Systems in Plants: roots,stems and leaves🌱🌿🍃

• Basic organ systems of plants

  • Root system
  • Stem system
  • Leaves
• Root

  An organ that anchors a vascular plant in the soil, and absorbs minerals and water
• Root


  • It grows downwards into the soil away from light (negatively phototropic)
  • It is nongreen and can synthesise organic food
  • It does not bear leaves and buds
  • Nodes and internodes are absent
  • The apex is subterminal because its tip is protected by a root cap
• Root hair


  Numerous unicellular structures near the tips of finer branches of roots to increase surface for absorption of water and minerals
• Roots


  • They bear lateral rootlets which are always endogenous in origin
  • They are negatively phototropic but positively geotropic and hydrotropic
• Root systems

  • Taproot system (eudicots and gymnosperms)
  • Fibrous root system (monocots)
• Functions of roots

  • Primary functions: Anchorage, Absorption, Conduction
  • Secondary functions: Storage of food, Additional support, Floating, Assimilation, Climbing
• Regions of a root from apex upwards

  • Root cap or Calyptra
  • Meristematic zone or Zone of cell division
  • Zone of elongation
  • Root hair zone or Zone of cell maturation (Differentiation)
  • Zone of differentiated cells
• Root cap


  A thimble-shaped or cap-like cellular structure that covers root apex in all plants
• Meristematic zone


  The growing subapical part of the root that helps in its growth
• Zone of elongation


  The cells in this zone undergo rapid elongation and enlargement, responsible for growth in length of the root
• Root hair zone


  The cells in this zone mature and differentiate into the epidermis, cortex and vascular bundles. Root hair arise as tubular outgrowth from the epidermal cells and increase surface for absorption
• Zone of differentiated cells


  The cells in this zone are mature and fully differentiated, providing mechanical support and forming bulk of the root
• Internal structures of a young dicot root


  • Epidermis (Epiblema or Piliferous layer)
  • Cortex
  • Endodermis
  • Pericycle
  • Vascular bundles
  • Conjunctive tissue
  • Pith
• Dicot root anatomy


  • Xylem bundles two to four in number, may be diarch, triarch and tetrarch
  • Pericycle gives rise to lateral roots and secondary meristem
  • Pith is usually absent
• Internal structures of a monocot root


  • Epidermis or Epiblema (Piliferous layer)
  • Cortex
  • Endodermis
  • Pericycle
  • Conjunctive tissue
  • Pith
  • Vascular bundles
• Monocot root anatomy


  • Cortex is massive with thin-walled parenchymatous cells with intercellular spaces
  • Vascular bundles are more numerous, usually 8 or more in number
  • Pericycle is partly parenchymatous and partly sclerenchymatous
  • Pericycle gives rise to lateral roots
  • Cambium is absent, so no secondary growth
  • Pith is large and well-developed
• Stem is the prolongation of plumule of the embryo and bears leaves, buds and flowers
• Monocot roots


  • Cortex is massive with thin-walled parenchymatous cells with intercellular spaces
  • Vascular bundles are more numerous, usually 8 or more in number
  • Pericycle is partly parenchymatous and partly sclerenchymatous
  • Pericycle gives rise to lateral roots
  • No secondary growth due to absence of cambium
  • Pith is large and well-developed
• Anatomical characteristics of monocot roots
• Dicot stem


  • Epidermis is the outermost protective layer
  • Cortex consists of hypodermis, general cortex, and endodermis
  • Pericycle is made of sclerenchyma patches
  • Vascular bundles are conjoint, collateral and open with endarch protoxylem
  • Medullary rays lie between vascular bundles
  • Pith is the central parenchymatous zone
• Monocot stem


  • Epidermis is the outermost layer
  • Hypodermis is made of sclerenchymatous cells
  • Ground tissue is parenchymatous without distinct tissues
  • Vascular bundles are scattered, more numerous towards the periphery, and are surrounded by a bundle sheath
  • Xylem has 4 distinct vessels in a 'Y' shape with a lysigenous cavity
  • Phloem has only sieve tubes and companion cells, no parenchyma
• Stem is the prolongation of the plumule of the embryo and forms the main axis of the plant
• Functions of stem

  • Primary: Support leaves and branches, conduct water/minerals and synthesised food, bear flowers and fruits
  • Secondary: Food storage, perennation, vegetative propagation, photosynthesis, protection, support
• Bud

  An underdeveloped or very young shoot having a condensed axis with closely crowded and folded young leaves
• Growth of axillary buds is suppressed due to the presence of the apical bud, a phenomenon called apical dominance
• Leaf


  • Always borne at the node of stem
  • Axillary bud always present in the axil
• Axillary bud


  • Exogenous in origin, develops from swollen leaf primordium
  • Growth is limited
• Leaf development


  Acropetal order (produced one after other from base to apex)
• Leaf lamina


  • Traversed by prominent vascular strands, called veins and veinlets
• Parts of a typical leaf

  • Leaf base (Hypopodium)
  • Petiole (Mesopodium)
  • Leaf blade or Lamina (Epipodium)
• Leaf base


  Part of leaf attached to the stem or a branch
• Petiole


  • Connects lamina with the stem or branch
  • Helps in exposing the leaf blade to sunlight
• Sessile leaf

  Petiole is absent
• Petiolate leaf


  Petiole is present
• Leaf blade or Lamina


  • Most important, green and flattened part
  • Mainly concerned with manufacture of food
  • Traversed medially from base to apex by the midrib, from which arise numerous thin lateral veins, and still thinner veins or veinlets
• Types of venation


  • Reticulate
  • Parallel
• Reticulate venation


  • Found in dicot leaves
  • Main vein divides into branches to form a net-like structure
• Types of reticulate venation

  • Unicostate reticulate
  • Multicostate convergent
  • Multicostate divergent
• Unicostate reticulate venation


  One midrib gives out lateral branches to make a network