What Is a Seed Coat?
When you look at a tough seed such as a bean, corn or nasturtium seed, you’re not viewing the actual seed but also the seed coat. A difficult seed coat protects the inner parts from drying out and prevents water and insects from accessing the tender embryo inside. In addition, it prevents premature germination by pushing the seed to remain dormant until the time is right.
Seed Structure
A seed consists of three major parts: an embryo, an endosperm and a seed coat. The embryo is just a very small plant that will grow to your full-sized plant once the seed germinates. A large part of the interior of a seed is taken up by the endosperm, which is composed of carbohydrates and proteins that nourish the embryo for the first few days after germination. These two structures are enclosed by the seed coat, which protects the seed until it germinates.
Seed Coat Dormancy
Hard seed coats that are impermeable to water and air induce a form of dormancy, known as seed-coat dormancy, by limiting the embryo’s access to water and air. Embryos can not grow without water and air, so the seed remains dormant until the seed coat is penetrated. This shields the embryo by preventing germination before the time is right. In nature, a seed coat can be broken down by microbes, weathering, fire or being partially digested by animals. (Reference 1)
Breaking Through Seed Coats
Nature has a strategy for breaking via seed coats, but if a gardener plants seeds in the backyard that he doesn’t want to wait for the seed to complete the seed-coat dormancy cycle. Manually abrading or softening the seed coat is known as scarification. You may scarify seeds by nicking them with nail clippers or a sharp knife, then abrading them with sandpaper or just soaking them in warm water. Be careful you don’t hurt the inner embryo when nicking or abrading seed coats. (Reference 3)
Seed Germination
A seed starts the germination process once the seed coat is interrupted and the internal areas of the seed begin to take water up. As the seed swells and the ejaculate increases access to oxygen, it begins to soften the accessible store of carbohydrates and also create proteins that will become radicles — the lower portion of this plant that becomes roots — and the plumule — the shoot which eventually becomes the upper foliage. As the roots kind they descend into the soil in search of nutrients and moisture, while the shoot pushes its way over the soil.