The Kingdom Plantae

 The Kingdom Plantae

It includes all the eukaryotic multicellular chlorophyllous photosynthetic autotrophs having cell wall made up of primarily of cellulose; zygote retained to become embryo and exhibiting heteromorphic alternation of generation e.g. moss, fern, pine, apple. Plants are adapted to living on land.

Terrestrial Adaptations in Plants: Living on land poses very different problems from living in water and it is a set of structural, chemical and reproductive adaptations for terrestrial living that distinguishes plants from algae.

• Structural Adaptations:

  • Absorption of water and minerals by roots.
  • Stomata for gaseous exchange.

• Chemical Adaptations:

  • Cell wall composed of cellulose.
  • Formation of cuticle to reduce the rate of transpiration.
  • Lignin to harden the cell wall.
  • Sporopollenin, a polymer that is resistant to environmental damages.

• Reproductive Adaptations:

  • Early plants produced their gametes within gametangia.
  • Organs having protective jackets of sterile cells that prevent gametes.
  • Embryo is formed by zygote within female body.

Classification of Plants: An outline of classification of plantae.

• Division 1:

  • Bryophyta (Non-vascular plants)
    • Class: Hepaticae (Liverworts)
    • Class: Musci (Mosses)
    • Class: Anthocerotae (Hornworts)

• Division 2:

• Tracheophyta (Vascular Plants)
• Subdivision: Psilopsida (Psilopsids)
• Subdivision: Lycopsida (Club mosses)
• Subdivision: Sphenopsida (Horse tails)
• Subdivision: Pteropsida (Ferns)
• Subdivision: Spermoside (Seed plants)

Bryophytes: Bryophytes are non-vascular plants showing heteromorphic alternation of generation with dominant gametophytes having amphibious nature. Gametophytes are chlorophyllous, photosynthetic autotrophs having thalloid body or differentiated in rhizoids, pseudostem, and leaves. Sporophytes are semi-parasite on gametophytes having a body differentiated in foot, seta, and capsule.

General Characteristics of Bryophytes:

• Bryophytes grow in humid and shady places. A few of them, for example, Riella, Ricciocarpos are aquatic.
• Vascular tissues i.e., xylem and phloem are absent.
• In most of the cases, plant body is thallus, i.e., not differentiated into root stem and leaves e.g., Marchantia.
• Most of them are small in size, up to 1-2 cm high and the largest is not more than 20cm in height.
• Alternation between externally and internally different sporophytic and gametophytic generations occurs.
• Gametophytic generation is dominant.
• Sporophyte is diploid and depends on gametophyte for nutrition and attachment.
• Instead of roots, rhizoids are present for absorption of soil materials and attachment.
• Reproductive structures are gametangia, male gametangium is called antheridium and female is called archegonium.
• Fertilization takes place inside archegonium.
• Fertilization needs water. So, they are called amphibious plants.

Classification: Bryophytes are classified into three classes. These are:

1. Class Hepaticae Characters:

   • Thallus is lobbed and the lobes resemble the lobes of liver.
   • The dominant generation is gametophyte which is a green, dorsoventrally flattened and dichotomously branched thallus.
   • Vegetative reproduction takes place by gemmae, produced in gemma cup.
   • Sexual reproduction takes place by archegoniophore and antheridiophore i.e., female and male receptacles respectively.
   • Sporophyte is simple, having foot, seta and capsule. Examples include Ricciocarpos, Marchantia, Riccia, etc.

2. Class Musci Characters:

   • Along with most shady places, they may also grow on dry places but water is still necessary for sexual reproduction.
   • Sporophyte consists of foot, seta and capsule.
   • The spores, on germination give rise to a filamentous structure called protonema.
   • Numerous shoots arise from protonema which compose the mature moss plant (gametophyte).
   • Gametophyte consists of pseudostem, leaves, and rhizoids. Examples include Funaria, sphagnum, polytrichum etc.

Class Anthocerotae Characters:

• Plant body is thalloid.
• Thallus is lobbed, dorsiventral and with or without midrib.
• Gametophyte is matlike.
• Sporophyte consists of long capsule resembling horns. Sporophyte has stomata and its cells can use their chloroplasts for photosynthesis.
• Sporophyte contains meristem due to which it can survive even after the death of gametophyte. Examples include anthoceros, Mequaceros etc.

Land Adaptations in Plants:

Rhizoids for Water Absorption: To absorb water from soil, the earliest land plants i.e., Bryophytes developed filamentous extension from the cells of lower epidermis. These extensions are called rhizoids.

Conservation of Water by Cuticle: Direct sunlight may cause death of plant by excess evaporation, but this problem has been solved by waxy cuticle over the exposed parts of land plants, as it limits evaporation.

Absorption of CO₂ by Aerating Pores: Water plants exchange gases with surrounding water. Early land plants have pores called aerating pores in their epidermis that allows CO₂ to move inside air chambers and finally to the wet surfaces of photosynthetic cells in air chambers and diffuse into cytoplasm.

Heterogamy: It is the production of two different types of gametes, one is male (motile) and the other is female (non-motile). Heterogamy increases the chances of fertilization and successful reproduction.

Protection of Reproductive Structures: In bryophytes, the male and female reproductive cells are well-protected inside antheridium and archegonium respectively. Moreover, they have hair-like structures called paraphyses that prevent drying of sex organs.

Formation and Protection of Embryo: Land plants observe an embryo stage i.e., the zygote divides to form an embryo, and for protection, the embryo is retained inside the archegonium.

Life Cycle of Bryophytes / Moss / Funaria: The life cycle shows heteromorphic alternation of generations with gametophyte as the dominant generation. The life cycle is completed into two stages:

Gametophytic Stage: The gametophyte is haploid, consisting of rhizoids, pseudostem, and leaves. In this phase, male and female reproductive organs are produced, antheridia (male) and archegonia (female).

The Antheridia:

• The antheridia are club-shaped. Each antheridium is surrounded by an outer jacket layer. Inside the antheridium, antherozoid mother cells or androcytes are produced. They divide and re-divide to form motile biflagellate antherozoids (male gametes) or spermatozoids.

The Archegonia:

• Each archegonium is flask-shaped. It consists of a stalk, venter, and neck. The stalk helps in the attachment of the archegonium. The venter is the middle swollen part. It contains a large egg cell and a smaller venter canal cell. The neck is the upper elongated tube-like part. It contains neck-canal cells.

Fertilization:

• The motile spermatozoids move toward the archegonium in the presence of water. They enter the archegonium through its open mouth, and one spermatozoid fuses with the egg cell, with the result that the zygote (2n) is formed.

Sporophytic Stage:

• The zygote develops into a sporophyte. The venter wall enlarges to form the protective layer around the embryo, called the calyptra. The sporophyte grows upon the gametophyte; it depends partially or completely for its nourishment upon the tissues of the gametophyte. The sporophyte consists of three parts: foot, seta, and capsule. The foot helps in the attachment of the sporophyte and in the absorption of food from the tissues of the gametophyte. The seta is the stalk of the capsule. The capsule produces spore-mother cells. They are diploid (2n); they divide by meiosis and form haploid (n) spores. Each spore can germinate into a new gametophyte during favorable conditions.

Tracheophytes: The Vascular Plants: Major Groups of Vascular Plants:

• Subdivision: Psilopsida (Psilopsids)
• Subdivision: Lycopsida (Club mosses)
• Subdivision: Sphenopsida (Horse tails)
• Subdivision: Pteropsida (Ferns)
• Subdivision: Spermospsida (Seed plants)

Psilopsida, Lycopsida, Sphenopsida, Pteropsida are non-flowering plants collectively called Pteridophyta. Spermospsida have flowers and seeds collectively called spermatophyte. Spermospsida are further divided into gymnosperms and angiosperms. Tracheophytes possess four important characters:

1. A protective layer of sterile jacket cells around the reproductive organs.
2. Multicellular embryos retained within the archegonia.
3. Cuticle
4. Xylem

Psilopsida:
Rhynia:
External Features of Rhynia:

• Rhynia is one of the most primitive vascular plants. It is a fossil which became extinct in the Devonian period. As the genus has been derived from the place Rhynia situated in Scotland, and therefore it is named after the name of the place of its origin and known as Rhynia. Till now only two species of Rhynia named as Rhynia major and R. gwynne-vaughani have been described.

