A seed coat protects the internal parts of the seed from fungi, bacteria and insects and prevents water loss. The seed coat must split open before a new plant may emerge.
The outer layer of the seed coat, called the testa, is generally hard and thick. The second layer of the seed coat, known as the tegmen, is softer. In some plants, the seed coat does not open unless environmental conditions are ideal for plant growth. This condition is known as dormancy. In many plants, the seed coat covers storage tissues. The embryonic plant uses these food reserves until it is able to emerge from the seed coat and make its own food.