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The root is usually an underground part of the plant which helps in fixation and absorption of water. The root with its branches is known as the root system.
(i) The root is the descending portion of the plant axis and is positively geotropic.
(ii) It is non-green or brown in colour.
(iii) The root is not differentiated into nodes and internodes.
(iv) As a rule the root does not bear leaves and true buds.
(v) Usually the root tip is protected by a root cap.
(vi) The root bears unicellular root hairs.
(vii) Lateral roots arise from the root which are endogenous in origin (arises from pericycle).
(2) Parts of the root : From the tip of the root upwards, the following parts can be traced in root.
(i) 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, Lemma and Eicchornia instead of root caps, they have root pockets for buoyancy. The root caps are absent in parasites and mycorrhizal roots.
(ii) Region of cell elongation : The region of cell division lies partly within and partly beyond the root cap. This is the meristematic region of the root which produces new cells by cell division.
(iii) Region of root hairs : This region is present above the region of elongation. In this region the epidermal cells produce many tubular, unicellular outgrowths called root hairs. This is also called Piliferous region. Water absorption mostly takes place through this region. The root hairs are absent in many aquatic plants.
(iv) Region of maturation : Above the root hair zone, mature region is present. This region consists of permanent cells. Lateral roots are produced endogenously from the mature region. Conduction of water and mineral salts takes place through this region.
(3) Types of root system : The root system is generally of two types :
(i) Tap root system
(ii) Adventitious root system
(i) Tap root system : The tap root system develops from radicle of the germinating seed. It is also called the normal root system. The radicle develops into a primary root which grows vertically downwards and become the tap root. The tap root is the true root that produces many lateral roots endogenously which grow obliquely. The tap root system is present in dicotyledonous plants.
(ii) Adventitious root system : 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. It is a type of adventitious root system. In this case the primary root formed from the radicle disappear soon. Then many slender roots develop from the base of the stem as cluster of fibres, hence called the fibrous root system. Shrub like monocots needs additional support because of the adventitious root. e.g., Stilt root in sugarcane.
(i) 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 :
(a) Conical : The swollen root is broad at the base and tapers gradually towards the apex giving a shape of cone, e.g., Carrot.
(b) Fusiform : The root is swollen in the middle and narrow towards both its base and apex giving a shape of spindle, e.g., Radish (Raphanus sativus). Half or less than half portion towards the base of fusiform root is formed by hypocotyl.
(c) 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).
(d) Tuberous : The storage root having no definite shape is called tuberous, .e.g., Mirabilis jalapa (4 O’clock plant), Trichosanthes (vern. Parwal), Echinocystis lobata (The tuberous root is lobed and weighs as much as 22 kg.).
(ii) Branched roots : They are following types :
(a) Nodular 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. This type of association between the bacterium and leguminous plant for mutual benefit is known as symbiosis and the organisms involved are called symbionts. This association is also called mutualism which is obligatory for both i.e., for bacteria and leguminous root.
(b) Pneumatophores or Respiratory roots : Roots also breathe and as such they also require air for gaseous exchange. Normally, the soil has a large number of small air spaces between the soil particles. This air is utilized by the plants for their respiration. But 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 geotrophic. These roots bear many minute pores called pneumathodes towards their upper ends. Gaseous exchange takes place through pneumathodes. Such aerial, porous negatively geotrophic roots which help in gaseous exchange are called breathing or respiratory roots, breathing roots or pneumatophores roots or pneumatophores e.g., Sonneratia, Heritiera, Rhizophora, Avicennia and Ceriops etc. and are found in sundarbans of West Bengal.
(a) Storage roots : The roots where adventitious roots become swollen to store food. They are 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 (Asparagus fern) 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. This gives the root a beaded appearance. e.g., Portulaca (Rose moss) Momordica (Bitter gourd) Cyperus (Guinea rush).
❒ 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, therefore, called palmate roots.
❒ Annulated roots : The roots of a medicinal plant, Ipecac (Cephaelis ipecacuanha) yields emetine that looks like discs placed one above another, therefore, called annulated.
(b) Epiphytic roots : These roots are also called ‘hygroscopic roots’. These roots develop in some orchids which grow as epiphytes upon the trunks or branches of trees. They hang freely in the air and absorb moisture with the help of special sponge like tissue called velamen. Velamen is modification of epidermis. e.g., Venda, Dendrobium etc.
(c) Parasitic or Haustorial roots : Plants which depend on plant partially or totally for their food material are known as parasites. The roots of parasitic plants, which penetrate into the host tissues to absorb nourishment, are called haustorial roots. The haustorial roots of Cuscuta (Dodder, vern. Amarbel) penetrates the host upto phloem and xylem to absorb organic food, water and minerals. The haustorial roots of partial parasite – Viscum (Mistletoe) penetrate upto xylem of host to absorb water and minerals.
Parasite which absorb their nutrients from the host stem are known as stem parasites while those which absorb their nutrients from the host root are know as root parasite.
(d) Saprophytic roots : They are also called mycorrhizal roots as here roots are associated with fungal hyphae either superficially (ectomycorrhizae) or internally (endomycorrhizae) for absorption of water and minerals. e.g., Monotropa and Sarcodes.
