SGB Amravati University B Sc II Paper IV: Dr. D. D. Khedkar

8/7/2019 SGB Amravati University B Sc II Paper IV: Dr. D. D. Khedkar

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Shri Shivaji Science College, Amravati ( 1 ) B. Sc. II

D. D. Khedkar Deptt. of Botany

UNIT I

GENERAL CHARACTERISTICS OF SEED PLANTS.

The seed plants are including two major plant groups a) Gymnosperms and b) Angiosperms.

These are well developed plants. Following are the main characteristic features of the seed plants

are

1. There are two types of vascular tissue. Phloem is the vascular tissue through which food moves.When food is made in the plant's leaves, it enters the phloem and travels to other parts of the plant.

Water and minerals travel in the vascular tissue called xylem.

2. They use pollen and seeds to reproduce.

3. They all have body plans that include leaves, stems, and roots.

4. Root system with a large surface area allowed for absorption of minerals, phosphates,

sulphates, fixed nitrogen, and water. Especially water.

5. The waxy cuticle and bark slowed water loss even in direct sunlight

6. Pollen delivers sperm cells directly near the eggs, therefore seed plants do not need water forfertilization to occur. Seeds are structures that contain a young plant inside a protective covering.

7. Flowers (color, scent, nectar) attracted pollinators.

8. Fruits encouraged animals to spread seeds at a distance from the plant

9. Seeds containing nutrients and energy for the plant embryo within, allowing the seed tosurvive for years before germinating, thus allowing the plant species to "skip a bad year for

germinating." Inside a seed is a partially developed plant. If a seed lands in an area where conditions arefavorable, it sprouts out of the seed and begins to grow. A seed has three main partsan embryo, stored food,

and a seed coat.

10.

Seed plants can live in a variety of environments.

SEED HABIT

The seed habit is the most complex and diverse means of sexual reproduction in vascular land

plants. The ecological diversity of this group generally is attributed to their reproductive system,

which permits these plants to exploit habitats not accessible to most lower vascular plants.

Evolution of the seed habit consists of at least two independent problems.

1. The evolution of the life history we call the seed habit, i.e., the delivery of a malegametophyte to a female gametophyte that is fixed on the parent sporophyte.

2. The evolution of ovular particularly in number of integuments and morphology.

One of the most important events in higher vascular plant evolution is the evolution of Seed

Habit, which is definitely an advance over the Pteridophytes. To attain this outstanding

achievement many important steps were involved in the evolution of reproductive system that

finally led up to the seed habit.

Three essential conditions for evolution were:

(i) Protection of the gametophytes and the young developing sporophytes from drying

and injury

(ii) Provision of nourishment for their proper development and

(iii) Freedom from external water required during fertilization for transference of gametes

All these conditions have been achieved in the seed of gymnosperms and angiosperms where the

three successive generations are represented by the parent sporophyte as integument and

nucellus, the gametophyte as endosperm and the daughter sporophyte as embryo.


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GEOLOGICAL TIME SCALE

To understand the geological relationships of different rock units, Nicolaus Steno in 1669

described two basic geologic principles.

1. Sedimentary rocks are laid down in a horizontal manner, and

2. The younger rock units were deposited on top of older rock units.

Fossils provided the opportunity for workers to correlate between geographically distinct areas.

This contribution was possible because fossils are found over wide regions of the earth's crust. In

1815 Smith produced a geologic map of England in which he successfully demonstrated the

validity of the principle of faunal succession.

The history of the earth is broken up into a hierarchical set of divisions for describing geologic

time. As increasingly smaller units of time, the generally accepted divisions are eon, era, period,

epoch, age. In the time scale shown at left, only the two highest levels of this hierarchy are

represented.

The Geologic Time Scale (mya = million years ago)Eon (period) Era (period) Epoch (period)Phanerozoic Eon(543 mya to present)

Cenozoic Era(65 mya to today)

Quaternary (1.8 mya to today)Holocene (10,000 years to today)

Pleistocene (1.8 mya to 10,000 yrs)

Tertiary (65 to 1.8 mya)

Pliocene (5.3 to 1.8 mya)Miocene (23.8 to 5.3 mya)

Oligocene (33.7 to 23.8 mya)

Eocene (54.8 to 33.7 mya)

Paleocene (65 to 54.8 mya)Mesozoic Era(248 to 65 mya)

Cretaceous (144 to 65 mya)

Jurassic (206 to 144 mya)

Triassic (248 to 206 mya)Paleozoic Era

(543 to 248 mya)Permian (290 to 248 mya)

Carboniferous (354 to 290 mya)

Pennsylvanian (323 to 290 mya)Mississippian (354 to 323 mya)

