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parts of the seeds

the parts of a seed and their functions in seed and plant development

There are three basic parts of a seed in the angiosperms: (a) an embryo , (b) a food storage or nutritive tissue , and (c) seed covering .

Embryo

A mature seed has a diploid (2N) embryo which develops from a fertilized egg or zygote. It results from the union of a sperm (1N), from a germinated pollen, with a female egg (1N) in the embryo sac. It is the embryo that ultimately gives rise to a new plant.

The embryo can be distinguished from the other major parts of a seed based on component parts and function. It consists of the epicotyl, hypocotyl, radicle, and one or two cotyledons. It is the one which develops into a plant with an upward growing shoot and a downward growing root system.

The epicotyl is a tiny shoot from which the entire plant shoot system develops. The growing tip of the epicotyl is the plumule. The hypocotyl is the transition zone between the rudimentary root and shoot; the radicle is a small embryonic root. Cotyledons are specialized seed leaves which develop from the plumule and occur singly in most monocot seeds but two in dicot seeds. They are the most prominent parts of a fully developed embryo. Monocot means one cotyledon while dicot means two cotyledons. (Click here to read relevant update)

The stored food is present in most seeds in the form of carbohydrates , fats and proteins. This stored food may be found in the following parts of a seed: endosperm, cotyledons, or in the perisperm. The stored food is used to support the embryo during seed germination. But in orchid seeds, a functional storage tissue is lacking.

Storage Tissue or Nutritive Tissue

The endosperm differs from other parts of a seed by having a triploid chromosome complement (3N). It results from the union of one sperm nucleus (1N), from a germinating pollen, with the two polar nuclei (2N) in the embryo sac. In corn and other cereals it represents the major bulk of the seed. In other seeds (e.g. beans), the endosperm is absent because it is utilized in the development of the embryo. In this case the cotyledons, not the endosperm, serve as the food-storage tissue. This is an example that of the different parts of a seed, the endosperm may be wanting.

The endosperm can be described as either mealy, horny, continuous, or ruminated. It is mealy when granular, horny when hard and bone-like, continuous when smooth and uninterrupted, and ruminated when there are irregular depressions, as if chewed, as in betel nut ( Areca catechu ). Coconut water is a liquid endosperm .

When the plant food is stored outside of the embryo in a large endosperm, the seed is called albuminous . When the embryo stores its own food reserve, usually within the cotyledons, the seed is called exalbuminous . In the latter case the endosperm is absent, having been digested by the embryo during development, or it is reduced to a thin layer around the embryo.

The perisperm is a storage tissue that originates from the nucellus. Thus, just like other parts of a seed other than the endosperm, it has a diploid chromosomal content. But it occurs only in a few families, e.g. Amaranthaceae (amaranth family), Chenopodiaceae (goosefoot family) and Caryopyllaceae (pink (family). It is usually digested by the endosperm during seed development.

Seed Covering or Protective Coat

The seed covering is of maternal origin. This part of a seed consists of the seed coat or remnants of the nucellus and endosperm. Sometimes it consists of parts of the fruit. It covers and provides mechanical protection to the other parts of a seed.

The seed coat is usually hard, thickened, brownish or otherwise colored, and partly impermeable to water. It prevents excessive loss of water from within the seed and serves as a barrier against the entry of parasites. Hard seed coats cause dormancy, a condition which prevents germination when environmental conditions are not favorable for sustained growth of seedlings.

The seed coat is developed from the outer covering of the ovule, or integument. But it is not immediately apparent in the angiosperms because the seed is encased in a fruit wall or pericarp. The outermost, visible part of the corn kernel is in fact the exocarp, the outermost part of the pericarp.

There are usually two layers of the seed coat. The outer layer, known as the testa, is thicker. The inner one is more delicate, known as tegmen.

Externally, some parts of a seed are obvious. On some seed coats, the opening in the integuments of the ovule, called micropyle , is visible. The hilum is usually visible also, the scar left by the stalk which attached the seed to the placenta. The hilum is equivalent to the navel in humans to which the umbilical cord is attached. It appears dark in color when the seed becomes physiologically mature and is thus used as an indicator of seed maturity.

From the outside, seeds may be smooth, wrinkled, or hairy as in cotton, or winged. In the castor bean (Ricinus communis), there is wart-like growth at the hilum, called the caruncle. In mangosteen, the seeds are enveloped by a white fleshy aril which is edible.

Note: Do you know that some seeds used in propagating plants may not be entirely seeds? Click here to read .

