Types of stomata n bark
Reading File
Searching the Web
types of stomata in plants classification with examples
Searching the Web
types of bark in plants outer inner bark classification botany
Here is a thorough overview of both topics:
Types of Stomata
Stomata are tiny pores on the plant epidermis (mainly on leaves) that regulate gas exchange and transpiration. They are classified based on the number, size, and arrangement of subsidiary (accessory) cells surrounding the guard cells.
1. Anomocytic (Ranunculaceous / Irregular-celled)
- Subsidiary cells are absent or indistinguishable from other epidermal cells.
- The stoma is surrounded by an irregular number of cells that look like ordinary epidermal cells.
- Examples: Ranunculus, Amaranthus, Solanum
2. Anisocytic (Cruciferous / Unequal-celled)
- Stoma is surrounded by 3 subsidiary cells, of which one is distinctly smaller than the other two.
- Examples: Cruciferae (mustard family), Nicotiana, Solanum
3. Paracytic (Rubiaceous / Parallel-celled)
- Two subsidiary cells flank the guard cells, with their long axes parallel to the guard cells and the stomatal pore.
- Examples: Rubiaceae, some grasses, Magnolia
4. Diacytic (Caryophyllaceous / Cross-celled)
- Two subsidiary cells surround the guard cells, and their common wall is perpendicular (at right angles) to the stomatal pore.
- Examples: Caryophyllaceae (carnations), Acanthaceae
5. Gramineous (Grass-type)
- Guard cells are dumbbell-shaped (not kidney-shaped like the others).
- Each guard cell is flanked by a subsidiary cell on either side.
- Examples: Grasses (Poaceae), bamboo, cereals like wheat and maize
Summary Table
| Type | Subsidiary Cells | Shape of Guard Cells | Family Example |
|---|---|---|---|
| Anomocytic | None / indistinct | Kidney-shaped | Ranunculaceae |
| Anisocytic | 3 (one smaller) | Kidney-shaped | Cruciferae |
| Paracytic | 2 (parallel) | Kidney-shaped | Rubiaceae |
| Diacytic | 2 (perpendicular) | Kidney-shaped | Caryophyllaceae |
| Gramineous | 2 (lateral) | Dumbbell-shaped | Poaceae (grasses) |
Types of Bark
Bark refers to all tissues outside the vascular cambium in woody plants. It is broadly divided into two layers:
A. Inner Bark (Phloem)
- The living portion, consisting of secondary phloem.
- Functions as a pipeline transporting food (sugars) made by photosynthesis down to roots and other parts.
- Generally functional for only about one year before being pushed outward.
B. Outer Bark (Rhytidome)
- The dead, protective outer layer.
- Made up of multiple layers of suberized (cork) periderm, dead phloem tissue, and cortex.
- Protects against water loss, temperature extremes, and insects.
Key Layers Within the Bark (from inside out):
| Layer | Type | Description |
|---|---|---|
| Secondary Phloem | Inner bark (living) | Conducts food; becomes non-functional phloem over time |
| Cork Cambium (Phellogen) | Meristem | Produces cork cells outward and phelloderm inward |
| Cork (Phellem) | Outer bark (dead) | Suberized dead cells; waterproof, insulating |
| Phelloderm | Inner bark (living) | Parenchyma produced inward by cork cambium |
| Rhytidome | Outer bark (dead) | Outermost layer; all tissues outside last-formed periderm |
Visual/Textural Types of Bark (by appearance):
- Smooth bark - e.g., Beech, young trees
- Fissured / Ridged bark - deep furrows, e.g., Oak, Ash
- Scaly bark - flaking scales, e.g., Black cherry, Pine
- Plated bark - irregular plates, e.g., Birch
- Peeling / Exfoliating bark - sheds in strips, e.g., Paper birch, Eucalyptus
- Corky bark - spongy and thick, e.g., Cork oak (Quercus suber)
- Warty bark - with prominent lenticels (pores), e.g., Cherry
Lenticels
Lenticels are small, raised pores on the bark surface that allow gas exchange between inner living tissues and the atmosphere - they are the bark's equivalent of stomata.