Devonian (417 to 354 mya)

Silurian (443 to 417 mya)

Ordovician (490 to 443 mya)

Cambrian (543 to 490 mya)

Tommotian (530 to 527 mya)Eon (period) Era (period) Epoch (period)Precambrian Time(4,500 to 543 mya)

Proterozoic Era

(2500 to 543 mya)

Neoproterozoic (900 to 543 mya)

Vendian (650 to 543 mya)Mesoproterozoic (1600 to 900 mya)

Paleoproterozoic (2500 to 1600 mya)

Archaean

(3800 to 2500 mya)Hadean(4500 to 3800 mya)


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GENERAL FEATURES OF GYMNOSPERMS

Gymnosperms (gymnos = naked, sperma = seed) include plants whose ovules are naked and

freely exposed for pollination. They are borne on microsporophylls, scales, or comparable

structures. In angiosperms (angios = closed, sperma = seed) ovules are enclosed in a carpel and

usually completely closed at the time of pollination.

The sporophyte is usually arborescent comprising of large or small woody trees or shrubs. Few

may be lianas or climbers. Gymnosperms show the following features:

1. The plants have a long lasting tap root system. Main elements of xylem are tracheids. Phloem

is composed of sieve cells and lacks companion cells.

2. The sporophyte shows unlimited growth of aerial trunk by means of apical and lateral

meristem which produce secondary vascular tissues.

3. Vascular bundle of stems are collateral, endarch or mesarch, open and arranged in a ring.

4. Secondary growth very pronounced. Secondary vascular tissues consisting mainly oftracheids and sieve cells. Normally xylem lacks vessel elements and the phloem lacks

companion cells. But both vessels and companion cells present in members of Gnetales.

5. Leaves are diverse in form and arrangement. They are both simple and compound ranging in

size from a minute scale to leaves a few meters long.

6. Vegetative methods of reproduction are rare in gymnosperms but vegetatively propagating

bulbils are known in Cycas.

7. Plants are heterosporous. They may be monoecious (Pinus) or dioecious (Cycas).

8. Reproductive structures are borne in cones or strobili that are either staminate (male) or

ovulate (female) except in Cycas where ovules are borne on loose megasporophylls.

Sporangia are borne on fertile leaves or leaf-like structures called microsporophylls (in male

cone) and megasporophylla (in female cones) which are arranged spirally around a central

axis.

9. Microsporangia are borne on abaxial or lower surface of microsporophylls.

10.Megasporangium or ovule is borne on adaxial or upper surface of megasporophyll or

ovuliferous scale and are generally orthotropous. Young megasporangium consists of anucellus which is surrounded by a sheath or integument and inside the nucellus is single

functional megaspore. A narrow passage above the nucellus in the integument is the

micropyle.

11.Microspore and megaspore germination in situ, producing micro-and megagametophytes

which are not autotrophic. Microspores have partly developed endosporic male gametophytes

when they are transferred to micropyle of ovule. The microspore or pollen grain at the time

of shedding may have only one prothallial cell (Cycas) or two prothallial cells (Pinus), the

former being liberated at three-celled stage and latter at four-celled stage. \

12.The microspores or pollen grains are borne by wind and enter the ovule directly through the

micropylar canal. The micropyle in almost all gymnosperms secretes a sugary exudate called

the "pollination drop" which not only receives the pollen grains but also transports them to

nucellus of ovule.

13.The development of female gametophyte is monosporic (only one megaspore out of four will

contribute in archegonium).

14.Archegonia are quite large and elongated and lack neck canal cells. Often the ventral canal

cell too, is eliminated. Gametophytic cells around the archegonia develop into a nutritive

layer or jacket.


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15.Fertilization is effected by means of a pollen tube (siphonogamy). The multiflagellate

spermatozoids or male cells within the pollen tube have no specialized means of locomotion

and occur within the ovule. The pollen tube bursts liberating two large flagellated sperms

into the cavity (archegonial chamber) directly above female gametophyte. One sperm

fertilizes the large egg cell giving rise to a zygote (2n).

16.At the beginning of embryogeny, zygote shows free nuclear division. Later embryo becomes

cellular after wall formation and gradually differentiates into a suspensor, shoot apex,

cotyledons, hypocotyl and radicle.

17.Embryo remains contained within the seed developed from the ovule. Mature embryo is

differentiated into root, stem and leaves.

18.The young embryo draws its nutrition from the endosperm which develops before

fertilization and is haploid (n). Endosperm develops from female gametophyte that has

absorbed the food from nucellus.

19.Gymnosperm ovules and seeds are unprotected and not surrounded by an ovary wall, hencetrue fruits like that of angiosperms are not formed.

