Unit 2 Structural Organisation in Plants and Animals PDF 2021-22

UNIT 2 STRUCTURAL ORGANISATION IN PLANTS AND ANIMALS Chapter 5 The description of the diverse forms of life on earth was made only by Morphology of observation – through naked ey...

UNIT 2 STRUCTURAL ORGANISATION IN PLANTS AND ANIMALS Chapter 5 The description of the diverse forms of life on earth was made only by Morphology of observation – through naked eyes or later through magnifying lenses Flowering Plants and microscopes. This description is mainly of gross structural features, both external and internal. In addition, observable and perceivable Chapter 6 living phenomena were also recorded as part of this description. Before Anatomy of Flowering experimental biology or more specifically, physiology, was established Plants as a part of biology, naturalists described only biology. Hence, biology remained as a natural history for a long time. The description, by itself, Chapter 7 was amazing in terms of detail. While the initial reaction of a student Structural Organisation in could be boredom, one should keep in mind that the detailed description, Animals was utilised in the later day reductionist biology where living processes drew more attention from scientists than the description of life forms and their structure. Hence, this description became meaningful and helpful in framing research questions in physiology or evolutionary biology. In the following chapters of this unit, the structural organisation of plants and animals, including the structural basis of physiologial or behavioural phenomena, is described. For convenience, this description of morphological and anatomical features is presented separately for plants and animals. 2021-22  KATHERINE ESAU was born in Ukraine in 1898. She studied agriculture in Russia and Germany and received her doctorate in 1931 in United States. She reported in her early publications that the curly top virus spreads through a plant via the food- conducting or phloem tissue. Dr Esau’s Plant Anatomy published in 1954 took a dynamic, developmental approach designed to enhance one’s understanding of plant structure and an enormous impact worldwide, literally bringing about a revival of the discipline. The Anatomy of Seed Plants by Katherine Esau was published in 1960. It was referred to as Webster’s of plant biology – it is encyclopediac. In 1957 she was elected to the National Academy of Sciences, becoming the sixth woman to receive that honour. In addition to this prestigious award, she received the National Medal of Science from President George Bush in 1989. When Katherine Esau died in the year 1997, Peter Raven, director of Anatomy and Morphology, Missouri Botanical Garden, remembered that she ‘absolutely dominated’ the field Katherine Esau of plant biology even at the age of 99. (1898 – 1997) 2021-22  C HAPTER 5 MORPHOLOGY OF FLOWERING PLANTS 5.1 The Root The wide range in the structure of higher plants will never fail to fascinate us. Even though the angiosperms show such a large diversity in external 5.2 The Stem structure or morphology, they are all characterised by presence of roots, 5.3 The Leaf stems, leaves, flowers and fruits. 5.4 The Inflorescence In chapters 2 and 3, we talked about classification of plants based on morphological and other characteristics. For any successful attempt 5.5 The Flower at classification and at understanding any higher plant (or for that 5.6 The Fruit matter any living organism) we need to know standard technical terms and standard definitions. We also need to know about the possible 5.7 The Seed variations in different parts, found as adaptations of the plants to their 5.8 Semi-technical environment, e.g., adaptions to various habitats, for protection, Description of a climbing, storage, etc. Typical If you pull out any weed you will see that all of them have roots, stems Flowering Plant and leaves. They may be bearing flowers and fruits. The underground 5.9 Description of part of the flowering plant is the root system while the portion above the Some Important ground forms the shoot system (Figure 5.1). Families 5.1 THE ROOT In majority of the dicotyledonous plants, the direct elongation of the radicle leads to the formation of primary root which grows inside the soil. It bears lateral