Seeds are an essential element of sexual reproduction in plants. It is formed as the end product of sexual reproduction in plants and is exclusive only to angiosperms and gymnosperms.
Gymnosperms have no fruits or flowers; hence, their seeds are exposed or “naked”. On the contrary, angiosperms have matured ovules that develop within the fruits after fertilisation. It has an embryo which is covered in a protective outer covering called the seed coat. Some seeds have been documented having a triploid endosperm. An embryo is composed of three parts- a radicle, an embryo axis, and cotyledons. There are two types of monocotyledonous and dicotyledonous seeds depending on the number of cotyledons.
Some of the examples of dicotyledons or dicot seeds are peas, almonds and cashews
Dicotyledons seeds are also called dicots as they belong from the group in which all the flowering plants or angiosperms were formerly divided. The name dicotyledons refer to the seed having two embryonic cotyledons and there are around 200,000 species of dicotyledons discovered till date.
In dicotyledons, the embryo has an embryo axis and two cotyledons. Cotyledons look swollen as it acts as a food reserve for the developing seedling. The embryo axis has two ends. The upper tip is named as plumule and therefore the lower end is called the radicle. The whole content is enclosed within a protective cover called the seed coat and the seed coat is made up of an outer layer that is called the Testa and an inner layer called Tegmen. Moreover, the seed is attached to the fruit through a structure that is called Hilum.
Other dicot seeds examples include apples, plums and peaches.
Some of the examples of monocot seeds or monocotyledons are Corn, wheat and rice
Embryos of a monocotyledonous seed possess just one large cotyledon called scutellum. The scutellum is usually shield-shaped and is located laterally towards a side of the embryo axis. The embryo axis of monocotyledons consists of a shoot tip, plumule, enclosed inside a sheath called coleoptile and a root tip, radicle, enclosed in coleorhiza as in dicotyledons. In a monocotyledonous seed, the endosperm is covered by a proteinous layer called aleurone layer.
Almost all monocotyledonous seeds are albuminous seeds, i.e., they have thick, swollen endosperms for nourishment. The endosperm is not completely consumed during embryo development, and it is the nourishing tissues in seeds. However, some monocotyledons like orchids can be treated as exceptions.
Some other examples of monocot seeds are ginger, banana, sorghum, onion, coconut and garlic.
Similar conditions are required for both the monocot and dicot seed germination. The seeds should be completely developed with an embryo, an endosperm and right numbers of cotyledons and a testa. In this process, cotyledons and endosperms support the growing plant as a food source until the photosynthesis begins. An optimal environmental condition will be required for seed germination.
Seed germination begins with a seed absorbing water, which results in the swelling and a softening of a seed’s coat or testa. The water initiates biochemical activity in the seed. Monocots have starchy seeds and require only 30 percent moisture content to germinate. Dicots have oily seeds and can begin germination after reaching a minimum of 50 percent of moisture content. After this, a lag phase gives the prospect for a seed to start the internal processes like the cell respiration, protein synthesis and metabolism of food stores. After this, cellular division and elongation occur, pushing out the seed’s root and radicle.
In monocots, the basis that emerges is roofed by a coleorhiza, or sheath. Its seedlings’ leaves then come forth, during a layer referred to as a coleoptile. A primary root emerges from the seed in dicots,. This root allows water absorption by the new plant as this is a radicle. An apical meristem will eventually develop from this radicle and produce the plant’s rootage. Then its shoot comes first from the seed, consisting of the cotyledons, hypocotyl and epicotyl. Seedlings grow slowly after they emerge above the soil in both monocots and dicots,.The seedling first develops its roots and then its true leaves which will photosynthesize and convert sunlight to energy for the plant.
1. What are Dicotyledons?
Dicotyledon is a classification of flowering plants where the seed possesses two embryonic leaves or cotyledons.
2. What are monocotyledonous seeds?
Monocotyledon is a classification of flowering plants. Unlike the dicotyledons, monocotyledons are characterised by just one embryonic leaf.
3. What is the difference between Angiosperm and Gymnosperms?
Gymnosperms have no fruits or flowers; hence, their seeds are exposed or “naked”. On the contrary, angiosperms have matured ovules that develop within the fruits after fertilisation.