Classification and Structure of Seed
Seed is aripened ovule which germinates to form a new plant.Its protective or hard covering is called seed coat or testa. It encloses a tiny embryo, which develops into a new plant.The embryo comprises a plumule or embryonic shoot, radicle or embryonic root and cotyledon which stores food for the nourishment of an embryo.
A seed remains dormant during unfavourable conditions.
On the basis of number of cotyledons, seeds are classified into monocots and dicots.
Seeds having one cotyledon are called monocot seeds. Maize, wheat, oat, etc. possess monocot seeds.
Maize is a single seeded fruit in which a seed coat and a fruit wall are fused together.
Its endosperm and embryonic part are separated by a thin epithelial layer. The outermost layer of its endosperm is called an aleurone layer. Its embryo consists of a scutellum, a radicle and a plumule. The radicle is enclosed in the coleorhiza, while the plumule is enclosed in the coleoptile.
On the other hand, seeds having two cotyledons are called dicot seeds. Bean, castor, pea, gram, etc., possess dicot seeds.
Bean seed is kidney-shapedwith convex and concave side. On its concave side, hilum is present. Its seed coat consists of testa and tegmen. Its embryoconsists of a plumule and a radicle.
Castor seed is also covered with a hard seed coat, which is divided into two parts:testa and tegmen.At the tip of testa, a massive outgrowth is present which is called caruncle or elaiosome.On one side of caruncle, a low ridge present which is called raphe.Hilum remains hidden beneath the caruncle. The fleshy storage tissue lying below its tegmen is the endosperm. Its embryo is embedded in endosperm and consists of cotyledons, radicle and plumule.
On the basis of presence of a persistent endosperm, seeds are classified into albuminous and exalbuminous.
Albuminous seeds have persistent endosperm. Their cotyledons are thin and membranous. They are of two types:dicot albuminous seeds and monocot albuminous seeds.
Custard apple and poppy seeds are dicot albuminous seeds, while seeds of corn, millets, etc., are monocot albuminous seeds.
Exalbuminous seeds do not have persistent endosperm. Their cotyledons are thick and fleshy.They are of two types:dicot exalbuminous seeds andmonocot exalbuminous seeds.
Gram seeds and mango seeds are dicot exalbuminous seeds, while seeds ofVallisneria, Orchid, Amorphophallus, etc., monocot exalbuminous seeds.
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The example of the plant having non-albuminous seeds isMarks:1
Explanation:Non-albuminous seeds have no residual endosperm as they are completely consumed during embryo development. The example is groundnut. The rest of the plants produce albuminous seeds.
Only one cotyledon is the characteristic feature of the monocotyledons. This feature can be noticed inMarks:1
Sugarcane belongs to the monocot, in which seeds have only one cotyledon. Rest of the plants are dicotyledonous.
Stalk of an ovule attached to a placenta is known asMarks:1
Explanation:Funicle is the structure by which ovule is attached to placenta.
Scutellum is a name given toMarks:1
Explanation:It is the part of embryo in seeds of Poaceae (grasses). It can be considered equivalent to the cotyledon of other monocotyledenous seeds. During germination, it absorbs degraded storage material from the endosperm and transfers it to the growing axis.
Micropyle of seed is involved inMarks:1
absorption of water.
Explanation:Micropyle performs the function of absorbing water during germination.