Current Affairs 11th Class

Systematic position         Division      :         Angiospermae         Class            :         Dicotyledonae         Subclass     :         Gamopetalae         Series          :         Inferae         Order          :         Asterales                     Family         :         Compositae (Asteraceae)                                     (Largest family among the angiosperms) Habit : Most of the plants are annual herbs (e.g., Chrysanthemum, Lactuca, Calendula, Helianthus, Tagetes). A few are shrubs (e.g., Artemisia, Pluchea lanceolata) or rarely trees (e.g., Vernonia arborea, Wilkesia, Leucomeris). Milkamia cordata is a twiner. Root : Usually there is a tap root, but in Dahlia and Taraxacum officinale fasciculated roots are present. Stem : Stem is usually herbaceous, erect, branched, solid, fibrous and sometimes with milky latex. In Jerusalem artichoke (Helianthus tuberosus) the stem is underground and tuberous. In Baccharis, it is winged like a leaf. Leaves : Leaves are mostly alternate and occasionally opposite (e.g., Helianthus) or whorled (e.g., Eupatorium, Zinnia verticillata). They are exstipulate, petiolate, simple, pinnately or palmately lobed or compound (e.g., Dahlia, Cosmos). Venation is reticulate. Inflorescence : Inflorescence is capitulum or head with an involucre of bracts at its base. The number of flowers in each inflorescence varies from 1000 (in large flowers of Helianthus) to 1 (in Echinops). Peduncle flat on which florets are attached. Flower : Epigynous, usually pentamerous with reduction in certain whorls, hermaphrodite or unisexual complete or incomplete, tubular (actinomorphic) or ligulate (zygomorphic), bracteate or ebracteate. (1) Ray florets : Towards periphery of head, sessile bracteate, pistillate or neutral, zygomorphic, ligulate, epigynous. Calyx : Absent or hairy pappus or scaly, persistant. Corolla : Petals 5, gamopetalous, ligulate, strap shaped. Androecium : Absent. Gynoecium : Bicarpellary, syncarpous, ovary inferior, unilocular, one ovule in each locule, basal placentation, style simple narrow, stigma branched. (2) Disc florets : In the centre of head, bracteate, bisexual, actinomorphic, tubular, pentamerous, epigynous. Calyx : Absent or pappus. Corolla : Petals 5, gamopetalous, tubular. Androecium : 2 stamens, epipetalous, syngenesious, dithecous, bilobed, introrse, filament free. Gynoecium : Bicarpellary, syncarpous, ovary inferior, unilocular, single ovule in the locule, basal placentation, style single, short, stigma bifid. (3) Neutral florets : Androecium and gynoecium both are absent. Remaining structures are similar to ray floret and disc florets. Fruit : Cypsella. Seed : Exalbuminous. Floral formula : Ray florets : Disc florets : Neutral florets : \[%\,\text{or}\,\oplus \,{{K}_{\text{0}}}\,{{C}_{\left( 5 \right)}}\,{{A}_{0}}\,{{G}_{0}}\]  

The arrangement of veins in the lamina of a leaf is called venation. The veins are the hard structures consisting of xylem and pholem. The veins give mechanical strength and shape to the lamina. Angiosperms exhibit two types of venation. (1) Reticulate venation In this type, the lateral veins divide and redivide to form many veinlets. These veinlets are arranged in a net like fashion or reticulum. Reticulate venation is the characteristic feature of dicotyledons. But exceptionally some monocotyledons also show reticulate venation. e.g., Smilax, Alocasia and Dioscorea etc. Reticulate venation is of two types : (i) Unicostate or Pinnate venation : This type of venation is characterized by the presence of a single strong midrib that extends upto the apex of lamina. The midrib produce lateral veins on either side which divide repeatedly. e.g., Ficus and Mangifera. (ii) Multicostate or Palmate venation : Here more than one prominent veins start from the base of the lamina and proceed upwards. The lateral veinlets, arising from main veins, form network. Multicostate venation is of two types : (a) Convergent : When the prominent veins converge towards the apex of lamina. e.g., Zizyphus and Cinnamonum camphora (kapoor), etc. (b) Divergent : When the prominent veins spread out towards the margins. e.g., Papaya, Ricinus, Cucurbita etc. (2) Parallel or Striate venation In this type, veins and veinlets run parallel to each other. Parallel venation is the characteristic feature of monocotyledons. Exceptionally few dicots show parallel venation, e.g., Calophyllum and Eryngium. It is of two types : (i) Unicostate or Pinnate venation : The leaf lamina possesses single prominent vein which gives rise to a large number of lateral veins. All the lateral veins run parallel towards margin. e.g., Banana, Canna, Curcuma etc. (ii) Multicostate or Palmate venation : The leaf lamina possesses several prominent veins which run parallel to each other. It is of two types : (a) Convergent : The prominent veins run parallel to each other and converge at the apex. e.g., Sugarcane, Maize, Wheat, Bambooes and Grasses. (b) Divergent : All the prominent veins of leaf lamina spread out towards the margin. e.g., Fan palm.

