The Seed: Embryo, Food Store and a Life in Waiting

A seed is a plant in a box. Inside is an embryo, a young plant that has stopped at a few hundred cells. Around it is food. Around that is a coat.

That arrangement lets a plant do something a fern cannot. It can put its next generation somewhere else, and it can leave it there for years until conditions improve.

This article follows the seed through the plant's life cycle: how it forms, what it carries, how it travels, how it waits, and what happens when it starts to grow.

What a Seed Is

A seed has three parts. The embryo is the young plant, with a shoot tip and a root tip. The food store feeds it until it can make its own sugar. The seed coat protects both.

Seed plants are the group that makes seeds, and they include the cone-bearing plants and the flowering plants. They make up most of the plants on land.

A seed is not a spore. A spore is a single cell that grows into a small plant, and most spores need damp ground to work. A seed is multicellular, carries its own food and can wait.

Part	What it does	Note
Embryo	The young plant, with a shoot tip and a root tip	It is already a plant, not a plan for one
Cotyledon	A seed leaf that stores or absorbs food	One in monocots, two in dicots
Endosperm	Starchy, oily or protein-rich tissue that feeds the embryo	Used up in a bean, kept in wheat
Seed coat	A tough outer layer that keeps water out and damage away	It must split before growth starts
Hilum	The scar where the seed was joined to the ovary wall	Easy to see on a bean
Micropyle	The small pore where the pollen tube entered	It is also where water enters

The parts of a seed, what each one does, and what to look for when you open one.

The number of cotyledons splits the flowering plants in two. A bean has two, and they swell with food. A grass such as wheat has one, pressed against the endosperm to absorb it.

Some seeds carry almost nothing. An orchid seed can weigh about 0.4 micrograms and has no real food store. It germinates only if a fungus supplies it with sugar, which is why orchids are hard to grow from seed.

Seeds of Phaseolus vulgaris, the common bean. Each one carries two thick cotyledons, a seed coat and a visible hilum. Image: Roger Culos, CC BY-SA 3.0, via Wikimedia Commons

How a Seed Forms

A seed starts as an ovule, a small structure inside the parent plant. It holds an egg cell and a supply of supporting tissue.

A pollen grain lands, grows a tube, and sends two sperm cells down it. What happens next is the strangest step in plant reproduction.

Double Fertilization, in Plain Words

One sperm fuses with the egg and forms the zygote. That cell divides and becomes the embryo.

The second sperm fuses with two polar nuclei in the same embryo sac. The result is a triploid cell, with three sets of chromosomes, and it becomes the endosperm.

So one pollen grain starts two tissues. The embryo becomes the plant. The endosperm becomes its food.

The food is used at different times. In a bean the endosperm is absorbed into the cotyledons before the seed matures. In wheat and maize it stays, which is why flour is mostly endosperm.

Seed development, from the zygote stage after double fertilization to a mature seed. Image: TheLAW14, CC BY-SA 3.0, via Wikimedia Commons

Gymnosperms do it differently. A pine delivers sperm to the egg, but there is no second fusion and no endosperm. The food sits in the female tissue around the egg.

Naked Seeds and Enclosed Seeds

Gymnosperms carry their ovules on the surface of cone scales. Nothing encloses them, which is why the group is called naked seeded. A pine seed sits on a scale, often with a wing, until the cone opens.

In flowering plants the ovule sits inside an ovary. After fertilization the ovule becomes the seed, and the ovary becomes the fruit.

That is why a fruit is not a seed. A sunflower seed sold in a shell is a fruit with one seed inside. A strawberry carries its seeds on the outside, each in its own tiny fruit. A coconut is a drupe: a fruit with a hard inner layer around a single seed.

The fruit is a dispersal device. It can be fleshy and eaten, dry and thrown, or winged and blown. The seed travels inside it.

How Seeds Travel

A seed that lands under its parent grows in its parent's shade and competes with it for water. Movement is worth a lot.

Plants use four main routes, and some use more than one.