(e) Photosynthetic or Assimilatory roots : These are green, aerial, adventitious roots which prepare food materials by photosynthesis are called photosynthetic roots or assimilatory roots e.g., Taeniophyllum, Trapa and Tinospora. In some epiphytes like Taeniophyllum, the stem and leaves are absent. The entire plant is represented by thin green, ribbon like roots which contain velamen. These roots absorb moisture from the atmosphere and manufacture food materials by photosynthesis. Since the roots are green and perform photosynthetic activity, these roots are called photosynthetic roots or assimilatory roots.
(f) Reproductive roots : Some fleshy adventitious root develop buds which can grow in to new plants. These are called reproductive root. These roots serve as means of vegetative propagation. e.g., Sweet potato, Dahlia etc.
(ii) For mechanical function
(a) Stilt roots : The aerial, adventitious obliquely growing roots that develop from the lower nodes of the stem to give additional support are called stilt roots. This roots bear several large overlapping root caps called multiple root caps. e.g., Sugarcane, Pandanus, Rhizophora, Sorghum and Maize. Pandanus (screw pine) is a common sea shore plant.
They also help in the absorption of water and minerals from the soil. In monocots, these roots arise in whorls from a few basal nodes of stem.
(b) Prop roots : These adventitious aerial roots arise from horizontal aerial branches of the trees like Ficus bengalensis (Banyan). Initially, they are hygroscopic in function, become red in moist condition and possess root-caps at their apieces. They grow vertically downward, penetrate the soil, become thick and assume the shapes of pillars. They provide support to the spreading branches of tree. Sometimes the main trunk dies and it is replaced by prop roots which assume the shapes of trunks.
In India, the biggest banyan tree having large number of prop roots are found at Indian Botanical Gardens, Kolkata and Kadiri (Andhra Pradesh).
(c) 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 ballast roots, e.g., Terminalia and Salmalia. In some huge and heavy trees, plank like roots develop at the base of the stem on the soil surface. These roots give additional support and act like ballasts. Hence these roots are called ballast roots.
(d) 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, e.g., Pothos, Piper betel, Vanilla and Hedera. Many weak stemmed plants climb up their supports in order to expose their leaves efficiently to sunlight. In Pothos and Hedera, climbing roots develop all over the stem. In Vanilla, single tendril like root arise at each node. Hence they are called tendrillar roots. In Piper betel, many short branched, adventitious roots arise at each node. These roots are called clinging roots.
(e) Floating roots : These roots develop from the nodes of floating aquatic plants like Jussiaea (=Ludwigia). They store air, become inflated and spongy, project above the level of water, make the plant light and function as floats.
(f) 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 called contractile or pull roots, e.g., Canna, Crocus, Allium, Lilium, Freesia, etc.
(g) 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 develop from the plumule of the germinating seed. Normally it is the aerial part of the plant body. The stem with it's branches, leaves, buds, flower and appandages is known as shoot system.
The stem shows the differentiation of nodes and internodes. The place where the leaf develops on the stem is called the node. The portion of the stem between two successive nodes is called the internode.
(i) Stem is an ascending axis of the plant and develops from the plumule and epicotyl of the embryo.
(ii) It is generally erect and grows away from the soil towards light. Therefore, it is negatively geotropic and positively phototropic.
(iii) The growing apex of stem bears a terminal bud for growth in length.
(iv) 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.
(v) The lateral organs of stem (i.e., leaves and branches) are exogenous in origin (from cortical region).
(vi) The young stem is green and photosynthetic.
(vii) Hair, if present, are generally multicellular.
(viii) In mature plants, stem and its branches bear flowers and fruits.
(i) 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.
(ii) Erect stems : Majority of angiosperms possess upright, growing-ascending, vertically-erect stems. They are fixed in the soil with the help of roots. Erect stems belong to four categories :
(a) Clum : Erect stems with solid nodes and hollow internodes. The nodes are swollen giving the stem a jointed appearance e.g., Bamboo (Bambusa arundinacea) and wheat (Triticum vulgare).
(b) Caudex : The main stem remains unbranched and bears a crown of leaves at its top. e.g., Coconut (Cocos nucifera), Palm, etc.
(c) Excurrent : The main stem is trunk like. It is thickest at the base and gradually tapers towards the apex. The branches arise in acropetal succession, i.e., oldest at the base and youngest at the apex. The tree appears cone-shaped. e.g., Casuarina, Eucalyptus, etc.
(d) Decurrent or Deliquescent : The apical bud of main stem is weak as compared to the buds of lateral branches. Thus, the lateral branches are prominent and spreading. The main stem grows upto a certain height after which it gives several branches. These branches dominate by giving the branches of several orders. The whole tree looks like dome-shaped. e.g., Banyan (Ficus bengalensis).
(iii) 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.
❒ 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 :
(i) Tendril climbers : Tendrils are thread like 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).
(ii) 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.
(iii) 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 (e.g., Zizyphus).
(iv) Lianas : These are woody perennial climbers found in deep forests. At first, they are just like ordinary twiners but once they reach to the top and get sunlight, become woody. e.g., Tinospora, Ficus, Bauhinia, Bignonia, etc.
(b) Prostrate weak stem
❒ Trailers : The stem creep on the ground but roots do not arise at the nodes. They are of three types :
(i) Procumbent : The stem creeps on the ground totally e.g., Tribulus, Bassela, Evolvulus.
