Morphology of Flowering Plants PDF

Morphology of Flowering Plants Introduction Angiosperms or flowering plants (sometimes also Definition referred to as phanerogams ) are those vascular plants in which seeds are enclosed inside fruits. Arboretum (L. -tree):...

Morphology of Flowering Plants Introduction Angiosperms or flowering plants (sometimes also Definition referred to as phanerogams ) are those vascular plants in which seeds are enclosed inside fruits. Arboretum (L. -tree): Often an outdoor place set for They are the most dominant plants of the the display of living plants. present day, comprising about 300,000 species. They occur in numerous habitats of the earth and Gray Matter Alert!!! show a great diversity of shape, size, and form. Smallest angiospermic plant— TYPES OF PLANTS BASED ON HABITAT (0.1 mm)  Mesophytes: Found growing well on land under Tallest Angiosperm— medium, climatic conditions, e.g., Mustard. (height of certain  Hydrophytes: Found growing well in water, e.g., specimens 130.5 m or 435 ft.)  Xerophytes: Found growing well in dry conditions, e.g., Cactus.  Epiphytes: Found growing well on other plants e.g., Orchid.  Psammophytes: Found growing well in sand, e.g.,  Halophytes: Found growing well in saline habitats, e.g.,  Lithophytes: Found growing well on rocks, e.g., ferns. ⚪ Most of the flowering plants are autotrophic in their mode of nutrition. ⚪ There are some which are parasitic ( ), saprophytic ( ) or insectivorous ( ). MORPHOLOGY AND ITS IMPORTANCE Morphology of Flowering Plants  Study of morphology is essential for recognition and identification of plants.  It provides important criteria for the classification of plants. Definition  Morphology gives information about the range of variations found in a species. Morphology: Branch of Biology  Knowledge of morphology is necessary for that deals with the study of studying various aspects of plant life like anatomy, external features of an organism. physiology, ecology, genetics, etc. 3.   It helps in the identification of deficiency and toxicity symptoms occurring in plants in response Keywords to shortage or excess of minerals.  It helps in the study of morphological adaptations of plants to di erent types of habitats and  Morphology enables horticulturists to adopt plants with  Tap root system morphological peculiarities for lawns, parks,  Primary root gardens, etc.  Secondary root  Tertiary root FLOWERING PLANTS  Fibrous root system Depending upon the life span, angiospermic  Adventitious root plants are classified as: Annuals Biennials Perennials 1. Annuals  These plants complete their life cycle in a single growing season, varying from a few weeks to few Definition months.  During this period, they grow, bear flowers, Annual Plants: These plants produce seeds and fruits and then die. complete their life cycle in a  They pass the unfavourable periods in the form single growing season, varying of seeds, e.g., wheat, rice, pea, mustard etc. from a few weeks to few months. 2. Biennials  These plants complete their life cycle in two growing seasons.  In the first season, they grow only vegetatively and store food in roots and underground stems.  In the second season, they produce flowers, fruits and seeds, and then die. For example, cabbage, Morphology of Flowering Plants radish, turnip, etc., (grow in cold regions). Definition 3. Perennials  These plants continue to grow for more than two Biennial Plants: These plants growing seasons to several years. complete their life cycle in two  They bear flowers and fruits during specific growing seasons. seasons. 4.  Polycarpic Plants: Several perennial plants bear flowers and fruits every year Mango, apple, Definition lemon, etc. Perennial Plants: These plants Monocarpic Plants: Some perennial plants bear continue to grow for more than flowers and fruits only once, after a long period two growing seasons to several of vegetative growth, e.g., , etc. years. They bear flowers and fruits PARTS OF A FLOWERING PLANT during a specific season. The plant body of an angiosperm or a flowering plant primarily consists of an axis, which is di erentiated into:  Root system  Shoot system ROOT SYSTEM  The root system normally lies underground and consists of a main root and its branches.  There is a most prominent root, which lies in the center and is called the primary root. It bears several lateral roots called secondary roots.  The secondary roots are further branched into tertiary roots and finer rootlets. The tips of rootlets are covered with root caps.  Behind the tips, there are few fine outgrowths called root hairs. Main Functions of the Root System  To anchor the plant in the ground.  To absorb water and minerals from the soil. SHOOT SYSTEM Morphology of Flowering Plants The shoot system is normally aerial and consists of:  Main Stem  Lateral branches  Leaves Stem  At intervals, the stem and its branches possess swollen areas called nodes. 5.   Part of the stem between two adjacent nodes is called internode. Keywords  The leaves are borne in the region of nodes.  The angle between the leaf and the upper part of stem is called axil.  Vegetative Organs  It bears an axillary bud, which later develops into  Nodes a branch.  Internode  A bud is also present at the tip of the stem or a  Axillary bud branch called terminal bud or apical bud.  Terminal bud  Apical Bud is responsible for elongation of the  Apical bud stem or the branch.  Veins Lateral Branches These are structurally similar to the stem. Leaf The leaf is a green, expanded, lateral outgrowth, which develops on the stem or its branches at the region of a node. Rack your Brain Parts of a Leaf Of what importance is the  Leaf base study of leaf morphology for a  Petiole physiologist?  Lamina or Leaf Blade The leaf lamina is interspersed with numerous vascular strands called veins. The lamina is specialized for photosynthesis. It is also the main site for transpiration and respiration. VEGETATIVE ORGANS AND REPRODUCTIVE ORGANS OF A PLANT Morphology of Flowering Plants  Root, stem, and leaves (vegetative organs)  The flowers (reproductive organ) Definition  Fruits and seeds (associated with reproduction and continuity of the race) Vegetative Organs: These organs are concerned with MORPHOLOGY OF ROOT nutrition, growth, and help in The root is a non-green, non-photosynthetic, the maintenance of the plant cylindrical, descending part of the plant that body. develops from the radicle of seed. 6.  