NEET Biology Morphology of Flowering Plants Notes

NEET Biology Chapter 5 Morphology of Flowering Plants notes covering the root and shoot systems, types and modifications of roots and stems, leaf structure, venation, phyllotaxy and leaf modifications, racemose and cymose inflorescences, the parts and types of flowers, aestivation, androecium, gynoecium and placentation, the classification of fruits and seeds, and the families Fabaceae, Solanaceae and Liliaceae with their floral formulae and economic importance.

Important Terms, Differences and Points to Remember

Terms:
1. Calyptra - the root cap that covers the root tip.
2. Napiform - a tap root that is much swollen at the upper end and tapers abruptly towards the lower end, as in turnip.
3. Moniliform - a root or stem that is swollen at different places, forming a beaded structure.
4. Buttress root - a horizontal root that arises from the base of the main stem and spreads in the soil like a plank.
5. Rhizome - a thick, prostrate underground stem that grows horizontally, with nodes, internodes and adventitious roots.
6. Corm - a highly swollen, vertical underground stem that is short and unbranched.
7. Stolon - an aerial or underground branch that grows horizontally from a node and forms new plants at its tip.
8. Sucker - a branch that arises from the axillary bud of an underground stem, grows obliquely upwards and forms a new plant.
9. Runner - a horizontal branch with long thin internodes that creeps over the soil surface and forms roots at its nodes.
10. Offset - a runner-like stem with thicker, shorter internodes that bears a rosette of leaves at its apex.
11. Phylloclade - a flattened or cylindrical green stem of unlimited growth that performs photosynthesis.
12. Cladode - a green stem of limited growth, usually one internode long, that performs photosynthesis.

Differences:
1. Phylloclades and cladodes - phylloclades are green stems of unlimited growth, while cladodes are green stems of limited growth.
2. Hypogynous, perigynous and epigynous flowers - in hypogynous flowers the ovary is superior, in perigynous flowers it is semi-inferior, and in epigynous flowers it is inferior.
3. Racemose and cymose inflorescence - in racemose inflorescence the main axis grows indefinitely, while in cymose inflorescence it grows definitely.
4. Simple and aggregate fruits - a simple fruit develops from a single ovary, while an aggregate fruit (etaerio) develops from many free carpels of one flower.

5. Etaerios of berries, achenes, drupes and follicles - these are aggregate fruits in which each free carpel of one flower forms a fruitlet that is a berry, an achene, a drupe or a follicle respectively.

At a Glance

• Root
  • Types of roots
  • Regions of roots
  • Modification of roots
• Stem
  • Underground modifications of stems
  • Sub-aerial modifications of stems
  • Aerial modification of stems
• Leaf
  • Types of leaves
  • Phyllotaxy
  • Modifications of leaves
• Inflorescence
  • Racemose and cymose inflorescence
• Flower
  • Parts of flower
  • Aestivation
  • Placentation
• Fruit
  • Classification of fruit
• Seed
  • Monocot and dicot seeds
• Description of Fabaceae, Solanaceae and Liliaceae families

INTRODUCTION TO ANGIOSPERMS

1. Angiosperms are flowering, fruit bearing, spermatophytic plants that are well adapted to land. They are the most advanced and evolved group of plants that exist today.
2. Angiosperms appeared in the lower Cretaceous period of the Mesozoic era, but flourished in the Tertiary period of the Cenozoic era.
3. They have enclosed seeds and bear flowers. They vary in size from small grasses to tall Eucalyptus or giant banyan trees.
4. Angiosperms lack archegonium, which is replaced by the pistil. They show double fertilisation, and the endosperm is triploid.
5. The male gametes are non-motile and are carried by the pollen tube, so that fertilisation does not depend on water.
6. Angiosperms are broadly classified into monocots and dicots. Monocots are more advanced than dicots and have probably evolved from primitive dicots.

Plant morphology refers to the study of the external form and structure of plants. Flowering plants have two major systems: the root system and the shoot system.

THE ROOT

Characteristics of the root
1. The root is the underground system, usually below the soil, and it originates from the radicle.
2. It is generally positively geotropic, negatively phototropic and positively hydrotropic.
3. Roots grow downwards for anchorage and for the absorption of water and nutrients from the soil.
4. The root lacks nodes, internodes, leaves and buds.
5. A unicellular root hair and a terminal root cap, or calyptra, are present.
6. Roots may be absent in some hydrophytes, but when present they are poorly developed and lack root hairs.

Connecting Concepts:
1. In a hydrophyte, Podostemon, the root performs the function of assimilation and reproduction. It is a plant that is all root.
2. Roots are absent in some angiosperms, for example, Utricularia, Wolffia, Balanophora and Cuscuta.
3. In a few hydrophytes the root cap is absent, and root pockets are present instead. A root pocket differs from a root cap in its mode of development. In Pandanus (screwpine), multiple root caps are present.

Functions of the root
1. Primary functions: fixation of the plant firmly in the soil, absorption of water and conduction of mineral nutrients.
2. Roots also prevent soil erosion.
3. Secondary or special functions: food storage, providing additional mechanical support, photosynthesis, respiration and vegetative multiplication.

Types of roots
Roots are of two types:
1. Tap root: the tap root, or primary root, develops from the radicle. It forms lateral branches, or secondary roots, which further branch to form tertiary roots. The tap root along with its branches forms the tap root system. It is generally found in dicotyledons.
2. Adventitious root: these roots develop from any part of the plant instead of the radicle. They can arise from the base of the stem, from leaves, and from the nodes and internodes of the stem.
(a) Roots arising from the base of the stem, for example, maize, wheat, rice and onion.
(b) Roots arising from leaves, for example, Bryophyllum and Pogostemon.
(c) Roots developing from the nodes and internodes of the stem, for example, Ficus (banyan) and Pothos (money plant).

[Figure: Fig. 5.1 Root. (A) Tap root with primary root, lateral roots, secondary roots and tertiary roots. (B) Fibrous or adventitious root system arising from the base of the stem.]

Regions of the root
A typical root can be differentiated into five regions: the root cap, the meristematic region, the region of elongation, the region of root hairs and the region of maturation. The first three regions take up little space, whereas the last region forms the major part of the root.

[Figure: Fig. 5.2 Zones or regions of a typical root, from the tip upwards: root cap, region of meristematic activity, region of elongation, region of root hairs and region of maturation.]

Labels of Fig. 5.2: Region of mature cells; root hair zone; root hair; region of elongation; growing point (meristematic zone); root cap.

1. Root cap (calyptra): derived from the calyptrogen. It covers the root tip and protects it against friction from soil particles. The root cap is rich in starch grains, which are responsible for the geotropic response. The root cap is absent in epiphytes, parasites, hydrophytes and mycorrhizal roots.
2. Region of active cell division (meristematic region): about 1 mm long. The growing point produces new cells for the root cap and the basal parts. The cells are thin-walled and non-vacuolated.
3. Region of elongation: about 4 to 8 mm long, behind the tip. The cells elongate rapidly due to vacuolation. This zone is responsible for the growth of the root in length.
4. Region of root hairs: about 1 to 6 cm long. Outer cells just above the region of elongation give rise to lobular, unbranched, unicellular root hairs, which increase the absorptive area. Root hairs are absent in parasitic and mycorrhizal roots.
5. Region of cell maturation: the outermost layer has thick-walled or impermeable cells, so this region cannot absorb water. Its function is to anchor the plant firmly in the soil. Lateral roots also arise from the interior of this region.

Modifications of the Root

Roots are modified to carry out special functions such as food storage, additional mechanical support, photosynthesis, respiration and vegetative multiplication.

Modified tap roots are fleshy and swollen for storage of food. They are classified by shape:
1. Fusiform: spindle-shaped, swollen in the middle and tapering at both ends, for example, radish (Raphanus sativus).
2. Napiform: much swollen at the upper end and abruptly tapering towards the lower end, for example, turnip (Brassica rapa) and beet.
3. Conical: broadest at the top and gradually tapering towards the lower end. The hypocotyl does not contribute to the swollen root, for example, carrot (Daucus carota).
4. Tuberous: irregularly swollen except at the base, for example, four o'clock plant (Mirabilis jalapa).
5. Nodulated (tuberculated) roots: in legumes, the roots are symbiotically associated with the nitrogen-fixing bacterium Rhizobium leguminosarum. This forms several nodules on the branches of the roots. Nodules are pinkish due to the pigment leghaemoglobin, which carries oxygen and provides an anaerobic environment for the enzyme nitrogenase to fix nitrogen.

