Biology PDF - General Morphology and Anatomy of Plants

GENERAL MORPHOLOGY AND ANATOMY OF PLANTS 1 I. GENERAL STRUCTURE AND ORGANIZATION OF THE PLANT BODY Among the vascular plants or tracheophytes (plants having specialized conducting tissues), the angiosperms or flowering plants are the most recently evolved and form the main par...

GENERAL MORPHOLOGY AND ANATOMY OF PLANTS 1 I. GENERAL STRUCTURE AND ORGANIZATION OF THE PLANT BODY Among the vascular plants or tracheophytes (plants having specialized conducting tissues), the angiosperms or flowering plants are the most recently evolved and form the main part of the earth’s vegetation. Starting with the seed, the general structure and organization of the angiosperm plant body is summarized as follows: The seed contains an embryo, a young plant enveloped by a protective seed coat and supplied with a source of stored food. The embryo contains a minute axis with two poles - the root growing point and the shoot growing point. On the minute axis occur laterally the cotyledons or seed leaves. The food required for the germinating plantlet may be stored in the cotyledons, or in a specialized tissue, the endosperm. Under suitable conditions, the seed germinates and a young plant or seedling emerges. The seedling grows, extends its roots into the soil and its shoots (stems and leaves) into the atmosphere. The growth of roots and shoots is due to the formation of new cells by meristematic tissues of the growing points, followed by growth and differentiation of these cells. When the plant attains mature size, flowers are formed. After pollination (transfer of pollen from the stamens to the stigma) and fertilization, a fruit containing seeds develops, thus completing the plant’s life cycle. II. THE PLANT CELL The cell is the basic unit of life. Structurally, plant cells differ from animal cells primarily due to the presence of a rigid cell wall and various forms of plastids. The plant cell has three main components; cell wall, cytoplasm and nucleus. The following are the parts and functions of the plant cell: A. Cell Wall - outer protective layer of cells - made up chiefly of cellulose which exists as a system of fibrils of different sizes - cellulose molecule micelle microfibril macrofibril (about as strong as a (microfibrils steel thread of wound together) equivalent size) - the cellulose framework of the wall is interpenetrated by a cross-linked matrix of non- cellulosic substances e.g. hemicelluloses, pectic substances or pectins and glycoproteins. Other substances like lignin may also be deposited in the wall adding to its rigidity. Fatty substances like cutins, suberin and waxes may also be present. - generally has 3 layers: - middle lamella - intercellular substance, primarily pectins, that cements adjacent cells together - primary wall - wall layer formed before and during growth of the cell 1 Review handout prepared by B.S. Belonias for the LSU 2003 Forestry Board Exam Review  - relatively thin and not rigid; stretched as the cell grows - consists of a loose network of cellulose microfibrils - have thin areas called primary pit fields traversed by numerous protoplasmic strands called plasmodesmata - secondary wall - rigid, thicker wall formed after cell completes growth - laid down to the inside of the primary wall and maybe several layers thick - consists of a compact network of cellulose microfibrils; has higher amount of cellulose; lignified making it more rigid - discontinuous layer due to the presence of pits, areas where no wall material is deposited B. Cytoplasm - all the protoplasm or living matter of the cell apart from the nucleus - the fluid or gel-like material in which the cell’s organelles and internal membrane systems are suspended cytoplasmic streaming/cyclosis - flowing movement of the cytoplasm - for efficient distribution of substances absorbed from outside of the cell and substances released by the nucleus and other organelles - consists of the following membrane systems and organelles: 1. Plasmalemma/plasma membrane/cell membrane - external membrane of the cell composed primarily of lipids which prevent most water soluble materials from passing through Functions: a. Mediates the transport of substances into and out of the cell b. Coordinates the synthesis and assembly of cell wall microfibrils c. Translates hormone and environmental signals involved in the control of cell growth and differentiation 2. Endoplasmic Reticulum (ER) - system of paired membrane sheets/tubules ramifying through the cytoplasm Types: a. Rough or granular ER - consists of flattened disks or sacs called cisternae with numerous ribosomes attached to its outer surfaces; found in cells that secrete or store proteins b. Smooth or granular ER - consists of a system of tubules; lacks ribosomes Functions: a. Communication system within the cell, channeling materials e.g. proteins and lipids to different parts of the cell b. Principal site of membrane synthesis; appears to synthesize vacuolar and microbody membranes as well