Systemic Position Pteridophyta:

• Division - Psilophyta

• Class - Psilophytopsidae

• Order - Psilophytales

• Family - Rhyniaceae

• Genus - Rhynia

• They were herbaceous plants.

• The plant body consisted of dichotomously branched horizontal rhizome and the erect, aerial dichotomously branched stem.

• The aerial branches were leafless shoots.

• The rhizoids were present in patches on the underside of the rhizome.

• The aerial branches were naked, leafless, cylindrical, dichotomously forked, and tapering at their apices.

• The terminal, elongated sporangia were found on the tapering vegetative apices. Sporangia contain spores.

• The main plant is sporophyte.

The Internal Anatomy of Rhynia:

• The internal structure of the rhizome and aerial stem was quite similar to each other. This was differentiated into epidermis, cortex, and stele.
• Epidermis:
• The epidermis was one cell in thickness with thick outer wall and cuticle on the outer side.
• The aerial stems bore the stomata on the epidermis.

Cortex:

• The cortex consists of two zones (a) the outer cortex and (b) the inner cortex.

Stele:

• The central xylem core was completely surrounded by a phloem layer four or five cell in thickness. The xylem consists of tracheids only. The phloem consists of elongated thin-walled cells with oblique end walls.

Evolution of Leaf in Vascular Plants:

• The primitive vascular plants lacked leaves in contrast to the present-day advanced ones. When the advanced plants evolved from their primitive ancestors, there occurred evolution of leaf, besides other changes.

Types of Leaves:

• In vascular plants leaves are of two types. One type is small, scale-like with a single vein (vascular bundle) and is hence called one-veined leaf or microphyllous leaf as found in club-mosses and horse-tails. The second type has a large blade having two or more veins. It is called many-veined leaf or megaphyllous leaf as found in many plants.

Evolution of One Veined Leaf:

• The fossil record does not help us to understand the evolution of one-veined leaf. Hence two possibilities have been put forth. One possibility is that it originated as a small outgrowth from the branches of the primitive ancestral plant. With an increase in size vascular tissue (a vein) was supplied for support and conduction of water. The second possibility is that it originated by a reduction in size of a part of a leafless branching system of the primitive vascular plant.

Evolution of Many Veined Leaf:

• Many-veined leaves have evolved from the forked branching system of the primitive vascular plants. This is evident from the study of fossil plants living in Devonian and Carboniferous periods. In the first step, the branches were brought in a single plane. Consequently, the branching system became flat. This is known as planation. Then the spaces between the branches became filled with photosynthetic tissue. This is called webbing because the leaf looked superficially like the webbed foot of a duck. The leaves of the majority of vascular plants had their evolutionary origin from a branching system of this kind.

Lycopsida: (The Club Mosses):

• The first representative of Lycopsida appeared in the middle of the Devonian period, almost 10 million years after the first psilopsids. During the late Devonian and the Carboniferous periods, these were among the dominant plants on land. Some of them were very large trees that formed the earth’s first forests. Toward the end of the Paleozoic era, however, the group was displaced by more advanced types of vascular plants, and only five genera are alive today. Two of these, Selaginella and Lycopodium (often called running pine or ground pine), are common in many parts of Pakistan.

Unlike the Psilopsids, Lycopsids have true roots. It is generally supposed that these arose from branches of the ancestral algae that penetrated soil and branched underground. Lycopsids also have true leaves, which are thought to have arisen as simple scale-like outgrowths (emergence) from the outer tissue of the stem. Certain of the leaves that become specialized for reproduction bear sporangia on their surfaces. Such reproductive (fertile) leaves are called sporophylls. In many Lycopsids, the sporophylls are congregated on a short length of stem and a cone-like structure (strobilus). The cone is rather club-shaped; hence the name "Club Mosses" for the Lycopsids, though Lycopsids are not related to the true mosses, which are bryophytes.

The spores produced by Lycopodium are all alike, and each can give rise to a gametophyte that will bear both archegonia and antheridia. However, some lycopsids (e.g., Selaginella) have two types of sporangia, which produce different kinds of spores. One type of sporangium produces very large spores called megaspores, which develop in female gametophytes bearing archegonia; the other type produces small spores called microspores, which develop into male gametophytes bearing antheridia. Plants like Lycopodium that produce only one kind of spore, and hence have only one kind of gametophyte that bears both male and female organs, are said to be homosporous. Plants like Selaginella that produce both megaspores (female) and microspores (male), i.e., in which the sexes are separate in the gametophyte generation, are said to be heterosporous.

Evolution of Seed: There are three steps in the evolution of seed:

1. Origin of heterospory
2. Development of integument for the protection of megasporangia
3. Retention of the mature megaspores in the sporangia to develop female gametophyte.

Development of Heterospory: The seedless green land plants such as the nonvascular plants and primitive vascular plants (Club mosses, Horsetails, Ferns) are homosporous, i.e., all the spores of a species are similar in size, structure, and function. The spores grow into similar bisexual gametophytes. On the other hand, the seed plants (Pines, their relatives, and flowering plants) are heterosporous. They produce two kinds of spores, viz., the microspores and megaspores. The former grow into male gametophytes and the latter into female gametophytes. The two different kinds of spores are produced in two kinds of sporangia, the micro and the megasporangia.

Formation Of Integuments Around The Megasporangium: During the course of evolution, the megasporangia became surrounded by protective envelopes. Some of the fern-like plants from amongst the fossils of the carboniferous period (280 - 350 million years ago) have been found to bear seed-like structures. Each of their megasporangia containing one or more megaspores was surrounded by branch-like outgrowths from the sporophyte. During evolution, these branches became fused around the megasporangium to form an integument (covering).

Retention Of Megaspore In The Sporangium: The megaspore of seed plants, unlike that of seedless plants, is retained and protected inside the integumented megasporangium where it grows into a small female gametophyte. The integumented megasporangium in which megaspore is retained is called an ovule (immature seed). Besides providing the protective covering of integuments, the ovule contains a large amount of stored food which is utilized for the production of new offspring when the seed matures and germinates. Seed production is one of the important characters that better adapts the vascular plants to their environment and makes them the predominant form of vegetation on the earth.

Sphenopsida: (The Horse Tails) The Sphenopsids first appeared in the fossil record late in the Devonian period. They became a major component of the land flora during the carboniferous period and then declined. Members of the lone living genus, Equisetum, are commonly called horse tails. Though most of these are small (less than one meter), some of the ancient sphenopsids were large trees. Much of the coal we use today was formed from the dead bodies of these plants. Like the lycopsids, sphenopsids possess true roots, stems, and leaves. The stems are hollow and are jointed. Whorls of leaves occur at each joint. Many of the extinct sphenopsids had cambium and hence secondary growth, but the modern species do not. Spores are borne in terminal cones (strobili). In Equisetum all spores are alike (i.e., the plants are homosporous) and give rise to small gametophytes that bear both archegonia and antheridia (i.e., the sexes are non-separate) e.g., Sphenophyllum.

Pteropsida: (The Ferns) The dominant plants of pteropsida are generally known as ferns. It is found all over the world. They usually grow in wet and shady places, some fern grow in land and some are grow in water.

Life Cycle Of Fern: The life cycle of fern shows the heteromorphic alternation of generation in which sporophyte-plant is dominant. All the fern are homosporous because they produce the same spores. The life cycle is completed in two phases.

• Sporophyte phase.
• Gametophyte phase.

Sporophyte Phase: The sporophyte of fern is the dominant plant. It is diploid (2n) and performs asexual reproduction. The sporophyte plant consists of the following parts.

• Root:
  Fern has an adventitious root that arises from the stem.

• Stem:
  Fern has an underground stem called rhizome, but some have an aerial stem.

• Leaf:
  Fern has both simple and pinnately compound leaves. Leaves are large in size and known as megaphyll.

Asexual Reproduction in Fern: Asexual reproduction takes place by means of haploid spores produced by meiosis inside the sporangium. During reproduction, a number of sporangia develop inside a single sorus. The sori are green but, when ripe, they become dark brown. The leaves bearing sori are called sporophyll. Sorus is surrounded by a protective layer called indusium.

