Nucellus is primarily a:
Nucellus constitutes central parenchymatous tissue of ovule derived from megasporangium forming massive bulk surrounding and protecting megaspore mother cell and later embryo sac. It serves primarily as nutritive tissue providing carbohydrates, amino acids, lipids, and hormonal cues to developing female gametophyte through apoplastic and symplastic transport pathways. Depending on crassinucellate or tenuinucellate configuration degree of tissue development may be substantial. After fertilization nucellus generally degenerates, but may occasionally persist as perisperm storage tissue in beet, pepper, black pepper, continuing important maternal nutritive contribution supporting embryo growth and seed filling.
Ref: Mohammad et al., Seed Sci; Reiser & Fischer: nucellus is nutritive tissue surrounding and feeding embryo sac.