(ii) Decumbent : Branches, after growing horizontally for some length, grow vertically upwards, e.g., Portulaca, Tridax, Lindenbergia, etc.
(iii) Diffuse : Branches grow profusely in all directions, e.g., Boerhaavia.
❒ Creepers : These weak-stemmed plants grow prostrate and develop adventitious roots from their nodes. Creepers are of three kinds – runners, stolons and offsets.
(i) Runners : This prostrate aerial stem has a long internode and creeps horizontally. Axillary buds arise from nodes to form aerial shoots and roots. Several small (daughter) plants are thus linked by runner which may break off later. e.g., Cynodon (doob grass) and Oxalis.
(ii) Stolons : 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 soil. e.g., Strawberry (Fragaria vesica), Peppermint (Mentha piperita), Jasminum (Jasmine).
(iii) Offsets : They are weak, elongated, horizontal branch of one internode that arises in the axil of a leaf. At the tip, it produces cluster of leaves above and tuft of roots below. The offset may break off from the parent plant and act as individual plants. They are found usually in aquatic plants and rarely is terrestrial plants. They are helpful for vegetative propagation. e.g., Eichhornia (water hyacinth), Agave, Pistia.
In angiosperms, always the branches are produced by the growth 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 structure like tendrils, thorns of flowers. Due to the terminal bud modification the growth of the main stem is definite. 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).
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. They are borne on stem in acropetal succession.
(i) The leaf is a lateral dissimilar appendage of the stem.
(ii) A leaf is always borne at the node of stem.
(iii) Generally there is always an axillary bud in the axil of a leaf.
(iv) It is exogenous in origin and develops from the swollen leaf primordium of the growing apex.
(v) The growth of leaf is limited.
(vi) The leaves do not possess any apical bud or a regular growing point.
(vii) A leaf has three main parts – Leaf base, petiole and leaf lamina. In addition, it may possess two lateral outgrowths of the leaf base, called stipules.
(viii) The leaf lamina is traversed by prominent vascular strands, called veins.
(2) 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.
(i) Leaf base (Hypopodium) : Leaf base is the lower most part of the leaf meant for attachment. It acts as a leaf cushion. In most of the plants it is indistinct. Some times leaf base shows different variations as follows :
(a) Pulvinate leaf base : In members of leguminosae the leaf is swollen. Such swollen leaf bases are called pulvinate leaf bases as seen in mango leaves. It helps in seismonastic movements (e.g., Mimosa pudica) and nyctinastic movements (e.g., Enterobium, Arachis, Bean).
(b) 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.
(c) 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. They are arranged concentrically to form a tunicated bulb. In Platanus and Robenia, the leaf bases protect the axillary buds and grow around them to form cup like structures.
(d) 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. Sometimes, small stipule like outgrowths are found at the base of leaflets of a compound leaf. They are called stipules.
❒ 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 : Stipules present in the axil of a leaf are called axillary stipule. These are also called intrapetiolar stipule, e.g., Tabernamontana and Gardenia.
❒ Ochraceous stipules : Membranous tubular stipules that ensheath the axillary bud and a part of internode is called ochraceous stipule. It is formed by the union of two stipules, e.g., Polygonum and Rumex.
❒ Hairy stipules : These are hair like stipules which are dry in nature, e.g., Anacampsora.
❒ Modification of stipule : To carryout different functions, stipules of some plants undergo modifications. They are classified as follows :
❒ Foliaceous : Green, expanded, leaf like stipules are called foliaceous stipules. They carryout photosynthesis, hence called assimilatory stipules, e.g., Pisum sativum and Lathyrus.
❒ Spinous : In some plants the stipules are modified into hard, pointed defensive organs called spines, e.g., Acacia arabica, Prosopis juliflora and Zizyphus.
❒ Convolute or Bud scales : Scales which protect the buds are called bud scales. Sometimes they are the modified to stipules. The bud scales fall off as the buds open, e.g., Artocarpus and Ficus.
(ii) Petiole (Mesopodium) : A petiole or leaf stalk is a cylindrical or sub cylindrical structure of a leaf which joins the lamina to the base. It raises the lamina above the level of stem so as to provide it with sufficient light exposure. A leaf with a petiole is called petiolate and the one without it is called sessile.
❒ Winged petiole : Green, flattened petioles may be called winged petioles, e.g., Citrus and Dionaea.
❒ Tendrillar petiole : In few plants the petioles are modified into tendrils and helps the plant in climbing. e.g., Clematis and Tropaeolum.
❒ Leaf like petiole (Phyllode) : A modified petiole which is flat, green and lamina like is called phyllode. It is a photosynthetic organ. e.g., Acacia auriculae formis.
❒ Swollen or Spongy petiole : Sometimes the petiole becomes swollen and spongy due to the development of aerenchyma. The type of petioles encloses much air and helps the plant to float. It is a hydrophytic adaptation e.g., Trapa bispinosa and Eichhornia.
❒ Spinous petiole : In few plants, the leaf blades fall off and the petioles become hard and spinous e.g., Quisqualis (Rangoon creeper).
