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ANATOMY OF FLOWERING PLANTS
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Anatomy, Study of internal organisation of, living organisms, , Histology, Study of tissues & tissue system, in multicellular organisms
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1. TISSUE, • Group of cells, having common origin, Tissues, , Meristematic, Tissue, , Permanent, Tissues, , Simple Permanent, Tissues, 1) Parenchyma, 2) Collenchyma, 3) Sclerenchyma, , Complex, Permanent, Tissues, 1) Xylem, 2) Phloem
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2. MERISTEMATIC TISSUES, • Cells have power of division, • A. Characteristics of Meristematic Tissues, Cells are thin walled, Have abundant cytoplasm, Retain power of division, No intracellular spaces
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B. Classification of meristems :, • Based on position in plant body, • (i) Apical meristems, •, Occur at apices, •, Differentiate into primary tissues, •, Cause increase in length, •, Axillary buds are present in axils of leaves
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(ii) Lateral meristems :, Arranged parallel to the sides of organs of, plant, Cells produced by them differentiate, into secondary tissues, , Cause increase in width of plant organ, e.g., Fascicular cambium & cork cambium
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(iii) Intercalary meristems :, Meristems occur in between mature/permanenet, tissues, Produce cells that form primary tissues, , Cause increase in length, Occur at bases of internodes & leaf sheaths of, grasses & other monocots;, They regenerate parts removed by grazing, animals
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Based on origin, (i) Promeristems :, Group of meristematic cells in embryo /, seedlings, Give rise to primary meristems
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(iii) Secondary meristems :, , Formed at a later stage in, the life of plant from, permanent tissues by process, of dedifferentiation, e.g., Cork, cambium & inter-fascicular, cambium
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3. PERMANENT TISSUES, • Cells have lost power of division & become, structurally & functionally specialised, Characteristics :, , Cells have lost power of division, Undergone differentiation into specific types for a particular function, 2 types:, (i) Simple permanent tissues ( Tissue composed of 1 type of cell), (ii) Complex permanent tissues ( Tissue is composed of more than 1, type of cell)
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B. Simple Permanent Tissues :, (i) Parenchyma, Cells are thin- walled, Isodiametric, Retain capacity to divide at maturity, No intracellular spaces, Main function is storage, When parenchyma cells contain a number of chloroplasts they are called, chlorenchyma & when they are arranged with regular system of intercellular air, spaces, they constitute aerenchyma, Forms major component of any organ of plant
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(ii) Collenchyma, Cells living at maturity, Cells are variously shaped, Cell wall is unevenly thickened, Occurs below epidermis of dicot stem, , Cells may possess chloroplast, Provides strength & flexibility to growing organs
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(iii) Sclerenchyma, Cells are dead at maturity, Cell wall is lignified evenly, , Gives mechanical support to organs, Has 2 types of cells :, (a) SCLEREIDS (STONE CELLS) :, , Oval/spherical & have very thick walls with narrow lumen, Occur in shells of nuts & in pulp of fruits & in tea leaves, (b) FIBRES :, Elongated & thick walled cells, Generally occur in groups, Present in xylem , phloem & cortex & pericycle
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C. Complex Permanent Tissues :, (i) XYLEM :, Forms continuous channel, Concerned with transport of water & minerals, Provides mechanical support, Composed of tracheary elements, xylem parenchyma & xylem fibres, (a) XYLEM VESSELS :, Long cylindrical tubular structures formed by many cells, End walls of vessel members have either single large opening / perforation / several, small openings, Have thick lignified walls, Vessles are dead at maturity & found in angiosperms only
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(b) XYLEM TRACHEIDS :, Elongated cells, Overlap one another at their slanting ends, Do not have perforation plates, Have thick lignified walls, Dead at maturity, (c) XYLEM PARENCHYMA ;, Thick/ thin walls of cellulose, Only living components of xylem, , Involved in short distance transport, Help in storage of sugars, starch, lipids & tannins