[Figure: Fig. 5.3 (A) Conical root of carrot, (B) fusiform root of radish, (C) nodulated root of a legume. Fig. 5.4 (A) Napiform root of turnip, (B) tuberous root of Mirabilis.]

Modified adventitious roots
1. Tuberous: arise from the nodes of the stem, and one root out of a bunch becomes tuberous and fleshy for storage, for example, sweet potato (Ipomoea batatas).
2. Fasciculated: arise in bunches (fascicles) from the lower nodes of the stem and become thick and fleshy for storage, for example, asparagus and dahlia.
3. Moniliform (beaded): swell at different places due to food storage, forming a beaded structure, for example, Vitis, Momordica and some grasses.
4. Nodulose: the terminal portions swell up, for example, Curcuma amada.
5. Annular: swelling occurs at different places in such a way that it looks like a stack of rings, for example, Psychotria.
6. Prop roots: from profusely branched, thick and heavy branches, roots arise and hang downwards in the air. They penetrate the soil and function as props for support, for example, Ficus bengalensis (banyan).
7. Stilt roots: arise from the lower nodes of the stem, enter the soil and become stronger. They protect the plant against wind, for example, sugarcane, maize and screwpine.
8. Climbing roots: arise from the nodes and help the plant climb, for example, Pothos and betel (Piper). These roots produce a viscous substance that dries in the air and attaches the roots to the substratum.
9. Buttress roots: horizontal roots that arise from the basal part of the main stem and spread in different directions in the soil. They are irregular, thick and broad, like planks of wood, for example, Bombax and Ficus.
10. Contractile roots: found in underground stems of plants such as Crocus and onion. Their apical part contracts and fixes the storage stem at a proper depth in the soil.
11. Sucking roots (haustoria): in parasitic plants such as Cuscuta, the roots arise from the stem and enter the host plant, developing contact with the xylem and phloem of the host stem.
12. Epiphytic or hygroscopic roots: aerial, hanging roots of epiphytes (plants growing on other plants for space only). They have a spongy tissue called velamen outside the cortex. The cells of velamen are dead and have pores for absorbing atmospheric moisture. The root cap and root hairs are absent, for example, orchids.
13. Floating roots: adventitious roots of some floating plants such as Jussiaea. Spongy aerial roots filled with air help the plant float.

[Figure: Fig. 5.5 Tuberous roots of sweet potato (Ipomoea batatas). Fig. 5.6 Fasciculated roots of dahlia. Fig. 5.7 Moniliform roots of grass. Fig. 5.8 Nodulose roots of Curcuma amada. Fig. 5.9 Annular roots of Psychotria. Fig. 5.10 Prop roots of banyan.]

[Figure: Fig. 5.11 Stilt roots of sugarcane. Fig. 5.12 Climbing roots of Piper beetle. Fig. 5.13 Buttress roots of Bombax. Fig. 5.14 Contractile roots of Crocus. Fig. 5.15 Sucking roots (haustoria) of Cuscuta on a host stem. Fig. 5.16 An orchid showing epiphytic and clinging roots. Fig. 5.17 Floating roots of Jussiaea.]

Other modified roots
1. Assimilatory or photosynthetic roots: some plants develop chlorophyll and perform photosynthesis, for example, Trapa and Tinospora.
2. Reproductive roots: in sweet potato, Asparagus and Dahlia, vegetative buds arise on adventitious roots. After separation from the parent plant, they form new plants.
3. Mycorrhizal roots: roots of some plants growing in humus soil have fungal hyphae. These roots lack root hairs, and the fungal hyphae function as root hairs, for example, Pinus.
4. Root thorns: in plants like Pothos, roots near the soil become hard like thorns. They serve as protective organs.
5. Clinging roots: arise from the node of a stem, pierce the stem of a host plant and fix the plant to the host, for example, orchid and ivy.
6. Leaf roots: adventitious roots produced on the margin of leaves, for example, Bryophyllum and Bignonia.
7. Pneumatophores (respiratory roots): short, vertical and negatively geotropic (grow upwards). They occur in halophytes growing in saline marshes (mangroves). They bear numerous minute pores or special lenticels (pneumatathodes) in their terminal parts, which take in atmospheric oxygen that is absent in saline water, for example, Rhizophora, Heritiera (sundari) and Avicennia (bina).

[Figure: Fig. 5.18 Assimilatory roots of Trapa. Fig. 5.19 Reproductive roots of Trichosanthes with adventitious buds. Fig. 5.20 Mycorrhizal roots of Pinus. Fig. 5.21 Root thorns of Pothos. Fig. 5.22 Clinging roots of ivy. Fig. 5.23 Leaf roots of Bryophyllum. Fig. 5.24 Pneumatophores of Rhizophora growing upwards from the mud.]

SHOOT SYSTEM

The shoot system is aerial, usually above the soil, and originates from the plumule. It consists of the stem, branches, leaves, flowers, fruits and seeds.

Characteristic features of the stem
1. The stem is a direct prolongation of the plumule.
2. It is negatively geotropic and positively phototropic.
3. It bears branches, leaves and flowers.
4. It is differentiated into nodes and internodes. It lacks a terminal root cap.
5. A node is the place from where a leaf arises on the stem. The space between two successive nodes is called an internode.
6. Branches and leaves arise from the nodes. The stem often bears multicellular hairs.
7. Growth of the shoot system is accomplished by buds, which may be vegetative or flowering.

Functions of the stem
The stem conducts water, minerals and food. It also produces and supports leaves and reproductive structures.

Modifications of the stem
The stem and branches of certain plants are modified to perform special functions: (a) perennation by underground modifications, (b) vegetative propagation by sub-aerial modifications, and (c) specialised functions by aerial modifications.

Underground modifications of stems
Some perennial herbs develop their stems underground for perennation during unfavourable conditions. The stem produces aerial branches every year when conditions become favourable. These underground stems are thick because of food deposits, so they also store food. They help in vegetative propagation by means of their buds. They are non-green and leafless like roots, but they differ from roots in having nodes and internodes, scale leaves, and axillary and terminal buds, and in lacking root hairs and a root cap.

Rhizome
1. It is a thick, prostrate stem that grows horizontally under the soil surface. It is colourless and apparently leafless, so it can be mistaken for a root.
2. Nodes and internodes are very distinct, and it is generally branched.
3. It bears several axillary and terminal buds, and adventitious roots all over.
4. Examples: banana (Musa), Canna, ginger (Zingiber), turmeric (Curcuma), and ferns.

Corm
1. It is a highly swollen, vertical stem.
2. Nodes and internodes are not very distinct, and it is generally unbranched.
3. It bears few axillary and terminal buds. Adventitious roots arise only from the basal nodes.
4. Examples: saffron (Crocus), Colocasia, Dioscorea, Colchicum, Gladiolus, Zamikand (Amorphophallus) and Freesia.

Tuber
1. It is an irregularly shaped, swollen stem that stores plenty of food.
2. It is differentiated into nodes and internodes. The 'eyes' on a potato tuber are axillary buds at the nodes.
3. It bears scaly leaves, which do not store food. Axillary buds arise at the nodes. It does not bear roots.
4. Example: potato (Solanum tuberosum).

[Figure: Fig. 5.25 Rhizome of ginger. Fig. 5.26 Corm of Crocus with adventitious roots from the basal nodes. Fig. 5.27 Tuber of potato with eyes (axillary buds) and scale leaves.]

Bulb
1. It is characterised by a discoid stem.
2. It does not store food in the stem. Since the stem is highly reduced, nodes and internodes are not distinct.
3. It bears large, fleshy scaly leaves that store food. Axillary buds arise in the axils of the fleshy leaves.
4. It bears several fibrous roots.
5. Bulbs are of two types: scaly or imbricate (as in garlic) and tunicate (as in onion).

[Figure: Fig. 5.28 Bulb of onion (tunicate), with outer dry scale leaves, fleshy leaves, a bud and bulbils. Fig. 5.29 Bulb of garlic (scaly), with fleshy scale leaves arranged around a discoid stem.]

Connecting Concepts:
1. The odour of onion and garlic is due to allyl sulphonate, called allicin, and eye tearing is due to volatile thiosulphonates.
2. The anticancerous substance in garlic is 'garlicin'.
3. When runners have thick internodes, they are called sobole.