Structure of Sporangium: Each sporangium consists of a stalk called sporangiophore and a biconvex capsule. The wall of the capsule is composed of two cell layers.

• Annulus:
  It is a thick outer layer.

• Stomium:
  It is a thin inner layer. The capsule contains a mother spore cell, which produces four haploid spores by meiosis. These spores are liberated through stomium. The spores are germinated and produce a bisexual gametophyte called prothallus.

Gametophyte Phase: The fern prothallus is short-lived, independent, autotrophic, heart-shaped, dorsoventrally flattened, lying prostrate on some wet substratum. It is not more than 1 cm in size.

• Rhizoid:
  It is a thread-like structure that arises from the lower end of the prothallus. It fixes the prothallus with the soil and helps in the absorption of water and nutrients. The prothallus is monoecious, having archegonia and antheridia on the same prothallus.

Structure of Archegonia: Each archegonium is flask-shaped and consists of two parts. The upper part is tube-like and known as the neck, while the lower part is swollen and called the venter. The venter contains a cell called the egg cell, known as the female gamete.

Structure of Antheridia: Antheridium is a rounded or oval-shaped structure and grows near the rhizoid. They produce a number of cells called antherozoides. Antherozoides produce ciliated male gametes called sperm.

Fertilization: Sperms move by chemotactic movement in water and reach the archegonium. Only one sperm fuses with the ovum to form an oospore (zygote), which is diploid.

Germination of Oospore: Oospore germinates into a young diploid sporophyte within the gametophyte. The prothallus of the fern is degenerated, and in this way, the life cycle is completed.

Subdivision Spermospsida: (Seeded Plants)

• Late Devonian plant.

• Herb, shrub, or trees.

• The gametophyte is even more reduced than ferns.

• Gametophyte is not photosynthetic or free-living.

• Sperms are not independent, free-swimming, or flagellated.

• Embryo is with rich food and enclosed in a seed (with a resistant seed coat).

• Divide into two groups:

• Gymnospermae (naked seed plants), e.g., Pinus, cycads, ginkgo.
• Angiospermae (fruit-enclosed seed), e.g., Monocots and dicots.

The Gymnosperms: (Gymnos = Naked; Sperma = Seed)
They have naked seeds because ovules are not covered by ovary. The first gymnosperms appeared in the fossil record in the late Devonian, some 350 million years ago. Many of those first seed plants had bodies that closely resembled the ferns, and indeed for many years their fossils were thought to be fossils of ferns. Slowly, however, evidence accumulated that some of the ‘ferns’ that were such important components of the coal-age forests produced seeds, not spores. Today these fossil plants, usually called the seed ferns, are grouped together as the class Pteridospermae of the subdivision Spermospsida. No members of this class survive today.

Pinus:
Pinus belongs to the group Gymnosperms. It is a long erect and evergreen tree consisting of three parts.

• Root
• Stem
• Leaf

It has a tap root. Stem produces two types of branches. One is long shoots, and the other is dwarf shoots, called Spur. The leaves are also of two types:

• Scaly leaves
• Foliage leaves (needle)

Scaly Leaves:
These are small scale-like leaves produced on long shoots at an early stage for protection. After that, they fall on the ground.

Foliage Leaves:
These leaves are produced on dwarf shoots. They are long needle-like, so-called needles. They are green in color and manufacture food material.

Life Cycle of Pinus:
The life cycle of the Pinus plant is completed in two stages. The first stage is called the sporophyte, and the second stage is known as the gametophyte. It shows heteromorphic alternation of generations.

Sporophyte Stage:
In this stage, asexual reproduction takes place. In this process, two types of cone-like structures are formed, called cones or strobili. They are produced on separate branches of the same plant. These cones are as follows:

• Staminate cone (Male cone)

• Ovulate cone (Female cone)

• Staminate Cone: (Male Cone)
  It is a small cone. Its size is less than 3 cm. Each cone consists of a central axis. From its both sides, spiral-shaped scales are developed.

called microsporophylls.
On the inner side of each scale, two microsporangia are present. In each microsporangium, numerous microspores are produced by meiosis. Each microspore consists of two layers, the outer layer is called exine and the inner one is known as intine. Exine layer is changed into two wing-like structures, by the help of which they are migrated to the ovulate cone by the agency of wind.

Ovulate Cone: (Female Cone)
It consists of a central axis. Round the axis, many thin, brownish scales are produced,
which are spirally arranged. They are called carpellary scales or bract scales. At the upper side of each carpellary scale, a large, hard, and woody scale is present, known as ovuliferous scale. It produces two ovules on the inner side. Each ovule consists of a central body, called nucellus or megasporangium. It is surrounded by an outer layer, called integument, which consists of two or three layers. These layers are arranged in such a manner that an opening is formed at the lower side known as micropyle, through which pollen tube enters the ovule in the nucellus or megasporangium. A megaspore-mother cell is produced which forms four megaspores by meiosis. Only one megaspore is functional, while others become degenerated. Megaspore takes part in the formation of the female gametophyte.

Gametophyte Stage:
In pinus, microspore forms male gametophyte and megaspore develops into female gametophyte.

Male Gametophyte:
Microspore starts its germination when it is still present in the microsporangium.

It forms male gametophyte, which is much reduced in size. The nucleus of microspore divides into two or three prothallus cells and an antheridial cell. The antheridial cell again divides into two cells, one is generative cell and another is tube cell. In this way a reduced male gametophyte is formed. After these changes the microspore (pollen grain) is migrated to the ovulate cone by wind.

Female Gametophyte:
Female gametophyte is formed by the germination of megaspore in the nucellus. In the nucellus, the megaspore increases in size. It forms a solid mass of tissues by nuclear division; this is the female gametophyte or prothallus. At the micropylar end of female gametophyte, 2 to 5 reproductive organs are produced, called archegonia. Each archegonium consists of two parts, lower venter and upper neck. In the venter, a large egg cell or female gamete is present, which takes part in fertilization.

Pollination And Fertilization:
Pollination takes place by wind. When the pollen grains reach the ovulate cone, they pass between the open scales and through micropyle reach at the base of nucellus. The outer layer.

exine of pollen grain bursts and inner layer inline germinates into a tube, called pollen tube. The generative-cell divides into two, one is stalk cell and another is body cell. They are migrated into the pollen tube, stalk cell is inactive and body cell divides into two male gamete. The pollen tube passes through the nucellus and finally reaches the neck of archegonium, where it bursts and one of the male gametes fuses with the egg cell to form zygote. It develops into embryo and ovule develops into seed. The part which provides food material to the embryo is called endosperm. After certain changes and development, many leaf like cotyledons, epicotyls and hypocotyl are produced and a complete seed is formed. The seed can germinate into a new plant during favorable conditions.

The Angiosperm:

• They have their seeds enclosed in fruit because ovules are covered by ovary.
• These plants became dominant land flora of the Cenozoic era.
• Flowers are the reproductive structure.
• Their vascular tissue is more complex than that of the gymnosperms.

Structure Of Typical Flower: The flower is borne at the node or apex of the branch (or stem) usually in the axil of small, leaf-like structure known as the bract. A typical flower consists of the following parts:

Axis Of The Flower: The axis consists of a stalk, the pedicel which is enlarged at its tip into a rounded, conical or flat structure, the Thalamus or Receptacle or Torus. The thalamus bears on it, the floral leaves usually arranged in four whorls or circles.

• Calyx:
  It is the outermost whorl of the flower and consists of small, usually green floral leaves, the sepals which enclose other floral parts in the bud condition.

• Corolla:
  It is the second whorl consisting of large and brightly colored floral leaves, the petals which serve to attract the insects for pollination.

Note: In some flowers such as Onion and Asphodel there is no distinction in color between the calyx and corolla. In such a case both these whorls are together known as Perianth and their floral leaves as perianthine leaves.

Androecium: This is the third whorl consisting of small rod-shaped floral leaves, the Stamens which are the male organs of the flower. The androecium may, therefore, also be called Male Whorl. Each stamen is made of slender stalk, the Filament which bears at its tip a swollen structure, the Anther. The anther usually consists of two anther lobes which contain innumerable small cells known as the pollen grains.

