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Tissue and Tissue System Chapter Unit IV: Plant Anatomy

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Tissue and Tissue System Chapter Unit IV: Plant Anatomy Unit IV: Plant Anatomy (Structural organisation) Chapter 9 Tissue and Tissue System Learning Objectives The learner will be able to, Nehemiah Grew • Study major types of plant cells and Father of Plant their function. Anatomy • Differentiate the various types of 1641–1712 cells. • Study the relationship between the Katherine Esau (1898–1997) distribution of tissues in the various A legendary Role model for women in parts of plants. science. She was a scintillating Botany • Describes the ground tissue system teacher and pioneering researcher for [cortex and pith] and vascular six decades. Her classic book Anatomy systems of Seed Plants is the best literature in Plant Anatomy. In • Interpret cross sections and recognition of her longitudinal sections of dicot and distinguished service monocot root, stem and leaf. to science, she was • Compare the internal organization awarded National of dicot root and monocot root. Medal of Science (1989) by USA. This chapter introduces the internal structure of higher Plants. The study of Chapter Outline internal structure and organisation of 9.1 Meristematic tissue plant is called plant Anatomy (Gk: Ana = 9.2 Permanent tissues as under; temnein = to cut). Plants have cells as the basic unit. The cells are 9.3 The tissue system organised into tissues. The tissues in turn 9.4 Epidermal tissue system are organised into organs. The different Fundamental tissue system 9.5 organs in a plant have different internal 9.6 Vascular tissue system structures. It is studied by means of 9.7 Comparision of primary structure dissection and microscopic examination. 1 Milestones in Anatomy of tissue is called Histology. A plant is made up of different types of tissues. • 1837 Hartig: Coined the term Sieve tubes There are two principal groups: • 1839 Schleiden: Coined the term 1. Meristematic tissues Collenchyma 2. Permanent tissues • 1857 Hofmeister: Proposed Apical cell 9.1 Meristematic Tissue theory • 1858 Nageli. C: Coined the term Xylem 9.1.1 Characteristics and classification and Phloem, Meristem and supporter The characters of meristematic tissues: of Apical cell theory (Gr. Meristos-Divisible) • 1865 Mettenius: Coined the term The term meristem is coined by Sclerenchyma C. Nageli 1858. • 1868 Hanstein: Proposed Histogen • The meristematic cells are isodiametric theory and they may be, oval, spherical or • 1885 Tschirch: Coined the term polygonal in shape. Sclereids Named Four types of • They have generally dense cytoplasm Sclereids (Brachy, Macro, Osteo & with prominent nucleus. Astro) in 1889 • Generally the vacuoles in them are • 1914 Haberlandt: Coined the term either small or absent. xylem as Hadrome and Phloem as Leptome and Classification of • Their cell wall is thin, elastic and meristem. essentially made up of cellulose. • 1924 Schmidt A: Proposed Tunica – • These are most actively dividing cells. Corpus theory • Meristematic cells are self-perpetuating. • 1926 Schűepp: Mass, rib, & plate meristem Classification of Meristem • 1946 Bloch: Discovered the Meristem has been classified into several Trichosclereids types on the basis of position, origin, • 1952 Popham: Explained the function and division. organization of Shoot apex of Apical meristem Angiosperms • 1955 Duchaigne: Discovered the Annular collenchyma Intercalary meristem • 1961 Clowes: Proposed Quiescent centre concept • 1963 Sanio: Coined the term Tracheids Lateral meristem The Tissues A Tissue is a group of cells that are alike in Figure 9.1: Different types of meristems origin, structure and function. The study on the basis of position in plant body 2 Classification of Meristem Position Origin Function Plane of division Apical meristem Protoderm Mass meristem Present in apices of root Primary It gives rise to It divides in all and shoot. It is responsible Meristem epidermal tissue planes. Example: for increase in the length It is derived system and endosperm,young of the plant, it is called as from develops into embryo and primary growth. embryonic epidermis,stomata sporangium stages and and hairs. differentiated into primary Intercalary meristem permanent Occurs between the Rib meristem or tissues. Procambium mature tissues. It is File meristem It gives rise to responsible for elongation It divides primary vascular of internodes. anticlinally in one tissues. Example: Secondary plane. Example: xylem and phloem . meristem It is development of derived during cortex and pith Lateral meristem later stage of Occurs along the development longitudinal axis of stem of the plant Plate meristem and root. It is responsible Ground Meristem It divides for secondary tissues and body. It It gives rise to anticlinally in two thickening of stem and produces cork all tissues except planes. Example: root. Example: vascular cambium and epidermis and development of cambium and cork interfascicular vascular strands. epidermis cambium. cambium. Theories of Meristem Organization and Shoot Apical Meristem Function Apical Cell