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Structure of Plant Cell

Cell parts and their functions
Cell wall:-A cell wall is a tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to act as a pressure vessel, preventing over-expansion when water enters the cell. They are found in plants, bacteria, fungi, algae, and some archaea. Animals and protozoa do not have cell wall and it permits the organism to build and hold its shape (morphogenesis). The cell wall also limits the entry of large molecules that may be toxic to the cell. It further permits the creation of a stable osmotic environment by preventing osmotic lysis and helping to retain water.

Cell membrane:-The cell membrane (also called the plasma membrane or plasma lemma) is one biological membrane separating the interior of a cell from the outside environment. The cell membrane surrounds all cells and it is selectively-permeable, controlling the movement of substances in and out of cells. It contains a wide variety of biological molecules, primarily proteins and lipids, which are involved in a variety of cellular processes such as cell adhesion, ion channel conductance and cell signaling. The plasma membrane also serves as the attachment point for the intracellular cytoskeleton and, if present, the extracellular cell wall. Golgi apparatus:-The Golgi apparatus (also Golgi body or Golgi Complex) is an organelle found in most eukaryotic cells.

It was identified in 1898 by the Italian physician Camillo Golgi and was named after him.
The primary function of the Golgi apparatus is to process and package macromolecules, such as proteins and lipids, after their synthesis and before they make their way to their destination; it is particularly important in the processing of proteins for secretion. The Golgi apparatus forms a part of the cellular endomembrane system. Cytoplasm:-The cytoplasm is the part of a cell that is enclosed within the cell membrane. the cytoplasm contains organelles, such as mitochondria, which are filled with liquid that is kept separate from the rest of the cytoplasm by biological membranes.

The cytoplasm is the site where most cellular activities occur, such as many metabolic pathways like glycolysis, and processes such as cell division. The part of the cytoplasm that is not held within organelles is called the cytosol. The cytosol is a complex mixture of cytoskeleton filaments, dissolved molecules, and water that fills much of the volume of a cell. The cytosol is a gel, with a network of fibers dispersed through water. Mitrochrondia:-In cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed organelle found in most eukaryotic cells.These organelles range from 0.5 to 10 micrometers (μm) in diameter.

Mitochondria are sometimes described as "cellular power plants" because they generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy. In addition to supplying cellular energy, mitochondria are involved in a range of other processes, such as signaling, cellular differentiation, cell death, as well as the control of the cell cycle and cell growth. Mitochondria have been implicated in several human diseases, including mitochondrial disorders and cardiac dysfunction and may play a role in the aging process.

Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.

Chromatin:- is the combination of DNA and proteins that makes up chromosomes.
The major components of chromatin are DNA and histone proteins, although other proteins have prominent roles too. The functions of chromatin are to package DNA into a smaller volume to fit in the cell, to strengthen the DNA to allow mitosis and meiosis, and to serve as a mechanism to control expression and DNA replication. Chromatin contains genetic material-instructions to direct cell functions. Chromoplasts :-are plastids responsible for pigment synthesis and storage. They, like all other plastids (including chloroplasts and leucoplasts), are organelles found in specific photosynthetic eukaryotic species.

Chromoplasts in the traditional sense are found in coloured organs of plants such as fruit and floral petals, to which they give their distinctive colors. This is always associated with a massive increase in the accumulation of carotenoid pigments. The conversion of chloroplasts to chromoplasts in ripening tomato fruit is a classic example. Deoxyribonucleic acid:- DNA is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses

The main role of DNA molecules is the long-term storage of information.
Chemically, DNA consists of two long polymers of simple units called nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds. These two strands run in opposite directions to each other and are therefore anti-parallel. Attached to each sugar is one of four types of molecules called bases. Endoplasmic reticulum :-is an eukaryotic organelle that forms an interconnected network of tubules, vesicles, and cisternae within cells.

Rough endoplasmic reticulum synthesize proteins, while smooth endoplasmic reticulum synthesize lipids and steroids, metabolize carbohydrates and steroids, and regulate calcium concentration, drug detoxification, and attachment of receptors on cell membrane protein. Leucoplasts:- are a category of plastid and as such are organelles found in plant cells. They are non-pigmented, in contrast to other plastids such as the chloroplast. Lacking pigments, leucoplasts are not green, so they are predictably located in roots and non-photosynthetic tissues of plants.