roots of several orders that are referred to as secondary, tertiary, etc. roots. The primary roots and its branches constitute the 2021-22  66 BIOLOGY tap root system, as seen in the mustard Flower plant (Figure 5.2a). In monocotyledonous plants, the primary root is short lived and is replaced by a large number of roots. Fruit These roots originate from the base of the Stem stem and constitute the fibrous root Leaf Shoot system, as seen in the wheat plant (Figure system 5.2b). In some plants, like grass, Monstera and the banyan tree, roots arise Node from parts of the plant other than the Internode { Bud radicle and are called adventitious roots (Figure 5.2c). The main functions of the root system are absorption of water and minerals from the soil, providing a proper Primary anchorage to the plant parts, storing root Root reserve food material and synthesis of Secondary system plant growth regulators. root Figure 5.1 Parts of a flowering plant Main root Laterals Fibrous roots Adventitious roots (a) (b) (c) Figure 5.2 Different types of roots : (a) Tap (b) Fibrous (c) Adventitious 2021-22  MORPHOLOGY OF FLOWERING PLANTS 67 5.1.1 Regions of the Root The root is covered at the apex by a thimble-like structure called the root cap (Figure 5.3). It protects the tender apex of the root as it makes its way through the soil. A few millimetres above the root cap is the region of meristematic activity. The cells of this region are very small, thin-walled and with dense protoplasm. They divide repeatedly. The cells proximal to this region undergo rapid elongation and enlargement and are responsible for the growth of the root in length. This region is called the region of elongation. The cells of the elongation zone gradually differentiate and mature. Hence, this zone, proximal to region of elongation, is called the region of maturation. From this region some of the epidermal cells form very fine Figure 5.3 The regions of the root-tip and delicate, thread-like structures called root hairs. These root hairs absorb water and minerals from the soil. 5.1.2 Modifications of Root Roots in some plants change their shape and structure and become modified to perform functions other than absorption and conduction of water and minerals. They are modified for support, storage of food and respiration (Figure 5.4 and 5.5). Tap roots of carrot, turnip and adventitious roots of sweet potato, get swollen and store food. Can you give some more such examples? Have you ever wondered what those hanging structures that support a banyan tree are? These are called prop roots. Similarly, the stems of maize and sugarcane have supporting roots coming out of the lower nodes of the stem. These are called stilt roots. In some plants such as Rhizophora growing in swampy areas, many roots come out of the ground and grow vertically upwards. Such roots, called pneumatophores, help to Figure 5.4 Modification of root for support: get oxygen for respiration (Figure 5.5b). Banyan tree 2021-22 68 BIOLOGY Turnip Carrot Sweet potato Asparagus (a) (b) Figure 5.5 Modification of root for : (a) storage (b) respiration: pneumatophore in Rhizophora 5.2 THE STEM What are the features that distinguish a stem from a root? The stem is the ascending part of the axis bearing branches, leaves, flowers and fruits. It develops from the plumule of the embryo of a germinating seed. The stem bears nodes and internodes. The region of the stem where leaves are born are called nodes while internodes are the portions between two nodes. The stem bears buds, which may be terminal or axillary. Stem is generally green when young and later often become woody and dark brown. The main function of the stem is spreading out branches bearing leaves, flowers and fruits. It conducts water, minerals and photosynthates. Some stems perform the function of storage of food, support, protection and of vegetative propagation. 