Plant Organization PDF

Unit I. INTRODUCTION 1. Levels of plant organization 2. Organs found in a vascular plant body 3. Features of vascular plants 4. Types of steles 5. Alternation of Generations 6. Overview of Extinct and Extant Vascular Plant Intended Learning Outcomes (ILOs) At the end of the unit, the...

Unit I. INTRODUCTION 1. Levels of plant organization 2. Organs found in a vascular plant body 3. Features of vascular plants 4. Types of steles 5. Alternation of Generations 6. Overview of Extinct and Extant Vascular Plant Intended Learning Outcomes (ILOs) At the end of the unit, the student must have: 1. discussed the levels of plant organization. 2. identified the organs found in a vascular plant body. 3. enumerated the features of vascular plants. 4. identified and described the type of steles. 5. discussed alternation of generations. 6. identified the extinct and extant vascular plants. Learning Activities/Outputs Lecture Discussion Portfolio/e portfolio ( Types of Stele) Concept map (on the alternation of generations of vascular plants) Group Role Playing on the Life Cycle of different Plant groups Worksheets (Basic morphological and anatomical terms Topics/Content 1. LEVELS OF PLANT ORGANIZATION  At the lowest level are cells Examples: Parenchyma, Sclerenchyma, Collenchyma, Cork, tracheids, vessels, sieve tube/cells  Cells are organized together to form tissues Examples: epidermis, cortex, xylem, phloem  Tissues are organized together to form organs (two or more tissues performing specific functions) Examples: Root, stem, leaf, flower, fruit  Organs are organized together to form organ systems Example: Root system and Shoot system Plant Tissues Plants are multicellular eukaryotes with tissue systems made of various cell types that carry out specific functions. Plant tissues are composed of cells that are similar and perform a specific function. Together, tissue types combine to form organs. Each organ itself is also specific for a particular function. Two general types of plant tissues: 1. Meristematic tissue regions of continuous cell division and growth/ no longer actively dividing cells 2. Permanent (or non-meristematic) tissue. MERISTEMATIC TISSUES Cells of the meristematic tissue are found in meristems, which are plant regions of continuous cell division and growth. Meristematic tissue cells are either undifferentiated or incompletely differentiated, and they continue to divide and contribute to the growth of the plant. In contrast, permanent tissue consists of plant cells that are no longer actively dividing. Meristematic tissues consist of three types, based on their location in the plant. a. Apical meristems contain meristematic tissue located at the tips of stems and roots, which enable a plant to extend in length. b. Lateral meristems facilitate growth in thickness or girth in a maturing plant. c. Intercalary meristems occur only in monocots, at the bases of leaf blades and at nodes (the areas where leaves attach to a stem). This tissue enables the monocot leaf blade to increase in length from the leaf base; for example, it allows lawn grass leaves to elongate even after repeated mowing. PERMANENT TISSUES Meristems produce cells that quickly differentiate, or specialize, and become permanent tissue. Such cells take on specific roles and lose their ability to divide further. They differentiate into three main types: dermal, vascular, and ground tissue. 1. Dermal tissue covers and protects the plant. Are complex tissues because they consist of multiple cell types. 2. Ground tissue serves as a site for photosynthesis, provides a supporting matrix for the vascular tissue, and helps to store water and sugars. Is a simple tissue, meaning that each ground tissue consists of only one cell type 3. Vascular tissue transports water, minerals, and sugars to different parts of the plant. Are complex tissues because they consist of multiple cell types. Dermal tissue covers the plant and can be found on the outer layer of roots, stems and leaves. Its main functions are transpiration, gas exchange and defense. The epidermis is an example of dermal tissue(Figure 3.1.3.1). stomata opening guard cells Scanning electron microscope of epidermal cells & guard cells; light micrograph & diagram of stoma. Figure 3.1.3.1 It is composed of a single layer of epidermis cells. It may contains stomata and guard cells that allow gas exchange. It may contain root hairs that increase surface area or or trichomes used in transpiration or defense. It may contain a waxy cuticle if found on the upper surface of leaves, to aid with lowering transpiration.: Openings called stomata (singular: stoma) allow a plant to take up carbon dioxide and release oxygen and water vapor. The (a) colorized scanning-electron micrograph shows a closed stoma of a eudicot. Each stoma is flanked by two guard cells that regulate its (b) opening and closing. The guard cells are more curved when the stoma is open compared to when it is closed. The (c) guard cells sit within the layer of epidermal cells. In woody plants, the epidermis breaks apart into a thick periderm as secondary growth allows the plant to grow in girth. The cork cambium, which makes cork cells, the cork cells (which are dead at maturity), and the phelloderm (parenchyma cells on the inside of the cork cambium) together make up the periderm (Figure 3.1.3.2). The periderm functions as the first line of defense for the plant, protecting it from fire or heat injury, dehydration, freezing conditions, and/or disease. makes cork cells dead at maturity allows plant to grow parenchyma cells in girth> on the inside of the cork cambium Cross section of a woody plant, labeled periderm, cork cambium, cork cells, and phelloderm Figure 3.1.3.2: Cross section of a woody stem. The periderm is composed of the cork cambium, cork cells, and phelloderm. Credit: Kammy Algiers (CC-BY). Ground Tissue Often times, tissues that are not considered dermal or vascular tissue are noted as ground tissue. These cells store molecules (such as starch), photosynthesize (such as mesophyll cells), or support the plant. There are three types of ground tissue: collenchyma, sclerenchyma, and parenchyma. Collenchyma (Figures 3.1.3.3−4) is living supportive tissue that has elongated cells and an unevenly thickened primary cell wall. Its main function is the mechanical support of young stems and leaves via turgor. Collenchyma cells in cross section. They contain uneven cell walls. Figure 3.1.3.3: Collenchyma cell walls are uneven in thickness, as seen in this light micrograph. They provide support to plant structures. (credit: modification of work by Carl Szczerski; scale- bar data from Matt Russell) Sclerenchyma is a dead supportive tissue that consists of long sclerenchyma fibers (Figure 3.1.3.4) or short, crystal-like cells (sclereids; Figure 3.1.3.5). Sclerenchyma fibers occur in groups (bundles). Sclereids may be branched or not and occur individually or in small clusters. Each cell has a uniformly thick secondary wall that is rich in lignin. Its main function is a support of older plant organs, and also hardening different parts of plants (for example, make fruit inedible before ripeness so no one will take the fruit before seeds are ready to be distributed). Without sclerenchyma, if a plant isn’t watered, the leaves will droop because the vacuoles will decrease in size which lowers the turgor. Fibers inside phloem (see below) are sometimes regarded as a separate sclerenchyma. Three cell types, parenchyma, sclerenchyma (cross- and longitudinal sections) and collenchyma. Figure 3.1.3.4: Left to right, top to bottom: parenchyma, sclerenchyma (cross- and longitudinal sections) and collenchyma. First three photos from the stem of Helianthus, fourth from Medicago stem. Magnification ×400. Figure 3.1.3.5Cross section of thick-walled, pink cells in a cluster in pear tissue A large pink cell in a