See page in:
1859
1860
1861
1866
1869
1872

Compare with:
1859
1861
1866
1869
1872

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.

in every part of the flower, even in the pollen, in the fruit, and in the cotyledons, can be crossed. Annual and perennial plants, deciduous and evergreen trees, plants inhabiting different stations and fitted for extremely different climates, can often be crossed with ease.
By a reciprocal cross between two species, I mean the case, for instance, of a
female-ass
stallion-horse
being first crossed
by
with
a
stallion,
female-ass,
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,
that is
or
of any
recognisable
recognisable
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
jalappa
jalapa
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.
jalappa,
Jalapa,
jalapa,
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
forms so
forms so
closely related
forms (as
(as
Matthiola annua and glabra)
which
that
many botanists rank
them
them
only as varieties. It is also a remarkable fact, that hybrids raised from reciprocal crosses, though