Sub-aerial modifications of stems
These are horizontally growing branches that grow either just above or just below the surface of the soil. They are produced for vegetative propagation. The sub-aerial modifications are runner, sucker, stolon and offset.
1. Runner: plants have long, thin internodes, and branches creep over the soil surface. Such branches develop adventitious roots at the nodes on the lower side. When the long branches break up, they form new plants. Examples: Doob grass, Oxalis and Hydrocotyle.
2. Sucker: arises from an axillary bud of an underground stem. The branch moves obliquely, or grows horizontally under the soil, and then comes out of the soil and grows obliquely upwards. Adventitious roots arise from the nodes of the underground portion, and the branches break up to form new independent plants. Examples: chrysanthemum, rose and mint.
3. Stolon: branches arise from the nodes of underground portions of the stem and grow horizontally. After some time, the apical region comes out of the soil, grows into the air, and roots arise from the lower side of the nodes. It is like a runner, but a stolon grows horizontally below the soil surface, while a runner grows above it. Examples: Colocasia and strawberry.
4. Offset: a stem like a runner, but with thicker and shorter internodes. Branches arise all around the main stem. The apex of each branch curves upwards, bearing a group of leaves at the apex and a bundle of adventitious roots below. The branches break off from the parent and become independent plants. Examples: Pistia and Eichhornia (water hyacinth).

[Figure: Fig. 5.30 Runner of strawberry. Fig. 5.31 Sucker of chrysanthemum. Fig. 5.32 Stolon of blackberry, and daughter rosette of houseleek. Each is drawn with adventitious roots and new shoots at the nodes.]

Labels: Fig. 5.30 Strawberry: runner, new plant from axillary bud, soil, adventitious roots. Fig. 5.31 Chrysanthemum: soil, new suckers, old sucker of the parent plant. Fig. 5.32 Blackberry: stolon, soil, roots. Houseleek (water plant): parent plant, scale leaves, daughter rosette, adventitious roots.

Aerial modifications of stems
Aerial modifications help plants survive unfavourable conditions by storing food, propagation, providing support and protection. Some aerial modifications are stem tendrils, stem thorns, phylloclades or cladophylls, cladodes, and bulbils.

Connecting Concepts: Thorns, spines and prickles are sharp, pointed, hard structures that perform similar functions. Thorns are modified stems, while spines are modified leaves or leaf parts. Both have cortex and vascular supply. Prickles are epidermal outgrowths of the stem that have no vascular supply.

Stem tendrils: thread-like, sensitive structures that coil around a support and help the plant climb. They may be branched or unbranched.

[Figure: Fig. 5.34 Types of stem tendrils, branched and unbranched.]

Stem thorns: stiff, sharp structures that have lost their growing point and become hard, for example, Citrus, Bougainvillea, Duranta, pomegranate and Alhagi.

Phylloclades: flattened, for example, Opuntia, or cylindrical, for example, Casuarina and Euphorbia. They are green stems of unlimited growth that have taken over the function of photosynthesis from leaves. Phylloclades help plants grow in dry habitats because transpiration is less from the stem. In some cases they store water, mucilage and latex.

Cladodes: green stems of limited growth, usually one internode long, that have taken over photosynthesis from leaves. The true leaves are reduced to scales or spines. In Ruscus aculeatus, cladodes are leaf-like, with a spiny tip, ovate outline and roughly parallel veins. In Asparagus, cladodes are slightly flattened, fleshy, straight or curved, pointed structures that develop in clusters in the axils of scale leaves.

[Figure: Fig. 5.35 Stem thorn with leaves modified as spines. Fig. 5.36 Phylloclade of Opuntia with roots. Fig. 5.37 (A) Cladodes of Asparagus with scale leaves at the base.]

LEAF

A leaf is a green, dorsoventrally flattened, exogenous lateral outgrowth that arises from a node of the stem or a branch. It is a specialised organ of photosynthesis, transpiration and gaseous exchange. A leaf generally bears a bud in its axil, called the axillary bud, which later develops into a branch.

Connecting Concepts: A dicot leaf is dorsiventral and horizontal in position. A monocot leaf is isobilateral and vertical in position.

Parts of a leaf (phyllopodium)
A leaf is distinguishable into three parts: leaf base, petiole and lamina.
1. Leaf base: the point of attachment of the leaf petiole to the stem. In some leguminous plants, the leaf base is swollen, and this is called the pulvinus.
2. Stipules: a pair of lateral outgrowths arising from the leaf base in most dicots. Sometimes a stipule is an appendage of the leaf base itself. Their main role is to protect the young axillary buds. A leaf with stipules is stipulate, and a leaf without stipules is exstipulate.
3. Petiole: the stalk of the leaf. When a distinct petiole is present, the leaf is petiolate. When it is absent, the leaf is sessile. An intermediate condition, sub-sessile, is seen when a poorly defined petiole is present. The petiole may be tendrillar in Clematis and Nepenthes, swollen in Eichhornia and winged in Citrus.
4. Lamina: the usually flattened, green, photosynthetic part of the leaf. Its upper surface is called adaxial, and its lower surface is called abaxial.

[Figure: Fig. 5.38 Parts of a leaf: lamina, petiole, leaf base, stipule and axillary bud.]

Venation
Venation is the arrangement of veins and veinlets in a leaf. It is of two types:
1. Reticulate venation: veins are arranged in a net-like manner, as in dicots. It can be pinnate, as in peepal, or palmate.
2. Parallel venation: veins are arranged parallel to each other, as in monocots, for example, Canna.

[Figure: Fig. 5.39 (A) Reticulate venation of peepal leaf. (B) Parallel venation of canna leaf.]

Types of leaves
A leaf may be simple or compound, depending on the incision of the lamina.
1. Simple leaf: the lamina is not divided completely into distinct leaflets.
2. Compound leaf: the incision of the leaf blade goes down to the rachis, so the leaf is broken up into several segments called leaflets. Compound leaves are of two types:
(a) Pinnate: feather-like leaves in which the leaflets are borne laterally along the midrib, or rachis.
(b) Palmate: fan-like leaves in which the leaflets are borne at the tip of the petiole, like fingers on a palm.

[Figure: Fig. 5.40 (A) Pinnately compound leaf. (B) Palmately compound leaf.]

Phyllotaxy
The arrangement of mature leaves on the stem or its branches is called phyllotaxy. Different arrangements ensure that every leaf gets the maximum amount of sunlight. It is of three types:
1. Alternate (spiral): only one leaf is borne at each node in an alternate manner, for example, mustard and sunflower.
2. Opposite: two leaves occur at each node. It is of two types:
(a) Decussate: when successive pairs of leaves arise at right angles to the preceding pair, for example, Calotropis and Ocimum.
(b) Superposed: when successive pairs of leaves on a branch arise in one vertical plane, for example, Quisqualis and Psidium.
3. Whorled (verticillate): when more than two leaves occur at each node, for example, Nerium and Alstonia.

Leaf duration
1. Caducous: leaves fall off soon after their formation, for example, Opuntia.
2. Deciduous (annual): leaves fall off under unfavourable conditions or at the end of the growing season, for example, mulberry and poplar.
3. Persistent (evergreen): leaves remain on the plant for more than one year and fall off individually at different times, so that the plant has an evergreen look, for example, Eucalyptus.

Modifications of leaves
1. Leaf tendrils: leaves or their parts are modified into tendrils that help in climbing, for example, Smilax, Clematis and Nepenthes. In Lathyrus aphaca (wild pea), the whole leaf is a tendril. In sweet pea (Lathyrus odoratus), the apical leaflets are modified into tendrils. In Gloriosa, the leaf tip is modified, and in Narvelia, terminal leaflets are modified. Stipules are modified into tendrils in Smilax.
2. Leaf spines: in some plants, leaves or their parts are modified into spines to escape transpiration, as in Opuntia and Asparagus, or for protection, as in barberry. The apex of leaves in Phoenix and Yucca, the leaf margin in Argemone, and the stipules in Acacia and Ziziphus jujuba are also modified into spines.
3. Phyllode: in Acacia auriculiformis (Australian acacia) and Parkinsonia, the leaf or lamina is shed, and the petiole is modified into a leaf-like structure that performs photosynthesis.
4. Scale leaves: in onion, scale leaves store food and water, and so they are thick and fleshy.
5. Pitcher: the leaf blade is modified into a pitcher-like structure with a lid, which is an outgrowth of the leaf apex. The petiole is modified into a tendril that holds the pitcher vertically. Pitchers are of two types: (a) non-insectivorous pitchers, in which adventitious roots enter and absorb accumulated humus, for example, Dischidia rafflesiana; and (b) insectivorous pitchers, which capture insects, for example, Nepenthes, Sarracenia, Cephalotus and Heliamphora.
6. Leaf bladder: in bladderwort (Utricularia), a submerged, floating hydrophyte, some leaf segments are modified into tiny bladders. These catch aquatic insects, and the insects provide nitrogen.