water lily leaf cross section with several projections (branches): The grainy texture of pears (Pyrus) is due to clusters of stone cells (sclereids), the thick-walled cells that stained pink (left, magnification = 400X). Water lily (Nymphea) leaves contains single, branched sclereids (right, magnification = 400X). Left and right image by Berkshire Community College Bioscience Image Library (public domain). Parenchyma (Figure 3.1.3.4) are spherical, elongated cells with a thin primary cell wall. It is a main component of young plant organs. The basic functions of parenchyma are photosynthesis and storage. They are also important in regeneration because they are totipotent (capable of differentiating into any cell type). Parenchyma cells are widespread in plant body. They fill the leaf, frequent in stem cortex and pith and is a component of complex vascular tissues (see below). TOTIPOTENT - capable of differentiating into any cell type  Xylem Vascular Tissue Phloem Vascular tissue is the plumbing system of the plant. It allows water, minerals, and dissolved sugars from photosynthesis to pass through roots, stems, leaves, and other parts of the plant. It is primary composed of two types of conducting tissue: xylem and phloem. The veins on leaves are an example of vascular tissue, moving material through the plant in the same manner that our blood vessels carry nutrients through our body. The xylem and phloem always lie adjacent to each other (Figure 3.1.3.6). In stems, the xylem and the phloem form a structure called a vascular bundle; in roots, this is termed the vascular stele or vascular cylinder. Light micrograph of a round plant stem cross section with epidermis, phloem, xylem, and vascular bundle labeled. Figure 3.1.3.6: This light micrograph shows a cross section of a squash (Curcurbita maxima) stem. Each teardrop-shaped vascular bundle consists of large xylem vessels toward the inside and smaller phloem cells toward the outside. Xylem cells, which transport water and nutrients from the roots to the rest of the plant, are dead at functional maturity. Phloem cells, which transport sugars and other organic compounds from photosynthetic tissue to the rest of the plant, are living. The vascular bundles are encased in ground tissue and surrounded by dermal tissue. Xylem tissue transports water and minerals from the roots to different parts of the plant. The conducting cells of the xylem are called tracheary elements. Parenchyma cells are also found in the xylem, and sclerenchyma fibers and sclereids are sometimes present. There are two type of tracheary elements: vessel elements and tracheids (Figure 3.1.3.7 ). Both cell types that are dead at maturity and have thickened secondary cell walls. These cells connect to one another and allow water to be transported through them. Structurally, the vessel elements are wider than tracheids and contain perforation plates between adjacent vessel elements (Figure 3.1.3.7−8). Wide openings (slits or pores) in perforation plates allow water to flow vertically between vessel elements, forming a continuous tube. Both types of tracheary elements contain pits, gaps in their secondary cell walls. Adjacent cells have pits in the same locations, forming pit pairs, which allow water and minerals to flow between adjacent cells through the pit membrane (the remaining, thin primary cell walls in these regions; Figure 3.1.3.9−10). Therefore, water flows through both perforation plates and pit pairs in vessel elements but only through pit pairs in tracheids. While water can move more quickly through vessel elements, they are more susceptible to air bubbles. An air bubble disrupts cohesion in the column of water moving up the tube of vessel elements preventing use of that particular pathway. In tracheids, an air bubble would only decommission a single tracheid rather than an entire column of vessel elements. Vessel elements are found only in angiosperms, but tracheids are found in both angiosperms and gymnosperms. Figure 3.1.3.7: Xylem transports water and minerals through vessel elements and tracheids, which are dead at maturity and have a thin primary and thick secondary cell wall internal to the primary cell wall. In pits, the secondary wall is thin or missing, allowing water to flow laterally. The xylem of angiosperms contains both types of tracheary elements: vessel elements, and tracheids. Vessel elements are stacked up top of each other and contain perforation plates in between cells. Tracheids are thinner and lack performation plates. Pits are thinned regions in the cell wall that allow movement of water between adjacent tracheary elements. Figure 3.1.3.8: Longitudinal section of vessel elements in a Cucurbita (squash) stem (magnification = 400X). Horizontal purple lines represent perforation plates between cells in a column. The rings around the cells are annular cell wall thickenings. Figure 3.1.3.9: Pits are thinned regions of the cell wall (left). Pits of adjacent cells together form pit pairs separated by a pit membrane. On either side of the pit membrane is a pit chamber. The pit aperature is the opening to the pit chamber. The pit membranes of gymnosperms have a thickened central region called the torus (right). 1: The margo is the part of the membrane surrounding the torus. 2: The torus can block the pit opening (aperture) as needed to prevent air bubbles from spreading throughout the xylem. Left and right image by Pagliaccious (CC-BY-SA). Tracheids appear as pink columns. Pit pairs look like stacks of bulls eyes along each tracheid. Figure 3.1.3.10 Figure 3.1.3.103.: Bordered pits in tracheids of pine (Pinus) wood appear as bulls eyes. Pit pairs of some species have thickened outer regions (borders). Inside of this is a thinned membrane (margo) and a thickened central portion (torus). Phloem tissue transports organic compounds such as sugars from the site of photosynthesis to rest of the plant (Figure 3.1.3.11−12). The conducting cells of the phloem are called sieve elements. In comparison to tracheary elements, sieve elements have only primary cell walls (and thus thinner cell walls overall) and are alive at maturity; however, they lack certain organelles, including a nucleus. Sieve-tube elements are the sieve elements found only in angiosperms while sieve cells are found only in gymnosperms while. Both types of sieve elements have pores in their cell walls (sieve areas) that allow transfer of materials between adjacent cells, but these are concentrated at sieve plates in sieve-tube elements and evenly distributed in sieve cells. Because they lack essential organelles, sieve elements rely on specialized parenchyma cells to support them. Companion cells support sieve-tube elements in angiosperms, and albuminous cells support sieve cells in gymnosperms. Additionally parenchyma cells and sclerenchyma cells (phloem fibers) are also found in the phloem. The cells of the phloem, including wide sieve-tube elements, which are separated by sieve plates, and thinner, companion cells with nuclei. sieve elements sieve tube elements - angiosperms sieve cells - gymnosperms Figure 3.1.3.11: Phloem transports sugars and other items. In angiosperms, sieve-tube elements contain the sugar solution. Sieve-tube elements are the conducting cells of the phloem in angiosperms. Sieve plates allow sieve-tube elements stacked on top of each other to connect. Sieve-tube cells are surrounded by various support cells. Companion cells are narrower than sieve-tube elements and each contain a nucleus. They are connected to sieve-tube elements via plasmodesmata and provide them with the molecules they need to function (energy molecules, proteins, etc.) Some companion cells are specialized as intermediary cells, which are between the bundle sheath (see below) and sieve-tube element. Transfer cells are parenchyma cells with cell wall ingrowths, which increase surface area