The stem develops from the plumule of the germinating seed. Normally it is the aerial part of the plant body. Characteristics of stem (1) Stem is an ascending axis of the plant and develops from the plumule and epicotyl of the embryo. (2) It is generally erect and grows away from the soil towards light. Therefore, it is negatively geotropic and positively phototropic. (3) The growing apex of stem bears a terminal bud for growth in length. (4) In flowering plants, stem is differentiated into nodes and internodes. A node occurs where leaves are attached to the stem. Internode is the portion of stem between the two nodes. (5) The lateral organs of stem (i.e., leaves and branches) are exogenous in origin (from cortical region). (6) The young stem is green and photosynthetic. (7) Hair, if present, are generally multicellular. (8) In mature plants, stem and its branches bear flowers and fruits. Diverse forms of stem (1) Reduced stems : In some plants, the stem is in the form of a reduced small disc which is not differentiated into nodes and internodes. e.g., (a) A reduced green-coloured disc-like stem lies just above the base of fleshy roots of Radish, Carrot and Turnip ; (b) Green-coloured small discoid stem occurs in free-floating Lemna, Spirodela and Wolffia; (c) Highly reduced non-green discoid stem occurs at the base of Onion and Garlic bulbs, etc. (2) Erect stems : Majority of angiosperms possess upright, growing-ascending, vertically-erect stems. They are fixed in the soil with the help of roots. (3) Weak stems : They are thin, soft and delicate which are unable to remains upright without any external support. They are of two types : upright weak stems and prostrate weak stems. (i) Upright weak stem Twiners : The stems are long, slender, flexible and very sensitive. They twin or coil around an upright support on coming in its contact due to a special type of growth movement called nutation. They may coil the support to the right (anticlockwise from the top or sinistrorse) e.g., Convolvulus sp., Ipomoea quamoclit Clitoria ternatea, etc. or to the left (clockwise or dextrorse), e.g., Lablab. Climbers : The stem is weak and unable to coil around a support. They usually climb up the support with the help of some clasping or clinging structure. They are of four types : (a) Tendril climbers : Tendrils are thread like green structure which help in climbing the plants. They may be modified stem (e.g., Vitis), stem branches (e.g., Passiflora) and inflorescence (e.g., Antigonon). (b) Root climbers : Adventitious roots arise from the nodes and penetrate into the upright support so that the climber climbs up, e.g., Betel vine (Piper betel), Tecoma, Ivy, etc. (c) Scramblers or Hook climbers : These weak stemmed plants slowly grow over other bushes and rest there. They attain this position with the help of curved prickles (e.g., Rose), curved hooks on flowering peduncle (e.g., Artabotrys), prickles on stem (e.g., Lantana), spines (e.g., Climbing Asparagus) or spinous stipules more...

The root is usually an underground part of the plant which helps in anchorage of plant in soil and absorption of water and minerals from the soil. The root with its branches is known as the root system. Characteristics of the root (1) The root is the descending portion of the plant axis and is positively geotropic and negatively phototropic. (2) It is non-green or brown in colour. (3) The root does not bear nodes, internodes, leaves and true buds. (4) Usually the root tip is protected by a root cap. (5) The root bears unicellular root hairs. (6) Lateral roots arise from the root which are endogenous in origin (arise from pericycle). Parts of the root (1) Region of root cap : The tip of the root is called calyptra or root cap. It is for protection of root tip against any injury. It is formed from meristem called calyptrogen. Pandanus is the only plant with multiple root caps. In the aquatic plants like Pistia, Lemna and Eicchornia instead of root caps, they have root pockets for buoyancy. The root caps are absent in parasites and mycorrhizal roots. (2) Region of cell formation or meristematic zone : This region of cell division lies protected below the root cap. It comprises of closely arranged, small, thin walled and isodiamatric cells which have dense protoplasm. Vacuoles of the cells are either reduced in size or absent. (3) Region of cell elongation : It lies behind the growing point. Cells of this region lose power of division. The cells elongate due to vacuolation i.e., formation of vacuoles. This region chiefly concerns with absorption of minerals along with some amount of water. (4) Region of cell differentiation or maturation (Root hair zone) : In this region elongated cells are differentiated into permanent tissues depending upon the functions they have to performs. It lies adjacent to the meristematic region some cell of the outermost layer of cells in this region develop root hairs. Most of the water absorption occurs through this region.       Types of root  Tap root : The tap root system develops from radicle of the germinating seed. It is also called the normal root system. The tap root system is present in dicotyledonous plants. Adventitious root : The root system that develops from any part of the plant body other than the radicle is called the adventitious root system. It is mostly seen in monocotyledonous plants. In grasses, fibrous root system is present.