REFERENCES

  1. AGROFORESTRY SEEDS CIRCULAR, March 1993. p. 30.
  2. FEININGER A. 1968. Trees. (1978 reprint). NY: The Viking Press. 116 p.
  3. FLORES HE, DAI Y, CUELLO JI, MALDONADO-MENDOZA IE, LOYOLA-VARGAS, VM. 1993. Green roots: photosynthesis and photoautotrophy in an underground plant organ. Plant Physiol. 101: 363-371. Retrieved November 27, 2010 from http://www.plantphysiol.org/content/101/2/363.full.pdf.
  4. FULLER HJ, RITCHIE DD. 1967. General Botany. 5th ed. NY: Barnes & Noble, Inc. 232 p.
  5. GOMEZ FP, PRADO CHBA. 2007. Ecophysiology of coconut palm under water stress. Brazilian Journal of Plant Physiology. Print version ISSN 1677-0420. Retrieved December 8, 2010 from http://www.scielo.br/scielo.php?pid=S1677-04202007000400008&script=sci_arttext.
  6. HARTMANN HT, KESTER DE. 1975. Plant Propagation: Principles and Practices. New Jersey: Prentice-Hall Inc. 662 p.
  7. http://www2.bioversityinternational.org/publications/Web_version/108/ch02.htm#TopOfPage, accessed Dec ember 7, 2010.
  8. JANICK J. 1972. Horticultural Science. 2nd ed. San Francisco: W. H. Freeman and Company. pp. 55-93.
  9. KESSELER R, STUPPY W. 2009. Seeds: Time Capsules of Life. P.O. Box 1338, Ellicott Station, Buffalo, NY: Firefly Books (U.S.) Inc. 264 p.
  10. KITAYA Y, YABUKI K, KIYOTA M, TANI A, HIRANO T, AIGA I. 2002. Gas exchange and oxygen concentration in pneumatophores and prop roots of four mangrove species. Retrieved December 7, 2010 from http://www.springerlink.com/content/0wtyb14gmpjc3qqu/.
  11. MADER SS. 1993. Biology Part 4: Plant Structure and Function. 4th ed. Dubuque, Iowa: Wm. C. Brown Publishers. pp. 474-493.
  12. MERRILL ED. 1912. A Flora of Manila. (1976 reprint), Manila: Bureau of Printing. 491 p.
  13. POINCELOT RP. 1980. Horticulture: Principles and Practical Applications. Englewood Ciffs, New Jersey: Prentice-Hall, Inc. 652 p.
  14. POSTLETHWAIT J, HOPSON JL. 1989. The Nature of Life. New York, NY: Random House, Inc. pp. 631-653.
  15. RYUGO K. 1988. Fruit Culture: Its Science and Art. NY: John Wiley & Sons. 344 p.
  16. UNIVERSITY OF ARIZONA. 1998. Botany: plant parts and functions. Retrieved November 27, 2010 from http://ag.arizona.edu/pubs/garden/mg/botany/plantparts.html.
  17. VERHEIJ EWM, CORONEL RE, eds. 1992. Edible fruits and nuts. Plant Resources of South-East Asia No. 2. Bogor, Indonesia: Prosea Foundation. 447 p.
  18. WENT FW, THE EDITORS OF LIFE. 1963. The Plants. NY: Time Incorporated. pp. 73-98.

(Ben G. Bareja 2010, edited Apr. 13, 2019)

Note: This page on parts of a seed is a component page of The Plant Structure in the Angiosperms . The references apply to the whole series of articles.

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The parts of a seed in the angiosperms and their role in seed and plant development are reviewed.

Parts of the seeds

Phase One: Planting the Seed

When a seed starts to grow, we say it germinates. The cotyledons store food for the baby plant inside the seed. When the seed starts to germinate, the first thing to grow is the main root. The seed’s growing conditions usually need to be damp, warm, and dark, like springtime soil. A dry seed will stay dormant until it soaks in some water, then it will start to germinate.

There are two different types of seeds: dicotyledons and monocotyledons. Dicotyledons are seeds with two parts and monocotyldons have only one part. You can call theses seed types dicots and monocots for short.

An example of a dicot would be a bean seed. A bean seed that has been soaked in water has a soft outer covering. This outer covering is the seed coat. Inside of the seed would be a tiny plant called the embryo. The two large parts of the seed are called the cotyledons. The cotyledons are stored food that the young plant will use while it is growing.

Monocots are seeds that have only one cotyledon, such as the corn seed. Monocots have a thicker seed coat that does not slip off easily like the bean seed. The corn seed does not split open like the bean seed, it stays in one piece. One cotyldeon surrounds the embryo and is called the endosperm.

Phase One Vocabulary Definitions:

Seed Coat – Protects the inside of the seed.

Embryo – the beginning of the new plant.

Endosperm – Stored food in a monocotyledon.

Stored Food – a plant uses stored food until it grows leaves that can make food.

Monocot – a type of seed that has only one cotyledon.

Dicot – a type of seed that has two cotyledons.

Cotyledon – Leaf-like structure that absorbs and digest food stored in the seed.

Germination – the process of growing a new plant from a seed.

Parts of the seeds Phase One: Planting the Seed When a seed starts to grow, we say it germinates. The cotyledons store food for the baby plant inside the seed. When the seed starts to