20.The detached seeds of all gymnosperms remain dormant for sometime undergoing a resting

period.

GYMNOSPERMS CLASSIFICATION.

Gymnosperms have been variously classified by different workers from time to time. The early

history of classification of gymnosperms is linked with the angiosperms. Robert Brown (1827),after recognizing the gymnosperms as a distinct group of plants placed them alongwith

angiosperms.

Benthem and Hooker (1862-1883) in their Genera Plantarum, placed them between the

Dicotyledones and Monocotyledones. They recognised only three orders of living gymnosperms:

Gnetaceae, Coniferae and Cycadaceae.

Some outstanding systems of classification of gymnosperms are being mentioned below:-

Van Tieghem (1898) recognized gymnosperms as one of the two major divisions of

Spermatophyta.


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PROCESS OF FOSSILIZATION

Fossils (from Latin fossus, literally "having been dug up") are the preserved remains or traces of

animals (also known as zoolites), plants, and other organisms from the remote past. The totality

of fossils, both discovered and undiscovered, and their placement in fossiliferous (fossil-

containing) rock formations and sedimentary layers (strata) is known as the fossil record. The

study of fossils across geological time, how they were formed, and the evolutionary relationships

between taxa (phylogeny) are some of the most important functions of the science of

paleontology. Such a preserved specimen is called a "fossil" if it is older than some minimum

age, most often the arbitrary date of 10,000 years ago. Following are the steps of fossilization:

Some animals were quickly buried after their death (by sinking in mud, being buried in a

sand storm, etc.).

Over time, more and more sediment covered the remains.

The parts of the animals that didn't rot (usually the harder parts likes bones and teeth)

were encased in the newly-formed sediment.

In the right circumstances (no scavengers, quick burial, not much weathering), parts of

the animal turned into fossils over time.

After a long time, the chemicals in the buried animals' bodies underwent a series of

changes. As the bone slowly decayed, water infused with minerals seeped into the bone

and replaced the chemicals in the bone with rock-like minerals. The process of

fossilization involves the dissolving and replacement of the original minerals in the object

with other minerals (and/or permineralization, the filling up of spaces in fossils with

minerals, and/or recrystallization in which a mineral crystal changes its form).

This process results in a heavy, rock-like copy of the original object - a fossil. The fossil

has the same shape as the original object, but is chemically more like a rock! Some of the

original hydroxy-apatite (a major bone consitiuent) remains, although it is saturated with

silica (rock).

Flow chart of fossil formation:

TYPES OF PRESERVATION

A. Permineralization

Occurs after burial, as the empty spaces within an organism (spaces filled with liquid or gas

during life) become filled with mineral-rich groundwater and the minerals precipitate from the

groundwater, thus occupying the empty spaces. This process can occur in very small spaces,

such as within the cell wall of a plant cell. Small scale permineralization can produce very

detailed fossils. For permineralization to occur, the organism must become covered by sediment


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soon after death or soon after the initial decaying process. The degree to which the remains are

decayed when covered determines the later details of the fossil. Some fossils consist only of

skeletal remains or teeth; other fossils contain traces of skin, feathers or even soft tissues. This is

a form of diagenesis.

B. Casts and molds

In some cases the original remains of the organism have been completely dissolved or otherwise

destroyed. When all that is left is an organism-shaped hole in the rock, it is called an external

mold. If this hole is later filled with other minerals, it is a cast. An endocast or internal moldis

formed when sediments or minerals fill the internal cavity of an organism, such as the inside of a

bivalve or snail or the hollow of a skull.

C. Authigenic mineralisation

This is a special form of cast and mold formation. If the chemistry is right, the organism (or

fragment of organism) can act as a nucleus for the precipitation of minerals such as siderite,

resulting in a nodule forming around it. If this happens rapidly before significant decay to theorganic tissue, very fine three-dimensional morphological detail can be preserved. Nodules from

the Carboniferous Mazon Creek fossil beds of Illinois, USA, are among the best documented

examples of authigenic mineralisation.

D. Replacement and recrystallization

Replacement occurs when the shell, bone or other tissue is replaced with another mineral. In

some cases mineral replacement of the original shell occurs so gradually and at such fine scales

that microstructural features are preserved despite the total loss of original material. A shell is

said to be recrystallizedwhen the original skeletal compounds are still present but in a different

crystal form, as from aragonite to calcite

TYPES OF FOSSILS.