The leaf is a green, flat, thin, expanded lateral appendage of stem which is borne at a node and bears a bud in its axil. It is exogenous in origin and develops from the leaf primordium of shoot apex. The green colour of leaf is due to presence of the photosynthetic pigment – chlorophyll which helps plants to synthesize organic food. The green photosynthetic leaves of a plant are collectively called foliage. Characteristics of leaf (1) The leaf is a lateral dissimilar appendage of the stem. (2) A leaf is always borne at the node of stem. (3) The growth of leaf is limited. (4) The leaves do not possess any apical bud or a regular growing point. Parts of a typical leaf The leaf consists of three parts namely, leaf base (usually provided with a pair of stipules), petiole and leaf blade or lamina. (1) Leaf base (Hypopodium) : Leaf base is the lower most part of the leaf meant for attachment. It acts as a leaf cushion. Some times leaf base shows different variations as follows : (i) Pulvinus leaf base : In members of leguminosae the leaf base is swollen. Such swollen leaf bases are called pulvinus leaf bases as seen in mango leaves. It helps in seismonastic movements (e.g., Mimosa pudica) and nyctinastic movements (e.g., Enterobium, Arachis, Bean).     (ii) Sheathing leaf base : In grasses and many monocots, the leaf base is broad and surrounds the stem as an envelope, such a leafbase is called sheathing leaf base. e.g., Sorghum, Wheat and Palms. In grasses (Sorghum, Wheat etc.) the sheathing leaf base protects the intercalary meristem. (iii) Amplexicaul : Leaf base completely encircles the stem. e.g., Polygonum. (iv) Modified leaf base : The leaf bases in few plants perform accessory functions and show modifications. In Allium cepa (Onion), the leaf bases store food materials and become fleshy. In Platanus and Robenia, the leaf bases protect the axillary buds and grow around them to form cup like structures. (v) Stipule : The stipules are the small lateral appendages present on either side of the leaf base. They protect the young leaf or leaf primordia. Leaves with stipules are called stipulate and those without them are called exstipulate. The stipules are commonly found in dicotyledons. In some grasses (Monocots) an additional outgrowth is present between leaf base and lamina. It is called ligule. The leaves having ligules are called ligulate. Types of stipules : Depending upon the structure and position various kinds of stipules are recognized. Free lateral stipules : A pair of freely arranged stipules present on either side of the leaf base are called free lateral stipules, e.g., Hibiscus and Cotton. Adnate stipules : The two stipules that fuse with the leaf base or petiole on either side are called adnate stipules, e.g., Arachis  and Rose. Inter petiolar stipules : Stipules present in between the petioles of opposite leaves, e.g., Ixora and Hamelia. Axillary stipules : more...

In angiosperms, always the branches are produced by the growth of axillary buds or lateral buds. This type of branching is known as lateral branching. The lateral branching is classified into two kinds racemose and cymose. (1) Racemose branching : In this type of branching, the terminal (or apical) bud of the main stem grows indefinitely and the axillary buds grow out into lateral branches in acropetal succession. This type branching is also called monopodial branching. Due to monopodial branching the shoot system of plant appears conical e.g., Eucalyptus, Polyalthia (Ashoka tree). (2) Cymose branching : In cymose branching the terminal bud is active for a short period and becomes modified into some permanent structures like tendrils, thorns of flowers etc. Due to the terminal bud modification the growth of the main stem is definite. This is also called sympodial branching. Further growth in the plant is carried by one or more axillary buds. Cymose branching may be of three types : (i) Uniparous or Monochasial type : In uniparous type of branching only one lateral branch is produced at each time below the modified terminal bud. Here the successive lateral branches that are formed unite to form a stem. Such a stem is called false axis or sympodium. The uniparous branching is of two kinds, helicoid and scorpoid. (a) Helicoid branching : If the successive lateral branches develop on one side it is called helicoid branching. e.g., Saraca, Canna and Terminalia. (b) Scorpioid branching : If the successive lateral branches develop on either side alternately, it is called scorpioid branching, e.g., Cissus, Gossypium and Carissa.     (ii) Biparous or Dichasial type : When the activity of terminal bud stops, further growth of plant takes place by two lateral branches, e.g., Viscum (Mistletoe), Silene, Stellaria, Mirabilis jalapa (Four O’ clock), Dianthus (Pink), Carissa carandas (Karonda), etc. (iii) Multiparous or Polychasial type : When the activity of terminal bud stops, further growth of plant takes place by a whorl of three or more axillary branches. The axis is said to be multipodial, e.g., Euphorbia tirucalli, Croton, Nerium odoratum (Oleander).

