When two plants, constantly different in one or several traits, are crossed, the traits they have in common are transmitted unchanged to the hybrids and their progeny, as numerous experiments have proven; a pair of differing traits, on the other hand, are united in the hybrid to form a new trait, which usually is subject to changes in the hybrids' progeny.

Gregor Mendel's Experiments on Plant Hybrids: A Guided Study (ed. Rutgers University Press, 1993) - ISBN: 9780813519210