for transport. The bundle sheath cells form the bundle sheath, which surrounds vascular bundles (where the xylem and phloem are located). Within the bundle sheath cell are oval chloroplasts, a nucleus (not labeled), and the central vacuole, which fills most of the cell. Cucurbita stem cross section showing the cells of the phloem, including wide sieve-tube elements, and small, dark companion cells. Figure 3.1.3.12: Phloem in a cross section of a Cucurbita (squash) stem, magnified at 400X. Each wide sieve-tube cell has a small, dark companion cell associated with it. (The companion cells are dark because each contains a nucleus.) The cross section cut exactly in between two sieve tube elements in some cases, revealing the sieve plate. The table below summarizes differences between xylem and phloem: Xylem Phloem Contains mostly Dead cells Living cells Transports Water & Minerals Sugar Direction Up Up and Down Biomass Big Small PLANT BODY Root System The root is non-green, cylindrical descending axis of the plant that usually grows into the soil (positively geotropic). It develops from the radicle which is the first structure that comes out when a seed is placed in the soil. Root is responsible for absorption of water and nutrients and anchoring the plant. ROOT Types of root I. Tap root system Primary root is the direct prolongation of the radicle. When the primary root persists and continues to grow as in dicotyledons, it forms the main root of the plant and is called the tap root. Tap root produces lateral roots that further branches into finer roots. Lateral roots along with its branches together called as secondary roots. II. Fibrous / Adventitious root system Root developing from any part of the plant other than radicle is called adventitious root. It may develop from the base of the stem or nodes or internodes. Example: Monstera deliciosa, Ficus benghalensis, Piper nigrum. In most of the monocots the primary root of the seedling is short lived and lateral roots arise from various regions of the plant body. These are bunch of thread-like roots equal in size which are collectively called fibrous root system generally found in grasses. Example: Oryza sativa, Eleusine coracana, Pennisetum americanum.  Regions of root Root tip is covered by a dome shaped parenchymatous cells called root cap. It protects the meristematic cells in the apex. In Pandanus multiple root cap is present. In Pistia instead of root cap root pocket is present. A few millimeters above the root cap the following three distinct zones have been classified based on their meristematic activity. absorption maturation indicator epidermis > cells differentiate int various tissues, also produce root cortex hairs which absorbs water and minerals from the soil xylem phloem tube > increase in length and cause enlargement of the root root cap / meristematic region > the main growing tip of the root > parenchymatous in structure  Orchids begonia parasitic plants e.g,.cuscuta Trapa plant terminalia climbing hydrangea sugarcane Mangroove Tap root modification S, B a. Storage root 1. Conical Root - These are cone like, broad at the base and gradually tapering towards the apex. Example: Daucus carota. Carrots 2. Fusiform root - These roots are swollen in the middle and tapering towards both ends. Example: Raphanus sativus Raddish 3. Napiform root -It is very broad and suddenly tapers like a tail at the apex. Example: Beta vulgaris Beet b. Breathing root Some mangrove plants like Avicennia, Rhizophora, Bruguiera develop special kinds of roots (Negatively geotropic) for respiration because the soil becomes saturated with water and aeration is very poor. They have a large number of breathing pores or pneumatophores for exchange of gases. fusiform coniform napiform breathing root Adventitious root modification S, M, V a. Storage roots T, F, N, M, A, 1. Tuberous root These roots are swollen without any definite shape. Tuberous roots are produced singly and not in clusters. Example: Ipomoea batatas. 2. Fasciculated root These roots are in cluster from the base of the stem Example: Dahlia, Asparagus, Ruellia. 3. Nodulose root In this type of roots swelling occurs only near the tips. Example: Maranta (arrow root) Curcuma amada (mango ginger), Curcuma longa (turmeric) 4. Moniliform or Beaded root These roots swell at frequent intervals giving them a beaded appearance. Example: Vitis, Portulaca, Momordica, Basella (Indian spinach). 5. Annulated root These roots have a series of ring- like swelling on their surface at regular intervals. Example: Psychotria (Ipecac) b. Mechanical support 1. Prop (Pillar) root These roots grow vertically downward from the lateral branches into the soil. Example: Ficus benghalensis (banyan tree), Indian rubber. 2. Stilt (Brace) root These are thick roots growing obliquely from the basal nodes of the main stem. These provide mechanical support. Example: Saccharum officinarum, Zeamays, Pandanus, Rhizophora. 3. Climbing (clasping or clinging) roots These roots are produced from the nodes of the stem which attach themselves to the support and help in climbing. To ensure a foothold on the support they secrete a sticky juice which dries up in air, attaching the roots to the support. Example: Epipremnum pinnatum, Piper betel, Ficus pumila. 4. Buttress root In certain trees broad plank like outgrowths develop towards the base all around the trunk. They grow obliquely downwards and give support to huge trunks of trees. This is an adaptation for tall rain forest trees. Example: Bombax ceiba (Red silk cotton tree), Ceiba pentandra (white silk cotton tree), Terminalia arjuna, Delonix regia, Pterygota alata. c. Vital functions velamen - spongy tissue which helps in absorption of moisture from the surrounding air. 1. Epiphytic or velamen root Some epiphytic orchids develop a special kind of aerial roots which hang freely in the air. These roots develop a spongy tissue called velamen which helps in absorption of moisture from the surrounding air. Example: Vanda, Dendrobium, Aerides. 2. Foliar root Roots are produced from the veins or lamina of the leaf for the formation of new plant. Example: Bryophyllum, Begonia, Zamioculcas. 3. Sucking or Haustorial roots These roots are found in parasitic plants. Parasites develop adventitious roots from stem which penetrate into the tissue of the host plant and suck nutrients. Example: Cuscuta (dodder), Cassytha, Orobanche (broomrape), Viscum (mistletoe), Dendrophthoe. 4. Photosynthetic or assimilatory roots Roots of some climbing or epiphytic plants develop chlorophyll and turn green which help in photosynthesis. Example: Tinospora, Trapa natans (water chestnut), Taeniophyllum. Shoot system STEM The plumule of the embryo of a germinating seed grows into stem. The epicotyl elongates after embryo growth into the axis (the stem) that bears leaves from its tip, which contain the actively dividing cells of the shoot called apical meristem. Further cell divisions and growth result in the formation of mass of tissue called a leaf primordium. The point from which the leaf arises is called node. The region between two adjacent nodes is called internode. I. Characteristic features of the stem 1. The stem is usually the aerial portion of the plant 2. It is positively phototropic and negatively geotropic 3. It has nodes and internodes. 4. Stem bears vegetative bud for vegetative growth of the plant, and floral buds for reproduction, and ends in a terminal bud. 5. The young stem is green and thus carries out photosynthesis. 6. During reproductive growth stem bears flowers and fruits. 7. Branches arise exogenously 8. Some stems bears multicellular hairs of different kinds. II. Functions of the stem Primary functions 1. Provides support and bears leaves, flowers and fruits. 