BOT 119 LAB LE 1

• Shoot and root apices consist of three distinct meristematic zones called a histogen: Dermatogen, Periblem, Plerome
• Apical Cell Theory
• No ONE or certain initial that will give rise to specific group of tissue
• Recognition of shoot apex as undeveloped region from which growth of plant proceeded
• Shoot Apical Meristem (SAM)


  • Dynamic structure that adds cells to the primary plant body (shoot part)
  • Repetitively produces phytomeres
• Origin of leaves

  1. The formation of leaves is initiated at the peripheral region of the apex

  2. Leaf buttress results from activity of the peripheral zone

  3. Plastochron is the period between the initiation of two successive leaf primordia

  4. Maximal area is when volume and surface area of apical meristem is at maximum

  5. Minimal area is when volume and surface area of apical meristem is at minimum

  6. Leaf primordia results from frequent periclinal divisions by the tunica and corpus

  7. Procambial strands give rise to the vascular tissues of leaves

  8. Leaves are produced in regular order or arrangement based on their phyllotaxy
• Zone boundaries are distinguished by cytological and histological differences
• Cytohistological Zonation Theory
• Main body of plant arises from a massive meristem of considerable depth
• Zone boundaries distinguished by

  • Cell size
  • Cell shape
  • Vacuolation
  • Dispersion
  • Stainability
  • Plane of cell division
  • What the meristem gives rise to
• Tunica-Corpus Theory
• Discovery of single, morphologically distinct initial cell
• Histogen Theory
• Apical Meristems


  • Group of meristematic cells at the apex of plant body
  • Includes Shoot Apical Meristem (SAM) and Root Apical Meristem (RAM)
  • Consists of PROMERISTEM and Initials + most recent derivatives
• This theory fits most of angiosperms but has undergone a few modifications
• Tunica-corpus was not observed in gymnosperms
• Learning Outcomes
• Leaves are produced in regular order or arrangement based on their phyllotaxy: Spiral
• Leaf arrangement based on phyllotaxy

  • Spiral
  • Distichous
  • Opposite
  • Decussate
  • Whorled
• Initiation of branching

  1. Bud is formed

  2. Periclinal and anticlinal division occurs in the leaf axil

  3. Bud meristem elevated above surface

  4. Apical meristem of the bud is organized

  5. Shell zone is formed - zone of parallel curving layers

  6. Initiation of leaf primordia if axillary bud is not dormant, leaf primordia is initiated following upward growth
• Classification in relation to the origin of the epidermis

  • Cortex and epidermis have common initials - The root cap arose from its own initials (calyptrogen)
  • Epidermis and rootcap have common origin - Initial is known as dermatocalyptrogen, common in eudicots
• Will the root apical meristem exhibit the same organization as the SAM?
• Origins of branches

  • Axillary buds - branches commonly originate as buds in the axils of leaves
  • Detached meristems - initiated later than leaves, arise from axil of 2nd or 3rd leaf from the apex
  • Adventitious buds - arise with no direct relation to the apical meristem
• Procambial strands


  Gives rise to the vascular tissues of leaves
• Root Cap is composed of dead cells and mucilage which aids root in penetrating soil, provides protection for the apical
• Root Apical Meristem is not terminal but subterminal in position, located beneath the root cap, grows more uniformly in length than the shoot, shows no periodic changes in shape and structure
• rimordia

  Results from frequent periclinal divisions by the tunica and corpus (or the initial site)
• Branching patterns

  1. Dichotomous - branch results from median division of apical meristem

  2. Monopodial - branches arise laterally at the apex
• Bud traces - procambial cells provide potential conducting channels to the bud during its early development
• Theories of Apical Organization in Roots

  • Apical Cell Theory
  • Histogen Theory
  • Open Type
  • Close Type
• Initial


  Known as dermatocalyptrogen
• Organs of a flower develop in an acropetal sequence from base to apex of the floral meristem
• Controls direction of root movement through the soil

  • Calcium calcareous granules (statoliths) found in statocytes (cells)
  • Accumulates at the ‘bottom’
  • Helps the plant reorient, for the roots to grow towards the force of gravity
• Growth Modes in Plants

  1. Plants have two basic growth modes: vegetative and flower and seed growth

  2. Aboveground vegetative growth develops from the apical meristem

  3. Plants will maintain a vegetative growth pattern until the apical meristem undergoes a change which alters the identity of the meristem
• Root Cap composition

  1. Composed of dead cells and mucilage

  2. Mucilage aids root in penetrating soil

  3. Provides protection for the apical meristem

  4. Controls direction of root movement through the soil
• Floral Meristem is a meristem that has shifted from making leaves to making flowers
• Epidermis and rootcap have common origin
• Quiescent Center


  • Contains initials but they do not divide, or they divide very slowly and occasionally
  • Not permanently non-functional
  • Hemispherical or discoid in shape
  • Not seen in roots with apical initial type of organization
• Quiescent Center is "Inactive"
• Root Cap composition

  • Composed of dead cells
  • Mucilage aids root in penetrating soil
  • Provides protection for the apical meristem
  • Controls direction of root movement through the soil