Plant Tissues

A cell is the basic structural and functional unit of life.

A group of cells that are similar in structure and perform the same function is called a TISSUE. Like animals, the plant is also made up of different kinds of tissues. These tissues are mainly classified into two types based on the cell’s ability to split or not. They are Meristematic tissues and Permanent tissues.

  • Meristematic Tissues

A group of cells that are in a state of division are known as Meristematic tissues.

The properties of Meristematic tissues are:

1.Undifferentiated

2.Capable of cell division

3.Helps in the growth of plants.

  • Permanent Tissues

A group of cells that do not bifurcate further and are distinguished based on the functions the tissues perform.

The Properties of Permanent Tissues are:

1. Differentiated.

2. Incapable of cell division.

3. Performs particular function.


The figure given below, depicts the types of plant tissues.


Meristematic Tissue

Based on the location, Meristematic tissues can be classified as:

1. Apical Meristem : Helps in primary growth. 

  • SAM(shoot apical meristem):Gives rise to organs like leaves and flowers. 

  • There are many Shoot apical meristem theories like; Apical cell theory,Histogen theory and Tunica corpus theory.

  • RAM(root apical meristem):Helps in the growth of future roots.

  • There are many root apical meristem theories like; Apical cell theory,Histogen theory and Korper-Kappe theory.

  • They are present in the apices of primary and secondary shoots of plants.

  • They are responsible for increase in length and all primary tissue which originates from them.


2. Lateral Meristem : Helps in the secondary growth.

  • Present along the sides of the stem.

  • Vascular cambium is present in gymnosperms(seed bearing plants) and angiosperms(flower bearing plants) that are are good examples for lateral meristems.

  • Eg: Cork(located below the bark of stem) and vascular cambium(located in vascular tissues).


  1. Intercalary Meristem : Present at internodes or regions of stem between the places where the leaves are attached. It helps in the growth of leaves, and stems.

Classification Based on Origin and Development:


1. Promeristem: The region of new growth that is present in the apices of shoots and roots where the organs form their foundation.

2. Primary meristem: First derivative of meristem which forms the basic parts of the plant.

3. Secondary meristem: Meristem which appears at the later stages of development of the plant organ.


Classification Based on Function:


1. Protoderm: It is the outermost layer of the meristematic layer which later develops into hair, and stomata.

2. Procambium: Meristem which develops into primary vascular tissues like xylem and phloem.

3. Ground meristem: Meristem which follows the ground tissue system and forms hypodermis, cortex, pith, pericycle, and medullary rays.


Classification Based on Histogen:


1. Dermatoger: The outermost layer of the histogen that forms the epiblema and epidermis in the root.

2. Periblem: The middle layer of histogen which forms the endodermis and the cortex.

3. Plerome: Histogens that form vascular strands like the pith, vascular bands, etc.


PERMANENT TISSUE

Meristematic cells that split up, extend, become differentiated, and perform particular functions are called permanent tissues.


There are two types of permanent tissues; simple and complex:


Simple Tissue: Dermal and ground tissues.


1. Dermal Tissues:

  • Form the outer layer of plant parts.

  • Cells of this tissue are elongated and flattened.

  • Intercellular spaces are absent.

  • They provide protection against adverse environmental conditions and predatory attacks. Therefore dermal tissues are also called protective tissues.

  • The gaseous exchange through stomata is achieved by this tissue.

  • The epidermis (outermost layer of plant body), and Cork (Light and thin layer chipping off from bark) constitutes the dermal tissue.


Note: The CUTICLE-Epidermis covering is made of a waxy substance called cutin. 

2. Ground Tissues (Supporting plant tissues):


The main function of ground tissues is to provide support, strength, and flexibility to plants.


The Three Types of Ground Tissues are:

1. Parenchyma

2. Collenchyma

3. Sclerenchyma



Parenchyma

Collenchyma

Sclerenchyma

Greek origin

Para; beside,

en,chein; to pour in.

Kolla; glue,

en,chein; to pour in.

Scleros; hard,

en,chein; to pour in.

Term coined

N Grew(1682)

Schleiden(1839)

Mettenius(1805)

Location

Found in every soft region of plants.

Found in epidermis, petiole and midribs of dicot leaves.

Found in mature parts of the plant like stem, roots, veins of leaves, and hard covering of nuts and seeds.

Cells

Un-specialized and living.

Specialized and living.

Specialized and dead at maturity.

Cell wall

Consists of cellulose and is thin.

Consists of cellulose and pectin and is unequally thin.

Consists of lignin and is hard and rigid.

Cells shape

Typically isodiametric

Oval, spherical or longitudinal.

Long, narrow, thick, and lignified with pointed or blunted ends.

Inter

cellular space

Present

Absent or little

Absent

Function

Packing tissue, food Storage, Photosynthesis, and gas exchange maintains shape and helps in floating of aqueous substances

Provides elasticity, mechanical, tensile strength, manufactures starch.

Provides mechanical support, protection, elasticity and helps to withstand strain.

Refractive index

No high refractive index

High refractive index

Comparatively low refractive index.

Ability to differentiate

Have ability to differentiate and produce secondary meristem.

Almost absent

No differentiation.


Complex Tissues

Vascular Tissues: Xylem and Phloem. These tissues are also known as conducting tissues because of their important role in water and food transportation. (image will be uploaded soon)


XYLEM

PHLOEM

Xylos; wood

Phlois; inner bark

Term coined and discovered by Nageli (1858)

Term coined and discovered by 

Nageli (1858)

Water conducting tissue

Food conducting tissue

Composed of four different types of cells called; tracheid, trachea, xylem parenchyma and xylem sclerenchyma.

Composed of four different types of cells called; sieve tubes, companion cells, Phloem parenchyma and phloem fibers.

Except Xylem parenchyma, all other cells are dead.

Except phloem fiber, all phloem cells are living.


XYLEM:

  • Xylem is called primary xylem if its elements are derived from procambium of apical meristem.

  • Xylem is called secondary xylem if its elements develop from vascular cambium during the process of secondary growth.

  • There are four types of Xylem based on the position of protoxylem with respect to metaxylem. They are as follows:


1. Exarch: Protoxylem located outside the metaxylem.

2. Mesarch: Protoxylem located in the middle of the metaxylem.

3. Centrarch: Protoxylem located in the center of the metaxylem.

4. Endarch: Protoxylem located inside the metaxylem.


PHLOEM:

  • Phloem is also known as Bast because it is also used for binding purposes. Eg; Hemp and flax.


Summary:

  • The meristematic cells keep on bifurcating.

  • Meristematic tissues based on their location are of three types namely; apical, lateral, and intercalary meristematic tissues.

  • Permanent tissues are of two types: Simple and Complex.



SIMPLE TISSUES

COMPLEX TISSUES

They are made up of only one type of cells 

They are made up of more than one type of cells

Helps in storage of food and mechanical support.

Helps in transportation of water, sugars, minerals, and other metabolites.

Eg: Parenchyma, Collenchyma, Sclerenchyma 

Eg: Xylem and Phloem.


  • Dermal or protective tissues are simple tissues. They form the outer covering of plant parts such as the stem, roots, fruits, flowers etc. The epidermis and cork are two types of dermal tissues.

  • The main function of the ground tissue is to provide support, strength, and flexibility to plants. The three types of ground tissues are; Parenchyma, Collenchyma, and Sclerenchyma.

  • Vascular tissues are also called conducting tissues as they play an important role in the transportation of water and food in plants.

  • Xylem is a water conducting tissue.

  • Phloem is a food conducting tissue.