[Figure: Fig. 5.41 Types of leaf tendrils: (A) whole leaf tendril of Lathyrus aphaca, (B) leaflet tendril of Lathyrus odoratus. Fig. 5.42 Leaf spines of (A) Aloe and (B) Argemone. Fig. 5.43 Phyllode of Acacia. Fig. 5.44 Leaf pitcher of Nepenthes with lid and tendril.]

THE INFLORESCENCE

An inflorescence is the mode of arrangement of flowers on a peduncle or mother axis. It makes flowers more conspicuous to pollinating agents and facilitates cross-pollination. Air pollination is also easier, because large numbers of pollen grains are shed from a group of flowers. Examples: cauliflower (compound corymb), sunflower (capitulum) and Euphorbia (cyathium).

Connecting Concepts: Families named after inflorescences include Umbelliferae (umbel inflorescence) and Amentiferae (amentum or catkin inflorescence).

There are two types of inflorescence: racemose and cymose.

Racemose (indeterminate or indefinite) inflorescence
1. The main axis has indefinite growth because there is no terminal flower.
2. Flowers are borne laterally in acropetal succession, that is, the oldest flowers are at the base, and younger ones are near the tip.

(A) Main axis elongated (racemose with long peduncle)
1. Raceme: the main axis is elongated and the flowers are pedicellate (stalked), for example, larkspur, mustard and radish.
2. Spike: the main axis is elongated, but the flowers are sessile, for example, Achyranthes.
3. Catkin: a pendulous spike that bears naked pistillate or staminate flowers, but not both, for example, mulberry.
4. Spadix: a spike with a fleshy axis that bears both male and female flowers. It is surrounded by a large, usually brightly coloured bract called spathe, for example, palm and Colocasia. Banana (Musa) produces a compound or mixed spadix.
5. Spikelet: a very small spike with one or a few flowers (florets). At its base, each spikelet bears two minute bracts called empty glumes. Slightly higher up, it bears a third bract called the flowering glume, fertile glume, lemma or lower palea. Opposite to the lemma, it bears a small glume called the upper or superior palea. Each flower of the spikelet is enclosed by a lemma and palea. Example: family Gramineae (wheat, rice and bamboo).

[Figure: Fig. 5.45 (A) Raceme of mustard, (B) spike of Achyranthes aspera, (C) catkin of mulberry. Fig. 5.46 (A) and (B) Spadix of Colocasia antiquorum with spathe, male, neuter and female flowers. (C) Spikelet of wheat with empty glumes, lemma, palea, lodicules, stamens, stigma and rachilla.]

(B) Main axis shortened (racemose with short peduncle)
1. Corymb: the main axis is comparatively short, and the lower flowers have much longer pedicels than the upper ones, so that all the flowers come to more or less the same level, for example, candytuft (Iberis).
2. Umbel: the main axis is very much reduced, and all flowers appear to arise from the same point. The younger flowers are in the centre, and the older ones are towards the periphery. The flowers are usually bracteate, for example, Hydrocotyle (Indian pennywort) and Prunus.

[Figure: Fig. 5.47 Corymb of Prunus cerasus. Fig. 5.48 (A) Umbel of Prunus cerasus, young and old, (B) outline plan of an umbel.]

(C) Main axis flattened (racemose with flattened axis)
1. Capitulum (head): the receptacle is flattened and bears numerous sessile, small florets in a centripetal manner, that is, the youngest in the centre and the oldest towards the periphery. Individual florets are bracteate. The whole cluster is surrounded by a whorl of bracts collectively called the involucre.
2. Two kinds of florets are found on the receptacle:
(i) Ray florets: arranged on the periphery, with distinct yellow colour and strap-shaped petals. These florets are female or sterile, and always zygomorphic. They may be arranged in one or more whorls.
(ii) Disc florets: placed in the centre, bisexual and actinomorphic.

[Figure: Fig. 5.49 Capitulum of sunflower with disc florets in the centre and ray florets on the periphery.]

Labels of Fig. 5.49: stigma, style, anther, corolla, calyx, ovary; disc floret and ray floret.

Cymose inflorescence
1. The growth of the main axis is definite, because the growing point of the peduncle is used up in forming a flower.
2. Further growth of the flowering axis is continued by one or more lateral branches, which also end in flowers.
3. Flowers are borne in basipetal (centrifugal) succession, that is, the oldest flower is at the top and the younger ones are lateral.

A. Uniparous (monochasial cyme)
A single lateral branch arises from the peduncle below the old flower and ends in a flower. Another lateral branch arises on the first lateral branch and also ends in a flower. It is of two types:
(a) Helicoid cyme (one-sided): the main axis ends in a flower. Its lateral branches arise from one side and each ends in a flower. Each branch gives rise to another lateral branch on the same side, so that all the lateral branches form a sort of helix, for example, Myosotis palustris and Drosera. It has two types: drepanium, in which all flowers are in one plane, and bostryx, in which flowers are borne in different planes.
(b) Scorpioid cyme: the lateral branches arise alternately on the left and right sides, for example, Heliotropium and Ranunculus. It has two types: rhipidium, in which flowers occur in one plane, and cincinnus, in which flowers are borne in different planes.

[Figure: Fig. 5.50 (A) Outline plan of a helicoid cyme, (B) Myosotis palustris. Fig. 5.51 (A) Outline plan of a scorpioid cyme, (B) Ranunculus bulbosus.]

B. Biparous (dichasial cyme)
The main axis bears a terminal flower and stops growing. At a node below it, two bracts arise, and two branches arise from these, one on each side. Each branch also ends in a flower, so there are three flowers, with the oldest in the centre. Further branching may repeat from the pedicel of each lateral flower, for example, Stellaria media, Spergula arvensis and Dianthus chinensis.

C. Multiparous (polychasial cyme)
The main axis bears a single terminal flower, and below it more than two lateral branches arise at a node. They also bear terminal flowers. The oldest flowers are in the centre. In Hamelia, this simple polychasial cyme becomes biparous and then uniparous during further branching. In Calotropis, there is an umbellate cyme, that is, groups of multiparous cymes in which the main axis is very short.

[Figure: Fig. 5.52 (A) Dichasial cyme of Dianthus chinensis, (B) polychasial cyme of Hamelia, (C) cymose hand of Acacia.]

D. Cymose head
In Acacia nilotica (keekar) and Albizzia lebbek, the main axis is condensed into a circular disc. It bears sessile or sub-sessile flowers. The oldest flower is in the centre, and the youngest towards the periphery. The flowers form a compact, globose head.

E. Scapigerous head
In Allium cepa (onion), the leafless flowering axis is called the scape. It bears a cluster of flowers that form a head, covered by one or more bracts called spathes. This head has many umbellate cymes.

THE FLOWER

The flower is the most characteristic structure of angiosperms. It is a complex unit consisting typically of those parts that directly or indirectly contribute to reproduction. It is a highly modified and condensed shoot meant for sexual reproduction. It develops on an axis called the mother axis or peduncle. A flattened peduncle is called a receptacle. The stalk of a flower is called the pedicel, and its upper swollen part is called the thalamus.

Connecting Concepts: The smallest flower is that of Wolffia (duck weed). The largest flower is that of Rafflesia arnoldi, about 1 m in diameter. Edible style and stigma are found in Crocus (saffron).

Bracts: a bract is a leaf-like structure at the base of the pedicel, in whose axil a flower arises. A flower is bracteate when the bract is present, and ebracteate when it is absent.

Symmetry
1. Asymmetrical: flowers that cannot be divided into equal halves by any radial plane, for example, Cassia and Canna.
2. Symmetrical: flowers that can be cut into two equal halves. Such flowers are of two types:
(a) Actinomorphic: radially symmetrical, that is, divisible into two equal halves by any radial plane.
(b) Zygomorphic: bilaterally symmetrical, that is, divisible into two equal halves by a single vertical plane.

