Structure and Germination of Seed

  • In this structure and germination of seed post we have briefly explained about seed, structure, and seed function.

Structure and Germination of Seed

Seed?

  • The seed is the part of a plant that develops from the ovules following fertilisation. They are contained within the fruit that develops from a fertilised ovary. The seeds are formed as a result of sexual reproduction and contain a young embryo that has the potential to develop into a new plant.

Structure

  • Seeds of different plants may vary in many ways, but the basic anatomy remains the same. A typical seed consists of the following parts:

Structure and Germination of Seed

  • Tesla: The testa of higher plant seeds protects the embryo from harmful environmental factors. Its primary seed function is to control germination through dormancy imposition and to limit the harmful activity of physical and biological agents during seed storage. It is a tiny pore in the testa that lies on the opposite of the tip of the radicle. It permits water to enter the embryo before active germination.
  • Hilum: Is a scar left by the stalk which attached the ovule to the ovary wall before it became a seed.
  • Cotyledon:  In some plants, this contains high quantities of starch and will provide a source of food for the developing embryo prior to germination, in other plants this role is performed by an endosperm. In monocotyledons, there is just one cotyledon whereas in dicotyledons there are two. Depending on the type of germination (epigeous or hypogeous) the cotyledons may remain below ground or be pulled above ground.
  • Radicle: This is the embryonic root which will develop into the primary root of the plant. It is usually the first part of the embryo to push its way out of the seed during germination.
  • Plumule: This is the embryonic shoot. It appears as a bud which will give rise to the shoot and the remaining structures in the plant.
  • Endosperm: In many plants, a separate part for storage of starch develops and this is called the endosperm. It is seen in maize and wheat.

Seed Function

Species Existence

  • The most seed function is to ensure the survival of a species. All of the different functionality mechanisms collaborate to keep the plant embryo inside the seed alive until the conditions are favorable for the seed to germinate with a chance of survival. A variety of factors influence seed germination, including the amount of sunlight, moisture, and temperature. When seeds fail to produce seedlings that flower and produce seeds, a species becomes extinct.

Seed Dispersal

  • If seeds fall next to the mother plant, seedlings become crowded and compete with each other as well as the parent plant, reducing the species’ survivability. The seed is important in both carrying plant life through periods of unfavourable conditions and in distributing plants from one location to another. 

  • Certain seeds are adapted to wind distribution; some have hair tufts (for example, poplar and milkweed), while others are winged (for example, maple and catalpa). Other seeds, such as coconut, are adapted to water distribution, while still others are carried by animals, either in the fur or the digestive tract. Water-resistant coats are required for seeds distributed by water to avoid premature germination.

Adaptations

  • Certain plant fruits have unique adaptations that aid in distribution. Some seeds, for example, are forcefully discharged from the fruit as a result of internal pressure buildup (touch-me-not, for instance). The seeds can be thrown for several feet (as is the case with Impatiens). In such cases, a mere touch will result in a violent outburst. Pansies and violets release their seeds one at a time from their pods. Mistletoe produces sticky seeds that cling to the beaks of birds. Later, the birds scrape the seeds from the bark of another tree.

Time Capsules

  • Plants that grow in harsh environments may take a long time, even decades, before favourable germination conditions for a specific species occur. In such cases, seeds act as time capsules, lying dormant in the soil awaiting the right conditions to sprout. Annual desert wildflowers have long-lasting seeds.

Food Source

  • Seeds provide enough food for the embryos they contain to survive germination. Carbohydrates, fats, and proteins can all be found in endosperm. Small, quick-sprouting, fast-growing seeds typically do not have a lot of endosperm. A large supply of endosperm allows seed and seedling survival in seeds that are exposed to harsh conditions for extended periods of time. Coconuts survive by floating thousands of miles to reach coastal beaches, where they can germinate for months. To get through this period, the seed provides an abundance of endocarp in the form of coconut flesh and milk.

Further Readings

Reference