Positively geotropic and hydrotropic that normally grows downwards into the soil. Definition Characteristics of the Root Root: The root is a non-green,  It does not bear nodes and internodes. non-photosynthetic cylindrical,  It does not bear leaves and buds. descending part of the plant  It is non-green. that develops from the radicle  A functional root is covered at the tip by a root of seed. cap.  Near the tip, the root bear unicellular tubular root hairs.  Endogenous in Origin: Root branches develop from the interior (usually pericycle) of the parent root.  A root is neutral or negatively phototropic, and Rack your Brain positively hydrotropic.  The geotropic response is also positive for the What will happen if the root tip main root. of a developing primary root is cut o ? THE REGIONS OF THE ROOT A typical root possesses five parts or regions, however, there is no definite demarcation.  Root Cap ⚪ It is a cap-like structure present at the tip of root. ⚪ The cells of the root cap secrete mucilage, which lubricates the passage of the root through the soil and help in easy penetration through the hard soil. ⚪ The cells of the root cap also possess starch grains, which are believed to be responsible for the perception of gravity. Morphology of Flowering Plants ⚪ The root cap also protects root meristem from friction between root and the soil particles.  Meristematic Region ⚪ It is one to a few millimeters in length and lies partly within and partly beyond the root cap. ⚪ The cells of this zone divide actively and add new cells to the root and root cap. 7.  ⚪ Root meristem keeps on adding new cells and replacing the worn-out cells. Keywords  Region or Zone of Elongation ⚪ It lies behind the meristematic zone and is about 4-8 mm in length.  Root cap ⚪ The cells of this region are newly formed  Region of meristematic activity cells, which lose the power of division. They  Region of elongation elongate rapidly and bring about an increase  Region of maturation in the length of the root.  Root hairs ⚪ They also possess the power of absorption of water and mineral salts from the soil.  Region of root hair ⚪ It lies above the region of elongation and bears a cluster of very fine tubular outgrowths called root hairs. ⚪ Root hairs are produced from the epiblema of the root. ⚪ The root hairs increase the exposed surface of the root for absorption. This zone also represents the zone of di erentiation or maturation because di erent types of primary tissues di erentiate or mature in this region. ⚪ As the root increases in length, the root hairs in older region get bruised and shed. ⚪ New root hair appears in the younger part of the zone of elongation.  Region or Zone of Maturation ⚪ This region forms a major part of the root and no change occurs in the cells of this region. ⚪ It forms the permanent zone of the root and gives out lateral roots. ⚪ The outermost layer of this region has Rack your Brain Morphology of Flowering Plants thick-walled cells and hence, does not help in absorption of water from the soil. Roots in strict sense are present in which of the following ? ROOT SYSTEM (1) Phanerogams only The roots along with their branches, constitute (2) Cryptogams only the root system. (3) Cryptogams and phanerogams both (4) Thallophyta 8.  TYPES OF ROOT SYSTEM  Taproot System Keywords  Fibrous Root System  Adventitious Root System  Tap root system  Fibrous root system  Adventitious roots  Pneumatophores  Prop roots  Stilt roots Definition 1. Tap Root System Taproot System: Tap root develops  Characteristic feature of most of the dicot plants. from the radicle of the seed.  It develops from the radicle of the embryo of a It has a main primary root that seed. further gives rise to secondary and  The first root is formed by the elongation of tertiary branches. radicle and is called primary root.  The primary root that persists throughout the life of the plant is termed as tap root.  It grows continuously and produces lateral roots that are called as secondary roots.  The secondary roots are further branched into tertiary roots and finer rootlets. The taproot and its branches together constitute a taproot system. (a) Deep Feeder Root System or Racemose Taproot System The taproot of perennial plants penetrates in Morphology of Flowering Plants the deeper layers of the soil, e.g., (b) Surface Feeder Root System or Cymose Taproot System The taproot of some annual plants does not penetrate much and the secondary roots spread horizontally near the soil surface only. 9.  2. Fibrous Root System  Roots that consist a bunch of root fibres originating from the base of the stem constitute fibrous root system.  In monocotyledonous plants, the primary root is short lived and replaced by many roots.  Here, the primary root that originates from the radicle is short lived, as it terminates into the root fibres, e.g., wheat plant, grasses, etc. 3. Adventitious Root System (L. –extraordinary)  Roots that develop from any part of the plant other than the radicle.  Adventitious roots may develop from the nodes or internodes of the stems, e.g.,  These arise from branches (banyan) or from the leaves ( ).  Several plants creeping on the ground, produce roots from nodes as in wood sorrel ( ), grass, etc.  These arise from branch cuttings of rose, Rack your Brain sugarcane, tapioca, when put into the soil.  Mostly adventitious roots do not penetrate deep into the soil, hence they are surface feeders. plant is able to Adventitious roots are characteristic feature of survive in marshy areas. How ? monocot plants. Morphology of Flowering Plants 10. MODIFICATIONS OF ROOT Modifications can be defined as morphological Rack your Brain changes (shape, form, or structure) in an organ to perform certain special functions, other than Carrot is a root and not a stem. or in addition to the normal functions. Comment. The roots of some plants are modified to perform specialized functions. MODIFICATIONS OF TAPROOT 1. Fleshy taproot The taproots of some plants become swollen and fleshy due to the storage of food. Hypocotyl may also join the taproot in storing food. The secondary and tertiary roots remain thin and fibrous. Depending upon the shape, fleshy taproots are of the following types: (i) Conical (Cone-shaped) ⚪ The primary root is broad at the base and tapers gradually towards apex like a cone. ⚪ Many thin, threads like secondary roots arise all along the conical root, e.g., Carrot ( ). (ii) Fusiform (spindle shaped) ⚪ The primary root is spindle shaped. It is almost uniformly thick except at the base and apex where it tapers. ⚪ The basal part of the root is derived from hypocotyl. ⚪ The root also bears a reduced discoid Morphology of Flowering Plants stem and radicle leaves (leaves arising from roots or appear to arise from roots). Radish ( ). (iii) Napiform (pitcher-shaped) ⚪ Globular or top-shaped and tapers abruptly towards the apex. ⚪ Bears a reduced discoid stem and radicle leaves. 