(iii) Lamina (Epipodium) : The green expanded portion of the leaf is called the lamina. It performs vital functions like photosynthesis and transpiration. The nature of lamina depends upon the species and age of the leaf. A leaf lamina shows variations in different aspects like shape, margin, apex, texture and venation.
(a) Shape of lamina : The shape of the lamina is the description of its form. It varies in different plants as follows.
(c) Apex of lamina : The apex of the leaf lamina shows variations in different plants.
(d) Surface of lamina : The surface of the lamina may be of many kinds.
❒ Glabrous : Smooth and without hair. e.g,. Mangifera indica.
❒ Glaucus : Covered by waxy coating with white tinge. e.g., Calotropis.
❒ Scabrous : Rough surface. e.g., Ficus.
❒ Viscose : Sticky surface. e.g., Cleome.
❒ Pubescent : Covered with soft and wooly hair. e.g., Tomato.
❒ Pilose : Covered with long distinct scattered hair. e.g., Grewia pilosa.
❒ Hispid : Covered with long rigid hair. e.g., Cucurbita.
❒ Spinose : Covered with small spines. e.g., Solanum xanthocarpum.
(e) Texture of lamina : The texture of lamina also varies in different species.
❒ Herbaceous : When the lamina is thin and soft.
❒ Coriaceous : When the lamina is leathery.
❒ Succulent : When the lamina is thick, soft and juicy.
❒ Hygrophytic : When the lamina is very thin, membranous and spongy.
(3) Types of leaves : On the basis of shape of lamina, the leaves are classified into two types, namely, simple leaf and compound leaf.
(i) Simple leaves : The leaf having single undivided lamina is called the simple leaf. The simple leaf may be entire (e.g., Mango and Hibiscus rosa sinensis) or lobed. The lobes of a simple leaf may be entire pinnately arranged (e.g., Brassica) or palmately arranged (e.g., Gossypium, Passiflora and Ricinus).
(ii) Compound leaves : A compound leaf is one in which the lamina or the leaf blade is completely divided into many segments or units called leaflets or pinnae. When pinnae of leaflets attached in various ways to the portion of leaf axis known as the rachis. The compound leaves may be of two types, namely, pinnate compound leaves and palmately compound leaves.
(a) Pinnate compound leaves : It is the most familiar and widesperead type of compound leaf in which the rachis is elongated and bears two rows of simple or divided leaflets. The leaflets may be arranged alternately or in pairs along with the rachis. It is of following types :
❒ Unipinnate compound leaf : Here the primary rachis is unbranched and bear leaflets on either side. Unipinnate leaves are of two types :
❒ Paripinnate : The unipinnate leaf with even number of leaflets. They are borne in pairs. e.g., Tamarindus indica (Imli), Cassia etc.
❒ Imparipinnate : The unipinnate leaf with odd number of leaflets. The rachis is terminated by single unpaired leaflet. e.g., Neem, Rose, Murraya.
❒ Bipinnate compound leaf : In this type, the primary rachis is divided once and produce secondary and tertiary rachis. The leaflets develop on the secondary rachis. e.g., Delonix and Acacia, Mimosa pudica, Albizzia.
❒ Tripinnate compound leaf : In this type the primary rachis divides twice and produces secondary and tertiary rachii. The leaflets develops on the tertiary rachii. e.g., Moringa (Soanjana) and Millingonia.
❒ Decompound leaf : Here the primary rachis divides many times without any definite order. The lamina is dissected into many units. e.g., Coriandrum.
(b) Palmate compound leaf : In a palmately compound leaf, the leaflets are arranged at the tip of the petiole. According to the number of leaflets present at the tip of the petiole. These leaves are following types :
❒ Unifoliate : In this case, a palmately compound leaf is reduced to a single terminal leaflet. The single leaflet is articulated to the top of petiole, e.g., Citrus (Khatta), Lemon, etc.
❒ Bifoliate : This type of leaf has only two leaflets attached side by side at the terminal end of petiole, e.g., Balanites roxburghii, Hardwickia binata, etc.
❒ Trifoliate : This type of leaf has three terminal leaflets, Aegle marmelos (Wood apple, vern. Bael), Oxalis corniculata, Trifollium (Clover), etc. These leaves differ from trifoliate imparipinnate (e.g., Lablab) in having all the three leaflets attached at the tip of petiole.
❒ Quadrifoliate : This leaf has four leaflets attached to the tip of petiole. e.g., Paris quadrifolia, Marsilea.
❒ Multifoliate : A palmately compound leaf having five or more terminal leaflets, arranged as fingers of the palm, e.g., Bombax malabarica, Cleome viscosa, Gynandropsis pentaphylla, etc.
(4) Phyllotaxy (Phyllotaxis) : The leaves may be stem borne (cauline), branch borne (ramal) or may appear to be root borne (radical). The arrangement of leaves on the stem is called phyllotaxy (Gk. Phyllon = leaf; taxis = arrangement). It is of three types :
(i) Alternate or Spiral : When only one leaf is found at each node. The leaves present at successive nodes alternate with each other. The arrangement is said to be alternate or spiral. The leaves are commonly arranged spirally around the stem. Each spiral is called the genetic spiral. The angular divergence (angular distance) between any two concecutive leaves is always constant. In spiral phyllotaxy, the leaves are arranged on the stem in regular vertical row. Such rows are called orthostichies. In practice the angular divergence is determined in the following manner :
Angular divergence of a circle i.e. 360°
A phyllotaxy is written by taking the number of spirals (circles) as numerator and the number of leaves as denominator. Based on the number of orthostichies seen on the stem, the spiral phyllotaxy may be described as given under.