Underground stem The underground stems lack green colour because of their geophillous nature. They can be identified as stems because of the presence of nodes, internodes, scale leaves, buds and branches. Based on the type of growth (transverse/vertical/oblique) and the part that stores food (main stem/ branch/ leaf base), the underground stems are classified into several types : (1) Sucker : This is a sub aerial branch that arises from the main stem. Initially it grows horizontally below the soil surface and later grows obliquely upward. They are shorter and stouter than the runners. e.g., Mentha arvensis (mint vern. Podina) and Chrysanthemum.     (2) Stem tuber : Stem tuber is the tuberous tip of an underground branch. It occurs beneath the soil at any depth. The axillary branches (stolons) that are produced near the soil surface grow into the soil and their tip become swollen due to accumulation of starch and proteins e.g., Solanum tuberosum (potato). In potato, the stem nature is evident by the presence of ‘eyes’ on its brownish corky surface. Each eye is a pit like structure and represents the node. Axillary bud is situated in the pit of the eye. The stem tubers are differentiated from the tuberous roots by the presence of vegetatively propagating eyes. (3) Rhizome : The rhizome is a thickened, underground dorsiventral stem that grows horizontally at particular depth within the soil. The rhizome is brown in colour. It can be distinguished from the modified root by the presence of nodes, internodes, terminal bud, axillary bud and scale leaves. The terminal bud develops aerial shoot that bears inflorescence. Adventitious roots develop on the ventral surface of the rhizome. The rhizomes are perennial and vegetatively propagating structures. It is of following types : (i) Rootstock : They are upright or oblique with their tips reaching the soil surface. e.g., Alocasia indica and Banana. (ii) Straggling : They are horizontal in position and generally branched (Sympodial or Monopodial), e.g., Nelumbo nucifera (Lotus), Zingiber officinale (Ginger), Curcuma domestica (Turmeric), Saccharum etc. (4) Corm : The corm is an underground modification of main stem. It grows vertically at particularly depth in the soil. The corm stores food materials and becomes tuberous. It is non green in colour and conical, cylindrical or flattened in shape. The corm bears scale leaves at each node. In the axils of these scale leaves axillary buds arise which grow into daughter corms. The terminal bud of the corm is large.     It grows into aerial shoot and bears leaves and flowers. Adventitious roots normally develop from the base or all over the body of the corm. With the help of some special adventitious roots called the contractile roots or pull roots, the corm remains constantly at a particular depth. The corm propagates vegetatively by daughter corms. e.g., Amorphophallus, Colocasia and Crocus (Saffron). (5) Bulb : A bulb is a specialized underground stem which more...

Sometimes the root performs other functions other than fixation, absorption and conduction so get modified structurally. Both tap roots and adventitious roots may undergo such modifications. There are many types of root modifications. Modification of tap roots (1) Storage roots : In some plants, the primary tap roots are modified for storing reserve food materials. The secondary roots remain thin and they are absorptive in function. The storage roots are usually swollen and assume various forms: (i) Conical : The swollen root is broad at the base and tapers gradually towards the apex giving a shape of cone, e.g., Carrot. (ii) Fusiform : The root is swollen in the middle and narrow towards both its base e.g., Radish (Raphanus sativus). (iii) Napiform : The root is nearly globular or spherical in shape. The basal portion of root is much swollen which suddenly tapers towards the apex giving a top-shaped appearance, e.g., Turnip (Brassica napus, vern, Shalgam) and Beet (Beta vulgaris, vern. Chukandar).     (iv) Tuberous : The storage root having no definite shape is called tuberous, .e.g., Mirabilis jalapa (4 O’clock plant), (2) Branched roots (i) Nodular roots (Tuberculated roots) : The primary tap roots and its branches of leguminous plants, i.e., plants belonging to sub-family papilionatae of the family leguminosae (e.g., Pea, Gram, Ground nut, Beans etc.), bear nodule like swellings, called root nodules. They are red in colour due to the presence of leg-haemoglobin. The nodules are inhabited by nitrogen fixing bacteria called Rhizobium leguminosarum. It converts atmospheric nitrogen into nitrates and supply them to the plant. In turn Rhizobium gets nutrients and shelter from the plant. (ii) Pneumatophores or Respiratory roots : The roots of some plants growing in saline marshes (mangrove plants) suffer from the lack of oxygen. This is due to the water logged condition of the soil. To cope with this situation some root branches grow vertically upwards.     They become aerial and negatively geotropic. These roots bear many minute pores called pneumathodes (lenticels) towards their upper ends. Gaseous exchange takes place through pneumathodes. Such aerial, porous, roots which help in gaseous exchange are called breathing roots. e.g., Sonneratia, Heritiera, Rhizophora, Avicennia and Ceriops etc. and are found in sundarbans of West Bengal. For physiological or Vital functions (1) Storage roots : The roots where adventitious roots become swollen to store food. They are of following types : Tuberous roots : These adventitious roots are swollen without any definite shape e.g., Ipomoea batata or (Sweet potato). Fasciculated roots : These are tuberous roots arising in cluster from the base of the stem. e.g., Dahlia, Ruellia (Menow weed), Asparagus etc.     Nodulose roots : These roots become swollen at their tips due to accumulation of food e.g., Maranta sp. (Arrowroot), Curcuma amanda (Mango – ginger). Moniliform or Beaded roots : These adventitious roots are swollen at frequent intervals. more...