2. It transports water and mineral nutrients to the other parts from the root. 3. It transports food prepared by leaves to other parts of the plant body. Secondary functions  Food storage- Example: Solanum tuberosum, Colocasia and Zingiber officinale  Perennation / reproduction – Example: Zingiber officinale, Curcuma longa   Water storage – Example: Opuntia  Bouyancy – Example: Neptunia  Photosynthesis – Example: Opuntia, Casuarina, Euphorbia  Protection – Example: Citrus, Duranta, Bougainvillea, Acacia  Support - Example: Passiflora, Bougainvillea, Vitis Leaf scar -a scar marking the former point of attachment of a leaf or petiole to the stem. Node - part of the stem marking point of attachment of leaves, buds and other stems. Internode -the part of the stem between the nodes. Lenticel – Loosely packed, rough areas on stems (and some fruits, ex. apple) where loosely packed cells extend from the cortex through the ruptured epidermis; they function as breathing pores for gas exchange. Buds are the growing points surrounded by protective scale leaves. The bud primordium matureinto bud. They have compressed axis in which the internodes are not elongated and the young leaves are closed and crowded. When these buds develop, the internodes elongate and the leaves spread out. Buds have architecture identical to the original shoot and develop into lateral branches or may terminate by developing into a flower or inflorescence. Based on Origin Buds are classified into (a) Terminal or Apical bud (b) Lateral or Axillary or Axil bud. Based on Function Buds classified into (a) Vegetative bud (b) Floral or Reproductive bud 1.Terminal bud or apical bud: These buds are present at the apex of the main stem and at the tips of the branches. 2. Lateral bud or Axillary bud: These buds occur in the axil of the leaves and develop into a branch or flower. 3. Extra axillary bud : These buds are formed at nodes but outside the axil of the leaf as in Solanum americanum. 4. Accessory bud : An extra bud on either side (collateral bud) or above (superposed bud or serial bud) the axillary bud. Example: Citrus and Duranta 5. Adventitious buds: Buds arising at any part other than stem are known as adventitious bud. 6. Bulbils (or specialized buds) : Bulbils are modified and enlarged bud, meant for propagation. When bulbils detach from parent plant and fall on the ground, they germinate into new plants and serve as a means of vegetative propagation. In Agave and Allium proliferum floral buds get modified into bulbils. In Lilium bulbiferum and Dioscorea bulbifera, the bulbils develop in axil of leaves. In Oxalis, they develop just above the swollen root. Types of Stem Majority of angiosperm possess upright, vertically growing erect stem. They are (i) Excurrent, (ii) Decurrent, (iii) Caudex, (iv) Culm. i. Excurrent The main axis shows continuous growth and the lateral branches gradually becoming shorter towards the apex which gives a conical appearance to the trees. Example: Casuarina. ii. Decurrent The growth of lateral branch is more vigorous than that of main axis. The tree has a rounded or spreading appearance. Example: Mangifera indica, Azadirachta indica, Tamarindus indicus iii. Caudex It’s an unbranched, stout, cylindrical stem, marked with scars of fallen leaves. Example: Cocus nucifera, Areca catechu iv. Culm Erect stems with distinct nodes and usually hollow internodes clasped by leaf sheaths. Example: Majority of grasses including Bamboo. STEM ANATOMY 3. Modification of Stem I. Aerial modification of stem 1. Creepers These are plants growing closer (horizontally) to the ground and produces roots at each node. Example: Cynodon dactylon, Oxalis, Centella 2. Trailers (Stragglers) It is a weak stem that spreads over the surface of the ground without rooting at nodes. They are divided into 3 types, i. Prostrate (Procumbent): A stem that grows flat on the ground. Example: Evolvulus alsinoides, Indigofera prostrata. ii. Decumbent: A stem that grows flat but becomes erect during reproductive stage. Example: Portulaca, Tridax, Lindenbergia iii. Diffuse: Atrailingstemwithspreading branches. Example: Boerhaavia diffusa, Merremia tridentata 3. Climbers These plants have long weak stem and produce special organs for attachment for climbing over a support. Climbing helps to display the leaves towards sunlight and to position the flower for effective pollination. i. Root climbers Plants climbing with the help of adventitious roots (arise from nodes) as in species of Piper betel, Piper nigrum, Hedera helix, Pothos, Hoya. ii. Stem climbers (twiners) These climbers lack specialised structure for climbing and the stem itself coils around the support. Example: Ipomoea, Convolvulus, Dolichos, Clitoria, Quisqualis. Stem climbers may coil around the support clockwise or anti-clockwise. Clockwise coiling climbers are called dextrose. Example: Dioscorea alata. Anti-clockwise coiling climbers are called sinistrose. Example: Dioscorea bulbifera. iii. Hook climbers These plants produce specialized hook like structures which are the modification of various organs of the plant. In Artabotrys inflorescence axis is modified into hook. In Calamus (curved hook) leaf tip is modified into hook. In Bignonia unguis- cati the leaflets are modified into curved hook (figure: 3.17). In Hugonia the axillary buds modified into hook. iv. Thorn climbers Climbing or reclining on the support with the help of thorns as in Bougainvillea and Carissa. v. Lianas (woody stem climber) Woody perennial climbers found in tropical forests are lianas. They twine themselves around tall trees to get light. Example: Hiptage benghalensis, Bauhinia vahlii, Entada pursaetha. vi. Tendril climbers Tendrils are thread-like coiling structures which help the plants in climbing. Tendrils may be modifications of Stem – as in Passiflora, Vitis and Cissus quadrangularis; Inflorescence axis – Antigonon; Leaf – Lathyrus; Leaflets - Pisum sativum; Petiole – Clematis; Leaftip – Gloriosa; Stipules – Smilax. In pitcher plant (Nepenthes) the midrib of the leaf often coils around a support like a tendril and holds the pitcher in a vertical position. Phylloclade This is a green, flattened cylindrical or angled stem or branch of unlimited growth, consisting of a series of nodes and internodes at long or short intervals. Phylloclade is characteristic adaptation of xerophytes where the leaves often fall off early and modified into spines or scales to reduce transpiration. The phylloclade takes over all the functions of leaves, particularly photosynthesis. The phylloclade is also called as cladophyll. Example: Opuntia, Phyllocactus, Muehlenbeckia (flattened phylloclade) Casuarina, Euphorbia tirucalli, Euphorbia antiquorum (cylindrical phylloclade). Cladode Cladode is a flattened or cylindrical stem similar to Phylloclade but with one or two internodes only. Their stem nature is evident by the fact that they bear buds, scales and flowers. Example: Asparagus (cylindrical cladode), Ruscus (flattened Cladode). Thorns Thorn is a woody and sharp pointed modified stem. Either the axillary bud or the terminal bud gets modified into thorns. In Carissa apical bud modified into thorns. In Citrus and Atalantia axillary bud is modified into thorns. II. Sub aerial stem modifications Sub aerial stem found in plants with weak stem in which branches lie horizontally on the ground. These are meant for vegetative propagation. They may be sub aerial or partially sub terranean. 1. Runner This is a slender, prostrate branch creeping on the ground and rooting at the nodes. Example: Centella (Indian pennywort), Oxalis (wood sorrel), lawn grass (Cynodon dactylon). 2. Stolon This is also a slender, lateral branch originating from the base of the stem. But it first grows obliquely above the ground, produces a loop and bends down towards the ground. When touches the ground it produces roots and becomes an independent plantlet. Example: Mentha piperita (peppermint), Fragaria indica (wild strawberry). 