b) The similarity in shape of the gametophyte and sporophytes might be due to cytoplasmic inheritance, which might be inherited from the mother. The increase in leaf size might be due to interplay between the contributions of the nuclear genome from both the mother and the father.
c) A simple way to test our theory would be to conduct repeated backcrosses. The female is used as the hybrid to test whether the shape of the leaves is maternally inherited and the increase in leaf size is due to nuclear factors.
The result of this test would be that the cytoplasmic inheritance would be constant while the nuclear information would become more like the backcross parent.
The phenotypic result would be that the leaf morphology would be constant while the leaf size would decrease rather than increase.