Plant Tissue Systems - All Global Updates

Plant Tissue Systems

·         Tissue systems are groups of tissues performing a similar function irrespective of its position in the plant body


·         Tissues systems are
:           

§  Dermal (Epidermal) tissue system,

§  vascular tissue system and

§  Fundamental (Ground) tissue system

§  Epidermal Tissue System:

§  In leaves there are guard cells

§  Chloroplasts: present only in the guard cells of the epidermis

§  Other epidermal cells usually do not have chloroplasts

§  Outer wall of epidermis is usually covered by cuticle          

§  The Stoma

·         Stoma is a minute pore surrounded by 2 guard cells

·         The stomata occur mainly in the epidermis of leaves

·         Trichomes

o   Are unicellular or multicellular appendages originating from the epidermal cells

o   Trichomes may be branched or unbranched


§  Functions of Epidermal Tissue System

§  Excessive loss of water due to the presence of cuticle

§  Epidermis protects the underlying tissues

§  Stomata are involved in transpiration and gaseous exchange

§  Trichomes help dispersal of seeds and fruits

§  Root hairs absorb water and mineral salts from the soil


·         Vascular Tissue System

§  Consists of xylem and phloem

§  Elements of xylem and phloem are always organized in groups called vascular bundles

§  In dicot stems, the vascular bundle consists of cambial tissue in between xylem and phloem (i.e. Open vascular bundle)

§  In monocot stem, cambium is absent in the vascular bundle (i.e. closed vascular bundle)

§  In roots, xylem and phloem are arranged in an alternate manner on different radii, this is called radial arrangement

§  In stems and leaves, xylem and phloem are arranged at the same radius and form a vascular bundle together (i.e. Conjoint vascular bundle)

§  Conjoint vascular bundles may be;

§  Collateral

·         Xylem and phloem on same radius, phloem is outward

§  Bicollateral

·         Phloem on outer and inner sides of xylem

§  Concentric vascular bundle

§  Either phloem or xylem surrounds the other completely

§  It is amphicribral if the phloem completely surrounds the xylem

§  It is amphivasal if the xylem completely surrounds the phloem


·         Ground or Fundamental Tissue System

§  Form the main body of the plants (bulk of plant)

    • Includes all the tissues except epidermis and vascular bundles

    • In monocot stem, ground tissue system is a continuous mass of parenchymatous tissue in which vascular bundles are found scattered i.e. ground tissue is not differentiated into cortex, endodermis, pericyclic and pith.

    • In the leaves, ground tissue is made of chlorenchyma tissues forming the mesophyll

    • These cells are arranged in a single layer without intercellular spaces

    • Cells in the pith generally store starch, fatty substances, tannins, phenols, calcium oxalate crystals, etc.

  • Secretory Tissues

    • Cells or organizations of cells that produce a variety of secretions

    • Secreted substance may remain deposited within secretory cell itself or may be excreted (released from the cell)

    • The substance maybe excreted to the surface of the plant or into intercellular cavities or canals

    • Some of the secretions are waste products e.g. resins, rubber, tannins and various crystals

    • Other secretions are useful in plants e.g. enzymes and hormones.

    • Secretory structures may be single cells or group of cells (glands)

    • Oil cells occur in ginger, pepper, mace, cardamoms, cinnamon and cassia

    • The latex cells (produce latex) are found e.g. in Cannabis sativa

References

Evans, W. C. (2009). Trease and Evans Pharmacognosy. India: Reed Elsevier Limited.



Close-Up Photography of Leaves With Droplets
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