3. Sucker Sucker develops from a underground stem and grows obliquely upwards and gives rise to a separate plantlet or new plant. Example: Chrysanthemum, Musa, Bambusa. 4. Offset Offset is similar to runner but found in aquatic plants especially in rosette leaved forms. A short thick lateral branch arises from the lower axil and grows horizontally leafless for a short distance, then it produces a bunch of rosette leaves and root at nodes. Example: Eichhornia (water hyacinth), Pistia (water lettuce). III. Underground stem modifications Perennial and some biennial herbs have underground stems, which are generally known as root stocks. Rootstock functions as a storage and protective organ. It remains alive below the ground during unfavourable conditions and resumes growth during the favourable conditions. Underground stems are not roots because they possess nodes, internodes, scale-leaves and buds. Rootstock also lack root cap and root hairs but they possess terminal bud which is a characteristics of stem. 1. Bulb It is a condensed conical or convex stem surrounded by fleshy scale leaves. They are of two types 1. Tunicated (coated) bulb: In which the stem is much condensed and surrounded by several concentric layers of scale leaves. The inner scales commonly fleshy, the outer ones dry. These are two types (a) Simple Tunicated bulb Example: Allium cepa (b) Compound Tunicated bulb. Example: Allium sativum. 2. Scaly bulb: They are narrow, partially overlap each other by their margins only. Example:Tulipa spp. Pseudobulb is a short erect aerial storage or propagating stem of certain epiphytic and terrestrial sympodial orchids. Example: Bulbophyllum. 2. Corm This is a succulent underground stem with an erect growing tip. The corm is surrounded by scale leaves and exhibit nodes and internodes. Example: Amorphophallus, Gladiolus, Colocasia, Crocus, Colchicum 3. Rhizome This is an underground stem growing horizontally with several lateral growing tips. Rhizome posses conspiquous nodes and internodes covered by scale leaves. Example: Zingiber officinale, Canna, Curcuma longa, Maranta arundinacea, Nymphaea, Nelumbo. 4. Tuber This is a succulent underground spherical or globose stem with many embedded axillary buds called “eyes”. Example: Solanum tuberosum, Helianthus tuberosus IV. Stem Branching - mode of arrangement of branches on a stem Branching pattern is determined by the relative activity of apical meristems. The mode of arrangement of branches on a stem is known as branching. There are two main types of branching, 1. Lateral branching and 2. Dichotomous branching. Based on growth pattern stems may show indeterminate or determinate growth. monopodial (a) Indeterminate: The terminal bud grows uninterrupted and produce several lateral branches. This type of growth is also known as monopodial branching. Example: Polyalthia, Swietenia, Antiaris.  sympodial (b) Determinate: The terminal bud caese to grow after a period of growth and the further growth is taken care by successive or several lateral meristem or buds. This type of growth is also known as sympodial branching. Example: Cycas. LEAF Leaves are green, thin flattened lateral outgrowths of the stem. Leaves are the primary photosynthetic organs and the main site of transpiration. All the leaves of a plant together are referred to as phyllome. PHYLLOME - all the leaves of a plant together I. Characteristics of leaf 1 Leaf is a lateral appendage of the stem. 2 It is borne at the node of the stem. 3 It is exogenous in origin. 4 It has limited growth. 5 It does not posses apical bud. 6 It has three main parts namely, leaf base, petiole and lamina. 7 Lamina of the leaf is traversed by vascular strands, called veins. II. Functions of the leaf Primary functions 1) Photosynthesis 2) Transpiration 3) Gaseous exchange 4) Protection of buds 5) Conduction of water and dissolved solutes. Secondary functions 1) Storage – Example: Aloe, Agave, Kalanchoe, Sedum, Brassica oleracea. 2) Protection – Example: Berberis, Opuntia, Argemone mexicana. 3) Support – Example: Gloriosa, Nepenthes 4) Reproduction - Example: Bryophyllum, Begonia, Zamioculcas. 1. Parts of the leaf Three main parts of a typical leaf are: i. Leaf base (Hypopodium) ii. Petiole (Mesopodium) iii. Lamina (Epipodium) I. Leaf base (hypopodium The part of the leaf attached to the node of the stem is called leaf base. Usually it protects growing buds at its axil. Pulvinus: In legumes leafbase become broad and swollen which is known as pulvinus. Example: Clitoria, Lablab, Cassia, Erythrina, Butea, Peltophorum. Sheathing leafbase: In many monocot families such as Arecaceae, Musaceae, Zingiberaceae and Poaceae the leafbase extends into a sheath and clasps part or whole of the internode. Such leaf base also leave permanent scars on the stem when they fall. II. Petiole (stipe or mesopodium) It is the bridge between lamina and stem. Petiole or leaf stalk is a cylindrical or sub cylindrical or flattened structure of a leaf which joins the lamina with the stem. A leaf with petiole is said to be petiolate. Example: Ficus, Hibiscus, Mangifera, Psidium. Leaves that do not possess petiole is said to be sessile. Example: Calotropis, Gloriosa. III. Lamina (Leaf blade) The expanded flat green portion of the leaf is the blade or lamina. It is the seat of photosynthesis, gaseous exchange, transpiration and most of the metabolic reactions of the plant. The lamina is traversed by the midrib from which arise numerous lateral veins and thin veinlets. The lamina shows great variations in its shape, margin, surface, texture, colour, venation and incision. lateral appendages > to protect the leaf in a bad condition Stipules In most of the dicotyledonous plants, the leaf base bears one or two lateral appendages called the stipules. Leaves with stipules are called stipulate. The leaves without stipules are called exstipulate or estipulate. The stipules are commonly found in dicotyledons. In some grasses (Monocots) an additional out growth is present between leaf base and lamina. It is called Ligule. Sometimes, small stipule like outgrowths are found at the base of leaflets of a compound leaf. They are called stipels. The main function of the stipule is to protect the leaf in the bud condition. Reticulate > midrib 2. Venation Parallel > do not form a prominent reticulum The arrangement of veins and veinlets on the leaf blade or lamina is called venation. Internally, the vein contains vascular tissues. Conventionally venation is classified into two types namely, Reticulate venation and Parallel venation. I. Reticulate venation In this type of venation leaf contain a prominent midrib from which several secondary veins arise that branch and anastomose like a network. This type of venation is common in all dicot leaves. It is of two types. 1. Pinnately reticulate venation (unicostate): In this type of venation there is only one midrib in the centre which forms many lateral branches to form a network. Example: Mangifera indica, Ficus religiosa, Nerium. 2. Palmately reticulate venation (multicostate): In this type of venation there are two or more principal veins arising from a single point and they proceed outwards or upwards. The two types of palmate reticulate venation are i. Divergent type: When all principal veins originate from the base and diverge from one another towards the margin of the leaf as in Cucurbita, Luffa, Carica papaya, etc., ii. Convergent: When the veins converge to the apex of the leaf, as in Indian plum (Zizyphus), bay leaf (Cinnamomum) Figure 3.12: Types of reticulate venation (a) Pinnately reticulate there is only one midrib in the center (b) Palmately reticulate (Divergent) the principal veins originate from the base of the leaf and then diverge. (c) Palmately reticulate (Convergent) veins converge to the apex of the leaf. II. Parallel venation Veins run parallel to each other and do not form a prominent reticulum. It is a characteristic feature of monocot leaves. It is classified into two sub types. 