Seeds are the means by which most plants reproduce and disperse. They contain the embryo of a new plant, plus stored food for its development, all wrapped in a protective shell or hull.
Some seeds have physical dormancy that can be broken by soaking, cold/moist stratification or scarifying. Others have internal chemical dormancy that can be broken by gibberellin or abscisic acid treatments.
Definition
Seed is the characteristic reproductive body of flowering plants (angiosperms) and the majority of gymnosperms, including conifers and cycads. It consists of a miniature undeveloped plant embryo and stored food reserves enclosed within a protective outer covering, the testa.
In tennis, a higher seed is a team that has been ranked better by the tournament organizers and assigned to a particular round so that it does not have to face a stronger opponent early in the competition. The term is also used in other sports like American football and ice hockey to rank teams according to their regular-season performance.
There are two main types of seeds, monocot and dicot. The seeds can be bean-shaped (reniform), square or oblong, triangular, or egg shaped, being elliptical with one end broader than the other.
Origin
Seeds are one of the greatest evolutionary innovations in plant evolution. They are the result of a complex combination of physiological and morphological innovations.
The development of seeds was triggered by an evolutionary event in the late Devonian period 385 million years ago. This event involved the emergence of heterospory in plants (the production of separate male and female gametophytes), the formation of an indehiscent megasporangium, and the evolution of an integument that delimited a micropyle.
The integument evolved from the fusion of sterile spore anlagen (telomes) within the indehiscent megasporangium. This process gave rise to a receptacle with a defined micropyle that resembled the ovule of modern flowering plants. It also prompted the development of dormancy, an important feature in gymnosperms such as conifers and cycads.
Function
Seeds function as the primary means by which plants disseminate their offspring, and they are responsible for the vast majority of terrestrial plant biodiversity. They are also a valuable food source for both humans and animals.
A seed contains a fertilized embryo, which is contained within the seed coat, and a food reserve called endosperm, which provides nutrients to the developing embryo. There are two types of seeds: monocots and dicots, which differ based on the number of cotyledons they contain.
Monocots have one set of cotyledons attached to the embryo, while dicots have two sets. The point at the apex of the cotyledons is known as the plumule. The cotyledons provide nutrition to the seedling during germination. The embryo is covered by the seed coat, which may be thick and papery or dense and leathery.
Varieties
Every year many new varieties of agricultural and vegetable seed reach the marketplace. These seed varieties enable farmers and home gardeners to achieve specific objectives such as higher yields, competitiveness in a specialized market or adaptability to growing conditions. Unfortunately, misrepresentation of seed variety names can cost growers, seed companies and plant breeders money.
The names of seed varieties must be legally enforceable to protect the integrity of the market. The original name given to a variety when it is introduced into commerce is the legal name. A company may not rename a variety, but it can use a descriptive term in a variety name that adequately distinguishes the seed from another. For example, a seed company may use “GBR” in the name of its sorghum, but not “Allen cucumber.” This is to avoid confusion with other varieties on the market.
Uses
Seeds are an important food source (grains, beans, nuts, and forest trees), as well as a key to plant reproduction. They usually give a sprouting young plant a better start than does a spore, because of their larger food reserves and multicellularity.
Some seeds, like chamomile, are used in medicine; others, such as flax and cotton, are cultivated for fibers, while essential oils, including linseed, jojoba, and crambe, come from the seeds of some plants. They are also used to produce a wide range of industrial products, such as paints and plastics.
Plant breeders use wild seeds from all over the world to acquire valuable characteristics, such as disease resistance or drought tolerance. The seeds of many wild plants serve as long-term storable food resources for animals, such as acorns and hazelnuts.
