Anatomy of flowering plants

• Plants have cells as the basic unit, which are organised into tissues and then into organs
• Different organs in a plant show differences in their internal structure
• Monocots and dicots are anatomically different within angiosperms
• Internal structures of plants show adaptations to diverse environments
• Three types of tissue systems based on structure and location in the plant body:

  • Epidermal tissue system
  • Ground or fundamental tissue system
  • Vascular or conducting tissue system
• Epidermal tissue system:

  • Forms the outermost covering of the plant body
  • Comprises epidermal cells, stomata, trichomes, and root hairs
  • Epidermis is single-layered and made up of elongated, compactly arranged cells
  • Epidermal cells have a small amount of cytoplasm and a large vacuole
  • Cuticle on the outside prevents water loss
  • Stomata regulate transpiration and gaseous exchange
  • Guard cells regulate opening and closing of stomata
  • Subsidiary cells and guard cells together form the stomatal apparatus
• Ground tissue system:

  • Consists of all tissues except epidermis and vascular bundles
  • Includes parenchyma, collenchyma, and sclerenchyma
  • Parenchymatous cells are present in cortex, pericycle, pith, and medullary rays
  • In leaves, ground tissue is called mesophyll
• Vascular tissue system:

  • Consists of phloem and xylem
  • Xylem and phloem together form vascular bundles
  • Dicot stems have cambium between phloem and xylem, allowing for secondary growth
  • Monocot stems lack cambium and do not undergo secondary growth
  • Vascular bundles can be radial or conjoint, with phloem usually on the outer side of xylem
• Dicotyledonous root anatomy:

  • Epiblema is the outermost layer with root hairs
  • Cortex consists of thin-walled parenchyma cells
  • Endodermis has casparian strips and barrel-shaped cells
  • Pericycle initiates lateral roots and vascular cambium
  • Pith is small or inconspicuous
  • Stele includes pericycle, vascular bundles, and pith
• Monocotyledonous root anatomy:

  • Similar to dicot root but with more xylem bundles
  • Pith is large and well-developed
  • No secondary growth in monocot roots
• Dicotyledonous stem anatomy:

  • Transverse section shows different layers and tissues
• Dicotyledonous Stem:

  • The epidermis is the outermost protective layer of the stem
  • The cortex consists of three sub-zones: hypodermis, parenchymatous cells, and endodermis
  • The endodermis is rich in starch grains and is also known as the starch sheath
  • Pericycle is present on the inner side of the endodermis and above the phloem in the form of semi-lunar patches of sclerenchyma
  • Vascular bundles are arranged in a ring, with each bundle being conjoint, open, and having endarch protoxylem
  • The pith consists of rounded, parenchymatous cells with large intercellular spaces
• Monocotyledonous Stem:

  • Has a sclerenchymatous hypodermis
  • Contains a large number of scattered vascular bundles, each surrounded by a sclerenchymatous bundle sheath
  • Has a large, conspicuous parenchymatous ground tissue
  • Vascular bundles are conjoint and closed
  • Peripheral vascular bundles are generally smaller than centrally located ones
  • Phloem parenchyma is absent, and water-containing cavities are present within the vascular bundles
• Dorsiventral (Dicotyledonous) Leaf:

  • Consists of epidermis, mesophyll, and vascular system
  • The mesophyll is made up of palisade parenchyma and spongy parenchyma
  • Vascular system includes vascular bundles surrounded by a layer of thick-walled bundle sheath cells
  • Adaxial epidermis generally bears more stomata than abaxial epidermis
  • Mesophyll carries out photosynthesis and possesses chloroplasts
  • Vascular bundles are dependent on the size of the veins and vary in thickness in the reticulate venation of dicot leaves
• Isobilateral (Monocotyledonous) Leaf:

  • Stomata are present on both surfaces of the epidermis
  • Mesophyll is not differentiated into palisade and spongy parenchyma
  • In grasses, adaxial epidermal cells along the veins modify into bulliform cells
  • Parallel venation in monocot leaves results in similar sizes of vascular bundles, except in main veins
• Plant Tissues:

  • Classified into meristematic (apical, lateral, intercalary) and permanent (simple, complex)
  • Functions include assimilation of food, storage, transportation of water, minerals, and mechanical support
  • Three tissue systems: epidermal, ground, vascular
  • Epidermal tissue system consists of epidermal cells, stomata, and epidermal appendages
  • Ground tissue system divided into cortex, pericycle, and pith
  • Vascular tissue system formed by xylem and phloem
  • Vascular bundles translocate water, minerals, and food material
• Monocotyledonous and dicotyledonous plants:

  • Show marked variation in internal structures
  • Differ in type, number, and location of vascular bundles
  • Secondary growth occurs in most dicotyledonous roots and stems