Categories
BLOG

seed facts

Did you know? Seeds

The function of all flowering plants is to produce seeds. Once the seeds have grown and ripened, the plant has to get them to somewhere that they will be happy growing. Find out how they do this.

On this page

  • How plants spread seeds
  • Interesting facts
  • Activity

Page options

How plants spread seeds

Plants have many ways of spreading or dispersing their seeds.

  • gravity – heavy seeds will just fall off the plant.
  • wind – very fine seeds will blow away on the wind. Some seeds have special parachutes or wings to help them fly, for example, dandelions.
  • hooks – the seeds are covered with hooks which catch on to a passing animals’ fur; they then catch a free ride to another place where they are rubbed off later.
  • animals – the seeds look like tasty treats for the animals to eat, but they pass undigested through the animal. Animals, including birds and insects, sometimes bury the seeds.
  • pepperpot – the seed-pod is like a little pepperpot and sprinkles the seeds over quite a wide area.
  • exploding – the seed-pod bursts suddenly, throwing all the seeds out over a large area.
  • floating – some seeds grow with air trapped in them, so they can float away from the parent plant.

Interesting facts

  • The largest seed in the world is the double coconut. It can measure up to 50cm (1.6ft) around the middle! Coconuts have a fibrous coating and an air space inside them, because they need to be able to float to a new home. Some coconuts have floated 2,000km over the sea before they find dry land!
  • Seeds provide the world’s daily food. Your breakfast cereal and toast, your pasta or pizza lunch and your rice dish for tea all started life as seeds from different grasses. Read more about cereals in our Did you know? article.
  • Some orchid seed-pods hold 3 million seeds.
  • Kapok is soft, fluffy stuff that comes from a seed-case. Years ago it was used to fill life jackets, because it is light, strong and waterproof. Nowadays, modern plastics have replaced it.
  • Some seeds found in frozen soil in Canada were grown and produced flowers – the seeds were thought to be more than 10,000 years old!
  • There are some very dangerous seeds, such as those that come from deadly nightshade; two berries could kill you. Even more dangerous are the seeds from the Castor-oil plant – one bean will kill an adult.
  • Most oak trees don’t grow acorns until they are at least 50 years old. If you have planted an acorn, how old will you be before you can plant its acorns?

Activity

Try growing an oak tree from an acorn in our home-grown project.

Discover interesting facts about seeds Gardening with Children from BBC Gardening

Seed facts for kids

A seed is the part of a seed plant which can grow into a new plant. It is a reproductive structure which disperses, and can survive for some time. A typical seed includes three basic parts: (1) an embryo, (2) a supply of nutrients for the embryo, and (3) a seed coat.

There are many different kinds of seeds. Some plants make a lot of seeds, some make only a few. Seeds are often hard and very small, but some are larger. The coconut is as big as a child’s head, but it contains more than just a seed. At the start, seeds are dormant (resting inside their coat) for a while. When the seed is ready to develop, it needs water, air and warmth but not sunlight to become a seedling.

Seeds carry the food that helps the new plant begin to grow. This food store is in the endosperm, and/or in the cotyledons. Many kinds of seeds are good food for animals and people. The many kinds of grain that people grow, such as rice, wheat, and maize, are all seeds. Seeds are often inside fruits.

Contents

  • Seed production
  • Development
    • Ovule
    • Embryo
  • Shape and appearance
  • Structure
    • Embryo
    • Nutrient storage
    • Size and seed set
  • Functions
    • Embryo nourishment
    • Dispersal
      • By wind (anemochory)
      • By water (hydrochory)
      • By animals (zoochory)
    • Dormancy
  • Germination
  • Economic importance
    • Seed market
    • Edible seeds
    • Other uses

Seed production

Angiosperm seeds are produced in a hard or fleshy structure called a fruit that encloses the seeds for protection in order to secure healthy growth. Some fruits have layers of both hard and fleshy material. In gymnosperms, no special structure develops to enclose the seeds, which begin their development “naked” on the bracts of cones. However, the seeds do become covered by the cone scales as they develop in some species of conifer.

Seed production in natural plant populations varies widely from year to year in response to weather variables, insects and diseases, and internal cycles within the plants themselves. Over a 20-year period, for example, forests composed of loblolly pine and shortleaf pine produced from 0 to nearly 5 million sound pine seeds per hectare. Over this period, there were six bumper, five poor, and nine good seed crops, when evaluated for production of adequate seedlings for natural forest reproduction.

Development

I Zygote
II Proembryo
III Globular
IV Heart
V Torpedo
VI Mature Embryo

Angiosperm (flowering plants) seeds consist of three genetically distinct constituents: (1) the embryo formed from the zygote, (2) the endosperm, which is normally triploid, (3) the seed coat from tissue derived from the maternal tissue of the ovule. In angiosperms, the process of seed development begins with double fertilization, which involves the fusion of two male gametes with the egg cell and the central cell to form the primary endosperm and the zygote. Right after fertilization, the zygote is mostly inactive, but the primary endosperm divides rapidly to form the endosperm tissue. This tissue becomes the food the young plant will consume until the roots have developed after germination.

Ovule

After fertilization the ovules develop into the seeds. The ovule consists of a number of components:

  • The funicle (funiculus, funiculi) or seed stalk which attaches the ovule to the placenta and hence ovary or fruit wall, at the pericarp.
  • The nucellus, the remnant of the megasporangium and main region of the ovule where the megagametophyte develops.
  • The micropyle, a small pore or opening in the apex of the integument of the ovule where the pollen tube usually enters during the process of fertilization.
  • The chalaza, the base of the ovule opposite the micropyle, where integument and nucellus are joined together.

The shape of the ovules as they develop often affects the final shape of the seeds.

Embryo

The main components of the embryo are:

  • The cotyledons, the seed leaves, attached to the embryonic axis. There may be one (Monocotyledons), or two (Dicotyledons). The cotyledons are also the source of nutrients in the non-endospermic dicotyledons, in which case they replace the endosperm, and are thick and leathery. In endospermic seeds the cotyledons are thin and papery. Dicotyledons have the point of attachment opposite one another on the axis.
  • The epicotyl, the embryonic axis above the point of attachment of the cotyledon(s).
  • The plumule, the tip of the epicotyl, and has a feathery appearance due to the presence of young leaf primordia at the apex, and will become the shoot upon germination.
  • The hypocotyl, the embryonic axis below the point of attachment of the cotyledon(s), connecting the epicotyl and the radicle, being the stem-root transition zone.
  • The radicle, the basal tip of the hypocotyl, grows into the primary root.

Shape and appearance

A large number of terms are used to describe seed shapes, many of which are largely self-explanatory such as Bean-shaped (reniform) – resembling a kidney, with lobed ends on either side of the hilum, Square or Oblong – angular with all sides more or less equal or longer than wide, Triangular – three sided, broadest below middle, Elliptic or Ovate or Obovate – rounded at both ends, or egg shaped (ovate or obovate, broader at one end), being rounded but either symmetrical about the middle or broader below the middle or broader above the middle.

Other less obvious terms include discoid (resembling a disc or plate, having both thickness and parallel faces and with a rounded margin), ellipsoid, globose (spherical), or subglobose (Inflated, but less than spherical), lenticular, oblong, ovoid, reniform and sectoroid. Striate seeds are striped with parallel, longitudinal lines or ridges. The commonest colours are brown and black, other colours are infrequent. The surface varies from highly polished to considerably roughened. The surface may have a variety of appendages (see Seed coat). A seed coat with the consistency of cork is referred to as suberose. Other terms include crustaceous (hard, thin or brittle).

Learn Seed facts for kids