Improving biological sciences education through development and use of interactive computer multimedia and networking technologies. This is a special Program Launched by UNESCO Regional Office, CAIRO, EGYPT In Collaboration with:
The part of the project is planned and being supervised by:
This pioneer project is designed as a collaborative efforts between Ain Shams University, Cairo, Egypt and Purdue University, West Lafayette, Indiana, USA. This effort is facilitated by the UNESCO\UNITWIN Program that encourages twining relationships between scientists in the Arab World and those in The United States of America for sharing of information and expertise, and for transfer of educational technology to improve biological sciences education in the Arab World.
The Plant Anatomy 1 is one of interactive computer-assisted courses introductory courses designed to help students learn different branches of botany. The project utilizes technical expertise of subject matter specialist (Prof. Dr. Sayed F. Khalifa, Ain Shams University, Cairo Egypt), visual and textual databases and information gathered from studies and research work in different fields of botany. It also benefits from Purdue University expertise in educational technologies and authoring systems.
Plant Anatomy 1 Menu
The objective of this lesson is to familiarize the students with different aspects of plant anatomy. This interactive lesson addresses the characteristic of the plant cells, different plant tissues, plant organs, ecological anatomy, and reproductive organs of plants. At the end of this lesson the student will be able to differentiate between meristematic and mature cells, living and non-living cellular components and will be able to identify the anatomical structures in the root, stem and leaf in monocotyledonous and dicotyledonous plants.
Plant anatomy, one of the most important branches of botany, is valuable for students in basic sciences, general biology, pharmacy, medicine, and agriculture. The physiological processes occurring within the plant and the physiological relationships between the various plant groups can be easily understood through knowledge in this field. Plant anatomy deals with the study of the elements and tissues from which the plant is constructed. This enables us to understand the adaptation of plant tissues to special functions as well as the adaptation to various environmental conditions.
Studying the anatomical and histological structure of plants facilitates the interpretation of the physiological, phytochemical and ecological experiments. The understanding of notable examples of functions, has been materially enhanced by studying the structure of the parts concerned, as, photosynthesis, movement of water, translocation of food, and absorption by roots. knowledge of plant anatomy is also indispensable for the advancement of research of pharmacology and plant pathology. The effect of a plant parasite can be easily understood when the normal structure of the invaded plant part is known. The explanations of the success or failure of many horticultural practices, such as grafting, pruning, vegetative propagation, and the associated phenomena of callus formation, wound healing, regeneration, and development of adventitious roots and buds, are more meaningful if the structural features underlying this phenomena are properly understood.
Anatomy I deals with the primary body of the plants, while anatomy II deals with structural changes that accompany secondary growth (thickening). This module present Plant anatomy I.
Plants that bears seeds are termed spermatophytes. These plants produce spores (newly formed embryo sacs and pollen grains ) and therefore they are sporophytes as they form zygote. Zygote comes from fertilization of an egg cell by male gamete then divides several times to form the embryo. The embryo usually consists of radicle, hypocotyle, cotyledon(s) and plumule. It is difficult to make a definite distinction between the radicle and hypocotyle, and therefore the axis of the embryo is called the hypocotyle-root axis. After seed germination, the radicle grows and penetrates deeper into the soil whereas the plumule elongates to give rise to the stem and the leaves. The leaf attaches the stem at a part which is called the node and the part between two successive nodes is called internode. Generally, the development of the (leaves and stem) and the root results from the activity of the apical meristems which are tissues directly descended from those of the embryo .
In some spermatophytes, the shoot, apical meristems, remain active through the life time and the shoots developing from the axillary buds remain secondary. Such branching is termed monopodial. In another spermatophytes the shoot apex becomes reproductive (forming flowers ) and the growth of the shoot is carried out by lateral (secondary ) buds. Such branching is called sympodial. In many cases, the buds and shoots develop from portions of plant, distant from the apical meristems, which are called adventitious organs and contain the same meristematic tissues as the apical meristems. Near the apex of the shoot and root three meristems of different tissues become observable :
In most dicotyledons and gymnosperms , one layer of procambial cells between the primary xylem and phloem forms new meristematic tissue is found and called the vascular cambium. The vascular cambium is responsible of the formation of the secondary xylem and phloem . The increase and the development of the secondary vascular tissue result in the peeling off the epidermis and the cortex , and then the function of protection against external damage is taken over by a secondary protective tissue ( the periderm ) . Periderm is formed of secondary meristematic tissue; the phellogen " cork cambium", which produces the phellem "cork cells" (layers of dead cork cells), in the majority of cases, periderm produces the phelloderm "secondary cortex" which consists of one - five layers of living cells. Thus, the complex of the plant tissues of primary body developing from primary meristems, and those tissues developing from the vascular cambium and phellogen constitute the secondary plant body.
The General Structure of Meristematic (young) Cells
The meristematic young cells are characterized by large nucleus, thin cell wall, dense cytoplasm, small vacuoles, small cubic cells, and dense chromatin materials. Click to see images.
The General Structure of Mature Cells
In mature cells,as represented by the strip of the upper epidermis of the fleshy leaf bases of onion " Allium cepa", the epidermal cells show cell wall, plasmalemma, cytoplasm lining the cell wall, tonoplast, large vacuoles, cytoplasmic strands, relatively thick cell, wall, irregular-shaped cells, and small nucleus.
The main components of the plant cell are the cytoplasm , the nucleus and the cell wall. The plant cell is surrounded by the cell wall which may be primary only or may include both primary and secondary walls. The wall may be traversed by cytoplasmic strands, the plasmodesmata. Immediately within the wall, the cell contents are delimited by a membrane, the plasma membrane or the plasmalemma. The typical plant cell is formed of protoplasmic and non-protoplasmic contents.
The living contents include cytoplasm, nucleus, plasma membranes and plastids.
Plastids
Definition and origin
These organelles represents a characteristic feature of the plant cell. They may be found in all living cells of a plant and probably are present in every cell in its early stages of development. Later , they become restricted to certain cells and are abundant only in those which having specialized functions, such as photosynthesis, storage, and color manifestation.
Plastids are present in large numbers in young meristematic cells in the form of rounded bodies that do not resemble plastids and are termed proplastids. As the cell grows, proplastids multiply freely and mature plastids gradually develop. Probably plastids arise only from preexisting plastids.
Types of plastids
They fall into two chief classes:
1) Colored Plastids
They are green in color due to the presence of the chlorophyll pigment. The chlorophyll is the photosynthetic pigment. The Chloroplasts of the higher plants are mostly uniform in size and chiefly flattened, ellipsoid or disc-like in shape. The Chloroplasts are bounded by two unit membranes, the inner one of which is involuted and folded in homogeneous stroma. At some places the lamellar folding are stacked upon one another like a pile of plates or stack of coins to form the grana. Grana are interconnected by stroma lamellae. Each granum consists of discoid double-membraned lamellae or thylakoids .There may be 2 to 100 thylakoids per granum and 25-100 grana per cell. The photosynthetic units are located on the thylakoid membranes.
Spiral chloroplast
slide 13: W.M. of Spirogyra filaments showing the spiral chloroplast
more info about slide No. 13
The Spirogyra filaments are characterized by the presence of mucilage layer, cell wall, cytoplasm, nucleus, cytoplasmic Strands, pyrenoid, and spiral-shaped chloroplast.
Stellate or star-shaped chloroplast
slide 140: W.M. of Zygnema filaments showing the star-shaped chloroplast
They are colored plastids. Their color may be red, yellow, orange or brown. The color of the chromoplasts is due to the presence of carotenoid pigments. Their shape may be spherical , angular, elongate, lobed or spiral. They are present in flowers, fruits (e.g. Tomato & red Pepper) and sometimes in roots, (Carrot) . It should be mentioned that the color of petals of flowers is not necessarily due to chromoplasts. In many flowers { e.g. Pelargonium the color of the petals is due to the presence of a colored cell sap in which the coloring pigments (anthocyanin) are dissolved in the cell vacuoles. However, in some other flowers, e.g. Tropaeolum the color of the petals is due to the presence of chromoplasts and a colored cell sap.
2) Colorless Plastids ( Leucoplasts )
They are formed in cells and tissues of higher plants which are unexposed to light. They are thus of frequent occurrence in roots, tubers, seeds and other organs which store starch. They charge into Chloroplasts or chromoplasts during cell maturation since they are present in immature cells. They change also upon exposure to light ( e.g. Potato Tubers ) . They store plant products such as starch (amyloplasts) and fats (elaioplasts)
The non-living contents include the following :
The ergastic substances are either reserve food material or by-products of metabolism. They occur in vacuoles, in the cell walls and in the protoplasmic components of the cell. They include many components, among which are the following:
a. Starch Grains
Groups or masses of cells that are alike in origin , structure and function form tissues. The plant body consists of vegetative tissue and reproductive tissue. In the higher plants, the plant body is somewhat more complex in its cellular structure. The cells differ very much in their kind, form and origin in higher plants . The tissues may be grouped in three principal groups .
MERISTEMS OR MERISTEMATIC TISSUES
Definition
Meristems and Growth in Plant Body
Beginning with the division of the oospore , the vascular plant generally produces new cells and forms new organs until die. In the beginning of the development of the plant embryo, cell division occurs throughout the development of the young organism . But as soon as the embryo develops and converts into an independent plant, the addition of new cells is gradually restricted to certain parts of the plant body , while the other parts of the plant remain concerned with activities other than growth. This shows that the mature plant is a composite of adult and juvenile tissues . These juvenile tissues are known as the meristems . The presence of the meristems remarkably differentiates the plants from animals . In the plants , the growth resulting from Meristematic activity is possible throughout the life of the organisms, whereas in the animal body, the multiplication of the cells mostly ceases when the organism attains adult size and the number of organs are fixed .