Sex
On the basis of sex, flowers are divided into three categories:
1. Unisexual: flowers that possess only one essential whorl. They may be staminate (male) or pistillate (female). Unisexual plants are of two types:
(i) Monoecious: staminate and pistillate flowers are borne on the same plant, for example, Cucurbitaceae.
(ii) Dioecious: staminate and pistillate flowers are borne on different plants, for example, Morus, Carica and Borassus.
2. Bisexual: both essential whorls are present in the same flower, for example, Cruciferae and Malvaceae.
3. Polygamous: some flowers are unisexual and some are bisexual.

Position of the flower
There are three possibilities for the position (attachment) of the floral whorls with respect to the ovary:
1. Hypogynous: the calyx, corolla and androecium arise below the ovary. The ovary becomes superior, for example, Cruciferae and Liliaceae.
2. Perigynous: the sepals, petals and stamens appear to arise from the middle of the ovary. The ovary is semi-inferior, for example, Saxifraga.
3. Epigynous: the sepals, petals and stamens appear to arise from the top of the ovary. The ovary is inferior, for example, Myrtaceae (Callistemon), Umbelliferae (Coriandrum), Compositae and Cucurbitaceae.

[Figure: Fig. 5.53 (a) Hypogynous, (b) perigynous and (c) epigynous flowers, showing the position of the calyx, corolla, stamens and the ovary.]

Parts of the flower
An angiospermic flower consists of two whorls of accessory or helping structures (calyx and corolla) and two whorls of reproductive or essential organs (androecium and gynoecium).

[Figure: Fig. 5.54 A flower in L.S., showing the position of the whorls on the thalamus: pedicel, sepal, petal, stamen with filament and anther, pistil with style, stigma and ovary, locule, ovule and placenta.]

Labels of Fig. 5.54: stamen (anther, filament); pistil (stigma, style, ovary); petal; sepal; locule; ovule; placenta; thalamus; pedicel.

Calyx
1. The outermost, non-essential but protective whorl of the flower. It is represented by the sepals.
2. Polysepalous: sepals are free. Gamosepalous: sepals are wholly or partially united.
3. Connecting concept: coloured sepals known as petaloid sepals are present in garden nasturtium. In dicotyledons, sepals are usually five, and in monocotyledons usually three.

Corolla
1. The second, or inner, non-essential attractive whorl of the flower. It consists of petals, which are variously coloured.
2. The bright colour of the petals, combined with the scent of essential oils present in some flowers, makes them attractive to insects, which act as agents of pollination.
3. Polypetalous: petals are free. Gamopetalous: petals are united to some degree.

Perianth
When there is no distinction between calyx and corolla, the whorl is called a perianth. It consists of tepals, for example, lily.

Aestivation
Aestivation is the arrangement of sepals or petals in relation to one another in a floral bud. There are five types:
1. Valvate: sepals or petals meet by their edges but do not overlap.
2. Twisted: sepals or petals overlap one another.
3. Imbricate: one sepal or petal is completely external, one is completely internal, and the rest overlap one another.
4. Quincuncial: two sepals or petals are external, two are internal, and the remaining one overlaps the others.
5. Vexillary: a butterfly-shaped corolla with five petals. The odd posterior petal is called the standard. It is the largest and outermost, and it overlaps a pair of smaller lateral petals called wings or alae. The alae in turn overlap a boat-shaped keel, or carina.

[Figure: Fig. 5.55 Types of aestivation: (A) valvate, (B) twisted, (C) imbricate, (D) quincuncial, (E) vexillary.]

Androecium
1. The third whorl of the flower, and the male reproductive organ, consisting of stamens.
2. Each stamen has an anther and a filament, joined by a connective. Each anther consists of two anther lobes, and each lobe contains two pollen sacs. Pollen grains are produced in the pollen sacs.

Fusion of stamens
1. Monadelphous: all the filaments are united into a single bundle, but the anthers are free, for example, China rose.
2. Diadelphous: the filaments are united into two bundles, and the anthers remain free, for example, pea, bean and gram.
3. Polyadelphous: the filaments are united into more than two bundles, but the anthers are free, for example, castor (Ricinus) and lemon (Citrus).
4. Syngenesious: the anthers are united into a bundle, but the filaments are free, for example, sunflower.
5. Synandrous: the anthers and filaments are united throughout their whole length, for example, Colocasia and most cucurbits.

[Figure: Fig. 5.56 Cohesion of stamens: (A) monadelphous, (B) diadelphous, (C) polyadelphous, (D) synandrous, (E) syngenesious.]

Adhesion
1. Fusion among members of different whorls is called adhesion. It may be epipetalous (fusion of stamens with petals) or epiphyllous (fusion of stamens with tepals).
2. Ocimum (family Labiatae) has four stamens, two long and two short. This is called the didynamous condition.
3. In Cruciferae (for example, mustard and radish), of the six stamens, four are longer and in an inner whorl, and two in an outer whorl are shorter. This is called the tetradynamous condition.

Gynoecium
1. The female reproductive part of the flower, the innermost essential whorl, comprising carpels.
2. It is distinguishable into a basal ovule-bearing region (ovary), a terminal pollen-receiving region (stigma), and a connecting style.

Placentation
The ovules are attached to the inner surface of the ovary wall on one or more cushions called placentae. The manner of arrangement of placentae inside the ovary is called placentation. The kinds of placentation are:
1. Marginal: a single-chambered ovary, with ovules borne on the margin, as in pea (Leguminosae).
2. Parietal: a single-chambered ovary, with ovules borne on the periphery, as in Cruciferae.
3. Axile: a several-chambered ovary, with the placenta on the central axis, and ovules attached to it, as in China rose.
4. Free-central: a one-chambered ovary, with the placenta arising from the base as a swollen central axis, and ovules borne all over its surface, as in Primulaceae (Dianthus and primrose).
5. Basal: a one-chambered ovary, with a very small placenta arising directly from the thalamus. Only one ovule is borne at the base of the ovary, as in sunflower and marigold (Compositae).

[Figure: Fig. 5.57 Types of placentation: A. marginal (L.S.), B. parietal, C. axile, D. free central, E. basal, F. superficial.]

THE FRUIT

1. A fruit is a mature or ripened ovary, developed after fertilisation.
2. Fertilisation has a dual effect on the ovary. After syngamy, the ovule changes into the seed, and after ripening, the succulent parenchyma and the ovary wall change into the pericarp.
3. The pericarp may be dry or fleshy. It is differentiated into an outer epicarp, a middle mesocarp and an inner endocarp.
4. If a fruit is formed without fertilisation of the ovary, it is called a parthenocarpic fruit.
5. The fruit protects the seeds and helps in their dispersal.
6. If the fruit develops from the ovary alone, it is a true fruit. Sometimes other floral parts take part in the formation of the fruit. Such fruits are called false fruits, for example, the thalamus in apple becomes fleshy and forms the edible part.

Classification of fruits
Morphologically, fruits are classified as:
I. Simple fruits: these develop from a monocarpellary ovary or a multicarpellary syncarpous ovary.
II. Aggregate fruits (etaerio): these develop from a multicarpellary apocarpous ovary.
III. Composite fruits (multiple): these develop from a complete inflorescence.

[Figure: Classification of fruits chart showing simple fruits (dry: dehiscent capsular fruits such as legume, follicle, siliqua, silicula and capsule; indehiscent achenial fruits such as achene, nut, samara, cypsela, caryopsis; schizocarpic fruits such as lomentum, cremocarp, regma, carcerulus and double samara; succulent (fleshy) fruits such as pome, drupe, berry, pepo, hesperidium, balausta, amphisarca and hipanthium), aggregate fruits (etaerio of follicles, achenes, berries and drupes) and composite fruits (sorosis and syconus).]

I. Simple fruits
Simple fruits are of two types:
1. Dry fruits: the pericarp is not distinguished into three layers.
2. Succulent (fleshy) fruits: the pericarp is generally distinguished into epicarp, mesocarp and endocarp. The mesocarp is fleshy or fibrous.

1. Dry fruits are divided into three groups:
(A) Dehiscent (capsular) fruits: the pericarp bursts automatically after ripening and the seeds are dispersed.
(B) Indehiscent (achenial) fruits: these do not dehisce after ripening, and the seeds remain inside the pericarp.
(C) Schizocarpic (splitting) fruits: after ripening, these fruits split into one-seeded segments, but the segments do not rupture further. This group is intermediate between dehiscent and indehiscent fruits.