Gynoecium Or Pistil: This is the fourth or innermost (central) whorl which consists of flask-shaped floral leaves, gynoecium may also be called “female whorl”. Each carpel comprises a basal swollen part, the ovary which contains ovules; a long tube or rod, the style that ends in a slightly enlarged tip, the stigma which receives pollen grains during pollination. The calyx and corolla are regarded as non-essential (accessory) parts of the flower while the androecium and gynoecium are called as the Essential parts, because these produce gametes.

Life Cycle Of An Angiosperm: Like all the other vascular plants, angiosperms show an “alternation of generations”. The mature plant with root, stem and leaves is the sporophyte. It produces two kinds of haploid spores viz., the pollen grains or microspores in the anthers of the stamens and the megaspores in the ovules contained in the pistil. The anther of the male organ (the stamen) usually consists of four elongated pollen sacs (microsporangia) containing numerous pollen grains (microspores). In the beginning each pollen grain is uninucleate. Later, its nucleus divides to produce two nuclei, a generative and a vegetative nucleus. At this stage, pollen sacs burst and the pollen grains are set free. The pollen grains are carried to the stigma by wind, water or insects. This transfer of pollen to the stigma is called pollination.

On the stigma, each pollen grain grows into a long, slender, thin-walled pollen tube. The growth of the pollen tube is stimulated by a sticky fluid rich in sugar and other substances which is secreted by the stigma. The pollen tube grows down through the style to the ovary until it pierces through an ovule. During this period both the nuclei of the pollen grain enter the pollen tube where generative nucleus divides to produce two elongated sperms. The vegetative nucleus now lies near the tip of the pollen tube, followed by the sperms. The pollen tube consisting of three cells is the male gametophyte. The ovary of the female organ may contain one, two or many egg-shaped (oval) ovules. Each ovule is borne on a stalk and is surrounded by one or two protective coats known as the integuments. The ovule contains a megaspore mother cell which through meiotic divisions forms four monoploid megaspores, of which three disintegrate. The remaining one produces by mitosis, an embryo sac filled with water and food. The embryo sac is actually female gametophyte consisting of seven cells, of which two are"One containing two polar nuclei lies in the center of the embryo sac while the other, the egg, is situated near the entrance of the pollen tube.

When the pollen tube enters the embryo sac its tip ruptures releasing the two sperms, of which one fuses with the egg to form a zygote. The zygote later develops into an embryonic plant within the ovule. By this time the two polar nuclei combine to form a fusion nucleus which is fertilized by the second sperm. Fertilization of the fusion nucleus stimulates the formation of triploid endosperm in which food is stored as the development of the ovule proceeds. The union of one sperm with the egg and the other with the fusion nucleus is called “double fertilization,” which is a characteristic of flowering plants only. It was discovered by Nawaschin in 1905."

This includes the text describing the process of double fertilization, a defining feature of angiosperms, where one sperm fertilizes the egg to form a zygote, and the other fertilizes the polar nuclei to form the endosperm, providing nourishment to the developing embryo.

Formation Of Fruit And Seed: After fertilization, the ovary develops into the fruit and the ovules into the seeds. Each ovule increases in size due to the formation of endosperm tissue and the embryo. The embryo consists of one or two cotyledons, an epicotyl, and hypocotyl. Both the epi-and hypocotyl are parts of the axis of embryo which is attached to the cotyledons. The cotyledons of some plants such as pea, gram, beans, etc., digest, absorb, and store the food from the endosperm as the ovule matures into a seed. Consequently, the cotyledons become thick and fleshy, and the endosperm disappears more or less completely. In many other plants, the endosperm exists as such when the ovule forms the seed, as in castor oil and the cereals. Further, changes occur in the ovule as it develops into the seed. For example, the integuments of the ovule form the seed coat, which may be tough in many seeds and serves to protect the embryo from injury. At this stage, all the parts of the flower are lost except the ovary, which enlarges rapidly and gives rise to the fruit containing the seeds. The fruits may be dry as the nuts and grains or fleshy such as mangoes, melons, tomatoes, peach, etc. In some plants, fruits are formed without fertilization, as in bananas and grapes. Such fruits are called parthenocarpic fruits, which lack seeds.

Spermospida As Successful Group Of Land Plants: Having studied representatives of the major groups of land plants, we can return to consider why the conifers and angiosperms are so well adapted to life on land. Their major advantage over other plants is related to their reproduction. Here they are better adapted in three important ways.

• The gametophyte generation is much reduced. It is always protected inside sporophyte tissue, on which it is totally dependent. In mosses and liverworts, where the gametophyte is conspicuous and in ferns, where it is a free-living prothallus, the gametophyte is susceptible to drying out.
• Fertilization is not dependent on water as it is in other plant groups, where sperms swim to the ovum. The male gametes of seed plants are non-motile and are carried within pollen grains that are suited for dispersal by wind or insect. Final transfer of the male gametes after pollination is by means of pollen tubes, the ova being enclosed within ovules.
• Conifers and flowering plants produce seeds. Development of seeds is made possible by the retention of ovules and their contents on the parent sporophyte. Other ways in which spermatophytes are adapted to life on land are summarized below.
  • Xylem and sclerenchyma are lignified tissues providing support in all vascular plants. Many of these show secondary growth with deposition of large amounts of wood (secondary xylem). Such plants become trees or shrubs.
  • True roots, also associated with vascular plants, absorb soil water efficiently.
  • The plant is protected from desiccation by an epidermis with waterproof cuticle, or by cork after secondary thickening takes place in dicot stems.
  • The epidermis of aerial parts, particularly leaves, is perforated by stomata, allowing gaseous exchange between plant and atmosphere.
  • Plants show many other adaptations to hot, dry environments.

ROSACEAE (ROSE FAMILY): It has about 100 genera and 2000 species. 213 species belonging to 29 genera have been reported from Pakistan.

Distinguishing Characters: Mostly actinomorphic, bisexual, Hypogynous to epigynous, Gamosepalous or polysepalous, polypetalous.

Floral Characters:

• Inflorescence: solitary, axillary, racemose, and cymose cluster.
• Flower: bisexual, pedicellate, complete actinomorphic, hypogynous to epigynous.
• Calyx: 5 sepals is, gamosepalo or polysepalo united at the base, usually green and hairy.
• Corolla: 5 petals or numerous in multiple of 5 free imbricate, rosaceous.
• Androecium: stamens numerous, sometimes 5 or 10, bend inward in bud stage, anther small and bilocular.
• Gynoecium: A simple pistil of 1 to numerous carpels or 2 to 5 carpels, ovary superior, ovules 2 or many, placentation axile, style long, stigma spathulate.

Floral Formula:
⊕, K_(5) or 5, C_5 or (5), A_∞ G_1 or (2 - 5) or ∞

(Includes Floral diagram)

Examples:

Botanical Names	Common Names
Malva silvestis / Pyrus malus	Apple
Rosa indica	Rose
Pynis pyrifolia / communis	Pear
Prunus persica	Peach
Prunus amygdalus	Almond

Economic Importance:

• Ornamental Use:
  The members of this family are very important in temperate regions for ornamentals. They rank third in commercial importance in the temperate zone among the family of flowering. E.g., Rosa indica (rose).

• Vegetative Use:
  The members of this family are also very important for vegetative purposes or as a fruit.

• Pyrus malus
• Pyrus pyrifolia
• Prunus persica
• Prunus amygdalus

Medicinal Use:
The rose-water (arq-gulab) is used for eye disease.

Commercial / Industrial Use:
In Asian countries, the petals of roses usually called "gulab," are used to make "gulkand." The petals of roses are also used for the extraction of essential oil (rose oil), used in perfumes. The branch of Crataegus and Cotoneaster provides excellent walking sticks, and wood. The wood of Pyrus pastia is used for making "tobacco pipes."

Family Solanaceae (Potato Family):
The common example of this family is the potato or tuber Solanum. Due to this reason, it is called the "potato family."

• Occurrence:
  It has about 2000 species belonging to 90 genera that are found growing in the tropical and temperate regions. 52 species belonging to 52 genera are found in Pakistan.