The term Meristem ( Greek meristos , meaning divisible ) emphasizes the cell-division activity characteristic of the tissues which bears this name. It is obvious that the synthesis of new living substance is a fundamental part of the process of the formation of new cells by division . The living tissues other than the meristems may also produce new cells ,but the meristemes carry on such activity, because they not only add cells to the plants but also perpetuate themselves, that is, some of the products of the division in the meristems do not develop into adult cells but remain meristematic .
The meristems usually occur at the apices of all main and lateral shoots and roots and thus their numbers in single plants are quite large. In addition, plants bearing secondary increase in thickness posses extensive meristems, the vascular and cork cambia, responsible of the secondary growth. The combined activity of these all meristems give rise to a complex and large plant body. The primary growth, initiated at the apical meristems expands the plant and produces the reproductive parts. On the other hand, the cambia , aid in maintenance of the expanding body by increasing the volume of the conducting system and forming supporting protecting cells.
Classification of Meristematic Tissues
Various systems of classification have been proposed by many workers which are based on the characteristics such as, stage of development , position in plant body, origin, function and topography. No system is exclusive and rigid . A few important types have been discussed here .
Classification of Meristematic Tissues Based on Origin of Initial Cells
i. Primary Meristems
slides 34,34a : L.S. of Root Apex of Zea mays showing the promeristem zone (growing point) which are differentiated into three types of primary meristems (protoderm , ground meristem, and procambim).
More info. about slides No. 34 & 34 a
The primary meristems are those that build up the primary part of plant and consists in parts of promeristems. In primary meristems, promeristems are always the earliest stage. The possession of promeristems continuously an early embryonic origin is characteristic of primary meristems. The main primary meristems are the apices of roots, stems, leaves and similar appendages.
ii. Secondary Meristemes
The secondary meristems appear later and are always found lateral along the side of the stem and root. The example of the secondary meristems are :
Vascular Cambium
slide 42 : T.S. of Clematis Stem showing the presence of two types of Vascular Cambium :;Fascicular Cambium "Primary Meristem which are lying in between the primary phloem and primary xylem and .Interfascicular Cambium "Secondary Meristem" which are forming the complete ring of vascular cambium .
Cork Cambium ''Phellogen''
slides 25c & 43 :: T.S. of Sambucus Stem Showing the formation of the periderm .
Classification of Meristematic Tissues Based on Position in Plant Body
The meristems may be classified into three groups :
i. Apical Meristems
ii. lateral Meristems
iii. Intercalary Meristems
i. Apical Meristems
It lies at the apex of the stem and root of vascular plants . Very often they are found at the apices of leaves. Due to the activity of these meristemes, the organ increase in length. The initiation of the growth takes place by one or more cells called "apical cells" situated at the tip of the organ and they always maintain their individuality and position. Solitary apical cells occur in Pteridophytes, whereas in higher vascular plants they occur in groups which may be terminal or subterminal in position .
a. Root Apex
b. Vegetative Shoot Apex
Structure of the Shoot Apex
slides 36 : L.S. of Shoot Apex of Colues Stem showing the growing point "Protomeristem", Protoderm, ground Meristem, Procambium, and leaf primordial.
slides 37 & 38 : L.S. of Shoot tips of two different taxa .
more info. about slide No, 36
The vegetative shoot apices vary in shape, size and cytohistologic structure, and in their relation to the lateral organs.
In the angiosperms the segregation of apical meristems zones is more definite than in lower groups. The leaves and lateral branches " Lateral or Secondary roots " are usually initiated beyond the region of the most active growth (Protomeristem) and they arise exogenously
ii. Lateral Meristems
The lateral meristems are composed of such initials which divide mainly in one plane (periclinally) and increase the diameter of an organ. They add to the bulk of existing tissues or give rise to new tissues. This tissues are responsible for growth in thickness of plant body. The vascular cambium and the cork cambium are the examples for this type are the following :
Vascular Cambium
slide 42 : T.S. of Clematis Stem showing the presence of two types of Vascular Cambium :;Fascicular Cambium "Primary Meristem which are lying in between the primary phloem and primary xylem and .Interfascicular Cambium "Secondary Meristem" which are forming the complete ring of vascular cambium .
Cork Cambium ''Phellogen''
slides 25c & 43 :: T.S. of Sambucus Stem Showing the formation of the periderm .
more info about slide No. 25c
The periderm is originated from the subepidermal layer and composed of the zones : Cork Cells "Phellum" multi-layers, Cork Cambium " Phellogen" 1-layer, and Secondary Cortex "Phelloderm" usually 1-layer.
iii. Intercalary Meristemes
The Intercalary meristems are internodal in their position . At early stages, the internode is wholly or partially meristematic , but later in some of its parts , become mature more rapidly than the rest and in the internode a definite continuous sequence of the development is maintained. The Intercalary meristems are found lying in between masses of the permanent tissues either at the leaf base or at the base of internode.
Endogenous Origin of the Lateral Roots
slides 38,38a: T.S. of Salix Root showing the Endogenous origin of the lateral "secondary" roots which are developed from the pericycl
slide 40 : T.S. of Vicia faba Root showing the endogenous origin of the lateral roots
Exogenous Origin of Leaves
slide 36: L.S. of Shoot Apex of Colues Stem showing the Exogenous origin of the leaves " Leaf primordial"
slide 40: L.S. of Elodea Shoot Apex
2. THE PERMANENT TISSUES
The permanent tissues are those in which growth has stopped either completely or for a time as sometimes they again become meristematic partially or wholly. The cells of these tissues may be living or dead and thin walled or thick-walled . The thin-walled permanent tissues are generally living whereas the thick-walled permanent tissues may be living or dead. The permanent tissues may be simple or complex. A simple tissue is made up of one type of cells forming a uniform or homogenous system of cells . The common simple tissues are parenchyma, chlorenchyma, collenchyma and sclerenchyma . A complex tissues is made up of more than one type of cells working together as a unit . The complex tissue consist of parenchymatous and sclerenchymatous cells , collenchymatous cells are not present in such tissues. The common examples are the xylem and the phloem.
Simple Tissues
From a single unicellular zygote, all vascular plants come in existence. The zygote develops into an embryo then into mature sporophyte or plant body. The cells in higher plants are differentiated into many types to form tissue system in which the cells maintain topographic continuity or physiologic similarity, or both together.
Generally, there are Four main Types of tissue systems :
1-THE DERMAL OR EPIDERMAL SYSTEM
The dermal system forms the outer protective covering of the plant body, by epidermis.
a. THE EPIDERMIS
The epidermis usually consists of a single layer of cells covering the whole outer surface of the plant body . The word is derived from two words of Greek origin , epi, upon, and dermis, skin . It is continuous layer except for certain small pores, called stomata and lenticels.
(Epidermis more information)
Epidermis is derived from protoderm or dermatogen of apical Meristem. In meristematic regions it is , of course, undifferentiated, and in older ones it may be destroyed by secondary growth. Mostly, the epidermis is single layer but in many plants it has been described as bi- or multiseriate. The epidermal cells may be irregular in outline, usually varying in shape and size and arranged very close to each other having no intercellular spaces among them. The cells possess a large central vacuole and thin peripheral cytoplasm . The cells may contain leucoplasts, anthocyanins, and chromoplasts, but no Chloroplasts except in guard cells. Sometimes , the substances like mucilage , tannin and calcium carbonate crystals (cystoliths) are also found .The walls of epidermal cells are unevenly thickened . The inner and radial walls are comparatively thicker . This additional thickness is due to impregnation of suberin or cutin for protection against mechanical injuries and water loss.
i. FUNCTIONS OF EPIDERMIS
ii. SHAPES & TYPES OF EPIDERMIS
Their several types and shape of epidermal cells :
Papillae or papillose
Tangential
slide 44 : T.S. of Dianthus Leaf
Radial
slide 45 : T.S. of Dicot Root of Vicia faba
Palisade like
slide. 150 : V.S. of Phaseolus Testa
Fiber - like
slides 46&46a : V.S. of Pinus Leaf
slides 47&47a : T.S. of Zea mays Stem with Thick cuticle
slides 19 a & 48: :V.S. of Ficus elastica Leaf and
slide 49: V.S. of Nerium oleander Leaf.
MULTIPLE EPIDERMIS ( Arising from protoderm meristems)
slides 19a & 48: V.S. of Ficus elastica Leaf
more info. about slide No. 19 a
Multiseriate epidermal cells are formed by anticlinal and periclinal divisions . enlarged lithocysts protrude inward in between the multiple epidermis.
HYPODERMIS (Arising from ground meristems)
slide 49 : V.S. of Nerium oleander Leaf
more info. about slide No. 49
The HYPODERMIS is composed of 4-5 layers of mostly tangentially elongated thick - walled parenchymatous cells.
EXODERMIS
slide 50 : T.S. of Young prop Root of Zea mays
more info. about slide No. 50
During secondary growth, in case of roots (especially in Monaco roots) , the piliferous layer may be replaced by another dermal system , the exoderm , with the thick walled cells forming new protective tissues.