11.  ⚪ Basal part of the fleshy root is hypocotyl. ⚪ For example, Turnip ( ), beetroot ( ). (iv) Tuberous roots (irregularly shaped) ⚪ The primary root becomes thick and fleshy. ⚪ No definite shape. four o’clock plant ( 2. Pneumatophores or Respiratory Roots  These are aerial roots or aerophores found in mangrove plants (plants growing in swamps near the seashores), e.g., (vern. ) etc.  The underground secondary and tertiary roots of the plants come out of swamp for exchange of gases.  They bear small pores called lenticels or pneumatothodes near their tips. The remaining surface of pneumatophores is covered with cork and the proximal submerged part bears many short absorbing roots. 3. Nodulated taproots  In some plants, secondary, tertiary and even primary roots bear many small irregular swellings called root nodules or tubercles.  The root nodules contain millions of minute Gray Matter Alert!!! nitrogen fixing bacteria of the genus (e.g. ). Green manure: Legumes add  These bacteria pick up free atmospheric nitrogenous compounds to the Morphology of Flowering Plants nitrogen and convert it into nitrogenous organic soil or increase the fertility of the compounds. This phenomenon is called nitrogen soil as nitrogen fixing bacteria fixation. are in their root nodules, hence  Plants belonging to family Leguminosae, such as the roots are left over in the soil pea ( ), gram, groundnut, etc. till the next harvest. 12.  MODIFICATIONS OF ADVENTITIOUS ROOT Storage adventitious roots: In some plants, Previous Year’s Question adventitious roots become thick and fleshy due to the storage of food. Pneumatophores are found in– Depending upon the shape and the swollen part, (1) The vegetation which is adventitious roots are of following types: found in marshy and saline lake (i) Tuberous Root or Root Tubers (2) The vegetation which is  Such roots arise singly at the nodes of prostrate found in acidic soil stem and are swollen without any definite shape. (3) Xerophytes (4) Epiphytes  Also called root tubers, e.g., Sweet potato ( vern. ). (ii) Fasciculated Roots  These are swollen roots which arise in clusters or fascicles at the base of the stem, e.g.,.  In , swollen are borne on the normal roots at intervals. The root system is often referred to as ‘crown’. Definition Morphology of Flowering Plants Reproductive Roots: Roots do not bear buds but the root tubers of sweet potato bear adventitious buds which give rise to new plants, hence they are also known as reproductive roots. 13.  Roots Modified for Additional Support (i) Prop or Pillar Roots  Pillar-like adventitious roots that arise from branches of the trees like banyan tree ( ).  Initially, these roots are aerial and hygroscopic.  As the roots reach the soil, they become thick and pillar-like and start absorbing water and minerals.  In old plants, the main trunk may die, but the crown of the tree is supported and nourished by the prop roots. (ii) Stilt Root or Brace Roots  These are short and thick supporting roots which develop obliquely from the basal nodes of the stem.  These roots penetrate down into the soil and give support to the plant, e.g., maize ( ), sugarcane ( ), sorghum ( ), screw pine ( ), etc. In , the stilt roots develop only from the lower surface of the obliquely bending stem. They bear much folded multiple caps at their tips. (iii) Clinging or Climbing Roots  These are non-absorptive adventitious roots found in some climbers.  These may arise from the nodes, e.g., (Money Plant), or from internodes and both, e.g., Ivy.  These roots either enter into crevices or cracks of the support or stick firmly to the support by Morphology of Flowering Plants secreting a cementing gummy substance.  These help the climbers to climb up the support. Previous Year’s Question The plant which bears clinging roots is (1) Screw pine (2) (3) (4) Orchid 14.  ROOTS MODIFIED FOR VITAL FUNCTIONS (i) Assimilatory or Photosynthetic Roots Previous Year’s Question  These are green roots, which are capable of photosynthesis, e.g., water chestnut ( ). Prop roots are–  In some submerged roots are highly (1) Taproot branched and green in colour to perform (2) Adventitious root photosynthesis (3) Secondary root (4) All (ii) Haustorial or Parasitic Roots  These roots occur in parasitic plants that are achlorophyllous.  These roots absorb nourishment by establishing contact with the vascular tissue of the host plant.  Hence, also called as sucking roots or suckers. e.g., (Dodder Plant) has non-green stem and bears scale leaves. Dodder plant is a total parasite on hosts like etc. and obtains both water and food from the host. (iii) Hygroscopic or Epiphytic Roots  These are adventitious roots found in some orchids ( , etc.)  Orchids grow as epiphytes upon the trunks or branches of the trees.  The epiphytes develop aerial roots which hang freely in the air.  Roots of orchids are whitish in colour and are covered with a specialized spongy tissue called velamen.  Velamen helps the roots in absorbing atmospheric moisture. Morphology of Flowering Plants (iv) Floating Roots or Root Floats  These are inflated buoyant roots, spongy in texture due to abundant aerenchyma, arising at the nodes of some aquatic plants like.  These roots grow out of water and keep the plant afloat. 15.   These also help in gaseous exchange for respiration. Definition (v) Reproductive Roots Epiphyte: A plant that grows  Some fleshy adventitious roots develop upon another plant only for adventitious buds. shelter but is not a parasitem,  Adventitious buds can grow into new plants e.g., orchid. under favourable conditions. Such roots are called reproductive roots. Sweet potato, , etc. FUNCTIONS OF ROOTS Roots perform two types of functions — primary and secondary. A. Primary or Main Functions (Performed by all the roots)  Anchorage: The roots fix the plant in the soil firmly and support the aerial shoot system. Rack your Brain  Absorption: The roots absorb water and mineral from the soil. Maximum growth of roots occur  Translocation: The absorbed water and minerals in the region just behind the are translocated to the stem through the xylem apex. Justify of the root.  