• Distinguishing Characters:
  Actinomorphic, bisexual, pentamerous, hypogynous, syncarpous, gamosepalous, fruit berry capsule.

• General Characters:
  Habitat: herbs, shrubs, rarely trees, cultivated.

Floral Characters:

• Inflorescence: Cymose inflorescence, typically an axillary cyme.
• Flower: Actinomorphic, pentamerous, complete, pedicellate, bisexual.
• Calyx: 5 sepals, gamosepalous, inferior, green, campanulate, valvate.
• Corolla: 5 petals, gamopetalous, inferior valvate.
• Androecium: 5 stamens, polyandrous, epipetalous, filament long but unequal in length.
• Gynoecium: Bicarpellary, syncarpous, hypogynous, many ovules.
• Placentation: Axile placentation.
• Fruit: Capsule, berry.

Floral Formula:
⊕, K_(5), C_(5), A_(5), G_(2)

(Includes Floral Diagram)

Example:

Botanical Names	Common Names
Solanum tuberosum	Potato
Solanum melongena	Brinjal
Datura alba	Thorn apple
Petunia alba	Petunia
Lycopersicum esculentum	Tomato
Capsicum annum	Red pepper
Nicotiana tobaccum	Tobacco
Cestrum nocturnum	Lady of night

Economic Importance:

• Medicinal Use:

  • Atropa belladonna (atropine)
  • Atropine is used for wound healing.
  • Datura stramonium is used in “kidney dialysis.”

• Ornamental Use:

  • Petunia alba is used as an ornamental plant.

• Vegetative Use:

  • Few members of the family Solanaceae are used for vegetative purposes. For example:
    • Solanum tuberosum (potato)
    • Solanum melongena (brinjal)
    • Lycopersicum esculentum (tomato)
    • Capsicum annum (red pepper)
    • Physalis peruviana (raspberry)

• Industrial Use:

  • Withenia coagulans is used in “milk coagulation.”
  • Nicotinia tobaccum is used in “tobacco.”

Family Fabaceae (Pea Family):

• Introduction:
  It is also called the pea family.

• Occurrence:
  It has about 9000 species belonging to 400 genera, distributed in all parts of the world. 587 species of 82 genera have been reported from Pakistan.

• Distinguishing Characters:
  Zygomorphic, gamosepalous, valvate, vexillary, monocarpellary, hypogynous, placentation, marginal, diadelphous.

Fruit:

• Legume.

General Characters:

• Habit: herbs, shrubs, cultivated, or may be wild.

Floral Characters:

• Inflorescence: racemose or solitary, axillary.
• Flower: pedicellate, complete, zygomorphic, bisexual, pentamerous, bracteates, papilionaceous or perigynous.
• Calyx: 5 sepals, gamosepalous, inferior, valvate, green.
• Corolla: 5 petals, polypetalous, vexillary, papilionaceous (the odd outer petal is large, called Standard or Vaxillum, two lateral ones free called wings and two innermost fused called keel or Carina).
• Androecium: 10 stamens, diadelphous, 9 fused, 1 free, inferior.
• Gynoecium: syncarpous, marginal, unilocular, bent at the base, flattened and hairy, stigma simple, ovary superior.

Floral Formula: $\oplus, K_{(5)}, C_{1+2+(2)}, A_{(9)+1}, G_1$

Floral Diagram: [Floral Diagram Image]

Examples:

Botanical Names	Common Names
Lathyrus odoratus	Sweet-pea
Archis hypogea	Pea-nut
Sesbania aegyptica	Sesbania
Pisum sativum	Edible - pea
Cicer arietinum	Gram
Datherigia sissor	Red - wood

Economic Importance:

• Source of Protein:
• All plants in this family are a good source of oil and protein because all types of grains are found in it, e.g.
• Pisum sativum (edible - pea)
• Archis hypogea (pea - nut)

Source Of Food: All plants in this family are also used as a food. E.g.

• Cicer arietinum (gram)
• Pisum sativum (edible - pea)
• Lens esculapta (massor)
• Phaseolus aureus (mung/moong)

Vegetative Use:

• Phaseolus moong (mash)
• Phaseolus vulgaris (kidney bean)

As a Fodder:

• Medicago sativa is one of the best fodders for horses.

Source Of Oil:

• The seeds of Archis hypogea (peanut) are edible and also used for the extraction of oil.

Medicinal Use: Most of the plants of this family are used as medicine. E.g.

• Glycyrrhiza glabra (cough and cold)
• Clitoria ternatea (snake bite)
• Abrus precatorius (white and red seeds) - used by jeweler as a weight called "ratti."

Ornamental Use: Some are also used as ornamental plants:

• Clitoria ternatea
• Sesbania sesban
• Lathyrus odoratus

All these are used as ornamental plants.

Source Of Dye:

• Indigo dyes are obtained from Indigofera tinctoria (neel).
• Butea monosperma is obtained from flowers and used as a yellow dye.

FAMILY MIMOSACEAE: (ACACIA FAMILY)

Introduction:

• Family Mimosaceae is also called "family acacia."

Occurrence:

• It has about 3000 species belonging to 56 genera found growing all over the world. 49 species of 11 genera have been reported from Pakistan.

Distinguishing Characters:

• Actinomorphic, gamosepalous, polypetalous or gamopetalous, valvet, monocarpellary, hypogynous, marginal, polyandrous, monoadelphous, lorrentum.

Floral Characters:

• Inflorescence: Spike-like a head, umbel, rarely racemose.
• Flower: Actinomorphic, bisexual, hypogynous.
• Calyx: 5 sepals, gamosepalous, imbricate or valvate, mostly green tubular shaped.
• Corolla: 5 petals, valvate, gamopetalous, hypogynous, slightly perigynous, lobed shaped.
• Androecium: 5 or 4 stamens, 10 stamens or infinite stamens, polyandrous, monoadelphous; arises from the base of corolla, anther versatile, often crown-shaped by the deciduous glands.
• Gynoecium: Monocarpellary, unilocular, ovary superior, many ovules, marginal, style long, stigma terminal or minute.

Floral Formula: $\text{BR, ⊕, } K_{(5)}, C_{(5)} \text{ or } (5), A_x \text{ or } 10 \text{ or } 4 \, G_1$

Floral Diagram: (An illustrated floral diagram is shown here)

Examples:

Botanical Names	Common Names
Acacia	Gumtree, baldbule, kikar
Mimosa pudica	Touch-me-not
Albizzia lebbek	Sivs
Prosopis glandulosa	Prosopis, devi
Acacia chatechu	Kath a plant

Economic Importance:

Source Of Wood:

• Many trees provide wood for fuel and furniture.
  • Acacia nilotica
  • Xylia
  • Albizzia lebbek

Source Of Dye:

• Some plants of this family are used as dye.
• Acacia chatechu

Purification Of Blood: The leaves of Acacia nilotica are used for blood purification.

Ornamental Use: Some plants are used as ornamental plants.

• Mimosa pudica

Family Caesalpiniaceae: (Casia Family)

Introduction: It has 2300 species belonging to 152 genera found growing worldwide. 60 species belonging to 16 genera have been reported from Pakistan.

Distinguishing Characters: Zygomorphic, gamosepalous, polypetalous, imbricate, monocarpellary, perigynous, unilocular, and marginal.

Floral Characters:

• Inflorescence: Axillary or terminal raceme, spike, umbel, rarely cymose.
• Flower: Bisexual, complete, zygomorphic, rarely actinomorphic, pedicellate, hypogynous or perigynous (bracteates).
• Calyx: 5 sepals, gamosepalous connate to the base, imbricate or rarely valvate, colored.
• Corolla: 5 petals, polypetalous, imbricate, the posterior petal innermost into the bud.
• Androecium: 10 stamens or fewer, rarely numerous, polyandrous.
• Gynoecium: Monocarpellary, ovary superior, unilocular, placentation marginal, ovules 1 or many, style 1, simple, stigma long.