(a) Distichous or 1/2 Phyllotaxy : Where the angular divergence is 1/2 of 360° i.e., 180°. e.g., Ravenella.
(b) Tristichous or 1/3 Phyllotaxy : Where the angular divergence is 1/3 of 360° i.e., 120°. e.g., Moss, Cyperus rotundus.
(c) Pentastichous or 2/5 Phyllotaxy : Where the angular divergence is 2/5 of 360° i.e., 140°. e.g., China rose.
(d) Octastichous or 3/8 Phyllotaxy : Where the angular divergence is 3/8 of 360° i.e., 135°. e.g., Carica papaya.
In these types, if one adds up two preceeding numerators and denominators, a series is formed called Schimper-Brown Series.
e.g., and so on.
(ii) Opposite : When two leaves are present at node opposite to each other the type of phyllotaxy is called opposite. It is of two type :
(a) Opposite superposed : All the pair of leaves of a branch arise in the same plane so that only two vertical rows of leaves are formed. e.g., Jamun, Guava, etc.
(b) Opposite decussate : A pair of leaves at one node stands at right angle to the next upper or lower pair so that four vertical rows are formed on the stem. e.g., Calotropis, Zinnia, Tulsi, Quisqualis.
(iii) Whorled : If more than two leaves are present at a node as whorl, it is called whorled phyllotaxy. It is also called cyclic or verticellate phyllotaxy. e.g., Nerium, Hydrilla and Alstoni scholaris.
(iv) Leaf mosaic : This is a special type of arrangement of leaves. Older leaves present at the lower nodes of the stem possess longer petioles with bigger lamina and the young leaves of upper nodes bear shorter petioles with smaller lamina. The smaller young leaves occupy the space present between the bigger ones. e.g., Begonia, Acalypha and Sycamore.
(5) Vernation : Arrangement of leaves in bud condition is known as vernation imbricate (irregular overlapping), contorted (twisted, regular overlapping of margins), induplicate (margin bent inwardly), equitant (conduplicate in two series, one overlapping the other completely), half equitant, supervolute (convolute leaves, one rolled over other).
(6) Heterophylly : It is the occurrence of more than one type of leaves on the same plant. Heterophylly is of four types :
(i) Adaptive heterophylly : Submerged leaves are different from floating and emerged leaves of the same plant due to different adaptations. e.g., Limnophila heterophylla, Sagittaria, Ranunculus aquatilis. The emerged leaves are broad and fully expanded while the submerged leaves are narrow, ribbon shaped, linear or highly dissected.
(ii) Environmental heterophylly : The heterophylly is due to change in environment including soil, temperature, humidity and air currents.
(iii) Developmental heterophylly : Young leaves are different from mature leaves, e.g., Eucalyptus.
(iv) Habitual heterophylly : Leaves of different shape and incisions occur at the same time, e.g., Jack fruit tree (Artocarpus heterophyllus), Ficus heterophylla, Hemiphragma heterophyllum, Broussonetia papyrifera. In Hemiphragma, the main stem bears ovate and entire leaves while branches possess acicular leaves.
(7) Modification of leaves : Some important leaf modification are as follows :
(i) Leaf tendrils : In many weak stemmed plants, the leaves are modified into slender wiry and coiled structures called leaf tendrils. The tendril may be formed by entire leaf or a part of the leaf.
❒ Entire leaf modified into tendril, e.g., Lathyrus aphaca (Wild pea).
❒ Terminal leaflets modified into tendril, e.g., Pisum sativum (Pea), Lathyrus odoratus (Sweet pea), Narvella.
❒ Leaf tip modified into tendril, e.g., Gloriosa.
❒ Petiole modified in to tendril, e.g., Clematis.
❒ Stipule modified into tendril, e.g., Smilax.
❒ Midrib modified into tendril, e.g., Nepenthes.
(ii) Spines : A pointed structure formed by the modification of entire leaf or part of a leaf is called a spine. Different part of a leaf or entire leaf may be modified in to spines. e.g., In Opuntia leaves of axillary branches are modified into spines. In Berberis entire leaf modified into three spines. In Phoenix leaf tip modified into spine. In Citrus first leaf of axillary branch modified in to spine. In Argimone leaf margin modified into spines. In Perkinsonia, Acacia and Zizyphus stipules modified into spines.
(iii) Scale leaves : In many xerophytes, the foliage leaves are reduced to scale leaves. They are thin, membranous, dry, small, sessile, colourless structure. e.g., Casuarina, Orobanche and Balanophora.
(iv) Phyllode : It is a green, expanded structure formed by the modification of petiole or rachis of leaf. Many xerophytes reduce the size of their leaves to minimize water loss. Such plant develop phyllodes to carry out photosynthesis e.g., Acacia, Melanoxylon and Parkinsonia.
(v) Storage leaves : Leaves become fleshy due to storage of water or food materials. Such leaves are called storage leaves. They are usually found in succulent plants. In plants like Aloe, Kalanchoe and Peperomia.
