Plant Structures: Seeds
A seed (mature ovule) is a miniature plant with a protective cover in a suspended state of development. Most seeds contain a built-in food supply called endosperm (orchid is an exception). The endosperm can be made up of proteins, carbohydrates, or fats.
Function
- Propagation
- Feed
- Horticultural uses
- Feed
- Food
- Oil
Structure and Emergence
Seeds of monocots and dicots differ in structure and method of emergence.
Monocot Seeds
- Seed coat – From the wall of the embryo sack (mother tissue)
- Endosperm – Food supply containing 3 sets of chromosomes (2 from the mother and 1 from the father)
- Embryo – Immature plant
- Cotyledon – Seed leaf
- Plumule – Shoot
- Radicle – Root
Figure 1. Cross section of a monocot seed (corn)
Figure 2. Emergence of a corn plant
Dicot Seeds
- Seed coat – From embryo sack wall and endosperm tissue (During development, the endosperm stops dividing and is absorbed into the embryonic tissues.)
- Embryo – Immature plant
- Cotyledon – Food storing seed leaf
- Plumule – Shoot
- Hypocotyl – Stem
- Radicle – Root
Figure 3. Cross section of a dicot seed (bean)
Figure 4. Emergence of a bean plant
Figure 5. Dicot seed emergence – Left: Epigeous emergence (cotyledon emerges from soil) - bean). Right: Hypogeal emergence (cotyledon stays in soil) - pea).
Seed Growth and Development Terms
- Dormancy – State of suspended growth to survive adverse conditions and aid in dispersion. Adapting plants to a variety of hostile environments, Mother Nature programs a variety of germination blocks. The following are common types.
- Seed coat dormancy – When the seed coat is impermeable to water, and gases (oxygen). It requires action by weathering, microorganisms, passage through an animal's digestive track, or fire to soften the seed coat.
- Embryo dormancy – Due to physiological conditions or germination blocks in the embryo itself. It requires a specific period of cold (or heat) with available moisture and oxygen. Embryo dormancy is common in woody plants.
- Double dormancy – Condition of both seed coat and embryo dormancy.
- Rudimentary embryo dormancy – Situation where the embryo is immature and requires a growth period before it can germinate
- Chemical inhibitor dormancy – Seed contains some type of chemical that blocks germination. Many desert plants contain chemical germination inhibitors that are leached out in a soaking rain.
- Stratification – Rechniques used by a horticulturist to overcome dormancy.
For details on dormancy, stratification and germination of any specific plant, refer to a book on plant propagation.
Additional Information
CMG GardensNotes on how plants grow (botany)
- Horticulture Classification, #121
- Taxonomic Classification, #122
- Plant Structures: Cells, Tissues, and Structures, #131
- Plant Structures: Roots, #132
- Plant Structures: Stems, #133
- Plant Structures: Leaves, #134
- Plant Structures: Flowers, #135
- Plant Structures: Fruit, #136
- Plant Structures: Seeds, #137
- Plant Growth Factors: Photosynthesis, Respiration and Transpiration, #141
- Plant Growth Factors: Light, #142
- Plant Growth Factors: Temperature, #143
- Plant Growth Factors: Water, #144
- Plant Growth Factors: Hormones, #145
- Homework: How Plants Grow. #147
- References and Review Questions: How Plants Grow, #120
- Worksheet: Plant Structures, #146
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Minor revisions December 2011