Quick memory aid for stomata types:
Anno All Pigs Don't Grasp = Anomocytic, Anisocytic, Paracytic, Diacytic, Gramineous
Trichomes
Searching the Web
types of trichomes in plants classification glandular non-glandular botany
Trichomes
Trichomes are epidermal appendages (outgrowths from the epidermis) found on stems, leaves, roots, and other plant surfaces. The word comes from the Greek trichoma meaning "growth of hair."
Major Classification
Trichomes are broadly divided into two main groups:
1. Non-Glandular (Non-Secretory) Trichomes
These are purely structural - they do not secrete any substance.
A. Unicellular Trichomes (Simple Hairs)
- Single-celled outgrowths from epidermal cells.
- May be straight, curved, or hooked.
- Example: Root hairs of most plants
B. Multicellular Trichomes
Further divided by structure:
| Subtype | Description | Example |
|---|---|---|
| Uniseriate | Single row of cells | Many dicots |
| Biseriate | Double row of cells | Nicotiana |
| Stellate (Star-shaped) | Arms radiate from a central point | Verbascum, Elaeagnus |
| Dendritic (Branched) | Tree-like branching | Some Solanaceae |
| Peltate (Scale-like / Squamiform) | Flat, shield-shaped; attached at center | Elaeagnus, Oleaster family |
| Hooked / Barbed | Curved tip to trap insects or aid dispersal | Galium |
| Stinging hairs | Sharp, brittle tip that injects irritants | Urtica (Nettles) |
2. Glandular (Secretory) Trichomes
These have a secretory head that produces and releases various substances (oils, resins, nectar, mucilage, salt). They are important in pharmacognosy and economic botany.
A. Capitate Trichomes
- Have a stalk (stipe) + a round secretory head (capitulum).
- Subtypes based on stalk length:
- Sessile capitate - stalk absent or very short; head sits directly on epidermis (e.g., Cannabis)
- Stalked capitate - distinct stalk present (e.g., Mentha, Pelargonium)
B. Peltate Trichomes
- Head is disc-shaped / shield-like, attached by a short stalk.
- Very common in the mint family (Lamiaceae).
- Example: Mentha (mint), Salvia, Lavandula
C. Bulbous Trichomes
- Very short stalk with a large, swollen secretory head.
- Example: Lycopersicon (tomato)
D. Colleters
- Multicellular glandular hairs that secrete sticky mucilage or resin.
- Found on stipules and bud scales for protection.
- Example: Gardenia, Cinchona
E. Nectaries (Extrafloral nectaries as trichomes)
- Some glandular trichomes secrete nectar to attract insects.
F. Hydathodes
- Specialized trichomes/structures that secrete water (guttation).
By Cell Number Summary
| Category | Unicellular | Multicellular |
|---|---|---|
| Non-glandular | Root hairs, simple epidermal hairs | Stellate, branched, peltate, stinging |
| Glandular | Some simple secretory hairs | Capitate, peltate, colleters, bulbous |
Functions of Trichomes
| Function | Type Involved |
|---|---|
| Reduce water loss (transpiration) | Non-glandular (reflects light, traps humid air) |
| Protection from herbivores | Hooked, stinging, glandular (sticky secretions) |
| Insect trapping (carnivorous plants) | Glandular mucilaginous |
| UV protection | Stellate, peltate (reflective) |
| Secretion of essential oils | Peltate, capitate glandular |
| Salt excretion (halophytes) | Salt glands |
| Absorption (root hairs) | Unicellular non-glandular |
| Seed dispersal aid | Trichomes on seeds (e.g., cotton fibers = Gossypium seed trichomes) |
Pharmacognostic Importance
Trichomes are used as a diagnostic character in identifying crude drugs:
- Belladonna leaf - uniseriate multicellular covering trichomes + club-shaped glandular trichomes
- Digitalis (Foxglove) - uniseriate glandular trichomes
- Tobacco (Nicotiana) - biseriate glandular trichomes
- Mentha (Peppermint) - peltate + capitate glandular trichomes
- Datura - covering + glandular trichomes on both surfaces
Memory tip: Think of trichomes in two big buckets - "hair" (non-glandular) vs "gland hair" (glandular) - then sub-classify by shape (stellate, peltate, capitate, etc.) and by cell number (uni vs multicellular).
This is a shared conversation. Sign in to Orris to start your own chat.