5.2.1 Modifications of Stem The stem may not always be typically like what they are expected to be. They are modified to perform different functions (Figure 5.6). Underground stems of potato, ginger, turmeric, zaminkand, Colocasia are modified to store food in them. They also act as organs of perennation to tide over conditions unfavourable for growth. Stem tendrils which develop from axillary buds, are slender and spirally coiled and help plants to climb such as in gourds (cucumber, pumpkins, watermelon) and grapevines. Axillary buds of stems may also get modified into woody, straight and pointed thorns. Thorns are found in many plants such as Citrus, Bougainvillea. They protect plants from browsing animals. Some plants of arid regions modify their stems into flattened (Opuntia), or fleshy cylindrical (Euphorbia) structures. They contain chlorophyll and carry 2021-22  MORPHOLOGY OF FLOWERING PLANTS 69 Axillary bud modified Ginger into tendril Potato Zaminkand (b) (a) Stem modified into spine Bougainvillea sp. Roots arising Oxalis sp. (c) from nodes (d) Figure 5.6 Modifications of stem for : (a) storage (b) support (c) protection (d) spread and vegetative propagation out photosynthesis. Underground stems of some plants such as grass and strawberry, etc., spread to new niches and when older parts die new plants are formed. In plants like mint and jasmine a slender lateral branch arises from the base of the main axis and after growing aerially for some time arch downwards to touch the ground. A lateral branch with short internodes and each node bearing a rosette of leaves and a tuft of roots is found in aquatic plants like Pistia and Eichhornia. In banana, pineapple and Chrysanthemum, the lateral branches originate from the basal and underground portion of the main stem, grow horizontally beneath the soil and then come out obliquely upward giving rise to leafy shoots. 5.3 THE LEAF The leaf is a lateral, generally flattened structure borne on the stem. It develops at the node and bears a bud in its axil. The axillary bud later develops into a branch. Leaves originate from shoot apical meristems and are arranged in an acropetal order. They are the most important vegetative organs for photosynthesis. A typical leaf consists of three main parts: leaf base, petiole and lamina (Figure 5.7 a). The leaf is attached to the stem by the leaf base and may 2021-22  70 BIOLOGY Lamina bear two lateral small leaf like structures called stipules. In monocotyledons, the leaf base expands Stipule into a sheath covering the stem partially or wholly. In some leguminous plants the leafbase may become swollen, which is called the pulvinus. The petiole help hold the blade to light. Long thin flexible Petiole petioles allow leaf blades to flutter in wind, thereby Axillary cooling the leaf and bringing fresh air to leaf surface. Leaf bud (a) base The lamina or the leaf blade is the green expanded part of the leaf with veins and veinlets. There is, usually, a middle prominent vein, which is known as the midrib. Veins provide rigidity to the leaf blade and act as channels of transport for water, minerals and food materials. The shape, margin, apex, surface and extent of incision of lamina varies in different leaves. 5.3.1 Venation The arrangement of veins and the veinlets in the lamina of leaf is termed as venation. When the veinlets form a network, the venation is termed as reticulate (Figure 5.7 b). When the veins run parallel to each other within a lamina, the venation is termed as parallel (Figure 5.7 c). Leaves of (b) (c) dicotyledonous plants generally possess reticulate Figure 5.7 Structure of a leaf : venation, while parallel venation is the characteristic (a) Parts of a leaf of most monocotyledons. (b) Reticulate venation (c) Parallel venation 5.3.2 Types of Leaves Rachis A leaf is said to be simple, when its lamina is entire or when incised, the incisions do not touch the midrib. When the incisions of the lamina reach up to the midrib breaking it into a number of leaflets, the leaf is called compound. A bud is present in the axil of petiole in both simple and compound leaves, but not in the axil of leaflets of the compound leaf. The compound leaves may be of two types (b) Silk Cotton (Figure 5.8). In a pinnately compound leaf a (a) Neem number of leaflets are present on a common axis, Figure 5.8 Compound leaves : the rachis, which represents the midrib of the leaf (a) pinnately compound leaf (b) palmately compound leaf as in neem. 2021-22  MORPHOLOGY OF FLOWERING PLANTS 71 In palmately compound leaves, the leaflets are attached at a common point, i.e., at the tip of petiole, as in silk cotton. 