They may become specialized for bulk storage of starch, lipid or protein and are then known as amyloplasts, elaioplasts, or proteinoplasts respectively’ Lysosomes :-are spherical organelles that contain enzymes (acid hydrolases) that break up endocytized materials and cellular debris. They digest excess or worn-out organelles, food particles, and engulfed viruses or bacteria. They are frequently nicknamed "suicide-bags" or "suicide-sacs" by cell biologists due to their role in autolysis .

Nuclear envelope:- is a double lipid bilayer that encloses the genetic material in eukaryotic cells. The nuclear envelope also serves as the physical barrier, separating the contents of the nucleus (DNA in particular) from the cytosol (cytoplasm). Many nuclear pores are inserted in the nuclear envelope, which facilitate and regulate the exchange of materials (proteins such as transcription factors, and RNA) between the nucleus and the cytoplasm.

Ribonucleic acid (RNA) is a biologically important type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nitrogenous base, a ribose sugar, and a phosphate. RNA is very similar to DNA, but differs in a few important structural details: in the cell, RNA is usually single-stranded, while DNA is usually double-stranded; RNA nucleotides contain ribose while DNA contains deoxyribose (a type of ribose that lacks one oxygen atom); and RNA has the base uracil rather than thymine that is present in DNA. RNA is transcribed from DNA by enzymes called RNA polymerases and is generally further processed by other enzymes. RNA is central to protein synthesis

Ribosomes:- are the components of cells that make proteins from amino acids.
Vacuole is a membrane bound organelle which is present in all plant and fungal cells and some animal and bacterial cells. functions of the vacuole include: Isolating materials that might be harmful or a threat to the cell Containing waste products Maintaining internal hydrostatic pressure or turgor within the cell Maintaining an acidic internal pH Containing small molecules Exporting unwanted substances from the cell

The Cell Cycle & Cell Division

The Cell Cycle

MITOSIS

Mitosis The process of cell division which results in the production of two daughter cells from a single parent cell. The daughter cells are identical to one another and to the original parent cell.

Mitosis can be divided into stages
Interphase Prophase Metaphase Anaphase Telophase & Cytokinesis

Interphase The cell prepares for division
Animal Cell DNA replicated Organelles replicated Cell increases in size Plant Cell DNA replicated Organelles replicated Cell increases in size

Interphase Plant Cell Animal Cell
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Prophase The cell prepares for nuclear division
Animal Cell Packages DNA into chromosomes Plant cell Packages DNA into chromosomes

Prophase Plant Cell Animal Cell
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Metaphase The cell prepares chromosomes for division
Animal Cell Chromosomes line up at the center of the cell Spindle fibers attach from daughter cells to chromosomes at the centromere Plant Cell Chromosomes line up at the center of the cell Spindle fibers attach from daughter cells to chromosomes at the centromere

Metaphase Plant Cell Animal Cell
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Anaphase The chromosomes divide
Animal Cell Spindle fibers pull chromosomes apart ½ of each chromosome (called chromotid) moves to each daughter cell Plant Cell Spindle fibers pull chromosomes apart ½ of each chromosome (called chromotid) moves to each daughter cell

Anaphase Plant Cell Animal Cell
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Telophase The cytoplasm divides
Plant Cell DNA spreads out 2 nuclei form Cell membrane pinches in New cell wall forms between to nuclei to form the 2 new daughter cells Animal Cell DNA spreads out 2 nuclei form Cell membrane pinches in to form the 2 new daughter cells

Telophase Plant Cell Animal Cell
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Mitosis Animation Animation

Animal Mitosis -- Review
Interphase Prophase Metaphase Anaphase Telophase

Plant Mitosis -- Review
Interphase Prophase Metaphase Anaphase Telophase

MEIOSIS

One parent cell produces four daughter cells.
Meiosis Meiosis is the type of cell division by which germ cells (eggs and sperm) are produced. One parent cell produces four daughter cells. Daughter cells have half the number of chromosomes found in the original parent cell

During meiosis, DNA replicates once, but the nucleus divides twice.

Four stages can be described for each division of the nucleus.
Meiosis Four stages can be described for each division of the nucleus.

First division of meiosis
Meiosis I First division of meiosis

First Division of Meiosis
Prophase 1: Each chromosome duplicates and remains closely associated. These are called sister chromatids. Metaphase 1: Chromosomes align at the center of the cell. Anaphase 1: Chromosome pairs separate with sister chromatids remaining together. Telophase 1: Two daughter cells are formed with each daughter containing only one chromosome of the chromosome pair.