(A) Dehiscent or capsular fruits are simple, dry, multi-seeded fruits. Depending on the mode of dehiscence, they are of five types: pod, follicle, siliqua, silicula and capsule.
1. Pod or legume: a multi-seeded, unilocular fruit derived from a superior monocarpellary pistil with marginal placentation. At maturity, it dehisces along both the dorsal (non-seed bearing) and ventral (seed bearing) sutures, for example, pea and bean.
2. Follicle: similar to a legume in being a multi-seeded, simple, unilocular, dry fruit formed from a superior monocarpellary pistil with marginal placentation. The fruit splits along one suture only, for example, larkspur and Calotropis. The dehiscent suture may be ventral or dorsal.
3. Siliqua: a bilocular, simple, dry, multi-seeded fruit developed from a bicarpellary pistil with parietal placentation. A false septum, or replum, is present between the two placentae. At maturity the fruit dehisces by both sutures into two valves that spread outwards from base to apex, exposing the replum with the attached seeds, for example, mustard.
4. Silicula: similar to siliqua but few-seeded, short and flat. At maturity, the fruit wall breaks open into two valves, exposing the replum with the seeds, for example, Iberis amaria (candytuft) and Capsella bursa-pastoris (shepherd's purse).
5. Capsule: a simple, dry, multi-seeded dehiscent fruit that dehisces by methods other than those of legume, follicle and silicula, for example, Antirrhinum, poppy, cotton (Gossypium), lady's finger (Abelmoschus), bhindi and Datura.

[Figure: Fig. 5.58 Legume of pea. Fig. 5.59 Follicle of Madar. Fig. 5.60 Siliqua of mustard, with valves, replum and seeds. Fig. 5.61 Silicula of Capsella. Fig. 5.62 Capsule fruits of bhindi and Datura.]

(B) Indehiscent or achenial fruits develop from a single-ovuled ovary with basal placentation, so they are single-seeded.
1. Achene: developed from a monocarpellary superior ovary. It is unilocular and one-seeded, and the pericarp is free from the seed coat, for example, Ranunculus, Clematis gouriana and Naravelia zeylanica.
2. Nut: unilocular and one-seeded, developed from a bi- or multicarpellary syncarpous superior ovary. The pericarp becomes hard and stony, for example, litchi, cashew nut (Anacardium), oak and Trapa bispinosa. In litchi, the single seed is covered by a white, translucent, fleshy and edible aril.
3. Samara: the pericarp becomes flat like a wing, which helps in dispersal by wind, for example, Holoptelea indica (chilbil). In some fruits the calyx becomes wing-like. Such fruits are called samaroid, for example, Hopea and sal (Shorea robusta).
4. Cypsela: developed from a bicarpellary, syncarpous, inferior ovary. It is unilocular and one-seeded, and the pericarp is free from the seed coat. A persistent hairy calyx called the pappus is attached to the fruit and helps in dispersal by wind through a parachute mechanism. It is usually found in family Compositae, for example, sunflower (Helianthus annuus), marigold (Tagetes erecta), Cosmos and dandelion (Taraxacum).
5. Caryopsis: developed from a monocarpellary superior ovary. It is unilocular and one-seeded, and the pericarp is inseparably fused with the seed coat. It is found in family Gramineae, for example, wheat, rice and maize. The grains of these plants are therefore fruits and not seeds. It is considered the most advanced kind of dry fruit.

[Figure: Fig. 5.75 Achene of Naravelia. Fig. 5.76 Nuts: (i) litchi, (ii) cashew nut. Fig. 5.77 Samara of Holoptelea. Fig. 5.78 Cypsela. Fig. 5.79 Maize: (i) cob, (ii) single grain (caryopsis), (iii) L.S. of maize grain showing style remnants, pericarp, starchy endosperm, aleurone layer, scutellum, embryo, coleoptile, plumule, radicle and coleorhiza.]

(C) Schizocarpic fruits split into one-seeded segments at maturity. The types shown in the classification are lomentum, cremocarp, regma, carcerulus and double samara.

2. Succulent or fleshy fruits are of the following types:
(i) Pome: a false fruit, because it develops from the fleshy thalamus and the true fruit remains inside the swollen thalamus. The fleshy swollen thalamus is the edible part, for example, apple (Pyrus malus), pear (Pyrus communis) and loquat (Eriobotrya japonica).
(ii) Drupe (stony fruit): develops from a mono- or multicarpellary, syncarpous, superior ovary. It has one or many seeds. The epicarp forms the rind, the mesocarp is fleshy or fibrous, and the endocarp is hard and stony. In mango (Mangifera indica), peach and cherry, the fleshy mesocarp is edible. In coconut, the mesocarp is fibrous and forms coir on drying, while the seed and oily endosperm are edible. In almond and walnut, the cotyledons of the seed are edible.
(iii) Berry: develops from a mono- or multicarpellary, syncarpous ovary. The ovary is superior and sometimes inferior, and the placentation is axile or parietal. The epicarp forms the rind of the fruit, the mesocarp is fleshy and the endocarp is thin and membranous, for example, tomato, papaya, sapodilla (chiku), areca nut (Areca catechu), brinjal, guava (Psidium guajava), banana, date palm and grape. The date palm and areca nut are single-seeded berries.
(iv) Pepo: resembles a berry but develops from an inferior ovary with parietal placentation. The epicarp forms a hard rind. It is found mainly in family Cucurbitaceae, for example, bottle gourd, cucumber (Cucumis sativus) and muskmelon (Cucumis melo).
(v) Hesperidium: develops from a multicarpellary, syncarpous, superior ovary with axile placentation. Many oil glands are present in the epicarp. The mesocarp is white and fibrous and is fused with the epicarp. The membranous endocarp forms distinct chambers, and many unicellular juicy hairs are present on its inner side. All citrus fruits, such as orange and lemon, are hesperidia.
(vi) Balausta: develops from a multilocular, syncarpous, inferior ovary. The testa (outer seed covering) is fleshy and edible, and the tegmen (inner seed covering) is hard. The seeds are dispersed within the fruit, and the pericarp is rough and leathery, for example, pomegranate.
(vii) Amphisarca: develops from a multicarpellary, syncarpous, multi-chambered superior ovary. The epicarp is hard, while the mesocarp and endocarp are fleshy and contain seeds. The mesocarp, endocarp and swollen placenta are eaten, for example, wood apple (Aegle marmelos).
(viii) Hypanthium: a false fruit in which the edible part is the fleshy thalamus. It differs from a pome in developing from a multicarpellary, apocarpous, semi-inferior ovary, for example, rose.

[Figure: Fig. 5.63 Pome of apple, L.S. Fig. 5.64 Drupe: (i) mango, (ii) peach. Fig. 5.65 Berry: (i) tomato, (ii) papaya. Fig. 5.66 Pepo in cucurbits. Fig. 5.67 Hesperidium of orange, T.S. Fig. 5.68 Balausta of pomegranate. Fig. 5.69 Amphisarca of wood apple.]

Labels of Fig. 5.67 (Hesperidium of orange, T.S.): epicarp (thick with oil glands); seed; mesocarp (fibrous); oil glands; glandular hair.

Labels of Fig. 5.63 (Pome of apple, L.S.): pericarp; outer limit of carpel (core line); seed; cortex of thalamus; pith of thalamus; endocarp; remnants of calyx and stamens. Labels of Fig. 5.64: Drupe (i) mango and (ii) peach: epicarp, mesocarp, endocarp, seed. Labels of Fig. 5.65: Berry (i) tomato and (ii) papaya: epicarp, mesocarp, endocarp, seeds. Labels of Fig. 5.66 (Pepo): placenta, seeds, epicarp, mesocarp, endocarp, central cavity, rind.

II. Aggregate fruits (etaerio)
Depending on the nature of the individual fruitlets, aggregate fruits are of the following types:
(i) Etaerio of follicles: each carpel develops into a follicle, and many follicles arranged on an enlarged thalamus form the etaerio, for example, Calotropis and Catharanthus (Vinca). An etaerio made of many follicles is found in Michelia.
(ii) Etaerio of achenes: each fruitlet is an achene, for example, Naravelia and Clematis. The achenes of rose are present on a saucer-like thalamus. In lotus, the thalamus becomes spongy and some achenes are embedded in it. In strawberry, the thalamus becomes fleshy and red on maturity, and it is the edible part.
(iii) Etaerio of berries: an aggregate fruit made of small berries, for example, custard apple (Annona squamosa, sharifa), in which many berries develop on a fleshy thalamus. The apical parts of the berries fuse with each other and form a common rind, as in Polyalthia.
(iv) Etaerio of drupes: many small drupes, developed from different carpels, are arranged in groups on a fleshy thalamus, for example, raspberry (Rubus idaeus).

