Chapter-6ANATOMY OF

FLOWERING PLANTSPresented by

B.PrabhakarPrincipal

JNV. Panchmahal (Guj)

The tissue system

• On the basis of their structure and location, there are three types of tissue systems. These are the

1. Epidermal tissue system,2. The ground or

fundamental tissuesystem

3. vascular or conducting tissue system.

Epidermal tissue system

• The epidermal tissue system forms the outer-most covering of the whole plant body and comprises epidermal cells, stomata and the epidermal appendages – the trichomes and hairs.

• The epidermis is the outermost layer of the primary plant body. It is made up of elongated, compactly arranged cells, which form a continuous layer. Epidermis is usually singlelayered.

• Epidermal cells are parenchymatous with a small amount of cytoplasm lining the cell wall and a large vacuole. The outside of the epidermis is often covered with a waxy thick layer called the cuticle which prevents the loss of water. Cuticle is absent in roots.

• Stomata are structures present in the epidermis of leaves. Stomata regulate the process of transpiration and gaseous exchange. Each stoma is composed of two beanshaped cells known as guard cells. In grasses, the guard cells are dumbbell shaped. The outer walls of guard cells (away from the stomatal pore) are thin and the inner walls (towards the stomatal pore) are highly thickened. The guard cells possess chloroplasts and regulate the opening and closing of stomata. Sometimes, a few epidermal cells, in the vicinity of the guard cells become specialised in their shape and size and are known as subsidiary cells. The stomatal aperture, guard cells and the surrounding subsidiary cells are together called stomatal apparatus (figure 6.4).

GROUND TISSUE SYSTEM• It is represented by the different regions in the plant body that are mainly involved in storage. In

the cylindrical parts of the plant body such as root and stem, the ground tissue becomes differentiated into various regions. In a typical condition, following regions can be recognised in the ground tissue.

• Hypodermis is a region that is found immediately below the epidermis in the stem. It is made up of a few layers of either collenchyma cells (as in dicot stem) or sclerenchyma cells (as in monocot stem). Hypodermis is meant for providing additional protection and mechanical support.

• Cortex is a major component of the ground tissue represented by many layers of loosely arranged parenchyma cells. Intercellular spaces are prominent. Cortex represents the major storage region in the plant body.

• Endodermis is the inner most layer of cortex represented by a single layer of compactly arranged barrel-shaped parenchyma cells. In the stem, it is meant for storage. In the root it plays an important role in the movement of absorbed water. Some of the cells in the root endodermis contain secondary thickenings called casparian thickenings, formed by a waxy substance called suberin.

• Pericycle is a region that lies immediately below the endodermis. In the stem, it is represented by a few layers of sclerenchyma cells while in the root, it is represented by a single layer of parenchyma cells.

• Medullary rays/Conjunctive tissue are represented by parenchyma cells that are found in between the vascular tissues. In the stem, the parenchyma cells are meant for storage of food and represent the medullary rays while in the root, they store water and represent the conjunctive tissue.

• Pith is the innermost part of the stem or root representing the axis. It is formed by loosely arranged parenchyma cells with prominent intercellular spaces. It is another major storage organ in the plant body. The pericycle, the medullary rays or conjunctive tissue, and the pith along with the vascular tissues, together represent a region, which is known as stele or central cylinder.

• The vascular tissue system is a derivative of procambium. It is represented by the conducting tissues-xylem and phloem. These vascular tissues occur in the form of vascular bundles or fascicles. In the leaf, the vascular bundles are known as veins. The vascular bundles may sometimes enclose a piece of meristematic tissue called cambium, which brings about secondary growth in the bundles.

• When cambium is present, the vascular bundle is described as open and

• when the cambium is absent, the vascular bundle is described as closed.

• . Accordingly, based on the relative position of xylem and phloem the bundles can be distinguished into three types

Types of vascular bundles• Conjoint Bundle

In conjoint bundle xylem and phloem occur in the same bundle along the same radius.

Ex- stem, leaves• Radial Bundle

When xylem and phloem within a vascular bundle are arranged in an alternate manner on different radii, the arrangement is called radial

Ex- root

Heart wood & sap wood