Theory Many anatomists illustrated the root Apical cell theory is proposed by and shoot apical meristems on the basis Hofmeister (1852) and supported by of number and arrangement and accordingly Nageli (1859). A single apical cell is the proposed the following theories – An structural and functional unit. extract of which are discussed below. Apical cell Tunica Leaf primodium Leaf primordia Dermatogen Periblem Histogen Corpus Plerome a. b. c. Figure 9.2: Shoot apical meristem a) Apical cell theory, b) Histogen theory, c) Shoot Tunica corpus theory 3 This apical cell governs the growth at their apices and the apical meristem and development of whole plant body. It is present below the root cap. The is applicable in Algae, Bryophytes and in different theories proposed to explain some Pteridophytes. root apical meristem organization is given below. Histogen Theory Apical Cell Theory Histogen theory is proposed by Hanstein Apical cell theory is proposed by (1868) and supported by Strassburgur. The Nageli. shoot apex comprises three distinct zones. The single apical cell or apical initial composes the root meristem. The apical 1. It is a outermost layer. Dermatogen: initial is tetrahedral in shape and produces It gives rise to epidermis. root cap from one side. The remaining 2. Periblem: It is a middle layer. It gives three sides produce epidermis, cortex and rise to cortex. vascular tissues. It is found in vascular 3. Plerome: It is innermost layer. It gives cryptogams. rise to stele Histogen Theory Tunica Corpus Theory Histogen theory is proposed by Hanstein Tunica corpus theory is proposed by (1868) and supported by Strassburgur. A. Schmidt (1924). The histogen theory as appilied to the Two zones of tissues are found in apical root apical meristem speaks of four meristem. histogen in the meristem. They are respectively 1. The tunica: It is the peripheral zone of shoot apex, that forms epidermis. i. Dermatogen: It is a outermost layer. It gives rise to root epidermis. 2. The corpus: It is the inner zone of shoot apex,that forms cortex and stele ii. Periblem: It is a middle layer. It gives of shoot. rise to cortex. Root Apical Meristem iii. Plerome: It is innermost layer. It gives Root apex is present opposite to the rise to stele shoot apex. The roots contain root cap iv. Calyptrogen: It gives rise to root cap. Epidermis Stele Cortex Cortex Stele Cortex Protoderm T Ground tissue Quiescent Vascular cambium Root centre cap Inverted ‘T’ division (Y division) Cap Plerome b. Calyptrogen c. Periblem Dermatogen / Calyptrogen Figure 9.3: Root apical meristem a) Histogen Theory, b) Korper kappe theory, Root cap a. c) Quiescent Centre Concept 4 Korper Kappe Theory Parenchyma (Gk: Para-beside; Korper kappe theory is proposed by enehein- to pour) Schuepp. There are two zones in root Parenchyma is generally present in all organs apex – Korper and Kappe of the plant. It forms the ground tissue in a 1. Korper zone forms the body. plant. Parenchyma is a living tissue and made up of thin walled cells. The cell wall is made 2. Kappe zone forms the cap. This theory is equivalent to tunica corpus up of cellulose. Parenchyma cells may be oval, theory of shoot apex.The two divisions polyhedral, cylindrical, irregular, elongated are distinguished by the type of T or armed. Parenchyma tissue normally has (also called Y divisions). Korper is prominent intercellular spaces. Parenchyma characterised by inverted T divisions may store various types of materials like, and kappe by straight T divisions. water, air, ergastic substances. It is usually colourless. The turgid parenchyma cells help Quiescent Centre Concept in giving rigidity to the plant body. Partial Quiescent centre concept was proposed conduction of water is also maintained by Clowes (1961) to explain root apical through parenchymatous cells. meristem activity. These centre is located between root cap and differentiating Intercellular spaces 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. 9.2 Permanent Tissues Figure 9.4: Parenchyma The Permanent tissues develop from apical meristem. They lose the power of cell Occsionally Parenchyma cells which division either permanently or temporarily. store resin, tannins, crystals of calcium They are classified into two types: carbonate, calcium oxalate are called idioblasts. Parenchyma is of different types 1. Simple permanent tissues. and some of them are discussed as follows. 2. Complex permanent tissues. Types of Parenchyma Simple Permanent Tissues Starch Simple tissues are composed of one type grainsg of cells only. The cells are structurally and Intercellular spaces functionally similar. It is of three types. 1. Parenchyma a. b. 2. Collenchyma Types of Parenchyma 3. Sclerenchyma Figure 9.5: a) Aerenchyma, b) Storage parenchyma 5 1. Aerenchyma: Parenchyma which contains air in its intercellular spaces. It helps in aeration and buoyancy. Example: Nymphae and Hydrilla. 5. Prosenchyma: 2. Storage Parenchyma: Parenchyma cells became Parenchyma stores food elongated, pointed and slightly Parenchyma materials. Example: Root and thick walled. It provides stem tubers. mechanical support.
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