Deep Dive into Plant Vegetative Anatomy

Overview

• Focus on vegetative organs: roots, stems, leaves of angiosperms (flowering plants).
• Aim to understand the form-function relationship and environmental influence on plant structure.

Roots

Primary Structure

• Three Main Tissue Systems:
  • Dermal System:
    • Outer layer, called rhizodermis.
    • Single layer, thin walls, connected by plasmodesmata.
    • Contains root hairs for increased surface area for absorption.
  • Fundamental System (Cortex):
    • Mostly parenchyma cells for storage and metabolism.
    • Defined boundaries include exodermis (outer) and endodermis (inner) with Casparian strip.
  • Vascular System:
    • Central part, develops from the procambium.
    • Contains pericycle, essential for lateral root formation and secondary growth.

Vascular Cylinder (Stele)

• Pericycle: Meristematic, initiates lateral roots.
• Xylem and Phloem:
  • Xylem development is exarch (outside-in).
  • Phloem bundles alternate with xylem arms.
  • Root types classified by xylem poles (diarch, tetrarch, polyarch).

Secondary Growth

• Lateral Meristems: Cambium and phellogen.
• Vascular Cambium: Between primary xylem and phloem, forms secondary xylem (wood) and phloem.
• Phellogen (Cork Cambium): Produces periderm (cork and phelloderm), replaces epidermis.

Stems

Primary Growth

• Apical Meristem (MAC): Located at shoot tip, produces primary tissues.
• Structure: Tunica (surface expansion) and corpus (bulk volume).

Primary Structure

• Three Systems:
  • Dermal: Epidermis with stomata, trichomes, and cuticle for protection.
  • Fundamental:
    • In dicots: cortex and central pith, often with support tissues.
    • In monocots: no distinct pith/cortex, ground tissue with scattered support bundles.
  • Vascular:
    • Vascular bundles in dicots (in a ring) and monocots (scattered).
    • Collateral, bicolateral arrangements.

Secondary Growth in Dicots

• Fascicular and Interfascicular Cambium: Forms a continuous ring for secondary xylem and phloem production.
• Periderm Formation: Phellogen arises in various tissues, forms bark.
• Lenticels: Provide gas exchange through bark.

Leaves

Structure

• Dermal System: Upper (adaxial) and lower (abaxial) epidermis, stomata, trichomes.
• Fundamental (Mesophyll):
  • Dicots: Dorsiventral (palisade and spongy layers).
  • Monocots: Isobilateral or less differentiated.

Specialized Structures

• Krantz Anatomy: In C4 plants for efficient photosynthesis.
• Bouliform Cells: In monocots for leaf curling under water stress.

Adaptations

• Xerophytic Adaptations: Thick cuticles, sunken stomata, sclerenchyma for dry environments.
• C4 Adaptations: Efficient CO2 concentration mechanism.

Reflection

• Structural adaptations are critically linked to function and survival.
• Impact of human activities and climate change on plant anatomy.
• Potential for further research on plant resilience and adaptation.

This exploration highlights the complexity and adaptability of plant structures, reflecting evolutionary fine-tuning for survival in diverse environments.