Prophase I

Metaphase I

Telophase I

Second Division of Meiosis

Second Division of Meiosis
Prophase 2: DNA does not replicate. Metaphase 2: Chromosomes line up at the center of the cell Anaphase 2: Centromeres divide and sister chromatids move separately to each pole. Telophase 2: Cell division is complete. Four haploid daughter cells are formed.

Prophase II

Metaphase II

Telophase II

Meiosis

Meiosis Animation Animation

Differences in Mitosis & Meiosis
Asexual Cell divides once Two daughter cells Genetic information is identical Meiosis Sexual Cell divides twice Four haploid daughter cells Genetic information is different

3 Tissue System Dermal, vascular, and ground tissue systems
Dermal tissue, or epidermis, is generally a single layer of tightly packed cells that covers and protects and the roots hairs are extensions of epidermal cells The epidermis of leaves and most stems secretes a waxy coating, the cuticle, that helps the plant retain water. 3 Tissue System

Ground tissue is tissue that is neither dermal tissue nor vascular tissue divided into pith, internal to vascular tissue, and cortex, external to the vascular tissue. Functions of ground tissue include photosynthesis, storage, and support

Xylem-water conducting elements
Vascular tissue, continuous throughout the plant, is involved in the transport of materials. Xylem-water conducting elements Tracheids and vessel elements, are elongated cells that are dead at functional maturity Tracheids are long, thin cells with tapered ends. Water moves from cell to cell mainly through pits. walls are hardened with lignin, tracheids function in support as well as transport. Vessel elements are aligned end to end, forming long micropipes, xylem vessels Phloem transport sucrose, other organic compounds, and some mineral ions move through tubes formed by chains of cells, sieve-tube members

Phloem

Plant Tissue---3Cell Types
Parenchyma, Collenchyma, and Sclerenchyma Parenchyma cells are the most abundant of cell types and are found in almost all major parts of higher plants cells. These cells are basically sphere shaped and have primary walls that are relatively thin and flexible, These cells have large vacuoles and may contain various secretions including starch, oils, tannins, and crystals. Some parenchyma cells have many chloroplasts and found in leaves. This type of tissue is called chlorenchyma. The chief function is photosynthesis, while parenchyma tissues without chloroplasts are generally used for food or water storage.

parenchyma cell can perform most of the metabolic functions of the plant, synthesizing and storing various and organic compounds. parenchyma cells do not generally undergo cell division. Most retain the ability to divide and differentiate into other cell types under special conditions - during the repair and replacement of organs after injury to the plant. In the laboratory, it is possible to regenerate an entire plant from a single parenchyma cell.

Collenchyma cells have a living protoplasm, like parenchyma cells, and may also stay alive for a long period of time. Their main distinguishing difference from parenchyma cells is the increased thickness of their walls. In cross section, the walls looks uneven. Collenchyma cells are found just beneath the epidermis and generally they are elongated. They provide flexible support for organs such as leaves and flower parts.

Sclerenchyma cells also function as supporting elements of the plant, with thick secondary walls usually imbedded with lignin and they cannot elongate and occur in plant regions that have stopped lengthening. At maturity, most sclerenchyma cells are dead and function in structure and support. Sclerenchyma cells can occur in two forms: Sclereids and sclerenchyma cells that are randomly distributed throughout other tissues. Sometimes they are grouped within other tissues in specific zones or regions. They are generally as long as they are wide.Sclereids are sometimes called stone cells. Fibers are sometimes found in association with a wide variety of tissues in roots, stems, leaves and fruits. Usually fiber cells are much longer than they are wide and have a very tiny cavity in the center of the cell.

Fibers and sclereids, are specialized entirely in support.
Fibres are used in the manufacture of textiles, ropes, string and canvas goods to name a few. Fibers and sclereids, are specialized entirely in support. Fibers are long, slender and tapered, and usually occur in bundles while sclerids shorter than fibers and irregular in shape, impart the hardness to nutshells.

