5.1 The Root
The root is the usually underground, non-green descending part that anchors the plant and absorbs water & minerals.
Types
| Type | Origin | Found in |
|---|
| Tap root | Develops from the radicle; one main root with branches | Dicots (mustard) |
| Fibrous root | Many roots from the base of the stem | Monocots (wheat) |
| Adventitious | Arise from parts other than the radicle | Banyan, grass, Monstera |
Regions of the root
Root capâRegion of meristematic activityâRegion of elongationâRegion of maturation (root hairs)
Modifications
- Storage: carrot, turnip (tap roots); sweet potato (adventitious) store food.
- Prop roots: hanging supportive roots of the banyan.
- Stilt roots: supporting roots from lower nodes of maize & sugarcane.
- Pneumatophores: roots that grow upward for gas exchange in mangroves (Rhizophora).
5.2 The Stem
The stem is the ascending axis bearing nodes, internodes, buds, leaves, flowers & fruits; it develops from the plumule. (Tip: nodes & buds tell a stem from a root.)
| Modification | Form | Examples |
|---|
| Underground (storage, perennation) | Tuber, rhizome, corm, bulb | Potato (tuber), ginger (rhizome), Colocasia (corm), onion (bulb) |
| Subaerial (vegetative propagation) | Runner, stolon, offset, sucker | Grass (runner), strawberry, Pistia/Eichhornia (offset), mint (sucker) |
| Aerial | Stem tendril, thorn, phylloclade | Cucumber/grapevine (tendrils), Citrus/Bougainvillea (thorns), Opuntia (phylloclade) |
Test: A potato is a stem (it has nodes, eyes/buds & scale leaves), while a sweet potato is a root (no nodes).
5.3 The Leaf
The leaf is a flattened lateral outgrowth of the stem borne at a node; it is the chief organ of photosynthesis. Parts: leaf base, petiole, lamina.
Venation
- Reticulate â veins form a network (dicots).
- Parallel â veins run parallel (monocots).
Leaf types
| Type | Description | Example |
|---|
| Simple | Lamina entire or incised but not reaching the midrib | Mango, guava |
| Pinnately compound | Leaflets along a common axis (rachis) | Neem |
| Palmately compound | Leaflets attached at a common point (petiole tip) | Silk cotton |
Phyllotaxy (arrangement on stem)
- Alternate â one leaf per node (china rose, mustard).
- Opposite â two per node (Calotropis, guava).
- Whorled â more than two per node (Alstonia).
Modifications: tendrils (pea), spines (cactus), phyllode (Australian acacia), storage (onion fleshy leaves), pitcher (insectivorous Nepenthes).
5.4 Inflorescence
An inflorescence is the arrangement of flowers on the floral axis. Two main types:
| Type | Growth of main axis | Flower opening order |
|---|
| Racemose | Continues to grow; flowers borne laterally | Acropetal â older below, younger above |
| Cymose | Tip ends in a flower; limited growth | Basipetal â older at top/centre, younger below |
5.5 The Flower
The flower is the reproductive unit. Four whorls on the thalamus: calyx (sepals), corolla (petals), androecium (stamens), gynoecium (carpels). Calyx + corolla are accessory; androecium + gynoecium are reproductive.
Symmetry
- Actinomorphic (radial) â mustard, chilli.
- Zygomorphic (bilateral) â pea, Cassia.
Position of ovary (with respect to other whorls)
| Term | Ovary position | Example |
|---|
| Hypogynous | Superior ovary; other parts below | Mustard, china rose |
| Perigynous | Half-inferior; parts at the rim, ~same level | Rose, plum |
| Epigynous | Inferior ovary; parts above | Guava, cucumber, sunflower |
Aestivation (arrangement of sepals/petals in bud)
- Valvate â margins touch, no overlap (Calotropis).
- Twisted â one margin overlaps the next (china rose).
- Imbricate â overlapping but not in a set direction (Cassia).
- Vexillary â special pea type: largest standard covers two wings, which cover the keel.
Placentation (arrangement of ovules in ovary)
| Type | Description | Example |
|---|
| Marginal | Ovules on the ventral suture, one chamber | Pea |
| Axile | Placenta axial, ovules in chambers | Tomato, lemon, china rose |
| Parietal | Ovules on inner wall / false septum | Mustard, Argemone |
| Free central | On central axis, no septa | Dianthus, Primrose |
| Basal | Placenta at base, single ovule | Sunflower, marigold |
5.6 Fruit, Seed & Floral Formula
Fruit
A fruit develops from the ovary after fertilisation. Wall = pericarp (epicarp + mesocarp + endocarp). A true fruit develops from the ovary only; a false fruit involves the thalamus too (apple).
- Drupe â single seed, stony endocarp (mango, coconut).
Seed
| Dicot seed (gram/bean) | Monocot seed (maize) |
|---|
| Cotyledons | Two, often store food | One; endosperm stores food |
| Special parts | Plumule, radicle, hilum, micropyle | Scutellum, coleoptile, coleorhiza, aleurone layer |
Reading a Floral Formula â symbols
Br = bracteate · â actinomorphic · % zygomorphic · âĨ bisexual
K = calyx · C = corolla · P = perianth · A = androecium · G = gynoecium
G (underlined) = superior ovary · GĖ
(line above) = inferior ovary · ( ) = fusion · + = whorls
Example (mustard, Brassicaceae): â âĨ K2+2 C4 A2+4 G(2) â radial, bisexual, 4 sepals (2+2), 4 petals, 6 stamens (2 short + 4 long = tetradynamous), bicarpellary superior ovary.
5.7 Three Families
| Fabaceae (pea) | Solanaceae (potato) | Liliaceae (lily) |
|---|
| Root | Tap, root nodules | Tap | Fibrous (monocot) |
| Calyx/Corolla | K5 (united) · C5 papilionaceous (1 standard, 2 wings, 2 keel) | K(5), C(5) united | Perianth P3+3 (tepals) |
| Androecium | A(9)+1 (diadelphous) | A5, epipetalous | A3+3 |
| Gynoecium | Monocarpellary, superior, marginal | Bicarpellary, syncarpous, superior, axile, obliquely placed | Tricarpellary, syncarpous, superior, axile |
| Aestivation | Vexillary | Valvate | Valvate |
| Examples / uses | Gram, pea, groundnut (pulses, dyes, fodder, Nâ-fixing) | Tomato, potato, brinjal, tobacco, belladonna (food, medicine) | Onion, garlic, tulip, Aloe, Colchicine |
Fabaceae: % âĨ K(5) C5 A(9)+1 G1
Solanaceae: â âĨ K(5) C(5) A5 G(2)
Liliaceae: â âĨ P(3+3) A3+3 G(3)