(vi) Reproductive leaves : In some plants the vegetative propagation is carried out by the production of epiphyllous buds on leaves. Such leaves are called reproductive leaves. The epiphyllous buds when come in contact with soil develop into new plants.
(vii) Absorbing leaves : In some rootless, aquatic plants, the submerged leaves are modified into root like structure to absorb water and mineral salts. Such modified leaves are called absorbing leaves. e.g., Utricularia.
(viii) Floral leaves : Floral parts such as sepals, petals, stamens and carpels are modified leaves. Sepals and petals are leafly stamens are considered pollen bearing microsporophylls and carpels are ovule bearing megasporophylls.
(ix) Cotyledons : The mature embryo shows either one (monocotyledons) or two cotyledons, (dicotyledons). Cuscuta a parasite is included in dicotyledon. However it has no cotyledon and many cotyledons, as in gymnosperms. These cotyledons are considered as embryonic leaves which are the first leaves of a shoot system.
(x)Trap leaves : The trap leaves are also called insectivorous leaves or carnivorous leaves. Plants having trap leaves usually grow in nitrogen-deficient soils (boggy soils). They have poorly developed root system. These plants get their nitrogenous requirement by capturing the insects. To attract, capture, kill and digest the insects, the leaves are modified into
It can be defined as modified dwarf shoot which is meant for sexual reproduction. It is characteristics feature of angiosperm whease reproductive organs have been aggregated as flowers.
(1) Parts of a typical flower : It comprises a stalk called pedicel which arises in the axis of leaves called bracts. Upon the pedicel there may be one to many small scaly structures called bracteoles. The terminal part of the pedicel is the thalamus or torus. It is a modified and condensed axis of the flower. Modified leaves called floral leaves or floral parts arises from the nodes of the thalamus as successive whorls. A typical flower of an angiosperm consists of four types of floral parts namely calyx, corolla, androecium and gynoecium.
(i) Calyx : It is the outermost whorl composed of sepals.
(ii) Corolla : It is composed of petals and is the second whorl.
(iii) Androecium : It is the third whorl composed of stamens.
(iv) Gyneocium : It is the innermost whorl and is also called pistil. It shows carpels.
(2) 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 pattern are recognized.
(i) Monoecious : Presence of male and female flowers on the same plant, e.g., Acalypha, Cocos and Ricinus.
(ii) Dioecious : Presence of male and female flowers on different plants, namely, male plants and female plants. e.g., Cycas, Carica papaya and Vallisneria.
(iii) Polygamous : Presence of unisexual and bisexual flowers on the same plant, e.g., Mangifera and Polygonum.
(3) 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 :
(i) Actinomorphic (Regular = Symmetrical) : Actinomorphic flowers can be divided (passing through center) by any vertical plane in to two equal and similar halves. e.g., Mustard, Brinjal, Catharanthus roseus.
(ii) Zygomorphic (Monosymmetrical) : Zygomorphic flowers can be divide into two equal halves by only one verticle division e.g., Pea, Larkspur, Ocimum.
(iii) Asymmetrical (Irregular) : Asymmetrical flowers can not be divided into two equal halves by any vertical division. e.g., Canna, Orchids.
(4) Arrangement of floral organs : On the basis of arrangement of floral organs, three types of flowers are recognized. They are :
(i) Acyclic : Here the thalamus is conical or convex and the floral parts are spirally arranged, e.g., water lily and Magnolia.
(ii) Cyclic : Here the floral organs are arranged in regular whorls at the nodes of the thalamus, e.g., Hibiscus and Datura.
(iii) 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.
Trimerous : Three floral parts in each whorl.
Tetramerous : Four floral parts in each whorl.
Pentamerous : Five floral parts in each whorl.
❒ A flower with different number of floral parts in each whorl is called anisomerous flower. The sepals, petals, stamens and carpels present at different whorls of a flower vary in their numbers. These are also called heteromerous flowers.
(5) Detailed structure of flower : Angiospermic flowers exhibit many variations in their external morphological characters. Detailed description of a flower helps in its proper identification.
(i) Bract : Bract (hypsophyll) is a small leaf like structure on the peduncle which produces a flower in its axil. The floral buds are usually protected by the bracts. Flower with a bract is described as bracteate and the flower without a bract is known as ebracteate. Bracteoles are small scale like structures present on the pedicel. Bracts are modified into following structures :
(a) Foliaceous bract : Leaf like, expanded green bract is called the foliaceous bract, e.g., Pisum, Lathyrus, Adathoda and Gynandropsis.
(b) Spathe : A large modified bract which encloses spadix inflorescence totally or partially. It may be leathery or woody, e.g., Alocasia, Cocoa, Musa and Typhonium.
(c) Petaloid bract : Brightly coloured petal like bract is known as petaloid bract, e.g., Bougainvillea, Poinsettia and Euphorbia.
(d) Involucre : One or two whorls of green bracts that protect young inflorescence is called involucre, e.g., Coriandrum, Tagetes and Heracleum.
(e) Epicalyx : Whorl of bracteoles present below the calyx or outside the calyx, e.g., Hibiscus rosa sinensis and Malvaviscus arborcus.
(f) Scaly bracts : Reduced, membranous, scale like bracts seen in head inflorescence, e.g., florets in Tridax and Helianthus.