Growth and Development
Meristemic tissue:- Tissues where cells are constantly dividing are called meristems or meristematic tissues. These regions produce new cells. These new cells are generally small, six-sided boxlike structures with a number of tiny vacuoles and a large nucleus, by comparison. Sometimes there are no vacuoles at all. As the cells mature the vacuoles will grow to many different shapes and sizes, depending on the needs of the cell.further they are of 3 types- Apical meristem- located at the tips of roots and in the buds of shoots, supply cells for the plant to grow in length. This growth by apical meristem is known as primary growth. Lateral meristem- progressive thickening of roots and shoots and it is also known as secondary growth, t tip is covered by a thimble-like root cap, which protects the meristem as the root pushes through the abrasive soil

The vascular cambium, the first type of lateral meristem, is sometimes just called the cambium. The cambium is a thin, branching cylinder that, except for the tips where the apical meristems are located, runs the length of the roots and stems of most perennial plants and many herbaceous annuals. The cambium is responsible for the production of cells and tissues that increase the thickness, or girth, of the plant. The cork cambium, the second type of lateral meristem, is much like the vascular cambium in that it is also a thin cylinder that runs the length of roots and stems. The difference is that it is only found in woody plants, as it will produce the outer bark.

Intercalary meristems- are found in grasses and related plants that do not have a vascular cambium or a cork cambium, as they do not increase in girth. These plants do have apical meristems and in areas of leaf attachment, called nodes, they have the third type of meristematic tissue. This meristem will also actively produce new cells and is responsibly for increases in length. The intercalary meristem is responsible for the regrowth of cut grass.

Monocot and Dicot

Monocot---Dicot

Annuals Complete their life cycle (from seedling to setting seed) within a SINGLE growing season. However, the growing season may be from fall to summer, not just spring to fall. These plants come back from seeds only.

Summer annuals Germinate from seed in the spring and complete flowering and seed production by fall, followed by plant death, usually due to cold temperatures. Their growing season is from spring to fall. Examples: marigolds, squash, and crabgrass. These are also called warm season annuals.

Winter annuals Germinate from seed in the fall, with flowering and seed development the following spring, followed by plant death. Their growing season is from fall to summer. Examples: winter wheat and annual bluegrass. These are also referred to as cool season annuals. Many weeds in the lawn (such as chickweed and annual bluegrass) are winter annuals.

Biennials Germinate from seed during the growing season and often produce an over-wintering storage root or bulb the first summer. Quite often they maintain a rosette growth habit the first season, meaning that all the leaves are basal. They flower and develop seeds the second summer, followed by death.

Biennials In the garden setting, we grow many biennials as annuals (e.g., carrots, onions, and beets) because we are more interested in the root than the bloom. Some biennial flowers may be grown as short-lived perennials (e.g., hollyhocks).

Perennials Live through several growing seasons, and can survive a period of dormancy between growing seasons. These plants regenerate from root systems or protected buds, in addition to seeds.

Perennials Herbaceous perennials develop over-wintering woody tissue only at the base of shoots (e.g. peony and hosta) or have underground storage structures from which new stems are produced. (Please note: Golden Vicary Privet can be either herbaceous or woody as grown in Colorado.)

Perennials Spring ephemerals have a relatively short growing season but return next season from underground storage organs (e.g. bleeding heart, daffodils). Woody perennials develop over-wintering tissue along woody stems and in buds, (e.g. most trees and shrubs grown in Colorado). Combination plants are usually classified as annual, biennial or perennial on the basis of the plant part that lives the longest. For example, raspberries have biennial canes and perennial roots

Morphology Morphology -“Study the form and structure of plants or any part of plant ” Definition - “It is an macroscopy of drug including its visual appearance to the naked eye and study of the part of the plant from which the drug obtained”

THE LEAF : TYPES Simple leaves show an undivided blade or , in case it has divisions, they do not reach the midrib. Compound leaves have a fragmented blade,with divisions reaching the midrib. Sometimes each one of these fragments is similar to a single leaf. They are called leaflets

Simple leaves:- (a) Pinnate or Unicostate- in unicostate leaves the incision always proceed from margin towards the mid-rib and on the basis of extent of incision these are of following types- Pinnatifid (e.g., Chyrsanthium), Pinnatipartite (e.g.,mustard) & Pinnatisect (Marigold). (b) Palmate or Multicostate- in this type the incisions always proceed from the margin to towards the base of the lamina. Types are:- Palmatifid (Cotton), Palmatipartite (Castor, Bitter ground) & Palmatisect (Cannabis).

