Seed Coat – Definition & Detailed Explanation – Botanical Terms Glossary

What is a seed coat?

A seed coat, also known as a testa, is the protective outer covering of a seed. It is a tough, outer layer that surrounds and protects the embryo and endosperm within the seed. The seed coat plays a crucial role in protecting the seed from physical damage, pathogens, and dehydration.

Why do seeds have seed coats?

Seeds have seed coats to protect the delicate embryo and endosperm inside from external threats. The seed coat acts as a barrier, preventing harmful microorganisms, insects, and animals from accessing the seed and damaging its contents. Additionally, the seed coat helps to maintain the moisture levels within the seed, ensuring that the embryo remains viable until conditions are favorable for germination.

How does the seed coat protect the seed?

The seed coat protects the seed in several ways. Firstly, it acts as a physical barrier, preventing mechanical damage to the embryo and endosperm. The tough outer layer of the seed coat can withstand pressure, abrasion, and other forms of physical stress. Secondly, the seed coat contains chemical compounds that deter pathogens and pests from attacking the seed. These compounds may have antimicrobial or insecticidal properties, helping to keep the seed safe from harm. Finally, the seed coat helps to regulate the moisture levels within the seed, preventing dehydration and maintaining the viability of the embryo.

What are the different layers of a seed coat?

The seed coat is composed of several layers, each with a specific function. The outermost layer of the seed coat is called the testa, which is a tough, protective layer that provides physical protection to the seed. Beneath the testa, there may be one or more additional layers, such as the tegmen or inner integument, which provide further protection and support to the seed. The innermost layer of the seed coat is the endotesta, which is in direct contact with the embryo and endosperm.

How does the seed coat affect germination?

The seed coat plays a critical role in the germination process. In many plant species, the seed coat must be breached or altered in some way for germination to occur. This can be achieved through physical scarification, where the seed coat is scratched or abraded to allow water and oxygen to penetrate the seed. Alternatively, chemical scarification can be used to soften the seed coat and promote germination. Some seeds require stratification, a period of cold or moist conditions, to break dormancy and allow germination to proceed. In some cases, the seed coat may inhibit germination by preventing water uptake or gas exchange, requiring specific conditions or treatments to overcome.

How can the seed coat be removed or altered for propagation?

There are several methods for removing or altering the seed coat to promote germination and propagation. Physical scarification involves scratching, nicking, or sanding the seed coat to break its protective barrier. This can be done manually with a knife or file, or mechanically using sandpaper or a seed scarifier. Chemical scarification involves treating the seeds with acid or other chemicals to soften the seed coat and promote germination. Another method is hot water treatment, where seeds are soaked in hot water to soften the seed coat. Finally, stratification involves exposing the seeds to cold, moist conditions to break dormancy and allow germination to occur. By carefully manipulating the seed coat, growers can improve germination rates and propagate a wider variety of plant species.