Current Affairs 11th Class

Systematic position         Division      :         Angiospermae         Class            :         Dicotyledonae         Subclass     :         Polypetalae         Series          :         Thalamiflorae         Order          :         Malvales                      Family         :         Malvaceae Habit : Plants are annual herbs (e.g., Malva, Sida, Malvastrum, Urena) shrubs (e.g., Hibiscus rosa-sinensis, H. mutabilis) or rarely trees (e.g., Kydia, Bombax). Root : Branched tap root system. Stem : Stem is erect, aerial, herbaceous or woody, usually solid, cylindrical and branched. Herbaceous portion of the stem is covered with stellate and scaly hairs; the woody part is fibrous. Plants usually have some mucilaginous substance. Leaves : Leaves are alternate and stipulate (stipules 2, free lateral and often Caducous). They are simple and petiolate, lamina is sometimes palmately lobed (e.g., Gossypium) or digitate (e.g., Bombax). Venation is multicostate reticulate. Inflorescence : Usually the flowers are solitary axillary or terminal. Occasionally, they are in panicle raceme (e.g., Kydia). Flowers : Flowers are bracteate or ebracteate, actinomorphic, bisexual (unisexual in Kydia), pentamerous and hypogynous. The number of bracteoles varies from 3 to many, they form a whorl of epicalyx below the calyx. Sometimes the epicalyx is absent (e.g., Sida and Abutilon). Calyx : Sepals 5, gamosepalous (connate at the base but free at the tip) and show valvate aestivation. Usually epicalyx present. Corolla : Petals 5, polypetalous (slightly fused at the base), usually adnate at the base to the staminal tube. They show twisted or imbricate aestivation. Androecium : It has indefinite stamens. They are monadelphous. Filaments of the stamens are united to form a long staminal tube or staminal column which encloses the style. Basal part of the staminal tube is fused with the petals; thus stamens are epipetalous. Anthers are monothecous, reniform, transversely attached to the filament and extrorse. In Bombax stamens are polyadelphaous. Gynoecium : It is 2 to many carpellary. It is bicarpellary in Plagianthus, tricarpellary in Kydia, pentacarpellary in Hibiscus and Sida, ten carpellary in Althaea rosea and 15 – 20 carpellary in Abutilon indicum. All the carpels are fused (syncarpous) to form a single ovary. Ovary is superior, multilocular with one or more ovules in each chamber. The placentation is axile. Style is usually long and enclosed in the staminal tube. Stigmas are as many as the number of carpels or double the number of carpels. Fruit : Fruit is a loculicidal capsule (e.g., Gossypium, Hibiscus), schizocarpic capsule (e.g., Abutilon, Sida) or a berry (e.g., Malvastrum). Seed : Seeds are albuminous. In Gossypium the seeds are pubescent, i.e., covered with hairs. Floral formula :

