The flower consists of an axis (receptacle) and lateral appendages (floral parts or floral organs). The sepals and petals which constitute the calyx and corolla respectively are the sterile parts. The stamens and the carpels are the reproductive parts. The stamens compose the androecium, whereas the carpels compose the gynoecium.
Importance of floral anatomy
The study of the vascular anatomy has helped in solving many problems of floral morphology. It has shown that many structures are not what they appear to be or what they are commonly taken to be.
Morphologically the flower is a determined shoot with appendages, these appendages are homologous with leaves. The floral vascular skeletons, differ in no essential way from leaf stems. In the present text the flower is treated on the basis of thehomology between the flower and the shoot in their phylogeny and ontogeny.
Pedicel
The Pedicel and the receptacle have typical structure, with a normal vascular cylinder. The cylinder may be unbroken or it may contain a ring of vascular bundles. In the region where floral organs are borne, the pedicel expand into the receptacle. The vascular cylinder also expands and the vascular bundles increase somewhat in number, and finally traces begin to diverge.
The appendage traces are derived from the receptacular stele exactly as leaf traces are derived in typical stems.
Sepals
The sepals are anatomically like the leaves of the plant. A sepal usually receives three traces derived from the same or different sources. As regards the morphological nature of the sepals, they have often been considered as equivalent to bracts and foliage leaves.
Petals
In their vascular supply the petals are sometimes leaf like, but much more often they are like stamens. The petals may have one (very common), three or several traces.
Stamens
A stamen generally receives a single trace which remians almost unbranched throughout its course in the filament. In the anther region it may undergo some branching.
Carpels
The carpel is commonly looked as a leaf-like organ folded upward, i.e., ventrally with its margins more or less completely fused and bearing the ovules. This conception has been supported by the anatomy. The carpel has one, three, five or several traces. The three trace carpel is most common. The median trace which leaves the stele below the other carpel traces, is known as the dorsal trace because it becomes the dorsal (midrib) bundle of the folded organ. The outermost traces are known as ventral or marginal traces because they become the bundles that run along the ventral edge of the carpel. The ovule traces are derived from the ventral bundles.
Functions: Anchorage and absorption of water and minerals.
The epidermis: Thin walled, without cuticle, having root hairs (piliferous layer), uniseriate or multiseriate (velamen) in air roots that act as absorptive tissue.
Thecortex: Parenchyma, no chlorophyll except in some hydrophytes and aerial roots of epiphytes, act as storage tissue.
Theexodermis: The outer subepidermal layer of the cortex, suberized or lignified, single layer or many layers, act as protective tissue.
Theendodermis: The inner boundary of the root cortex, with casperian strip and passage cells, regulates the water passage to xylem.
Thevascularcylinder: Surrounded by the pericycle that is the origin of the lateral roots, the vascular bundle of radial type, the protoxylem exarch.
Monocot roots
The xylem is polyarch; more than 17 arches.
Dicotroots
The xylem is limited; from 2-12 arches.
The Stem
The epidermis: The outer layer of the stem, fiberous epidermis may be present in monoct stems, trichomes may be present.
The cortex: Between the epidermis and the vascular cylinder, of parenchyma, chlorenchyma, collenchyma or fibers, in monocot stems the ground tissue is undifferentiated into cortex nor pith.
The starch sheath: The innermost layer of the cortex, containing starch grains.
The primary vascular system: External phloem and internal xylem (conjoint vascular bundles), the protoxylem endarch.
The pith: Parenchyma with leucoplastids, may contain crystals, tannins or sclereids.
Monocot stems
The vascular bundles are:
numerous, scattered, collateral, closed, xylem vessels in the form of V or Y, presence of xylem cavity, presence of fiber sheath around the bundle.
Dicot stems
The vascular bundles are:
few, arranged, collateral or bicollateral, opened, xylem vessels in the form of rows, absence of fiber sheath .
Root-Stem Transition
The root and the stem make a continuous structure called the axis of the plant. The vascular bundles are continuous from the root to the stem, but the arrangement of vascular bundles is quite different in the two organs; the stems possess collateral bundles with endarch xylem, whereas the roots possess radial bundles with exarch xylem. The change of position involving inversion and twisting of xylem strands from exarch to endarch type is referred to as vascular transition, and the part of the axis where these changes occur is called transition region.