5.3.3 Phyllotaxy Phyllotaxy is the pattern of arrangement of leaves on the stem or branch. This is usually (b) Guava (a) China rose of three types – alternate, opposite and whorled (Figure 5.9). In alternate type of phyllotaxy, a single leaf arises at each node in alternate manner, as in china rose, mustard and sun flower plants. In opposite type, a pair of leaves arise at each node and lie opposite to each other as in Calotropis and guava plants. If more than two leaves (c) Alstonia arise at a node and form a whorl, it is called whorled, as in Alstonia. Figure 5.9 Different types of phyllotaxy : (a) Alternate (b) Opposite (c) Whorled 5.3.4 Modifications of Leaves Leaves Leaves are often modified to perform modified Leaf functions other than photosynthesis. They tendril into spines are converted into tendrils for climbing as in peas or into spines for defence as in cacti (Figure 5.10 a, b). The fleshy leaves of onion and garlic store food (Figure 5.10c). In some plants such as Australian acacia, the leaves are small and short-lived. The petioles in these plants expand, become green and synthesise food. Leaves of certain insectivorous plants such as pitcher plant, venus-fly trap are also modified leaves. (b) Cactus (a) Pea 5.4 THE INFLORESCENCE A flower is a modified shoot wherein the shoot apical meristem changes to floral meristem. Internodes do not elongate and the axis gets condensed. The apex produces different Fleshy kinds of floral appendages laterally at leaves (c) Onion successive nodes instead of leaves. When a Figure 5.10 Modifications of leaf for : shoot tip transforms into a flower, it is always (a) support: tendril (b) protection: solitary. The arrangement of flowers on the spines (c) storage: fleshy leaves 2021-22 72 BIOLOGY floral axis is termed as inflorescence. Depending on whether the apex gets developed into a flower or continues to grow, two major types of inflorescences are defined – racemose and cymose. In racemose type of inflorescences the main axis continues to grow, the flowers are borne laterally in an acropetal succession (Figure 5.11). In cymose type of inflorescence the main axis terminates in a flower, hence is limited in growth.The flowers are borne in a basipetal order (Figure 5.12). 5.5 THE FLOWER The flower is the reproductive unit in the angiosperms. It is meant for sexual reproduction. A typical flower has four different kinds of whorls arranged successively on the swollen end of the stalk or pedicel, called thalamus or receptacle. These are calyx, corolla, androecium and Figure 5.11 Racemose inflorescence gynoecium. Calyx and corolla are accessory organs, while androecium and gynoecium are reproductive organs. In some flowers like lily, the calyx and corolla are not distinct and are termed as perianth. When a flower has both androecium and gynoecium, it is bisexual. A flower having either only stamens or only carpels is unisexual. In symmetry, the flower may be actinomorphic (radial symmetry) or zygomorphic (bilateral symmetry). When a flower can be divided into two equal radial halves in any radial plane passing through the centre, it is said to be actinomorphic, e.g., mustard, datura, chilli. When it can be divided into two similar halves only Figure 5.12 Cymose inflorescence in one particular vertical plane, it is zygomorphic, e.g., pea, gulmohur, bean, Cassia. A flower is asymmetric (irregular) if it cannot be divided into two similar halves by any vertical plane passing through the centre, as in canna. A flower may be trimerous, tetramerous or pentamerous when the floral appendages are in multiple of 3, 4 or 5, respectively. Flowers with bracts -reduced leaf found at the base of the pedicel - are called bracteate and those without bracts, ebracteate. 2021-22  MORPHOLOGY OF FLOWERING PLANTS 73 (a) (b) (c) (d) Figure 5.13 Position of floral parts on thalamus : (a) Hypogynous (b) and (c) Perigynous (d) Epigynous Based on the position of calyx, corolla and androecium in respect of the ovary on thalamus, the flowers are described as hypogynous, perigynous and epigynous (Figure 5.13). In the hypogynous flower the gynoecium occupies the highest position while the other parts are situated below it. The ovary in such flowers is said to be superior, e.g., mustard, china rose and brinjal. If gynoecium is situated in the centre and other parts of the flower are located on the rim of the thalamus almost at the same level, it is called perigynous. The ovary here is said to be half inferior, e.g., plum, rose, peach. In epigynous flowers, the margin of thalamus grows upward enclosing the ovary completely and getting fused with it, the other parts of flower arise above the ovary. Hence, the ovary is said to be inferior as in flowers of guava and cucumber, and the ray florets of sunflower. 