The Embryonal axis is divided into two major sections:
The section of the embryonal axis above the level of the cotyledons that terminates in a stem tip or plumule is referred to as the epicotyl.
It is the cylindrical section of a plant’s root system below the level of its cotyledons, which finishes in the root tip or radicle.
Root tips are normally protected by a root cap, which allows for easier soil penetration.
- The embryonic axis is made up of three sections, which are as follows: – the axis of rotation; – the axis of rotation; and – the axis of rotation.
- The plumule, the radicle, and the hypocotyl are all parts of the plant.
- The hypocotyl is the portion of the embryo axis between the cotyledon attachment point and the radicle (the term “hypocotyl” refers to “below the cotyledons”), whereas the epicotyl is the portion of the embryo axis between the plumule and the cotyledonary node (the term “epicotyl” refers to “above the cotyledons”).
Parts of the embryonal axis
A cotyledon is a critical component in the embryonic development of a plant’s seed. The embryonic leaf is the very first leaf to develop on a seed-bearing plant, and it is the leaf from which the very first leaves grow or appear. The seed contains an outer covering known as the seed coat, which protects an embryo that has been differentiated into three parts: the plumule, the radicle, and the cotyledons. It is the upper terminal section of the embryo that elongates and develops into the future shoot which is known as a plumule. The radicle, which grows into a future root, is located at the lower end of the embryo.
- The hypocotyl is the zone of transition between the shoot and the root, as well as the radicle. It is the portion of the embryo plant’s stem that lies beneath the stalks of the seed leaves, also known as cotyledons, and right above the root system.
- During embryonic development, epicotyl refers to the portion of the embryonic axis that is between the plumule and the point of attachment of the cotyledons. An embryonic or seedling stem’s portion above the cotyledon is referred to as the hypocotyl. With almost all plants, the epicotyl eventually develops into the plant’s leaves.
- In monocotyledon plants, the coleorhiza is a sheath-like structure located in the seed that serves as a protective covering for the radicle.
- Coleoptile can be defined as the pointed protective sheath that covers the emerging shoot in monocotyledons, such as grasses, and in which only a few leaf primordia and the shoot apex of the monocot embryo remain enclosed during development. Coleoptiles are divided into two circulatory bundles, one on either side of the spine.
Epicotyl
When a dicot embryo is formed, the distinction between epicotyl and hypocotyl can be distinguished by the fact that the latter is a part of the embryonal axis that is present above the cotyledons in the first stage of development. While the hypocotyl is a portion of the embryonal axis that is present beneath the cotyledon in a dicot embryo, the cotyledon is not.
Cotyledon
It is a seed leaf that develops within the embryo of a seed, in conclusion, Cotyledons assist in supplying the nutrition that a plant embryo requires to germinate and establish itself as a photosynthetic organism. Cotyledons may also serve as a source of nutritional reserves, or they may aid the embryo in metabolising nutrition that has been stored in other parts of the seed.
Conclusion
Angiosperms (flowering plants) whose embryos have a single cotyledon are classified as monocots or monocotyledonous plants; angiosperms (flowering plants) whose embryos have two cotyledons are classified as eudicots or eudicotyledons plants. The number of cotyledons in the embryos of gymnosperm seeds varies widely, ranging from 8 to 20 or more in some cases.