Evidence of animals that lived long ago is preserved in rocks as fossils. Fossils are marks or

material left in rock layers by living things. Fossils are created in several ways. These are some

fossil types:

Mold : hollow impression of a living thing in rock after it

Cast: solid mineral deposit that filled a mold, leaving a copy of the living thing

Imprint: an impression in rock made by a living thing during its life activities

Petrification: plant or animal tissue replaced by minerals

Whole Organism: an entire plant or animal encased and preserved in ice, sap, or another

CALYMATOTHECA HOENINGHAUSII


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PINUS

Kingdom: Plantae

Division: Pinophyta

Class: Pinopsida

Order: Pinales

Family: Pinaceae

Genus: Pinus L.

GENERAL CHARACTERS OF PINUS

Commonly called as Pine

Pines are trees in the genus Pinus from the family Pinaceae.

Monotypic subfamily Pinoideae.

115 species world wide and 6 in India

Native of the Northern Hemisphere.

The Himalaya and Southeast Asia, with one species (Sumatran Pine) just crossing the

Equator in Sumatra to 2S.

In North America, they range from 66N in Canada (Jack Pine) south to 12N inNicaragua (Caribbean Pine).

The highest diversity in the genus occurs in Mexico and California.

Indian Distribution:

The range extends from Northern Pakistan (North-West Frontier Province, Azad

Kashmir), across Northern India (Jammu and Kashmir, Punjab, Himachal Pradesh,

Uttarakhand, Sikkim) and Nepal to Bhutan.

Trees occurs in Himalayan moist temperate and dry temperate forest and found in thealtitude of 2000 mts to 3000 mts.

Includes yellow or hard pines

Habit: It is a strong, light demander, frost hardy, drought resistant and fire resistant

Habitat: Grows well in well - drained porous soil, tertiary sandstone and rainfall zone of 150

300 cms

Appearance: Large evergreen tree with blue colored foliage, branches occurs in the form of

whorls and an evergreen tree growing to 40 mts. The flowers are monoecious and are pollinatedby wind. The Male flower appears in January and mature in Feb April and the Female appears

in Feb.

General discription

Trees or shrubs, aromatic, evergreen;

crown usually conic when young, often rounded or flat-topped with age.

Bark of older stems variously furrowed and plated, plates and/or ridges layered or scaly.

Branches usually in pseudowhorls;


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Shoots dimorphic with long shoots and dwarf shoots;

Dwarf shoots borne in close spirals from axils of scaly bracts and bearing fascicles of leaves

(needles).

Branchlets stout, ending in a compound bud with many bud scales.

Buds ovoid to cylindric, apex pointed (blunt), usually resinous.

Leaves dimorphic, spirally arranged;

Foliage leaves (needles) (1)2-5(6) per fascicle, persisting 2-12 or more years,

Terete or 2-3-angled and rounded on abaxial surface, sessile, sheathed at base by 12-15

overlapping scale leaves,

These (at least firmer basal ones) persisting for life of fascicle or shed after first season

LEAVES OF PINUS

It has Scaly leaves & Needles (Photosynthetic).

1. These range in size from a few mm. to 30 cm.

2. There is only one centrally located vascular bundle in the leaf.

3. However, it is often partitioned into separate strands.

4. The vascular tissue is surrounded by a "transfusion tissue".

5. This is composed ofparenchyma and tracheids. An Endodermis surrounds the vascular

bundle.


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ECOLOGICAL CHARACTERS OF NEEDLE

On the ecological point of view leaves are modifies in the form of scaly and needles. The needles

shows following xerophytic characters

Morphology

1. The needles are sharply pointed and highly reduced in sizes.

2. They are fascicled i.e. arranged in clusters, 3-5 in one group.

3. They are flat and water stress tolerant.

Anatomy

STEM ANATOMY


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Shri Shivaji Science College, Amravati (10 ) B. Sc. II



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CONES

Pines are mostly monoecious, having the male and female cones on the same tree, though a few

species are sub-dioecious with individuals predominantly, but not wholly, single-sex. The male

cones are small, typically 15 cm long, and only present for a short period (usually in spring,

though autumn in a few pines), falling as soon as they have shed their pollen. The female cones

take 1.53 years (depending on species) to mature after pollination, with actual fertilization

delayed one year. At maturity the female cones are 360 cm long. Each cone has numerous

spirally arranged scales, with two seeds on each fertile scale; the scales at the base and tip of the

cone are small and sterile, without seeds. The seeds are mostly small and winged, and are

anemophilous (wind-dispersed), but some are larger and have only a vestigial wing, and are bird-

dispersed (see below). At maturity, the cones usually open to release the seeds. The seeds are

stored in closed ("serotinous") cones for many years until a forest fire kills the parent tree; the

cones are also opened by the heat and the storedseeds are then released in huge numbers to re-

populate the burnt ground.