Systematic position         Division      :         Angiospermae         Class            :         Monocotyledonae         Series          :         Coronarieae         Order          :         Liliales         Family         :         Liliaceae Habit : Usually perennial herbs growing by means of rhizomes (e.g., Aloe, Polygonatum), bulbs (e.g., Lilium, Allium) and corms (e.g., Colchicum). Some herbs are annual (e.g., Asphodelus). Shrubs occur in Aloe, Agave, Yucca (Dagger plants, Adam’s Needle), Dracaena (Dragon plant), and Ruscus (Butcher’s Broom). They mostly grow in arid areas and are hence xerophytic (e.g., Aloe, Yucca). Xanthorrhoea of Australia is tree-like. Climbers are seen in Smilax, Gloriosa and species of Asparagus.                           Root : Adventitious, fibrous or tuberous (e.g., Asparagus). Stem : Erect or climbing as Smilex, branched or unbranched, herbaceous, phylloclade as Ruscus. Cladode as Asparagus, Bulb as Allium cepa. Leaves : Radical or cauline and ramal show various types of phyllotaxy (alternate, opposite or whorled), exstipulate, stipulate in Smilax where the stipules are prolonged into tendrils, sessile or petiolate with sheathing leaf bases, venation parallel but reticulate in Smilax, leaves may be scaly, leathery, fleshy or modified into spines (e.g., Asparagus), leaf apex is tendrillar in Gloriosa. The leaves of Phormium tenax (New Zealand Hemp) are 3 metres long and 10 cm broad. Inflorescence : Recemose, sometimes solitary (e.g., Tulipa, Gloriosa) or umbellate condensed cymes (umbel cyme), e.g., Onion. In several cases the inflorescence possesses a leafless peduncle called scape. Flower : Bracteate or ebracteate, pedicellate, regular, actinomorphic, zygomorphic in a few cases (e.g., Gilliesia), complete or incomplete, perfect, unisexual in Smilax and Ruscus, hypogynous, generally pentacyclic, trimerous (rarely bimerous or tetramerous). Accessory floral organs undifferentiated and collectively called perianth. Perianth : Tepals 6, in two whorls of 3 each, free or fused, sepaloid or petaloid, scarious or membranous, aestivation valvate or imbricate, distinguished into calyx and corolla in Trillium. Androecium : Stamens 6 (3 in Ruscus, \[912\] in Tofieldia), free (polyandrous) or monadelphous (e.g., Ruscus), arranged in two whorls, antiphyllous (antitepalous), may be epiphyllous (or epitepalous), anthers fixed variously (basifixed, dorsifixed, versatile), dehiscence longitudinal or by pores. Gynoecium : Tricarpellary, syncarpous, ovary superior, trilocular with 2-many ovules in each locules, placentation axile, rarely parietal, styles united or separate, stigma free or fused, trilobed. Fruit : A capsule (e.g., Asphodelus, Gloriosa) or berry (e.g., Asparagus). Seed : Endospermic and monocotyledonous. Floral formula :

Systematic position Division      :         Angiospermae         Class            :         Dicotyledonae         Subclass     :         Polypetalae         Series          :         Calyciflorae         Order          :         Rosales         Family         :         Leguminosae Habit : Annual or biennial, herb, shrub or tree. Root : Tap root system. Stem : Erect or creeping, solid or weak. Leaf : Alternate or whorled, stipulate, petiolate, simple or usually compound, reticulate venation. On the basis of inflorescence and flower characters, this family is divided in to 3 subfamilies :   Subfamily - Papilionatae (Papilionaceae) Inflorescence : Racemose or solitary axillary. Flower : Bracteate or ebracteate rarely bracteolate (e.g., Arachis), pedicellate, complete, irregular, zygomorphic, hypogynous, pentamerous. Calyx : Sepals 5, gamosepalous, usually campanulate, lobes unequal, rarely tubular (e.g., Cyamopsis), odd sepal anterior, may be persistent, inferior. Corolla : Petals 5, polypetalous, papilionaceous, descending imbricate aestivation, one posterior long standard, two lateral short wings, two anterior petals jointed to each other forming keel. Androecium : Stamens 10, usually diadelphous (9+1 in Lathyrus, 5+5 in Aeschynomene) or monadelphous (9 in Dalbergia, 10 in Arachis and Erythrina indica), rarely free (e.g., Sophora), nectar gland often present on the inner bases of filaments, anther lobes bilocular, dorsifixed, introrse. Gynoecium : Monocarpellary, ovary superior, unilocular with marginal placentation ovary covered by staminal tube, style bent, stigma simple or capitate. Fruit : Legume or lomentum. Floral formula :   Subfamily – Caesalpinoideae (Caesalpiniaceae)   Inflorescence : Raceme, umbel or a solitary flower. Flower : Bracteate or ebracteate, pedicellate, hermaphrodite, complete, zygomorphic, hypogynous. Calyx : Sepals 5, polysepalous, imbricate aestivation. Corolla : Petals 5, polypetalous, ascending imbricate aestivation. Androecium : 10 stamens, or staminodes are found as in Cassia, free filaments of unequal size, anther lobes bilocular, introrse, versatile. Gynoecium : Monocarpellary, unilocular, ovary superior, marginal placentation, stigma capitate. Fruit : Legume. Floral formula : or     Subfamily – Mimosoideae (Mimosaceae) Inflorescence : Head or capitulum or spike, flowers arranged in acropetal succession. Flower : Bracteate or ebracteate, sessile, hermaphrodite, complete actinomorphic, hypogynous, pentamerous. Calyx : 5 sepals (4 in Mimosa) gamosepalous, connate at the base, valvate aestivation, rarely imbricate (e.g., Parkia). Corolla : 5 petals (4 in Mimosa) gamopetalous or polypetalous, membranous, valvate aestivation. Androecium : In most of the members, stamens are indefinite and polyandrous. However, there are only 4 stamens in Mimosa pudica and 10 each in Prosopis and Dichrostachys. Filaments are long, usually connate at the base, sometimes they are coloured and gland dotted. Anthers are dithecous and introrse. Gynoecium : Monocarpellary, unilocular, ovary superior, style long, cylindrical, stigma single and capitate, marginal placentation. Fruit : Lomentum. Floral formula :  