(g) Glumes : The bracts found on the rachilla of spikelet are called (ii) Thalamus : The terminal part of the pedicel is called thalamus or torus or receptacle. It is a condensed axis of the flower from which all floral parts arise. Depending upon the position of gynoecium on the thalamus with respect to other parts, flowers are of three kinds – hypogynous, perigynous and epigynous (See details in Embryology Module-II).
In many flowers, the thalamus is condensed and the internodes are not seen clearly. But there are some flowers with elongated, distinct floral internodes as mentioned below :
(a) Anthophore : This is the first elongated internode between the calyx and corolla, e.g., Silene, Pennsylvania and Lychnis.
(b) Androphore : It is the second elongated internode between corolla and androecium, e.g., Gynandropsis.
(c) Gynophore : It is the third elongated internode between androecium and gynoecium e.g., Capparis and Gynandropsis.
(d) Gynandrophore : It is an elongated stalk like part between non essential and essential organs of the flower. It is equivalent to androphore, e.g., Passiflora.
(e) Carpophore : This is a stalk like connection present between two carpels. It is formed due to expansion of the thalamus between the carpels, e.g., Coriandrum and Foeniculum.
(iii) Perianth : The non essential organs, calyx and corolla are together called perianth. The perianth protects the stamens and carpels. In angiospermic flowers, the perianth exists in different forms.
(a) Achlamydeous : Perianth is absent and the flowers appear naked. Mostly the achlamydeous flowers occur in cyathium inflorescence. e.g., Euphorbia, Poinsettia.
(b) Chlamydeous : Perianth is present and the flowers usually appear attractive. The chlamydeous flowers are of two types. They are :
❒ Monochlamydeous flowers are with perianth in one whorl, e.g., Amaranthus and Ricinus.
❒ Dichlamydeous flowers are with perianth differentiated into calyx and corolla. They are arranged in two different whorls. The dichlamydeous condition is of two types :
❒ Homochlamydeous : The two whorl or the perianth (calyx and corolla) are similar in all respects and are not identified by different colours, e.g., Michelia.
❒ Heterochlamyoeous : The two whorls of the perianth are dissimilar in many respects. The outer whorl consists of small, green sepals and the inner whorl with large variously coloured petals, e.g., Datura and Hibisus. The term “tepals” is used to describe the perianth lobes which appear like petals, e.g., most of the monocots.
(iv) Calyx : It is the outermost whorl of the flower. It consist of sepals. Usually, the sepals are small and green. They protect other floral organs when the flower is in bud condition. The calyx is described as polysepalous when the sepals are free (e.g., Anona, Tomato) and gamosepalous when the sepals are united (e.g., Datura and Hibiscus). If sepals are fused less than half of the length of calyx tube it is called as partite and if the fusion of sepals is very little, just at the base of calyx tube, it is said to be connate. The sepals may be deciduous or persistent. Usually the persistent calyx do not show any growth after fertilization. Such a calyx is termed as marcescent (e.g., Brinjal, Chillis). Sometimes the persistent calyx shows continuous growth even after, fertilization. This type of calyx called acrescent (e.g., Physalis and Shorea).
In some plants a whorl of green sepals like structure is present at the base of calyx called epicalyx. Epicalyx is considered a whorl of the bracteoles and mostly found in the flowers of family Malvaceae (Althaea, Cotton). The calyx may show number of modifications. They are :
(a) Campanulate : Bell shaped, e.g., Althaea.
(b) Cupulate : Cup like, e.g., Gossypium.
(c) Urceolate : Urn shaped, e.g., Hyoscyamus.
(d) Infundibuliform : Funnel shaped, e.g., Atropa belladona.
(e) Tubular : Calyx tube like, e.g., Datura.
(f) Bilabiate : Calyx forms two lips, e.g., Ocimum.
(g) Spurred : One or two sepals forming a beak like structure, e.g., Larkspur.
(h) Pappus : Calyx are modified into hairs e.g., Sonchus, Tridax (Asteraceae).
(i) Spinous : When calyx forms spines, e.g., Trapa.
(j) Hooded : When sepals enlarged to form a hood over the flower, e.g., Aconitum.
(k) Petaloid : Enlarged and brightly coloured sepals, e.g., Clerodendron, Mussaenda, Sterculia, Caesalpinia and Saraca.
(v) Corolla : It is the second whorl of the flower consisting of petals. Usually the petals are brightly coloured and scented. They attract the insects which act as agents for pollination. The corolla may be polypetalous (with free petals), gamopetalous (with united petals) or apetalous (without petals). The corolla may undergo modifications or possess some special appendages.
❒ Sepaloid : Green or dull coloured sepal. e.g., Anona, Polyalthia and Artabotrys.
❒ Saccate : The corolla tube may form a pouch on one side. e.g., Antirrhinum.
❒ Spurred : Sometimes one or two petals or the entire corolla tube grow downwards forming a spur that usually stores nectar. e.g., Aquilegia vulgaris.
❒ Corona : Special appendages of different kinds like scales, hairs develop from the corolla. Such appendages are called corona. e.g., Passiflora, Oleander and Nerium.
