I. Introduction:

• Similarities and variations in external morphology of plants and animals.
• Study of internal structure termed anatomy.
• Basic organizational levels: cells → tissues → organs.

II. Basic Organization:

1. Cells:
   • Fundamental unit in plants.
2. Tissues:
   • Cells are organized into tissues.
3. Organs:
   • Tissues form organs with distinct functions.

III. Internal Structure Variation:

1. Monocots vs. Dicots:
   • Angiosperms exhibit anatomical differences.
2. Adaptations:
   • Internal structures reflect adaptations to diverse environments.

IV. Plant Anatomy:

1. Cell Types:
   • Various cell types are specialized for specific functions.
2. Tissue Types:
   • Different tissues (e.g., epidermal, vascular, ground) and their functions.
3. Organ Variation:
   • Differences in internal structure among various plant organs.

V. Monocots and Dicots:

• Detailed exploration of anatomical distinctions between monocots and dicots.
  • Vascular bundle arrangement.
  • Leaf venation patterns.
  • Root structure variations.

VI. Environmental Adaptations:

• Examination of internal structures that exhibit adaptations to environmental conditions.
  • Examples of adaptations in roots stems, and leaves.
  • How internal structures aid in survival and growth.

THE TISSUE SYSTEM

Epidermal Tissue System

I. Structure of Epidermis:

• Composition:
  • Made up of elongated, single-layered parenchymatous cells.
  • The small cytoplasmic region along the cell wall and a large vacuole.
• Cuticle:
  • A waxy thick layer covers the outside of the epidermis.
  • Prevents water loss through transpiration.
  • Absent in roots.

II. Stomata:

• Location:
  • Present in the epidermis of leaves.
• Structure:
  • Composed of two bean-shaped guard cells enclosing the stomatal pore.
  • Guard cells regulate stomatal opening and closing.
• Function:
  • Regulates transpiration and gaseous exchange in leaves.

III. Subsidiary Cells:

• Description:
  • Specialized epidermal cells in the vicinity of guard cells.
• Function:
  • Assist in the regulation of stomatal apparatus.

IV. Trichomes (Epidermal Hairs):

• Root Hairs:
  • Unicellular elongations of epidermal cells in roots.
  • Aid in water and mineral absorption from the soil.
• Stem Trichomes:
  • Present on stems and referred to as trichomes.
  • Multicellular, may be branched or unbranched, and soft or stiff.
  • Help prevent water loss due to transpiration.
  • Some trichomes may be secretory.

The Ground Tissue System

The Vascular Tissue System

I. Components of Vascular System:

• Phloem:
  • Conducts food materials (sugars).
• Xylem:
  • Conducts water and minerals.
• Vascular Bundles:
  • Aggregates of phloem and xylem tissues.

II. Vascular Bundle Types:

• Dicotyledonous Stems:
  • Open Vascular Bundles:
    • Cambium is present between the phloem and xylem.
    • Can form secondary xylem and phloem.
• Monocotyledonous Stems:
  • Closed Vascular Bundles:
    • Lack cambium and cannot form secondary tissues.

III. Vascular Bundle Arrangements:

• Radial Arrangement:
  • The xylem and phloem are arranged alternately along different radii.
  • Common in roots.
• Conjoint Type:
  • The xylem and phloem are jointly situated along the same radius.
  • Found in stems and leaves.
• Phloem Location:
  • Typically on the outer side of the xylem in conjoint vascular bundles.

ANATOMY OF DICOTYLEDONOUS AND MONOCOTYLEDONOUS PLANTS

Dicotyledonous Root

I. Epiblema (Outermost Layer):

• Formed by epidermal cells.
• Some cells protrude as unicellular root hairs.

II. Cortex:

• Consists of several layers of thin-walled parenchyma cells.
• Intercellular spaces are present.
• Innermost layer is the Endodermis:
  • A single layer of barrel-shaped cells without intercellular spaces.
  • Tangential and radial walls have water-impermeable Casparian strips (composed of suberin).

III. Pericycle:

• Few layers of thick-walled parenchymatous cells.
• Initiates lateral roots and vascular cambium during secondary growth.

IV. Pith:

• Small or inconspicuous.
• Parenchymatous cells present.

V. Conjunctive Tissue:

• Parenchymatous cells lie between the xylem and phloem.
• Usually two to four xylem and phloem patches.

