Anatomy

• Anatomy


  The study of the internal structure of plants
• Tissue

  A group of cells having a common origin and usually performing a common function
• Types of tissues

  • Meristematic tissues
  • Permanent tissues
• Meristematic tissues


  • Cells are capable of dividing
  • Found in regions of active cell division
• Types of meristems

  • Apical meristems
  • Intercalary meristems
  • Secondary/lateral meristems
• Apical meristems

  Occur at the tips of roots and shoots, produce primary tissues
• Intercalary meristems

  Occur between mature tissues, found in grasses, regenerate parts removed by grazing
• Secondary/lateral meristems


  Occur in mature regions of roots and shoots, produce secondary tissues
• Permanent tissues

  Cells are structurally and functionally specialised, lose ability to divide
• Types of permanent tissues

  • Simple tissues
  • Complex tissues
• Simple tissues

  • Parenchyma
  • Collenchyma
  • Sclerenchyma
• Parenchyma

  Thin-walled cells, perform various functions like photosynthesis, storage, secretion
• Collenchyma


  Cells with thickened corners, provide mechanical support to growing parts
• Sclerenchyma

  Cells with thick, lignified walls, provide mechanical support
• Complex tissues


  • Xylem
  • Phloem
• Xylem

  Conducts water and minerals, provides mechanical support
• Phloem


  Transports food materials, usually from leaves to other parts
• Tissue systems

  • Epidermal tissue system
  • Ground/fundamental tissue system
  • Vascular/conducting tissue system
• Epidermal tissue system


  Outermost covering of the plant body, includes epidermis, stomata, trichomes and hairs
• Tissue systems

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

  • Forms the outermost covering of the whole plant body
  • Comprises epidermal cells, stomata and epidermal appendages (trichomes and hairs)
• Epidermis


  • Outermost layer of the primary plant body
  • Made up of elongated, compactly arranged cells
  • Covered with a waxy thick layer called the cuticle
  • Cuticle absent in roots
• Stomata

  • Regulate the process of transpiration and gaseous exchange
  • Composed of two bean-shaped or dumb-bell shaped guard cells
  • Guard cells possess chloroplasts and regulate opening and closing of stomata
  • Subsidiary cells surround the guard cells
• Ground tissue system

  • All tissues except epidermis and vascular bundles
  • Consists of parenchyma, collenchyma and sclerenchyma
• Vascular tissue system

  • Consists of xylem and phloem
  • Xylem and phloem together constitute vascular bundles
  • Vascular bundles can be radial, conjoint closed, or conjoint open
• Dicotyledonous root

  • Epidermis with root hairs
  • Cortex with endodermis and pericycle
  • Vascular bundles with xylem and phloem
  • Pith small or inconspicuous
• Monocotyledonous root

  • Similar to dicot root
  • More than 6 xylem bundles (polyarch)
  • Pith large and well developed
  • No secondary growth
• Dicotyledonous stem

  • Epidermis with cuticle and trichomes
  • Cortex with hypodermis, endodermis, and pericycle
  • Vascular bundles arranged in a ring
  • Pith large and parenchymatous
• Monocotyledonous stem

  • Sclerenchymatous hypodermis
  • Scattered vascular bundles with bundle sheath
  • Large parenchymatous ground tissue
  • Vascular bundles conjoint and closed
• Dicotyledonous (dorsiventral) leaf

  • Epidermis with cuticle
  • Mesophyll differentiated into palisade and spongy parenchyma
  • Vascular bundles in veins and midrib
• Monocotyledonous (isobilateral) leaf

  • Stomata on both surfaces
  • Mesophyll not differentiated
  • Bulliform cells in grasses
• Secondary growth

  Increase in girth of roots and stems, involving vascular cambium
• Isobilateral leaf

  • Stomata present on both surfaces of epidermis
  • Mesophyll not differentiated into palisade and spongy parenchyma
• Grass leaves

  • Adaxial epidermal cells along veins modify into large, empty, colourless bulliform cells
  • Bulliform cells absorb water and expose leaf surface
  • Bulliform cells lose water and make leaves curl inwards to minimise water loss
• Parallel venation in monocot leaves is reflected in near similar sizes of vascular bundles (except in main veins)
• Primary growth

  Growth of roots and stems in length with apical meristem
• Secondary growth

  Increase in girth, occurs in dicotyledonous plants
• Tissues involved in secondary growth

  • Vascular cambium
  • Cork cambium
• Vascular cambium

  Meristematic layer that cuts off xylem and phloem
• Formation of cambial ring

  1. Intrafascicular cambium between primary xylem and phloem

  2. Interfascicular cambium from medullary ray cells

  3. Continuous ring of cambium formed