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 consists of an embryo which is enclosed in a protective outer covering called 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. Depending on the number cotyledons, seeds have been classified into two – monocotyledonous and dicotyledonous seeds. Continue reading to explore more about dicotyledonous and monocotyledonous seeds.
Structure of a Dicotyledonous Seed
- Peas, almonds and cashews are examples of dicotyledons or dicot seeds.
- Dicotyledons are also known as dicots. They are the groups into which all the flowering plants or angiosperms were formerly divided. The name dicotyledons refer to the seed having two embryonic cotyledons. There are around 200,000 species of dicotyledons discovered till date.
- In dicotyledons, the embryo consists of an embryo axis and two cotyledons. Cotyledons generally have a swollen appearance as it acts as a food reserve for the developing seedling. The embryo axis has two ends. The one which forms the shoot tip is called plumule and the portion at the lower end which forms the root tip is called radicle. The whole content is enclosed within a protective cover called the seed coat. The seed coat is made up of an outer layer called testa and an inner layer called tegmen. Moreover, the seed is attached to the fruit through a structure called hilum.
- Other dicot seeds examples include apples, plums and peaches.
Structure of a Monocotyledonous Seed
- Corn, wheat and rice, are examples of monocot seeds or monocotyledons.
- Embryos of a monocotyledonous seed possess only one large cotyledon called scutellum. The scutellum is generally shield-shaped and is located laterally towards a side of the embryo axis. As in dicotyledons, the embryo axis of monocotyledons possesses a shoot tip, plumule, enclosed in a sheath called coleoptile and a root tip, radicle, enclosed in coleorhiza. In a monocotyledonous seed, the endosperm is covered by a proteinous layer called aleurone layer.
- The majority of the 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 show exceptions.
- Other monocot seeds examples include ginger, banana, sorghum, onion, coconut and garlic.
Frequently Asked Questions
1. What is a dicotyledonous seed?
2. Highlight the structure of a dicotyledonous seed.
3. What is a monocotyledon?
4. Highlight the structure of a monocotyledonous seed.
A monocotyledonous seed has embryos that possess only one large cotyledon called scutellum. Generally, the scutellum is shaped like a shield. It is located laterally towards the side of the embryo axis. Like dicotyledons, the embryo axis of monocotyledons possesses a shoot tip called the plumule. It is enclosed in a sheath called coleoptile. It also has a root tip called the radicle, which is enclosed in coleorhiza. In a monocotyledonous seed, the endosperm is covered by the aleurone layer.