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(d) XYLEM FIBRES ( SCLERENCHYMA), Dead elements, Provide mechanical support, Xylem formed in primary plant body by procambium is called primary xylem, 1st formed primary xylem is called protoxylem, Later formed is called metaxylem, In stems, protoxylem lies towards pith & metaxylem towards periphery ; such, an arrangement is called endarch, In roots, protoxylem lies towards periphery & metaxylem towards pith ; such, an arrangement is called exarch, Xylem constituents formed by fascicular cambium constitue secondary xylem
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(ii) PHLOEM, • Concerned with transport of organic, substances, • Composed of sieve elements, companion cells,, phloem parenchyma & phloem fibres
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(a) SIEVE TUBES:, Formed by elongated sieve tube members, Cross walls have number of perforations, Mature sieve tube has peripheral cytoplasm, Functions are controlled by nucleus of companion cells, Members are characteristically present in angiosperms
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(a) SIEVE CELLS :, Sieve areas are found to occur, throughout the end walls & lateral, walls, Cells are living, but lack nucleus, Found in lower vascular plants
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(c) COMPANION CELLS:, Found in association with sieve tube, members, , Sieve tube elements & companion, cells are connected by pit fields, Help in maintaining the pressure, gradient
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(d) PHLOEM PARENCHYMA :, Cells are elongated & cylindrical, Have dense cytoplasm & prominent, nucleus, Stores food materials & other substances, , Absent in monocot plants
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(e) PHLOEM FIBRES (BAST FIBRES) :, Found along with other elements of phloem, Elongated & thick walled cells, Dead at maturity, Absent in primary phloem, 1st formed primary phloem is known as protophloem, Later formed is known as metaphloem, Elements formed by fascicular cambium constitute secondary, phloem
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TISSUE SYSTEM IN PLANTS, • 3 tissue sysytems:, (i) Epidermal tissue system, (ii) Vascular tissue system, (iii) Ground/ fundamental tissue system
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(i) EPIDERMAL TISSUE SYSTEM, • Forms outermost covering of plant body, • Consists of epidermal cells, epidermal appendages &, stomata, • Epidermis is outermost layer, • Epidermis is single-layered, • Each cell has small amount of cytoplasm & large, vacuole, • Outer surface is covered with thick layer, • Cuticle prevents loss of water from aerial part of plants, • Epidermis is interrupted by small pores called stomata, • Stoma is surrounded by 2 guard cells
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• Guard cells are bean-shaped in dicot plants & dumb bell in, monocots, • Outer wall is thin & inner wall is thick, • They possess chloroplasts & carry out photosynthesis, • Epidermal cells in their vicinity become specialised in their size, & shape, • Stomatal apparatus – stomatal aperture, guard cells &, surrounding epidermal cells, • Epidermis also bears appendages, • Root hairs are unicellular elongation of epidermal cells of the, root, • Appendages on stem epidermis are called trichomes, • Help in preventing water loss by transpiration, • Glandular/ secretory in many plants
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(ii)VASCULAR TISSUE SYSTEM, • Includes xylem & phloem, • They occur as discrete strands called vascular, bundles, • Occur along same radius, vascular bundle is, called collateral, • When strip of cambium is present b/w xylem, & phloem – open vascular bundle, • No cambium in vascular bundle – closed, vascular bundle
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• 2 phloem poles occur in a vascular bundle ,, separated from central xylem – bicollateral, vascular bundle, • Xylem & phloem occur along different radii,, alternating with each other – radial bundle, • When protoxylem is towards periphery &, metaxylem is towards centre – exarch, • When protoxylem is towards centre &, metaxylem is towards periphery - endarch
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(iii) GROUND TISSUE SYSTEM, • Ground tissue – all tissues except epidermis &, vascular bundles, • Consists of simple permanent tissues, • Parenchyma cells present in cortex, pericycle;, pith & medullary rays, • Ground tissue in leaves - mesophyll
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My special thanx goes to my, biology teacher Mrs Alermelu, Natchair who gave and confirmed, this permission and encouraged me, to go ahead.
