A seed consists of three parts: Seed coat:It is an outer covering of the seed,also called testa.It provides protection for the tiny plant within it.It also prevents the seed from drying up. Endosperm:It is the plant's food supplier that provides food for the growing embryo enclosed within it. Embryo:An embryo is a small plant,which grows into an adult plant on finding suitable conditions.
Definition of Seed:
A true seed is defined as a fertilized mature ovule that possesses embryonic plant, stored material, and a protective coat or coats. Seed is the reproductive structure characteristic of all phanerogams. The structure of seeds may be studied in such common types of pea, gram, bean almond or sunflower.
They are all built on the same plan although there may be differences’ in the shape or size of the seed the relative proportion of various parts.
There are hundreds of variations in the seed size, shape, colour and surface. The seeds range in size from tiny dust particles, as found in some orchids, to large double-coconuts. The seed surface may be smooth, wrinkled, striate, ribbed, furrowed, reticulate, tuberculate, alveolate, hairy, and pulpy or having patterns like finger prints.
In the seed, life activities are temporarily suspended in order to enable the plant to successfully pass through unfavourable and injurious climatic conditions. On the approach of favourable conditions, the seed resumes active life and grows into full plant. In the form of seeds, a plant can be carried to long distances without special precautions.
Structure of Seed:
The various parts of a seed may be easily studied after it has been soaked in water for a day or so varying according to the nature of the seeds. A mature seed contains an embryonic plant (with a radicle and plumule), and is provided with reserve food materials and protective seed coats. A mature pod of pea (Pisum sativum) has a number of seeds arranged in two rows.
The seeds are attached to the fruit wall by a small stalk, the funiculus. At maturity, on one side of the seed coat a narrow, elongated scar representing the point of attachment of seed to its stalk is distinctly seen, this is the hilum. Close to the hilum situated at one end of it there is a minute pore, micropyle. During seed germination, water is absorbed mainly through this pore, and the radicle comes out through it