Stem & Root Internal Anatomy
⭐ Plant Anatomy Core Distinction
7 Parameters
Stem Anatomy: Dicot Stem vs Monocot Stem (Internal Organization)
Comparative histological matrix of hypodermis composition, vascular bundle arrangement, cambium presence, and ground tissue differentiation.
| Anatomical Zone / Feature | Dicot Stem (e.g. Helianthus / Sunflower) | Monocot Stem (e.g. Zea mays / Maize) |
|---|---|---|
| Hypodermis Tissue Type | Collenchymatous (thickened cellulose corners; provides flexible tensile strength) | Sclerenchymatous (lignified dead cells; provides rigid mechanical support) |
| Ground Tissue Differentiation | Differentiated clearly into Cortex, Endodermis, Pericycle, Medullary Rays, and Pith | Undifferentiated mass of parenchymatous ground tissue from hypodermis to center |
| Vascular Bundle Arrangement | Arranged in a single orderly ring (Eustele) | Scattered irregularly throughout ground tissue (Atactostele; peripheral smaller, central larger) |
| Bundle Sheath Presence | Absent (no sclerenchymatous bundle sheath around individual bundles) | Present (each bundle enclosed by a prominent sclerenchymatous bundle sheath) |
| Vascular Cambium & Open/Closed | OPEN (fascicular cambium present between xylem and phloem) | CLOSED (no cambium; xylem and phloem in direct contact) |
| Xylem Vessel Arrangement | Radial rows or clusters | Y-shaped or V-shaped arrangement with lysigenous water cavity (protoxylem lacuna) |
| Pith & Medullary Rays | Prominent parenchymatous central pith and radial medullary rays present | Completely absent |
Stem Diagnostic Key
Dicot Stem
Hypodermis: Collenchyma
Bundle Layout: Ringed, Open
Pith: Prominent
Monocot Stem
Hypodermis: Sclerenchyma
Bundle Layout: Scattered, Closed
Pith: Absent
Complex Vascular Tissues (Xylem vs Phloem)
⭐ Complex Permanent Tissue Matrix
5 Parameters
Vascular Tissues: Xylem vs Phloem (Components, Direction & Physiology)
Comparative matrix of conducting elements, living vs dead cell proportions, direction of translocation, and driving physical forces.
| Property | Xylem (Hadrome) | Phloem (Leptome) |
|---|---|---|
| Primary Transported Substance | Water and dissolved inorganic mineral salts (nitrates, phosphates, potassium) | Organic assimilates (Sucrose), amino acids, phytohormones, signaling RNAs |
| Direction of Conduction | Strictly UNIDIRECTIONAL (upward from roots to stems and leaves) | BIDIRECTIONAL / MULTIDIRECTIONAL (from source to variable sink tissues) |
| Chief Conducting Elements | Tracheids (tapered, pitted) and Vessel Elements (perforated end plates; in angiosperms) | Sieve Tube Elements (with sieve plates; in angiosperms) and Sieve Cells (gymnosperms) |
| Living vs Dead Cell Status | Mostly DEAD at functional maturity (Vessels, Tracheids, Xylem Fibers dead; ONLY Xylem Parenchyma is living) | Mostly LIVING at functional maturity (Sieve tubes, Companion cells, Phloem Parenchyma living; ONLY Phloem Fibers dead) |
| Physical Driving Mechanism | Passive Transpiration Pull (Cohesion-Tension theory: negative xylem pressure/tension) | Active Pressure-Flow (Münch hypothesis: hydrostatic turgor pressure gradient generated by ATP loading) |
Conducting Biology Contrast
Key Point
Tissue: Xylem
Direction: Unidirectional (Up)
Living Cells: Parenchyma only (25%)
Driving Force: Negative Tension Pull
Key Point
Tissue: Phloem
Direction: Bidirectional (Source-Sink)
Living Cells: Sieve+Companion (75%)
Driving Force: Positive Turgor Push