[Figure: Fig. 5.70 Etaerio of achenes in lotus (achenes embedded in the spongy thalamus). Fig. 5.71 Etaerio of berries in Anona squamosa. Fig. 5.72 (i) Etaerio of drupes in Rubus, (ii) L.S. of the etaerio.]

III. Composite fruits (multiple fruits) develop from the whole inflorescence. They are of two types:
(i) Sorosis: develops from a spike, spadix or catkin inflorescence. In jackfruit (Artocarpus integrifolia), the pistillate flowers are very close to each other around the rachis, and the bracts, perianth and seeds become succulent and are eaten. In pineapple (Ananas sativus), the rachis, bracts and perianth are edible. In mulberry (Morus alba), the fleshy perianth around the dry achenes is eaten.
(ii) Syconus: develops from a hypanthodium inflorescence. The receptacle becomes fleshy and many achenes develop from the pistillate flowers. The fleshy receptacle (rachis) is the edible part, for example, fig (Ficus carica). The fig has three types of flowers: female flowers, gall flowers and male flowers.

[Figure: Fig. 5.73 Sorosis. Fig. 5.74 Syconus of Ficus carica, L.S. of fruit and the three types of flowers: female, gall and male.]

Edible parts of some common fruits

THE SEED

1. A seed is a ripened ovule that contains an integumented embryo, or miniature plant, with adequate reserve food for the future development of the embryo.
2. Seeds are the characteristic feature of spermatophytes (gymnosperms and angiosperms).
3. A seed may have one or two coverings, called seed coats, which develop from the integuments of the ovule. The outer seed coat is called the testa, and the inner one is called the tegmen.
4. The surface of the seed has a fine pore at one end, called the micropyle. The micropyle permits the entry of water needed at the time of germination.
5. Just behind the micropyle is the hilum, a scar left on the seed coat when the seed is detached from the fruit wall.
6. Within the seed coat is the embryo, which consists of an embryonal axis and two cotyledons. The cotyledons are often fleshy and full of reserve food. At the micropylar end of the embryonal axis is the radicle, and at the other end is the plumule.
7. In some seeds, such as castor, the endosperm is persistent. It is formed as a result of double fertilisation and is a food-storing tissue.

Types of seeds
1. Albuminous (endospermic) seeds: food is stored in the endosperm, for example, maize, wheat, castor and onion.
2. Exalbuminous (non-endospermic) seeds: the endosperm is used up during development and is absent in the mature seed. Reserve food is stored in the cotyledons, for example, bean, gram and pea.

Connecting Concepts:
1. Spermology is the study of seeds.
2. The smallest and lightest seeds belong to orchids, weighing about 0.004 mg.
3. The largest and heaviest seed belongs to Lodoicea maldivica (double coconut), weighing about 6 kg.
4. Cuscuta is a dicot whose seed lacks cotyledons.

[Figure: Fig. 5.80 Seed and structure of a dicotyledonous seed, showing seed coat, cotyledon, plumule, hilum, radicle and micropyle.]

Structure of a monocotyledonous seed
1. The maize grain shows the structure of a typical monocotyledonous seed. In maize, the seed coat is fused with the pericarp.
2. The major part of the grain is occupied by a large endosperm, which is rich in starch.
3. The endosperm has a one- to three-layered peripheral protein layer called the aleurone layer, which separates the embryo from the endosperm.
4. The embryo consists of a cotyledon and an embryonal axis. The cotyledon is called the scutellum in cereals, and it is laterally attached to the embryonal axis.
5. The lower end of the axis is the radicle, which is covered by a protective sheath called the coleorhiza.
6. The upper end of the axis is the plumule, which is covered by the coleoptile.

[Figure: Fig. 5.81 Structure of a monocotyledonous seed.]

Structure of a dicotyledonous seed
1. A dicotyledonous seed contains seed coats, two cotyledons and an embryonal axis.
2. The embryonal axis is attached to the cotyledons, from which it absorbs nutrition during germination.
3. The two ends of the embryonal axis are the radicle, which gives rise to the root system, and the plumule, which gives rise to the shoot system.
4. The portion of the embryonal axis between the radicle and the point of attachment of the cotyledons is the hypocotyl. The portion between the plumule and the cotyledons is the epicotyl.
5. Most dicot seeds are exalbuminous, because the endosperm is consumed by the developing cotyledons. A few dicots, such as castor, bean and rubber, have albuminous seeds, and their cotyledons are thin and papery.

SEMI-TECHNICAL DESCRIPTION OF A TYPICAL FLOWERING PLANT

Symbols for floral formula
(A) Bracts (Br): Br for bracteate, Ebr for ebracteate.
(B) Symmetry of the flower: ⊕ for actinomorphic, % for zygomorphic.
(C) Sex: staminate (male), pistillate (female) and hermaphrodite (bisexual).
(D) Calyx (K): K4 means 4 polysepalous sepals (free); K(4) means 4 gamosepalous sepals (fused); K2+2 means 4 sepals in two whorls of two each.
(E) Corolla (C): C4 means 4 polypetalous petals; C(4) means 4 gamopetalous petals; C2+2 means 4 petals in two whorls of two each.
(F) Perianth (P): P6 means 6 polytepalous tepals; P3+3 means 6 tepals in two whorls of three each; P(3)+(3) means 6 gamotepalous tepals.
(G) Androecium (A): A6 means 6 polyandrous stamens; A2+4 means 6 stamens in two whorls of two and four each; A0 means stamens absent; A∞ means stamens indefinite; A10 means 10 monoadelphous stamens; A1+(9) means 10 diadelphous stamens. Epipetalous and epiphyllous describe stamens fused with petals or tepals.
(H) Gynoecium (G): G0 means gynoecium absent; G2 means 2 apocarpous carpels; G(2) means 2 syncarpous carpels; G(2-) means a bicarpellary, syncarpous, inferior ovary; G(2) means a bicarpellary, syncarpous, superior ovary.

Connecting Concepts:
1. Apocarpous gynoecium: consists of two to many free carpels, and each carpel forms its own pistil.
2. Syncarpous gynoecium: consists of two to many carpels fused laterally to form a compound pistil.

DESCRIPTION OF SOME IMPORTANT FAMILIES

FABACEAE OR LEGUMINOSAE

1. Fabaceae is commonly called the pulse family. It is the fourth largest family of the plant kingdom, after Compositae, Orchidaceae and Gramineae. It is the second most valuable family, after Gramineae, and it provides the maximum timber.
2. Habit: annual or biennial herb, shrub or tree.
3. Root: tap root system.
4. Stem: erect or creeping, solid or weak.
5. Leaf: alternate or whorled, stipulate, compound, with reticulate venation.
6. The family is divided into three subfamilies: Papilionaceae, Caesalpiniaceae and Mimosaceae.

Connecting Concepts: The main characters of Leguminosae, or Fabaceae, are:
1. Polypetalous condition.
2. Monocarpellary condition, with a single carpel.
3. Perigynous condition and marginal placentation.

[Figure: Fig. 5.82 Floral diagram of Pisum sativum (garden pea). Fig. 5.83 Floral diagram of Cassia fistula (amaltas). Fig. 5.84 Floral diagram of Acacia arabica (kikar).]

Economic importance of Papilionaceae
Plants used as food:
1. Pulses: various pulses are obtained from this family, for example, garden pea (Pisum sativum), chickpea or gram (Cicer arietinum), lobia (Vigna unguiculata), arhar (Cajanus cajan), masoor (Lens esculenta), urad (Phaseolus mungo) and mung (Phaseolus aureus).
2. Pulses are rich in protein. They contain all amino acids except that they are poor in methionine, lysine and tryptophan. They also provide fodder, fibre, timber and oil.
3. Groundnut (Arachis hypogaea): its embryo is used to prepare vegetable oil. Soyabean (Glycine max) is rich in protein.
4. Sesbania and Trifolium are used as fodder.
5. Sem (Dolichos lablab), lobia (Vigna unguiculata) and pea (Pisum sativum) are used as vegetables. Leaves of Trigonella are also used as a vegetable.