Type A: In Fumaria, Mirabilis and Dipsacus, and others, each xylem strand of the root divides by radial division forming branches, they swing in their lateral direction; one towards right and the other goes to the left. These branches join the phloem strands on the inside. The phloem strands, do not change their position and also remain unchanged in their orientation. They remain in the form of straight strands continuously from the root into the stem. In this type as many primary bundles are formed in the stem as many phloem strands are formed in the root.
Type B: In Cucurbita, Phaseolus, Acer and Trapaeolum and others, the xylem and phloem strands fork, the branches of the strands of both swing in lateral direction and join in pairs. After joining in the pairs they remain in the alternate position of the strands in the root. The xylem strands become inverted in their position and the phloem strands do not change their orientation. This way, in the stem, the number of bundles becomes double of the phloem strands found in the root. This type of transition is more commonly found.
Type C: In Lathyrus, Medicago and Phoenix, the xylem strands do not fork and continue their direct course into the stem. These strands twist through 180 degrees. The phloem strands divide soon and the resulting halves swing in the lateral direction to the xylem positions. The phloem strands join the xylem strands on the outside. In this type as many bundles are formed as there are phloem strands in the root (as in type A).
Type D: This type is rarely found and is known in only a few monocotyledons (e.g., Anemarrhena). In this type half of the xylem strands fork and the branches swing in their lateral direction to join the other undivided strands of xylem which become inverted. The phloem strands do not divide but they become united in pairs. These united phloem strands unite with the triple strands of the xylem. Thus, a single bundle of the stem consists of five united strands. In this type half as many bundles are formed in the stem as there are phloem strands in the root.
The Leaf
The epidermis: contains stomata and trichomes, upper (adaxial) and lower (abaxial).
The ground tissue: the ground tissue of the leaf is called mesophyll.
Types of leaves:
Dorsiventral:
Palisade below the upper epidermis, the spongy at abaxial surface.
Isolateral:
Palisade is found on both ad- and abaxial surfaces, one row at each side.
Isobilateral:
Palisade found on both sides, two rows at each.
The vascular system:
The vascular bundles are called veins, the arrangement of veins is called venation, the phloem is directed towards the lower epidermis.
Monocot leaves
The blade is undifferentiated into midrib nor wings.
The ground tissue is undifferentiated into palisade nor spongy.
Vascular bundles are numerous.
Mechanical tissue of sclerenchyma beneath epidermis.
Dicot leaves
The blade is differentiated into midrib and wings.
The ground tissue is differentiated into palisade and spongy.
Vascular bundles are one median and numerous laterals.
Mechanical tissue of collenchyma beneath epidermis in midrib region.
In which growth has stopped completely or for a time. The cells may be living or dead, thin or thick walled.
Tissue types based on kind of constituent cells:
A. Simple
Homogenous, consisting of one kind of cells.e.g. parenchyma, collenchyma, sclerenchyma.
B. Complex
Heterogenous, consisting of more than one kind
of cells working together as a unit. e.g. xylem and phloem.
The Tissue Systems
All the tissues of a plant which perform the same general function form a tissue system.
There are four main tissue systems:
1. The dermal or epidermal tissue system.
2. The fundamental or ground tissue system.
3. The vascular tissue system.
4. The secretory and excretory tissue system.
The Dermal or Epidermal Tissue System
The dermal system forms the outer protective covering of the plant and is represented in the primary plant body by the epidermis. During secondary growth the epidermis may be replaced by another dermal system; the periderm forming the new protective tissue.
1.Epidermis (epi= upon, derma= skin).
Composition: Continuous single layer of cells except for certain small pores, called stomata and lenticels. In many plants it may be bi- or multiseriate.
In the case of roots the outermost layer is known as epiblema, piliferous layer or rhizodermis.
Origin: From protoderm or dermatogen of apical meristem.
Functions:-
•Protects the internal tissue from damage.
•Prevents evaporation of water.
•Serves in gas exchange.
•Plays a role in photosynthesis and secretion.
•Acts as store for water in Xyrophytic plants.
