MORPHOLOGY OF FLOWERING PLANTS

The most evolved and dominating members of Kingdom Plantae are the flowering plants are Angiosperms. There is a great diversity in the structure of different parts of flowering plants. There are about 3,00,000 species of flowering plants. These species show variations in their structure. In spite of this diversity, they follow a basic similar plan of construction of the body.

The study of external structure of an organism or an organ is called external morphology.

The study of internal structure is called internal morphology or anatomy.

The body of a typical flowering plant (angiospermic plant) can be divided into

1. underground root system: The root system is homogeneous and it consists of a main root and its lateral branches.

2. aerial shoot system: The shoot system is heterogeneous and consists of stem, branches, leaves and flowers.

 

- Vegetative parts: The parts of the plant body which are mainly concerned with vital functions such as nutrition and growth are called vegetative parts, e.g. root, stem and leaves.

- Reproductive parts: The parts of the plant body which are concerned with sexual reproduction are called the floral or reproductive parts, such as the flower.

MORPHOLOGY AND FUNCTIONS OF DIFFERENT PARTS OF FLOWERING PLANTS :

 Morphology and functions of root :

Root is defined as the descending part of the plant axis, which grows downwards into the soil. Thus it is positively geotropic.

It grows towards water, i.e. positively hydrotropic and away from light, i.e. negatively phototropic.

It develops from the radicle of embryo during seed germination.

The root exhibits various characteristics such as -

1. Roots are generally non-green and cylindrical.
2. They produce only similar organs i.e. secondary and tertiary roots, endogenously. (from the pericycle)
3. They do not produce dissimilar organs like leaves.
4. They are not differentiated into nodes and internodes.

A typical root shows following five parts or regions:

1. Region of root cap:

The tender apex of the root is protected with a multicellular cap-like structure called root cap.

The cells of the root cap secrete mucilage for lubricating the passage of root through the soil.

In many hydrophytes like Pistia and Eichhornia, root cap is replaced by root pocket.

2. Region of cell division or Meristematic Region:

It is a small region about 1 mm in length. This is the growing point of a root and is protected by the root cap.

It is made up of compactly arranged, thin- walled, meristematic cells which have the power of division.

This region helps in longitudinal growth of root by the addition of new cells.

3. Region of elongation:

It lies just above the meristematic region.

The cells of this region are newly formed and they elongate rapidly.

This increases the length of the root.

The cells of this region help in absorption of mineral salts.

4. Region of root hair or Region of absorption:

Surface of this area is covered with numerous root hairs.

The cells of outer layer, known as piliferous layer, or epiblema, produce root hairs.

The root hairs are elongated, single- celled, tubular structures which remain in contact with soil particles.

The root hairs increase the surface area of absorption. Root hairs are short-lived and,-are replaced by new root hairs after every 10-15 days.

This region is responsible for absorption of water.

5. Region of Maturation or Cell Differentiation:

It forms the major part of the root.

The outermost layer of this region has thick-walled impermeable cells.

The enlarged cells undergo differentiation to form different types of primary root tissues like cortex, endodermis, xylem, phloem, etc.

This region helps in fixation of plant body in the soil and also in conduction of absorbed Substances.

Lateral roots also develop from this region of root.

 

Functions of the Root:

The normal functions of root are

1. Fixation or anchorage of plant body in the soil (substratum),

2. Absorption of water and minerals from the soil

3. conduction of absorbed materials up to the base of the stem.

In some plants roots perform certain special functions and such roots undergo necessary modifications.

1. Some roots become fleshy or swollen for the storage of food materials. e.g. carrot, radish, Dahlia, sweet potato, Asparagus, etc .

2. After becoming green, some roots manufacture food by photosynthesis. e.g. Tinospora, Trapa, Orchids, etc.

3. Some roots help in exchange of gases (respiration). e.g., Rhizophora, Sonneratia. etc.

4. In parasitic plants like Cuscuta, adventitious roots penetrate the host stem to obtain food and water.

5. Sometimes roots take part in vegetative reproduction. e.g. sweet potato.

6. Aerial roots absorb moisture from the air, e.g., orchids.

Thus modified roots perform different functions.