MALE CONE

Male cone are known as staminate or

micrsporangiate strobilus. Following are main

features

1. Mature earlier than female cones

2. Forms in clusters at the base of long shoots


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3. It consist ofcentral axis of about 5 cms

4. The axis bears number of spirally arranged microsporophylls5. Each microsporophylls is triangular in outline and has a short stalk and a sterile tip. 6. Microsporophylls bears two microsporangia at the base

FEMALE CONE

Female cone are also known as megasporangiate or ovulate strobilus. Following are main

features

1. Mature later than male cones2. Forms singly in the axils of the scaly leaves3. It is hard, woody, reddish to pinkish in colour4. It consist ofcentral axis of about 5 cms5. The axis bears number of spirally arranged

bract scales and ovuliferous scales together

known as Megasporophylls.

6. Ovuliferous scales is stout, woody and ariseson the top portion of the cone.

7. Each Ovuliferous scales (megasporophyll)bears two naked ovules at thebase8. The terminal sterile tip of the megasporophyll is known as apophysis

LIFE CYCLE


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GNETUM.

Kingdom: Plantae

Division: Gnetophyta

Class: Gnetopsida

Order: Gnetales

Family: Gnetaceae

Genus: Gnetum L.

GENERAL CHARECTERISTIC

Native to southeast Asia and the western Pacific Ocean islands,

From Assam south and east through Indonesia and Malaysia to the Philippines and Fiji.

They are sometimes called padi oats or paddy oats.

They are small to medium-size tree,and lianas

Growing to 15-20 m tall.

The leaves are evergreen, opposite, 8-20 cm long and 3-10 cm broad, entire, emerging

bronze-coloured, maturing glossy dark green.

The fruit-like strobilus consist of little but skin and a large nut-like seed 2-4 cm long inside.

Fleshy strobili weigh about 5.5 g, the seed alone 3.8 g. Strobili mature mainly from June toSeptember in NE Philippines. The red strobili are eaten by birds, mammals and reptiles.

The ovule may contain 2-3 archegonia, and the micropyle actually extends as a neck, and

exudes a pollination droplet, sucks in several pollen grains to the pollen chamber.

Pollen germinates to form a pollen tube that grows down the neck of the archegonium, and

one sperm nucleus emerges to fertilize the egg - it is non-motile as in conifers and

angiosperms.

Seed is hard and black, surrounded by red fleshy bracts of megastrobilus.

STEM ANATOMY

Cuticle: Thick, sunken stomata

Epidermis: single layered Rectangular cells

Cortex: 10-15 parenchymatous,

Chlorenchymatous (in Older Sclerenchymatous)

Spicular cells

Endodermis & pericycle not distinct

VB: 20-24 collateral & endarch

Pith: Laticifers


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LEAF

MALE CONE MALE FLOWER

Microsporangium

Stamen (Filament)

Perianth


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FEMALE CONE


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UNIT-III : ANGIOSPERMS :

FLOWER : A MODIFIED SHOOT

A flower is regarded as a modified stem with shortened internodes and bearing, at its nodes,

structures that may be highly modified leaves.[1]

In essence, a flower structure forms on a

modified shoot or axis with an apical meristem that does not grow continuously (growth is

determinate). Flowers may be attached to the plant in a few ways. If the flower has no stem but

forms in the axil of a leaf, it is called sessile. When one flower is produced, the stem holding the

flower is called a peduncle. If the peduncle ends with groups of flowers, each stem that holds a

flower is called a pedicel. The flowering stem forms a terminal end which is called the torus or

receptacle. The parts of a flower are arranged in whorls on the torus. The four main parts or

whorls (starting from the base of the flower or lowest node and working upwards) are as follows:

An example of a "perfect flower", this Crateva religiosa flower has both stamens (outer ring)

and a pistil (center).

Calyx: the outer whorl of sepals; typically these are green, but are petal-like in some

species.

Corolla: the whorl ofpetals, which are usually thin, soft and colored to attract animals

that help the process of pollination. The coloration may extend into the ultraviolet, which

is visible to the compound eyes of insects, but not to the eyes of birds.

Androecium (from Greekandros oikia: man's house): one or two whorls of stamens, each

a filament topped by an anther where pollen is produced. Pollen contains the male

gametes.

Gynoecium (from Greekgynaikos oikia: woman's house): one or more pistils. The femalereproductive organ is the carpel: this contains an ovary with ovules (which contain

female gametes). A pistil may consist of a number of carpels merged together, in which

case there is only one pistil to each flower, or of a single individual carpel (the flower is

then called apocarpous). The sticky tip of the pistil, the stigma, is the receptor of pollen.

The supportive stalk, the style becomes the pathway for pollen tubes to grow from pollen

grains adhering to the stigma, to the ovules, carrying the reproductive material.

