HYBRIDISATION. 
917 
containing embryos, but these embryos having no power of germination. Fmlher 
steps are indicated by the number of embryos which have the power of germination 
that are produced in the ovary ^ 
5. When pollen from different species is applied simultaneously to the same 
stigma, only one kind is potent, viz. that from the species which has the greatest 
sexual affinity to the one that is pollinated. And since, as a general law, pollen is 
most efficacious on a different flower of the same species — in other words, the highest 
degree of sexual affinity occurs between different individuals of the same species — 
when a stigma is pollinated at the same time with pollen of the same and of another 
species, the first only is potent. But since, on the other hand, hybrids are sometimes 
more easily produced between varieties than between individuals of the same variety, 
in this case the foreign pollen may be prepotent over that of the same kind. When 
the pollen of different species reaches the stigma at the same time, and if that which 
reaches it later has a greater sexual affinity, it can only be potent when the first is 
not potent or acts injuriously. In Nicotiana the production of hybrids can no longer 
be prevented by its own pollen after two hours, in Malva and Hibiscus after three 
hours, in Dianthus after five or six hours. 
6. The hybrid is possessed of external characters intermediate between those of 
its parent-forms, usually nearly half way between; less often it resembles one of the 
parent-forms more nearly than the other, and this is more often the case with variety- 
hybrids than with species-hybrids. It follows that in reciprocal hybrids from the 
species A and B, the hybrid A B is generally similar externally to the hybrid B A, 
though the two forms may differ somewhat internally. Thus, according to Gärtner, 
the hybrid Nicotiana paniculato-rustica is more fertile than the reciprocal hybrid 
Nicotiana rustico-panicutata ^. An internal difference between reciprocal hybrids is 
also shown by the fact that one is more variable than the other ; thus, according to 
Gärtner, the progeny of Digitalis piirpureo-lutea is more variable than that of D. luteo- 
purpurea^ the progeny of Dianthus pulchello-arenarius more variable than that of 
D. arenario-pulchellus. 
When two species A and B hybridise, and the one species A exercises a 
greater influence on the form and properties of the hybrid than the other species 
B, the hybrid or its descendants, if fertilised by A, will revert more quickly to the 
parent-form A than it will to the parent-form B if fertilised by it. Thus Gartner 
states that the hybrid of Dianthus chinensis and D. Caryophyllus reverts to the 
latter form after three or four generations if repeatedly fertilised by it, while it 
requires fertilisation for five or six generations by D. chinensis in order to revert to 
that form. 
7. The characteristics of the parent-forms are as a rule so transmitted to the 
hybrid that the influence of both is manifested in all its characters, producing a 
fusion of the different peculiarities. This is more evident in the species- than in 
the variety-hybrids ; in the latter some of the non-essential characters of the parents 
sometimes present themselves in the offspring uncombined side by side ; e.g. various 
^ See Hildebrand, Bastardiningsversuche an Orchideen, Bot. Zeit. 1865, No. 31. 
^ In this mode of designating hybrids, the name of the male parent-plant stands first ; thus 
Nicotiana rustico-paniciilata is the product of the fertilisation of N. paniadata by the pollen of 
N. riisiica. 