Formation of fruit : Fruit is defined as fertilized ovary. The ovary develops into fruit. The ovary wall at maturity forms the wall of the fruit, which is known as pericarp. Sometimes, other parts of flower such as tepals, (e.g., Morus), bracts (e.g., Ananas) or thalamus (e.g., Pyrus) are also involved in the formation of fruit and such fruits are called false fruits or pseudocarps. The fate of various parts of the ovary during the formation of fruits is summarized below :   Types of fruits They are classified into three groups : Simple, aggregate and multiple or compound fruit. Simple fruits : They are formed from mono-or polycarpellary but syncarpous ovary. They may be dry or fleshy. (1) Simple dry fruits have thin, hard and dry, pericarp. They are of three kinds : (i) Dehiscent or Capsular  (ii) Achenial or Indehiscent  (iii) Schizocarpic (i) Dehiscent fruit : These fruits are dry, many seeded and split open at maturity. They are of following types : Legume or Pod : It is characteristic of the family leguminosae; developed from monocarpellary unilocular superior ovary with marginal placentation. It can open or dehisces by both ventral and dorsal sutures. e.g., in Cicer arietinum (Gram); Pisum sativum (Pea) and Phaseolus mungo (Black gram). Follicle : It is very much resembles the legume but on ripening it opens generally along the ventral suture. e.g., Calotropis, Larkspur, etc. Siliqua : The fruit is developed from bicarpellary, syncarpous and superior ovary which bears ovules on two parietal placenta. The ovary is unilocular but later becomes bilocular due to the development of a false partition wall called replum. It dehisces from the base towards the apex by both the sutures e.g., In Brassica (Mustard) and is characteristic of the family Cruciferae. Silicula : It is flattened and short in length from siliqua type, found in Iberis (Candytuft) and Capsella bursa (Shepherd’s purse). Capsule : It is mono or polycarpellary, dry dehiscent, many seeded fruit which developes from a superior or inferior ovary. It dehisces in almost all the ways i.e., longitudinal and transverse, along both the sutures. Majority of capsules show longitudinal-dehiscence which again are of different types : Loculicidal : Lines of dehiscence appear along the dorsal sutures, e.g., Gossypium herbacium (Cotton) and  Abelmoschus esculentus (Lady’s finger). Septicidal : Lines of dehiscence appear along the ventral sutures or septations of the ovaries e.g., in Viola (Pansy), Linseed (Linum). Septifragel : Lines of dehiscence along irregular lines, but the seeds remain attached to the placenta, as in Datura stramonium (Thorn apple). (ii) Achenial or Indehiscent fruits : These fruits do not burst at maturity but the seeds are liberated only by the decaying of the pericarp. These are of following types : Achene : It is small, dry one seeded fruit which develops from a superior or inferior monocarpellary ovary. In this type, the pericarp is tough but thin and free from the seed coat, e.g., in Mirabilis (four o’clock more...