5.5.1 Parts of a Flower Each flower normally has four floral whorls, viz., calyx, corolla, androecium and gynoecium (Figure 5.14). 5.5.1.1 Calyx The calyx is the outermost whorl of the flower and the members are called sepals. Generally, sepals are green, leaf like and protect the flower in the bud stage. The calyx may be gamosepalous (sepals united) or polysepalous (sepals free). 5.5.1.2 Corolla Corolla is composed of petals. Petals are usually brightly coloured to attract insects for pollination. Like calyx, corolla may also be 2021-22 74 BIOLOGY Androecium Gynoecium Corolla Calyx Pedicel Figure 5.14 Parts of a flower gamopetalous (petals united) or polypetalous (petals free). The shape and colour of corolla vary greatly in plants. Corolla may be tubular, bell- shaped, funnel-shaped or wheel-shaped. Aestivation: The mode of arrangement of sepals or petals in floral bud with respect to the other members of the same whorl is known as aestivation. The main types of aestivation are valvate, twisted, imbricate and vexillary (Figure 5.15). When sepals or petals in a whorl just touch one another at the margin, without overlapping, as in Calotropis, it is said to be valvate. If one margin of the appendage overlaps that of the next one and so on as in china rose, lady’s finger and cotton, it is called twisted. If the margins of sepals or petals overlap one another but not in any particular direction as in Cassia and gulmohur, the aestivation is called imbricate. In pea and bean flowers, there are five petals, the largest (standard) overlaps the two lateral petals (wings) which in turn overlap the two smallest anterior petals (keel); this type of aestivation is known as vexillary or papilionaceous. (a) (b) (c) (d) Figure 5.15 Types of aestivation in corolla : (a) Valvate (b) Twisted (c) Imbricate (d) Vexillary 2021-22  MORPHOLOGY OF FLOWERING PLANTS 75 ( )a 5.5.1.3 Androecium Androecium is composed of stamens. Each stamen which represents the male reproductive organ consists of a stalk or a filament and an anther. Each anther is usually bilobed and each lobe has two chambers, the pollen-sacs. The pollen grains are produced in pollen-sacs. A sterile stamen is called staminode. (a) Stamens of flower may be united with other members such as petals or among themselves. When stamens are attached to the petals, they are epipetalous as in brinjal, or epiphyllous when attached to the perianth as in the flowers of lily. The stamens in a flower may either remain free (polyandrous) or may be united in varying degrees. The stamens may be united into one bunch or one bundle (monoadelphous) as in china rose, or two bundles (diadelphous) as in pea, or into more than two bundles (b) (polyadelphous) as in citrus. There may be a variation in the length of filaments within a flower, as in Salvia and mustard. 5.5.1.4 Gynoecium Gynoecium is the female reproductive part of the flower and is made up of one or more carpels. A carpel consists of three parts namely stigma, style and ovary. Ovary is the enlarged basal part, on which lies the elongated tube, the style. The style connects the ovary to the (c) stigma. The stigma is usually at the tip of the style and is the receptive surface for pollen grains. Each ovary bears one or more ovules attached to a flattened, cushion-like placenta. When more than one carpel is present, they may be free (as in lotus and rose) and are called apocarpous. They are termed syncarpous when carpels are fused, as in mustard and tomato. After fertilisation, the ovules develop into seeds and the ovary matures into a fruit. (d) Placentation: The arrangement of ovules within the ovary is known as placentation. The placentation are of different types namely, marginal, axile, parietal, basal, central and free central (Figure 5.16). In marginal placentation the placenta forms a ridge along the ventral suture of the