as cisternae of dictyosomes 3. Dictyosome/Golgi Apparatus - stacks of smooth, flat, disk-shaped sacs or cisternae often branched into a complex series of tubules and vesicles at their margins Functions: a. Secrete protein and carbohydrate products from the cell to its exterior e.g. nectar b. Synthesis of cell wall polysaccharides 4. Microtubules - long, thin, cylindrical structures about 24 nm in diameter of varying lengths - each microtubule is built up of subunits of the protein called tubulin, these subunits are arranged in helix to form 13 vertical filaments around a hollow core Functions: a. Involved in the orderly growth of the cell wall especially in the alignment of the cellulose microfibrils b. Direct dictyosome vesicles toward developing wall c. Comprise the spindle fibers which play a role in cell plate formation in dividing cells d. Form important components of cilia and flagella involved in the movement of these structures 5. Microfilaments - contractile proteins composed of actin similar to that of muscle tissue which occur as long filaments 5 to 7 nm thick; occur in bundles Function: - play a causative role in cytoplasmic streaming 6. Plastids - largest cytoplasmic organelles which vary in size, form and pigmentation - bounded by a double-membrane envelope - ground substance is called stroma Types: a. Chloroplasts - usually disk-shaped about 4-6 um in diameter - green due to the predominance of chlorophyll pigment - a single mesophyll cell may contain 40 to 50 chloroplasts Functions: 1. site of photosynthesis 2. amino acid and fatty acid synthesis 3. temporary storage of starch (for actively photosynthesizing organs b. Chromoplasts - yellow, orange or red due to presence of carotenoid pigments - may develop from previously existing chloroplasts Function: - act as attractants to insects and other animals due to bright colors they give to the plant organ  c. Leucoplasts - non-pigmented plastids; occur in storage cells Types: 1. Amyloplasts - contain starch 2. Proteinoplasts - contain proteins 3. Elaeioplasts - contain fats and oils 7. Mitochondria - spherical, elongated and sometimes lobed organelles, about half a micrometer in diameter - double-membrane bounded, inner membrane is extensively folded into pleats or invaginations called cristae - plant cells contain hundred of thousands of mitochondria especially actively metabolizing cells Function: - site of respiration, producing principal energy source (ATP) for the cell’s metabolic reactions 8. Microbodies - spherical organelles bounded by a single membrane, about 0.5 to 1.5 um in diameter Functions: a. Some microbodies called peroxisomes play an important role in glycolic acid metabolism associated with photorespiration b. Others called glyoxysomes contain enzymes needed for the conversion of fats into carbohydrates during germination in many seeds 9. Ribosomes - small particles, about 17-23 nm in size containing RNA and protein - either simply suspended in the cytoplasm as free ribosomes or attached to the endoplasminc reticulum as membrane-bound ribosomes - ribosomes actively involved in protein synthesis occur in clusters or aggregates called polysomes or polyribosomes Function: a. Site of protein synthesis 10. Vacuoles - membrane-bounded regions within the cell filled with a non-living liquid called cell sap; the outer membrane is called tonoplast - “dumping house” of the cell, contains water and other substances e.g. salts, sugars, proteins, mineral ions, pigments, toxic secondary metabolic products, crystals, etc - immature plant cells contain numerous small vacuoles which increase in size and fuse into a single central vacuole as the cell enlarges; in mature cells, as much as 90% of the cell volume is occupied by the vacuole Functions: a. A means for the cell to increase in size  b. Important storage compartments for various metabolites such as reserve proteins in seeds and malic acid in CAM plants c. Remove toxic products from the cytoplasm e.g. nicotine d. Site of pigment deposition especially anthocyanins e. Involved in the breakdown of macromolecules and their recycling within the cell f. May be a site of the breakdown or degradation of whole organelles (“digestive” function) C. Nucleus - most prominent structure within the cytoplasm; considered the “heart of the cell” - bounded by a pair of membranes, the nuclear envelope - the nuclear envelope has numerous pores which are continuous with the ER in the cytoplasm allowing exchange of materials between the nucleus and the cytoplasm - contains DNA, the genetic material in dark-staining thread-like structures called chromatin (chromosomes when condensed) and nucleoli Function: - Controls cell maintenance and development by instructing the cell’s ribosomes to synthesize particular proteins a. Nucleolus - spherical dark-staining structures found in non-dividing nuclei - site of synthesis of ribosomal proteins  III. TISSUES AND ORGANS OF THE PLANT BODY A. MERISTEMS Following the development of the embryo, the formation of new