In this chapter: root, stem and leaf with their modifications; inflorescence; flower and its parts (aestivation, androecium, placentation); fruit; seeds of dicots and monocots; floral formula; families Fabaceae, Solanaceae, Liliaceae.The root
- Tap root: the primary root and its branches, in most dicots (mustard).
- Fibrous root: the primary root is short-lived and replaced by many roots from the base of the stem, in monocots (wheat).
- Adventitious roots: arise from parts other than the radicle (grass, Monstera, banyan).
Regions of the root tip: root cap (protects the apex), region of meristematic activity, region of elongation, and region of maturation, where root hairs arise.
| Root modification | Function | Examples |
|---|---|---|
| Storage (tap root) | Food storage | Carrot, turnip |
| Storage (adventitious) | Food storage | Sweet potato |
| Prop roots | Support; hanging from branches | Banyan |
| Stilt roots | Support; from lower nodes | Maize, sugarcane |
| Pneumatophores | Grow upwards for oxygen in swampy soil | Rhizophora (mangrove) |
The stem
The stem develops from the plumule and bears nodes (where leaves arise) and internodes. It carries water, minerals and food, and bears leaves, flowers and fruits.
| Stem modification | Examples |
|---|---|
| Underground storage (and perennation) | Potato (tuber), ginger, turmeric (rhizome), zaminkand, Colocasia (corm) |
| Stem tendrils (from axillary buds) | Cucumber, pumpkin, watermelon, grapevine |
| Thorns (from axillary buds) | Citrus, Bougainvillea |
| Photosynthetic stems in arid regions | Opuntia (flattened), Euphorbia (fleshy, cylindrical) |
| Underground stems that spread (vegetative propagation) | Grass, strawberry |
| Stolon (slender lateral branch arching to the ground) | Mint, jasmine |
| Offset (short internode, rosette of leaves and roots at each node) | Pistia, Eichhornia (aquatic) |
| Sucker (underground lateral branch growing obliquely up) | Banana, pineapple, Chrysanthemum |
The leaf
The leaf develops at the node and bears a bud in its axil. Its parts are the leaf base (may bear stipules; swollen pulvinus in legumes), petiole and lamina. Venation is reticulate in dicots and parallel in monocots.
- Compound leaves: pinnately compound (leaflets on a common rachis: neem) or palmately compound (leaflets at one point, the tip of the petiole: silk cotton).
- Phyllotaxy: alternate (china rose, mustard, sunflower), opposite (Calotropis, guava), whorled (Alstonia).
- Modifications: tendrils (peas), spines (cactus), fleshy storage leaves (onion, garlic), phyllode (Australian Acacia: the petiole becomes green and flat, leaves are short-lived), and insectivorous traps (pitcher plant, Venus fly trap).
Inflorescence
The arrangement of flowers on the floral axis. In racemose, the main axis keeps growing and flowers are borne laterally in acropetal order (older at the base). In cymose, the main axis ends in a flower, so growth is limited, and flowers are in basipetal order.
The flower
The flower is a modified shoot meant for sexual reproduction. The four whorls on the thalamus are calyx, corolla, androecium and gynoecium. When calyx and corolla are not distinct, they form a perianth (lily).
- Symmetry: actinomorphic (radial: mustard, datura, chilli), zygomorphic (only one plane: pea, gulmohur, bean, Cassia), asymmetric (canna).
- Number: trimerous, tetramerous or pentamerous when floral parts are in multiples of 3, 4 or 5.
- Bracts: reduced leaves at the base of the pedicel; bracteate or ebracteate flowers.
| Position of ovary | Flower called | Examples |
|---|---|---|
| Superior (other parts below the ovary) | Hypogynous | Mustard, china rose, brinjal |
| Half-inferior (other parts at the rim of a cup-shaped thalamus) | Perigynous | Plum, rose, peach |
| Inferior (thalamus fused with the ovary; other parts above it) | Epigynous | Guava, cucumber, ray florets of sunflower |
Aestivation (arrangement of sepals or petals in the bud)
| Type | Arrangement | Examples |
|---|---|---|
| Valvate | Margins just touch, do not overlap | Calotropis |
| Twisted | Each overlaps the next, regularly | China rose, lady's finger, cotton |
| Imbricate | Overlapping, but not in a particular direction | Cassia, gulmohur |
| Vexillary (papilionaceous) | Five petals: the largest (standard) overlaps two lateral wings, which overlap two smallest anterior petals (keel) | Pea, bean |
Androecium
- Epipetalous: stamens attached to petals (brinjal). Epiphyllous: attached to the perianth (lily).
- Monoadelphous: filaments united into one bunch (china rose). Diadelphous: two bundles (pea). Polyadelphous: more than two bundles (Citrus).
- Stamens may differ in length (Salvia, mustard). A sterile stamen is a staminode.
Gynoecium and placentation
Apocarpous: carpels free (lotus, rose). Syncarpous: carpels fused (mustard, tomato).
| Placentation | Description | Examples |
|---|---|---|
| Marginal | Placenta a ridge along the ventral suture of a one-chambered ovary; ovules in two rows | Pea |
| Axile | Placenta axial, ovules on it, in a multilocular ovary | China rose, tomato, lemon |
| Parietal | Ovules on the inner wall; ovary one-chambered but may become two-chambered by a false septum | Mustard, Argemone |
| Free central | Ovules on a central axis; septa absent | Dianthus, Primrose |
| Basal | Placenta at the base of the ovary; a single ovule | Sunflower, marigold |
The fruit
The fruit is the mature ovary, formed after fertilisation. A fruit formed without fertilisation is parthenocarpic. The fruit wall (pericarp) may be dry or fleshy; when fleshy, it has an outer epicarp, middle mesocarp and inner endocarp. In a drupe (mango, coconut) the fruit develops from a monocarpellary superior ovary and is one-seeded. Mango has an edible fleshy mesocarp and a hard, stony endocarp; coconut has a fibrous mesocarp.