1. Pinnately Parallel Venation (Unicostate) When there is a prominent midrib in the center, from which arise many veins perpendicularly and run parallel to each other. Example: Musa, Zinger, Curcuma, Canna. 2. Palmate Parallel Venation (Multicostate) In this type several veins arise from the tip of the petiole and they all run parallel to each other and unite at the apex. It is of two sub types. i. Divergent type: All principal veins originate from the base and diverge towards the margin, the margin of the leaf as in fan palm (Borassus flabelliformis) ii. Convergent type: All principal veins run parallel to each other from the base of the lamina and join at the apex as in Bamboos, rice, water hyacinth (a) Pinnately parallel venation (b) Palmately parallel(Convergent) (c) Palmately parallel (Divergent) 3. Phyllotaxy The mode of arrangement of leaves on the stem is known as phyllotaxy (Gk. Phyllon = leaf ; taxis = arrangement). Phyllotaxy is to avoid over crowding of leaves and expose the leaves maximum to the sunlight for photosynthesis. The four main types of phyllotaxy are (1) Alternate (2) Opposite (3) Ternate (4) Whorled. 1. Alternate phyllotaxy In this type there is only one leaf per node and the leaves on the successive nodes are arranged alternate to each other. Spiral arrangement of leaves show vertical rows are called orthostichies. They are two types. i. Alternate spiral: In which the leaves are arranged alternatively in a spiral manner. Example: Hibiscus, Ficus. ii. Alternate distichous or Bifarious: In which the leaves are organized alternatively in two rows on either side of the stem. Example: Monoon longifolium (Polyalthia longifolia). 2. Opposite phyllotaxy In this type each node possess two leaves opposite to each other. They are organized in two different types. i. Opposite superposed: The pair of leaves arranged in succession are in the same direction, that is two opposite leaves at a node lie exactly above those at the lower node. Example: Psidium (Guava) ii. Opposite decussate: In this type of phyllotaxy one pair of leaves is placed at right angles to the next upper or lower pair of leaves. Example: Zinnia 3. Ternate phyllotaxy In this type there are three leaves attached at each node. Example: Nerium 4. Whorled (verticillate) type of phyllotaxy In this type more than three leaves are present in a whorl at each node forming a circle or whorl. Example: Allamanda, Alstonia scholaris. 4. Leaf mosaic In leaf mosaic leaves tend to fit in with one another and adjust themselves in such a way that they may secure the maximum amount of sunlight with minimum amount of overlapping. The lower leaves have longer petioles and successive upper leaves possess decreasing length petioles. Example: Acalypha, Begonia. 5. Leaf type The pattern of division of a leaf into discrete components or segments is termed leaf type. Based on the number of segments I. Simple leaf A leaf is said to be simple when the petiole bears a single lamina; lamina may be entire (undivided) Example: Mango or incised to any depth but not upto the midrib or petiole. Example: Cucurbita. II. Compound leaf Compound leaf is one in which the main rachis bears more than one lamina surface, called leaflets. Compound leaves have evolved to increase total lamina surface. There is one axillary bud in the axil of the whole compound leaf. The leaflets however, do not possess axillary buds. 1. Pinnately compound leaf A pinnately compound leaf is defined as one in which the rachis, bears laterally a number of leaflets, arranged alternately or in an opposite manner, as in tamarind, Cassia. i. Unipinnate: The rachis is simple and unbranched which bears leaflets directly on its sides in alternate or opposite manner. Example: Rose, Neem. Unipinnate leaves are of two types. · when the leaflets are even in number, the leaf is said to be paripinnate. Example: Tamarindus · when the leaflets are odd in number, the leaf is said to be imparipinnate. Example: Rosa, Azadirachta (Neem), i. Bipinnate: The primary rachis produces secondary rachii which bear the leaflets. The secondary rachii are known as pinnae. Number of pinnae varies depending on the species. Example: Mimosa, Acacia nilotica, Caesalpinia. ii. Tripinnate: When the rachis branches thrice the leaf is called tripinnate. (i.e) the secondary rachii produce the tertiary rachii which bear the leaflets. Example: Moringa iii. Decompound: When the rachis of leaf is branched several times it is called decompound. Example: Daucus carota 2. Palmately compound leaf A palmately compound leaf is defined as one in which the petiole bears terminally, one or more leaflets which seem to be radiating from a common point like fingers from the palm. i. Unifoliolate: When a single leaflet is articulated to the petiole is said to be unifoliolate. Example: Citrus ii. Bifoliolate: When there are two leaflets articulated to the petiole it is said to be bifoliolate. Example: Balanites roxburghii, Hardwickia binata, Zornia diphylla iii. Trifoliolate: There are three leaflets articulated to the petiole it is said to be trifoliolate. Example: Clover (Trifolium), Oxalis iv. Quadrifoliolate: There are four leaflets articulated to the petiole it is said to be quadrifoliolate. Example: Marsilia v. Multifoliolate or digitate: Five or more leaflets are joined and spread like fingers from the palm, as in Ceiba pentandra, Bombax ceiba ANATOMY OF THE LEAF waxy layer 6. Modification of Leaf The main function of the leaf is food preparation by photosynthesis. Leaves also modified to perform some specialized functions. They are described below. I. Leaf tendrils > slender wiry coiled structure which helps in climbing the support In some plants Stem is very weak and hence they have some special organs for attachment to the support. So some leaves are partially or wholly modified into tendril. Tendril is a slender wiry coiled structure which helps in climbing the support. Some of the modification of leaf tendrils are given below: Entire leaf—Lathyrus, stipules—Smilax, terminal leaflet—Naravelia, Leaf tip— Gloriosa, Apical leaflet—Pisum, petiole— Clematis. II. Leaf hooks In some plants, leaves are modified into hook-like structures and help the plant to climb. In cat,s nail (Bignonia unguis-cati) an elegant climber, the terminal leaflets become modified into three, very sharp, stiff and curved hooks, very much like the nails of a cat. These hooks cling to the bark of a tree and act as organs of support for climbing. The leaf spines of Asparagus also act as hooks. III. Leaf Spines and Prickles Leaves of certain plants develop spinesent structures. Either on the surface or on the margins as an adaptation to herbivory and xeric conditions. Example: Argemone mexicana (Prickly poppy), Solanum trilobatum, Solanum virginianum. In xerophytes such as Opuntia (Prickly pear) and Euphorbia leaves and stipules are modified into spines. Prickles are small, sharp structure which are the outgrowths from epidermal cells of stem or leaf. It helps the plant in scrambling over other plants. It is also protective against herbivory. Example: Rosa spp, Rubus spp. IV. Storage Leaves Some plants of saline and xerophytic habitats and members of the family Crassulaceae commonly have fleshy or swollen leaves. These succulent leaves store water, mucilage or food material. Such storage leaves resist desiccation. Example: Aloe, Agave, Bryophyllum, Kalanchoe, Sedum, Sueada, Brassica oleracea (cabbage-variety capitata). V. Phyllode Phyllodes are flat, green-coloured leaf-like modifications of petioles or rachis. The leaflets or lamina of the leaf are highly reduced or caducous. The phyllodes perform photosynthesis and other functions of leaf. Example: Acacia auriculiformis (Australian Acacia), VI. Pitcher The leaf becomes modified into a pitcher in Nepenthes and Sarracenia. In Nepenthes the basal part of the leaf is laminar and the midrib continues as a coiled tendrillar structure. The apical part of the leaf as modified into a pitcher the mouth of the pitcher is closed by a lid which is the modification of leaf apex. VII. Bladder In bladderwort ( Utricularia), a rootless free-floating or slightly submerged plant common in many water bodies, the leaf is very much segmented. Some of these segments are modified to form bladder-like structures, with a trap-door entrance that traps aquatic animalcules. VIII Floral leaves > attract pollinators Floral parts such as sepals, petals, stamens and carpels are modified leaves. Sepals and petals are leafy. They are protective in function and considered non-essential reproductive parts. Petals are usually coloured which attract the insects for pollination. Stamens are considered pollen bearing microsporophylls and carpels are ovule bearing megasporophylls. 