cells, tissues and organs becomes restricted almost entirely to the meristems - the perpetually young tissues that play a central role in growth. Two Types of Meristems: 1. Apical meristems - responsible for growth in length or primary growth - found in tips of roots and shoots 2. Lateral meristems - responsible for growth in size or secondary growth The apical meristems give rise to primary meristems, which are partly differentiated tissues. The primary meristems give rise to the plant’s primary tissue systems. Lateral meristems, on the other hand give rise to secondary tissues. Types of Primary Meristems: 1. Protoderm - gives rise to the primary dermal tissue, the epidermis 2. Procambium - give rise to primary vascular tissues primary xylem and phloem, vascular cambium and pericycle 3. Ground meristem - give rise to the primary ground tissues cortex and pith B. TISSUE SYSTEMS Types of Tissue Systems: 1. Dermal tissue system - includes the epidermis in the primary plant body and later, the periderm in the secondary plant body 2. Vascular tissue system - includes the primary and secondary xylem and phloem, vascular cambium, pericycle 3. Ground tissue system - cortex and pith The principal organs of the plant body are categorized into two: 1. vegetative organs i.e. roots, stems and leaves 2. reproductive organs i.e. flowers, fruits and seeds C. ORGANS The Root  Root - usually the subterranean or underground organ of the plant - differs from stems due to the absence of nodes and internodes  Primary Functions: 1. Absorption of water and minerals from the soil 2. Anchorage  Specialized Functions:  1. Support - e.g. prop roots of corn, butresses of forest trees 2. Photosynthesis - e.g. green roots of orchids 3. Food storage - e.g. fleshy roots of sweetpotato, cassava, carrots 4. Water storage - e.g. succulent roots of singkamas 5. Protection - e.g. spring roots of ubi 6. Gas exchange - e.g. pneumatophores of mangrove species  Types of Root Systems: 1. Tap root system - has a large main root from which lateral roots originate - deep-penetrating, hence efficient for anchorage - characteristic root system of dicots - develops from the radicle of the embryo 2. Diffuse/Fibrous root system - no main root; frequently formed by adventitious roots - characterized by numerous fine roots of approximately same sizes and lengths - characteristic root system of monocots - shallow-penetrating  Zones or Regions of the Root Tip: 1. Root cap - thimble-shaped mass of parenchymatous cells at the extreme tip of the root - loosely-packed, hence constantly sloughed off as the root elongates and penetrates the soil - functions to protect underlying meristematic cells 2. Apical meristem or meristematic region - region of cell division or where new cells are formed by mitosis 3. Elongation region - cells undergo rapid enlargement chiefly in the longitudinal direction 4. Root hair zone or maturation region - cells have become differentiated in structure and in function, and thus become mature tissues Root hairs - specialized epidermal cells formed in the maturation region; increases the root’s surface area for absorption  Growth in Roots: Roots, as well as stems, grow in two ways: 1. Primary growth - growth in length; produces the primary tissues of the roots 2. Secondary Growth - growth in size; produces secondary tissues - made possible by the formation of secondary tissues in the radial direction  Primary Growth in Roots: - made possible by the constant formation or addition of new cells by the root apical meristem, and the subsequent longitudinal growth or elongation of these newly formed cells  Primary Tissues of the Root: 1. Epidermis - non-cutinized outermost layer of cells which serves for protection of underlying tissues against excessive water loss - some epidermal cells become specialized into root hairs 2. Cortex - ground tissue; consists mainly of thin-walled storage parenchyma cells, but may contain strengthening collenchyma and sclerenchyma cells 3. Endodermis - innermost layer of cortical cells; a continuous band of suberin called Casparian Strip, deposited on its radial and transverse walls 4. Stele or central vascular cylinder - central core of the root a. Pericycle - outer cell layer of the stele; origin of lateral roots b. Primary xylem - consists of a central “core” of xylem elements (younger metaxylem) with several radiating arms (older protoxylem), between which are groups of phloem elements; between these two tissues are one or more layers of vascular cambium - no. of protoxylem arms vary from 2 to 4 in dicots to as many as 20 in monocots - consists of the following cell types: vessel members, tracheids. xylem fibers, xylem parenchyma and xylem rays d. Primary phloem - form in spaces between the radiating protoxylem arms - older protophloem occur at the periphery of the phloem, younger metaphloem forms towards the inside - consists of the following cell types: sieve tube members, companion cells, phloem rays, phloem fibers and phloem parenchyma e. Vascular cambium - thin layer of meristematic cells derived from the procambium lying between primary xylem and phloem in dicots - absent in monocots - gives rise to secondary vascular tissues 5. Pith - loose mass of thin parenchymatous cells at the center of monocot roots  Secondary Growth in Roots: The primary tissues of roots generally are not capable of supplying the needs of a long- lived plant body. In these cases, secondary tissues are developed. As in stems, two secondary or lateral meristems are required to form these tissues; the vascular cambium and the cork cambium.  