1. Plant Tissues
Plant tissues are broadly categorized into two main groups based on their capacity for cellular division: Meristematic Tissues and Permanent Tissues.
A. Meristematic Tissues
Active zones of continuous cell division, sub-classified by their location:
- Apical Meristem: Located at the absolute shoot and root tips; responsible for primary elongation.
- Intercalary Meristem: Positioned at the nodes (e.g., in grasses); allows regeneration of parts removed by herbivores.
- Lateral Meristem: Comprises the cambium layers; responsible for secondary growth, increasing the plant's girth.
B. Permanent Tissues
Mature cells that have lost the capacity to divide, split into two structural formats:
Simple Permanent Tissues (Homogeneous Cells)
- Parenchyma: Living cells, thin-walled, primary site for photosynthesis and storage.
- Collenchyma: Provides mechanical support, characteristically thick at corners due to cellulose/pectin deposits.
- Sclerenchyma: Dead cells at maturity with highly thickened, lignified walls.
Complex Permanent Tissues (Heterogeneous Cells)
- Xylem: Conducts water and minerals. Made of tracheids, vessels, xylem fibers, and living xylem parenchyma.
- Phloem: Translocates organic food. Made of sieve tubes, companion cells, phloem fibers, and phloem parenchyma.
2. Tissue Systems
Plants feature three major integrated tissue systems working in tandem:
| Tissue System | Primary Components & Characteristics |
|---|---|
| Epidermal System | Outer protective covering containing epidermal cells, guard cells (stomata), and appendages like trichomes or root hairs. |
| Ground System | Forms the main bulk of the plant body. Dominated by parenchyma, collenchyma, and sclerenchyma; active in photosynthesis and storage. |
| Vascular System | Consists of complex tissues (Xylem + Phloem) arranged in various structural patterns (radial, conjoint, open, or closed bundles). |
3. Anatomy of Dicot and Monocot Root
Dicot Root (e.g., Bean)
- Vascular arrangement: Alternate radial bundles, containing fewer xylem bundles (diarch to tetrarch).
- Secondary Growth: Active cambium ring forms, allowing regular secondary growth.
Monocot Root (e.g., Maize)
- Vascular arrangement: Polyarch condition with numerous xylem bundles.
- Internal structure: Central pith is large and well-developed; no secondary growth takes place.
4. Anatomy of Dicot and Monocot Stem
Dicot Stem
Vascular bundles are arranged symmetrically in a distinct ring structure. These bundles are conjoint, collateral, and **open** (possess intrafascicular cambium), making secondary growth fully possible.
Monocot Stem
Vascular bundles are characteristically scattered throughout the ground tissue. These bundles are conjoint, collateral, and **closed** (lack cambium), meaning no secondary growth can occur.