PERIDERM
slides 25,25b& 51 : T.S. of Sambucus Stem
more info. about slide No. 25
During secondary growth , in both roots and stems , the epidermis may be replaced by another dermal system , the periderm , with the cork cells forming new protective tissues.
PILIFEROUS LAYER
slides 58 & 138: T.S. of Ruscus Root :
more info. about slides No.58 & 138
In case of root, the outermost layer is known as epiblema, piliferous layer or rhizodermis from which tubular unicellular root hairs extend outward to help in the absorption of water and mineral nutrients from the soil.
g. STOMATA
The stomata are minute pores which occur in the epidermis of the plants. Each surrounded by kidney or bean shaped epidermal cells , the guard cells . They occur on any part of the plant except the roots .The epidermal cells bordering the guard cells are called the accessory or subsidiary cells. Generally ,the term stomata is applied to the stomatal opening and the guard cells. The guard cells are living cells containing Chloroplasts and larger proportion of protoplasm than other epidermal cells .
more info. about Stomata
They are much abundant in upper surface than in the lower one. In floating leaves, stomata are confined only to the upper surface of the leaf. Under normal conditions, the stomata remain closed in the absence of light or in night or remain opened in the presence of light or in day time .
Functions of Stomata
1- Gas exchange between the plant and the atmosphere . To facilitate this function, each stoma opens in a sub- stomatal chamber or respiratory cavity .
Water transpiration & evaporation.
a. Type of Stomata
Monocotyledonous Stomata
slide 59 : V.S. of Zea mays Leaf showing level position and the presence of two subsidary cells).
slide 61: S.V. of Zea mays Leaf
more info. about slides No. 59 & 61
In monocots, especially members of Gramineae and Cyperaceae, stomata posses guard cells of which the middle portions are narrower than the ends so that the cells appears in the surface view like dumb - bells .Stomata are arranged in parallel rows .The epidermal cells bordering the guard cells are called the accessory cells or subsidiary cells.
Slide165 : S.V. of Tradescantia Leaf (Canna Type)
Slide163 : S.V.. of monocot Leaf (Iris Type)
Dicot Stomata
slide 60 : V.S. of Dicot Leaf showing level position and the absence of subsidary cells
slide 62 : S.V. of Dicot leaf ( irregular)
more info about slide No. 62
Each stomta is surrounded by kidney or bean shaped epidermal cells , the guard cells
(e.g. Vicia faba or Gossypium leaf).
Slide164 : S.V. of Sedum Leaf (Anomocytic Type)
slide 63 : S.V. of Dicot Leaf of Begonia ( Paracytic Type)
b. Relative Position of Guard Cells
Leveled "surface
slide 59 : V.S. of Monocot leaf of Zea mays ,
Raised
slide … : V.S. of Dicot leaf of Cucurbita ,
Sunken
slides 46a,65&123 : V.S. of Pinus Leaf
slides 66 & 124 : V.S. of Cycus Leaf
Sunken in Grooves
slides 49a&130 : V.S. of Nerium oleander Leaf
h. TRICHOMES OR HAIRS
Some of the epidermal cells of most plants grow out in the form of trichomes . They are found singly or in groups , unicellular or multicellular and occur in various forms. They vary from small protuberances of the epidermal cells to complex branched or stellate multicellular structures. The cells may be dead or living. Very frequently, the hairs loose their protoplasm and become dead . If alive, they contain little cytoplasm in their cells.
more info about trichomes
a. Structure of the Cell Wall
The cell walls of trichomes are commonly of cellulose and covered with a cuticle . They may be lignified . Plant hairs often produce secondary walls and sometimes impregnated with silica or calcium carbonate .
b. Development
A trichome is initiated as protuberance from an epidermal cell
c. Functions
1- control the rate of transpiration.
2- Reduce the heating effect of the sun light .
Protection of plant body from outer injurious agencies.
d. Types of Trichomes
There are many types of hairs such as :
stinging hairs, laticiferous hairs, bladder-like hairs, mucilage hairs, calcified or silicified hairs, non-glandular shaggy hairs, glandular shaggy hairs, non-glandular tufted hairs, two armed non-glandular hairs, stellate glandular hairs, branched non-glandular hairs; branched glandular hairs, capitate sessile hairs, glandular capitate stalked hairs, non-glandular peltate hairs, glandular peltate, and uniseriate hairs.
Some important types are described as follows :
Stinging Hairs
slide … : S.V. of Dicot Leaf of Urtica
more info. about slide No. …
They are one of interesting types of trichomes. They contain poisonous liquid and consist of a basal, bulb like portion from which a stiff, slender and tapering structure is given out which ends in a small knob like or a sharp point. The tip is some what oblique , and as the body of animal or human comes in its contact with some force, the tip is broken off, and the sharp pointed end readily penetrates the skin of the animal, the fluid is transferred from the basal knob of the hair to the body of the animal.
Eglandular Hairs
Unicellular Non-branched
slide 49a : V.S. of Nerium oleander Leaf (in groove)
Unicellular Branched
slide … : T.S. of Matthiola Stem or leaf
Multicellular Non-branched
slide 54 : T.S. of Pelargonium Stem
Slide 186 : S.V. of Cucurbita or Abutilon Leaf
Multicellular Branched
slide 125 : V.S. of Solanum Leaf
Multiseriate
slide 55: T.S. of Helianthus Stem
Glandular Hairs
slide 54: T.S. of Dicot Stem of Pelargonium
slide 57: T.S. of Dicot Stem of Nicotiana
more info about slide No. 54
Many plants posses glandular hairs. These hairs may secrete oil, resin or mucilage. A typical glandular hair possesses a stalk and enlarged terminal portion, which may be referred to as gland. Active secretory cells of glandular trichomes have dense protoplasts and elaborate various substances, such as volatile oil, resin and mucilage.
Scale or Peltate Hairs
slide 169 : T.S. & S.V. of Olea europaea " Olive " leaf
more info. about slide 169
The word peltate ( from the Latin peltatus , target shaped or shield like , and attached by its lower surface ). A scale consist of discoid plate of cells , often borne on a stalk or attached directly to the foot.
2. GROUND OR FUNDAMENTAL SYSTEM
Stems usually possess the vascular system in the form of solid cylinder. The ground tissue found in between the epidermis and vascular cylinder is called cortex. The central tissue is called medulla or pith and the rays of parenchyma cells arising from the pith are called medullary or pith rays. In monocots, the vascular bundles are found in dispersed condition , then the ground tissue is not differentiated into cortex and pith .
Types of Cells and Tissues of Ground System
a. Parenchymatous Tissues
The word parenchyma is derived from the Greek para, beside enchym, to pour. The parenchyma cells having sufficiently developed intercellular spaces among them, some cells contain Chloroplasts at least in young stem. They also contain starch, tannins and crystals. Generally, they have thin-walls, and concerned with the vegetative activities of the plant. The cells are living with sufficient amount of cytoplasm and with one or more nuclei. Parenchyma makes up various parts in plants such as pith, cortex, mesophyll of leaves, pulp of fruits, endosperm of seeds ,and also in xylem and phloem.
Shape
The different shape of parenchymatous cells is summarized as the following :
Polyhedral
slide 67: T.S. of Zea mays Stem
slide 68 : T.S. of Dicot Root of Vicia faba
slides 69,69a : T.S. of Ambrosia Stem
Armed
slide 146: T.S. of Cyperus Stem
slide 75: V.S. of Dicot Leaf
Lacunate ( Aerenchyma)
slide 71: T.S. of Hydrophytic Stem of Potamogeton
more info. about slide No. 71
In aquatic plants, parenchyma cells possess well developed air spaces (intercellular spaces ) and such tissues known as Lacunate parenchyma "Aerenchyma. Parenchyma may be specialized as water storage tissues in many succulent and xerophytic plants such as Aloe, Agav, Mesembryanthemum, and Hakea.
Plicate (Lobed)
slides 46a & 72 : V.S. of Pinus Leaf
b. Chlorenchymatous Tissues
Isodiametric Cells
slide 73 : T.S. of Cucurbita Stem
Palisade Cells
slides 74&75 : V.S. of two different Dicot Leaves
more info. about slides No. 73 , 74 & 75
When the parenchymatous cells are exposed to light they develop Chloroplasts and such tissue is known as chlorenchyma.
c. Collenchymatous Tissues
Collenchyma is aliving tissue composed of somewhat elongated cells with thick primary non-lignified walls. The cell wall consists of cellulose and pectin. Collenchyma are usually arranged as a cylinder or in the form of strands. In dicots collenchyma are often found in the ridges, in the corner or in other portions to give temporary support to the plant. Sometimes, few layers of fibers or collenchyma develop just beneath the epidermis forming an outer protective layer called HYPODERMIS. The function of these cells is supporting of the plant body .
Types of Collenchyma
There are four types of Collenchyma :
Angular
slide 69a : T.S. of Ambrosia Stem
more info. about slide No. 69 a
In the angular type the cells are irregularly arranged and the thickening with cellulose in the angles.
Lamellar
slide 51 : T.S. of Sambucus Stem
more info. about slide No. 51
In lamellar types, the thickening with cellulose lies on
the tangential walls.
Annular
slide 73: T.S. of Cucurbita Stem and slide 23: T.S. of Helianthus Stem
more info. about slides No. 23 &73
In this type, the cells are irregularly arranged and the thickening with cellulose on the whole wall of the cells with intercellular spaces.
