Base-set-hero

Fletchling is correct. If you want to breed any hidden ability at all, the mother has to have the hidden ability. (In XY, it's possible for the father to pass it down as well, though the chances are much lower.)

I just saw your question on DNA's Page. He doesn't play XY, but I can help.
No, sadly, you cannot breed a Chlorophyll Bulbasaur by Breeding 2 Overgrow Bulbasaur, as the mother needs to have the Hidden Ability to pass it down.