Forms of corolla : Both polypetalous and gamopetalous corolla exhibit great variation in their forms. It is following types :
(a) Polypetalous corolla : They are of following types :
❒ Cruciform : Four free clawed petals arranged in the form of a cross, e.g., Mustard and Radish.
❒ Rosaceous : Five free sessile petals withlobes spreading outwards, e.g., Rose, Hibiscus.
❒ Caryophyllaceous : Five free clawed petals with limbs at right angles to the claw, e.g., Dianthus.
❒ Papillionaceous : Five free unequal petal arranged in definite fashion. The posterior petal is largest and is called standard vexillum. On either side of the standard, two lateral petals unite called wings are present. The remaining two anterior petals to form a boat shaped structure called the keel. e.g., plants of papillionaceae.
(b) Gamopetalous corolla : They are of following types :
❒ Tubular : Five united petals form a cylindrical tubular structure, e.g., disc florets of Asteraceae.
❒ Infundibuliform : It is a funnel shaped corolla, e.g., Datura.
❒ Companulate : It is bell shaped corolla, e.g., Thevetia.
❒ Rotate : Short tubular corolla with spread out lobes appearing like a wheel e.g., Brinjal.
❒ Hypocrateriform : It is a salver shaped corolla. It is provided with a elongated narrow tube having lobes at the top placed at right angles, e.g., Vinca.
❒ Ligulate : Corolla with a short tube which is drawn out into a tongue shaped structure e.g., ray florets of Asteraceae.
❒ Bilabiate : The irregular corolla is united, in such a way that it appears two lipped. It is the characteristic corolla of labiatae, e.g., Leucas.
(vi) Aestivation : The arrangement of sepals and petals in bud condition of the flower is called “aestivation”. It is may be of following types :
(a) Open : If the margins of perianth members in a whorl are free with wide gap between them, then the type of aestivation is called ‘open’, e.g., sepals of Mustard.
(b) Valvate : Here the edges of perianth members in a whorl are very nearly touching each other bud do not overlap, e.g., calyx and corolla in Annona.
(c) Twisted : In this type, the perianth members of a whorl show one edge outside and one edge inside. Thus they regularly overlap the neighbouring members on one side. The twisted aestivation is also called contorted or convolute aestivation, e.g., corolla of Hibiscus.
(d) Imbricate : Here in a whorl of perianth members, one is completely inside and another is completely outside. The remaining perianth members show one edge inside and the other edge outside. The imbricate aestivation is of two types, namely, descending imbricate and ascending imbricate.
❒ Descending imbricate : Here the odd petal is posterior and completely outside. The anterior pair of petals are completely inside. The remaining petals show regular overlapping in the descending manner. It is also called vexillary aestivation, e.g., Tephrosia, Crotalaria and Dolichos.
❒ Ascending imbricate : Here the odd petal is posterior and completely inside. One of the anterior petals is completely outside. The remaining petals show regular overlapping in ascending manner, e.g., Cassia and Delonix.
(e) Quincuncial : In this type, out of the five perianth members in a whorl two are completely outside, two are completely inside and the remaining has one edge outside and one-edge inside. This is confined to pentamerous flowers only, e.g., sepals of Ipomoea, Vinca and Thevetia.
(vii) Androecium : It is the third whorl of a flower consisting of stamens or microsporophylls. Fertile stamens produce pollen grains . Staminodes are the sterile stamens. Petaloid stamens are brightly coloured and appear like petals, e.g., Canna.
(a) Structure of stamen : A stamen shows a long or short stalk called the filament. The filament ends with a terminal fertile part known as the anther. It encloses microsporangia within which microspores or pollen grains are produced. The filament of the stamen is connected to the anther by means of a “connective”. The anther may be monothecous or dithecous. The monothecous anther has only one sac. It is bilocular or bisporangiate, e.g., Hibiscus. The dithecous anther consists of two sacs and is tetralocular or tetrasporangiate in as Datura.
When the face of anther is towards centre of flower it is called introrse e.g., tomato when it is towards the periphery it is called extrorse e.g., Ranunculus.
(b) Fixation : The mode of attachment of a filament to anther by connective is called fixation. It is of following types :
❒ Adnate : Filament attached to the total length of the anther on the back. e.g., Michelia (Campa).
❒ Basifixed : Filament is attached to the base of the anther e.g., Datura, Mustard, Radish.
❒ Dorsifixed : Filament is attached to the anther on the dorsal side at middle portion e.g., Passiflora.
❒ Versatile : Filament is attached to the anther at a point so that anther can swing freely in all direction. e.g., Grasses.
(c) Length of stamens : Based on the relative lengths of the stamens, the conditions of androecium varies :
❒ Didynamous : When there are four stamens in a flower of which two are long and two are short, the condition is described as didynamous, e.g., Ocimum.
❒ Tetradynamous : Out of the six stamens that are found in a flower, four stamens are long and the two are short. This condition is called tetradynamous, e.g., Raphanus and Brassica.
The stamens are described as inserted when they do not extend beyond the petals or corolla tube (Dolichos). When the stamens extend beyond the petals or corolla tube, the stamens are known as (Acacia).
(d) Insertion of stamens : Based on the insertion of stamens, the condition of androecium varies :
❒ Isostemonous : When the stamen form a single whole and the number of stamen is the same as that of sepals and petals, the flower is isostemonous.