Synthesis of plant growth regulators  Prevention of soil erosion: Roots hold the soil particles firmly and prevent the soil from erosion. B. Secondary or Accessary Functions: The secondary functions are specialized functions and are performed only by those roots which are modified accordingly. Previous Year’s Question Morphology of Flowering Plants  Storage of food: Some roots store food and become fleshy, e.g., carrot, radish, , Root nodule is a modified , sweet potato, etc. structure of —  Additional support: Some roots like prop roots (1) Adventitious root and stilt roots provide additional support to the (2) Taproot plant, e.g., , (Maize), (3) Fibrous root etc. (4) Lateral root  Climbing: Some weak stemmed plants climb up 16.  a support with the help of clinging roots, e.g., (money plant), etc. Rack your Brain  Nitrogen fixation: The roots of some leguminous plants ( pea, gram, groundnut, etc.) contain Roots are not always geotropic. nitrogen-fixing bacteria in their nodules. These Justify bacteria fix free atmospheric nitrogen. Thus, enrich the soil by adding nitrogen compounds.  Breathing: Respiratory roots or pneumatophores of mangrove plants have lenticels that help in exchange of gases.  Moisture absorption and retention: Hygroscopic Gray Matter Alert!!! roots of some orchids (e.g., ) absorb moisture directly from the air. Rootless Plants: Submerged  Absorption of food: In parasitic plants (e.g., aquatic plants like , ), spine-like adventitious roots penetrate , etc. do the host and obtain food and water from the not possess roots. They absorb latter. water and minerals directly from  Assimilation: The green roots of , water the surfaces of stem and leaves. chestnut ( ) etc., carry out photosynthesis.  Floating: The roots of some aquatic plants (e.g., ) store air and function as floats.  Balancing: Cluster of adventitious roots arising in free floating aquatic plants (e.g., etc.) helps in balancing the plants over water, Keywords surface.  Reproduction. The roots of some plants have  Nodes adventitious buds (e.g., sweet potato) which help  Internodes in reproduction.  Tendril  Thorns THE STEM A stem is the main structural axes of vascular plants, it supports leaves, flowers and fruits, Morphology of Flowering Plants transports water and dissolved substances between the roots and the shoots via xylem Definition and phloem respectively, stores nutrients, and produces new structures from time to time. Stem: It is the main structural axes of vascular plants, it Morphology of the Stem supports leaves, flowers and  Stem develops from the plumule and epicotyl of fruits. It develops from the seed the embryo. plumule. 17.   It is generally an aerial and ascending part of the plant axis. Previous Year’s Question  Its apex bears a terminal bud for growth in length.  It bears nodes and internodes. Lateral organs of the stem are —  The stem nodes bear leaves. (1) Endogenous in origin  The young stem is green and is thus photosynthetic. (2) Exogenous in origin  In the mature state, it bears flowers and fruits. (3) Both  Stem branches and leaves develop exogenously. (4) None of the above  Stem exposes leaves, flowers and fruits to their most suitable position in the environment for optimum function.  Hair, if present, is generally multicellular.  Stem is positively phototropic and negatively geotropic. BUDS  A bud is a compacted underdeveloped shoot having a growing point, surrounded by closely placed immature leaves.  As the bud grows, the internodes become longer and the leaves spread out, resulting in the formation of a young shoot. Protection of Buds  Buds when covered by a series of overlapping and protective bud scales are called covered or closed buds or winter buds, e.g., Rack your Brain (Peepal) etc.  Buds without protective scales are called naked Which type of buds are buds found in herbaceous plants. found in the axile of leaves ?  The bud scales are often covered with hair or a coating of waxy, oily or resinous matter to Vegetative buds, floral buds or Morphology of Flowering Plants prevent desiccation and injuries due to extremes mixed buds. of temperature. 18. CLASSIFICATION OF BUDS On the basis of — (1) nature or structure (2) position 1. According to the nature or structure, buds are of the following types:  Vegetative Buds: Give rise to leafy shoots.  Floral or Flower Buds: Give rise to flowers or floral shoots.  Mixed Buds: Give rise to both vegetative shoots and flowers. 2. According to the origin and position, the buds are of following type: Terminal or Apical Buds  Occur at the tips of the main stem and its branches.  Help in length-wise increase of stem and its branches. Lateral Buds  Present on the stem and branches at various places except apices.  Adventitious Buds: Develop at places other than stem.  Foliar or epiphyllous: Found on leaves e.g.,  Radical: Found on roots, e.g., sweet potato  Cauline: Found on the stem and its branches, at places other than nodes and apices, e.g., rose ( ). Modifications of Buds Tendrillar Buds  Buds in some plants are modified into long spring-like threads called tendrils.  They help the plant with weak stem in climbing over some support, e.g., gourds (cucumber, pumpkins, watermelon) and grapevines. Bud Thorns  Axillary buds of stems may also get modified into woody, straight and pointed thorns.  They protect plants from browsing animals, to reduce.  Transpiration and act as organ of defense against grazing, e.g., Citrus,. Bulbils and Turions  Bulbils: These are specialized buds, which become fleshy due to the storage of Morphology of Flowering Plants food and take part in vegetative reproduction.  Bulbils may be axillary (e.g., lily), on the leaf, e.g., hairy Bittercress ( ), in place of flower on the floral axis (e.g., Onion, ) or base of the swollen roots (e.g., ).  Turions: The fleshy buds found in many aquatic plants perform the function of perennation e.g., etc. 19.  Primary or Main Functions of the stem  Stem bears leaves, flowers and fruits.  It conducts water and minerals from the roots to the leaves, flowers, and fruits.  It also transports food, manufactured by the leaves to the roots, fruits and other storage organs of the plant.  It adds new cells, tissues, and organs, which are required for the continued functioning of the plant. Previous Year’s Question Secondary or Accessory Functions Which of the following is an  A large number of plants store food and water underground stem? in their underground stems like rhizomes (e.g., (1) Ginger ginger), corms (e.g., ) and tubers (e.g., (2) Sweet potato potato). The stem of sugarcane ( (3) Radish ) stores sugar in it. (4) Turnip  The stems of several succulent plants (e.g., ) store water.  