ovary and the ovules are borne on this ridge forming two rows, as in pea. When the placenta is axial and the ovules are attached to it in a multilocular ovary, the placentaion is (e) said to be axile, as in china rose, tomato and lemon. In parietal Figure 5.16 Types of placentation, the ovules develop on the inner wall of the ovary or placentation : on peripheral part. Ovary is one-chambered but it becomes two- (a) Marginal chambered due to the formation of the false septum, e.g., mustard (b) Axile (c) Parietal and Argemone. When the ovules are borne on central axis and (d) Free central septa are absent, as in Dianthus and Primrose the placentation is (e) Basal 2021-22 76 BIOLOGY called free central. In basal placentation, the placenta develops at the base of ovary and a single ovule is attached to it, as in sunflower, marigold. 5.6 THE FRUIT The fruit is a characteristic feature of the flowering plants. It is a mature or ripened ovary, developed after fertilisation. If a fruit is formed without fertilisation of the ovary, it is called a parthenocarpic fruit. Generally, the fruit consists of a wall or pericarp and seeds. The pericarp may be dry or fleshy. When pericarp is thick and fleshy, it is differentiated into the outer epicarp, the middle mesocarp and the inner endocarp. (a) (b) Figure 5.17 Parts of a fruit : (a) Mango (b) Coconut In mango and coconut, the fruit is known as a drupe (Figure 5.17). They develop from monocarpellary superior ovaries and are one seeded. In mango the pericarp is well differentiated into an outer thin epicarp, a middle fleshy edible mesocarp and an inner stony hard endocarp. In coconut which is also a drupe, the mesocarp is fibrous. 5.7 THE SEED The ovules after fertilisation, develop into seeds. A seed is made up of a seed coat and an embryo. The embryo is made up of a radicle, an embryonal axis and one (as in wheat, maize) or two cotyledons (as in gram and pea). 5.7.1 Structure of a Dicotyledonous Seed The outermost covering of a seed is the seed coat. The seed coat has two layers, the outer testa and the inner tegmen. The hilum is a scar on the seed coat through which the developing seeds were attached to the fruit. Above the hilum is a small pore called the micropyle. Within the seed 2021-22  MORPHOLOGY OF FLOWERING PLANTS 77 coat is the embryo, consisting of an Seed coat Cotyledon embryonal axis and two cotyledons. The Plumule cotyledons are often fleshy and full of reserve food materials. At the two ends of the embryonal axis are present the radicle and the plumule (Figure 5.18). In some seeds Hilum such as castor the endosperm formed as a Radicle result of double fertilisation, is a food storing Micropyle tissue and called endospermic seeds. In plants such as bean, gram and pea, the Figure 5.18 Structure of dicotyledonous seed endosperm is not present in mature seeds and such seeds are called non- endospermous. 5.7.2 Structure of Monocotyledonous Seed Generally, monocotyledonous seeds are endospermic but some as in orchids are non-endospermic. In the seeds of cereals such as maize the seed coat is membranous and generally fused with the fruit wall. The endosperm is bulky and stores food. The outer covering of endosperm separates the embryo by a proteinous layer called aleurone layer. The embryo is small and situated in a groove at one end of the endosperm. It consists of one large and shield shaped cotyledon known as scutellum and a short axis with a plumule and a radicle. The plumule and radicle are enclosed in sheaths which are called coleoptile and coleorhiza respectively (Figure 5.19). Seed coat & fruit-wall Endosperm Aleurone layer Scutellum Coleoptile Endosperm Plumule Embryo Radicle Coleorhiza Figure 5.19 Structure of a monocotyledonous seed 2021-22  78 BIOLOGY 5.8 SEMI-TECHNICAL DESCRIPTION OF A TYPICAL FLOWERING PLANT Various morphological features are used to describe a flowering plant. The description has to be brief, in a simple and scientific language and presented in a proper sequence. The plant is described beginning with its habit, vegetative characters – roots, stem and leaves and then floral characters inflorescence and flower parts. After describing various parts of plant, a floral diagram and a floral formula are presented. The floral formula is represented by some symbols. In