The Tissue System

Plants consist of cells as the basic unit. These cells are organized into tissues, which serve specific functions. These tissues, in turn, are arranged into organs with specialized roles. Different organs in the plant have different internal structures. Tissues are classified based on their location in the plant body. Plants tissues are of two types:

• Meristematic Tissue:
  • Apical Meristem: Found at the tips, produces primary tissues (dermal, vascular, ground).
  • Intercalary Meristem: Present in grasses, located between matured tissues.
  • Lateral Meristem: Generates secondary tissues, such as cambium.
• Permanent Tissue: Cells that no longer divide after achieving their specialized structure and function.
  • Simple Tissue: Composed of a single cell type with uniform structure and function.
  • Complex Tissue: Consists of multiple cell types working in coordination.

There are three types of tissue systems based on their structure and location. These are:

• The Epidermal tissue system
• The ground or fundamental tissue system
• The vascular or conducting tissue system.

Epidermal Tissue System

The epidermal tissue system forms the outermost layer of the plant. It consists of epidermal cells, stomata and the epidermal appendages – the trichomes and hairs.

Epidermis

• It forms the outermost covering of the plant.
• It is made up of elongated, compactly arranged cells, which form a single continuous layer.
• These cells are parenchymatous with a large vacuole and small amount of cytoplasm lining the cell wall.
• A waxy thick layer known as cuticle covers the outer surface of epidermis. It prevents the loss of water and is absent in roots.

Stomata

• Stomata are present in the epidermis of leaves and regulate the process of transpiration and gaseous exchange.
• Each stoma is composed of two beanshaped cells known as guard cells.
• The guard cells possess chloroplasts and control the opening and closing of the stomatal pore by changing their shape. The outer wall of the guard cell is are thin and the inner wall is highly thickened. In grasses, the guard cells are dumb-bell shaped.

Epidermal Appendages

Epidermal cells have the following features:

• Epidermal cells of plants bear hairs.
• In roots, these hairs are unicellular extensions of epidermal cells.
• Root hairs aid in the absorption of water and minerals from the soil.
• Epidermal hairs on stems are called trichomes.
• Trichomes in the shoot system are typically multicellular.
• They can be branched or unbranched, and may be soft or stiff.
• Functions of Trichomes are:
  • Prevent water loss due to transpiration.
  • Provide protection against herbivores.
  • Some trichomes may have secretory functions.

The Ground Tissue System

Ground tissue is formed of all types of tissue except epidermis and vascular bundles. It consists of simple tissues such as parenchyma, collenchyma and sclerenchyma. The ground tissue system forms the main bulk of the plant. It is divided into three zones – cortex, pericycle and pith. In the primary stems and roots parenchymatous cells are present in cortex, pith, pericycle, and medullary rays. In the leaves the ground tissue is called mesophyll and consists of thin-walled chloroplast containing cells.

The Vascular Tissue System

The vascular system consists of complex tissues, the phloem and the xylem. The xylem and phloem together constitute vascular bundles. In dicotyledonous stems, cambium is present between phloem and xylem and have the ability to form secondary xylem and phloem tissues, and are called open vascular bundles. In the monocotyledons, the vascular bundles have no cambium present in them and therefore, lack secondary tissues. They are called closed vascular bundles. The xylem and pholem form different pattern in the leaves and roots. These arrangement are as follows:

• Within a vascular bundle when Xylem and phloem are arranged in an alternate manner along the different radii, the arrangement is called radial. For example Roots.
• Within a vascular bundle when Xylem and phloem are arranged jointly along the same radius of vascular bundles, the arrangement is called cojoint. Usually the phloem is located only on the outer side of xylem.For example in shoot and leaves.

Also Read: Difference between xylem and phloem

Anatomy of flowering plants includes stems for structural support and transport of water and nutrients, roots for anchorage and nutrient absorption, leaves for photosynthesis, and reproductive structures such as flowers containing essential organs like stamens and pistils for sexual reproduction. The plant tissues are broadly classified into meristematic (apical, lateral, and intercalary) and permanent (simple and complex). The main functions of tissues include the assimilation of food and its storage, transportation of water, minerals, and photosynthates, and mechanical support to the plant.