A seed is an important part of a flowering plant. They give rise to a new plant. They may be of different shapes, colours and sizes. They may be round, wrinkled, winged or hairy. They are in a dormant condition until they receive adequate sunlight, water, and soil. The growth of the plant from a seed is known as germination. A seed has three parts:
- Seed Coat
A seed coat protects the internal parts of a seed. The seed coat has two layers. The outer layer is thick and known as testa. The inner layer is thin and is known as tegmen.
A thick seed coat protects the seed from sunlight and water. It prevents the loss of water and entry of parasites within the seeds. The hard seed coats prevent germination during unfavourable environmental conditions.
An opening in the integument of the ovule known as the micropyle is visible on some seed coats. The hilum is also visible which is equivalent to the naval in humans where the umbilical cord is attached.
The endosperm contains the nutrients stored in it. It provides nutrients to the seed in the form of starch, carbohydrates and proteins to support the embryo during germination. It is located below the seed coat. The seeds remain viable with the intake of nutrients until germination.
The endosperm may be mealy, horny, continuous or ruminated. An endosperm has a triploid chromosome complement.
In corns and other cereals, endosperm constitutes a major portion of the seed. In seeds like beans, the endosperm is utilized in the embryo development and is absent in the seed. Coconut is a liquid endosperm.
Also read: Seed Dormancy
The embryo is the most important part of a seed. It is diploid developed from the fertilized egg. All the cells that need to develop into a mature embryo are present within the embryo. An embryo comprises of the following parts:
Epicotyl is a small shoot which gives rise to the entire plant shoot system.
The primary root emerges first during germination. It is also known as hypocotyl. It anchors the plant firmly in the soil.
Radicle is a small embryonic root.
The cotyledons provide nourishment to different parts of the embryo. It emerges as a tiny or fleshy leaf from the soil with the seedling during growth. It stores food in the form of starch and protein.
The embryonic leaves are the first to appear above the ground. An embryo develops from a fertilized egg.
Types of Seeds
There are two types of seeds:
- Monocotyledonous seeds
- Dicotyledonous seeds
These comprise of a single cotyledon emerging from the seeds on germination. For eg., rice, wheat, barley, mango, lilies, etc.
These comprise of two cotyledons emerging from the seeds on germination. For eg., corn, wheat, sugarcane, bamboo, etc.
Also read: Dicotyledonous and Monocotyledonous Seeds
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