The dermal system provides a protective covering to the plant body, and consists of two types of tissues-epidermis and peridermis. The epidermis is the outermost layer of the plant body. It is made up of elongated, compactly arranged cells which constitute a continuous layer without any inter-cellular space. It is a complex tissue having many types of cells mostly parenchyma and covers the plants parts during primary growth. The outside wall during the growth becomes, thicker compared to inside part to give protection to the plant. The epidermal parenchyma are devoid of chloroplast, but allow the light energy to penetrate into interior of the tissue of stem and leaf for photosynthesis.
The epidermal cells protect plant against evaporation by secreting a wax layer on the outer walls known as cuticle. The root epidermis does not synthesis cuticle as it should allow water to enter it from the soil. Epidermis in root has evolved root hair known as trichomes which are extension of epidermal cells that increase the surface area of root for absorption. Tichomes present on the aerial parts of desert plants cool the internal tissues by reflecting light away from the plants and thus decrease water loss. The cuticle also functions as a barrier against gases. The exchange of gases such as carbon dioxide, oxygen, water vapor takes place through stomata pores. Hypodermis consists of one to several layer of thick walled cells and occurs just below the dermis.
Bast fibers are sclerenchymatous fibers, occurring in the phloem or bast and are meant to provide mechanical support. Bast fibers are also known as hard bast. These are much elongated, unbranched (rarely branched) and have pointed needle like apex. Their cell wall is quite thick with simple or slightly bordered. pits. At maturity these fibers lose their protoplast and become dead. These occur in groups, as sheet or cylinders e.g. In Linunm Usitatissimum (flax) and Corchorus Capsularis (jute).