Lacuner '' tubular''
slide 20 a, & b : T.S. of Ambrosia Stem
more info. about slides No. 20 a &b
In this type, the intercellular spaces are present and the thickening with cellulose is on the wall around the intercellular spaces.
c. Sclerenchymatous Tissues
The Sclerenchyma (Greek, sclerous, hard; enchyma, an infusion) consists of thick walled cells , often lignified, whose main function is mechanical. This is a supporting tissue that withstand strains resulting from stretching and bending of the plant organs without any damage to the thin -walled softer cells.
Classification of Sclerenchyma
Most commonly, Sclerenchyma are grouped into fibers and Sclereids .
i. Fibers
Elongated Sclerenchyma cells with pointed ends and lignified cell walls . Fibers occur in patches , in continuous bands or singly among other cells .
The fibers are divided into two large groups :
Xylary (Xylem Fibers " Wood Fibers")
Wood Fibers of the primary xylem
slides 27,27b &69a : T.S. of Ambrosia Stem
more info. about slide No. 27
The xylem fibers develop from the same meristematic tissues as the other elements of xylem. Thus, the fibers are present in-between xylem elements.
Wood Fibers of the secondary xylem
slides 78,79&80 : T.S. of different Old Dicot Stems
b. Extra xylary fibers
These are fibers outside xylem elements. Thus, some of the Extraxylary fibers are related to the phloem. In the stem of monocots the fibers form continuous cylinder arise in the ground tissue under the epidermis and known as cortical fibers. The fibers present in the peripheral region of the vascular cylinder, often close to the phloem, are known as pericyclic fibers. The Extraxylary fibers are sometimes combined into a group termed bast fibers. Generally, the term Extraxylary fibers is used for phloem fibers, fibers originating in primary or secondary phloem; cortical fibers; fibers originating in the cortex; perivascular fibers; fibers found in the peripheral region of the vascular cylinder inside the inner most cortical layer but not originating in the phloem, fibers of bundle sheath in Monaco stems and leaves, fibers of epidermal cells in fibrous epidermis.
Types of Extraxylary Fibers
Fibrous Epidermis
slide 67: T.S. of Zea mays Stem
slides 46a& 65: V.S. of Pinus Leaf
Fibrous Ground Tissues
slide 82 : T.S. of Zea mays Stem
Perivascular Cylinder
slide 81 : T.S. of Cucurbita Stem
Phloem Bast Fibers & Phloem Fibers of the secondary phloem
slides 78,79&80 : T.S. of different Old Dicot Stems
Patches of Pericycle
slides 76&77 : T.S. of Ambrosia Stem
Bundle Sheath of Monaco Vascular Bundles
slide 82 : T.S. of Zea mays Stem ( Enlarged part)
Lignified Pith
slide 125 : T.S. of Lygos raetam Stem
ii. Sclereids
Sclereids are usually not much longer than they are broad, occurring singly or in groups. They are commonly found in the cortex and pith of gymnosperms and Dicot plants in many parts such as in the leaf mesophyll , in fruits and hard seeds. The secondary walls of the Sclereids are typically lignified and vary in thickness.
Classification of Sclereids
The Sclereids are classified as follows :
Brachysclereids "stone cells"
slide 83: Crushed Pericarp "Powder" of Almond (Prunus amygdalus) Fruit showing the thick-walled cells with small lumnae and branched canal pits.
more info. about slide No. 83
Thick-walled cells with small lumnae and branched canal pits (e.g. of fruit of Psidium guajava and of pericarp " endocarp" powder of fruit of Prunus amygdalus " Almond ")
Macrosclereids (palisade-like)
slide 150 : V.S. of Phaseolus Testa
Astrosclereids (star-shaped)
slide 153 : T.S. 0f Nymphaea Petiole
Osteosclereids (bone shaped)
slide 86 : V.S. of Hakea leaf
e. Endodermis
slide 50 : T.S. of Zea mays Root showing endodermis as a last layer of the cortex (in case of the roots).
slide 52 : T.S. of Dicot Root of Vicia faba showing the endodermis with Casparian Stripes and the Passage Cells.
slide 53 : T.S. of Monaco Root of Iris showing the endodermis with Casparian Stripes and the Passage Cells (more details).
(more info about Endodermis)
Functions of Endodermis
1- Protective layer or sort of accessory inner epidermis.
2- Connected with the maintenance of root pressure.
Acts as an air dam which prevents diffusion of air into the vessels and thus,
cells escape from closing.
4-Serves as storage tissue having starch grains in many dicotyledonous stems.
f. starch sheath
slides 69,69a&27: T.S. of Ambrosia Stem showing the starch sheath as a last layer of the cortex (in case of the stems).
more info. about slides No. 69 & 69 a
This is uniseriate layer delimiting cortex from stele. It consists of barrel shaped cells arranged quite close to each other having no intercellular spaces among them. Due to the presence of starch in the endodermal cells, it is also known as starch sheath. In stems, it is found in the form of wavy layer whereas in root this layer is well defined and circular in appearance. Commonly, the endodermal cells are of two types: primary (thin walled ) and secondary (thick -walled). In primary cells, certain thickening of suberin is developed in the form of band or strip which runs completely around the cells from the radial and the end walls, and called Casparian strips. In the secondary endodermal cells, the radial and inner walls and sometimes all walls are thickened by suberin, among the thick-walled cells occasionally occur isolated thin walled cells usually opposite to the protoxylem elements, which are known as passage or transfusion cells through which the sap absorbed by the root hairs enters to the xylary elements (Roots of Vicia faba & Hemerocallis).
g. Pericycle
In the stems of dicots, the pericycle is a multilayered zone found in between the endodermis and the vascular bundles , as a thin cylinder of tissues completely encircling the vascular bundles and the pith. The inner side of pericycle zone is limited by the primary phloem while the outer side is limited by the endodermis. It may be sclerenchymatous zone or it consists of both sclerenchyma and parenchyma. Generally, the pericycle is uniseriate in roots which have distinct pericycle. In gynnosperms and some roots of monocot and dicot, the pericycle is multiseriate. It mwy contain laticifers and secretory ducts. In monocots, where there is usually no secondary thickening part or all of the pericycle become sclerified.
(more info. about Pericycle)
The Origin of Pericycle
The pericycle is usually consider as belonging to the vascular system. However, some consider it as belonging to the ground system, it is present in plant organ. Stems and roots of lower vascular plants typically show an endodermis and pericycle. Root of higher vascular plants also show a pericycle. Most of stems of seed plants lack an endodermis and pericycle. The fibers which might be present at the periphery of the primary phloem are in fact fiber of the protophloem.
Functions of Pericycle
1- In dicotyledonous roots, they become meristematic and form the vascular cambium and phellogen.
2- Gives rise to lateral " secondary " roots (endogenous origin).
3- Gives rise to adventitious roots in the stems; laticiferous cells; secretory cells; and other specialized cells may occur in it.
Aids in storage.
Composition of the Pericycle
One Layer Thin
slide 52: T.S. of Dicot Root of Vicia faba
slide 53 : T.S. of Monaco Root of Iris
In Patches ( Baste Phloem Fibers)
slides 69,69a&27: T.S. of Ambrosia Stem
Perivascular Cylinder
slide 73: T.S. of Cucurbita Stem
h. Cortex
The ground tissue found beneath the epidermis which surrounds the central cylinder and is delimited from the vascular cylinder by endodermis is called cortex.
(more info. about the cortex)
Function of Cortex
1- Protective tissue for the stem.
2- Helps in carbon assimilation, water storage and food storage.
3- Collenchyma of the cortical region aids in temporary mechanical support of plant body.
4- In roots, it is a storage tissue and helps in pumping water from hairs to the xylem.
Composition of Cortex
Usually, the cortex of the stem consists of one , two or more types of cells The cortex may contain collenchyma, sclerenchyma and Sclereid in addition to ordinary parenchyma. Collenchyma cells are usually arranged as a cylinder or in the form of strands. In dicots, collenchyma are often found in the ridges, in the corner or in other portions to give temporary support to the plant. Sometimes, few layers of fibers or collenchyma develop just beneath the epidermis forming an outer protective layer called hypodermis. The cortex of the root is more homogeneous than that of the stem and consists of parenchyma only.
Types of Cortex
The type of cortex is classified as follows :
Ground Tissue Undifferentiated
slide 67 : T.S. of Zea mays Stem
Ground Tissue Differentiated
One Type of Cells (Parenchyma)
slide 68 : T.S. of Dicot Root of Vicia faba
slide 149 : T.S. of Ranunculus Stem
Two Types of Cells (Parenchyma & Collenchyma)
slide 69 : T.S. of Amberosia Dicot Stem
Three Type of Cells (Parenchyma, Collenchyma & Chlorenchyma)
slide 154 : T.S. of Vitis Dicot Stem
Four Type of Cells (Parenchyma, Chlorenchyma, Collenchyma and Sclerenchyma)
slide 73 :T.S. of Cucurbita Dicot Stem
i. PITH
The pith or medulla forms the central ,region of the root and stem. In dicots, the pith is largely parenchymatous with sufficiently developed Intercellular spaces ,devoid chlorophyll in the mature state but starch forming leucoplasts are found in it .
more info. about the pith
Functions of Pith
1- Sclerenchymatous pith provides mechanical strength to plants.
2- Parenchymatous pith serves as channels for transport of food material and water from the central part (pith) to peripheral region (cortex ) of the stem.
3- In dicotyledonous stems, some of the parenchyma cells of medullary rays become meristematic giving rise to interfascicular cambium.
