In-depth Notes on Anatomy of Flowering Plants

Anatomy of Flowering Plants

Introduction to Plant Anatomy

• Definition: Study of the internal structure of plants is termed anatomy.

• Basic Unit: Cells are the fundamental unit; organized into tissues, contributing to organs.

• Organ Variability: Different organs exhibit varied internal structures.

• Angiosperms: Distinctions are evident between monocots and dicots in anatomy.

• Environmental Adaptations: Internal structures adapt according to diverse environments.

Tissue Systems

• Plant tissues can be categorized based on structure and localization into three systems:

  1. Epidermal Tissue System

  2. Ground (Fundamental) Tissue System

  3. Vascular (Conducting) Tissue System

6.1 Epidermal Tissue System

• Function: Forms the outer protective layer; consists of epidermal cells, stomata, and appendages like trichomes.

  • Epidermis:

  • Comprises a single layer of elongated, compact cells (parenchymatous).

  • Covered by a waxy cuticle to prevent water loss, absent in roots.

  • Root Hairs:

  • Unicellular extensions from epidermal cells to absorb water and minerals.

  • Trichomes:

  • Can be multicellular, branched/unbranched, and can produce secretions.

  • Help enhance water retention by reducing transpiration.

  • Stomata:

  • Critical for regulating transpiration and gas exchange.

  • Composed of guard cells that control the opening/closing of stomatal pores.

6.1.2 Ground Tissue System

• Definition: Comprises all plant tissues excluding epidermis and vascular bundles.

• Types of Simple Tissues:

  • Parenchyma: Found in cortex, pericycle, and pith.

  • Collenchyma: Provides support, particularly in growing shoots.

  • Sclerenchyma: Offers strength and support with thick lignified walls.

• Mesophyll: In leaves, parenchymatous cells with chloroplasts facilitate photosynthesis.

6.1.3 Vascular Tissue System

• Components: Consists of complex tissues, specifically phloem and xylem.

• Vascular Bundles:

  • Dicots: Open bundles with cambium, allowing for secondary growth.

  • Monocots: Closed bundles lacking cambium; do not form secondary tissues.

  • Arrangement Types:

  • Radial: Alternating xylem and phloem, typically in roots.

  • Conjoint: Xylem and phloem on the same radius, commonly seen in stems and leaves.

6.2 Anatomical Differences in Roots and Stems

6.2.1 Dicotyledonous Root

• Structure:

  • Outer Layer: Epiblema, with root hairs for absorption.

  • Cortex: Composed of parenchyma, with an inner layer (endodermis) lacking intercellular spaces.

  • Pericycle: Thickened parenchyma allowing lateral root initiation.

  • Stele: Contains vascular bundles and pith.

6.2.2 Monocotyledonous Root (Similar to Dicot)

• Characteristics:

  • More xylem bundles (polyarch) compared to dicots.

  • Large, well-developed pith.

  • No secondary growth.

6.2.3 Dicotyledonous Stem

• Structure:

  • Epidermis: Thin layer with possible trichomes and stomata.

  • Cortex: Thin-walled parenchymatous cells with three sub-zones (hypodermis, cortex layers, endodermis).

  • Vascular Bundles: Arranged in a ring, open and conjoint with endarch protoxylem.

6.2.4 Monocotyledonous Stem

• Features:

  • Scattered vascular bundles surrounded by sclerenchyma.

  • Conjoint and closed vascular bundles;

  • Ground tissue predominance.

6.2.5 Dorsiventral (Dicotyledonous) Leaf

• Structure:

  • Epidermis: Covered with cuticle, often more stomata on lower surface.

  • Mesophyll: Consists of palisade and spongy parenchymas for photosynthesis.

  • Vascular System: Dependent on leaf vein structure with vascular bundles interconnected in the veins.

6.2.6 Isobilateral (Monocotyledonous) Leaf

• Differences:

  • Stomata present on both surfaces; mesophyll not differentiated.

  • Presence of bulliform cells around veins to prevent water loss through curling under stress.

Summary

• Plants consist of distinct tissue types classified as meristematic and permanent.

• The three tissue systems (epidermal, ground, vascular) serve functions such as food assimilation, storage, transportation, and structural support.

• Significant variations exist in internal structures of monocots vs dicots, affecting their growth patterns and tissue organization.