Anatomy of Flowering Plants - Quick Revision
Tissues
- Plant tissues are broadly classified into MERISTEMATIC (apical, lateral, intercalary) and PERMANENT (simple and complex).
- Simple permanent tissues: parenchyma (storage, mesophyll), collenchyma (mechanical support in young stems), sclerenchyma (mechanical strength, dead, thick-walled).
- Complex permanent tissues: xylem and phloem (the conducting tissues).
Three tissue systems
- EPIDERMAL: epidermal cells, stomata, and appendages (trichomes, root hairs). Cuticle on outside (absent in roots). Single-layered.
- GROUND (fundamental): all tissue except epidermis and vascular bundles; zones are cortex, pericycle and pith. In leaves it is the mesophyll.
- VASCULAR (conducting): xylem and phloem forming vascular bundles; translocate water, minerals and food.
Vascular bundle types
- OPEN (cambium present, secondary growth possible) vs CLOSED (no cambium). Dicot stem = open; monocot stem = closed.
- RADIAL (xylem and phloem on different radii, in roots) vs CONJOINT (xylem and phloem on same radius, in stems and leaves; phloem usually outer).
Dicot vs monocot anatomy
- Root: both radial; dicot few (2-4) xylem groups + secondary growth; monocot polyarch (more than six) + large pith + no secondary growth.
- Stem: dicot = ring of conjoint open endarch bundles, collenchymatous hypodermis, starch sheath endodermis; monocot = scattered conjoint closed bundles, sclerenchymatous hypodermis and bundle sheath, phloem parenchyma absent.
- Leaf: dicot (dorsiventral) = mesophyll split into palisade + spongy, more stomata abaxial; monocot (isobilateral) = undifferentiated mesophyll, stomata both surfaces, bulliform cells in grasses.
Common traps
- Open/closed refers to cambium, NOT to whether bundles touch.
- Cuticle is absent in roots.
- Secondary growth occurs in most dicot roots/stems, not in monocots.