Different Types of Pith
Pith Hollow
slide 149 : T.S. of Ranunculus Stem
slide 90 : T.S. of Helianthus Stem (as a result of the decomposition of pith parenchyma ).
Pith Solid
slide 108 : T.S. of Prop Root of Zea mays
Pith Wider than Cortex (Main feature of the Stems)
slide 90 : T.S. of Helianthus Stem
Pith narrower than cortex (Main feature of the Roots)
slide 87 : T.S. of Hemerocallis Root
slide 88 : T.S. of Vicia faba Root (The pith is much reduced and may be disappear).
3- THE VASCULAR TISSUE SYSTEM
The vascular tissue consists of a number of vascular bundles which are found to be distributed in the stele. The stele is a central cylindrical portion of the stem and the root , commonly surrounded by the endodermis , and consists of vascular bundles , (Pericycle , pith)?? and medullary rays .
more info. about the vascular system
Function of Vascular System
1. The function of this system is to conduct water and other nutrients from root to leaves
2. Translocation of prepared carbohydrates from leaves to the other storage organs of the plant through phloem .
The vascular bundles are derived from procambial strands of primary meristems. The vascular bundles arranged as circular ring in the stems and roots of Dicot plants (e.g. Stems of Helianthus & Luffa), whereas in monocots they are found to be scattered through the axis of the stem (e.g. Stems of Zea mays & Cyperus ).
Primary Vascular Tissue
The procambium forms the vascular cylinder in which the first maturing cells in young strand are phloem cells, which are followed by the first xylem cells, thereafter the first mature xylem and phloem are separated radially by procambium in stems and leaves and tangentially by promeristem in roots.
The Vascular Bundles
1. Constituents of Vascular Bundle
The vascular bundle of dicotyledonous stem consists of three major zones :
a- Xylem or Wood Element
b- Phloem or Bast Element
c- Vascular Cambium
Xylem or Wood Element
Main Components of Xylem
The main components of the xylem element are :
i. Vessels or trachea
ii. Tracheids
iii. Wood fibers
iv. Wood parenchyma
i. Xylem Vessels
slides 90 & 91 : T.S. of Helianthus Stem
more info. about slides No. 90 & 91
This slides are showing : Epidermis, cortex of two types; collenchyma and parenchyma, starch sheath, pericycle in patches (Bast Phloem Fibers), vascular bundles limited and arranged in one ring, presence of xylem vessels (endarch protoxylem & exarch metaxylem) , primary phloem, fascicular & interfascicular cambium, and wide pith.
The vessels are formed from longitudinal series of meristematic cells which are either produced from the procambial activities in the primary body or from the vascular cambium derivatives in the secondary body. The walls of the vessels are hard and lignified. Vessels in contrast to tracheids are perforated at points of contact with other vessels. Sap pass through the perforation from vessel to vessel, while it cannot pass in tracheids except through the pit membrane. Perforation are usually on the end walls of vessels but may also occur on lateral walls. The patterns of perforations are different and may be annular, spiral, sclariform, reticulate, or pitted. Annular or/and spiral are common in the protoxylem elements, while reticulate, sclariform, or pitted vessels are common in the metaxylem and the secondary xylem.
ii. Xylem Tracheids
slide 89 : T.S. of Zea mays Stem
more info. about slide No. 89
This slide is showing : Numerous and scattered vascular bundles, fibrous epidermis, undifferentiated ground tissue, presence of bundle sheath and xylem cavity, metaxylem Exarch & protoxylem endarch, trachieds, xylem fibers, and the phloem with prominent sieve & companion cells.
The tracheids are found to be associated with vessels as well as fibers and wood parenchyma. Vessels and tracheids function in water and mineral salt conduction from root to leaves, whereas the wood parenchyma are living and aid in storage, The wood fibers give mechanical support
The tracheids are a non-living elongated cells with tapering ends. It is considered more primitive than the vessels. The vessel is formed of a series of longitudinal expanded cells, while the traced is unicellular. The wall of the tracheids are hard and lignified with characteristic pitting. Pits of tracheids are mostly of the bordered type.
iii. Xylem or Wood Parenchyma
slides 90 & 91 : T.S. of Helianthus Stem
more info. about slides No. 90 & 91
This slides are showing : Epidermis, cortex of two types; collenchyma and parenchyma, starch sheath, pericycle in patches (Bast Phloem Fibers), vascular bundles limited and arranged in one ring, presence of xylem vessels, xylem or wood parenchyma, xylem fibers, endarch protoxylem & exarch metaxylem, primary phloem, fascicular & interfascicular cambium, and wide pith.
The wood or xylem parenchyma are common in the xylem of almost all plants. They remain live for a long period. Their walls may be thin or lignified. They play a role in conduction of water and solutes, but also serve for storage of food.
iv. Xylem or Wood Fibers
slides 90 & 91 : T.S. of Helianthus Stem
more info. about slides No. 90 & 91
This slides are showing : Epidermis, cortex of two types; collenchyma and parenchyma, starch sheath, pericycle in patches(Bast Phloem Fibers), vascular bundles limited and arranged in one ring, presence of xylem vessels, xylem parenchyma, xylem or wood fibers, endarch protoxylem & exarch metaxylem, primary phloem, fascicular & interfascicular cambium, and wide pith.
The wood or xylem fiber are drive from tracheids by increase in wall thickness, decrease in length and reduction in size of bordered pits. The fibers appear longer than tracheids.
Exarch and Endarch Xylem
slides 87 & 87a : T.S. of Hemirocallis Root
more info. about slides No. 87 & 87a
This section showing : Exoderm, cortex, endodermis, pericycle, pith, and xylem polyarch with Exarch protoxylem and endarch metaxylem.
When the development of protoxylem is toward the periphery centripetal the xylem strand said to be exarch such as in roots. When the protoxylem develops towards the center , the xylem is called centrifugal xylem, the xylem strand said to be endarch such as that of the stems.
Protoxylem and Metaxylem
slide 88 : T.S. of Vicia Dicot Root
more info. about slide No. 88
This section showing : Epidermis, cortex, endodermis, pericycle, pith, and xylem tetrarch with exarch protoxylem and endarch metaxylem.
According to the age; there are two types of xylem, young protoxylem and it is made up of wood parenchyma, tracheids and narrow vessels with thickening which may be annular, spiral or sclariform. The older xylem is called metaxylem and possess reticulate and pitted wider vessels.
Type of Liginification of Xylem Vessels
The vessels may possess various kinds of thickening such as :
Spiral and Sclariform lignification
slide 92 : L.S. of Xylem Vessels
Annular, Spiral and Reticulate lignification
slide 93 : L.S. of Xylem vessels
Spiral, Sclariform, Reticulate, and Pitted lignification
slide 94: L.S. of Xylem Vessels
b. Phloem or Bast Phloem Elements
In stems, phloem is found away from the center of the axis towards the periphery and consists of sieve tubes or sieve cells only, or sieve tubes and companion cells only in monocots, or sieve tubes, companion cells and phloem parenchyma in dicots. Companion cells and phloem parenchyma possess simple pits in their walls, particularly which lie against the sieve tubes. Phloem serves for translocation of carbohydrates from leaves to other parts of the plant , sieve tubes translocate proteins and some other carbohydrates , phloem parenchyma and companion cells translocate many soluble food materials such as amino-acids, amines, .....etc.
(more info. about the phloem elements)
Protophloem and Metaphloem
The first cell of the phloem to mature are known as Protophloem, which consists of narrow sieve tubes and is found towards periphery. The inner portion of the phloem is the
Metaphloem which consists of well developed cells of all types such as sieve tubes, companion cells and phloem parenchyma and sometimes phloem. and Sclereids
Sieve Elements (sieve cell, sieve tube, sieve area, and sieve plates)
The sieve elements are of two types; the sieve cells of gymnosperms, and lower vascular plants and the sieve tube members which are characteristic of angiosperms.
The sieve elements are commonly long and slender with tapering ends. They have sieve area on their walls. The sieve area is a depressed wall area with groups of perforations or pores. The part of the wall occupied by the sieve area is known as the sieve plate. The sieve plate consisting of a single area is known as a simple sieve plate.
The sieve tube members are usually disposed end to end in long series which are the sieve tube. Thus, the sieve plates occur mainly at end walls
Companion Cells
slide 95 : T.S. of Zea mays Stem
more info. about slide No. 95
This section is showing : Enlarged vascular bundles which characterized by the presence of sieve cells and the companion cells .
slide 96 : L.S. 0f Phloem elements showing the sieve tube, companion cells, sieve area, and sieve plate.
more info. about slide No. 96
They are highly specialized parenchyma cells with the sieve tube members of both monocots and dicots. A companion cell arises from the same meristematic cell which develops into sieve tube member. One or more longitudinal divisions occur in the meristematic cell to produce two or more longitudinal cells, one of which usually of a large sized differentiated into the sieve tube member, and the other becomes the companion cell. Consequently one or more companion cells may be associated with a sieve tube member on one of its sides. The companion cell retain its nucleus . Its cytoplasm is abundant and granular. The companion cells are present in the phloem of angiosperms and absent from gymnosperms and lowers vascular plants.
Albuminous Cells
The phloem of gymnosperms is characterized by the presence of a special type of cells known as the Albuminous cells. They are joined to the sieve cells by sieve areas. They stain deeply with cytoplasmic stain as if rich in proteins. For this reason, they have been termed Albuminous cells. They develop from phloem parenchyma.