Important events in secondary growth: 1. Vascular cambium between primary phloem and xylem becomes actively dividing, continually producing secondary xylem towards the inside and secondary phloem towards the outside. This causes the root to expand radially. 2. As the root continues to grow in size, splitting, sloughing off and destruction of the cortex and epidermis result. However, expansion stress, plus activity of growth hormones stimulates the still intact pericyclic cells to become active and resume division and form the cork cambium. 3. The cork cambium or phellogen divide actively and produces cork tissue (phellem) towards the outside and cork parenchyma (phelloderm) towards the inside. The Stem  Stem - the most conspicuous feature of most plants; in woody species forms the largest portion of the plant body - main axis of the plant which bears the leaves, flowers and fruits - develops chiefly from the epicotyl portion of the embryo, in some, from the hypocotyl and epicotyl  Primary Functions: 1. Production and support of leaves and reproductive structures 2. Serves as the main pathway for the transport of water and minerals from the roots to the upper parts of the plant, and the food from the leaves to the other parts of the plant  Specialized Functions: 1. Food storage - e.g. potato tubers, gabi corm, ginger rhizomes 2. Water storage - e.g. cladodes of cactus 3. Photosynthesis - e.g. cladodes of cactus 4. Vegetative reproduction - e.g. stolons of bermuda grass 5. Support – e.g. stem tendrils of cadena de amor 6. Protection - e.g. prickles of bougainvillea  External Structure of the Stem: 1. Node - point in the stem where leaves and buds arise 2. Internode - region between two successive nodes 3. Leaf scar - a mark left on the stem after a leaf falls off 4. Vascular bundle scar - tiny raised dots within a leaf scar representing the broken ends of the vascular bundles that extend from the stem into the leaf stalk 5. Terminal bud - bud located at the tip or apex of a stem or branch 6. Lateral or axillary bud - bud borne on the axil of the leaf or along the side of the stem above the leaf scar  7. Lenticels - small raised areas in the bark which function for gas exchange 8. Leaf axil - angle between the petiole of the leaf and the stem  Structure of the Shoot Apex: 1. Shoot apical meristem or promeristem - dome-shaped mass of meristematic cells at the extreme tip of shoots 2. Bud scales - young modified leaves enclosing and protecting the shoot tip 3. Leaf primordia - elongated protuberances at the flanks of the apical meristem - give rise to foliage leaves 4. Primary meristems a. Protoderm - outermost layer of superficial meristematic cells that give rise to the epidermis b. Procambium - the provascular meristem consisting of narrow, slightly elongated cells that develop into primary xylem and phloem c. Ground meristem - relatively large, thin-walled and isodiametric cells comprising the greater portion of meristematic tissue of the shoot tip; gives rise to pith and cortex  Primary Tissues of the Stem: The primary tissues of the stem are similar to those in roots, except for the absence of the pericycle, endodermis and root hairs, the presence of a pith tissue in dicots, and the different arrangement of its vascular tissues. In the stem, the vascular tissues occur in separate bundles with the primary phloem found towards the outside and the primary xylem towards the inside. The bundles are arranged in a concentric ring around the stem. A vascular cambium occurs between xylem and phloem and may be present only within each bundle (fascicular cambium) or may join with cambia developed inbetween bundles forming a complete ring of cambium around the stem (interfascicular cambium). In monocot stems, as in monocot roots, the cambium is absent and the vascular bundles are scattered in the ground tissue.  Secondary Growth in Stems: As in roots, secondary growth in stems requires the activity of two lateral meristems, the vascular cambium and cork cambium. However, the cork cambium in stems originates from the inner cortical cells or from remnants of the epidermis and phloem cells. Continued longitudinal divisions of these cambial tissues result to the production of secondary tissues and consequently, growth in girth of the stem.  