Trifoliolate (Aegle marmelos),
Compound leaves:- In a compound leaf the lamina is completely disected into leaflets, which are completely seprated from each other & distinctly articulated. Types:- (a) Pinnate compound leaves:- in this type of compound leaves the leaflets are usually attached in pairs to the continuation of the midrib. Types :- Unipinnate (Rose, neem), Bipinnate (Acacia arabica), Tripinnate (Horse radish) & Decompound (Carrot) (b) Palmate compound leaves:- in this type all the leaflets are attached toa common point at the tip of petiole. These leaflets are petiolate or sessile.Types:- Unifoliolate (Citrus), Bifoliolate (Balanites), Trifoliolate (Aegle marmelos), Quardifoliolate (Marsilea) & Multifoliolate (Bombax malabaricum)

Parts of a leaf- leaf base, petiole and lamina
Leaf base-lowermost part by which it is joined to the node of stem. Petiole- cylinderical or subcylindrical stalk of the leaf which lifts the lamina above the level of the stem so as to provide it with maximum exposure. Lamina- terminal thin, expanded, green and conspicuous part of the leaf which is specilazed to perform photosynthesis.

Petiolated leaves are those that have a petiole
Petiolated leaves are those that have a petiole. This can be different in length from one plant to another. Sessile leaves do not possess a petiole. The blade expands itself directly from the stem.

Leaf classification according to arrangement along the stem
alternate: springing one per node at different levels of the stem. opposite: two per node, facing opposite sides of the stem. whorled: Several leaves disposed at the same level around the stem. rosulate forming a rosette, like a ring around the stem.

Leaf classification according to arrangement along the stem
opposite alternate whorled rosulate

Leaf modifications Leaf Spines
In some plants, leaves or parts of leaves may be modified into spines. Scale Leaves In many desert plants, the leaves are highly reduced and appear as scales. The scale leaves are thin, membranous, dry, stalkless and brownish or colourless. In plants where the leaves are reduced to scales in order to minimise transpiration, the function of photosynthesis is relegated to the stems

Flowers Flowers are important in making seeds.
Flowers can be made up of different parts, but there are some parts that are basic equipment. The main flower parts are the male part called the stamen and the female part called the pistil . A complete flower has a stamen, a pistil, petals, and sepals. An incomplete flower is missing one of the four major parts of the flower, the stamen, pistil, petals, or sepals.

Parts Of A Flower

Calyx: the outer whorl of sepals; typically these are green, but are petal-like in some species.
Corolla: the whorl of petals, which are usually thin, soft and colored to attract animals that help the process of pollination. The coloration may extend into the ultraviolet, which is visible to the compound eyes of insects, but not to the eyes of birds.Z

Gynoecium or Pistil Gynoecium is the innermost whorl and is the female reproductive part of the flower. The gynoecium has three parts, the basal ovary, the elongated style and the terminal stigma. The ovary is made up of one to many units called carpels. Depending on the number of carpels present, ovary is described as follows: a. Monocarpellary (having one carpel) e.g. Beans. b. Bicarpellary (having two carpels) e.g. Brassica c. Tricarpellary (having three carpels) e.g. Ricinus (Castor) d. Tetracarpellary (having four carpels) e.g. Bergia e. Pentacarpellary (having five carpels) e.g. Hibiscus, apple The carpels in the ovary may be free from one another or fused. The ovary is described as apocarpus, when the carpels are free e.g. Michelia. The ovary is described as syncarpous, when the carpels are united e.g. Ricinus, Citrus.

Depending upon its position the ovary may be
i) Inferior: When all the floral parts arise from above the ovary as in epigynous flowers. ii) Semi-inferior: Where the floral parts are seen developing from about the middle of ovary as in perigynous flowers. iii) Superior: When all the floral parts arise from the base of the ovary as in hypogynous flowers.

Fruit fruit is a mature ovary. As seeds develop from ovules after fertilization, the wall of the ovary thickens to form the fruit. Fruits protect dormant seeds and aids in their dispersal Pass through an animals digestive tract unharmed and conveniently land in a pile of fertilizer some time later Various modifications in fruits help disperse seeds. Many angiosperms use animals to carry seeds. Edible fruits are eaten by animals

Fruits

Fruit Classification

Simple Fruit Simple fruits can be either dry or fleshy, and result from the ripening of a simple or compound ovary in a flower with only one pistil. Dry fruits may be either dehiscent (opening to discharge seeds), or indehiscent (not opening to discharge seeds ). Types of dry, simple fruits, with examples of each, are: Achene - Most commonly seen in aggregate fruits (e.g. strawberry) Capsule – (Brazil nut) Caryopsis – (wheat) Cypsela - An achene-like fruit derived from the individual florets in a Capitulum (e.g. dandelion). Fibrous drupe – (coconut, walnut) Follicle – is formed from a single carpel, and opens by one suture (e.g. milkweed).)