Plants used in medicine:
1. Roots of Glycyrrhiza glabra (liquorice, mulethi) are used for sore throat. Glycyrrhizin, a glycoside in the root, is about 50 times sweeter than sugar.
2. Seeds of Psoralea corylifolia (babchi or khatmi) are used for leucoderma.
3. Roots of Desmodium gangeticum are used for diarrhoea and cough.
4. Leaves and flowers of Clitoria ternatea are used for snake bite.
5. Desmodium gangeticum is also used for asthma, and for snake and scorpion bites.

Soil fertility: The roots of plants of this family are nodulated and contain the nitrogen-fixing bacterium Rhizobium. Crotalaria, Sesbania and Cyamopsis are used as green manure. Sesbania rostrata has two nitrogen-fixing bacteria: Rhizobium in root nodules and Azorhizobium in stem nodules.

Fibre yielding plants: The secondary phloem of the stem of Crotalaria juncea (sunn hemp) provides fibre.

Ornamental plants:
1. Sesbania grandiflora.
2. Butea monosperma (flame of the forest), which has deep red flowers.
3. Lathyrus odoratus (sweet pea, wild pea), which has variously coloured flowers.

Miscellaneous uses:
1. Crotalaria juncea (sunn hemp): bast fibres are obtained from the phloem and pericycle of the stem, used for making ropes and mats. It is also an important green manure crop.
2. Indigofera tinctoria (indigo or neel): indigo dye, used for dyeing and printing cotton, is obtained from this plant.
3. Astragalus gummifer: gum tragacanth, used commercially as an emulsifier, in cosmetics, in confectionery and in the textile industry.
4. Desmodium gyrans (Indian telegraph plant): shows spontaneous leaf movement.
5. Abrus precatorius: the seeds are used by jewellers for weighing, as each seed has a constant weight of 1.75 grains. The leaf juice is used for leucoderma.

Economic importance of Caesalpiniaceae
Food plants:
1. Bauhinia variegata (kachnar): flower buds are used as a vegetable.
2. Tamarindus indica (imli): the fruits are used as a condiment.

Medicinal plants:
1. Cassia fistula (senna or amaltas): the pulp of the fruit and the leaves are laxative and are used in churnas.
2. Saraca indica (ashok): one of the most sacred trees of India. Its bark is used for menstrual disorders.

Ornamental plants:
1. Cassia fistula (amaltas) has beautiful yellow flowers.
2. Delonix regia (gulmohar) has scarlet flowers.
3. Saraca indica (ashok or sita ashok) has orange flowers used for decorating temples.
4. Parkinsonia aculeata (vilayati kikar) has fragrant yellow flowers and is grown along roadsides and railway platforms.

Others:
1. Caesalpinia sappan (sappan): the heartwood gives a red-orange dye, which is the source of gulal used in the Holi festival.
2. Haematoxylon campechianum (logwood): a dye called haematoxylin is obtained from its wood. It is used as a stain in anatomical preparations.

Economic importance of Mimosaceae
1. Acacia arabica (kikar or babul): gum arabic is obtained from its bark. Tannin is also obtained from the bark.
2. Acacia catechu (katha): katha is obtained from its wood. Lac insects survive on this plant.
3. Albizzia lebbeck (siris): a special type of gum called sresh is obtained from the bark.
4. Pithecellobium dulce (jungle jalebi or rain tree): a hedge plant. The juicy aril surrounding the seed is edible.
5. Mimosa pudica (touch-me-not or chui-mui): shows seismonastic movements.
6. Leucaena leucophloea (white popinac): a tree grown under social forestry nowadays.

SOLANACEAE

1. It is a large family commonly called the potato family.
2. Vegetative characters: plants are mostly herbs, shrubs or small trees. The stem is herbaceous, rarely woody, aerial, erect, cylindrical and branched, solid or hollow, and hairy or glabrous. In potato (Solanum tuberosum), the stem is underground. The leaves are alternate, simple, rarely pinnately compound, exstipulate, with reticulate venation.
3. Floral characters: the inflorescence is axillary, solitary or cymose, as in Datura. The flower is ebracteate, actinomorphic, hermaphrodite, pentamerous and hypogynous.
4. Calyx: sepals 5, gamosepalous, valvate, persistent.
5. Corolla: petals 5, gamopetalous, valvate or twisted.
6. Androecium: stamens 5, epipetalous. The filaments are of unequal length.
7. Gynoecium: bicarpellary, syncarpous, superior, bilocular ovary, with many ovules in each locule. The ovary is obliquely placed, with a swollen placenta.
8. Fruit: generally a berry, or a capsule in Datura.
9. Floral formula: Ebr. ⊕ K(5) C(5) A(5) G(2), with C(5) and A(5) joined by an arc to show epipetalous stamens.

[Figure: Fig. 5.85 Floral diagram of Solanaceae.]

Economic importance of Solanaceae
Food plants:
1. Solanum tuberosum (potato): the most important stem vegetable (tubers) in the world.
2. Solanum melongena (brinjal or egg plant): the fruits are a source of vegetables.
3. Lycopersicon esculentum (tomato): the fruits are a source of vegetables and salad.
4. Capsicum annuum (chillies or red pepper): the fruits are a source of spice.
5. Capsicum frutescens (shimla mirch): the fruits are used as a vegetable.

Medicinal plants:
1. Atropa belladonna: the alkaloid atropine is extracted from the roots and forms the drug belladonna.
2. Datura stramonium: the alkaloids atropine, hyoscyamine and hyoscine are present. The drug stramonium is obtained from the dried leaves and is used in the treatment of asthma. The seeds are deadly poisonous.
3. Hyoscyamus niger (henbane): the dried leaves and flowering tops yield the drug henbane, which is used in the treatment of asthma and whooping cough.
4. Withania somnifera (ashwagandha): the drug Ashwagandha (agandh), obtained from the root, is used in rheumatism, female disorders and cough.
5. Nicotiana tabacum (tobacco): the alkaloid nicotine is extracted from this plant and is used as an antispasmodic sedative. Fermented leaves are the source of tobacco, used for smoking, chewing and snuffing. Its seeds provide an oil used in paints and varnishes.

Ornamental plants:
1. Petunia alba and P. hybrida: flowers of different colours, such as white and pink.
2. Cestrum nocturnum (night jasmine or rat ki rani).
3. Cestrum diurnum (day jasmine or din ka raja).
4. Nicotiana alata.
5. Brunfelsia hopeana (yesterday, today, tomorrow plant).
6. Schizanthus (butterfly flower).
7. Salpiglossis, and others.

Others: Solanum nigrum (night shade plant or makoi).

Floral diagram of Solanum nigrum (Makai):

Distinguishing features of Solanaceae: generally five persistent sepals; five stamens with filaments of unequal length; ovary obliquely placed, with a swollen placenta.

LILIACEAE

1. It is commonly called the lily family. Plants are generally perennial herbs.
2. Habit: usually perennial herbs, such as Polygonatum, or sometimes small shrubs, such as Ruscus.
3. Root: adventitious and fibrous.
4. Stem: erect or climbing, as in Smilax; branched or unbranched; herbaceous.
5. Leaf: exstipulate, alternate or whorled, with parallel venation.
6. Inflorescence: raceme, umbel or sometimes solitary.
7. Flower: pedicellate, bracteate, hermaphrodite, actinomorphic, trimerous and hypogynous.
8. Perianth: six tepals (3+3) in two whorls, with imbricate aestivation.
9. Androecium: six (3+3) stamens in two whorls, antiphyllous, that is, opposite the tepals.
10. Gynoecium: tricarpellary, syncarpous, superior ovary, trilocular, with axile placentation and two or more ovules in each locule.
11. Fruit: capsule, or rarely berry.
12. Floral formula: ♀ Br. ⊕ P3+3 A3+3 G(3).

[Figure: Fig. 5.86 Floral diagram of Liliaceae.]

Economic importance of Liliaceae
Food plants: Allium cepa (onion), Allium sativum (garlic) and Asparagus racemosus are used as vegetables.

Medicinal plants:
1. Leaves of Allium cepa (onion) are used for dental and ear troubles.
2. Leaves of Allium sativum (lahsun) are used for cough and fever.
3. The leaf extract of Crinum latifolium (sukhdarshan) is used for ear pain.
4. The bulb and leaves of Crinum asiaticum are used for urinary troubles.
5. Aloe is used for skin problems.

Ornamental plants: Dracaena terniflora, Yucca species, Lilium candidum, Gloriosa superba (glory lily), and others.

Other commercial uses: Colchicine, an alkaloid obtained from Colchicum autumnale, is used to induce polyploidy in plants.