The Leaf  Leaf - food-manufacturing organ of the plant - usually flattened and expanded in form for efficient light interception - develops from leaf primordia formed at the flanks of the shoot apical promeristem  Primary Functions: 1. Photosynthesis – process of food manufacture in green plants 2. Transpiration – loss of water from the plant, usually from leaves, in vapor form  Specialized Functions: 1. Food storage - onion bulb 2. Water storage - banana, Aloe 3. Reproduction - Bryophyllum, Kalanchoe 4. Protection - bud scales of jackfruit, spines of pineapple 5. Support - leaf tendrils of pea 6. Insect-trapping - Venus-fly trap, pitcher plant 7. Floating - water lily, water hyacinth 8. Humus gathering - scale leaves of Drynaria  Principal Parts of a Leaf: 1. Leaf blade - flat expanded portion 2. Petiole - stalk supporting the blade in dicots Leaf Sheath – expanded portion supporting the blade in monocots  Accessory Parts: 1. Stipules - pair of leaf-like, thorn-like or wing-like appendages at the base of the petiole in some dicot leaves 2. Ligule - thin membranous flap of tissue at the junction of blade and sheath in monocot leaves 3.Auricles – pair of ear-like structures at the base of the blade in monocot leaves  Types of Leaves: 1. Simple - blade is entire or in one piece 2. Compound - blade completely dissected into leaflets on a common petiole a. Pinnate - leaflets arise from the sides of a stalk called rachis b. Palmate - leaflets arise from a common point  Types of Leaf Arrangement (phyllotaxy): 1. Alternate - one leaf per node; two successive leaves lie on opposite sides of the stem 2. Spiral - one leaf per node; leaves arranged spirally on the stem 3. Opposite - two leaves per node 4. Whorled - 3 or more leaves per node  Internal Structure of a Dicot Leaf: 1. Upper epidermis 2. Lower epidermis  - stomata, trichomes, 3. Mesophyll tissue – photosynthetic tissue of the leaf a. Spongy mesophyll – loosely packed layer of cells of the mesophyll; has intercellular spaces b. Palisade mesophyll – closely packed layer of mesophyll cells 4. Vascular bundle sheath – single layer of cells that enclose the vascular tissues 5. Vascular tissues a. Xylem – tissues that transport water and minerals b. Phloem – tissues that transport food Internal Structure of a Monocot Leaf: 1. Upper epidermis - ordinary epidermal cells, bulliform cells, trichomes, silica cells, cork cells 2. Lower epidermis - stomates 3. Mesophyll tissue - generally not differentiated into palisade and spongy layers 4. Vascular bundle sheath 5. Vascular tissues a. Xylem b. Phloem The Flower  Floral Parts The flower is a shortened axis of determinate growth which initiates the reproductive cycle of flowering plants, the angiosperms. It functions to facilitate the formation and fusion of gametes. There are about 150,000 species of flowering plants. Within this large group, there is considerable diversity in flower structure. Nonetheless there exists a fundamental structure of the flower. A typical flower is an assemblage of spirals or whorls (cycles) of sterile and fertile parts borne on an enlarged end of the axis, the receptacle and subtended by a stalk, the pedicel. The sterile or accessory parts of the flower are the sepals and petals. They are so called because they are not involved in the production of gametes. The sepals generally are the outer, green, foliaceous structures that occupy the lowermost whorl of the axis. The sepals taken collectively constitute the calyx. The petals, on the other hand, are the conspicuous, colored and attractive floral parts. They occupy the next whorl of parts in the axis. The petals taken together constitute the corolla which serves to attract and guide the movement of pollinators. The calyx and the corolla make up the perianth. The fertile or essential parts are the stamens and the pistil, which are collectively known as the androecium and the gynoecium, respectively. The stamen is the male reproductive part consisting of an anther supported by a slender stalk, the filament. The pistil consists of an enlarged basal portion the ovary, a receptive surface for pollen, the stigma and a slender stalk joining the ovary and stigma, the style.  Variation in Floral Structure  Flowers in which all four parts are present are called complete flowers. Flowers which lack one or more of these parts are incomplete flowers. A flower with no corolla is described as apetalous, e.g., Antigonon and Bougainvillea. Flowers with both essential parts present, regardless of the presence or absence of perianth parts, are perfect or bisexual flowers. Flowers which lack either stamens or pistils are imperfect or unisexual flowers. Imperfect flowers are of two kinds, staminate flowers and pistillate flowers. Species which have both kinds of imperfect flowers on the same individual plant are monoecious, those in which only one kind is borne by an individual plant are dioecious. Flowers exhibit distinct symmetry. Many flowers appear radially symmetrical when viewed from points on projections from their axes. These are regular or actinomorphic flowers. Others, which are not radially symmetrical, are irregular or zygomorphic flowers.  