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Morphology of Flowering Plants, , , , , , Morphology (Gr. Morphos = Form; logos = Study) is the, branch of science which deals with the study of form and structure., In botany, it generally means the study of external features, forms, and relative positions of different organs on plants., , Parts of a flowering plant : Flowering plants consist of, root, stem, leaves, flower, fruits and seeds., , The root, , , , ‘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 soll. 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) Itis 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 aquaiic plants lke Pistia, Lemna and, , Eichhomia instead of root caps, they have root pockets for buoyancy., ‘The root capsare absent in parasites and mycorthizal 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) Regton of cell elongation : It lies behind the growing, point. Cells ofthis region lose power of division. The cells elongate due, to vacuolation Le,, 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) : [n this region, elongated cells are differentialed, into permanent tissues depending, upon the functions they have to, perform. 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., , , , Fig : 2.1-1 Regions of the root, Types of root, , Tap rast : Tap root is the primary root which develops from, the elongation of the radicle of embryo and persists throughout the, life of plant. It forms lateral brenches or secondary roots which are, further branched to form tertiay roots. Thus tap root along with its, branches Le., secondary and tertiary roots form tap roct system., , 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.

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Modification of roots, , Sometimes the root performs functions other than fixation,, absorption and conduction so get modified structurally, Both tap, roo's 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) Conteal : The swollen root is broad at the base and tapers, ‘gradually towards the apex giving a shape of cone, eg, Carrot,, , (ii) Fusiform : The root is swollen in the middle and narrow, towards both its base e.g., Radish (Rophanus sativus),, , (ili) 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., Tumip (Brassica napus, vern, Shalgam) and Beet (Beta vulgaris,, vern, Chukandar)., , , , Fig :2.1-2 Tap root modifications (a) Fusiform, (b) Conical (c) Napiform (d) Tuberous, , (iv) Tuberous : The storage root having no definite shape is, called tuberous, .e.g., Mirabilis jalapa (4 O'clock plant)., , (2) Branched roots, , () Nodular roots (Tuberculaied roots) : The primary tap, roots and its branches of leguminous plants, Le., plants belonging, to sub-family papilionatae of the family leguminosae (eg, Pea,, Gram, Ground nut, Beans etc), bear nodule like swellings, called, root nodules., , They are red in colour due to the presence of leghaemoglobin. The nodules are inhabited by nitrogen fixing, bacteria called Rhizobium leguminosarum. It converts atmespheric, nitrogen into nitrates and supply them to the plant. In tun, Rhlzobtum 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., , , , Fig: 2.1-3 Pneumatophores :, (a) Plants showing pneumatophores, (W) Part of pneumatophores showing breathing pores, , 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 aetial, 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 ta store food. They are of following types :, Tuberous roots : These adventitious roots are swollen, without any definite shape e.g., jpomoea batata or (Sweet potato)., Fasciculated roots : These are tuberous roo's arising in, cluster from the base of the stem, e,g., Dahlic, Fuellia (Menow, weed), Asparagus ete., , (a), , , , fe) ©, , Fig : 2.1-4 Modification of adsentitious root : (a) Tuberous root, , , , of sweet potato (b) Fasciculated roots of dahita, (c) Nodulose, roats of mango ginger, (d) Moniliform root of Momordica,, {e) Palmate roots of Orchis, (f) Annulated roots of Ipecac, , Nodulose roots : These roots become swollen at their tips, due to eccumulation of food eg., Maranta sp. (Arrowroot),, Curcuma amanda (Mango — ginger).

