Fig. 1. The anatomical structures of Arabidopsis ovules were outlined at three developmental stages. (A) Ovule primordia emerge from the placenta and differentiate into three distinct zones: the nucellus (n), chalaza (c), and funiculus (f). (B) The inner integument (ii) and outer integument (oi) initiate from the chalaza. The megaspore mother cell (mmc) undergoes meiosis, forming four megaspores. (C) The largest megaspore undergoes three rounds of cell division and these cells differentiate into the embryo sac (shaded), which contains the antipodals, synergids, egg cell (e), and central cell (cc).