Aggregate and Multiple Fruits
Aggregate fruits form from single flowers that have multiple carpels which are not joined together, i.e. each pistil contains one carpel. Each pistil forms a fruitlet, and collectively the fruitlets are called an etaerio. Four types of aggregate fruits include etaerios of achenes, follicles, drupelets, and berries.eg- rasberry, strawberry, blackberry etc. A multiple fruit is one formed from a cluster of flowers (called an inflorescence). Each flower produces a fruit, but these mature into a single mass.eg- pineapple, fig, mulberry, osage-orange, and breadfruit.

Multiple fruits

Bark Bark consists of external tissues of stems and roots removed by peeling them after making a suitable longitudinal and transverse incisions through the outer layers. (Wallis T.E., fifth edition, CBS publishers & Distributors) Bark consist of all tissues outside the cambium. In botany the term bark is sometimes restricted to the outer bark- that is, the periderm and all the tissues lying outside it. A young bark is composed of the following tissues- i) Epidermis: a layer of closely fitting cuticularized cells with occasional stomata. ii) Primary cortex: a zone usually consisting of chlorophyll-containing collenchyma and parenchyma. iii) Endodermis: or inner layer of the cortex, which frequently contains starch. iv) Pericycle: which may be composed of parenchyma or of fibers. Groups of fibers often occur opposite each group of phloem. Phloem : which consists of sieve tubes, companion cells and phloem parenchyma separated by radically arranged medullary rays. (Evans W.C., Trease and Evans, fifteenth edition, Saunders,an imprint of Elsevier)

Characterization of bark
Flat- large pieces of bark are often dried under pressure (e.g.- cinchona and quillaia) Curved - slightly concave on the inside (wild cherry, cassia) Recurved - Concavity on the outerside ( kurchi bark) Channeled -deep curvature on the inside to form deep trough (Ashoka, cinchona) Quill – more curvature and one edge overlaps the other (cascara, cinnamon) Double quill – each edge rolled independently into quill (Java cinnamon) Compound Quill – in this type one quill is packed within the other quill and other pieces of bark. This type of bark is man made to make the size of barks compatible for packing and transportation (e.g., cinnamon bark’s compound quill)

Charcterstics of outer surface of bark
When the cork is evenly developed, smooth surface results and is frequently marked by lenticels as in cascara. Cracks and fissures of characteristic type arise in the outer surface owing to the lack of elasticity in the dead tissues and the continued increase in girth of the tree. These cracks are characteristic, having, for example, clean cut edges in Cinchona succirubra, but thickened, Recurved edges in Cinchona officinalis. The shrinkage of the softer tissues results in formation of Wrinkles externally, if the troughs between wrinkles are very wide they are termed furrows. An additional character is sometimes provided by presence of epiphytes upon the outer surface, most commonly Lichens, Liverworts and Mosses.

Charcterstics of inner surface of bark
Shrinkage of inner surface results into Parallel longitudinal ridges called as striations Parallel transverse wrinkles called as corrugations (e.g. Cascara bark) When bark broken across transversely termed as fracture Smooth - short Round - granular Pointed - splintery Threads - fibrous Tangential - laminated

SEED A seed is a ripened fertilized ovule which contains an embryonic plant, reserve food & protective covering. In seeds metabolic activities get suspended to pass over the unfavorable period & when sown in soil it can give rise to a new plant, i.e. a new generation starts with the formation of seeds. Seed can also be defined as, “a plant member derived from a fertilized ovule; which contains an embryo & is constructed so as to facilitate its transportation”. Embryo is the future plant which is in miniature condition. Wallis T.E .Textbook of Pharmacognosy. 5th edition; Pg:188. Seed have one or two coverings called seed coats. The outer or the only seed coat is called testa, while the inner one is named tegmen.

Nature of Seed ENDOSPERMIC OR ALBUMINOUS SEEDS
The seeds which store their food in Endosperm are called Endospermic seed or albuminous . E.g. Colchicum, Isabgol, Nux-vomica etc. NON-ENDOSPERMIC OR EXALBUMINOUS SEEDS The seeds which store their food in cotyledons are called Non- endospermic seed or Exalbuminous. E.g. Sunflower, Cotton, soyabean & Tamarind etc. Wallis T.E. Textbook of Pharmacognosy. 5th edition; Pg:194.

