| → circumstances and rules 1859 1860 1861 1866 1869 |
| laws 1872 |
|
| → chiefly drawn up 1859 1860 1861 1866 1869 |
| drawn up chiefly 1872 |
|
| → of the same genus applied to the stigma of some one species, 1859 1860 1861 1866 |
| of the same genus applied to the stigma of some one of the species, 1869 |
| applied to the stigma of some one species of the same genus, 1872 |
|
|
and in hybrids, is an extremely general result; but that it cannot, under our present state of knowledge, be considered as absolutely universal. |
|
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| We will now consider a little more in detail the
→circumstances and rules
governing the sterility of first crosses and of hybrids. Our chief object will be to see whether or not
indicate that species have
endowed with this quality, in order to prevent their crossing and blending together in utter confusion. The following
conclusions are
→chiefly drawn up
from
admirable work on the hybridisation of plants. I have taken much pains to ascertain how far
apply to animals,
considering how scanty our knowledge is in regard to hybrid animals, I have been surprised to find how generally the same rules apply to both kingdoms. |
|
| It has been already remarked, that the degree of fertility, both of first crosses and of hybrids, graduates from zero to perfect fertility. It is surprising in how many curious ways this gradation can be
but only the barest outline of the facts can here be given. When pollen from a plant of one family is placed on the stigma of a plant of a distinct family, it exerts
more influence than so much inorganic dust. From this absolute zero of fertility, the pollen of
species
→of the same genus applied to the stigma of some one species,
yields a perfect gradation in the number of seeds produced, up to nearly complete or even quite complete fertility; and, as we have seen, in certain abnormal cases, even to an excess of fertility, beyond that which the
own pollen
So in hybrids themselves, there are some which never have produced, and probably never would produce, even
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