the floral formula, Br stands for bracteate K stands for calyx , C for corolla, P for perianth, A for androecium and G for Gynoecium, G for K2+2 C4 A2+4 G(2) superior ovary and G for inferior ovary, for male, for ⊕ female, for bisexual plants, ⊕ for actinomorphic and Figure 5.20 Floral diagram with for zygomorphic nature of flower. Fusion is indicated by floral formula enclosing the figure within bracket and adhesion by a line drawn above the symbols of the floral parts. A floral diagram provides information about the number of parts of a flower, their arrangement and the relation they have with one another (Figure 5.20). The position of the mother axis with respect to the flower is represented by a dot on the top of the floral diagram. Calyx, corolla, androecium and gynoecium are drawn in successive whorls, calyx being the outermost and the gynoecium being in the centre. Floral formula also shows cohesion and adhesion within parts of whorls and between whorls. The floral diagram and floral formula in Figure 5.20 represents the mustard plant (Family: Brassicaceae). 5.9 DESCRIPTION OF SOME IMPORTANT FAMILIES 5.9.1 Fabaceae This family was earlier called Papilionoideae, a subfamily of family Leguminosae. It is distributed all over the world (Figure 5.21). Vegetative Characters Trees, shrubs, herbs; root with root nodules Stem: erect or climber Leaves: alternate, pinnately compound or simple; leaf base, pulvinate; stipulate; venation reticulate. 2021-22  MORPHOLOGY OF FLOWERING PLANTS 79 (b) (c) (e) (f) (a) (d) Figure 5.21 Pisum sativum (pea) plant : (a) Flowering twig (b) Flower (c) Petals (d) Reproductive parts (e) L.S.carpel (f) Floral diagram Floral characters Inflorescence: racemose Flower: bisexual, zygomorphic Calyx: sepals five, gamosepalous; valvate/imbricate aestivation Corolla: petals five, polypetalous, papilionaceous, consisting of a posterior standard, two lateral wings, two anterior ones forming a keel (enclosing stamens and pistil), vexillary aestivation Androecium: ten, diadelphous, anther dithecous Gynoecium: ovary superior, mono carpellary, unilocular with many ovules, style single Fruit: legume; seed: one to many, non-endospermic Floral Formula: % K(5) C1+2+(2) A(9)+1 G1 Economic importance Many plants belonging to the family are sources of pulses (gram, arhar, sem, moong, soyabean; edible oil (soyabean, groundnut); dye (Indigofera); fibres (sunhemp); fodder (Sesbania, Trifolium), ornamentals (lupin, sweet pea); medicine (muliathi). 5.9.2 Solanaceae It is a large family, commonly called as the ‘potato family’. It is widely distributed in tropics, subtropics and even temperate zones (Figure 5.22). Vegetative Characters Plants mostly herbs, shrubs and rarely small trees Stem: herbaceous rarely woody, aerial; erect, cylindrical, branched, solid 2021-22 80 BIOLOGY (d) (b) (c) (a) (e) (f) Figure 5.22 Solanum nigrum (makoi) plant : (a) Flowering twig (b) Flower (c) L.S. of flower (d) Stamens (e) Carpel (f) Floral diagram or hollow, hairy or glabrous, underground stem in potato (Solanum tuberosum) Leaves: alternate, simple, rarely pinnately compound, exstipulate; venation reticulate Floral Characters Inflorescence : Solitary, axillary or cymose as in Solanum Flower: bisexual, actinomorphic Calyx: sepals five, united, persistent, valvate aestivation Corolla: petals five, united; valvate aestivation Androecium: stamens five, epipetalous Gynoecium: bicarpellary obligately placed, syncarpous; ovary superior, bilocular, placenta swollen with many ovules, axile Fruits: berry or capsule Seeds: many, endospermous Floral Formula: ⊕ Economic Importance Many plants belonging to this family are source of food (tomato, brinjal, potato), spice (chilli); medicine (belladonna, ashwagandha); fumigatory (tobacco); ornamentals (petunia). 