The correct answer is nucleus
In flowering plants the gametophyte phases are reduced to a few cells dependant for their nutrition on the Sporophyte. The gametophyte comprises the main plant, while the diploid sporophyte is much smaller and is attached to the gametophyte. Both spores and the resulting ganetophyte are haploid, which means they only have one set of chromosomes. The mature gametophyte produces male or female gametes by mitosis. The fusion of male and female gametes produces a diploid zygote which then develops into a new sporophyte.
