Plant Anatomy & Morphology

Plants are everywhere in Nepal -- from the rhododendron (Nepal's national flower) in the hills to the sal forests of the Terai. Understanding plant anatomy (internal structure) and morphology (external form) helps us appreciate how plants grow, transport water, and produce food.

Plant Tissues

Plant tissues are organized groups of cells that perform specific functions. They are broadly classified into two types:

Meristematic Tissues

These are actively dividing cells found at growth points. They are responsible for plant growth.

• Apical meristem: At root tips and shoot tips. Causes growth in length (primary growth).
• Lateral meristem (cambium): Along the sides of stems and roots. Causes growth in thickness (secondary growth).
• Intercalary meristem: At the base of leaves and internodes. Found in grasses.

Permanent Tissues

Cells that have stopped dividing and specialized for specific functions.

Simple permanent tissues:

• Parenchyma: Thin-walled, living cells. Functions: storage, photosynthesis (when containing chloroplasts, called chlorenchyma), and gas exchange
• Collenchyma: Thickened corners, living cells. Provides flexible support (found in leaf stalks)
• Sclerenchyma: Thick, lignified walls, dead cells. Provides rigid support (fibres, sclereids in coconut shells)

Complex permanent tissues:

• Xylem: Transports water and minerals upward from roots to leaves. Made of vessels, tracheids, fibres, and parenchyma. Vessels are dead, hollow tubes.
• Phloem: Transports food (sucrose) from leaves to all parts. Made of sieve tubes, companion cells, fibres, and parenchyma. Sieve tubes are living.

Root Anatomy

A cross-section of a typical dicot root (from outside to inside):

• Epidermis: Outer protective layer with root hairs for absorption
• Cortex: Storage parenchyma
• Endodermis: Single layer with Casparian strip (regulates water entry)
• Pericycle: Gives rise to lateral roots
• Vascular bundle: Xylem (star-shaped in centre) and phloem (between xylem arms)

Stem Anatomy

Dicot stem cross-section:

• Epidermis: Outer layer with cuticle
• Cortex: Collenchyma and parenchyma layers
• Vascular bundles: Arranged in a ring. Each has xylem (inside), phloem (outside), and cambium between them
• Pith: Central parenchyma for storage

Leaf Anatomy

• Upper epidermis: Protective layer with cuticle
• Palisade mesophyll: Columnar cells packed with chloroplasts (main site of photosynthesis)
• Spongy mesophyll: Loosely arranged with air spaces for gas exchange
• Lower epidermis: Contains stomata (pores) for gas exchange
• Vascular bundles (veins): Xylem and phloem for transport

Key Takeaways

• Meristematic tissues divide actively; permanent tissues are specialized
• Xylem transports water upward (dead vessels); Phloem transports food in all directions (living sieve tubes)
• Root, stem, and leaf each have distinctive tissue arrangements
• Understanding plant anatomy helps in agriculture and forestry