•Some develops into secretory tissues, stomata and absorbing hairs.
Shapes and Types of epidermal cells:-
2.Multiple epidermisDevelpos from protoderm.
3.HypodermisDevelops from ground meristem.
4.Piliferous layer
In Monocot roots, called (epiblema or rhizodermis) from which absorbing root hairs arise.
5.Exodermis
Replaces the ruptured piliferous layer during secondary growth, with thick walled cells.
6.Periderm
During secondary growth in roots and stems, the epidermis replaced
by the periderm, with dead,
suberized cork cells forming new protective tissue.
7.Stomata
•Openings in the epidermis, bounded by two guard cells.
•Subsidiary cells = 2 or more cells adjacent to guard cells and differ from otherepidermal cells may be found or not.
•Stomatal opening + The guard cells = Stoma.
•Stomatal opening + The guard cells + subsidiary cells = Stomatal complex or stomatal apparatus.
•Found on the aerial parts of the plant.
Functions of stomata
•Gas exchange with aid of substomatal chamber.
•Water transpiration and evaporation.
Positions of guard cells
•Leveled:- At the same level of the epidermal cells.
•Sunken :- Blow the level of the epidermal cells.
•Sunken in chamber :- In grooves, covered with hairs.
Types of Stomata
A. Monocotyledonous Types
•Iris type•Gramineae type
No subsidiary cells.Two lateral subsidiary cells , one on each side.
•Palmae type•Canna type:-
Four subsidiary cells, two round & smaller.Four - six subsidiary cells.
Two or more subsidiary cells parallelTwo subsidiary cells perpendicular
to the long axis of the pore.to the long axis of the pore.
8. Epidermal Appendages (Trichomes or Hairs)
Outgrowth of the epidermal cells, either covering (non-glandular) or glandular.
Functions of trichomes
•Control the rate of transpiration.
•Reduce the heating effect of sun light.
•Protect the plant against outer injurious effects.
Types of trichomes
I. Non-glandular (e-glandular)
A. Unicellular: Formed of one cell.
a. Papilloseb. Unbranchedc. Branchedd. Stellate
B. Multicellular: Formed of more than one cell.
a. Unbranched (simple).
b. Branched
1. Simple-branched2. Tree-like
Uniseriate body ending with two branches.Radiating unicellular hairs.
3. Peltate (scale hair)4. Candelabra
Very short stalk ending withUniseriate axis from which arise
plate-like structure.numerous unicellularbranches of hairs.
II. Glandular
Has a swollen head formed of one or more secreting cells which may be:
A. Unicellular
(Pearl gland) with embedded foot and the head projecting outside.
B. Multicellular
a. Uniseriate stalk
1. Unicellular head2. Multicellular head
One of the most interisting type of trichomesis Stinging hair
Contains poisonous liquid, consisting of basal bulb-like portion from which a stiff, slender, tapering , small knob-like point,when the animal or human body comes in contact with it , the sharp pointed end penetrates the skin and the fluid is transferred from the basal bulb to the body causing irritation.
A meristem is the tissue in all plants consisting of undifferentiated cells (meristematic cells) and found in zones of the plant where growth can take place. Differentiated plant cells generally cannot divide. The term meristem was derived from the Greek word merizein, meaning to divide. Meristematic cells are analogous in function to stem cells in animals.
Characteristics ofMeristematic Cells
•Incompletely or not at all differentiated,
•Capable of continued cellular division (youthful).
•Small and protoplasm fills the cell completely.
•The vacuoles are extremely small.
•The cytoplasm does not contain differentiated plastids, although they are present in rudimentary form (proplastids).
•Meristematic cells are without intercellular cavities.
•The cell wall is a very thin primary cell wall.
Classification of Meristems According to Origin
A. Primary Meristems
•Protoderm - lies around the outside of the stem and develops into the epidermis.
•Procambium - lies just inside of the protoderm and develops into primary xylem and primary phloem. It also produces the vascular cambium, a secondary meristem.
•Ground meristem - develops into cortex and pith. It produces the cork cambium, another secondary meristem.
These meristems are responsible for primary growth, or an increase in length.
