Plant Structures: Seeds

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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

Cross section of monocot seed

Figure 1. Cross section of a monocot seed (corn)


Corn emergence
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

Cross section of dicot seed

Figure 3.  Cross section of a dicot seed (bean)


Emergence of a bean plant

Figure 4.  Emergence of a bean plant


Dicot seed emergence

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 – Techniques 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.


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Authors: David Whiting (CSU Extension) with Michael Roll and Larry Vickerman (former CSU Extension employees). Artwork by Scott Johnson and David Whiting.

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Revised December 2011

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