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308 Morphology of Flowering Plants, , , , , , , , Moniliform or Beaded roots : These adventitious roots are, swollen at frequent intervals, Ths gives the root a beaded, appearance. eg, Portulaca (Rose moss), Momordica (Bitter, gourd), Cypenus (Guinea rush).7, , Palmate tuberous roots : In Orchis there is a pair of, succulent tuberous root, one of which perishes every year while, another new one is formed by its side. Such orchid roots may, sometimes be of palmate shape, thereiore, called palmate roots., , Annulated roots : The roots of a medicinal plant, Cephaelis,, ipecacuanha (Ipecac) yields emetine that looks like discs placed, ‘one above another, therefore, called annulated., , (2) Epiphytic roots ; These roots are also called ‘hygroscopic, roots’. These roots develop In some orchids which grow as epiphytes, upon the trunts or branches of trees, They hang freely in the air and, absorb moisture with the help of special sponge like tissue called, velamen. Velen is modification of epidennis. eg, Vanda,, Dendrobium etc., , (3) Parasitic or Haustorial or Sucking roots : The roots, of parasitic plants, which penetrate into the host tissues to absorb, nourishment, are called haustorial roots. e.g,, Cuscuta (Dodder,, Vern, Amarbel)., , (4) Saprophytie roots (Mycorrhizal roots) : The woots are, associated with fungal» hyphee either _—_ superficially, (ectomycorthizae) oF intemally (endomycohizae) for absorplion, of water and minerals, e.¢., Monotropa and Sarcocies,, , , , , , , , (5) Photosynthetic or Assimilatory roots : These are, green, aerial, adventitious roots which prepare food materials by, photo:ynthess are called photosynthetic roots or assimilatory roots, 9, Taenfopiyllum, Tropa and Tirespora. In some epiphytes like, Toeniophylum, the stem and leaves are absent. The entire plant is, represented by thin green, ribbon like rools which contain, velamen, These roots absorb moisture from the atmosphere and, manufacture food materials by photosynthes!s, , (6) Reproductive roots : Some fleshy adventitious root, develop buds which can grow into new plants. These are called, reproductive root. These roo!s serve as means of vegetative, propagation. e.g., Sweet potato, Daiilla etc., , For mechanical function, , (1) Stilt roots (Brace roots) : The aerial, adventitious, obliquely growing roots that develop from the lower nodes of the, stem to give additional support are called stilt roots. These roots, bear several large overlapping root caps called multiple root caps., eg., Sugarcane, Pandanus, Rhizophora, Sorghum and Maize., Pandanus (screw pine) is a common sea shore plant, , (2) Prop roots or Pillar or Columnar roots : These, adventitious aerial roots arise from horizontal aerial branches of the, trees like Feus benghalensis (Banyan). They grow vertically, downward, penetrate the soll, become thick and assume the, shapes of pillars. They provide support to the spreading branches, of tree. Prop roots possess lenticels for aeration., , In India, the blagest banyan tree having large number of prop, roots are found at Indian Botanical Gardens, Kolkata and Kaditi, (Andhra Pradesh)., , (3) Buttress roots : The horizontal plank like aerial,, adventitious roots that develop at the base of the stem to give, additional support are called buttress roots or ballatt roots, e.g.,, Terminal and Salmalia.., , (4) Climbing roots : The aerial adventitious roots that arise, from the nodes or internodes of weak stemmed plants to climb up, their support are called climbing roots,, eg., Pothos, Piper betel, Vanilla and, Hedera. in Pothos and Hedera,, climbing roois develop all over the, stom In Vanilla, single tendril like root, arise at each node. Hence they ate, called tendrillar roots. In Piper betel,, ‘many short branched, adventitious roots, arise at each node. These rools are, called clinging roots., , , , Fig : 2.1-5 Climbing, root of Piper betel, , (5) Floating roots ; These roots, develop from the nodes of floating aquatic plants like Jussiaea, (=Ludwigia). They store air, become inflated and sponay, project, above the level of water, make the plant light and function as, floats., , (6) Contractile or Pull roots : Some roots of plants with, underground stems contract or swell so that the aerial shoots are, kept in a proper depth in the soil. These roots are calied contractile, ‘or pul reots, e.g., Canna, Crocus, Allium, Lilium, Freesia, etc,, , , , (7) Root thorns : In aroids like Pothos and many palms, (Acanthorhiza and Iriartea) the adventitious roots become hard, and pointed hence called root thorns., , The stem, , , , ‘The stem develops from the plumule of the germinating seed., Normally itis 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 epicatyl of the embryo., , (2) itis generally erect and grows away fram the soil towards, light. Therefore, it is necatively geotropic and positively, phototropie,, , (3) The growing apex of siem 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 slem., Internode is the partion of stem between the two nodes,, , (5) The lateral organs of stem (Le.,, exogenous in origin (from cortical region)., , , , leaves and branches) are, , (6) The young stem is green and photosynthetic., (7) Hi, , (8) In mature plants, stem and its branches bear flowers, and fruits., , if present, are generally multicellular.