B. Secondary Meristems
•Vascular Cambium - produces secondary xylem and secondary phloem, this is a process which may continue throughout the life of the plant. This is what gives rise to wood in plants. Such plants are called arborescent. .
•Cork Cambium - gives rise to the periderm which replaces the epidermis.
Classification of Meristems According to Position
•Apical Meristems - (Shoot apex) - The source of all above-ground organs, (Root apex) - It is covered by the root cap, which protects the apical meristem from the rocks, dirt and pathogens and (Floral meristem) - When plants begin flowering, the shoot apical meristem is transformed into an inflorescence meristem which goes on to produce the floral meristem which produces the familiar sepals, petals, stamens, and carpels of the flower.
•Lateral Meristems - they are involved in lateral growth e.g. Vascular cambium and Cork cambium.
•Intercalary Meristem - Occur only in monocot (particularly grass) in stems at the base of nodes and leaf blades. Intercalary meristems at the nodes allow for rapid stem elongation, while those at the base of leaf blades allow damaged leaves to rapidly regrow.
Theories of Development and Differentiation of Meristems
Apical Cell Theory
Solitary apical cells occur in many bryophytes and pteridophytes formed all tissues and organs of the plant. The apical cell theory was proposed as the basis for an understanding of the method of growth and morphology in many groups. But the theory was not applicable to seed plants.
Histogen Theory
Under this theory the more or less distinct major regions of the stem and root apex were called histogens (tissue builders). This theory, in contrast to the apical cell theory, placed the origin of axis apices in a group of initials. The histogens were:
The dermatogen: a uniseriate, external layer; formed the epidermis.
The periblem: the region between plerome and dermatogen. Formed the cortex.
The plerome: a central core; formed the pith and primary vascular tissues.
Tunica and corpus Theory
The growing apex of the stem is differentiated into:
Corpus: in the middle of apical meristem, divide to form the central vascular cylinder and cortex.
Tunica: outer enveloping layer around the corpus, divide to form the epidermis and part of the cortex in some cases.
Promeristem theory
The promeristem region is differentiated into:
Protoderm: formed the epidermis in stem and piliferous layer in the root.
Procambium: formed primary phloem and primar xylem.
Ground meristem: formed the cortex and the pith.
Mature Tissues (Permanent Tissues)
In which growth has stopped completely or for a time. The cells may be living or dead, thin or thick walled.
Tissue types based on kind of constituent cells:
A. Simple
Homogenous, consisting of one kind of cells.e.g. parenchyma, collenchyma, sclerenchyma.
B. Complex
Heterogenous, consisting of more than one kind
of cells working together as a unit. e.g. xylem and phloem.
The Tissue Systems
All the tissues of a plant which perform the same general function form a tissue system.
There are four main tissue systems:
1. The dermal or epidermal tissue system.
2. The fundamental or ground tissue system.
3. The vascular tissue system.
4. The secretory and excretory tissue system.
The Dermal or Epidermal Tissue System
The dermal system forms the outer protective covering of the plant and is represented in the primary plant body by the epidermis. During secondary growth the epidermis may be replaced by another dermal system; the periderm forming the new protective tissue.
1.Epidermis (epi= upon, derma= skin).
Composition: Continuous single layer of cells except for certain small pores, called stomata and lenticels. In many plants it may be bi- or multiseriate.
In the case of roots the outermost layer is known as epiblema, piliferous layer or rhizodermis.
Origin: From protoderm or dermatogen of apical meristem.
Functions:-
•Protects the internal tissue from damage.
•Prevents evaporation of water.
•Serves in gas exchange.
•Plays a role in photosynthesis and secretion.
•Acts as store for water in Xyrophytic plants.
•Some develops into secretory tissues, stomata and absorbing hairs.
Shapes and Types of epidermal cells:-
2.Multiple epidermisDevelpos from protoderm.
3.HypodermisDevelops from ground meristem.
4.Piliferous layer
In Monocot roots, called (epiblema or rhizodermis) from which absorbing root hairs arise.
5.Exodermis
Replaces the ruptured piliferous layer during secondary growth, with thick walled cells.
6.Periderm
During secondary growth in roots and stems, the epidermis replaced
by the periderm, with dead,
suberized cork cells forming new protective tissue.
