high degree which is universal with species when rendered widely distinct. 1866

between pure species, which have their reproductive systems perfect, seems to depend on several circumstances; in some cases largely on the early death of the embryo. 1859 1860 1861

and of their hybrid progeny has not, as far as we can judge, been acquired through natural selection. 1869

and of their hybrid progeny has not been acquired through natural selection. In the case of first crosses it seems to depend on several circumstances; in some instances in chief part on the early death of the embryo. 1872

→ With 1866

In the case of 1869

→ between pure species, in which the reproductive system is in a perfect condition, the sterility 1866

it 1869

→ cases largely 1866

instances in chief part 1869

↑ 2 blocks not present in 1859 1860 1861 1866 1869; present in 1872

In the case of hybrids, it apparently depends on their whole organisation having been disturbed by being compounded from two distinct forms; the sterility being closely allied to that which so frequently affects pure species, when exposed to new and unnatural conditions of life. He who will explain these latter cases will be able to explain the sterility of hybrids.

→ With hybrids, in which the reproductive system is in an imperfect condition, and in which this system as well as the 1866

The sterility of hybrids, which have their reproductive systems imperfect, and which have had this system and their 1859 1860 1861

In the case of hybrids, it perhaps depends on their 1869

→ has been disturbed 1866

disturbed 1859 1860 1861

having been disturbed 1869

→ forms, the sterility apparently is 1866

species, seems 1859 1860 1861

forms; the sterility being 1869

→ the crossing of forms only slightly differentiated favours 1866

the crossing of forms only slightly different is favourable to 1859 1860 1861

first, the crossing of forms only slightly differentiated favours 1869

firstly, slight changes in the conditions of life add to 1872

→ their offspring; and that slight changes in the 1859 1860 1861 1866

their offspring, whilst close interbreeding is injurious; and secondly, that slight changes in the 1869

all organic beings; and secondly, that the crossing of forms, which have been exposed to slightly different 1872

→ apparently add to the 1866 1869

are apparently favourable to the 1859 1860 1861

or which have varied, favours the size, 1872

→ all organic beings. 1859 1860 1861 1866

all organic beings, whilst greater changes are often injurious. 1869

their offspring. 1872

→ connecting in all cases 1866

in all cases connects 1869 1872

→ drive us to conclude that in all cases 1866

clearly leads to the conclusion that 1869 1872

endowed with various degrees of sterility to prevent

their

them

crossing and blending in nature, than to think that trees have been specially endowed with various and somewhat analogous degrees of difficulty in being grafted together in order to prevent →them becoming inarched in our forests.

The sterility of first crosses →and of their hybrid progeny has not, as far as we can judge, been increased through natural selection so as to attain that high degree which is universal with species when rendered widely distinct. →With first crosses →between pure species, in which the reproductive system is in a perfect condition, the sterility seems to depend on several circumstances; in some →cases largely on the early death of the

embryo.

~~but~~

~~this~~

~~apparently~~

~~depends~~

~~some~~

~~imperfection~~

~~the~~

~~original~~

~~act~~

~~impregnation.~~

↑ →With hybrids, in which the reproductive system is in an imperfect condition, and in which this system as well as the whole organisation →has been disturbed by being compounded

from

two distinct →forms, the sterility apparently is closely allied to that

sterility

....

which so frequently affects pure species, when

their

exposed to

natural

unnatural

conditions of

life

have

been

disturbed.

This view is

strongly supported

supported

by a parallelism of another

kind;—

kind:—

kind:

namely,

that,

that

→the crossing of forms only slightly differentiated favours the vigour and fertility of →their offspring; and that slight changes in the conditions of life →apparently add to the

vigour,

vigour

and fertility of →all organic beings.

The

But the

facts given on the sterility of the illegitimate unions of dimorphic and trimorphic plants and of their illegitimate progeny,

perhaps render

render

it probable that

~~there is~~

there is

some unknown bond →connecting in all cases the degree of fertility of first unions with that of their offspring. The consideration of these facts on dimorphism, as well as

of the

the

results of reciprocal crosses, →drive us to conclude that in all cases the primary cause