A seed is a fundamental reproductive unit for flowering plants and conifers. Its primary purpose is to safeguard and provide initial nourishment for a developing plant embryo, allowing it to survive until conditions are favorable for growth. This compact structure ensures the continuation of plant life by offering protection and a stored food supply for the young seedling. Each seed contains the core components necessary to potentially grow into a mature plant.
The Seed’s Protective Shell
The outermost layer of a seed, known as the seed coat or testa, provides a crucial protective barrier. This tough covering shields delicate internal structures from physical damage and acts as a defense against pathogens. Its composition often includes hard tissues that vary in thickness and texture among different plant species.
Beyond physical protection, the seed coat also plays a significant role in preventing desiccation. It regulates the passage of water and gases into and out of the seed, helping to maintain a stable internal environment. This regulation is essential for dormancy, ensuring the seed does not germinate prematurely until conditions are suitable for its survival and growth.
The Tiny Plant Within
Nestled inside the protective seed coat is the embryo, the rudimentary plant itself. This “baby plant” contains all the essential parts that will develop into a mature plant once germination occurs. The embryo comprises several distinct structures, each with a specific role in future development.
The radicle is the embryonic root, usually the first part to emerge during germination, growing downwards into the soil. Its initial function is to anchor the seedling and begin absorbing water and nutrients. The plumule represents the embryonic shoot, which will develop into the plant’s stem and leaves, growing upwards. Connecting these two regions is the hypocotyl, an embryonic stem that links the radicle and plumule.
The Seed’s Stored Food
For the embryo to begin its growth journey, it requires a source of energy and nutrients. Seeds store food in one of two primary ways: through the endosperm or within specialized embryonic leaves called cotyledons. This stored food provides the initial nourishment necessary for the seedling’s development before it can produce its own food through photosynthesis.
The endosperm is a nutritive tissue that develops alongside the embryo, serving as a food reserve. Many monocot seeds retain a significant endosperm that provides sustenance to the developing embryo. In contrast, cotyledons are embryonic leaves that can become thick and fleshy, directly storing food for the embryo. While some seeds primarily rely on endosperm, many dicots absorb its nutrients into their cotyledons, which then become the main storage organs.