Phloem Parenchyma
The phloem of most dicots and few of monocots contains parenchymatous cells which are essentially for storage of food.
Phloem Fibers and Sclereids
esent in the primary and secondary phloem of many seed plants and are rare or absent from the phloem of living Pteridophyta, some gymnosperms and angiosperms.
Vascular Cambium
slides 90 & 91 : T.S. of Helianthus Stem
more info. about slides No. 90 & 91
This slides are showing : Epidermis, cortex of two types; collenchyma and parenchyma, starch sheath, pericycle in patches(Bast Phloem Fibers), vascular bundles limited and arranged in one ring, presence of xylem parenchyma xylem fibers, endarch protoxylem & Exarch metaxylem, primary phloem, Vascular Cmbium (fascicular & interfascicular), and wide pith.
It is present in Dicot stem in-between xylem and phloem . The cambia cells are living , thin-walled , rectangular, sufficiently elongated and posses oblique ends , and may be uniseriate or multi-seriate . There are two types of vascular cambium ; fascicular & interfascicular.
2. Type of Vascular Bundles
The vascular bundles usually consists of xylem and phloem of several types of arrangement. The xylem and phloem tissues are mostly of a primary origin. According to the arrangement of the xylem and phloem in the vascular bundles, there are three types :
i RADIAL (Xylem & Phloem on alternated radii)
slides 50 & 87a : T.S. of Prop Root of Zea mays (Polyarch)
slide 52 : T.S. of Vicia faba Root (Tetrarch)
more info. about slides No. 50,87a & 52
In this type the xylem and phloem lie radially side by side . This is the most primitive
type. This type is the characteristic feature of Monaco ( polyarch; more than 17 arches) and Dicot (2 -12 arches) roots.
ii CONJOINT
The xylem and phloem lie together on the same radius in the position that xylem lies inwards and the phloem lies outwards. In which the xylem and phloem together form a bundle This type is classified in three subtypes:
Collateral Open (Vascular Cambium present)
slide 98 : T.S. of Ambrosia Stem
more info. about slide No. 98
In Dicot plants, the cambium is present between the xylem and phloem , such bundles are called open.
Collateral closed (Vascular Cambium absent)
slide 97 : T.S. of Zea mays Stem
more info. about slide No. 97
In Monaco plants the cambium is absent and the bundles are called closed
Bicollateral (Presence of outer and inner Phloem)
slide 99 : T.S. of Cucurbita Stem
more info. about slide No. 99
Here the phloem is found to be present on both sides of xylem and two cambium strips also occur. The various elements are arranged as following: outer phloem , outer cambium, xylem, parenchyma and inner phloem. Such bundles are always open.
iii. CONCENTRIC
Those in which one type of the tissue ensheaths the other . There are two types of closed concentric bundles :
Amphivasal Bundles (Xylem vessels are surrounding the central phloem)
slide 100 : T.S. of Dracaena Stem
more info. about slide No. 100
In this section the xylem surrounds the phloem . This type is found in Monaco and some Dicot plants.
Amphicrebral Bundles" Amphiphloic" (Phloem elements are surrounding the central xylem).
slide 101 & 148 : T.S. Of Polypodium Rhizome
more info. about slides No. 101 & 148
In this sections the phloem surrounds the xylem. This type is found in ferns.
4. SECRETORY AND EXCRETORY SYSTEM
Secretion of plant cells is the separation of certain substances from the protoplast. These substances are deposited in non-living cells or vacuoles of living cells, in cavities, or in canals. The secreted substances are of two types: The first kind of substances are products of dissimilatory metabolism, which are no longer utilized by the plants (e.g. terpenes, resins, tannins, various crystals ). The second type of substances have a special physiological function after they are secreted ( e.g. enzymes, hormones ). The role of many of the secreted substances, is not known.
EXTERNAL SECRETORY STRUCTURES
a. GangularTrichomes
Stalked
slide 102 T.S. of Helianthus Stem
Sessile
slides 103 & 104 : V.S. of Two Different Leaves showing the sessile glands
more info. about slides No. 102, 103 & 104
The external secretory structures have many forms. Part of the epidermis itself is sometimes secretory {Papillose epidermal cells}. In some plants, the secretory structures are in the form of epidermal appendages (Trichomes e. g. Helianthus, Pelargonium stem & Abutilon petiole }. These glands are borne on a stalks of non glandular cells.
Digestive glands
slide 105 : S.V. of Drosera Leaf showing the modified blade for abnormal nutrition. Note the long tentacles each is ending by a digestive gland.
more info. about slide No. 105
In certain plants called "insectivorous" and "carnivorous" there are special glands which secrete protein digesting enzymes . These enzymes act upon insects and other organisms, the products of digestion can be absorbed by the plant .
Examples of these plants are : Drosera, Nepenthes, and Dionaea.
c. Nectaries
Nectaries are occur usually in flowers specially on sepals , petals, stamens, ovaries or the receptacle and also found on vegetative parts of the plants such as stems, leaves, stipules, and pedicels of flowers. They secrete sugary liquid.
d. Hydathodes
Hydathodes are glands secreting water from their tissues and they may be also a part of leaves with pathways along which the water flowing from the ending of the xylem to the surface of the leaf meets with little resistance.
INTERNAL SECRETORY STRUCTURES
a. Secretory cells
They are specialized cells. They are dispersed among less specialized cells. They are called secretory idioblasts. They have a wide variety of contents. They occur in the vascular and the ground tissues of the stem and the leaf. Oil cells with unspecified contents are also present in other families (e.g. Rutaceae) In some dicots (e.g. Meliaceae) cells containing resins are present. Other (e.g. Malvaceae) mucilaginous cells are present and sometimes they contain raphide crystals. Many plants families ( e.g. Leguminosae & Myrtaceae) contain tannins cells. Tannins is an Ergastic substance in the parenchyma cells. Tannin cells (tanniniferous idioblasts) occur often associated with vascular bundles and may form connected systems. The tannin compounds in the tannin cells are oxidized to brown and reddish brown substance.
b. SECRETORY CAVITIES AND CANALS
They are resulted from either the dissolution of cells (Lysigenous spaces) or a separation of cells (Schizogenous spaces).
Lysigenous Ducts
slide 106 : V.S. of Citrus pericarp showing the trace of lysis cells in the cavity of the ducts.
more info. about slides No. 106
In this type of ducts, partly disintegrated cells appear along the periphery of the space and usually found in Citrus, Eucalyptus, & Gossypium.
Schizogynous Ducts
slide 107 : T.S. of Pinus Stem
slides 46,46a & 72: V.S. of Pinus leaf
more info. about slides No. 107, 46, & 72
In this type, the spaces are lined with intact cells and usually found in Compositae(canals with resins), conifers and woody dicots (e. g. Helianthus stem} and occur in the vascular and the ground tissues of all plant organs, and Umbelliferae Schizogenous canals containing gums and resins are called gum ducts and resins ducts.. They are long intercellular spaces lined with resin-producing epithelial cells (e. g. Pinus stem & leaf ).
c. Laticifers
Laticifers are specialized structures composed of a series of cells or single long cells. These structures contain latex which is a viscous liquid forming a suspension or an emulsion. Among the suspended materials found are rubber particles, waxes, resins, proteins, essential oils, mucilage, and also starch grains besides, salts, organic acids, and other substances. Certain plants contain, in the latex, sugars (Compositae) , tannins
(Musa), alkaloids(Papaver somniferum), and in Carica papaya, a proteolytic enzyme , papeins, is present. Latex has different colors which vary in the different plant species, e.g. it may be white and milky (Euphorbia, Lactuca, Asclepias), yellow-brown (Cannabis), yellow to orange (Papaver) or colorless (Morus). Laticifers are secretory system and latex contains metabolic by-products. When the Laticifers are cut the latex is extruded because the latex is found under pressure.
THE ROOT
The root comprises the lower part of the plant axis. It occurs in the sporophytes of vascular plants. The main function of the root is absorbing and anchoring. The root usually develops below the soil surface. Some roots grow in the air. The shape and structure of roots have much variability. In most dicots and gymnosperms. The root system consists of a tape root with lateral branches. But. in monocots roots are usually adventitious and develop from the stems and leaf, while the tap root develops the radicle of the seed.
MONOCOTYLEDONARY ROOTS
slide 108 : T.S. of Prop Root of Zea mays
DICOTYLEDONARY ROOTS
slide 109 & 110: T.S. of Dicot Roots
more info. About slides No. 108, 109 & 110
Primary Tissues in the Root
The Epidermis
Root epidermal cells are often thin-walled. They are usually devoid of cuticle. Sometimes the outermost cell walls, including those of the root hairs, undergo cutinization. The epidermis of roots is usually uniseriate. A well known example of a multiseriate epidermis is the velamen of air roots of tropical Orchadaceae and epiphytic Araceae. The velamen consisted of compactly arranged non living cells with thickened walls. During dry weather the cells are filled with air . When it reins, however, the velamen cells become filled with water, It acts as absorptive tissue. Root hairs are produced from the root epidermis (e. g. Ruscus & Zea root )
The root Cortex
The root cortex often develops from one or two layers of cells (ground meristem) derived from the apical initials (promeristem). In most of the dicots and gymnosperms the cortex of the root consists mainly of parenchyma cells. In many monocots much sclerenchyma develops in addition to the parenchyma. The cortical parenchyma of roots is usually devoid of chlorophyll. Chloroplasts are found in the cortex of roots of some water plants, and aerial roots of many epiphytes. Secretory cells, resin ducts, and Laticifers are found in the root cortex of different plants. If sclerechyma is present in the root cortex, it is found as cylindrical arrangement, several cell layers in depth, either beneath the epidermis directly, or beneath the exodermis, or next to the endodermis.
