Question

structure of seed give 2 example each of seeds with 1 or 2 cotyledons

Answer 1

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.

Continuous with the hilum there is sort of ridge in the seed coat, the raphe. The seed is covered by two distinct seed coats; the outer whitish one is the testa, while the other inner thin, hyaline and membranous covering is the tegmen. The seed coats give necessary protection to the embryo which lies within.

The whitish fleshy body, as seen after removing the seed-coats is the embryo. It consists of two fleshy cotyledons and a short axis to which the cotyledons remain attached. The position of the axis lying outside the cotyledons, bent inward and directed towards the micropyle is the radicle and the other portion of the axis lying in between the two cotyledons is the plumule.

The plumule is crowned by some minute young leaves. The radicle gives rise to the root, the plumule to the shoot and the cotyledons store up food material. Since the reserve food material is stored in the massive cotyledons and the seed lacks a special nutritive tissue, the endosperm.

The seeds which lack endosperm at maturity are called non-endospermous or exalbuminous. On the other hand in several other plants such as castor bean (Ricinus communis), coconut (Cocos nucifera) and cereals, food is stored in the endosperm. Such seeds where endosperm persists and nourishes the seedling during the initial stages are called endospermous or albuminous.

Examples of monocots include rice, wheat, barley, mango, pineapples, lilies, tulips, callas and onions.

Dicots include many of the most popularly grown garden flowers and vegetables, including the legumes, the cabbage family, and the aster family, such as apples, beans, broccoli, carrots, cauliflower, cosmos, daisies, peaches, peppers, potatoes, roses, sweet pea, tomatoes.