Route	How it works	An example
Wind	A wing or a parachute of hairs slows the fall	Maple samara, dandelion
Water	A waterproof coat keeps the seed afloat	Coconut
Eaten by an animal	The coat survives the gut and is dropped elsewhere	Berries, figs
Carried on fur	Hooks or sticky mucus grip a passing animal	Burdock, mistletoe
Carried by ants	A fatty attachment feeds the ants, which drop the seed underground	Violets, trilliums
Thrown	The fruit dries, twists and snaps	Gorse, some violets

The main routes of seed dispersal, how each one works, and a plant that uses it.

Wind is the cheapest route and the least precise. A dandelion seed can travel for kilometers, and almost none of them land anywhere useful.

Winged seeds, or samaras, of red maple. The wing spins the seed as it falls, which slows the drop and lets the wind carry it sideways. Image: Dcrjsr, CC BY 3.0, via Wikimedia Commons

Water carries seeds that can float. A coconut can cross an ocean and still germinate, because its coat is thick and its interior holds water of its own.

A coconut, whole and opened. The hard shell and the fibrous husk protect a single large seed, and the liquid inside is part of its endosperm. Image: Ivar Leidus, CC BY-SA 4.0, via Wikimedia Commons

Animals move seeds in two ways. Fruit eaters carry a seed in the gut and drop it later. Mammals with fur pick up seeds that have hooks or sticky mucus, and the burdock is the classic case.

Fruits of greater burdock. Each hook catches fur or clothing, and the whole head travels with the animal until it is pulled off. Image: Famberhorst, CC BY-SA 4.0, via Wikimedia Commons

The Extremes of Size

Seed size runs from dust to a bowling ball.

The largest seed belongs to Lodoicea maldivica, the coco de mer, a palm found only in the Seychelles. A single seed can weigh up to 25 kilograms.

That size is expensive to make, so the tree produces few seeds, and they fall at the base of the parent. One hypothesis is that competition between parent and offspring favored seedlings with enough stored food to survive in deep shade.

A fruit of Lodoicea maldivica, the coco de mer. It holds the largest seed of any plant, up to 25 kilograms. Image: Hannes Grobe, CC BY-SA 4.0, via Wikimedia Commons

At the other end, an orchid seed can weigh about 0.4 micrograms. A plant that makes dust can make millions of seeds, but each one needs the right fungus to survive.

The trade is plain. Many small seeds buy distance and numbers. Few large seeds buy a seedling that starts with reserves.

Dormancy and Germination

A dormant seed is alive and not growing. It can sit in dry soil for years and still be viable.

Dormancy is not the same as being dry. A dormant seed will not germinate even when it is wet and warm, because something is still holding it back.

Two kinds are common. Coat-imposed dormancy is a physical barrier: the coat keeps out water or oxygen. Embryo dormancy is internal: the embryo is immature, or it is held back by chemicals.

Signal	What it tells the seed	An example
Cold	Winter has passed	Apple, many temperate trees
Heat or fire	A gap has opened in the canopy	Many Australian plants
Light	The seed is close to the surface	Lettuce, some grasses
A worn coat	The covering has been scraped or digested	Legumes, gut-passed berries
A long soak	Rain has washed the inhibitors away	Desert annuals

Signals that break seed dormancy, what each one tells the seed, and a plant that waits for it.

Why Some Seeds Wait Years

Waiting is a strategy. A desert annual may germinate only after a rain heavy enough to fill the soil, and its seed may wait a decade for that rain.

Some seeds wait far longer. In 2005, Israeli researchers sprouted a preserved date palm seed about 2,000 years old. The tree, a male named Methuselah, became the oldest seed known to have germinated with human help.

A soil seed bank does the same work at scale. Buried seeds come back when ground is disturbed, which is why old weeds appear in a newly dug garden.

What Happens When a Seed Wakes

Germination starts with water. The seed takes it up, swells, and its coat splits. The process is called imbibition.

Water switches on enzymes that break the stored starch and protein into sugars and amino acids. Those travel to the embryo.

The root tip, the radicle, comes out first. It anchors the seedling and starts taking up water. The shoot follows, usually with a bend that drags the tip through the soil instead of pushing it.

The cotyledons may rise above ground, as a bean's do, or stay below it, as a pea's do. Either way they feed the seedling until the first true leaves open.