VI. Stele:

• All tissues on the inner side of the endodermis.
• Includes pericycle, vascular bundles, and pith.
• Vascular Bundles:
  • Usually two to four patches.
  • Cambium Ring:
    • Develops between xylem and phloem.

Monocotyledonous Root

I. Epidermis:

• The outermost layer of the root.

II. Cortex:

• Tissue between the epidermis and vascular bundles.

III. Endodermis:

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

IV. Pericycle:

• Tissue layer giving rise to lateral roots.

V. Vascular Bundles:

• Usually more than six (polyarch).
• Consists of xylem and phloem.

VI. Pith:

• Large and well-developed.

VII. No Secondary Growth:

• Monocotyledonous roots do not undergo secondary growth.

Dicotyledonous Stem

I. Epidermis:

• Outermost protective layer.
• Covered with a thin cuticle.
• May bear trichomes and stomata.

II. Cortex:

• Multiple layers between epidermis and pericycle.
• Three sub-zones:
  1. Outer Hypodermis:
     • Consists of collenchymatous cells for mechanical strength.
  2. Middle Cortex:
     • Rounded, thin-walled parenchymatous cells with intercellular spaces.
  3. Inner Endodermis (Starch Sheath):
     • Cells rich in starch grains.

III. Pericycle:

• Present on the inner side of the endodermis.
• Semi-lunar patches of sclerenchyma above the phloem.

IV. Medullary Rays:

• Radially placed parenchymatous cells between vascular bundles.

V. Vascular Bundles:

• Numerous, arranged in a ring.
• Conjoint, open, with endarch protoxylem.

VI. Pith:

• Large central region.
• Composed of rounded, parenchymatous cells with large intercellular spaces.

Monocotyledonous Stem

I. Hypodermis:

• Sclerenchymatous layer beneath the epidermis.

II. Vascular Bundles:

• A large number of scattered bundles.
• Each bundle is surrounded by a sclerenchymatous bundle sheath.
• Conjoint and closed vascular bundles.
• Peripheral bundles are generally smaller than centrally located ones.

III. Ground Tissue:

• Large, conspicuous parenchymatous ground tissue.

IV. Phloem Parenchyma:

• Absent in the vascular bundles.

V. Water-Containing Cavities:

• Present within the vascular bundles.

Dorsiventral (Dicotyledonous) Leaf

A vertical section of a dorsiventral leaf reveals three main components:

I. Epidermis:

• Covers both upper (adaxial) and lower (abaxial) leaf surfaces.
• Conspicuous cuticle present.
• The abaxial epidermis generally bears more stomata than the adaxial epidermis.
• Mesophyll lies between the upper and lower epidermis.

II. Mesophyll:

• Contains chloroplasts and performs photosynthesis.
• Composed of parenchyma cells.
• Two types of cells:
  • Palisade Parenchyma: Adaxially placed, elongated cells arranged vertically and parallel.
  • Spongy Parenchyma: Oval or round cells, loosely arranged below palisade cells, extending to the lower epidermis. Numerous air spaces and cavities are present between cells.

III. Vascular System:

• Includes vascular bundles found in veins and the midrib.
• The size of vascular bundles depends on vein size.
• Veins vary in thickness in the reticulate venation.
• Vascular bundles are surrounded by a layer of thick-walled bundle sheath cells.

Isobilateral (Monocotyledonous) Leaf

The anatomy of an isobilateral leaf shares similarities with the dorsiventral leaf but exhibits characteristic differences:

I. Epidermis:

• Stomata are present on both the upper (adaxial) and lower (abaxial) surfaces of the epidermis.
• Bulliform cells may be present on the adaxial epidermis, especially along the veins.

II. Mesophyll:

• Mesophyll is not differentiated into distinct palisade and spongy parenchyma.
• Lack of a clear distinction between upper and lower layers in terms of cell arrangement.

III. Bulliform Cells:

• Large, empty, colorless cells can be found in certain adaxial epidermal cells along the veins.
• These cells play a role in leaf movement; when turgid, they expose the leaf surface, and when flaccid, they cause the leaves to curl inward, minimizing water loss during water stress.

IV. Vascular System:

• Parallel venation is a characteristic feature in monocot leaves.
• Vascular bundles, except in main veins, tend to be of near-similar sizes in vertical sections of the leaves.