Ovule Ovule means "small egg."
In seed plants, the ovule is the structure that gives rise to and also contains the female reproductive cells. It consists of three parts: Integuments ; forming its outer layer, Nucellus Megaspore-derived female gametophyte or Megagametophyte; also called embryo sac in flowering plants, its in center and produces the egg cell for fertilization. These ovule develops into a seed after fertilization. ( .org/ cgi content/full/51/343/249) Botany:-A brief introduction to plant biology.

Location within the plant
IN FLOWERING PLANTS Ovule is located within the actual flower, the part of the carpel known as the ovary, which ultimately becomes the fruit. Flowers may have one or multiple ovules per ovary depending on the plant, the ovule is attached to the placental wall of the ovary through a structure known as the funiculus, the plant equivalent of an umbilical cord. Different patterns of ovule attachment, or placentation are found among plants: In Parietal Placentation; Ovules are attached to the outer ovary wall In Free Central Placentation; Ovules are attached to a central column within the ovary. In Axil Placentation; Ovules are attached to radial spokes within the ovary. Raven, Peter H , Ray Franklin Evert & Helena Curtis. Biology of plants. Pg:410.

Morphology A typical seed is characterized by the following structures:- Testa :- It is the protective covering of the seed. Micropyle:- It is a small pore at one of seed coat through which water is absorbed by the seed. Funiculus:-The stalk of seed from which it is attached to the fruit wall is called funiculus. Hilum:- A large scar, where the seed breaks from stalk of funiculus is called hilum. Raphe:- It is a median line which divides the seed lengthwise into two similar halves and situated beyond the hilum, opposite the micropyle. Embryo:-The most important part of seed which developes from zygote after fertilization . Kernel:- All structure of seed enclosed by seed coat is called kernel. (Fahn.A, Plant anatomy, Butterworth publishers, 1997, pg-515)

Microscopy of Seed Microscopy of seeds can be explained by examining the TS of various pharmaceutical important seeds as Nux-vomica (Strychnos nux-vomica) and Linseed (Linum usitatissimum) TS of Strychnos nux-vomica

Description of TS of Strychnos nux-vomica
Testa : Hairy epidermis single layered; each epidermal cell forms a lignified trichome with pitted bulbous base & elongated projection & slightly bent beyond the base. Collapsed parenchyma : 2 layered , collapsed parenchymatous cells with yellowish brown contents. Endosperm : Outermost layers of the endosperm below the collapsed parenchyma appear palisade like whereas the inner layers contains cells which are polyhedral , thick walled but non-lignified parenchymatous cells. A characteristic feature of the endosperm is the presence of well inter-connected PLASMODESMATA. Endosperm cells also contain aleurone grains & oil droplets (Iyenger M.A. Pharmacognosy of powdered crude drugs,81)

Quality Standards of Seeds
SEED GERMINATION It is the transformation of an embryo into a seedling. During the process of germination, the metabolism & growth which are suppressed or suspended are resumed. Requirements Water is the basic requirement for initiating the chemical reactions. Optimum temperature is essential for good germination. Temperature range for germination is normally OC. Oxygen is required for respiration.

SEED VIGOUR It is defined as the condition of seed that permits germination to proceed rapidly & uniformly and allows production of uniform seedling stand. Hybrid seeds normally possess greater vigour due to inherent genetic makeup. SEED VIABILITY It is defined as the degree to which a seed is metabolically active & capable of germinating under favorable conditions. Seed viability is the highest at the time of physiological maturity. SEED LONGEVITY It means the duration of the viability of seeds. Normally the seeds possess maximum germination potential during the physiological maturity & the deterioration of seed quality occurs from this point of maturation onwards.

STEM A stem is one of two main structural axes of a vascular plant.
The stem is normally divided into nodes and internodes, the nodes hold buds which grow into one or more leaves, inflorescence (flowers), cones or other stems etc. The internodes distance one node from another. The term shoots is often confused with stems; shoots generally refer to new fresh plant growth and does include stems but also to other structures like leaves or flowers. The other main structural axis of plants is the root. In most plants stems are located above the soil surface but some plants have underground stems.

Functions of Stems For Support and the elevation of leaves, flowers and fruits. The stems keep the leaves in the light and provide a place for the plant to keep its flowers and fruits. Transport of fluids between the roots and the shoots in the xylem and phloem. Storage of nutrients. The production of new living tissue. The normal life span of plant cells is one to three years. Stems have cells called meristems that annually generate new living tissue.

