Anatomy Of Angiosperms

One must understand that anatomy of flowering plants is the study of the gross internal structure of plant organs as observed after section cutting. Flowering plants constitute different kinds of tissues.

A tissue is a group of cells with a common origin. The cells of tissue, usually perform a common function.

The plant tissues are broadly classified into:

• Meristematic Tissues (apical, lateral and intercalary)

• Permanent Tissues (simple and complex).

Types of Tissues

There are two types of tissues in the flowering plants:

Meristematic Tissues

• They are made up of the cells which have the capability to divide.

• Meristems in plants are restricted to specialized regions and are responsible for its growth.

• They can be further classified into three groups,

Apical meristem- It is the one which occurs at the tips of roots and shoots, the primary meristem and helps increase the length of plants.

Intercalary meristem- It occurs between the mature tissue, is short-lived and capable of forming branches and flowers. The auxiliary bud or the buds which are present in the axils of leaves are responsible for forming branches or flowers. Intercalary meristems occur between mature tissues and go on to form primary meristems along with apical meristems since they contribute to plant body formation in the early life of a plant.

Lateral meristem- It occurs in the mature regions of roots and shoots. It is also known as the secondary meristem and appears later than primary meristem and is responsible for secondary growth. Example: Fascicular vascular cambium.

• Meristems at the tip of the shoots and roots produce apical meristems.

• Shoot and root apical meristems are occupied at the stem axis and tip of the root, respectively.

• Axillary buds give rise to the formation of a flower or a branch as a result of being ‘left behind’ from shoot apical meristems

Permanent Tissues

• These are derived from meristematic tissue and are composed of cells that have lost the ability to divide.

• They are divided into simple and complex tissues, which are further divided.

• The simple tissues constitute the parenchyma, which is thin-walled cells with cellulose in the cell wall and performs photosynthesis, storage and secretion. The collenchyma are formed of closely packed isodiametric cells, providing mechanical support and the sclerenchyma which are made up of dead cells also meant for mechanical support, having two types of cells, fibres, and sclereids.

• The complex tissues consist of the xylem, conducting minerals and water to other parts of the plant and the phloem, which transports food material to various parts of the plant.

Simple Tissues

It is made up of one type of cell, namely: Parenchyma, Collenchyma and sclerenchyma.

Complex Tissues

• Made up of more than one type of cell, but functions as a unit. Xylem and phloem are complex tissues.

• Xylem conducts water and mineral salts from the roots to other parts of plants. It provides mechanical support and consists of 4 parts – Tracheids, Vessels, Xylem parenchyma and Xylem fibres.

• Phloem transports food materials from the leaves to all parts of a plant. It is composed of the following parts – Sieve tube elements, companion cells, phloem parenchyma, phloem fibres.

Classification of the Tissue System

The Tissue System is classified into three parts,

• Epidermal tissue system, has root hairs, epidermis, cuticle, epidermal hairs, stomata, and trichomes.

• Ground tissue system, composed of sclerenchyma, parenchyma and collenchyma, forms the main bulk of the plant; and

• Vascular tissue system which is composed of xylem and phloem. The vascular bundles form the conducting tissue and translocate water, minerals and food material.

Monocotyledonous and dicotyledonous plants show marked variation in their internal structures. They differ in type, number and location of vascular bundles.

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