Comparison with 1861 |
|
union. The hybrids, moreover, produced from reciprocal crosses often differ in fertility. |
|
Now do these complex and singular rules indicate that species have been endowed with sterility simply to prevent their becoming confounded in nature? I think not. For why should the sterility be so extremely different in degree, when various species are crossed, all of which we must suppose it would be equally important to keep from blending together? Why should the degree of sterility be innately variable in the individuals of the same species? Why should some species cross with facility, and yet produce very sterile hybrids; and other species cross with extreme difficulty, and yet produce fairly fertile hybrids? Why should there often be so great a difference in the result of a
reciprocal cross between the same two species? Why, it may even be asked, has the production of hybrids been permitted? to
grant to species the special power of producing hybrids, and then to stop their further propagation by different degrees of sterility, not strictly related to the facility of the first union between their parents, seems
to be to be 1859 1860 1861 1866 | to be 1869 1872 |
a strange arrangement. |
|
The foregoing rules and facts, on the other hand,
ap- pear ap- pear 1860 1861 | appear 1859 1866 1869 1872 |
to me clearly to indicate that the sterility both of first crosses and of hybrids is simply incidental or dependent on unknown
differences, differences, 1859 1860 1861 | differences 1866 1869 1872 |
chiefly chiefly 1859 1860 1861 | chiefly 1866 1869 1872 |
in
the the 1859 1860 1861 | their 1866 1869 1872 |
reproductive
systems, systems, 1859 1860 1861 | systems; 1866 1869 1872 |
of of 1859 1860 1861 | of 1866 1869 1872 |
the the 1859 1860 1861 | the 1866 1869 1872 |
species species 1859 1860 1861 | species 1866 1869 1872 |
which which 1859 1860 1861 | which 1866 1869 1872 |
are are 1859 1860 1861 | are 1866 1869 1872 |
crossed. crossed. 1859 1860 1861 | crossed. 1866 1869 1872 |
The The 1859 1860 1861 | the 1866 1869 1872 |
differences being of so peculiar and limited a nature, that, in reciprocal crosses between
two two 1859 1860 1861 1866 |
the same two 1869 1872 |
species
the male sexual element of the one will often freely act on the female sexual element of the other, but not in a reversed direction. It will be advisable to explain a little more fully by an example what I mean by sterility being incidental on other differences, and not a specially endowed quality. As the capacity of one plant to be grafted or budded on another is
so so 1861 1866 1869 | so entirely 1859 1860 | so 1872 |
unimportant for
its its 1859 1860 1861 1866 1869 | their 1872 |
welfare in a state of nature, I presume that no one will suppose that this capacity is a
specially
endowed quality, but will admit that it is incidental on differences in the laws of growth of the two plants. We can sometimes see the reason why one tree will not take on another, from differences in their rate of growth, in the hardness of their wood, in the period of the flow or nature of their sap, &c.; but in a multitude of cases we can assign no reason whatever. Great diversity in the size of two plants, one being woody and the other herbaceous, one being evergreen and the other deciduous, and adaptation to widely different climates, does
not always prevent the two grafting together. As in hybridisation, so with grafting, the capacity is limited by systematic affinity, for no one has been able to graft
trees together trees together 1859 1860 1861 1866 1869 | together trees 1872 |
belonging to quite distinct families; and, on the other hand, closely allied species, and varieties
|
union. The hybrids, moreover, produced from reciprocal crosses often differ in fertility. |
|
Now do these complex and singular rules indicate that species have been endowed with sterility simply to prevent their becoming confounded in nature? I think not. For why should the sterility be so extremely different in degree, when various species are crossed, all of which we must suppose it would be equally important to keep from blending together? Why should the degree of sterility be innately variable in the individuals of the same species? Why should some species cross with facility, and yet produce very sterile hybrids; and other species cross with extreme difficulty, and yet produce fairly fertile hybrids? Why should there often be so great a difference in the result
of a of a 1859 1860 1861 1869 1872 | of a 1866 |
reciprocal cross between the same two species? Why, it may even be asked, has the production of hybrids been permitted?
To To 1861 1866 1869 1872 | to 1859 1860 |
grant to species the special power of producing hybrids, and then to stop their further propagation by different degrees of sterility, not strictly related to the facility of the first union between their parents, seems
....... 1869 1872 | to be 1859 1860 1861 1866 |
a strange arrangement. |
|
The foregoing rules and facts, on the other hand,
appear appear 1859 1866 1869 1872 | ap- pear 1860 1861 |
to me clearly to indicate that the sterility both of first crosses and of hybrids is simply incidental or dependent on unknown
differences differences 1866 1869 1872 | differences, 1859 1860 1861 |
....... 1866 1869 1872 | chiefly 1859 1860 1861 |
in
their their 1866 1869 1872 | the 1859 1860 1861 |
reproductive
systems; systems; 1866 1869 1872 | systems, 1859 1860 1861 |
....... 1866 1869 1872 | of 1859 1860 1861 |
....... 1866 1869 1872 | the 1859 1860 1861 |
....... 1866 1869 1872 | species 1859 1860 1861 |
....... 1866 1869 1872 | which 1859 1860 1861 |
....... 1866 1869 1872 | are 1859 1860 1861 |
....... 1866 1869 1872 | crossed. 1859 1860 1861 |
the the 1866 1869 1872 | The 1859 1860 1861 |
differences being of so peculiar and limited a nature, that, in reciprocal crosses between
the same two the same two 1869 1872 |
two 1859 1860 1861 1866 |
species, species, 1861 1866 1869 1872 | species 1859 1860 |
the male sexual element of the one will often freely act on the female sexual element of the other, but not in a reversed direction. It will be advisable to explain a little more fully by an example what I mean by sterility being incidental on other differences, and not a specially endowed quality. As the capacity of one plant to be grafted or budded on another is
....... 1872 | so entirely 1859 1860 | so 1861 1866 1869 |
unimportant for
their their 1872 | its 1859 1860 1861 1866 1869 |
welfare in a state of nature, I presume that no one will suppose that this capacity is a
specially
endowed quality, but will admit that it is incidental on differences in the laws of growth of the two plants. We can sometimes see the reason why one tree will not take on another, from differences in their rate of growth, in the hardness of their wood, in the period of the flow or nature of their sap, &c.; but in a multitude of cases we can assign no reason whatever. Great diversity in the size of two plants, one being woody and the other herbaceous, one being evergreen and the other deciduous, and adaptation to widely different climates,
do do 1861 1866 1869 1872 | does 1859 1860 |
not always prevent the two grafting together. As in hybridisation, so with grafting, the capacity is limited by systematic affinity, for no one has been able to graft
together trees together trees 1872 | trees together 1859 1860 1861 1866 1869 |
belonging to quite distinct families; and, on the other hand, closely allied species, and varieties
|