Perisperm is:
Perisperm is the persistent nucellus in a seed. It plays a crucial role in providing nourishment to the developing embryo in certain plant species. Here is a detailed explanation of perisperm:

Definition:
Perisperm refers to the part of the seed that is derived from the nucellus of the ovule. It is a nutritive tissue that surrounds the embryo in certain plants.

Function:
Perisperm serves as a source of nutrients for the growing embryo during germination. It provides essential substances such as proteins, lipids, and carbohydrates to support the early stages of seedling development.

Composition:
Perisperm is composed of cells containing reserve food materials that are utilized by the embryo. These food reserves are stored in the perisperm to ensure the successful germination and growth of the seedling.

Origin:
Perisperm originates from the nucellus of the ovule, which is the central part of the female reproductive structure in plants. As the seed develops, the nucellus undergoes changes to form the perisperm.

Examples:
Some plant species that have perisperm include members of the families Caryophyllaceae, Polygonaceae, and Amaranthaceae. These plants rely on perisperm to provide nutrients to the developing embryo.
In conclusion, perisperm is the persistent nucellus in a seed that serves as a source of nourishment for the embryo. It is an essential component of certain plant seeds, ensuring the successful germination and early growth of the seedling.