Step 1: Formation of the proembryo.
After fertilization in flowering plants, the zygote divides transversely into two cells: an apical cell (upper cell) and a basal cell (lower cell). These two cells have different roles in embryo development.
Step 2: Fate of the apical cell.
The apical cell divides repeatedly to form the main body of the embryo. It gives rise to important structures such as the cotyledons, plumule, hypocotyl, and most of the embryo axis. Thus, the apical cell is responsible for forming the developing plant embryo.
Step 3: Fate of the basal cell.
The basal cell divides to form a structure called the suspensor. The suspensor helps in pushing the embryo into the endosperm so that it can obtain proper nourishment during development. The uppermost cell of the suspensor (called the hypophysis) later contributes to the formation of the root apex and root cap.
Final Answer:
(a) Apical cell: Forms the main body of the embryo (cotyledons and embryo axis).
(b) Basal cell: Forms the suspensor which helps in nutrition and positioning of the embryo.