1. Seed Structure and Seed Germination

2. Monocots vs Eudicots (Dicots)

3. Structure of the Mature Seed
A seed consists of an embryo, endosperm, and seed coat.
Seed coat
Embryo
Endosperm
The embryo and its food supply are enclosed by a hard, protective seed coat
The seed enters a state of dormancy

4. Definitions
Cotyledons: the embryo’s “seed leaves.” Embryonic shoots and roots also form.
Endosperm: a tissue produced inside the seeds that surrounds the embryo and provides nutrition for the embryo.
Seed coat: is a tough outer layer that protects the embryo from damage, dehydration, and predators.
Hypocotyl: the stem of a germinating seedling, found below the cotyledons and above the radicle (root).
Epicotyl: the embryonic shoot above the cotyledons. In most plants the epicotyl will eventually develop into the leaves of the plant.
Radicle: embryonic root
Plumule: the rudimentary shoot or stem of an embryo plant.

5. (a) Common garden bean, a eudicot with thick cotyledons
Seed coat
Epicotyl
Hypocotyl
Radicle
Cotyledons
Figure 38.8a Seed structure
(a) Common garden bean, a eudicot with thick cotyledons

6. (b) Castor bean, a eudicot with thin cotyledons
Seed coat
Endosperm
Cotyledons
Epicotyl
Hypocotyl
Radicle
Figure 38.8b Seed structure
(b) Castor bean, a eudicot with thin cotyledons

7. Pericarp fused Scutellum with seed coat (cotyledon) Endosperm
Coleoptile
Epicotyl
Hypocotyl
Coleorhiza
Radicle
Figure 38.8c Seed structure
(c) Maize, a monocot

8. Seed Dormancy: An Adaptation for Tough Times
Seed dormancy increases the chances that germination will occur at a time and place most advantageous to the seedling
The breaking of seed dormancy often requires environmental cues, such as temperature or lighting changes
Seed Germination and Seedling Development
Germination depends on imbibition, the uptake of water due to low water potential of the dry seed
The radicle (embryonic root) emerges first
Next, the shoot tip breaks through the soil surface
In many eudicots, a hook forms in the hypocotyl, and growth pushes the hook above ground
The hook straightens and pulls the cotyledons and shoot tip up

9. Foliage leaves Cotyledon Epicotyl Hypocotyl Cotyledon Cotyledon
Figure 38.9a Two common types of seed germination
Radicle
Seed coat
(a) Common garden bean

10. In maize and other grasses, which are monocots, the coleoptile pushes up through the soil
Foliage leaves
Coleoptile
Coleoptile
Figure 38.9b Two common types of seed germination
Radicle
(b) Maize