The outer layer is called testa and the inner layer is called tegmen. There is a scar on the seed coat through which the developing seed was attached to the fruit. This scar is called hilum.

The Hilum
The scar on the seed coat through which the developing seed is attached to the fruit is called the hilum. The hilum is an important structure that plays a crucial role in the development and function of the seed.

Location and Appearance
The hilum is usually located at one end of the seed and appears as a small, oval-shaped scar or mark. It is formed where the seed was attached to the ovary wall during the development of the fruit. The hilum marks the point of connection between the seed and the placenta of the fruit.

Function
The hilum serves several important functions in the seed. These functions include:

1. Nutrient Absorption: The hilum contains small openings called micropyles that allow for the absorption of nutrients and water from the surrounding environment. These nutrients are essential for the growth and development of the seed.

2. Gas Exchange: The hilum also facilitates gas exchange, allowing oxygen to enter the seed and carbon dioxide to be released. This exchange of gases is necessary for cellular respiration and energy production within the seed.

3. Seed Dispersal: In some plants, the hilum also acts as a point of attachment for structures involved in seed dispersal, such as hooks, hairs, or wings. These structures aid in the dispersal of the seed away from the parent plant, increasing the chances of successful germination and establishment in new habitats.

4. Seed Germination: The hilum plays a vital role in seed germination. It is through the hilum that the embryonic root, known as the radicle, emerges during germination. The radicle grows downward, anchoring the seedling into the soil, and absorbs water and nutrients to support further growth.

Conclusion
In summary, the hilum is the scar on the seed coat that marks the point of attachment between the developing seed and the fruit. It serves important functions such as nutrient absorption, gas exchange, seed dispersal, and seed germination. Understanding the role of the hilum can provide valuable insights into the development and growth of seeds in plants.