7. Ptyxis Rolling or folding of individual leaves may be as follows: 1 Reclinate - when the upper half of the leaf blade is bent upon the lower half as in loquat (Eriobotrya japonica). 2 Conduplicate - when the leaf is folded lengthwise along the mid-rib, as in guava, sweet potato and camel’s foot tree (Bauhinia). 3 Plicate or plaited – when the leaf is repeatedly folded longitudinally along ribs in a zig- zag manner, as in Borassus flabellifer. 4 Circinate - when the leaf is rolled from the apex towards the base like the tail of a dog, as in ferns. 5 Convolute - when the leaf is rolled from one margin to the other, as in banana, aroids and Indian pennywort. Musa and members of Araceae. 6 Involute - when the two margins are rolled on the upper surface of the leaf towards the midrib or the centre of the leaf, as in water lily, lotus 7 Crumpled - when the leaf is irregularly folded as in cabbage. 8. Leaf duration Leaves may stay and function for few days to many years, largely determined by the adaptations to climatic conditions. Cauducuous (Fagacious) Falling off soon after formation. Example: Opuntia, Cissus quadrangularis. Deciduous Falling at the end of growing season so that the plant (tree or shrub) is leafless in winter/summer season. Example: Maple Evergreen Leaves persist throughout the year, falling regularly so that tree is never leafless. Example: Mimusops, Calophyllum. Marcescent Leaves not falling but withering on the plant as in several members of Fagaceae. 9. Leaf symmetry 1. Dorsiventral leaf When the leaf is flat, with the blade placed horizontally, showing a distinct upper surface and a lower surface, as in most dicotyledons, it is said to be dorsiventral. Example: Tridax. 2. Isobilateral leaf When the leaf is directed vertically upwards, as in many monocotyledons, it is said to be isobilateral leaf. Example: Grass. 3. Centric leaf When the leaf is more or less cylindrical and directed upwards or downwards, as in pine, onion, etc., the leaf is said to be centric. 4. Heterophylly Occurrence of two different kinds of leaves in the same plant is called heterophylly. Heterophylly is found in many aquatic plants. Here, the floating or aerial leaves and the submerged leaves are of different kinds. The former are generally broad, often fully expanded, and undivided or merely lobed, while the latter are narrow, ribbon-shaped, linear or much dissected. Heterophylly in water plants is, thus, an adaptation to two different conditions of the environment. Example: water crowfoot (Ranunculus aquatilis) Terrestrial (land) plants also exhibit this phenomenon. Among them Sterculia villosa, jack (in early stages), Ficus heterophylla show leaves varying from entire to variously lobed structures during different developmental stages. Young leaves are usually lobed or dissected and the mature leaves are entire. Such type is known as developmental heterophylly. Example: Eucalyptus, Artocarpus heterophyllus. REPRODUCTIVES STRUCTURES The lifecycle of angiosperms follows the alternation of generations. In the angiosperm, the haploid gametophyte alternates with the diploid sporophyte during the sexual reproduction process of angiosperms. Flowers contain the plant’s reproductive structures. Flower Structure A typical flower has four main parts, or whorls: the calyx, corolla, androecium, and gynoecium. The outermost whorl of the flower has green, leafy structures known as sepals, which are collectively called the calyx, and help to protect the unopened bud. The second whorl is comprised of petals, usually brightly colored, collectively called the corolla. The number of sepals and petals varies depending on whether the plant is a monocot or dicot. Together, the calyx and corolla are known as the perianth. The third whorl contains the male reproductive structures and is known as the androecium. The androecium has stamens with anthers that contain the microsporangia. The innermost group of structures in the flower is the gynoecium, or the female reproductive component(s). The carpel is the individual unit of the gynoecium and has a stigma, style, and ovary. A flower may have one or multiple carpels. SEPALS - outermost whorl of the ANDROECIUM - male reproductive PETALS - brightly colored flower which has green leafy structure - collectively called COROLLA structure. - collectively called CALYX GYNOECIUM - female reproductive PERIANTH components CARPEL - individual unit of gynoecium and has stigma, style, and ovary Figure 40.3.1.140.3.1.1: Structures of the flower: The four main parts of the flower are the calyx, corolla, androecium, and gynoecium. The androecium is the sum of all the male reproductive organs, and the gynoecium is the sum of the female reproductive organs. If all four whorls are present, the flower is described as complete. If any of the four parts is missing, the flower is known as incomplete. Flowers that contain both an androecium and a gynoecium are called perfect, androgynous, or hermaphrodites. There are two types of incomplete flowers: staminate flowers contain only an androecium; and carpellate flowers have only a gynoecium. Figure 40.3.1.140.3.1.1: Staminate and carpellate flowers: The corn plant has both staminate (male) and carpellate (female) flowers. Staminate flowers, which are clustered in the tassel at the tip of the stem, produce pollen grains. Carpellate flower are clustered in the immature ears. Each strand of silk is a stigma. The corn kernels are seeds that develop on the ear after fertilization. Also shown is the lower stem and root. If both male and female flowers are borne on the same plant (e.g., corn or peas), the species is called monoecious (meaning “one home”). Species with male and female flowers borne on separate plants (e.g., C. papaya or Cannabis)are termed dioecious, or “two homes.” The ovary, which may contain one or multiple ovules, may be placed above other flower parts (referred to as superior); or it may be placed below the other flower parts (referred to as inferior). Figure 40.3.1.140.3.1.1: Superior and inferior flowers: The (a) lily is a superior flower, which has the ovary above the other flower parts. (b) Fuchsia is an inferior flower, which has the ovary beneath other flower parts. Inflorescence is the reproductive shoot, bearing a number of flowers.  It may be terminal or axillary in position.  It is of two types; viz. racemose and cymose.  Besides, there is also a special type of inflorescence which fits into none of these groups. 1. Racemose inflorescence:  In this type of inflorescence, the main axis is unlimited in growth, branched or unbranched.  