| → 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 |
|
| → Hybrids 1859 1860 1861 1866 1869 |
| The hybrids raised 1872 |
|
| → can 1859 1860 1861 1866 |
| as in the genus Verbascum, can 1869 1872 |
|
|
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 with the pollen of
pure
a single fertile seed: but in some of these cases a first trace of fertility may be detected, by the pollen of one of the pure parent-species causing the flower of the hybrid to wither earlier than it otherwise would have done; and the early withering of the flower is well known to be a sign of incipient
From this extreme degree of sterility we have self-fertilised hybrids producing a greater and greater number of seeds up to perfect fertility. |
|
|
→Hybrids
from two species which are very difficult to cross, and which rarely produce any offspring, are generally very sterile; but the parallelism between the difficulty of making a first cross, and the sterility of the hybrids thus
classes of facts which are generally confounded
by no means strict. There are many cases, in which two pure
→can
be united with unusual facility, and produce numerous hybrid-offspring, yet these hybrids are remarkably sterile. On the other hand, there are species which can be crossed very rarely, or with extreme difficulty, but the hybrids, when at last produced, are very fertile. Even within the limits of the same genus, for instance in Dianthus, these two opposite cases occur. |
|
| The fertility, both of first crosses and of hybrids, is more easily affected by unfavourable conditions, than is
of pure species. But the
of
|
