Unit-II: Internal Tissue Structures

The objective of this unit is to understand the microscopic organization of internal tissues in plants, focusing on their structural characteristics and arrangement in various organs.

Practical identification of meristematic regions using permanent slides or photographs.

• Apical Meristem: Located at the tips of roots and shoots; characterized by small, thin-walled, isodiametric cells with dense cytoplasm and large nuclei.
• Vascular Cambium: A lateral meristem responsible for secondary growth; appears as a ring or patches between the primary xylem and phloem.

Observation of ground tissue cells that are structurally and functionally uniform.

• Parenchyma: Most common living tissue; thin-walled cells often with intercellular spaces for storage or photosynthesis.
• Collenchyma: Living mechanical tissue; cells have unevenly thickened primary walls, particularly at the corners, providing flexibility and support.
• Sclerenchyma: Dead mechanical tissue at maturity; characterized by thick, lignified secondary walls (e.g., sclereids and fibers).

Complex tissues are composed of different types of cells working together for conduction.

• Xylem Elements: Identification of tracheids, vessels, xylem parenchyma, and xylem fibers. Vessels appear as wide, hollow tubes.
• Phloem Elements: Identification of sieve tube elements, companion cells, phloem parenchyma, and phloem fibers. Sieve tubes are identified by the presence of sieve plates.

Detailed study of the arrangement of tissue systems across different plant organs.

A. Root Anatomy

• Dicot Root: Xylem and phloem are arranged radially; typically has fewer xylem bundles (diarch to hexarch).
• Monocot Root: Similar radial arrangement but characterized by a large number of vascular bundles (polyarch) and a well-developed pith.

B. Stem Anatomy

• Dicot Stem: Vascular bundles are arranged in a ring (eustele); bundles are conjoint, collateral, and open (possessing cambium).
• Monocot Stem: Vascular bundles are scattered throughout the ground tissue (atactostele); bundles are conjoint, collateral, and closed (no cambium).

C. Leaf Anatomy

• Dorsiventral (Dicot) Leaf: Differentiated into upper and lower epidermis; mesophyll is divided into palisade and spongy parenchyma.
• Isobilateral (Monocot) Leaf: Epidermis on both sides is similar; mesophyll is not clearly differentiated into palisade and spongy layers.
• Kranz Anatomy: Specialized leaf structure found in C4 plants, showing large bundle sheath cells surrounding the vascular bundles.

Laboratory Checklist

• Use double-staining methods (Safranin and Fast Green) for temporary stem and leaf preparations.
• Focus on the vascular bundle arrangement to differentiate between Dicots and Monocots.
• Identify secondary growth features if observing woody specimens.