The underground stems such as rhizomes, corms, tubers, etc. perform the function of perennation ( tiding over unfavourable growing period).  In many plants, stems serve as a means of vegetative propagation as in the case of runner (e.g., grass), stolons (e.g., strawberry), o sets (e.g., ) and underground stems (e.g., mint, Potato, etc.). Rack your Brain  The stems of some weak-stemmed plants may be modified into tendrils (e.g., , Grapevine, Potatoes are cultivated by their etc.), thorns (e.g., ) and hooks (e.g., tubes. comment. ) to help them in climbing.  The stem of some plants is modified into thorns Morphology of Flowering Plants ( etc.), phylloclades (e.g., ) and cladodes (e.g., ) to reduce transpiration.  The stem thorns as in etc., act as organs of defence and protect the plant from browsing animals.  The stem in younger state and when modified into phylloclades (e.g., ) and cladodes ( 20.  etc.), performs the function of photosynthesis.  The stem when modified into a flower performs the function of sexual reproduction. DIFFERENT FORMS OF STEM  In most plants, stems grow above the soil surface. These are called aerial or epiterranean stems.  The aerial stems of some plants trail or creep on the ground. They are called sub-aerial or sub- epiterranean stems.  In some plants, the stems grow in the soil. Such stems are called underground or subterranean stems.  The aerial stems or epiterranean stems are of three types: ⚪ Reduced Rack your Brain ⚪ Erect ⚪ Weak Which part of the bulb stores 1. Reduced stems: The stem is reduced to a food ? small disc above the base of the root. Nodes and internodes are not distinct, and leaves arise crowded together on the stems.  Such leaves appear to arise directly from the root and are called radical leaves, e.g., radish, turnip, carrot, etc.  A reduced discoid, flattened stem is found in some free-floating aquatic plants such as etc.  It is green and leafless and floats on the surface of the water. Morphology of Flowering Plants  The underground structures called bulbs found in onion, garlic, etc., also possess a reduced and non-green stem. 21.  2. Erect stems: These are the most common type of aerial stems. The stems are strong enough to remain erect or upright without any external support. The erect stem is of the following types:  Culm: Erect, unbranched, cylindrical, hollow, nodes visible as rings and swollen. Stems are joined at nodes, e.g., bambino (family Gramineae).  Caudex: Erect, unbranched, cylindrical stem. On the stem, scars of fallen leaves are visible, e.g., coconut date palm.  Excurrent: The main stem is thicker than the branches, tapers towards the apical part, branching is acropetal. The appearance of the tree is just like a cone e.g., , ashoka tree, etc. Morphology of Flowering Plants  Decurrent or deliquescent: The main stem is short, and branching does not follow any definite manner and spread more laterally than vertically. At the stem top, the branches appear like a crown. The tree appears dome shaped, e.g., banyan ( ) 22.  3. Weak stems: These are thin, delicate, and slender stems, which cannot stand erect. Therefore, they require support to expose their leaves and reproductive organs. The weak stems may climb up support or grow prostrate on the ground. Thus, they are of two types: upright and prostrate. Previous Year’s Question A. Upright weak stems: These are weak stemmed plants, which climb up support to expose their foliage and reproductive A thin spirally coiled structure organs. The upright weak stems are of two sensitive to contact is— types: twiners and climbers. (1) Stem  Twiners. These have long, flexible, and (2) Root sensitive stems. The stem can coilaround (3) Tendril support like a rope, e.g., (4) Root hair (Bean)  Climbers: These have weak and flexible stems, which climb up a support with the help of certain clasping or clinging structures. Accordingly, climbers are of four types: ⚪ Root climbers: The stem cling to the support by adventitious roots, e.g., money plant ⚪ Tendril climbers: Tendrils are highly sensitive structures, specialized, thread-like structures, which can coil around a support, and help the weak stemmed shoot to climb up the support. When in contact with a support, the side of the tendril, which is Morphology of Flowering Plants opposite to that in contact grows more rapidly. This results in the coiling around the support and gives a firm grip for climbing. ⚪ Scramblers or ramblers: These are weak stemmed plants that climb up the support with the help of 23.  thorns (e.g., ), prickles (e.g., ) etc. ⚪ Lianas. These are woody twiners or climbers, e.g.,. B. Sub-aerial or sub-epiterranean stems (prostrate or weak stems): These weak stems spread on the ground for exposing their leaves and reproductive organs. Types of sub-aerial stems: Runners, suckers, stolon and O sets.  Runners ⚪ The sub-aerial weak stem and their slender lateral branches grow horizontally along the soil surface. ⚪ Adventitious roots arise from nodes and nodes bear new a tuft of leaves. ⚪ Runners serve as means of vegetative propagation. ⚪ The nodes bear scale leaves and axillary budsm, e.g., (lawn grass).  Stolon ⚪ They are elongated, horizontal or arched runners with long internodes like runners, these are slender axillary branches, which develop adventitious roots on coming in contact with the soil. ⚪ Each stolon has one or more nodes possessing scale leaves and axillary Morphology of Flowering Plants buds. ⚪ The axillary buds may either form a secondary stolon or may grow up as an erect short aerial stem. ⚪ Stolons also propagate vegetatively, e.g., jasmine, strawberry 24.  Sucker ⚪ These are sub-aerial, non-green branches that arise from the underground base of the aerial shoot or crown and runs parallel to the soil surface upto short distance then emerges out of the soil obliquely. ⚪ These sub-aerial branches are shorter and stouter than the runners. ⚪ Each sucker has one or more nodes with scale leaves and axillary buds. The axillary buds can also sprout into new shoots. ⚪ A sucker also bears adventitious roots at the nodes, e.g., mint, etc.  