What is a Seed and its types?

Introduction to Seed and Types of Seeds:

            Seeds play a vital role in crop production. It is an important key for agricultural progress and important component in agriculture. Seed quality plays an important role in the production of agricultural and horticultural crops. Seeds are of immense economic and biological importance.

In this post, we will let you know about what is a seed and its types, seed simple definition, what is a seed embryo, types of seed, seed definition biology, seed structure, parts of a seed, seed germination, seed formation, seed coat, two main types of seeds, examples of seeds, types of seed germination, examples of monocot seeds, examples of dicot seeds, what are the two main types of seeds, types of seeds in India, what are the two main types of seeds, seed definition biology.

What is Seed and Seed Classes

Definition of seed:

There are various definitions for a seed. A seed is defined as the matured and ripened ovule formed after fertilization and with the tissues from the mother plant. The formation of the seed is the process of reproduction in the crop plants. They contain reserve food materials like starch, proteins and other components that are necessary for the proper embryonic development and growth of plants. Any plant part which can be used for propagation purposes is called seeds. All vegetative materials like rhizomes, bulbs, tubers, corms, sucker, runner, stolon, setts and cuttings are considered as seed. In the presence of favorable environmental conditions like temperature, light and adequate soil moisture, the seed will develop into an independent and healthy plant bearing flowers and seeds during its life cycle.

Types of seeds/ Seed types

             The seed is the embryonic plant that is enclosed inside the protective outer layer. The structure is the most distinguishable specific genetic components that may vary among different each and every seed. This varies with the kind of crop but not with the variety.

However, based on the number of cotyledons present in the seed, they are classified as monocot seeds and dicot seeds.

Monocot seeds/ Monocotyledons:

            These are the seeds of angiosperms with single cotyledon. The seeds of monocots are single seeds usually embedded in a fruit called caryopsis and utricle. The seed coat and fruit coat are fused to form pericarp. It consists of minute embryo present at one end of the seed which is a viable part. The storage tissue present in monocots are endosperm and it is generally non – viable which occupies the major portion of the seed that is bulky. The embryo generally consists of embryonic axis having radicle and plumule which gets encloses in coleorhiza and coleoptile. The single cotyledon present in monocots is called as scutellum which is generally situated between radicle and plumule. The outer covering of endosperm is called the aleurone layer. Coleoptile protects the shoot meristem and plumule during field emergence. The coleorhiza protects radicle during germination. The major parts of monocot seeds are seed coat which is generally membranous and fused with fruit wall. It has generally only one outer covering on the seed.

Examples of monocot seeds are paddy, wheat, maize, ragi, bajra, barley, sorghum, ginger, banana, sorghum, onion, coconut and garlic.

Dicot seeds/ Dicotyledons:

            These are the seeds of angiosperms with two fleshy cotyledons. The dicot seeds generally consist of a primary embryonic axis and a storage tissue called cotyledon which combines and forms the embryo of the seeds. Usually, these embryo gets enclosed in the seed coat. Mostly these dicots don’t have the endosperm since it is fully utilized by the embryo for its development during its early stages. The cotyledon is the sole storage food organ as it absorbs the food from the endosperm. Seeds are generally round to oval surrounded by a protective seed coat with the scar of hilum and micropyle. The major parts of dicot seeds are seed coat which has two layers called the outer testa and inner tegmen which covers the inner embryo and endosperm, hilum which is a scar present on the seed coat at the point of attachment of seed with the funicle, micropyle which is the small hole present at one end of the seed, radicle and plumule.

 Examples of dicot seeds are chickpea, bitter gourd, castor, black gram, green gram, horse gram, soya bean, broad bean, cowpea, coconut, tomato, sesame, linseed, tobacco, lettuce, mustard, fenugreek, cotton, beet, coffee, litchi, mango, neem and bottle gourd.

            Based on the utilization of endosperm present inside the seeds, they are classified as albuminous seeds and exalbuminous seeds.

Albuminous or endospermic seeds:

            This endosperm provides nutrition to the developing embryo but it remains even during the germination of the seeds. Most monocots are called as albuminous seeds

            Examples of albuminous or endospermic seeds are paddy, maize, barley, sorghum, pearl millet, wheat, and all other monocots except orchids and onion.

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Exalbuminous or non-endospermic seeds:

             These are the seeds which have the storage food and cotyledons in a structure called as kernel and the endosperm gets completely utilized by the embryo for its development and will not remain until the seeds mature. Mostly dicots are called as exalbuminous seeds.

            Examples of exalbuminous or non-endospermic seeds are pigeon pea, chickpea, coriander, black gram, green gram, horse gram, broad bean and all other dicots except castor and sunflower.

            Based on the germination of seeds, seeds are classified as epigeal, hypogeal and hypo-epigeal germination seeds.

Epigeal germination:

             In this type of germination, the hypocotyl emerges and elongates quickly that pushes upwards leading to the pulling of cotyledons that generally move above the soil. Bean, castor, papaya, gourd, sunflower, watermelon, cucumber, lilies, pumpkin, cotton and onion generally have this type of epigeal germination.

Hypogeal germination:

            In this type of germination, the epicotyl elongates where the plumule is carried upwards and the cotyledons remain below the soil. Pea, mango, maize, rice, gram, groundnut, horse gram, green gram and coconut have this type of hypocotyl germination. The epicotyl expands to rise the first true leaf of the soil and the hypocotyl remains short and compact.

Hypo-epigeal germination:

            In this type of germination, where one cotyledon leaves beneath the soil as hypogeal germination while the other comes out of the soil as epigeal germination. Example of hypo- epigeal germination is Peperomia peruviana. Epicotyl is the portion of the embryonic axis that lies above the cotyledon in the embryo of dicots. The terminal end of epicotyl is plumule. Hypocotyl is the portion of the embryonic axis that lies below the cotyledon in the embryo of dicot seeds.

Conclusion of seed and seed types: Germination is one of the most important criteria which determines the seed quality as it affects the crop establishment and considerably the yield. Thus, seeds serve several functions for the plants or mother plants that produce them.