The below mentioned article provides a short note on Epidermal Tissue System of Plant. After reading this article you will learn about: 1. Subject Matter of Epidermis 2. Functions of the Epidermis.
Subject Matter of Epidermis:
The epidermis usually consists of a single layer of cells which cover the whole outer surface of the plant body. The word is derived from two words of Greek origin, epi, upon, and derma, skin. It is a continuous layer except for certain small pores, called stomata and lenticels. According to the histogen theory introduced by Hanstein in 1870, it is derived from dermatogen of apical meristem.
In meristematic regions it is, of course, undifferentiated, and in older stem and roots it may have been destroyed by secondary growth. Mostly the epidermis is single layered, but in many plants it has been described as bi-or multiseriate. In the leaves of India rubber plant (Ficus elastica), banyan tree (Ficus bengalensis), oleander (Nerium spp.), etc.
It becomes two to multi-layered. The epidermal cells may be somewhat irregular in outline, usually varying in shape and size and arranged very close to each other having no intercellular spaces among them. The cells possess a large central vacuole and thin peripheral cytoplasm.
The cells may contain leucoplasts, anthocyanins and chromoplasts, but no chloroplasts except in guard cells. In the epidermal cells of certain aquatic (e.g., Hydrilla) and shade loving plants the chloroplasts are also found. Sometimes, the substances like mucilage, tannin and calcium carbonate crystals (cystoliths) are also found in these cells.
The walls of epidermal cells are unevenly thickened. The inner and radial walls are comparatively thicker. This additional thickness is due to the impregnation of suberin or cutin. The suberization and cutinization of the walls protect the epidermis from mechanical injuries and prevent from loss of water.
In the case of roots the outermost layer is known as the epiblema, piliferous layer or rhizodermis. Usually its cells extend outwards in the form of tubular unicellular root hairs, which help in the absorption of water and mineral nutrients from the soil.
Functions of the Epidermis:
1. The epidermis is primarily a covering layer which helps in the protection of the internal soft tissues against mechanical injury.
2. It prevents excessive evaporation of water from the internal tissues, for this, several adaptations like development of thick cuticle, wax, hairs, etc., take place.
3. It also serves in photosynthesis and secretion.
4. The epidermis acts as store house of water in many xerophytic plants.
5. Some of the epidermal ceils develop into the secretory tissues of nectaries, the stomata of leaves and stems, and the absorbing hairs of roots.