O set ⚪ These are one internode long, stout, slender and condensed runner found in rosette plants at the ground or water level. ⚪ An o set arises from an axillary bud at the base of the cluster of leaves. ⚪ It runs horizontally and terminates in a bud at a short distance that develops into adventitious roots and a rosette (cluster) of leaves, e.g., (water lettuce), (water hyacinth), etc. Morphology of Flowering Plants Gray Matter Alert!!! Trailers (Stragglers or Creepers): Spread without rooting, e.g.,. 25.  UNDERGROUND OR SUB-TERRANEAN STEMS  These stems lie below the soil surface.  These are non-green, store food and are adapted for perennation (i.e., surviving unfavourable conditions)  The underground stem sheds o aerial shoots or Rack your Brain leaves at intervals during favourable seasons.  The aerial shoots wither or die on the approach of unfavourable growth period, but the underground An exposed potato tuber during stems tide over this unfavourable period by cultivation develops chlorophyll remaining dormant. and turns green. Give reason.  They resume their activity on the return of favourable conditions and develop new aerial shoots. Such stems can be used as ‘seeds’ to produce new plants. How to di erentiate between underground stem and a root? Underground stems appear root like in their appearance, but they can be distinguished from roots by — (i) Absence of root caps; (ii) Absence of root hair; (iii) Presence of terminal bud; (iv) Presence of nodes and internodes; (v) Presence of foliage or scale leaves on the nodes; (vi) Presence of buds in the axils of scale leaves; (vii) Exogenous branching; (viii) Stem like internal structure. TYPES OF UNDERGROUND STEMS 1. Stem tuber  Fleshy, swollen, rounded or oblong distal portions of underground axillary or adventitious branches that arise from the underground basal nodes (present on tubers). Underground axillary or adventitious branches Morphology of Flowering Plants  are termed as stolons.  The tips of these branches become enlarged in the form of tubers, due to the accumulation of surplus food material manufactured by the aerial shoots.  Stem tubers are covered over by corky skin having lenticels for aeration.  Each tuber possesses several spirally arranged 26.  depressions called eyes.  Each eye represents a node that has a scale leaf in the form of a ridge. Each eye contains 1–3 dormant buds.  The stem tuber lacks adventitious roots, e.g., potato ( ), etc. Previous Year’s Question Example What is the eye of potato? Potato: The stem tuber of potato contains (i) Axillary bud reserve food in the form of starch. Stem (ii) Accessory bud tubers serve as a means of vegetative (iii) Adventitious bud propagation. A piece of stem tuber having an (iv) Apical bud eye can form a new plant. The tubers are cut into small pieces, having at least one or two eyes and are sown into the soil. The axillary buds present on these pieces (also called seeds) grow into aerial shoots, which then produce stolon and repeat the formation of tubers. 2. Rhizome  It is fleshy, horizontally growing, perennial, underground stem which continues to grow for an indefinite period producing new leaves or shoots during favourable conditions.  The aerial leaves or shoots wither or die on the approach of unfavourable conditions and are replaced by the new ones on the arrival of next favourable period.  A rhizome bears nodes and internodes.  The nodes bear scale leaves that protect axillary Morphology of Flowering Plants buds.  It also bears adventitious roots on the nodes and on the lower side.  Examples are (ginger), (turmeric, vern. Haldi), (banana), ferns such as , 27.  3. Corm  It is a vertically growing, thick, fleshy usually unbranched spherical or sub-spherical underground stem.  It bears several circular nodes with scales, which represent thin sheathing bases of fallen dead leaves.  The nodes bear axillary buds. Many adventitious roots are also borne at the base of the corm.  Corms take part in perennation.  They develop aerial shoots from their buds during favourable period. The aerial shoots manufacture food and store the same in their bases, where new corms are formed. The new corms may appear either above (e.g., ) or on the side (e.g., ) of the old ones.  The aerial shoots die o during the unfavourable season.  The old corms generally shrivel due to utilization of the stored food in forming the new aerial shoot in the next favourable season, e.g., (vern. Kesar), (vern. ), (elephant’s foot, vern. ) 4. Bulb  It is an underground spherical structure that possesses a reduced discoid stem and several fleshy, sheathing bases (usually called scales), enclosing a terminal bud. The base of the discoid Previous Year’s Questions stem bears fibrous adventitious roots.  The whole structure takes the shape of a bulb. The new banana plant develops The terminal bud normally forms a leafless hollow from— Morphology of Flowering Plants floral axis called scape, that bears a terminal (1) Rhizome cluster of flowers. (2) Sucker (3) Stolon Bulbs are of two types –Tunicate bulbs and (4) Seed non-tunicate bulbs (scaly bulbs). ⚪ Tunicate or laminate bulbs: These have fleshy scales arranged concentrically. Each scale completely envelops the younger one 28.  within it. The outer scale becomes dry and membranous forming a protective covering Keywords called as tunic. Types of tunicate bulbs  Caducous  Simple tunicate bulb  Phylloclade In this type of bulb, the fleshy scales represent  Axillary bud leaf bases in the outer region and scale leaves  Rhizome in the central part. The bulb is covered with a  Bulb whitish or pinkish tunic, e.g., (onion),  Corm (Tulips).  Tuber  Compound tunicate bulb (a) In this type, the fleshy scales represent axillary buds. Each axillary bud has its own tunic. (b) These fleshy buds are called bulblets or cloves. (c) The concentric rings of tunicate bulblets are in turn surrounded by overlapping tunics, e.g., (garlic) ⚪ Atunicate or scaly imbricate bulbs These bulbs lack tunic or covering sheath. The fleshy scales are narrow and overlap one another on the margins only. Such a bulb is never a compact body, e.g., (lily). Morphology of Flowering Plants 29.  MODIFICATIONS OF AERIAL STEMS In some plants, stems undergo an extreme degree of modifications and depict specific appearances to perform certain special functions besides the normal functions. How to recognize stem modification? By observing the following:  Position-axillary,  Origin-exogenous,  Presence of nodes and internodes,  Occurrence of occasional branching,  Presence of scale or reduced leaves,  Formation of flowers,  Internal structure (like that of a stem.  types of vascular bundle, etc.) TYPES OF AERIAL STEMS 1. Stem Tendrils These are thin, thread-like sensitive, leafless spring-like structures, which coil around a support and help the plant in climbing. Stem tendrils can be branch or unbranched. Branched stem tendrils may bear scale leaves in the region of forking. Stem tendrils are of the following types:  Axillary bud tendril— Axillary bud modifies into a tendril, e.g., (passion flower), (vern. ), (vern. ).  