| Comparison with 1866 |
|
The sterility is of all degrees, and is often so slight that the two
most careful experimentalists who
have ever lived, have come to
diametrically opposite conclusions in ranking forms by this test. The sterility is innately variable in individuals of the same species, and is eminently susceptible 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
hybrids | hybrids 1866 1869 1872 | | hybrid 1859 1860 1861 |
|
|
| In the same manner as in grafting trees, the capacity of one species or variety to take on another, is incidental on generally unknown differences
in their vegetative systems, so in crossing, the greater or less facility of one species to unite with another,
is incidental on unknown differences in their reproductive systems. There is no more reason to think that species have been specially endowed with various degrees of sterility to prevent 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. | 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 |
| 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 |
| from 1866 1869 | | of 1859 1860 1861 |
| forms, the sterility apparently is 1866 |
| species, seems 1859 1860 1861 |
| forms; the sterility being 1869 |
| ..... 1866 1869 | | sterility 1859 1860 1861 |
|
The sterility is of all degrees, and is often so slight that the
two | two 1859 1860 1861 1866 | two 1869 1872 |
| who 1859 1860 1861 1866 | who 1869 1872 |
| ever lived, have come to 1859 1860 1861 1866 |
| arrived at 1869 1872 |
| of 1859 1860 1861 1866 |
| to the action of 1869 1872 |
| hybrid 1859 1860 1861 | | hybrids 1866 1869 1872 |
|
|
In the same manner as in grafting trees, the capacity of one species or variety to take on another, is incidental on
generally unknown differences | generally unknown differences 1859 1860 1861 1866 |
| differences, generally of an unknown nature, 1869 1872 |
| another, 1859 1860 1861 1866 | | another 1869 1872 |
| them 1859 1860 1861 1866 | | their 1869 1872 |
| them becoming inarched 1859 1860 1861 1866 |
| their inarching 1869 1872 |
|
|
The sterility of first crosses
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. | 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 increased through natural selection so as to attain that high degree which is universal with species when rendered widely distinct. 1866 |
| 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 |
| 1 blocks not present in 1859 1860 1861 1872; present in 1866 1869 | | 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 on some imperfection in the original act of impregnation.
|
| The sterility of hybrids, which have their reproductive systems imperfect, and which have had this system and their 1859 1860 1861 |
| With hybrids, in which the reproductive system is in an imperfect condition, and in which this system as well as the 1866 |
| In the case of hybrids, it perhaps depends on their 1869 |
| disturbed 1859 1860 1861 |
| has been disturbed 1866 |
| having been disturbed 1869 |
| of 1859 1860 1861 | | from 1866 1869 |
| species, seems 1859 1860 1861 |
| forms, the sterility apparently is 1866 |
| forms; the sterility being 1869 |
| sterility 1859 1860 1861 | sterility 1866 1869 |
|
