Chapter 6: Anatomy of Flowering Plants

Understanding the internal structure and organization of higher plants, known as plant anatomy, is crucial for differentiating between various types of plants, such as monocots and dicots, and understanding their adaptations to diverse environments.

6.1 The Tissue System

Types of Tissue Systems

• Epidermal Tissue System: Outermost covering consisting of epidermal cells, stomata, and epidermal appendages (trichomes and hairs).
  • Root Hairs: Unicellular elongations aiding in water and mineral absorption.
  • Trichomes: Multicellular structures in shoots that prevent water loss.
• Ground Tissue System: Comprising parenchyma, collenchyma, and sclerenchyma, it forms most of the plant's bulk.
  • Parenchyma: Found in cortex, pericycle, pith, and medullary rays.
  • Mesophyll: In leaves, made of chloroplast-containing cells responsible for photosynthesis.
• Vascular Tissue System: Composed of complex tissues, xylem, and phloem, forming vascular bundles.
  • Open Vascular Bundles: Found in dicots, allowing secondary growth.
  • Closed Vascular Bundles: Found in monocots, lacking secondary growth.
  • Radial and Conjoint Vascular Arrangements: Different configurations of xylem and phloem.

6.2 Anatomy of Dicotyledonous and Monocotyledonous Plants

Dicotyledonous Root

• Structure: Includes epiblema, cortex, endodermis, pericycle, and small or inconspicuous pith.
• Casparian Strips: Waxy deposits in endodermis preventing water permeability.
• Stele: Comprising pericycle, vascular bundles, and pith.

Monocotyledonous Root

• Similar Structure: To dicot roots with more xylem bundles (polyarch) and a well-developed pith.
• Lacks Secondary Growth.

Dicotyledonous Stem

• Structure: Outermost epidermis, cortex (with sub-zones including hypodermis), and pericycle.
• Ring Arrangement: Characteristic of dicot stems.
• Pith: Parenchymatous cells at the center.

Monocotyledonous Stem

• Features: Sclerenchymatous hypodermis, scattered vascular bundles with bundle sheaths, and conspicuous parenchymatous ground tissue.
• Vascular Bundles: Conjoint and closed with phloem parenchyma absent.

Dorsiventral (Dicotyledonous) Leaf

• Three Main Parts: Epidermis, mesophyll, and vascular system.
• Mesophyll Types: Palisade and spongy parenchyma.
• Vascular Bundles: Surrounded by thick-walled bundle sheath cells.

Isobilateral (Monocotyledonous) Leaf

• Similarities: To dorsiventral leaf with stomata on both surfaces.
• Bulliform Cells: In grasses, help minimize water loss.

Summary

• Plant tissues are categorized as meristematic or permanent.
• Three tissue systems exist: epidermal, ground, and vascular.
• Vascular bundles play roles in transporting water, minerals, and food and vary between monocots and dicots.
• Secondary growth is prevalent in dicot roots and stems.

Exercises

1. Illustrate anatomical differences between monocot and dicot roots and stems.
2. Examine a plant stem under a microscope to determine if it is a monocot or dicot.
3. Identify plant material based on vascular bundle characteristics.
4. Explain the stomatal apparatus.
5. List and describe the three basic tissue systems in flowering plants.
6. Discuss the significance of studying plant anatomy.
7. Describe the internal structure of a dorsiventral leaf with diagrams.