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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, intemodes. eg, (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 al the base of Onion and Garlic bulbs, ete, , (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 remain 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 jong, slender, flexible and very, sensitive, They twin or coll around an upright support on coming, in its contact due to a special type of growth movement called, nutation. They may coil the support io the right (anticlocinuise from, the top or sinisirorse) e.g., Convatoulus sp,, Ipomoea quamoclit, Clitoria teratea, ete. or to the left (clockwise or dextrore), €.9,, Labiab., , Climbers : The stom is weak and unable to coil around a, support, They usually climb up the support with the help of some, lasping 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 (eg,, Vitis), stem branches (e.g, Passifiora) and inflorescence, (eg., Antigonon)., , (b) Root climbers : Adventitious rools arise from the nodes, and penetrate into the upright support so that the climber climbs, up, e., Betel vine (Piper betel), Tecoma, lup, etc., , (c) Scramblers or Hook climbers : These weak siemmed, 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.,, Artabotrys), prickles on stem, (eg, Lantana), spines (eg, Climbing Asparagus) or spinous, stipules (e.g,, Zizyphus)., , (4) Lianas : These are woody perennial climbers found in, deep forests, At first, they are just lke ordinary twiners but once, they reach to the top and get sunlight, become woody. eg.,, Tinospora, Ficus, Bauhinia, Bignonia, etc., , (ii) Prostrate weak stem, , Trailers : The stem creep on the ground but roots do not, arise at the nodes, They are of three types, , (a) Procumbent : The stem creeps on the ground totally e.g.,, Tribulus, Basella, Evotuulus,, , Morphology of Flowering Plants 309, , , , {b) Decumbent : Branches, after growing horizontally for, some length, grow vertically upwards, e.g., Portulaca, Tridax,, Lindenbergia, ete., , (c} Diffuse : Branches grow profusely in all ditections, eg.,, Boerhaaia., , , , Creepers : These weak-stemmed plants grow prostrate and, develop adventitious roots from their nodes. Creepers are of, three kinds, , (a) Runners : This prostrate aerial stem has a long internode, and creeps horizontally. Axillary buds arise from nodes to form, aerial shoots and roats. e.g., Cymodon (doob grass) and Oxalis., , (b) Stofons : They are special kinds of runners which initially, grow upwards like ordinary branches and then arch down to, develop new daughter plants on coming in contact with the sol, eg., Stravbeny (Fragaria vesica), Colocasia, Peppermint (Mentha, piperita), Jasminum (Jasmine)., , (c) Offsets : They are weak, elongated, horizontal branch of, one internode that arises in the axil of a leaf. At the tp, it produces, duster of leaves above and tuft of roots below. The offset may, break off from the parent plant and aet as individual plants. They, are found usually in aquatic plants and rarely ts terrestrial plants., They are helpful for vegetative propagation. e.g., Eichhornia (water, hyacinth), Agave, Pistia., , Modification of stem, 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(verticaVoblique) 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 upwani., ‘They are shorter and stouter than, the runness. €.g,, Mentha arvensis, (mint ven. 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 ther 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 isa pit lke 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., , , , Fig :2.1-6 Sucker