The seed
| Dicot seed (e.g. bean, gram, pea) | Monocot seed (e.g. maize) |
|---|---|
| Seed coat of two layers: outer testa, inner tegmen | Seed coat membranous, generally fused with the fruit wall |
| Hilum (scar of attachment to the fruit) and micropyle above it | Endosperm bulky, stores food; separated from the embryo by a protein-rich aleurone layer |
| Embryo: embryonal axis with two cotyledons; radicle and plumule at the ends | Embryo small, in a groove at one end; one large shield-shaped cotyledon, the scutellum |
| Endosperm present in castor; absent in bean, gram, pea (non-endospermous) | Plumule enclosed in the coleoptile, radicle in the coleorhiza. Generally endospermic (orchids are non-endospermic) |
Floral formula symbols
Br = bracteate; K = calyx; C = corolla; P = perianth; A = androecium; G = gynoecium (a line above G means inferior ovary, below means superior). ⊕ actinomorphic; % zygomorphic; ⚥ bisexual. Numbers in brackets = fused parts. A line connecting two whorls = adhesion (e.g. epipetalous stamens).
Three families to know
| Fabaceae (pea family) | Solanaceae (potato family) | Liliaceae (lily family, monocot) | |
|---|---|---|---|
| Vegetative | Root nodules; leaves pinnately compound or simple, pulvinate, stipulate, reticulate venation | Stem herbaceous, rarely woody; underground stem in potato; leaves alternate, simple, exstipulate | Perennial herbs with bulbs, corms or rhizomes; leaves mostly basal, linear, exstipulate, parallel venation |
| Inflorescence | Racemose | Solitary, axillary or cymose | Solitary or cymose; often umbellate clusters |
| Flower | Bisexual, zygomorphic | Bisexual, actinomorphic | Bisexual, actinomorphic |
| Calyx / corolla | Sepals 5, gamosepalous, imbricate. Petals 5, papilionaceous (standard, 2 wings, 2 keel), vexillary | Sepals 5, united, persistent, valvate. Petals 5, united, valvate | Perianth of 6 tepals (3+3), often united into a tube, valvate |
| Androecium | 10, diadelphous (9)+1, anthers dithecous | 5, epipetalous | 6, in two whorls (3+3) |
| Gynoecium | Monocarpellary, superior, unilocular, many ovules, marginal placentation | Bicarpellary, obliquely placed, syncarpous, superior, bilocular, swollen placenta, axile | Tricarpellary, syncarpous, superior, trilocular, axile |
| Fruit / seed | Legume; seeds non-endospermic | Berry or capsule; seeds endospermous | Capsule, rarely berry; seeds endospermous |
| Floral formula | % ⚥ K(5) C1+2+(2) A(9)+1 G1 | ⊕ ⚥ K(5) C(5) A5 G(2) (C and A linked) | Br ⊕ ⚥ P(3+3) A3+3 G(3) |
| Uses | Pulses (gram, arhar, moong, soybean), oil (soybean, groundnut), dye (Indigofera), fibre (sunhemp), fodder (Sesbania, Trifolium), ornamentals (lupin, sweet pea), medicine (muliathi) | Food (tomato, brinjal, potato), spice (chilli), medicine (belladonna, ashwagandha), fumigatory (tobacco), ornamental (petunia) | Ornamentals (tulip, Gloriosa), medicine (Aloe), vegetable (Asparagus), colchicine (Colchicum autumnale) |
Common traps: (1) Pea has marginal placentation; tomato and china rose have axile; mustard has parietal. (2) Twisted aestivation is china rose, not Calotropis (valvate). (3) Guava and cucumber are epigynous; rose is perigynous. (4) In Solanaceae, the carpels are obliquely placed.NEET focus
- Root and stem modifications with examples.
- Phyllotaxy, aestivation and placentation examples.
- Ovary position (hypo-, peri-, epigynous) and androecium types.
- Monocot seed parts: aleurone layer, scutellum, coleoptile, coleorhiza.
- Floral formulae and economic importance of the three families.
Practice questions
Pneumatophores are found in:
- Banyan
- Maize
- Rhizophora
- Sweet potato
Show answer
Twisted aestivation is found in:
- Calotropis
- China rose
- Pea
- Cassia
Show answer
Placentation in mustard is:
- Marginal
- Axile
- Parietal
- Basal
Show answer
A perigynous flower is found in:
- Guava
- Mustard
- Plum
- Cucumber
Show answer
The protein-rich layer separating endosperm and embryo in a maize grain is the:
- Scutellum
- Coleoptile
- Aleurone layer
- Tegmen
Show answer
Diadelphous stamens are characteristic of:
- Solanaceae
- Fabaceae
- Liliaceae
- Malvaceae (china rose)
Show answer
Phyllode is a modification of the petiole in:
- Pea
- Australian Acacia
- Opuntia
- Onion