NEET Botany Tissue And Tissue System Chapter Notes

Learning Objectives

 

 

 

Katherine Esau (1898–1997)

A legendary Role model for women in science. She was a scintillating Botany teacher and pioneering researcher for six decades. Her classic book Anatomy of Seed Plants is the best literature in Plant Anatomy. In recognition of her distinguished service to science, she was awarded National Medal of Science (1989) by USA.

This chapter introduces the internal structure of higher Plants. The study of internal structure and organisation of plant is called plant Anatomy (Gk: Ana = as under; temnein = to cut). Plants have cells as the basic unit. The cells are organised into tissues. The tissues in turn are organised into organs. The different organs in a plant have different internal structures. It is studied by means of

Milestones in Anatomy

 

• 1837 Hartig: Coined the term Sieve tubes

• 1839 Schleiden: Coined the term Collenchyma

• 1857 Hofmeister: Proposed Apical cell theory

• 1858 Nageli. C: Coined the term Xylem and Phloem, Meristem and supporter of Apical cell theory

• 1865 Mettenius: Coined the term Sclerenchyma

• 1868 Hanstein: Proposed Histogen theory

• 1885 Tschirch: Coined the term Sclereids Named Four types of Sclereids (Brachy, Macro, Osteo & Astro) in 1889

• 1914 Haberlandt: Coined the term xylem as Hadrome and Phloem as Leptome and Classification of meristem.

• 1924 Schmidt A: Proposed Tunica – Corpus theory

• 1926 Schűepp: Mass, rib, & plate meristem

• 1946 Bloch: Discovered the Trichosclereids

• 1952 Popham: Explained the organization of Shoot apex of Angiosperms

• 1955 Duchaigne: Discovered the Annular collenchyma

• 1961 Clowes: Proposed Quiescent centre concept

• 1963 Sanio: Coined the term Tracheids

 

The Tissues

 A Tissue is a group of cells that are alike in origin, structure and function. The study of tissue is called Histology. A plant is made up of different types of tissues. There are two principal groups:

 

1. Meristematic tissues

2. Permanent tissues

 

9.1 Meristematic Tissue

 

9.1.1 Characteristics and classification

The characters of meristematic tissues:

(Gr. Meristos-Divisible)

 

The term meristem is coined by C. Nageli 1858.

• The meristematic cells are isodiametric and they may be, oval, spherical or polygonal in shape.

• They have generally dense cytoplasm with prominent nucleus.

• Generally the vacuoles in them are either small or absent.

• Their cell wall is thin, elastic and essentially made up of cellulose.

• These are most actively dividing cells.

• Meristematic cells are self-perpetuating.

 

Classification of Meristem

Meristem has been classified into several types on the basis of position, origin, function and division.

 

Theories of Meristem Organization and Function

Shoot Apical Meristem

Histogen Theory

Histogen theory is proposed by Hanstein (1868) and supported by Strassburgur. The shoot apex comprises three distinct zones.

1. Dermatogen: It is a outermost layer.It gives rise to epidermis.

2. Periblem: It is a middle layer. It gives rise to cortex.

3. Plerome: It is innermost layer. It gives rise to stele

Tunica Corpus Theory

Tunica corpus theory is proposed by

A. Schmidt (1924).

Two zones of tissues are found in apical meristem.

1. The tunica: It is the peripheral zone of shoot apex, that forms epidermis.

2. The corpus: It is the inner zone of shoot apex,that forms cortex and stele of shoot.

Root Apical Meristem

 Root apex is present opposite to the shoot apex. The roots contain root cap at their apices and the apical meristem is present below the root cap. The different theories proposed to explain root apical meristem organization is given below.

 Apical Cell Theory

Apical cell theory is proposed by Nageli. The single apical cell or apical initial composes the root meristem. The apical initial is tetrahedral in shape and produces root cap from one side. The remaining three sides produce epidermis, cortex and vascular tissues. It is found in vascular cryptogams.

Histogen Theory

Histogen theory is proposed by Hanstein (1868) and supported by Strassburgur.The histogen theory as appilied to the root apical meristem speaks of four histogen in the meristem. They are respectively

i. Dermatogen: It is a outermost layer. It gives rise to root epidermis.

ii. Periblem: It is a middle layer. It gives rise to cortex.

iii. Plerome: It is innermost layer. It gives rise to stele

iv. Calyptrogen: It gives rise to root cap.

Korper kappe theory is proposed by Schuepp. There are two zones in root apex – Korper and Kappe

1. Korper zone forms the body.

2. Kappe zone forms the cap. This theory is equivalent to tunica corpus theory of shoot apex.The two divisions are distinguished by the type of T (also called Y divisions). Korper is characterised by inverted T divisions and kappe by straight T divisions.

Quiescent Centre Concept

Quiescent centre concept was proposed by Clowes (1961) to explain root apical meristem activity. These centre is located between root cap and differentiating cells of the roots. The apparently inactive region of cells in root promeristem is called quiescent centre. It is the site of hormone synthesis and also the ultimate source of all meristematic cells of the meristem