Germination of a bean seedling, from the dormant seed to a seedling with open leaves. Image: HudsonFlagg, CC0, via Wikimedia Commons

A seedling needs three things: water, oxygen and a suitable temperature. Light matters too, and its role depends on the species: some seeds need light to germinate, and others need to be buried.

Seeds and People

Most of the calories people eat come from seeds. Wheat, rice and maize are grass seeds. Beans, peas and lentils are legume seeds. Peanuts, sunflower and rapeseed are grown for their oil.

We selected those seeds for size, taste, storage and yield over thousands of years. The result is a food supply built on a small number of species, and on a narrow range within each one.

That narrowness is a risk, and it is one reason seed collections exist.

Seed Banks as Insurance

A seed bank dries seed, chills it and stores it in sealed containers. Most crop seeds survive this, and can be kept for decades.

The largest backup sits inside a sandstone mountain on Spitsbergen, in the Svalbard archipelago, about 1,307 kilometers from the North Pole. The Svalbard Global Seed Vault holds duplicates of seeds already kept in national gene banks.

It is a backup, not a museum. A gene bank that loses its collection to war, fire or a failed freezer can ask for its duplicate back.

Not every seed can be stored this way. Avocado, mango, cocoa and oak seeds die if they are dried or frozen, so those collections are kept as living plants or in tissue culture.

The entrance to the Svalbard Global Seed Vault, set into a sandstone mountain above the Arctic Circle. Image: Miksu, CC BY-SA 3.0, via Wikimedia Commons

Collections are also tested. A sample is germinated every few years, and if too few grow, the stock is regrown from fresh seed.

A seed is a small bet on the future. It carries an embryo, a meal and a coat, and it waits for the moment when the odds improve. Most plants on land, and most of the food on a plate, depend on that arrangement.

Key Terms in Plain English

These are the words in this article that would send you to a dictionary. Each one is given here the way it is actually used above.

Term	What it means
Seed	A plant embryo with a food store, wrapped in a protective coat.
Embryo	The young plant inside a seed, with a shoot tip and a root tip.
Cotyledon	A seed leaf that stores food or absorbs it from the endosperm.
Endosperm	The food tissue of a seed, formed when a sperm fuses with two polar nuclei.
Seed coat	The tough outer layer of a seed, also called the testa.
Hilum	The scar on a seed where it was attached to the ovary wall.
Micropyle	The small pore in the seed coat where the pollen tube entered.
Ovule	The structure inside the ovary that becomes a seed after fertilization.
Ovary	The part of a flower that holds the ovules and becomes the fruit.
Double fertilization	The two fusions in a flowering plant: sperm with egg, and sperm with two polar nuclei.
Zygote	The cell formed when a sperm fuses with an egg.
Triploid	Having three sets of chromosomes, as the endosperm does.
Gymnosperm	A seed plant with seeds exposed on cone scales, such as a pine.
Angiosperm	A flowering plant, whose seeds sit inside a fruit.
Fruit	The structure that develops from the ovary and encloses the seed.
Dispersal	The movement of seeds away from the parent plant.
Samara	A winged fruit or seed that spins as it falls, as in a maple.
Mycorrhizal fungus	A fungus that lives with a plant root and supplies it with nutrients.
Dormancy	A live seed state in which growth does not start even when conditions are wet and warm.
Imbibition	The uptake of water by a dry seed, which makes it swell and split its coat.
Radicle	The root tip of the embryo, which emerges first at germination.
Plumule	The shoot tip of the embryo, which becomes the stem and leaves.
Seed bank	A collection of stored seed, kept to preserve crop or wild plant diversity.
Recalcitrant seed	A seed that dies if it is dried or frozen, such as avocado or oak.

Terms used in this article, defined in plain words.

Key Takeaways

• A seed holds an embryo, a food store and a coat, and that package can travel and wait.
• A spore is a single cell that grows on its own, while a seed is multicellular and carries reserves.
• Flowering plants build a seed by double fertilization: one sperm makes the embryo, the other makes the endosperm.
• A bean absorbs its endosperm into two cotyledons, while wheat keeps the endosperm as flour.
• Gymnosperms leave their seeds exposed on cone scales, and flowering plants enclose them in a fruit.
• Dispersal by wind, water, animals or the plant itself moves a seed away from its parent's shade.
• Dormancy is a live pause that a coat or an immature embryo imposes, and a signal such as cold or fire ends it.
• Germination begins with water, then the radicle emerges, and the cotyledons feed the seedling until its leaves open.
• Seed size is a trade between many small seeds that travel far and few large seeds that start with reserves.
• Seed banks store duplicates of crop diversity, and the Svalbard vault is the backup of last resort.