The flowers are arranged in some definite manner on the plant in each species of the flowering plants. The mode of arrangement of flowers on a specialised branch on top of the plant which bears flowers is called inflorescence. The stalk of the inflorescence is called peduncle. Depending upon the arrangement of flowers, inflorescence is classified as follows :  

It can be defined as modified dwarf shoot which is meant for sexual reproduction. It is characteristic feature of angiosperm. Parts of a typical flower : A typical flower of an angiosperm consists of four types of floral parts namely calyx, corolla, androecium and gynoecium. General description of a flower The flowers are termed pedicellate if they possess stalks and sessile if they lack them. The flower may be described as complete if it bears all the floral parts and incomplete, when one or more floral parts are absent. Flowers are called bisexual if they bear both androecium and gynoecium. The unisexual flowers have either androecium or gynoecium. The unisexual flowers may be male flowers or female flowers. The male flower are also called staminate flowers as they have stamens only. The female flowers have only the carpels and hence called pistillate flowers. Flowers with sterile sex organs are described as neutral flowers. According to the distribution of male, female and bisexual flowers, various patterns are recognized. Monoecious : Presence of male and female flowers on the same plant, e.g., Acalypha, Cocos and Ricinus. Dioecious : Presence of male and female flowers on different plants, namely, male plants and female plants. e.g., Cycas, Carica papaya and Vallisneria. Polygamous : Presence of unisexual and bisexual flowers on the same plant, e.g., Mangifera and Polygonum. Symmetry of flower The number, shape, size and arrangement of floral organs in a flower determines its symmetry. On the basis of symmetry flowers can be of the following types : Actinomorphic (Regular = Symmetrical) : Actinomorphic flowers can be divided (passing through center) by any vertical plane into two equal and similar halves. e.g., Mustard, Brinjal, Catharanthus roseus. Zygomorphic (Monosymmetrical) : Zygomorphic flowers can be divided into two equal halves by only one vertical division e.g., Pea, Larkspur, Ocimum. Asymmetrical (Irregular) : Asymmetrical flowers can not be divided into two equal halves by any vertical division. e.g., Canna, Orchids.     Arrangement of floral organs On the basis of arrangement of floral organs, three types of flowers are recognized. They are : Acyclic : Here the thalamus is conical or convex and the floral parts are spirally arranged, e.g., Water lily and Magnolia. Cyclic : Here the floral organs are arranged in regular whorls at the nodes of the thalamus, e.g., Hibiscus and Datura. Hemicyclic (Spirocyclic) : Here some floral parts (sepals and petals) are arranged in regular whorls and the remaining parts (stamens and carpels) are arranged spirally. e.g., Annona  and Polyalthia. Number of floral parts in whorl is called the merosity. There are two kinds of flowers based on the merosity of the flower. They are isomerous flowers and anisomerous flowers. If the number of sepals, petals, stamens and carpels of flower is equal, such flowers are called isomerous flowers. Dimerous : Two floral parts in each whorl. e.g., Poppy flower. Trimerous : Three floral parts in each whorl. e.g., Monocot flowers (Liliaceae). Tetramerous : Four more...


You need to login to perform this action.
You will be redirected in 3 sec spinner

Free
Videos