2021-22  MORPHOLOGY OF FLOWERING PLANTS 81 5.9.3 Liliaceae Commonly called the ‘Lily family’ is a characteristic representative of monocotyledonous plants. It is distributed world wide (Figure 5.23). Vegetative characters: Perennial herbs with underground bulbs/corms/ rhizomes Leaves mostly basal, alternate, linear, exstipulate with parallel venation Floral characters Inflorescence: solitary / cymose; often umbellate clusters Flower: bisexual; actinomorphic Perianth tepal six (3+3), often united into tube; valvate aestivation Androecium: stamen six, 3+3, epitepalous Gynoecium: tricarpellary, syncarpous, ovary superior, trilocular with many ovules; axile placentation Fruit: capsule, rarely berry Seed: endospermous Floral Formula: Br ⊕ P(3+3) A3+3 G(3) Economic Importance Many plants belonging to this family are good ornamentals (tulip, Gloriosa), source of medicine (Aloe), vegetables (Asparagus), and colchicine (Colchicum autumnale). (b) (c) (d) (a) Figure 5.23 Allium cepa (onion) plant : (a) Plant (b) Inflorescence (c) Flower (d) Floral diagram 2021-22 82 BIOLOGY SUMMARY Flowering plants exhibit enormous variation in shape, size, structure, mode of nutrition, life span, habit and habitat. They have well developed root and shoot systems. Root system is either tap root or fibrous. Generally, dicotyledonous plants have tap roots while monocotyledonous plants have fibrous roots. The roots in some plants get modified for storage of food, mechanical support and respiration. The shoot system is differentiated into stem, leaves, flowers and fruits. The morphological features of stems like the presence of nodes and internodes, multicellular hair and positively phototropic nature help to differentiate the stems from roots. Stems also get modified to perform diverse functions such as storage of food, vegetative propagation and protection under different conditions. Leaf is a lateral outgrowth of stem developed exogeneously at the node. These are green in colour to perform the function of photosynthesis. Leaves exhibit marked variations in their shape, size, margin, apex and extent of incisions of leaf blade (lamina). Like other parts of plants, the leaves also get modified into other structures such as tendrils, spines for climbing and protection respectively. The flower is a modified shoot, meant for sexual reproduction. The flowers are arranged in different types of inflorescences. They exhibit enormous variation in structure, symmetry, position of ovary in relation to other parts, arrangement of petals, sepals, ovules etc. After fertilisation, the ovary is modified into fruits and ovules into seeds. Seeds either may be monocotyledonous or dicotyledonous. They vary in shape, size and period of viability. The floral characteristics form the basis of classification and identification of flowering plants. This can be illustrated through semi-technical descriptions of families. Hence, a flowering plant is described in a definite sequence by using scientific terms. The floral features are represented in the summarised form as floral diagrams and floral formula. EXERCISES 1. What is meant by modification of root? What type of modification of root is found in the: (a) Banyan tree (b) Turnip (c) Mangrove trees 2. Justify the following statements on the basis of external features: (i) Underground parts of a plant are not always roots. (ii) Flower is a modified shoot. 3. How is a pinnately compound leaf different from a palmately compound leaf? 4. Explain with suitable examples the different types of phyllotaxy. 2021-22 MORPHOLOGY OF FLOWERING PLANTS 83 5. Define the following terms: (a) aestivation (b) placentation (c) actinomorphic (d) zygomorphic (e) superior ovary (f) perigynous flower (g) epipetalous stamen 6. Differentiate between (a) Racemose and cymose inflorescence (b) Fibrous root and adventitious root (c) Apocarpous and syncarpous ovary 7. Draw the labelled diagram of the following: (i) gram seed (ii) V.S. of maize seed 8. Describe modifications of stem with suitable examples. 9. Take one flower each of the families Fabaceae and Solanaceae and write its semi-technical description. Also draw their floral diagram after studying them. 10. Describe the various types of placentations found in flowering plants. 11. What is a flower? Describe the parts of a typical angiosperm flower. 12. How do the various leaf modifications help plants? 13. Define the term inflorescence. Explain the basis for the different types inflorescence in flowering plants. 14. Write the floral formula of a actinomorphic, bisexual, hypogynous flower with five united sepals, five free petals, five free stamens and two united carples with superior ovary and axile placentation. 15. Describe the arrangement of floral members in relation to their insertion on thalamus. 2021-22