Aim:

To identify the different parts of an embryo of a dicot seed (such as pea, gram, or red kidney bean) after soaking it in water.

Material Required:

1. A few seeds of gram, pea, or red kidney bean.
2. Beaker or Petri dish.
3. Water.
4. Forceps and a dissecting needle.
5. A hand lens or a dissecting microscope.
6. Blotting paper.
7. Practical notebook for recording observations.

Theory:

A seed is a mature, fertilized ovule that contains an embryo and stored food, enclosed within a protective seed coat. Dicotyledonous (dicot) seeds are those which have two embryonic leaves, or cotyledons.

The main parts of a dicot seed are:

1. Seed Coat: The outermost protective covering of the seed. It consists of two layers:
   • Testa: The thick, outer layer.
   • Tegmen: The thin, inner layer.
     The seed coat has a scar called the hilum, which marks the point where the seed was attached to the fruit. Above the hilum is a tiny pore called the micropyle, which allows the entry of water and oxygen during germination.
2. Embryo: The embryo is the young plantlet within the seed. It consists of:
   • Cotyledons (Two): These are thick, fleshy structures that store food for the embryo.
   • Embryonal Axis (Tigellum): This is the main axis of the embryo to which the cotyledons are attached. It has two ends:
     • Plumule: The part of the axis that develops into the future shoot (stem and leaves). It is typically feathery in appearance.
     • Radicle: The part of the axis that develops into the future root system. It is a pointed structure at the lower end.

Procedure:

1. Take 5-6 healthy seeds of gram, pea, or red kidney bean.
2. Place them in a beaker filled with water and allow them to soak overnight. This process, called imbibition, makes the seed swell and softens the seed coat, making it easier to dissect.
3. The next day, take one of the soaked seeds and place it in a petri dish or on a piece of blotting paper.
4. Observe the external features of the seed. Identify the tough outer covering (seed coat), the scar (hilum), and the small pore (micropyle).
5. Carefully remove the seed coat (testa) using forceps and a needle. It should peel off easily from the soaked seed.
6. Once the seed coat is removed, you will see two large, fleshy cotyledons.
7. Hold the seed firmly and gently separate the two cotyledons with your fingers or a needle. Be careful not to break the delicate embryo.
8. The embryo (embryonal axis) will be seen attached to one of the cotyledons near the pointed end.
9. Place the cotyledon with the attached embryo under a hand lens or a dissecting microscope for a closer look.
10. Identify the different parts of the embryo: the feathery plumule (future shoot) and the pointed radicle (future root).
11. Draw a neat, well-labeled diagram of the external view of the seed and the internal parts of the embryo as observed.

Observation:

1. The seeds swelled up after being soaked in water.
2. The outer covering of the seed, the seed coat, was easily removed.
3. A scar, the hilum, and a tiny pore, the micropyle, were visible on the external surface of the seed.
4. Inside the seed coat, there were two thick and fleshy cotyledons.
5. A small, whitish structure, the embryonal axis, was seen attached between the two cotyledons.
6. The embryonal axis consisted of two distinct parts:
   • A feathery, leaf-like structure at the upper end, identified as the plumule.
   • A pointed, root-like structure at the lower end, identified as the radicle.

(Space for Diagrams)

Two diagrams should be drawn here: (1) The external view of the seed, and (2) The opened seed showing the embryo.

Diagram 1: External View of Gram/Bean Seed
Labels: Seed Coat, Hilum, Micropyle

Diagram 2: Parts of a Dicot Embryo
Labels: Cotyledon, Plumule, Radicle, Embryonal Axis

Result:

The different parts of the embryo of the given dicot seed (gram/pea/bean) were successfully identified. The embryo consists of two cotyledons and an embryonal axis, which is composed of a plumule and a radicle.

Precautions:

1. Select only healthy, unbroken seeds for the experiment.
2. Soak the seeds for an adequate amount of time (8-10 hours or overnight) to ensure they are soft enough.
3. Handle the soaked seeds gently to avoid damage.
4. Use the forceps and needle carefully to remove the seed coat without damaging the embryo inside.
5. Separate the cotyledons very gently, as the embryonal axis is delicate and can break easily.
6. Draw neat and accurately labeled diagrams of your observations.