Unit 5: Embryo and Endosperm

Syllabus Reference: Embryo: Structure development & Types, Endosperm types, structure and functions; Dicot and monocot embryo; [cite_start]Embryo-endosperm relationship, Apomixis and polyembryony: Causes and application [cite: 559-560].

1. Endosperm

Nutritive tissue formed by Triple Fusion (3n). It nourishes the developing embryo.

Types of Endosperm:

1. Nuclear (Most Common): PEN divides repeatedly without wall formation. Free nuclei in cytoplasm (e.g., Coconut water). Wall formation may occur later (Coconut meat).
2. Cellular: Every nuclear division is followed by wall formation (e.g., Datura, Petunia).
3. Helobial: Intermediate type. First division forms two chambers (micropylar & chalazal). Free nuclear division occurs in the micropylar chamber (e.g., Monocots like Asphodelus).

2. Embryo Development (Embryogeny)

• Dicot Embryo (Crucifer Type):
  Zygote → Proembryo → Globular Stage → Heart-shaped Stage → Mature Embryo.
  Mature Dicot embryo has: Embryonal axis + 2 Cotyledons. Radicle (root tip) and Plumule (shoot tip).
• Monocot Embryo:
  Similar early stages but only 1 Cotyledon (called Scutellum in grasses) develops laterally. The axis is terminal.
  Protective sheaths: Coleoptile (shoot) and Coleorhiza (root).

3. Apomixis and Polyembryony

• Apomixis (Agamospermy): Production of seeds without fertilization.
  Significance: Produces clones. Very useful in agriculture to maintain hybrid vigor (farmers don't need to buy hybrid seeds every year).
• Polyembryony: Occurrence of more than one embryo in a seed.
  Simple: Fertilization of more than one egg.
  Cleavage: Splitting of the proembryo (e.g., Orchids).
  Adventive: Embryos develop directly from Nucellus or Integuments (e.g., Citrus, Mango).