Frequently Asked Questions

What is a seed in simple words?

It is a young plant, paused. Inside the coat is an embryo, a store of food and enough water to keep the cells alive. When conditions suit it, the seed takes up water and starts to grow.

What are the three main parts of a seed?

The embryo, the food store and the seed coat. The food store is endosperm in wheat and maize, and the cotyledons in a bean, where the endosperm has already been absorbed.

What is double fertilization?

It is the pair of fusions that happens in a flowering plant. One sperm joins the egg and forms the embryo. The other joins two polar nuclei and forms the triploid endosperm that feeds it.

How is a seed different from a fruit?

A seed is the fertilized ovule. A fruit is the ovary around it, and it can be fleshy, dry, hard or winged. Many things sold as seeds, such as sunflower seeds in the shell, are really fruits.

Why do seeds need dormancy?

Dormancy stops a seed from germinating at the wrong time, such as in a dry spell or in the middle of winter. The seed waits for a signal that the season has changed and a seedling has a chance.

How long can a seed stay alive?

It depends on the species and the storage. Most crop seeds last years in a dry, cold bank, and a date palm seed about 2,000 years old was germinated in 2005. Many seeds in ordinary soil die within a few seasons.

What does a seed need to germinate?

Water, oxygen and a suitable temperature, plus whatever signal breaks its dormancy, such as cold, light or a split coat. Some also need light, and some need to be buried in the dark.

Why are seed banks important?

They keep the genetic variety that plant breeding depends on, and they hold a backup if a crop fails or a collection is lost. A narrow food supply is a fragile one, and stored seed is the reserve.

Key references
• Seed — structure, development and the largest seed (Wikipedia)
• Germination — imbibition, the radicle and what breaks dormancy (Wikipedia)
• Seed dispersal — wind, water, animals and ants (Wikipedia)
• Seed dormancy — coat-imposed and embryo dormancy (Wikipedia)
• Double fertilization — the two fusions and the endosperm (Wikipedia)
• Seed bank — storage, orthodox and recalcitrant seed (Wikipedia)
• Svalbard Global Seed Vault — the Arctic backup (Wikipedia)
• Recalcitrant seed — seeds that will not survive drying (Wikipedia)
• Cotyledon — one seed leaf or two (Wikipedia)
• Lodoicea — the coco de mer and its fruit (Wikipedia)
• Judean date palm — the 2,000-year-old seed called Methuselah (Wikipedia)

Sources: the Wikipedia article on seeds, for the parts of a seed, the separation of gymnosperm and angiosperm seeds, the orchid seed of about 0.4 micrograms with no significant reserves, the largest seed at up to 25 kilograms, and the note that many structures sold as seeds are dry fruits; the article on germination, for imbibition, the emergence of the radicle and plumule, the stored reserves, cold stratification, and the fire, soaking and gut-passage cues that end dormancy; the article on seed dispersal, for wind, water and animal routes and for the elaiosome that ants collect; the article on seed dormancy, for coat-imposed dormancy and the heat, fire, freezing and digestive signals that break it; the article on double fertilization, for syngamy and triple fusion and the triploid endosperm; the article on seed banks, for orthodox seed that survives drying and cold storage and for the Svalbard vault inside a sandstone mountain about 1,307 kilometers from the North Pole; the article on the Svalbard Global Seed Vault, for its role as a duplicate store for national gene banks; the article on recalcitrant seed, for avocado, mango, cocoa and oak seed that dies when dried or frozen; the article on cotyledons, for one seed leaf in monocots, two in dicots, and the acotyledonous orchids; the article on Lodoicea, for the coco de mer and the hypothesis that competition between parent and offspring favored large fruit; and the article on the Judean date palm, for the 2,000-year-old seed sprouted in 2005 and the male tree named Methuselah. Each source was opened and read in full. Figures are from Wikimedia Commons under the credit named in each caption. This article is written for education.