III. B - The Root

• Types of root systems

  1. Fibrous - "Nerve-like"
  2. Taproot - "Carrot-like"
• Types of root modifications (type - modification - function)

  1. Buttress - adventitious roots - support
  2. Climbing - adventitious - attaches itself to tree for support
  3. Prop - adventitious - support
  4. Pneumatophores - lateral roots - gas exchange and respiration
  5. Root nodules - lateral roots - houses bacteria for nitrogen fixation
  6. Strangler roots - entire root system - support
  7. Storage - taproot or adventitious - storage
  8. Stilt - lateral - support
• Root anatomy of monocot

  1. Epidermis - thicker cell wall
  2. Exodermis - sub-epidermal
  3. Cortex
  4. Endodermis - lignified
  5. Stele - collection of vascular organs (pericycle, phloem, xylem, pith)
  6. Pericycle - outermost layer of stele
  7. Metaxylem
  8. Phloem - origin of lateral roots
  9. Xylem
  10. Pith - parenchyma
• Root anatomy of young dicot

  1. Epidermis
  2. Intercellular space
  3. Cortex
  4. Primary phloem - smaller than xylem
  5. Protoxylem
  6. Metaxylem - bigger than protoxylem
  7. Pith
• Root anatomy of old dicot - has secondary growth

  1. Lenticel - "cracks"
  2. Periderm
  3. Cork / phellem
  4. Cork cambium / phellogen
  5. Cork parenchyma / phelloderm
  6. Cortex (crushed)
  7. Secondary phloem
  8. Vascular cambium - larger than phloem; below phloem
  9. Xylem ray - "cut" / line
  10. Secondary xylem
• Types of metaxylem poles

  1. Diarch
  2. Triarch
  3. Tetrach
  4. Polyarch
• Root anatomy differences

  1. Root hairs - in TYPICAL MONOCOT only
  2. Epidermis layers - uniseriate - YOUNG DICOT and TYPICAL MONOCOT; multiseriate - SPECIALIZED MONOCOT
  3. Exodermis - in all MONOCOT types
  4. Protoxylem - POLYARCH in all monocot types; TETRARCH in young dicot
  5. Pith - in all except OLD DICOT