Floral Formula: $\dagger, K_{(5)} \text{ or } 5, C_5 \text{ or } 5, A_{10} \text{ or } \alpha, G_1$

Floral Diagram: (An illustrated floral diagram is shown here)

Examples:

Botanical Names	Common Names
Tamarindus indica	Tamarind / imli
Cassia fistula	Amaltas
Parkinsonia roxburghii	Vilayti kikar
Bauhinia vergata	Camel’s foot / kachnar
Poinciana regia Economic Importance: Medicinal Use: Some of the plants of this family are used for medicinal purposes. Leaves of Cassia fistula are used for the treatment of ringworm. C. Senna, C. obtava is cultivated to obtain the drug for laxative. Ornamental Use: The plants of this family are also used as an ornamental use, e.g. Bauhinia variegata Cassia fistula Parkinsonia roxburgii Vegetative Use: They are used for vegetative purposes, e.g. Tamarindus indica used as a vegetable for tartaric acid. The leaves and flowers and buds of Bauhinia variegata are used as a vegetable. Source Of Dye: The hard wood of Hematoxylon is used for the formation of hematoxylin dye. Family Poaceae / Gramineae: (Grass Family) Introduction: It is also called the grass family or gramineae. Occurrence: It has about three thousand (3000) species belonging to 56 genera are found growing worldwide, 49 species of 11 genera are found in or reported from Pakistan. Distinguishing Characters: Zygomorphic, Marginal, Parienth, Caryopsis / grain, Bracteate, Spikelets, Polyandrous, Hypogynous. Floral Characters: Inflorescence: Racemose spikelet. Flower: Bracteate, actinomorphic or zygomorphic, bisexual or unisexual, hypogynous. Parienth: It consists of two small leaves-like structures called "lodicules". Androecium: 3 stamens or 6 in two groups (3+3) or 0 stamen in the same plant, long filament, polyandrous. Gynoecium: Mono carpellary or zero carpel, hypogynous, unilocular, marginal, stigma hairy. Fruit: Caryopsis. Floral Formula: $BR, \oplus, \text{or} \dagger, P_2, A_3 \text{ or } 3 + 3 \text{ or } 0, G_1 \text{ or } (3) \text{ or } 0$ Floral Diagram: Examples: Botanical Names Common Names Triticum indicum Wheat Bambusa arundicea Bamboo Hordeum viligarea Barley (jawar) Zea may Indian corn Oryza sativa Rice Saccharum officinarum Sugar cane Pennisetum typhoideum Bajra Avena sativa Oats Economic Importance: Medicinal Use: It is used for kidney dialysis and excretion of kidney stones. Ginger oil, Coronella oil used as an insecticide. Industrial Use: Kash plant (perfume) Makkai (corn oil) Vegetative Use: Triticum indicum (wheat) Oryza sativa (rice) Saccharum officinarum (sugar cane) Zea may Source Of Sugar: Saccharum officinarum is a good source of sugar.	Flame of the forest / gul-e-monar

THE KINGDOM FUNGI

 THE KINGDOM FUNGI

“Fungi are non-chlorophyllous, multicellular (except yeast) eukaryotes having fungus cellulose or chitinous cell wall, body mycelium consists of hyphae, absorptive heterotrophs.”

TAXONOMIC STATUS: (PLANT LIKE CHARACTERS) Previously fungi were regarded as plants because of the following characters:

• Having cell wall
• Lacking centriole
• Non-motile

Animal Like Characters: By showing the following characters, fungi resemble more animals than plants.

• They are heterotrophs (chloroplast is absent).
• Lack cellulose in their cell wall.
• Fungi are different from all other organisms.

They have characteristics of mitosis called nuclear mitosis, during which the nuclear membrane does not break, and the spindle is formed within the nucleus.

Conclusion: Fungi are neither completely plants nor animals and are assigned to a separate kingdom: Fungi.

THE BODY OF FUNGUS: Vegetative Structure: The fungi have a very simple body. In the majority of fungi, the body consists of a network of branched thread-like structures called the hyphae. When the hyphae form a mass, it is known as mycelium. In some lower fungi, the body does not form mycelium. They are single-celled structures, for example, Synchytrium and Saccharomyces. The cell wall of mycelium does not consist of true cellulose. It is composed of chitin or fungal cellulose.

The mycelium is of two types:

• Coenocytic Mycelium: In zygomycetes, the mycelium is unseptate and multinucleate; it is called coenocytic mycelium.
• Septate Mycelium: In Ascomycetes and Basidiomycetes, the mycelium is septate, and hyphae are divided into cells. The cells may be uninucleate or multinucleate. The cells of mycelium are filled up with colorless cytoplasm, which contains nuclei and vacuoles. The food is stored in the form of glycogen or oil; starch is absent.

NUTRITION IN FUNGI: Fungi are nonchlorophyllous and absorptive heterotrophs. They are classified into the following groups based on their mode of nutrition.

• Saprotrophs (Saprobes / Decomposers)
• Parasites
• Predators
• Symbiotic fungi

Saprotrophs: (Saprobes/Decomposers) The saprophytic fungi obtain their food from dead organic compounds. Saprobic fungi anchor to the substrate by modified hyphae called rhizoids. When rhizoids contact the substrate, they secrete digestive enzymes which digest dead organic matter and convert it into simple compounds.

Parasites: These are fungi that depend on a living host for nutritional requirements, known as parasitic fungi. They obtain food from the host through special hyphae called haustoria. Parasitic fungi may be obligate or facultative.

• Obligate Parasite: They can grow only on their living host and cannot be grown without it, e.g., mildews and rust.
• Facultative Parasites: They can grow parasitically on their host as well as by themselves on artificial growth media, e.g., Aspergillus, Trichophyton.

Predators: These fungi trap other living organisms like nematodes, protozoans, etc., and use them as food. They show many parasitic adaptations, such as Arthrobotrys traps soil nematodes by forming a constricting ring, while other predators secrete sticky substances.

Symbiotic Fungi: Symbiosis is an association between two organisms in which neither partner is harmed. Fungi form two key mutualistic symbiotic associations (both partners get benefits).

• Lichen: It is a mutualistic symbiotic association between fungi and certain phototrophs, either green algae or cyanobacterium, or sometimes both. Lichen is an important group that includes about 400 genera and 1600 species. They vary in color, shape, and overall growth form. Most of the visible part of lichen consists of fungi, while algae present within the hyphae provide protection to the algal partner from strong light and desiccation, and itself gets food from the algae. They are ecologically very important as bioindicators of air pollution.

• Mycorrhizae:

• Myco - Fungi; (Rhizae – Root)
• Some fungi form an association with the roots of vascular plants. This association is mutualistic, in which both organisms live together on mutual bases, and both get benefits.

hyphae of fungi increase the soil contact and help in the absorption of important substances, like phosphorus, zinc, copper, and other nutrients. The plant gets all these substances, and as a result of which the plant supplies organic compounds to the Fungus. In this way fungi and higher Plants live together.

There are two types of mycorrhizal fungi.

• Edomycorrhizae
• Ectomycorrhizae

Edomycorrhizae: When the hyphae of fungi penetrate into the inner side of root cells, these are called endomycorrhizal fungi, such as orchids.

Ectomycorrhizae: When the fungal hyphae surround the roots and remain between the cells, but do not penetrate into the cells, these are called ectomycorrhizal fungi, e.g., Pinus, fir, oak, etc.

Reproduction: Most fungi can reproduce asexually as well as sexually (except imperfect fungi in which sexual reproduction has not been observed).

• Asexual Reproduction: Asexual reproduction takes place by spores, conidia, fragmentation, and budding.

Spores: Spores are produced inside the reproductive structures called sporangia, which are cut off from the hyphae by complete septa. Spores may be produced by sexual or asexual processes, are haploid, non-motile, and do not need water for dispersal. Spores are a common means of reproduction in fungi.

Conidia:
Conidia (singular conidium) are non-motile, asexual spores which are cut off at the end of modified hyphae called conidiophores, and not inside the sporangia, usually in chains or clusters.

Fragmentation:
Fragmentation is simple breaking of mycelium of some hyphal fungi, each broken fragment giving rise to a new mycelium.

Budding:
Unicellular yeasts reproduce by budding (an asymmetric division in which tiny outgrowth or bud is produced which may separate and grow by simple relatively equal cell division).