MALE SEX ORGAN: ANDROECIUM

Called as a stamen. It has following components

StamenThis is the male part of the flower. It is made up of the filament and

anther, it is the pollen producing part of the plant. The number ofstamen is usually the same as the number of petals.

Anther lobesThis is the part of the stamen that produces and contains pollen.

It is usually on top of a long stalk that looks like a fine hair.

FilamentThis is the fine hair-like stalk that the anther sits on top of.

ConnectiveIt is the connecting point of anther lobes and the filament. Itdetermines the position and the fixation of the anther.


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Anther T. S.

A cross section of the developing anther displays following features

1. The four or two chambers divided from the central part called connective.

2. These chambers are called as anther lobes or pollen sacs. Each pollen sac is filled with

sporogenous cells containing large nuclei.

3. As the anther grows, each of these sporogenous cells transformed into microspore mother

cells and goes through two meiotic divisions, forming a tetrad (four microspores in agroup). These cells are called microspores formed in microsporogenesis.

4. Each one of these microspores eventually becomes a pollen grain in the process called as

microgametogenesis.

5. The walls layers of anther are

a. Each pollen sac is enclosed by a protective epidermis.

b. Temporary 2 3 middle layers adjust the increasing pressure of developing spores.

c. The endothecium isa layer of fibrous, radially elongated cells.

d. Inside the fibrous layer there is the tapetum. This is a physiologically important cellular

layer. It food store and will provide energy for future cell divisions. The cells are big

sized and polyploidy.

e. Sporogenous tissue is centrally located cellular mass resulting in to formation of the

pollen grains at the final stage of anther development.

6. Stomium: The anther lobes are connected with a thin cellular connection. The stomium is

the region of the anther where dehiscence occurs.

TAPETUM

During microsporogenesis, the cells of tapetum provide various enzymes, hormones, amino acids

and other nutritive materials to the dividing microsporocytes. In angiosperms, the cells of

tapetum are of two types

(i) Glandular (or Secretory) tapetum, the cells of which secrete substances and finally

breakdown at the time of pollen maturation, and


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(ii) Periplasmodial (or Amoeboid) tapetum, the cells of which breakdown early by

dissolution of their walls so that the tapetal protoplasts form a multinucleate

periplasmodium which provides nourishment to dividing microspore mother cells or

developing microspores.

The main functions of tapetum are

(a) Transportation of nutrients into anther locule at the time of meiosis in spore mothercells

(b) Secretion of enzymes and hormones,(c) Production ofUbisch bodies which are coated with sporopollenin to cause thickening

of exine,

(d) Secretion of an oily material (pollenkitt) over out-erside of mature pollen, and(e) Secretion of special proteins for pollen to recognise compatibility.

MICROSPOROGENESIS

The development of the microspores from microspore mother cells is called as

microsporogenesis. Following are the sequential events

1. During the development of microsporangium, the cells ofsporogenous tissue may divide in

various planes and finally separate from each other to function as microsporocytes or

microspore mother cells.

2. Some of the microsporocytes degenerate and provide nourishment to others. The surviving

microsporocytes are connected with each other by cytoplasmic interconnections (plas-

modesmata) and have prominent diploid nuclei.

3. Each microsporocyte then develops an internal layer of callose which breaks the

cytoplasmic interconnections with other microsporocytes.

4. The separated microsporocytes then divide by meiosis and give rise tetrads of haploid

microspores by the process called cytokinesis.

MICROGAMETOGENESIS

Microgametogenesis comprises events which lead to the progressive development of the

unicellular microspores into mature microgametophytes (POLLEN GRAINS) containing

the gametes. The events during the process are

1. The expansion of the microspore which is commonly associated with the formation of a

single large vacuole.

2.

Vacuolation is accompanied by the displacement of the microspore nucleus to aneccentric position against the microspore wall.


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3. In this position the nucleus undergoes first pollen mitosis (pollen mitosis I) which results in

the formation of two unequal cells,

A. a large vegetative cell and

B. a small generative cell each containing a haploid nucleus.

4. The generative cell subsequently detaches from the pollen grain wall and is engulfed by the

vegetative cell forming a unique 'cell within a cell' structure.

5. The engulfed generative cell divides once more by mitosis (pollen mitosis II) to form the

two sperm cells completely enclosed within the vegetative cell cytoplasm either before

pollen is shed (tricellular pollen) or within the pollen tube (bicellular pollen).

6. Pollen Stratification(POLLEN GRAIN): The pollen grains are generally globose in shape,

though several other shapes are also found (oval to polyhedral). The term sporoderm is

usually used to designate collectively the two major wall layers

A. The exine, which is the outer layer and chiefly composed of sporopollenin (an organic

polymer that is resistant to oxidation and leaching). In angiosperm pollen grains, theexine is mainly derived from tapetal substances during sporogenesis.

