Generally, with respect to crossing, the effects may be diametrically opposite.

If you cross two very distinct races, you may make (not that I believe such has often been made) a third and new intermediate race; but if you cross two exceedingly close races, or two slightly different individuals of the same race, then in fact you annul and obliterate the difference.

In this latter way I believe crossing is all-important, and now for twenty years I have been working at flowers and insects under this point of view.

I do not like Hooker's terms, centripetal and centrifugal (80/2.

Hooker's "Introductory Essay to the Flora of Tasmania," pages viii.