I recall reading about research into graft-induced hybridization, whereby cotyledon stage scion is grafted onto mature rootstock and a one-way migration of genetic material occurs into the grafted scion tissue, allegedly beyond simple chimerism. The authors claimed said material could be passed down through subsequent self-seeding in the fruits of the scion tissue, and the effect was magnified with multiple grafts.
Granted, this sounds like science fiction to me, and it seems most of the scientific community still doubts the validity of such claims. Still, food for thought.
edit: Though, I guess rootstock is the wrong word, as the point is to attach the cotyledon (or at least, very young plant) to the primary growth of the base plant, then strip the scion of its own vegetation to encourage the process of assimilation. Wish I had the link...