Dispersal by wind (Anemochory) The wind is probably the most important agency of seed dispersal in nature. The fruits and seeds show following devices which help in dispersal by wind. Light weight and minute seeds : Seeds of some plants (e.g., Orchids) are sufficiently light and minute in size to be easily carried away to great distances by air currents. Winged seeds and fruits : Some seeds (e.g., Oroxylon, Cinchona, Moringa) or fruits (Acer, Hiptage, Terminalia, Dipterocarpus) develop one or more thin membranous wings to ensure their dispersal by wind. Parachute mechanism : In members of the family Asteraceae (Compositae) e.g., Taraxacum, Sonchus, sepals are modified into tufts of hairs called pappus. The pappus is persistent and hence found attached to even small, single seeded fruits. It acts like a parachute that allows the wind to carry them to great distances. Seeds of many nasty weeds are also dispersed by this method. Censer mechanism : In Antirrhinum (dog flower), Aristolochia, Papaver (poppy), Argemone mexicana (Prickly poppy), Nigella (love-in-a-mist), etc. the fruit is a capsule. At maturity it ruptures but the seeds do not come out. However, when the capsule is shaken violently by the wind, the seeds are scattered in all directions. In this process all the seeds do not escape together. Rolling mechanism : In some species, like Amaranthus albus, Chenopodium album, etc., plants dry out after bearing fruits and seeds. Eventually the entire plant breaks off at the base of the stem due to the force of wind and rolls over the ground, shedding the seeds all along the way. Such rolling plants are collectively known as tumble weeds. Hairs : In cotton, hairs are the outgrowth from the seed coat and occur all along its surface. Persistent styles : Clematis, Naravelia, Geranium etc. have persistent and feathery styles which help the fruit to be easily carried by wind. Balloon like appendages : In plants like Cardiospermum and Nicandra fruits develop balloon like appendages which make the fruits light to be easily carried by wind. Dispersal by water (Hydrochory) Fruits and seeds, specialized for dispersal by water, generally develop some kind of floating devices and a protective covering which makes them water resistant. e.g., fibrous mesocarp in Coconut, spongy thalamus in Lotus. Dispersal by animals (Zoochory) Fruit and seeds dispersed by animals can be divided into following three categories on the basis of their adaptive features : Hooked fruits and seeds : The surface of many fruits is covered with hooks (e.g., Xanthium, Urena), barbs (e.g., Andropogon), spines (e.g., Tribulus), bristles (e.g., Pupalia), or stiff hairs (e.g., Aristida), by means of which they adhere to the body of animals or clothes of human beings and they are carried unwarily from one place to another.                 Sticky fruits and seeds : Some fruits like those of Boerhaavia, Cleome, and Plumbago have sticky glands by which they adhere to the fur of grazing animals and are thus dispersed. Seeds of Viscum (mistletoe), Loranthus, etc. have a viscid layer which adhere more...

Systematic position         Division      :         Angiospermae         Class            :         Dicotyledonae         Subclass     :         Polypetalae         Series          :         Calyciflorae         Order          :         Passiflorales         Family         :         Cucurbitaceae Habit : These are trailing or climbing annuals or perennial herbs. Rarely they are shrubs (e.g., Acanthosicyos) or trees (e.g., Dendrosicyos). Stem : Herbaceous, branched, pentangular, fistular, tendrils in axil of leaf or opposite to leaves. The morphological nature of tendril is of dispute. Leaves : Leaves are cauline and ramal. They are alternate, exstipulate, simple, petiolate and cordate (e.g., Cucurbita maxima, Coccinia grandis) or deeply palmately lobed (e.g., Luffa cylindrica, Cyclanthera pedata). Venation is reticulate multicostate. Inflorescence : Flowers are either solitary axillary (e.g., Cucurbita, Coccinia) or in cymose clusters (e.g., Cucumis, male flowers of Luffa). Most of the members of the Cucurbitaceae are monoecious but a few are dioecious (e.g., Coccinia cordifolia, Trichosanthes dioica). Flower : Flowers are bracteate or ebracteate, pedicellate, unisexual, incomplete actinomorphic, pentamerous and epigynous. Schizopepon is the only exception which has bisexual flowers. Male flower Calyx : Sepals 5, gamosepalous, quincuncial aestivation. Corolla : Petals 5, gamopetalous, campanulate or rotate, imbricate or valvate aestivation. Androecium : Stamens 5, polyandrous as in Fevillea, or \[(2)+(2)+1\] as in Momordica, anthers twisted, alternate to petals, sometimes epipetalous, dehiscence longitudinal. Gynoecium : Absent. Female flower Calyx : Similar to male flower. Corolla : Similar to male flower.                 Androecium : Absent but sometimes 2, 3 or 5 staminodes present. Gynoecium : Tricarpellary, syncarpous, unilocular, ovary inferior, numerous ovules, parietal placentation but looks as axile placentation, style is simple, stigma 3. Fruit : Pepo (variation of berry). Seeds : Exalbuminous. Male flower : Female flower :

