Seed Structure — Core Principles

Core Principles

A seed is a fundamental reproductive unit in flowering plants, formed from a fertilized ovule. It comprises three main parts: the protective seed coat, the embryo (a miniature plant), and food reserves.

The seed coat shields the embryo from damage and desiccation, often featuring a hilum (attachment scar) and a micropyle (pore for water/gas entry). The embryo consists of an embryonal axis with a radicle (embryonic root), a plumule (embryonic shoot), and one or two cotyledons (seed leaves).

Cotyledons either store food directly (non-endospermic seeds like pea) or absorb it from a separate storage tissue called the endosperm (endospermic seeds like maize). Monocot seeds have one cotyledon (scutellum) and often protective sheaths like the coleoptile (for plumule) and coleorhiza (for radicle), along with an aleurone layer surrounding the endosperm.

Dicot seeds have two cotyledons and lack these sheaths. Seeds are vital for plant propagation, survival, and are a major source of human food.

Important Differences

vs Dicotyledonous Seed

Aspect	This Topic	Dicotyledonous Seed
Number of Cotyledons	One (Scutellum)	Two
Endosperm	Generally present and large (endospermic), e.g., maize, wheat, rice. Primary food storage.	Generally absent or very reduced (non-endospermic), e.g., pea, bean, gram. Food stored in cotyledons.
Seed Coat & Pericarp	Often fused with the fruit wall (pericarp) in cereals (caryopsis).	Distinct seed coat, separate from the fruit wall.
Embryo Size	Relatively small, located at one end of the endosperm.	Relatively large, often filling the entire seed cavity.
Protective Sheaths	Presence of coleoptile (covering plumule) and coleorhiza (covering radicle).	Absence of coleoptile and coleorhiza.
Aleurone Layer	Present, separating endosperm from embryo (proteinaceous layer).	Absent.
Examples	Maize, Wheat, Rice, Sorghum, Onion, Lily	Pea, Bean, Gram, Castor, Groundnut, Mango

Monocot and dicot seeds exhibit fundamental structural differences reflecting their evolutionary paths and germination strategies. Monocot seeds typically possess a single cotyledon (scutellum), a prominent endosperm for food storage, and specialized protective sheaths like the coleoptile and coleorhiza. Their seed coat is often fused with the fruit wall. In contrast, dicot seeds have two cotyledons, which often serve as the primary food storage organs (making them non-endospermic), and lack the protective sheaths. These distinctions are critical for identifying plant types and understanding their developmental biology.