It never terminates into a flower and bears flowers in acropetal (growing upward from the base or point of attachment)  The main types of racemose inflorescence are: Raceme: The main elongated axis bears stalked flowers. E.g. mustard, radish, goldmohur etc. Spike: This is like raceme but flowers are sessile or unstalked. E.g. adhatoda, chaff-flower (Achyranthes). Catkin: This is like spike but differs from the later in having a long and pendulous axis, usually bearing unisexual flowers. E.g. mulberry, cat’s tail (Acalypha sanderiana). Spadix or thyrse: This is a spike with fleshy axis enclosed by one or several large and brightly colored bracts, called the E.g. banana, aroids (Colocosia). Corymb: Here, the axis is not elongated as in the above mentioned inflorescences. It is short and bears stalked flowers in such a manner that they are placed almost at the same level. E.g. Lantana, cherry etc. Umbel: All the flowers arise from one plant. The axis may or may not be branched, simple umbel if unbranched, compound umbel if branched. Bracts are present (involucre) at the base of the flowers. E.g. carrot, coriander etc. Head or capitulum:  The main axis is a flattened, more or less convex structure, the receptacle, on which the florets (small flowers) are arranged in a centripetal order.  The whole inflorescence is surrounded by an involucre (a whorl of bracts) and bears only one or two types of flowers: inner disc florets and outer ray florets. E.g. sunflower. Different types of racemose inflorescence 2. Cymose inflorescence:  In this type, the main axis is always limited in growth and terminates into a flower.  They are usually stalked, and borne in a basipetal (growing downward towards the base or from the point of attachment) order.  The main types of cymose inflorescence are: Monochasial cyme:  The main axis terminates into a flower and one lateral branch axis develops from its base which also ends in a flower.  There are two types of monochasial cyme:  Scorpioid type in which the lateral branches of the axis bearing a terminal flower alternate as in Rananculus bulbosus.  Helicoid type in which each lateral branch bearing a terminal flower develops on the same side forming a helix as in Heliotropium. Dichasial cyme: Here, two lateral branches develop on either side of the terminal flower. The lateral branches may again branch similarly. E.g. Jasmine, Dianthus Polychasial cyme: Here, more than two lateral branches arise from the base of the apical flower. E.g. Calotropis.  Different types of cymose inflorescence 3. Special types of inflorescence: Hypanthodium:  Here, the main axis forms a cup shaped receptacle with a small opening at the top. Flowers are enclosed within the cup in cymose groups. E.g. Ficus. Cyathium:  Here, the cup shaped structure is formed by the involucre.  The reduced flowers (without perianth) are placed on a receptacle.  There is one central female flower represented by a single pistil which is surrounded by a large number of male flowers each represented by a single statmen only.  The stalked flowers are subtended by a bracteole. There are also nectar glands on the cup. E.g. Poinsettia. Verticillaster:  Here, one inflorescence consisting of two clusters develops from each of the two opposite axils of the leaves.  Each cluster is a dichasial cyme reduced to two scorpioid.  Flowers are sessile and appear in a false whorl or vertically around the stem. E.g. sacred basil (Ocimum sanctum). FRUIT Trees are recognizable mostly by the fruits they produce. The fruit is a characteristic of a flowering plant. It is a mature, ripe ovary that encloses the seed. Some fruits are fleshy, sweet, juicy, and colorful, while others are dry, sour, and dull. Mango, apple, papaya, apricot, banana, tomato, cucumber, acorns, and almonds are some common examples of fruits. The fruit consists of two main parts: 1) pericarp and 2) seed. Parts of a Fruit Diagram 1) Pericarp It is the edible part of the fruit formed from the wall of the ripened ovary. The pericarp may be fleshy as in apple, mango, and guava or dry as in walnut and apricot. It is further divided into three parts: a) Epicarp: Also known as exocarp, it is the outermost layer of the pericarp that forms the tough, outer skin of the fruit. It protects the inner parts of the fruit from damage. In citrus fruits, the epicarp layer is called flavedo. b) Mesocarp: It is the middle layer of the pericarp. It is the fleshy, edible part of the fruit found in apples, mangoes, and peaches. In citrus fruits, the white mesocarp layer after the flavedo is called albedo. c) Endocarp: It forms the innermost layer of the pericarp that immediately surrounds the seed. It protects the seed from damage. The endocarp is generally not consumed, but in citrus fruits like oranges, they form the central juicy, edible part. 2) Seed They are structures that enclose the developing embryo of a plant. Seeds are the ripened, fertilized ovules consisting of three parts: a) Seed Coat: It is the protective outer covering of the seed. It further consists of two layers, the thick outer testa and the delicate inner tegmen. The seed coat protects the seed from mechanical damage. b) Endosperm: Found below the seed coat, it is rich in starch and proteins that act as reserve foods for the developing embryo.  c) Embryo: It is the developing plant with underdeveloped tissues like stems and roots. They are further divided into four parts: epicotyl, hypocotyl, radical, and cotyledons. The embryo later gives rise to a new plant. SEED Parts of a Seed and Their Functions A seed is a structure that encloses the embryo of a plant in a protective outer covering. Under favorable conditions of growth, a seed gives rise to a new plant, using the nutrients stored in them. Parts and Structure of a Seed Parts of a Seed Diagram A typical seed consists of three main parts: 1) seed coat, 2) endosperm, and 3) embryo. 1) Seed Coat They are the protective outer covering of a seed that is usually hard, thick, and brownish in color. The seed coat is formed from the outer covering of the ovule called the integument. It usually contains two layers: i) testa – the thick outer layer, and ii) tegmen – the delicate inner layer. A seed coat has the following four parts: a) Micropyle – the small opening present at one end of the seed coat, b) Funiculus – the seed stalk with which the seed is attached to the fruit body, the integument, c) Hilum – the region from which the seed breaks off from the fruit, leaving a scar, and d) Raphe – the base of the funiculus that is fused with the integument. Functions  Protecting the seed from physical and mechanical damage  Preventing the seed from germination even under favorable conditions of growth (seed dormancy)  Preventing the excessive loss of water from the seeds  Acting as a physical barrier against the entry of parasites 2) Endosperm It is a tissue that is rich in oil, starch, and protein. Depending on the presence or absence of endosperm, seeds are of two types: i) Non-endospermic or exalbuminous seeds – Characterized by the complete absence of the endosperm, such as the seeds of the pea plant, groundnut, and gram. ii) Endospermic or albuminous seeds – Characterized by the presence of the endosperm, such as the seeds of millets, palms, and lilies. Functions  Storing of reserve foods that provide nourishment to the developing plant  Protecting the embryo, the next part of the seed, by acting as the mechanical barrier 3) Embryo They are the young plant that is developing inside the seed coat. An embryo contains the underdeveloped tissues of leaves, stem, and roots of a plant. What are the Parts of an Embryo of a Seed  Epicotyl – The tiny shoot of an embryo, from which the entire shoot system develops. The tip of the epicotyl is called plumule.  Hypocotyl – The stage of transition for the growing shoot and root of the embryo  Radicle – The tiny root of the embryo  Cotyledons – They are the leaves of the embryo that provide nourishment to the developing plant. There are two types of cotyledons present in flowering plants: i) monocotyledonous or monocots – embryo with one cotyledon and ii) dicotyledonous or dicots – embryo with two cotyledons. Functions  Giving rise to a new complete new plant  Storing food and nourishing the baby plant