Plant tissue

Plant tissue

A group of plant cells performing essentially the same function and common to the similar structure is a plant tissue. On the basis of the stages of development, plant tissues are divided into two types:

1. Meristematic tissue
2. Permanent tissue

Meristematic tissue

The group of young cells which have the capacity of active cell division is called meristem. On the basis of origin, they are classified as primary and secondary meristems.

Primary meristems:

Those meristems, which are derived directly from the meristems of embryo and responsible for primary growth and lie mainly on the apices of stems and roots, are called primary meristems. They are apical meristems (root apical and shoot apical meristems), intercalary meristems (only in monocots). They help increase the length of the plant.

Secondary meristems:

They are the meristems which are formed as new meristems in permanent cells by re-differentiation and are responsible for increasing the diameter of the plant organ. They are of two types vascular cambium and cork cambium collectively known as lateral cambium (lateral meristem). They help plant to increase its girth. Secondary meristems are divided into three types which are as follows;

1. Apical meristems: These meristems are found in the apices or the growing points of root and shoot.They help to increase the height of the plant.
2. Lateral meristems: This meristem is found on the lateral side of stem and roots.They are found embedded in the permanent tissues. They are responsible for the increases in girthor diameter of the plant body. Vascular cambium and cork cambium are the examples of the lateral meristem.
3. Intercalary meristems: These meristems lie between the permanent tissue as remains of apical meristems. They found at the base of the node or at the base of internodes or at the base of leaf or sheathing leaf of monocots. They are responsible for the increase of the length of the axis of plants.

Permanent tissue

They are made up of cells that have lost the power of division and are differentiation to carry out various functions. The permanent tissues are of following types:

• Simple permanent tissue
• Complex permanent tissue and
• Special tissue.

Simple permanent tissue

These tissues are concerned with manufactured and storage of food and to provide mechanical support to plants. On the basis of structure, it is of following types:

1. Parenchyma: They are made of thin- walled oval or spherical cells. They are loosely packed and contains intracellular spaces. They form cortex,pith mesophyll cells of leaves, fruit pulp and endosperms of seeds. The main function of parenchyma is to manufacture and store the food.
2. Collenchyma: They are made up of thick-walled cell. They have thicker corners due to the deposition of cellulose. They are found in the outer cortex region of the plants like in stem, midrib of leaves, petioles, etc. It provides support and elasticity and helps in photosynthesis.
3. Sclerenchyma: Cells are long, thick-walled and lignified with tapering ends. Cells are of two types, fibres and sclereids. They form a layer in the cortex below the epidermis of stems and roots. They are mainly responsible for providing mechanical strength and save the plant from various environmental forces like strong wind.

Complex permanent tissue

They are made up of different types of cells. The most important complex tissues are xylem and phloem.

1. Xylem: They are found in the inner portions of the root, stem, leaf and other hard parts of the plant. They are made up of four kinds of cell that are trachieds, vessels, xylem fibres and xylem parenchyma. Xylem is also called wood. It conducts water and mineral from the root to the leaves.
2. Phloem: It is complex permanent tissue in which tubes are composed of living cells. It also made of four types of cell which are sieve tubes, campanion cells, phloem fibres and phloem parenchyma. It is mainly responsible for transportation of food.

Special permanent tissue

They are concerned with the secretion of materials like gums, oils, latex and other substances. They are further subdivided into two groups which are given below,

Lactiferous tissues: These are thin walled,elongated and specialized tube like structures. These ducts are filled with white or yellow latex. They are distributed irregularly in parenchymatous cells. They are responsible for food storage or waste products.

Glandular tissue: It consists if different types of glands which are made of isolated cells or small group of cells. They secrete various digestive enzymes in plants.These secrete resin, oil, mucilage, tannin, gums, nectar etc.

Relation between Cell, Tissue, and System in Plants

The plant body mainly consists root system and shoot system. The root system lies under the ground whereas the shoot lies above the ground. The root system and shoot system are made of different types of organs. The root system is made of organs like root cap, root tip, lateral root etc. whereas shoot system is made of organs like leaves, stem, flower, fruit, buds etc. Again these organs are made of different types of tissues like parenchyma, (epidermis, cortex, endodermis, and pith), schlerenchyma (pericycle) xylem and phloem (vascular tissues etc.) pericycle, vascular tissues and pith are called stele group. And these tissues are made of different cells.