Study Notes on Anatomy of Flowering Plants

Anatomy of Flowering Plants

Introduction

  • Higher plants exhibit complex body organization consisting of:

    • Cells: Form the basic unit of tissues.

    • Tissues: Groups of similar cells working together.

    • Organs: Structures composed of tissues.

    • Organ Systems: Combinations of organs working together.

  • Cell Division: The process of cell multiplication.

  • Cell Differentiation: The process through which cells become specialized for different functions.

  • All plant cells originate from meristematic cells, which undergo differentiation during maturation.

  • Differentiation leads to the formation of various cells, each performing specific roles.

  • The branch of biology studying internal structures of organisms is Anatomy.

  • Nehemiah Grew: Known as the “Father of Plant Anatomy”; introduced the term 'Tissue'.

Plant Tissues

  • Defined as a group of similar or dissimilar cells having a common origin that cooperate to perform similar functions.

  • Classification based on the capacity to divide:

    1. Meristematic Tissues: Ever-dividing tissues.

    2. Permanent Tissues: Non-dividing tissues formed after differentiation.

Historical Context on Plant Tissues

  • Nehemiah Grew (1682): Coined 'Tissue' and 'Parenchyma'.

  • Nageli (1858): Introduced terms like Meristems, Xylem, and Phloem.

Definitions

  • Tissue: A group of similar/dissimilar cells with a common origin, cooperating for a similar function.

  • Anatomy: The study of internal organization of plants.

Meristematic Tissues (Meristems)

  • Characteristics:

    • Composed of similar cells capable of continuous division.

    • Cells are thin-walled, compactly arranged (no intercellular spaces).

    • Only primary cell wall present, made of cellulose.

    • Cells typically have dense cytoplasm with small/absent vacuoles.

    • Do not store reserve food as they are highly metabolically active.

    • Ergastic substances are generally absent.

Classification of Meristems

  • Based on: Origin, position, and functions.

    1. On the Basis of Origin:

      • Promeristem (Primordial/Embryonic Meristem): Found in germinating embryos or young seedlings, gives rise to primary meristems.

      • Examples: Apical and intercalary meristems.

    2. On the Basis of Position:

      • Apical Meristems: Located at stems' apex and roots' apex; responsible for lengthwise growth.

      • Intercalary Meristems: Found at bases of leaves or between nodes; help in elongation of internodes.

      • Lateral Meristems: Located laterally; increase girth (thickness).

      • Secondary Meristems: Derive from permanent tissues; important examples include interfascicular cambium.

Functions of Meristems

  • Primary Meristem: Emerges early in plant life, retains division capacity throughout life, derived from promeristem.

  • Secondary Meristem: Formed from permanent tissues via differentiation; appears later, contributes to secondary growth.

Interfascicular Cambium and Related Terms

  • Fascicular Cambium: Forms secondary vascular tissues, contributes to increase in girth/diameter.

    • Examples include:

    • Interfascicular cambium (in dicot stems),

    • Cork cambium (phellogen).

  • Wound Cambium: Formed during tissue mending post-injury.

Summary of Types of Meristems Based on Functions

  • Apical Meristem: Responsible for primary growth.

  • Lateral Meristem: Responsible for secondary growth, contributing to increased thickness.

  • Intercalary Meristem: Assists in elongating stems and leaves.

Root Cap

  • Composed of parenchyma cells, shorter lifespan.

  • Contains starch grains for geotropic response.

  • Acts as protective shield for root meristem, secretes mucilaginous substances aiding in soil penetration.

Quiescent Centre

  • A small region with low mitotic activity, acting as a reserve meristem; significant in root apex organization.

  • Supports structural integrity of root apical meristem shape.

Anatomy of Dicot Root

  • Primary Dicot Root: Transverse section reveals epiblema, cortex, endodermis, stele, and pericycle.

  • Epiblema (Piliferous Layer): Outermost root layer, facilitates water absorption through root hairs.

  • Cortex: Storage and transport role; pericycle sits just inside the endodermis.

  • Endodermis: Inward boundary of cortex, essential for controlling water and nutrient passage.

Vascular Tissue System

  • Comprised of xylem for water/mineral transport and phloem for organic nutrient distribution.

  • Xylem functions entirely consist of dead tissues aiding in vertical conduction, while phloem involves living components allowing bidirectional transport of food.

  • Vascular bundles typically arranged in rings in dicots; scattered in monocots.

Secondary Growth

  • Secondary growth brings about thickening in woody plants, primarily driven by the vascular and cork cambium.

  • Formation of secondary xylem/wood and phloem, producing structural support while facilitating nutrient and water movement.

  • Heartwood: Non-functional central core in older trees, provides structural stability.

  • Sapwood: Active, functional shell of secondary xylem conducting water and nutrients.

Important Classifications of Plant Tissues

  • Simple Permanent Tissues: Homogeneous, i.e., parenchyma, collenchyma, sclerenchyma.

  • Complex Permanent Tissues: Heterogeneous, including xylem (conducts water) and phloem (transports food).

Definitions of Key Terms

  • Guttation: Loss of water in liquid form via specialized structures called hydathodes.

  • Hydathodes: Pores involved in the process of guttation, typically found at leaf margins.

Conclusion

  • Understanding of plant anatomy is essential for botany, ecology, and practical applications such as agriculture, horticulture, and forestry.