The exine consists of two major layers

a) The outer sexine: The sexine is also made up of two layers

a) The inner endosexine and

b) outer tectum and

b) The inner nexine. The nexine can be further resolved into two layers

a) the inner endexine and

b) outer foot layer.

The exine surface of pollen grains often bear various patterns of microsculptur-ing and

ornamentation. At one or more places, the exine is very thin or absent. These regions are called

apertures through which the pollen tube emerges at the time of germination on stigma.

B. The intine, which is the inner layer and chiefly composed of pecto-cellulose. Intine is

derived from the male gametophyte during the development.


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7. The size and shape of spores and pollen ; exine microsculpturing and the number, position

and characters of apertures are of great taxonomic importance. These are studied under a

separate branch of botany called palynology.

FEMALE SEX ORGAN: GYNOECIUM

Pistil

This is the female part of the flower. It is

made up of the stigma, style, and ovary.

Each pistil is constructed of one to many

rolled leaflike structures. The components

of carpel are as follows

Stigma

One of the female parts of the flower. It is

the sticky bulb that you see in the center of

the flowers, it is the part of the pistil of a

flower which receives the pollen grains and

on which they germinate.

Style

Another female part of the flower. This is the long stalk that the stigma sits on top of.

Ovary

The part of the plant, usually at the bottom of the flower, that has the seeds inside and turns into

the fruit that we eat. The ovary contains ovules.

Ovule

The part of the ovary that becomes the seeds.

OVULE

Ovule literally means "small egg." In seed plants,

the ovule is the structure that gives rise to and

contains the female reproductive cells. It consists of

three parts:

1. The integuments forming its outer layer.

Gymnosperms typically have one integument

layer while angiosperms typically have outer

and inner integuments. The integuments

develop into the seed coat when the ovule

matures after fertilization.

a) The integuments do not enclose the

nucellus completely but leave an

opening at its apex referred to as the micropyle. The micropyle opening allows the

pollen tube to enter the ovule for fertilization.


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b) Located opposite from the micropyle is the chalaza where the nucellus is joined to

the integuments.

c) Nutrients from the plant travel through the phloem of the vascular system to the

funiculus

2. The nucellus (or megasporangium), and

3. The megaspore-derived female gametophyte (or megagametophyte) in its center. The

megagametophyte (also called embryo sac in flowering plants) produces the egg cell for

fertilization. After fertilization, the ovule develops into a seed.

MEGASPOROGENESIS AND MEGAGAMETOGENESIS

The ovule develops as a protruberance of the placental tissue. In young megasporangium a single

cell differentiates as archesporium. It cuts off

some parietal cells and becomes megasporemother cell. The megaspore mother cell

undergoes meiosis to form four haploid

megaspore cells.

In the meantime two integuments develop

from base of the ovule of the four megaspore

cells, three degenerates and one enlarges.

This develops the female gametophyte

(embryo sac). The nucleus of embryo sac

divide mitotically to form eight nuclei (4 ateach pole) one nuclei from each Pole move to

the centre of embryo sac and is called

secondry nuclei. Three nuclei at the base form

antipodal cells while those on the top (at

chalazal end) form egg apparatus having two

synergids and an egg cells.

TYPES OF EMBRYO SACS:

Depending on the number of megaspore contributing in development of embryo sac there are

a) Monosporic Embryo Sac: Only one megaspore of the four formed in meiotic division

will survive and remaining three degenerate

b) Bisporic Embryo Sac: Only two megaspore of the four formed in meiotic division will

survive and remaining two degenerate

c) Trisporic Embryo Sac: All four megaspores participate in embryo sac formation

Monosporic embryo sac is found in two types:

1. Polygonum type: family polygonaceae, eight nucleated sac

2. Oenothera type: family polygonaceae, four nucleated sac


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TYPES OF PLACENTATION

1. Free-cental Placentation

Placenta is in central column within a non-

sectioned ovary.

Ovules are not attached to ovary walls

Compound carpel

2. Apical Placentation

Placenta is at the apex (top) of the ovary.

Ovules are attached to apex of ovary walls

Simple or compound carpel

3. Basal Placentation

The placenta is at the base (bottom) of the

ovary.

Ovules are not attached to base of ovary walls

Simple or compound carpel.

4. Marginal Placentation

There is only one elongated placenta on one side

of the ovary.

This is conspicuous in legumes.

Ovules are attached to one margin of ovary walls

Simple carpel.

5. Axile Placentation

The ovary is sectioned by radial spokes with

placentas in separate locules.

