inheritable) should be sterile: it does not seem improbable that the cross from an alpine and lowland plant should have its constitutional powers deranged, in nearly the same manner as when the parent alpine plant is brought into a lowland district. Analogy, however, is a deceitful guide, and it would be rash to affirm, although it may appear probable, that the sterility of hybrids is due to the constitutional peculiarities of one parent being disturbed by being blended with those of the other parent in exactly the same manner as it is caused in some organic beings when placed by man out of their natural conditions{255}. Although this would be rash, it would, I think, be still rasher, seeing that sterility is no more incidental to _all_ cross-bred productions than it is to all organic beings when captured by man, to assert that the sterility of certain hybrids proved a distinct creation of their parents. {248} <Note in original.> Animals seem more often made sterile by being taken out of their native condition than plants, and so are more sterile when crossed. We have one broad fact that sterility in hybrids is not closely related to external difference, and these are what man alone gets by selection. {249} See _Var. under Dom._, Ed. ii. vol. II. p. 132; for the case of the cheetah see _loc cit._ p. 133. {250} _Var. under Dom._, Ed. ii. vol. II. p. 148. {251} Quoted in the _Origin_, Ed. i. p. 9. {252} See _Var. under Dom._, Ed. ii. vol. II. p. 147. {253} _Var. under Dom._, Ed. ii. vol. II. p. 89. {254} See _Var. under Dom._, Ed. ii. vol. II. p. 147. {255} _Origin_, Ed. i. p. 267, vi. p. 392. This is the principle experimentally investigated in the author's _Cross-and Self-Fertilisation_.