Permanent tissue systems
Permanent tissues are made of cells that are produced by the meristems and are formed to various shapes and sizes depending on their intended function in the plant. Sometimes the tissues are composed of the same type of cells throughout, or sometimes they are mixed. They may be living or dead.
There are other tissues in plants that do not actively produce new cells. These tissues are called permanent (or) non-meristematic tissues.
Permanent tissues are made of cells that are produced by the meristems and are formed to various shapes and sizes depending on their intended function in the plant. Sometimes the tissues are composed of the same type of cells throughout, or sometimes they are mixed. They may be living or dead. Permanent tissues are of three types:
- Dermal Tissue (Protective Tissue)
- Vascular Tissue (Conducting Tissue)
- Ground Tissue (Supporting Tissue)
Dermal Tissue System: The Dermal Tissue system is the outer protective covering. It consists of the epidermis and the periderm. The epidermis is a single layer of closely packed cells. It both covers and protects the plant. It can be thought of as the plant's "skin." Depending on the part of the plant that it covers, the dermal tissue system can be specialized to a certain extent. For instance, the epidermis of a plant's leaves secretes a coating called the cuticle that aids the plant in the prevention of water loss – an important adaptation to living on land.
The periderm, also called bark, replaces the epidermis in plants that undergo secondary growth (woody plants). The periderm consists of cork cells and protects the plant from pathogens, prevents excessive water loss and provides insulation for the plant. In addition to protecting the plant from water loss and disease, the epidermis has specialized characteristics in each organ.
Vascular tissues–Xylem and Phloem
Xylem vessels are involved in the movement of water through a plant from its roots to its leaves. Phloem vessels are involved in translocation. This is the movement of food substances from the stems to growing tissues and storage tissues.
Vascular tissue system: Vascular tissue, also called the conducting tissue, provides passage for water and dissolved materials to be transported between roots and shoots. Xylem and phloem are two types of conducting tissues. Xylem conveys water and dissolved minerals upward from roots into the shoots. Phloem transports organic nutrients such as sugars from where they are made (usually the leaves) to where they are needed–usually roots and sites of growth, such as developing leaves and fruits. Both xylem and phloem are composed of a variety of cell types, including cells highly specialized for transport.
Ground Tissues: Tissues that are neither dermal nor vascular are part of the ground tissue system. The ground tissue comprises the bulk of the primary plant body. Ground tissue that is internal to the vascular tissue is called pith, and ground tissue that is external to the vascular tissue is called cortex. The ground tissue system is more than just filler. The ground tissue system is responsible for most of the plant's metabolic functions as it synthesizes organic compounds, supports the plant and provides storage for the plant. It is mostly made up of parenchyma cells but can also include some collenchyma and sclerenchyma cells as well.