Sexual Reproduction:
Details of sexual reproduction vary in different groups of fungi, but fusion of haploid nuclei and meiosis are common to all. When fungi reproduce sexually, hyphae of two genetically different but compatible mating types come together. Their cytoplasm fuses, followed by nuclear fusion of nuclei (karyogamy). In Basidiomycetes and Ascomycetes, nuclear fusion does not take place immediately after the fusion of cytoplasm (plasmogamy); instead, the two genetic types of haploid nuclei from two individuals may coexist and divide in the same hyphae for most of the life of the fungus. Such a fungal hypha/cell having 2 nuclei of different genetic types is called dikaryotic also heterokaryotic hypha/cell.

Classification of Fungi:
There are four major divisions / phyla of fungi.

• Zygomycota
• Ascomycota
• Basidiomycota
• Deuteromycota

Zygomycota:

• Zygomycota is a group of Sapnophyte fungi.
• Zygomycota is the smallest group of fungi includes about 600 species group bread molds.
• These fungi have coenocytic mycelium i.e., it is multinucleate and unseptate. The septa are formed only at the formation of sporangia or gametangia.
• In these fungi, there is complete absence of motile cells.

Asexual Reproduction:

• Asexual reproduction takes place by spores, produced in sporangia.
• Sexual reproduction takes place by the fusion of isogametes, due to which zygospores are formed, so the group is called zygomycota. e.g. Mucor, Rhizopus.

Life Cycle Of Zygomycota: In the life cycle of zygomycota, asexual and sexual reproduction occur.

Asexual Reproduction: It takes place during favorable conditions. Many erect branches arise from the mycelium, called sporangiophores. At the tip of each sporangiophore, a rounded body is formed, into which the cytoplasm, nuclei, and oil globules are transferred from the mycelium. The oil globules arrange themselves to form a layer, and the rounded body divides into two parts.

The upper larger part is known as sporangium, while the smaller lower part is known as columella. In sporangium, many spores are formed. After spores' maturation, the columella exerts pressure on the sporangium, so its wall ruptures, and spores are liberated out. The spores are very small in size, light in weight, and dry. Whenever they find food material, they germinate into new mycelium of fungus.

Sexual Reproduction: Sexual reproduction occurs by the fusion of gametangia. At the time of sexual reproduction, two hyphae of opposite strains (+ and -) come parallel to each other. Each hypha produces an outgrowth, the papilla, which divides into two cells. The lower cell is called the basal cell or suspensor cell. The upper cell is called gametangium. In each gametangium, a gamete is formed. These gametes are externally similar, so they are known as isogametes. The isogametes are fused together; this process is called conjugation. As a result of conjugation, a zygospore is formed.

Germination Of Zygospore: The zygospore consists of two layers: the outer layer is thick and spiny, called exospore, and the inner layer is thin and smooth, known as endospore. At the time of germination, the exospore ruptures, and the endospore germinates into a tube-like body, called promycelium.

At the tip of promycelium a sporangium is produced. The nucleus and reserved cytoplasm of zygospore are migrated into the sporangium. The nucleus divides by meiosis into many nuclei, then cytoplasm also divides into many pieces, each piece of cytoplasm surrounds the nucleus, in this way many spores are formed. After the maturation of spores, the wall of sporangium ruptures and all spores become free. They remain in air and by the availability of organic food substance, they germinate into new mycelium of fungus.

Ascomycota: The Ascomycetes (Gr. askos, bladder; myles, fungi) or the sacfungi constitute a class of fungi. They include about 2,500 genera and 35,000 species which have to almost half of the entire number of Fungi. Among the known examples of Ascomycetes are: the yeasts, the common green and blue molds, the powdery mildews, the morels, the cup-fungi and the truffles.

Occurrence: Ascomycetes occur in variety of habitats almost throughout the year. Some of them are parasitic. Many members cause serious plants-diseases, such as peach leafcurl, brown rot of stone fruits apple scab, bitter-rot of apple, powdery mildews ergot of rye. Others are saprobic (saprophytic). A few are hypogeal (Gr. hypo, below; ge, earth) and stain permanently underground. A large majority of the Ascomycetes are coprophilous (Gr. kepros, dung; philein, to love), growing on dung of certain animals. Fruiting season is short, lasting for three or four weeks.

Somatic Structure: The mycelium is usually well developed and profusely branched except in yeasts (Saccharomycetes), which are unicellular and where the mycelium is absent. The hyphae are septate each cell may be uninucleate or multinucleate. The septa, however, perforated and permit the streaming of the protoplasm from cell to cell. The cell wall contains a large amount of chitin. The mycelium in the fruiting bodies is often organized into fungi tissues, which may prosenchymatous or pseudoparenchymatous. In some, the hyphal cells separate with age forming oidia or become thick-walled, forming chlamydospores.

Asexual Reproduction: Asexual reproduction takes place by means of conidia, spores cut off by septa at the end of modified hyphae called conidiophores. Many conidia are multinucleate.

Sexual Reproduction:
In Ascomycota sexual reproduction takes place by the formation of male and female reproductive organs. The male organs are called antheridia and female are called ascogonia. They are usually developed at the apex of hyphae. The ascogonium forms a special structure, called trichogyne. It acts as a fertilization tube through which male nuclei from the antheridium is transferred into ascogonium. By the fusion of male and female nuclei zygote is formed.

Formation Of Ascus:
In Ascomycetes when male and female gametes are fused together, zygote is formed. This zygote is changed into a special structure, called ascus. Sometimes ascogonia of certain species are changed into asci without fertilization. In the lower fungi of Ascomycetes the zygote nucleus divides by meiosis and forms 4 to 8 nuclei, which form ascospores. At maturity the ascus bursts at certain point and ascospores are liberated.

Ascocarp:
Ascocarps or fruity bodies are made up tightly interwoven monokaryotic and dikaryotic hyphae. Within an ascocarp, on special fertile layer of dikaryotic hyphae, the asci are formed. The ascocarps of the cup fungi and the morels are open, with the asci lining the open cups called apothecium, other ascocarps are closed or have a small opening at the apex called cleistothecium and perithecium respectively; the ascocarps of neurospora, an important organism of genetic research, are of this latter kind.

Yeast: (Saccharomyces)
Systematic Position:
Class - Ascomycetes
Sub-class - Protoascomycetes (Hemiascomycetes)
Order - Endomycetales
Family - Saccharomycetaceae
Genus - Saccharomyces

Occurrence And Habit:
The yeasts first described by Leuwenhoek in 1680, are the simplest and the most widely distributed of the Ascomycetes. They are unicellular and particularly abundant in sugary substances, containing small amounts of nitrogen and sulphur. Such as the nectar of flowers, the surface of fruits like grapes, date-palm (khajoor), sugar-cane, as also fruit juices, exuded sap of plants and the soil of wine-yards, etc. Some of them are pathogenic on plants causing leaf-curl diseases of various species, while others are even pathogenic on man and animals.

Fermentation:
Yeasts obtain energy by a process known as alcoholic fermentation of sugar. During the process, the yeast cells absorb sugar and decompose it by enzyme (zymase) with the formation of carbon dioxide and alcohol (ethyl) with traces of glycerine, succinic acid and acetic acid, as shown by the following equation.

$\text{C}_6\text{H}_{12}\text{O}_6 + \text{zymase} \rightarrow 2\text{C}_2\text{H}_5\text{OH} + 2\text{CO}_2$
Ethyl alcohol | Carbon dioxide

Fermentation takes place when there is insufficient supply of oxygen.

Economic Importance: Yeast is particularly useful because of their ability to ferment carbohydrates; hence the name Saccharomycetes. Saccharomyces cerevisiae (The Beer Yeast) is the best-known species extensively cultivated in bakeries, breweries, and distilleries. Alcohol and carbon dioxide, brewers and bakers use yeasts extensively in their industries. Different yeasts give different flavors to the alcohol, cider, wine, beer, ale, brandy, rum, and other liquors.