Systematic position         Division      :         Angiospermae         Class            :         Dicotyledonae         Subclass     :         Polypetalae         Series          :         Thalamiflorae         Order          :         Parietales         Family         :         Cruciferae (Brassicaceae) Habit : Annual, biennial or perennial herbs. Farsetia jacquemontii is an undershrub. The plants possess pungent juice having sulphur-containing glucosides. Root : Tap root alongwith hypocotyl is swollen in Radish (Raphanus sativus) and Turnip (Brassica rapa). Stem : Erect, cylindrical, hairy or glabrous, herbaceous or rarely woody. It is reduced in the vegetative phase in Radish and Turnip. The stem is swollen in Kohlrabi (Knol-Kohl = Ganthgobi, Brassica oleracea var. gongylodes). Axillary buds enlarged in Brussel’s Sprouts ( = Button gobhi) or Brassica oleracea  var. gemmifera. Brassica oleracea var. capitata (Cabbage) has the largest terminal bud. Leaves : Radical, cauline and ramal, alternate or sub-opposite but forming rosettes when radical, exstipulate with sheathing leaf base, sessile simple or rarely compound (e.g., Nasturium officinale), hairy. Bulbils occur in the leaf axils of Dentaria bulbifera and on the leaves of Cardamine pratensis. Inflorescence : Flowers are usually arranged in corymbose racemes. Occasionally they are in corymbs (candituft). Flower : Ebracteate or rarely bracteate (e.g., Rorippa montana), pedicellate, complete, perfect, regular, actinomorphic, rarely zygomorphic (e.g., Iberis, Teesdalia), tetramerous or bimerous, hypogynous (perigynous in Lepidium), cyclic, cruciform. Calyx : Sepals 4, polysepalous, aestivation imbricate, generally arranged in two whorls, outer of antero-posterior sepals and inner of lateral sepals, lateral sepals generally saccate or pouched at the base, green or petaloid, inferior. Corolla : Petals 4, polypetalous, arranged in one whorl and alternate with sepals, often with long claws and spread out in the form of a Greek cross. This arrangement of petals which is characteristic of the family is known as the cruciform arrangement and corolla is described as cruciform corolla, valvate aestivation. Petals reduced or absent in Lepidium and Rorippa. Androecium : Stamens 6, (four in Cardamine hirsuta, two in Coronopus didymus, 16 in Megacarpaea), free (polyandrous), tetradynamous, arranged in two whorls, outer of two short lateral stamens while the inner whorl is made up of 4 long stamens arranged in two median pairs, anthers basifixed or dorsifixed, dehiscence longitudinal. Green nectaries are often associated with the bases of stamens. Gynoecium : Bicarpellary (tricarpellary in species of Lepidium, tetracarpellary in Tetrapoma and Tropidocarpum), syncarpous, carpels placed transversely, ovary superior, placentation parietal, ovary bilocular due to the presence of a false septum called replum, style short, stigma capitate, simple or lobed. Fruit : Siliqua or silicula, lomentaceous siliqua occurs in radish. Seed : Non-endospermic, often oily. Floral formula :  Ebr     

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...


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