The Pistil, Carpel, Ovary and Ovule Pistils are believed to have been derived from carpels which, in past geologic ages, resemble flat, leaf-like structures bearing marginal ovules. In modern plants the margins of the carpels have rolled inwards, enclosing the ovules. A pistil is therefore a structure composed of one or more enrolled carpels. The enlarged basal portion of the pistil is the ovary, a hollow structure having from one to several cavities called locules. Inside the locules are the ovules which become seeds after fertilization. The tissue within the ovary to which the ovule is attached is the placenta. In most flowering plants, flowers are borne in clusters or groups termed as in inflorescence. Each flower is subtended by a stalk, the pedicel. Flowers without pedicels are said to be sessile. An individual flower, whether sessile or pedicellate, is always subtended by a small, modified leaf called the bract. In the composite family, e.g. Helichrysum and Helianthus, a collection of these bracts makes up the involucre. The following are the different types of inflorescences: 1. spike - Peperomia, Piper 2. raceme - Caesalpinia 3. catkin - Acalypha 4. spadix - Typhonium, Caladium 5. panicle - Panicum, Oryza 6. cyme - Premna, Jatropha 7. umbel - Dracaena, Belamcanda 8. head - Tridax, Leucaena, Helianthus Microsporogenesis - process wherein a pollen mother cell or megasporocyte in the anther divides by meiosis to give rise to four haploid microspores, which then mature into pollen grains Microgametogenesis - series of events undergone by the nucleus inside the pollen grain which lead to the formation of a tube nucleus and sperm nuclei or male gametes Megasporogenesis - megassporocyte in the nucellus divides by meiosis to form 4 haploid megaspores; but only one is functional, all others degenerate Megagametogenesis - series of events in the megaspore which leads to the formation of the female gametes or eggs. Mature embryo sac - end product of megagametogenesis Parts of Mature Embryo Sac: 1. one egg cell 2. two synergids 3. two polar nuclei 4. three antipodals Pollination – transfer of pollen from the anther to the stigma Fertilization – in general, the fusion of egg and sperm to form the zygote; in angiosperms, double fertilization occurs, a process unique to angiosperms Double Fertilization in Angiosperms: 1 egg + 1 sperm = diploid zygote embryo 2 polar nuclei + 1 sperm = triploid endosperm nucleus endosperm tissue Agents of Pollination: 1. Biological - insects, birds, bats, man and other animals 2. Non-biological - wind, water The Fruit  Structure The fruit botanically defined is a ripened ovary which encloses one or more seeds. After fertilization in the flower, the ovule develops and enlarges to become the seed. Two processes therefore, precede fruit development: pollination and fertilization. Some plants, however, regularly produce fruits without fertilization, thus the resulting fruits are seedless. This condition that is common in banana and pineapple is called parthenocarpy. There are fruits, however, that produce seeds even without fertilization. Such seeds are formed through the process called apomixis. During fruit development, the ovary wall undergoes histologic development and becomes the fruit wall or pericarp. The pericarp generally differentiates into three layers of tissues: the outermost layer is the exocarp, the middle layer is the mesocarp, and the innermost layer is the endocarp.  Types of Fruit A. Simple Fruits legume/pod silique Dehiscent follicle Dry capsule drupe nut Indehiscent grain/caryopsis samara achene drupe Fleshy berry special types of berry hesperidium pepo B. Compound Fruits 1. Aggregate - a cluster of ripened ovaries from one flower ex. atis, jackfruit 2. Multiple or Collective - derived from several ovaries of several flowers fused into a single unit ex. pineapple, figs Two Forms: a. Psorosis - ex. pineapple b. Synconium - ex. figs The Seed  Seed Structure The seed is defined as a fertilized ovule. It completes the reproductive process initiated in the flower. The seed of angiosperms consists of 1) embryo or the embryonic plant which develops from the zygote, 2) seed coat or testa, the outermost covering of the seed derived from the integuments of the ovule, and 3) endosperm or the nutritive tissue derived from the primary endosperm cell. In most dicots, the endosperm is absorbed by the embryo and food is stored in the cotyledons before the seed reaches maturity. Seeds of this type are called non-endospermic or exalbuminous seeds and are observed in the families Cruciferae, Cucurbitaceae, Compositae and some members of leguminosae. In many monocots, the endosperm persists and thus they are referred to as endospermic or albuminous seeds.  The embryo of the seed consists of an embryonic shoot, the plumule consisting of young stem and young leaves, one or two seed leaves or cotyledons, and an embryonic root the radicle. In grass seeds, the plumule is enclosed by a sheath called coleoptile, and the radicle is enclosed by a sheath , the coleorhiza.