Ovules are attached to infoldings of ovary walls

joining at centre

Compound carpel.


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6. Parietal Placentation The placentas are in the ovary wall within a non-

sectioned ovary.

Ovules are attached to infoldings of ovary walls (notjoining at centre)

Compound carpel.

TYPES OF POLLINATION

The transfer of pollen from the anthers of a flower to the stigma of the same flower or of another

flower. Pollination is a prerequisite for fertilization: the fusion of nuclei from the pollen grain

with nuclei in the ovule.

MODES OF POLLINATION

1. Anemophily: Wind Pollination

Nondirectional & wasteful process

Hit or Miss affair

108 10

Pollens are produced

Small conspicuous flowers

Stigma feathery (Grasses) brush like (Typha) or sticky (Oak)

Organs, Stamens are freely exposed, versatile anthers

Ovule number is reduced

The pollen grains are light, smooth, dry and not easily wetted by rain.

POLLINATIONMechanism

Self Pollination

Autogamy

(same flower)

Geitonogamy

(Diff flowers of the sameplant)

Cross Pollination

Allo / Xenogamy

Abiotic Agencies

1. Anemophily

2. Hydrophily

Biotic Agencies

3. Entomophily4. Ornithophily

5. Cheipterophily


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The flowers are unisexual

Example: Coconut, palm, maize, grasses etc.

3. Hydrophily

a. Ephydrophily: above water

1. The plant is dioecious.

2. On maturity the male flowers get detached from the parent plant and float up

3. At the same time the female flowers also rise

4. The detached male flowers cluster around a floating female flower and dehisce thereby

performing pollination.

5. Soon after the pollination, the long stalks of the female flower begin to coil down to budlevel where the fruit ripens.

b. Hyphydrophily : Below water

1. Hypohydrophily is the true hydrophily

2. Occurs in such plants where the pollen grains are water borne.

3. In Zostera marina, the pollen grains are elongated and lack an exine.

4. The pollen grains float below the surface of water, and on reaching the stigma, coil

around it and germinate.

4. Entamophily

It is the most sure and least wasteful method.

Insects, visit the flowers not to effect pollination but to collect nectar, edible pollen or for

shelter.

As the insect visits a flower, its body gets dusted with pollen grains.

When the loaded insect visits another flower, its body brushes against the stigma and

inadvertently transfers the pollen to it bringing about pollination. E.g., bees, moths,

butterflies

Some of the characteristic features of insect pollinated flowers are:

1. The flowers are large, conspicuous and brightly coloured.

2. When flowers are small, they aggregate in the form of inflorescence.

3. The flowers have a pleasant fragrance and sweet nectar.

4. Pollen grains are usually rough and sticky and often show spinous outgrowths.

5. Ornithophily

Bird pollination is considered as a costly strategy

attract birds, those that exclude insects

protect against nectar theft and pollination mechanisms in the strict sense


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the ovules of bird flowers also tend to have adaptations that protect them from damage

Most bird pollinated flowers are red and have a lot of nectar. They also tend to be

unscented

explosive flowers that shower pollen on a bird that forages near it

6. Cheipterophily

Pollination through the bats. Adaptive features

flowers tend to be large and showy, white or light coloured, open at night and have strong

odours.

They are often large and bell-shaped.

Bats drink the nectar, and these plants typically offer nectar for extended periods of time.

Sight, smell, and echo-location are used to initially find the flowers

Flowers often have sulfur-scented compounds

Bigger pollen than their relatives.

ATTRACTIONS AND REWARDS FOR POLLINATORS

Major kinds of rewards for pollinator are as follows

1. Deception of mating or egg laying sites in the flowers

2. Food value of pollen, nectar and floral parts

3. Nest building material

4. Nutrients: fats, oils, minerals, vitamins, etc.

5. Fragrance

6. Colours

POLLEN-PISTIL INTERACTION.


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DOUBLE FERTILIZATION AND TRIPLE FUSION

During fertilisation in plants, one male gamete fuses with the egg cell and forms the zygote (this

process is called syngamy). The other male gamete fuses with the secondary nucleus (this is

called triple fusion). The syngamy and triple fusion together are called double fertilization. This

phenomenon was studied for the first time S. G. Nawaschin (1898), therefore it is also called as

NAWASCHIN PHENOMENON.

Triple Fusion:

First Tow or more polar nuclei fusion = Secondary nuclei

Second Sperm + Egg = Zygote

Third Sperm + Secondary Nuclei = EMN or Endosperm Mother Nuclei

SGB Amravati University B Sc II Paper IV: Dr. D. D. Khedkar

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Transcript of SGB Amravati University B Sc II Paper IV: Dr. D. D. Khedkar