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(3) Rhizome : The thizome is a thickened, underground, dorsiventral stem that grows horizontally at particular depth, within the soil, The thizome {s 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 thizomes are perennial and vegetatively propagating, structures. Itis of following types :, , (i) Rootstock : They are upright or oblique or vertical with, their tips reaching the soil surface. eg, Alocasia indica and, Banana,, , (i) Straggling : They are horizontal in position and generally, branched (Sympodial or Monopodial), ¢.9., Nelumbo nucifera, (Lotus), Zingiber officinale (Ginger), Curcuma domestica, (Turmeric), Saccharum ete., , (4) Corm : The corm is an urderground modification of main, stem with more diameter than length. 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 comms. The terminal bud of the comm is large., , Node Intemode, , , , (d), , (), Fig: 2.1-7 Underground modification of stem, , (2) Tuber s of potato (b) Rhizome of ginger, (c) Corm of colocasia (d) Bulb of onion, , 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 roo's or pull roots, the corm remains, constantly at a particular depth. The corm propagates vegetatively, by daughter corms. eg., Amorphophallus, Gladiolus, Colocasia, and Crocus (Saffron)., , (5) Bulb : A bulb is a specialized underground stem which, bears roots on it’s lower side and rosette of fleshy leef bases or, fleshy scales on the upper side. In a bulb, the stem is reduced and, , ‘becomes discoid. On the lower side of the disc adventitious roots, develop in clusters, The upper side of the disc shows compactly, ‘arranged scale leaves so as to form an underground bulb. The leaf, bases or scales become fleshy due to accumulation of food, (carbohydrates) and water. The terminal bud grows into, inflorescence or aerial shoot (scape), while some of the axillary, buds develop into daughter bulbs, Bulbs are of two types,, tunicated bulb and scaly bulb., , (i) Tunicated bulb : In tunicated bulb, the fleshy leaf bases, are arranged in a concentric manner. The entire bulb is covered by, peripheral dry membranous leaf bases called tunics, hence called, the tunieated bulb. eg., Allium cepa (Onion), Narcissus end Tulip,, ‘Compound tunicated bulbs asin Allium sativum (garlic)., , (ii) Sealy or Imbricated bulb : In scaly bulb, the fleshy, scale leaves are arranged loosely overlapping one another. Such, bulbs are not covered by any tunics, hence called naked bulbs or, scaly bulbs. e.g., Lilium bulbifera (Lily)., , Aerial stem, , (1) Tendrils : The tendrils are thin, wiry, leafless and spirally, coiled branches. The terminal part of a tendril is sensitive. It holds, the support by coiling round it. The tendrils help the weak stems to, climb the support. In some weak stemmed plants, the axillary bud, or terminal bud may modify to form tendrils which are specially, called stem tendrils. Stem tendrils are of following four types :, , (i) Axillary : e.g., Passiflora., , (ii) Extra-axillary < .g., Luffa (vem, Ghiatori), Cucurbita (vern., Kaddoo), Lagenaria (vem. Lauli)., , (iil] Apical bud tendrils :e.g., Grape Vine (Vitis vinifera)., (iv) Floral bud or Inflorescence tendrils : e.g, Antigonon., , (2) Stem thorns : The axillary buds of some plants become, arrested and get modified into stiff, sharp and pointed structures,, called thoms, They are deep seated structures having vascular, connecions with stem. Besides reducing transpiration, they protect, the plant from browsing animals. eg, Citrus, Duranta,, Bougainuillea, Pomegranate, Flacourtia, Aegle mormelos etc, In, Alhagi the thoms bear flowers., , (3) Phylloclades : The phyllodade is special modified, photosynthetic stem present mostly in xerophytes. It is green,, flattened or cylindrical structure which has distinct nodes and, internodes. Xerophytes show many adaptations to check the rate, of transpiration, Reduction of leaf size, early leaf fll, formation of, scale leaves, spines, thoms, thick cuticle, presence of fewer stornata, are some of the xerophytic characters, In such cases, the stems, ‘become flattened to carryout photosynthesis. These modified stems, are called phyllodades, Usually the phylloclades retain water in the, form of mucilage e.9., Opuntia, Casuarina, Cocoloba and Ruscus., , In Opuntia, the leaves are modified into spines and the stems, becomes fleshy leaf like phyllociade. In Casuarina the leaves are, modified into scales. The phylloclade in Ruscus Is leaf like and bear, flowers. In Cocoloba, after the modification of leaves into scales, the stem becomes ribbon like phylloclade with distinct nodes and, internodes.