Apical bud tendril— Morphology of Flowering Plants ⚪ The apical bud gets modified into a tendril. ⚪ The growth of the axis is continued by successive lateral axillary buds on either side of the axis. ⚪ Thus, a sympodial axis is formed, and the tendrils are opposite to leaves, e.g., (grapevine). 30.  2. Stem Thorns  These are modified axillary buds, which have lost Previous Year’s Question the capacity for growth.  These are sti , woody, sharp and pointed. The prickles of rose are—  Reduce transpiration. (1) Modified leaves  Prevent browsing by animals. (2) Modified stipules  Stem thorns of are curved and help (3) Exogenous in origin in climbing. (4) Endogenous in origin  Examples are (glory of the garden),. Rack your Brain Morphology of Flowering Plants How are thorns di erent from spines ? 31.  3. Phylloclade  These are green flattened or cylindrical stem or branches, which appear leaf like, and have taken over the function of photosynthesis in the absence of normal green leaves.  The true leaves are Caducous (fall o soon after their appearance) or reduced to scales or spines to reduce transpiration.  Phylloclades are succulent due to storage of water, food and are of unlimited growth. Phylloclades are characteristics of some xerophytic plants such as , cacti, etc. Examples of Phylloclade Previous Year’s Question  It is flattened, succulent leaf-like and develops in Phylloclade is found in— the axil of a caducous leaf, which falls and leaves (1) (2) Cactus behind a scar. (3) (4) Both (1) & (2)  A phylloclade bears raised areas (called areoles) that are nodes and bear leaf scars, one or two large spines and several sti hairs called bristles or glochidia.  The spines are modified leaves of suppressed axillary branches and prevent transpiration.  Thick, angular and contain milky gates.  It bears caducous leaves at the nodes during the favourable growth period.  The stipules are modified into spines. Morphology of Flowering Plants 4. Cladodes ( ):  These are green cylindrical or flattened stem branches of limited growth (usually one internode long).  They have taken over the function of photosynthesis from leaves.  The true leaves are reduced to scales and spines 32.  to reduce transpiration.  The cladodes arise in the axils of scaly or spiny leaves at the nodes on the normal stem, e.g., (butcher’s broom), , etc. Example of Cladode  The cladodes of are green, leathery and leaf like.  They are borne singly in the axil of scale leaves.  A floral bud with a basal scale leaf develops in the middle of a cladode, which is one internode long.  They develop in clusters in the axil of scale or spine leaves. Each cluster represents a suppressed, cymosely divided branch. Rack your Brain How is a cladode di erent from a phyllode ? Morphology of Flowering Plants 33.  MORPHOLOGY OF LEAF  Leaf is a flattened, lateral outgrowth, which is Definition borne exogenously on the node of a stem or its branches and bears bud in its axil. Leaf: Lateral, flattened  Typically, it is green in colour due to the presence outgrowth found attached on of chlorophyll and is the chief photosynthetic nodal areas of the stem and is organ of the plant. exogenous in origin.  All the green leaves of a plant are collectively called foliage. Characteristics of a leaf  The leaf is a dissimilar lateral outgrowth of the stem.  It is borne on the node of the stem in acropetal order.  It is exogenous in origin.  It often bears axillary bud.  The leaf does not bear an apical bud or regular growing point.  A leaf is di erentiated into three parts—leaf base, petiole and lamina.  The leaf base may possess two lateral outgrowths called stipules.  The lamina is traversed by prominent streaks called veins. Parts of a leaf (i) leaf base or hypopodium, (ii) petiole or mesopodium and (iii) lamina or leaf blade or epipodium. 1. Leaf Base (Hypopodium)  Leaf base is the lowermost part of the leaf, by Morphology of Flowering Plants which the leaf is joined to the node of the stem or its branch.  Usually, it protects a small bud in its axil.  Leaf base is often indistinguishable from the petiole. In many leguminous plants, it is swollen. The swollen leaf base is called pulvinus.  It is responsible for sleep or shock movements of certain plants (e.g., ). 34.  Keywor  Hypo  Meso  Epipo  Pulvin  Ampl  In several monocot plants (e.g., cereals, grasses,  Stipu etc.) the leaf base is broadened. It clasps and  Axilla forms a sheath like structure around the stem at  Semi- the node. Such a leaf base is called a sheathing leaf base.  When the leaf base surrounds the stem partially, it is called semi amplexicaul.  When the leaf base surrounds the stem, it is called amplexicaul. Stipules: In many plants, the leaf base possesses two lateral outgrowths, called stipules. They protect leaf primordia.  The stipules vary in size and form and can be free or fused.  The fused stipules cover and protect leaves in the bud e.g., (banyan tree, rubber tree).  In pea and wild pea, the stipules are large and Gray Matter Alert!!! green to take part in photosynthesis. They are called foliaceous stipules. Broadest Leaf—  In and the stipules are modified (diameter 1.5—1.8m) into spines to reduce transpiration. They also Longest Leaf— (10 protect the plant from grazing animals. Such - 15m) stipules are called spiny stipules.  In , the stipules are modified into tendrils to help the plant in climbing. They are called tendrillar stipules. Morphology of Flowering Plants 35.  2. Petiole (Mesopodium)  It is a cylindrical or sub-cylindrical stalk of the Previous Year’s Question leaf.  It raises the lamina above the stem to provide The broad part of a leaf is — maximum exposure. (1) Leaf base  In some plants, the leaves are without petioles, (2) Petiole such leaves are called sessile leaves. (3) Lamina  The leaves with petioles are called petiolate (4) All leaves. 3. Lamina (leaf blade or Epipodium)  It is green, expanded portion of the leaf.  It is the main site of photosynthesis and also helps in exchange of gases.  