| → male-ass with a mare: 1859 1860 1861 1866 1869 |
| mare by a male-ass; 1872 |
|
| → whole organisation. 1859 1860 1861 |
| whole organisation, except in their reproductive systems. 1866 1869 |
| structure or constitution, excepting in their reproductive systems. 1872 |
|
| ↑ 1 blocks not present in 1859 1860 1861; present in 1866 1869 1872 |
| The diversity of result
in reciprocal crosses between the same two species was long ago observed by Kölreuter.
|
|
| → generally 1859 1860 1861 |
| though they rarely 1866 1869 1872 |
|
| → fertility 1859 1860 1861 |
| external characters, yet generally differ in fertility 1866 1869 1872 |
|
|
By a reciprocal cross between two species, I mean the case, for instance, of a
being first crossed
a
and then a
→male-ass with a mare:
these two species may then be said to have been reciprocally crossed. There is often the widest possible difference in the facility of making reciprocal crosses. Such cases are highly important, for they prove that the capacity in any two species to cross is often completely independent of their systematic affinity,
of any
difference in their
→whole organisation.
↑
On the other hand, these cases clearly show that the capacity for crossing is connected with constitutional differences imperceptible by us, and confined to the reproductive system. This difference in the result of reciprocal crosses between the same two species was long ago observed by Kölreuter. To give an instance: Mirabilis
can easily be fertilised by the pollen of M. longiflora, and the hybrids thus produced are sufficiently fertile; but Kölreuter tried more than two hundred times, during eight following years, to fertilise reciprocally M. longiflora with the pollen of M.
and utterly failed. Several other equally striking cases could be given. Thuret has observed the same fact with certain sea-weeds or Fuci. Gärtner, moreover, found that this difference of facility in making reciprocal crosses is extremely common in a lesser degree. He has observed it even between
closely related
Matthiola annua and glabra)
many botanists rank
only as varieties. It is also a remarkable fact, that hybrids raised from reciprocal crosses, though of course compounded of the very same two species, the one species having first been used as the father and then as the mother,
→generally
differ in
→fertility
in a small, and occasionally in a high degree. |
|
| Several other singular rules could be given from
|
