Mature embryo surrounded by nutritive tissue and protected by a coat
The mature embryo is surrounded by a nutritive tissue called endosperm or perisperm. This tissue provides nourishment to the developing embryo. In some plants, the endosperm is formed by the fusion of two sperm cells with the central cell of the female gametophyte. In other plants, the perisperm is formed by the proliferation of the nucellus tissue surrounding the embryo sac.
The mature embryo is also protected by a coat, which is commonly referred to as a seed coat. This seed coat is derived from the integuments of the ovule and provides a protective covering for the embryo. The seed coat helps to prevent desiccation, mechanical damage, and fungal or bacterial infection. It may be thick and hard or thin and membranous, depending on the plant species. The seed coat often has specialized structures, such as micropyles or hilums, which serve as entry points for water and gases during germination.
A mature embryo surrounded by nutritive tissue and protected by a coat refers to the structure found in seeds. Seeds are the reproductive structures of plants, containing a developed embryo that is capable of growing into a new plant under suitable conditions. Here are the steps involved in the formation and structure of a mature seed:
1. Fertilization: After pollination, the ovule in the flower's ovary becomes fertilized by the pollen. This triggers the development of the seed.
2. Embryo development: Within the ovule, the zygote (fertilized egg) undergoes cell division and differentiation to form an embryo. The embryo consists of different parts, including the embryonic axis and the cotyledons (seed leaves), which serve as the primary nutrient storage tissue.
3. Nutritive tissue: The cotyledons or embryonic axis often contain endosperm or cotyledonary tissue, which acts as a nutrient source for the developing embryo. Endosperm is a tissue derived from the fertilized central cell of the ovule, while cotyledonary tissue is formed from the embryo itself.
4. Seed coat formation: As the embryo develops, the ovule wall forms layers around it, forming the seed coat or testa. The seed coat protects the seed from environmental factors such as desiccation, pathogens, and physical damage. It is usually hard and provides mechanical support to the developing embryo.
5. Maturation: As the seed continues to develop, it accumulates reserves of nutrients, such as carbohydrates, proteins, and oils, within the cotyledons or endosperm. These nutrient reserves provide energy and essential substances for seed germination and early seedling growth.
Once the seed reaches maturity, it undergoes a dormant period, during which it remains inactive until suitable conditions for germination are encountered. When conditions such as moisture, temperature, and light become optimal, the seed undergoes germination, leading to the growth of a new plant.