Intercellular spaces are very common in the root cortex. Large intercellular spaces (lysigenous) often develop in addition to the small ones (schizogenous) in the root cortex of certain plants such as the Gramineae and Cyperaceae. The root cortex is usually wider than the stem cortex. The root cortex plays a larger role in storage.
The Exodermis
The exodermis (e. g. Hemerocallis , Zea & Ruscus roots) is formed in the outer subepidermal layers of the cortex, the cells become suberized. In addition to suberin, lignin is often deposited in the walls of these cells. The thickness of the exodermis varies from a single cell layer to many layers. The exodermis is a protective tissue, may be accompanied, on its inner side, by sclerenchyma. Exodermis is common in roots of gymnosperms and angiosperms. It is rarely absent in roots of monocots.
The Endodermis
The endodermis consists of one layer of cells and represents the inner boundary of the root cortex. In that part of the root where the primary vascular system is starting to mature, Casparian strips appear on the radial and cross walls of the endodermal cells. The chemical composition and the structure of the Casparian strips have not yet been finally clarified. They may contain both lignin and suberin.
In addition to the Casparian strip, the cell walls are covered with suberin lamella on the inside of the cell. Moreover, a thick cellulose layer is deposited over the suberin layer, sometimes mainly on the inner tangential wall. Endodermal cells with Casparian strips only and which are facing the xylem remain without thickening. These cells are called passage cells. They are assumed to be the passage ways for a limited transfer of material between the cortex and the vascular cylinder (e. g. Hemerocallis , Zea & Ruscus roots).
The Vascular Cylinder
The central portion of the root is usually occupied by the vascular cylinder. The vascular cylinder is composed of the vascular system and the associated parenchyma. It is clearly delimited from the cortex because of the presence of the endodermis. The primary vascular tissue is surrounded by a region of cells which is termed the pericycle. The pericycle consists of thin walled parenchyma. It generally consists of one or more layers of thin-walled parenchyma cells. In angiosperms and gymnosperms the pericycle retains its meristematic activity. The lateral roots, the phellogen. and part of the vascular cambium is formed from the pericycle cells. In the angiosperms the pericycle is commonly uniseriate. It the angiosperms the pericycle is commonly uniseriate. It consists of several layers in many monocots and few dicots. The gymnosperms have multiseriate pericycle. Pericycle may not be found among water plants and parasites. The pericycle may contain Laticifers and secretory ducts. In monocots, where there is usually no secondary thickening part or all of the pericycle become sclerified.
Vascular System
The xylem is exarch, i.e. the protoxylem is situated on the outer side of the metaxylem. The protophloem is closet to the pericycle while the metaphloem is closest to the axis of the root. The number of protorxylem groups in the root i.e. wherever one, two, three, etc.(e. g. Tropaeolum "2". Vicia faba "4", Salix "6, & Ficus "10" roots),is expressed by the terms monarch, diarch, triarch, respectively . A root in which there are many protoxylem groups is said to be polyarch. When the diameter of the vascular cylinder is large a pith is usually present and the number of protoxylem groups is large. In gymnosperms and dicots the number of the xylem strands in the root is generally small (di-, tri, or tetrarch). There are some dicots in which there are more xylem strands. The number of xylem strands in the adventitious roots of monocots are polyarch (e. g. Hemerocallis, Zea & Ruscus roots). It may reach one hundred.
In certain monocots, one large vessel is found in the center of the vascular cylinder. Parenchyma tissue is found between this vessel and the peripheral xylem strands. In other plants the large metaxylem vessels form a circle around the pith. The number of these large vessels is not always equal to that of the peripheral strands. In certain plants two peripheral xylem strands are associated with a single large inner vessel. In woody monocots the inner vessels may be arranged in two or three circles or they may be scattered in the center of the cylinder. In few other monocots, phloem strands are scattered in center of the root. (e. g. Hemerocallis, Zea & Ruscus roots).
Generally, the primary phloem of root does not contain fibers, although fibers occur in the primary phloem of certain plants. Some roots are polystelic. A number of vascular cylinders each of which is surrounded by an endodermis can be seen.
2. THE STEM
The embryo axis in the seed consists of a hypocotyl and radicle. One or more cotyledons and the bud of the shoot are found at the tip of the hypocotyl. The cotyledons and the bud are called the plumule. The bud of the shoot usually consists of an axis containing a few internodes, which have not elongated and some leaf primordial. After seed germination, the embryo enlarges and start to grow. The apical meristem of the young shoot adds further leaf primordial and the internodes elongate. In many plants buds develop in the axils of the developing leaves giving rise to a branched shoot. The part of the stem from which a leaf or leaves develop is called the node. That portion of the stem between two such nodes is the internode.
MONOCOTYLEDONARY STEMS
slide 113 : T.S. of Zea mays Stem
slide ??? : T.S. of Cyperus Stem
DICOTYLEDONARY STEMS
slide 111 : T.S. of Helianthus Stem
slide 112 : T.S. of Cucurbita Stem
more info. about Slides No. 113, 111, 112, & ???
Primary Tissues in the Stem
As in the primary body of the root, the primary body of stem develops from the protoderm, procabium and ground meristem. The arrangement and structure of the primary tissues is as follows:
a. The Epidermis
The stem is bounded by the epidermis. The variations and functions of the epidermis have been considered before (Plant Tissues).
b. The Stem Cortex
It is the cylindrical region between the epidermis and the vascular cylinder. The cortex contains various cell types. The cortex of stems typically contains much parenchyma cells with intercellular spaces. In many stems, some or all of the cortical cells may have chloroplasts, in addition to the temporary stored starch, tannins, and crystals. Collenchyma tissue is very often present in the cortex. The collenchyma or fibers may form a continuous cylinder or they may be present in the form of separated strips. The stem cortex may contain lysigenous oil cavities, secretory cells, and laticifiers. The cortex of gymnosperms may develop resin ducts.
c. The Endodermis
The endodermis which is a specialized cells delimiting the cortex from the vascular cylinder is not usually developed. In the spermatophytes, the endodermis is usually most obvious in the root, but it may be found in some herbaceous plants, such as rhizomes, than in aerial stem. In young Dicot stems, the innermost cortical layer usually contains many large starch grains. This layer has been termed the starch sheath (e. g. Helianthus stem). In the stems of the lower vascular plants & in the roots of all vascular plants, the layer of endodermis is generally followed by a layer of pericycle.
d. The Primary Vascular Systems
The vascular system of the stem comes internal to the cortex. The vascular system consists of a cylinder encircling the pith, in most Dicot plants and gymnosperms. The cylinder of the vascular system may be continuous or splits. Two types of vascular tissues can be distinguished, the phloem and the xylem. The phloem is usually external and the xylem is usually internal. In the case of the split cylinder each strand is termed a vascular bundle. A vascular bundle in which the phloem is only external to the xylem is said to be a collateral bundle (e. g. Helianthus stem). In some Dicot families (e.g. Cucurbitaceae and Solanaceae) internal as well as external phloem is also present. The internal phloem may be present in close contact with the inner side of the xylem, or it may be present as separate strands on the border of the pith. This type of vascular bundles is termed bicollateral bundle (e. g. Luffa & Cucurbita stem). The third type of vascular bundles is called concentric. In this type one kind of vascular tissue completely surrounds the other.
In some monocots, the xylem surrounds the phloem. Such bundles are termed amphivasal bundles (e. g. Dracaena stem). Bundles in which the phloem surrounds the xylem are termed amphicribral bundles. This type of vascular bundle is common in the Pteridophyta. There are also collateral vascular bundles in which the xylem is seen to be V or U- shaped in T.S. In some grass bundles the xylem and phloem meet along a curve, and two large metaxylem vessels appear on the flanks (e. g. Zea mays stem). In the other the phloem is enclosed between the two arms of the V-xylem. In most monocots and in a few dicots no distinct vascular cylinder exists. The primary vascular system consists of a large number of bundles which are scattered irregularly. It is impossible to distinguish between the cortex, the vascular cylinder and the pith. In most of the dicots and in the gymnosperms the vascular bundles have a persisting vascular meristem" Vascular Cambium " between the xylem and the phloem. This is the cambium which develops from the procambium at the end of the extension growth of the primary body. In most of the lower vascular plants, the monocots, and some herbaceous dicots, the vascular bundles retain no Procambium after the primary vascular tissues mature.
e. The Pith
The pith of stems is largely composed of parenchyma. It is devoid of chlorophyll in the mature state but has leucoplasts. Intercellular spaces are common in the mature pith. The pith of many plants is partially destroyed during the growth of the stem. Certain pith cells are specialized as depositories of crystals or tannins. Some may develop thick walls or differentiated into sclereids. thick or thin-walled cells may become lignified. Specialized structures like laticifers or secondary canals, occur in the pith.
