Fate of Endosperm

• Endosperm nucleus divides through transverse cytokinesis, forming two unequal cells: a larger micropylar cell and a smaller chalazal cell.
• The micropylar cell grows faster than the chalazal cell.
• Development in both cells resembles nuclear endosperm formation, resulting in a multinucleate stage followed by wall formation, like in Asphodelus.
• The chalazal chamber often stays smaller and can degenerate.

Fate of Endosperm

• During growth, the endosperm crushes the nucellus which is then consumed by growing embryo.
• In endospermic or albuminous seeds (e.g., Castor, Cereals, Coconut), the endosperm persists.
• In nonendospermic or exalbuminous seeds (e.g., Pea, Bean, Sunflower) the endosperm is fully absorbed, and food reserve is stored in cotyledons.
• Ruminate endosperm, seen in Areca and Passiflora, has a convoluted structure.
• Areca, Date (Pheonix), and Vegetable Ivory (Phytelephas microcarpa) have very hard endosperms.
• Cellulosic hard endosperm from vegetable ivory is used for making buttons, umbrella handles, and billiard balls.

Embryo – Structure, Types, and Development

• Embryogeny comprises all changes during the development of a mature embryo from a zygote or oospore.

Embryogeny in Dicots

• Zygote elongates and divides via a transverse wall into two unequal cells.
• The larger basal cell becomes the suspensor cell
• The suspensor cell divides transversely to form a filamentous suspensor of 6–10 cells, pushing the embryo into the endosperm.
• The first suspensor cell towards the micropylar end swells and functions as a haustorium, featuring wall ingrowths.
• The last suspensor cell adjacent to the embryo is known as the hypophysis.
• Hypophysis develops the radicle and root cap.
• The embryo cell undergoes two vertical divisions (quadrant stage) and one transverse division to produce eight cells in two tiers (octant stage).
• Epibasal (terminal) cells generate the two cotyledons and the plumule.
• Hypobasal cells (near suspensor) form the hypocotyl, except for its tip.
• The eight embryonic cells divide periclinally to create an outer layer of protoderm or dermatogen.
• Inner cells differentiate into procambium (plerome) and ground meristem (periblem).
• Protoderm forms epidermis, procambium forms stele or vascular strand, and ground meristem forms cortex and pith.
• The early embryo has radial symmetry and is globular and undifferentiated, referred to as the proembryo.
• It transforms into an embryo featuring the radicle, plumule, and cotyledons.
• Two cotyledons differentiate from the sides with a faint plumule in the center making the embryo heart-shaped.
• Rapid cotyledon growth leads to elongation while the plumule remains a small mound of undifferentiated tissue.

Structure of Dicot Embryo

• Dicot embryo features an embryonal axis and two cotyledons.
• Epicotyl is the part of the embryonal axis above the cotyledons; it terminates with the plumule (future shoot).
• Hypocotyl is located below the cotyledons and terminates in the radicle (future root).
• A root cap (calyptra) covers the root tip.