Q.Explain the development of dicot embryo.

The dicot zygote first forms a two-celled proembryo (suspensor initial + embryonal initial), the suspensor pushes the embryo into the endosperm, and the embryonal initial passes through an octant stage before differentiating into the heart-shaped, then horseshoe-shaped, mature embryo with plumule, cotyledons, hypocotyl, and radicle. …

Step 1 -- Proembryo formation. The zygote's first division is transverse and unequal, producing a two-celled proembryo: a larger basal (suspensor initial) cell nearer the micropyle, and a smaller terminal (embryonal initial) cell nearer the chalaza.

Step 2 -- Suspensor development. The suspensor initial divides transversely, in a single plane, to build a filamentous suspensor of about six to ten cells. Its uppermost cell swells into an absorptive haustorium, and its lowermost cell, next to the true embryo, becomes the hypophysis. The suspensor's role is purely mechanical: it pushes the developing embryo deeper into the nutritive endosperm.

Step 3 -- Octant stage. The embryonal initial cell divides three times in mutually perpendicular planes, producing an eight-celled octant. Its lower tier of four cells will form the hypocotyl and radicle; its upper tier of four cells will form the plumule and cotyledons; the adjoining hypophysis contributes further to the radicle and root cap. …

Sequence proembryo formation, suspensor elongation, the octant stage, and …

• Mixing up which octant tier (upper vs lower) gives rise to the plumule/cotyledons versus the hypocotyl/radicle. …