3. THE LEAF
ANATOMY OF THE MONOCOTYLEDONARY LEAVES
slide 120 : V.S. of Zea mays Leaf
slide 121 : V.S. of Triticum Leaf
slide 122 : V.S. of Saccharum Leaf
more info. about slides No. 120, 121, & 122
ANATOMY OF THE MONOCOTYLEDONOUS LEAF
The leaves of this groups are not made up of stipules, petiole and leaf blade. The leaf with parallel venation. The internal structure of leaves are similar in upper and lower surfaces. The epidermis on either sides contain stomata and the mesophyll is usually not differentiated into palisade and spongy but only consists of parenchyma cells, having Chloroplasts and intercellular spaces among them .
Anatomy of Monocot Leaf (e.g. Zea mays "maize" leaf).
a. Epidermis
The epidermis is found on both upper and lower surfaces of the leaf. The epidermal layer is uniseriate and composed of more or less oval cells. The outer wall of the epidermal cells is cuticularized and the stomata are confined to both epidermal layers. In general, the epidermis of grasses contain a variety of cells (enlarged bulliform cells which forming bands of various widths and numbers.
b. Mesophyll
Monocot hydrophytes have leaves resembling that of the dicots. In Lilium leaf palisade parenchyma is found on the adaxial (upper) side. In Musa the leaf has several layers of palisade and a wide region of spongy parenchyma with large lacunae. In grasses , the mesophyll shows no distinct differentiation into palisade and spongy parenchyma.
Mechanical Tissues
Many monocots have leaves with large amounts of sclerenchyma. The fibers may be associated with the vascular bundles or may appear also as strands. Grass leaves have strongly developed sclerenchyma. So, the large vascular bundles may be enclosed in fibers (bundle sheath which continued to the upper & lower epidermis and the epidermal cells in such region may also become fiber-like). The small bundles may be also, associated with plates of fibers on both sides (form I-girders).
Vascular Tissue
The vascular bundles are collateral and closed as found in monocot stems. Usually, each bundle remains surrounded by a bundle sheath consisting of thin-walled parenchyma cells containing starch grains in them. The bundles consist of phloem, xylem and sclerenchyma cells. The scelernchyma are also, occurred in patches at both ends of the large vascular bundles which give mechanical support to the leaf.
ANATOMY OF THE DICOTYLEDONARY LEAVES
slide 114 : V.S. of Gossypium Leaf
slide 115 : V.S. of Ficus elastica Leaf
slides 116-119 : V.S. of Different Dicot Leaf (Write short reports)
more info. about slides No. 114 & 115
ANATOMY OF THE DICOTYLEDONOUS LEAF
The internal structure of the leaf is as follow :
a. Epidermis
The leaf is covered on both surfaces by single-layered epidermis. The outer walls of the epidermis are usually thickened and covered by waxy substance called cutin and the outer surfaces are frequently covered with a thin or thick cuticle (e.g. Ficus elastica & Nerium oleander leaf), this is to reduce the rate of transpiration , prevent the entrance of the pathogens into the interior of the leaf and to protect the soft internal tissues. In the xerophytic plants the epidermal cells become radially elongated and somewhat lignified. In Nerium leaf the epidermis is multilayered "hypodermis'' Epidermis contains stomata which is more abundant in the lower surface. In the floating leaves stomata are confined to the upper surface whereas in xerophytic plants stomata are sunken (e.g. in Pinus -leaf} or situated inside the depressions (e.g. in Nerium oleander leaf). Stomata are useful in gas exchange and removal of the excess of water through transpiration.
b. Mesophyll Tissues
The tissue of leaf lies between the upper and lower epidermis and between the veins consists of typically thin-walled parenchyma known as mesophyll and form the major portion of the inner of leaf. Commonly the mesophyll consists of two types of cells; the palisade and spongy parenchyma and always contain chloroplast in them.
The palisade parenchyma is composed of elongated more or less cylindrical cells , and the cells seems to be close together, but really they are separate from each other having intercellular spaces among them. The competence of the palisade parenchyma dependence upon light intensity. The leaves which receive direct light "sunny places" develop more compact parenchyma in comparison to the leaves developed in shady places. The palisade may consist of one single or more layers. These cells are arranged near to the upper surface of the leaf , where they receive sunlight and facilitate the function of photosynthesis. Sometimes the palisade parenchyma are present in both sides when the two sides are equally illuminated . the leaf is said to be isolateral or isobilateral. In certain plants palisade tissue is present on one side of the leaf and the spongy parenchyma on the other is termed dorsiventral or bifacial (e.g. Gossypium Dicot leaf). Thus, this lower portion of the mesophyll '' spongy parenchyma '' is composed of loose, irregular, thin-walled cells having big intercellular spaces. The spongy cells are more adapted in gas exchange more than photosynthesis as chloroplasts are much abundant in palisade tissues.
c. Mechanical Support
The function of the mid-rib and the lateral veins are to strengthen the leaf. The important tissues giving the mechanical strength are, collenchyma, sclerenchyma, turgid parenchyma, and woody xylem.
Collenchyma
Present in the center of the upper portion of the mid-rib just below the epidermis, and also above the lower epidermis. Collenchyma is composed of living cells with walls which are thickened at the angles. The thick places of the walls increase the strength of the cells while the thin places allow the transfer of material from cell to another.
Sclerenchyma
Sclerenchyma "fiber" are associated with the vascular tissues of the leaves. They occur as caps of vascular bundles adjacent to the phloem. Some times fibers are found on both sides of bundles. Usually, these cells are thick-walled, dead and lignified. Sclerenchyma present just exterior to phloem giving it mechanical protection. The fibers are greatly elongated in the longitudinal direction of the mid - rib.
Turged Parenchyma
The region between the collenchyma and the central portion of the mid-rib is occupied by parenchyma cells. On account of their turgidity, they strengthen the mid -rib.
d. Xylem
Usually, the vessels and tracheids of xylem conduct water, but due to the thick-walled nature they also give mechanical support to the leaf. The xylem elements are composed of dead and lignified cells.
i. Orientation of the Vascular Tissue
In the leaf traces of a flowering plant, before they leave the stele, the phloem is always found towards the outside of the stem. The leaf traces after their entrance in the petiole and lamina, altering their position i.e., phloem is always found towards the lower side and the xylem towards the upper side of the leaf.
ii. Conducting System
The tissues of the conducting system are situated near or at the center of the mid-rib. This system may have various shapes, the form of a ring, crescent-shaped ring, a crescent or scattered patches, or the form of a ring. In the ring shaped, parenchyma are present in the center of the ring. The inner part of the ring is composed of xylem (towards upper surface), and phloem (towards lower surface).
iii. Veins
The structure of large veins is more or less similar to that of the mid-rib as they pass from the base of a leaf blade towards the apex or the margin of the leaf. The mesophyll chlorenchyma are arranged so that the conduction of materials to and from the veins is facilitated.
iv. Bundle Sheath
In dicots, the vascular bundles remain surrounded by parenchyma cells with small number of chloroplasts whereas the small vascular bundles occurring in the mesophyll are enclosed by the bundle sheath or border parenchyma.
ANATOMY OF THE GYMNOSPERM LEAVES
slides 66 & 124 : V.S. of Cycus Leaf
slide 46,65,72& 123 : V.S. of Pinus Leaf
more info. about slides No. 46, 65, 72, & 123
ANATOMY OF THE GYMNOSPERM LEAVES
The leaves of gymnosperms are usually evergreen and are highly independent of environmental conditions.
Pinus leaf
It is needle-like, originated on dwarf branches single or in groups of two or more. They characterized by the following features :
1. Thick-walled epidermal cells, covered with a thick cuticle.
2. Stomata are found scattered on all sides of the leaf, they are sunken and overarched by subsidary cells.
3. Hypodermis of thick-walled cells.
4. The mesophyll is not differentiated into palisade and spongy parenchyma. It consists of parenchymatous cells with folded walls (lobed or plicate parenchyma).
5. Resin ducts are also present in the mesophyll.
4. The vascular system is present in the center of the leaf. There is one vascular bundle, or two, which are then closed to one anther.
5. The xylem is on the adaxial (upper), the phloem on the abaxial (lower) side.
6. The vascular bundle is surrounded by a transfusion tissue.
HYDROPHYTES
Hydrophytic Stem
slide 132 : T.S. of Hydrophtic Stem of Potamogeton
slide 133 : T.S. of Enlarged Part of Hydrophytic Stem
Hydrophytic Leaf
slide 134 : V.S. of Hydrophytic Leaf
slide 137 : V.S. of Elodea Leaf
XEROPHYTES
Xerophytic Stem
slide 125 : T.S. of Lygos reatama Stem
slide 126 & 127 : T.S. of Lygos Reatama Stem (Enlarged Parts)
Xerophytic Leaf
slide 128 : V.S. of Ammophila arenaria (= Calmagrostis) Leaf
slide 129 : V.S. of Ammophila arenaria Leaf (Enlarged Part)
slide 130 : V.S. of Nerium oleander Leaf
slide 131 : V.S. of Xerophytic Leaf
MESOPHYTES
Mesophytic Stem
slide 111 : T.S of Helianthus Stem
Mesophytic Leaf
slide 114: VS. of Gossypium Leaf
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The mesophyll is not differentiated into palisade and spongy but, it is composed of compactly arranged thin -walled parenchyma having well developed intercellular spaces among them .
c. Vascular Bundles
The vascular bundles are collateral and closed as found in monocotyledonous stems. Usually, each bundle remains surrounded by a bundle sheath consisting of thin walled parenchyma cells containing starch grains in them. The bundles consist of phloem, xylem and sclerenchyma cells also occur in patches at both ends of the large vascular bundles which give mechanical support to the leaf.