Stem Structure Stem usually consist of three tissues, dermal tissue, ground tissue and vascular tissue. The dermal tissue covers the outer surface of the stem and usually functions to waterproof, protect and control gas exchange. The ground tissue usually consists mainly of parenchyma cells and fills in around the vascular tissue. It sometimes functions in photosynthesis. Vascular tissue provides long distance transport and structural support

Types of Stems Monocot stems:-Vascular bundles are present throughout the monocot stem, although concentrated towards the outside. This differs from the dicot stem that has a ring of vascular bundles and often none in the center. The shoot apex in monocot stems is more elongated. Monocots rarely produce secondary growth and exceptions are Palms and Bamboo. Gymnosperm stems:- The trunk of this redwood tree is its stem.All gymnosperms are woody plants. Their stems are similar in structure to woody dicots except that most gymnosperms

produce only tracheids in their xylem, not the vessels found in dicots
produce only tracheids in their xylem, not the vessels found in dicots. Gymnosperm wood also often contains resin ducts. Woody dicots are called hardwoods, e.g. oak, maple and walnut. Fern stems:- Most ferns have rhizomes with no vertical stem.The stem anatomy of ferns is more complicated than that of dicots because fern stems often have one or more leaf gaps in cross section. A leaf gap is where the vascular tissue branches off to a frond. In cross section, the vascular tissue does not form a complete cylinder where a leaf gap occurs. Many fern stems have phloem tissue on both sides of the xylem in cross-section.

Dicot Stem:-Dicot stems with primary growth have pith in the center, with vascular bundles forming a distinct ring visible when the stem is viewed in cross section. The outside of the stem is covered with an epidermis, which is covered by a waterproof cuticle. The epidermis also may contain stomata for gas exchange and multicellular stem hairs. A cortex consisting of Hypodermis (collenchyma cells) and Endodermis (starch containing cells) is present above the pericycle and vascular bundles.

Modifications of Stems
Stolon Rhizomes Tubers Bulb

Stolons:- Stems that run horizontally above ground are termed stolons or runners.
Rhizomes:- Stems that run horizontally below the ground surface are termed rhizomes. Tubers:- The enlarged, fleshy tips of certain rhizomes (such as those of the Irish potato) are modifed for food storage and are temed tubers. Bulbs:- These are unusual below ground structures that consist of a shortened, upright stem with modified, fleshy leaves attached to it.

Roots Root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial (growing above the ground) or aerating (growing up above the ground or especially above water).So, it is better to define root as a part of a plant body that bears no leaves, and therefore also lacks nodes. Function of roots are-1) absorption of water and inorganic nutrients, 2) anchoring of the plant body to the ground and 3) storage of food and nutrients. roots also synthesise cytokinin, which acts as a signal as to how fast the shoots can grow.

Modification of Roots Tap Root Storage roots
The primary root of tap root become fleshy and swollen due to storage of food. These are of following types: Conical. Root is broad t the base and gradually tapers towards apex e.g. Raphanus sativus (Radish), Daucus carota (Carrot). (b) Napiform. The food gets accumulated only in upper parts to give it a top-shaped appearance e.g. Beta vulgaris (beet root) and Brassica napus (turnip). (c) Fusiform. The root is swollen in middle and tapers towards the base and apex e.g. Raphanus sativus (radish).

2. Nodulated tap roots These are roots modified for N2-fixation. These roots are observed in leguminous plants (pea, gram). These roots bear many small irregular swellings called root nodules. These nodules are living places for nitrogen fixing bacteria, Rhizobium leguminosarum. These bacteria fix and convert free atmospheric nitrogen into nitrates which are absorbed by roots.

3. Pneumatophores or respiratory roots
These are aerial (-ively geotropic) roots or aerophores produced in mangrove plants e.g. Sonneratia, Avicennia, Rhizophora. The underground roots of plants sent out aerial roots or Pneumatophores. These bear several pores or lenticels which help in gaseous exchang

3. Pneumatophores or respiratory roots
These are aerial (-ively geotropic) roots or aerophores produced in mangrove plants e.g. Sonneratia, Avicennia, Rhizophora. The underground roots of plants sent out aerial roots or Pneumatophores. These bear several pores or lenticels which help in gaseous exchange.

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