ANATOMY OF FLOWERING PLANTS

Introduction

• Examines both external morphology and internal structure of plants.

• Plant anatomy refers to the study of internal structure and functional organization of higher plants.

• Basic unit of life in plants: Cells

• Cells are organized into tissues, which compose organs.

• Variations exist in the internal structure of different plant organs.

• Within angiosperms, monocots and dicots differ anatomically.

• Internal structures adapt to diverse environments.

6.1 The Tissue System

• Plant tissues vary based on location within the plant body, affecting structure and function.

• Three main types of tissue systems:

  • Epidermal tissue system

  • Ground tissue system

  • Vascular tissue system

6.1.1 Epidermal Tissue System

• Forms the outermost covering of the plant body.

• Composed of:

  • Epidermal cells: tightly packed outer layer.

  • Stomata: openings for gas exchange.

  • Epidermal appendages: including trichomes and hairs.

• Root hairs: unicellular extensions aiding water mineral absorption.

• Trichomes: multicellular, prevent water loss.

6.1.2 Ground Tissue System

• Comprises all tissues except the epidermal and vascular tissues.

• Includes simple tissues: Parenchyma, Collenchyma, Sclerenchyma.

• In leaves, ground tissue is called mesophyll, containing chloroplasts.

6.1.3 Vascular Tissue System

• Consists of complex tissues: Xylem and Phloem.

• Forms vascular bundles:

  • In dicots: vascular bundles are open (contain cambium).

  • In monocots: vascular bundles are closed (lack cambium).

• Arrangement types:

  • Radial arrangement: xylem and phloem alternating in roots.

  • Conjoint arrangement: both xylem and phloem situated along the same radius in stems and leaves.

6.2 Anatomy of Dicotyledonous and Monocotyledonous Plants

• A study of transverse sections helps understand the internal structure of roots, stems, and leaves.

6.2.1 Dicotyledonous Root

• Outermost layer: Epiblema, with unicellular root hairs.

• Cortex: multiple layers of parenchyma cells with air spaces.

• Endodermis: single layer of barrel-shaped cells with Casparian strips.

• Pericycle: thick-walled cells initiating lateral roots and vascular cambium.

• Vascular bundles: typically 2-4 patches of xylem and phloem.

6.2.2 Monocotyledonous Root

• Similar structure to dicots with notable differences:

  • More than six xylem bundles (polyarch).

  • Pith is large and well-developed.

  • No secondary growth.

6.2.3 Dicotyledonous Stem

• Epidermis: protective outer layer, possibly with trichomes and stomata.

• Cortex: three sub-zones with hypodermis, cortical layers, and endodermis rich in starch.

• Vascular bundles: arranged in a ring, joint structure with endarch protoxylem.

• Pith: occupied by parenchymal cells with air spaces.

6.2.4 Monocotyledonous Stem

• Sclerenchymatous hypodermis and scattered vascular bundles.

• Each vascular bundle surrounded by a sclerenchymatous bundle sheath.

• Large ground tissue filled with parenchyma.

6.2.5 Dorsiventral (Dicotyledonous) Leaf

• Three main parts: epidermis, mesophyll, vascular system.

• Mesophyll: contains chloroplasts; divided into palisade and spongy parenchyma.

• Vascular bundles visible in veins, surrounded by bundle sheath cells.

6.2.6 Isobilateral (Monocotyledonous) Leaf

• Stomata on both surfaces of the epidermis; mesophyll is not differentiated.

• Presence of bulliform cells for water regulation.

• Parallel venation with similar vascular bundle sizes.

Summary

• Plant anatomy involves various tissue types, broadly classified into meristematic and permanent tissues.

• Main functions of tissues: food assimilation/storage, water/mineral transport, mechanical support.

• The three tissue systems (epidermal, ground, vascular) perform specialized functions.

• Notable differences between monocotyledonous and dicotyledonous plants include variations in internal structures, vascular bundles, and secondary growth tendencies.

Exercises

1. Illustrate anatomical differences between monocot and dicot roots; monocot and dicot stems.

2. Observe a transverse section of a young stem; determine its classification as monocot or dicot with reasons.

3. Identify plant material featuring:

   • Conjoint, scattered vascular bundles surrounded by sclerenchymatous sheaths.

   • Absence of phloem parenchyma.

4. Explain the stomatal apparatus and structure of stomata with a diagram.

5. List the three basic tissue systems in flowering plants and their corresponding tissues.

6. Discuss the usefulness of studying plant anatomy.

7. Describe the internal structure of dorsiventral leaves with diagrams.