Lamina is interspersed with a number of veins and veinlets. Definition  The veins and veinlets contain vascular tissues for the transport of water and food. They also Heterophylly: A condition where provide rigidity to the lamina and keep the latter a plant has di erent leaf forms expanded. at di erent stages in its life  There are one or more prominent veins in the cycle. lamina. They are called midribs or mid-veins. Types of Leaves Leaf Duration: Based on the life span, leaves are of three types:  Caducous (Fugacious): Leaves falling down soon after their appearance, e.g.,  Deciduous (Annual): Leaves falling o simultaneously at the end of growing season, leaving the plant leafless. The phenomenon is called leaf fall, e.g., Mulberry, Poplar etc.  Persistent (Evergreen): Leaves live for more than one season. They fall down individually at di erent times. Plants with persistent leaves are called evergreen, e.g., etc. Morphology of Flowering Plants Venation Keywords The arrangement of veins and veinlets in the lamina of a leaf is called venation.  Venation  The veins are the conducting channels for water,  Reticulate venation minerals and organic food.  Parallel venation  Veins also provide firmness to the lamina and  Furcate venation keep it expanded. 36.  The lamina has one or more prominent veins termed as midribs, which arise from the petiole.  Midrib (prominent/main vein) gives rise to lateral veins that traverse the entire lamina.  The veins and veinlets are more prominent on the undersurface of the lamina in dorsiventral leaves. Types of Venation — Reticulate, Parallel and Furcate.  Reticulate Venation  The veins arising from the midrib, branch and re-branch to form a network of veins, this network is reticulate venation.  It is a characteristic feature of the leaves of dicot plants.  Exception: ,  Based on the number of main veins or midribs in the lamina, reticulate venation has two Morphology of Flowering Plants sub-types: (i) Pinnate or Unicostate Reticulate Venation  The lamina has a single principal vein or midrib extending from base to the apex.  It produces lateral veins.  Lateral veins branch and re-branch into veinlets forming a network-like structure, e.g., leaf of Banyan, Mango, etc. 37.  (ii) Palmate or Multicostate Reticulate Venation:  The lamina has more than one prominent or Previous Year’s Question principal veins arising from the tip of the petiole and reaching either the apex or margin of the lamina. Which type of leaf arrangement is  They give rise to lateral veins and further to found in ? veinlets. (1) Alternate  Multicostate reticulate venation has two forms: (2) Spiral  Convergent: The principal veins converge towards (3) Opposite the apex of the lamina, e.g., ( ) (4) Whorled  Divergent: The principal veins diverge towards the margin, e.g., Castor. 2. Parallel Venation  The veins arising from midrib or main veins run parallel to each other towards the margin Morphology of Flowering Plants or the apex of the lamina.  The veinlets are inconspicuous and reticulation or network of veinlets is absent.  Parallel venation is characteristic of the leaves of monocot plants.  Exception: , ,  Parallel venation is of two sub-types. 38.  (i) Pinnate or Unicostate Parallel Venation  The lamina has a single prominent vein or midrib running from the base to the apex of the lamina.  It gives o lateral veins that run parallel toward the margin of the lamina, e.g., (banana), , etc. Types of Parallel Venation A. Unicostate parallel venation of banana; B. Multicostate convergent of bamboo; C. Multicostate divergent venation of Fan Palm. (ii) Palmate or Multicostate Parallel Venation  The lamina has several principal veins arising from the base and running towards the apex or margin of the lamina.  The main veins do not branch further. (a) Multicostate parallel venation has two forms  Convergent: The principal veins converge towards Rack your Brain the apex, e.g., bamboo, grass.  Divergent: The principal veins diverge towards Why are vascular bundles the margin Fan palm. arranged in linear rows in monocot leaves ? Morphology of Flowering Plants 3. Furcate Venation  The veins give o dichotomous branching.  The finer branches do not form reticulum.  Furcate venation is common in ferns.  Among higher plants, it is found in 39.  Phyllotaxy Phyllotaxy (Gk. –leaf, – Previous Year’s Question arrangement) is the arrangement or distribution of leaves on the stem or its The arrangement of leaves on a branches so that they may receive maximum stem branch is— sunlight to perform photosynthesis. (1) Venation (2) Aestivation (3) Inflorescence (4) Phyllotaxy Types of Phyllotaxy 1. Alternate or Spiral  Only one leaf is borne on a node and the leaves of the adjacent nodes lie roughly towards the opposite sides, e.g., (shoe flower), sunflower, mustard, etc.  In this phyllotaxy, the leaves are arranged spirally around the stem.  The leaves appear to form vertical rows and are termed orthostichous.  In such cases, phyllotaxy is determined by passing a thread along with the bases of successively higher leaves till a leaf comes Morphology of Flowering Plants to lie exactly above the first one (which is counted as zero).  This forms a spiral path on the stem. It is called genetic spiral. 40.  2. Opposite Phyllotaxy  Two leaves are borne opposite to each other at Keywords a node.  For example guava, etc.  Opposite phyllotaxy is of two types.  Phyllotaxy  Opposite superposed  Opposite phyllotaxy Leaves of the successive node lie in the same  Alternate phyllotaxy plane so that only two rows are formed on the  Whorled phyllotaxy stem, e.g., (rangoon creeper), , etc.  Opposite Decussate: The opposite leaves of the adjacent nodes lie at right angle so that four rows of leaves are formed on the stem. (vern. Ak), (vern. ). Rack your Brain How are alternate and spiral phyllotaxes di erent and similar? Morphology of Flowering Plants 3. Whorled or Verticillate  More than two leaves are borne on a node.  They are arranged in a circle or a whorl.  The leaves of one whorl generally alternate with those of the adjacent whorls to provide maximum exposure, e.g., (oleander), (devil tree/ pencil tree). 41.  Simple and Compound leaves Simple leaf  The simple leaf has single or undivided lamina.  The lamina of a simple leaf may have incisions, but the incisions do not reach the midrib and the lamina does not divide into separate lobes, e.g., Castor, , (marigold), etc. Incisions of Lamina  It is the process of dividing or partitioning the lamina. The degree of incisions varies in di erent plants.  In pinnately veined leaves the incision proceeds from the margin to the midrib. Morphology of Flowering Plants