Because of their high vitamin contents (e.g., vitamin B, B2, and G) and digestible compounds, especially proteins, fats, carbohydrates, enzymes, etc., yeasts are particularly valuable as food (e.g., Cryptococcus), as also in the treatment of certain skin and intestinal diseases. Some species of yeast cause food spoilage, giving yeasty flavor, while others are pathogenic, causing plant diseases, of tomato fruits (Nematospora lycopersici), garden beans (Nematospora phasoli), cotton (Nematospora gossypii). Several species of the genus Torula are pathogenic on man, causing several diseases, best known of which is blastomycosis or torulosis, which attacks the skin and central nervous system; yeast vaginitis causes vaginal thrash, while “cryptococcosis and moniliasis” are caused by Cryptococcus neoformans and Candida albicans. Cryptococcosis involves the central nervous system and may cause meningitis, abscess, or brain tumor, while Moniliasis involves nails and cuticle but sometimes also involves pericardium of heart and lungs.

Somatic Structure: Like other Ascomycetes, the mycelium in yeast is not a branched filamentous structure but consists of isolated cells. The cells of Saccharomyces are very minute, measuring 1/100th of a millimeter (10µ) and are either spherical, elongated, rectangular, or slightly oval. They possess a definite cell wall, which is made up of polysaccharides, chitin, phosphoric acid, and glycogen. Inside is the protoplasm which in the older cells is differentiated into an outer ectoplasm and an inner endoplasm. The endoplasm surrounds a large central (nuclear) vacuole, which represents the nucleus, traversed by chromatin fibrils. The nucleus contains a normal nucleolus on one side, but the chromatin matter is relatively small.

According to the most recent view, the enlarged nuclear vacuole encloses a small nucleolus, which is connected to the centrosomes by means of chromosomes. The centrosome lies at one end and is surrounded by centrioles and heterochromatin. Other inclusions such as mitochondria, starch grains, oil globules, glycogen grains, and grains of volition (which is ribonucleic acid - RNA or one of its salts) are embedded in the ectoplasm.

Though ordinarily unicellular, the yeast cells sometimes adhere in chains, forming a pseudomycelium. When grown on gelatin, individually, the yeast cells are colorless, but when grown on solid media, they form colonies, which may appear white, cream-colored, or brownish. These colony characteristics are used in classifying yeasts.

Nitrogen: Yeasts, like other fungi, lack chlorophyll and are, therefore, heterotrophic in their mode of nutrition. They are mainly saprophytic and live in sugary substances containing small amounts of nitrogen and sulfur. The yeast cells manufacture two types of enzymes, which completely destroy the sugar in the surrounding medium. One of these enzymes is invertase, an extracellular enzyme, which passes out of the other enzyme, zymase, which remains within the yeast cell and converts invert sugar into alcohol and carbon dioxide.

Vegetative Reproduction: Vegetative reproduction takes place by:

• Budding:
  In S. cerevisiae, the common bread yeast, the vegetative reproduction takes place by budding. When the food supply is in abundance, the mother cell gives rise to a small outgrowth, which gradually increases in size till it is as large as the mother cell itself. Sometimes, a bud may repeat the process of budding a number of times.

• Fission:
  In some species, such as Schizosaccharomyces octo-sporus, which is very common on grapes, the vegetative multiplication takes place by fission or cell.

Division:
During fission, the nucleus of the mother cell divides into two daughter nuclei, and this is followed by a transverse cytokinesis that results in the formation of two daughter cells of approximately equal sizes.

Sexual Reproduction:
This occurs under conditions unfavorable for active vegetative growth, such as scarcity of food or water. Sexual union in yeasts takes place either between two somatic cells or between two ascospores, which assume the function of gametes. Two gametes unite and form a diploid zygote cell. Eventually, the zygote forms an ascus, which contains four to eight or more ascospores of variable shapes, though often globose or oval. The resulting ascospores function directly as new yeast cells.

Basidiomycota:
The basidiomycetes have about 16,000 named species. More is known about some members of this group than about any other fungi. Among the basidiomycetes are not only the mushrooms, toadstools, puffballs, jelly fungi, and shelf fungi, but also many important plant pathogens among the groups called rusts and smuts. Many mushrooms are used as food, but others are deadly poisonous. Still other species are poisonous to some people and harmless to others.

Vegetative Structure:
The mycelium of basidiomycota fungi is advanced. It is branched and septate. The cell wall is composed of chitin. The mycelium is intracellular or intercellular. Each cell contains cytoplasm and nucleus. The mycelium with uninucleate cells, called primary mycelium (monokaryotic mycelium), and with two nuclei is called secondary mycelium (dikaryotic mycelium).

Life Cycle of Basidiomycota:
In this division of fungi, the reproductive bodies are called basidiospores. These spores are produced by special organs, called basidia. In basidiomycetes, new mycelium is formed by the germination of basidiospores. In the beginning, the mycelium is uninucleate or monokaryotic, called primary mycelium. After some time, two different hyphae come in contact. The cytoplasms of the cells are fused together while nuclei are not fused. This is called plasmogamy. By this process, dikaryotic mycelium is formed. It contains two nuclei in each cell and is also called secondary mycelium. The dikaryotic mycelium takes part in reproduction.

Formation of Basidia and Basidiospore:
At the time of reproduction, special spores are produced in the cells of dikaryotic mycelium, called chlamydospores or teliospores. These spores remain inactive for a particular time, after that they start germination. The two haploid nuclei of chlamydospore fuse together to form a diploid nucleus. This process is called karyogamy. The chlamydospores form a tube-like structure, called basidium. The diploid nucleus divides into four nuclei. The basidium divides into four cells; each nucleus is migrated into each cell. From each cell of basidium, a small stack arises, called sterigma, the tip of sterigma becomes swollen, the nucleus of cell is migrated into this swollen end, it is called basidiospore. In this way, four basidiospores are formed. After maturation, the basidiospores are separated from sterigma. They can germinate during favorable conditions and develop into mycelium.

Deuteromycota (Fungi Imperfecti):
Most of the fungi imperfecti are Ascomycota that have lost the ability to reproduce sexually. The fungi that are classified in this group, however, are simply those in which the sexual reproductive stages have not been observed. There are some 17,000 described species of fungi imperfecti. Even though sexual reproduction is absent among fungi imperfecti, there is a certain amount of genetic recombination. This becomes possible when hyphae of different genetic type fuse, as sometimes happens spontaneously. Within the heterokaryotic hyphae that arise from such fusion, genetic recombination of special kind called parasexuality may occur. In parasexuality, the exchange of portions of chromosomes between their genetically distinct nuclei within a common hypha takes place. Recombination of this sort also occurs in other groups of fungi and seems to be responsible for some of the production of new pathogenic strains of wheat rust.

Among the economically important genera of fungi imperfecti are penicillium and aspergillus. Some species of penicillium are sources of the well-known antibiotic penicillin, and other species of the genus give the characteristic flavors and aromas to cheese. Species of Aspergillus are used for fermenting soya sauce and soya paste processes in which certain bacteria and yeast also play important roles. Citric acid is produced commercially with members of this genus under highly acidic conditions. In addition, the enrichment of livestock feed by the products of fermentation of other species is being investigated.

Land Adaptations of Fungi:
Following characteristics enable fungi to live on land.

• Hyphae that absorb water and soluble nutrients also anchor the plant.
• Thick-walled drought-resistant spores are produced in large numbers.
• Instead of forming gametes having flagella, special gametes are produced which need no water for fertilization.

Economic Importance:
In many ways, bacteria and fungi are similar in their importance to man. Like bacteria, fungi show both harmful and useful activities to human beings.

Useful Fungi:

• Food:
  Many kinds of edible fungi in the form of mushrooms are a source of nourishing and delicious food dishes. Some of them are poisonous and popularly called toad-stools or death-stools. Yeasts, another kind of fungi, are utilized in the baking industry. Others are used in brewing and in cheese and organic acid-producing industries.

• Medicines:
  Fungi have explored a new field in medicine by producing antibiotics like penicillin, chloromycetin, terramycin, neomycin, etc.

• Soil Fertility:
  They maintain soil fertility by decomposing the dead organic matter, e.g., Mycorrhizal fungi.

Harmful Fungi:

• Food Spoilage:
  Fungi cause tremendous amounts of spoilage of foodstuff by many of the saprophytic fungi.

• Human Diseases:
  Fungi cause a number of diseases in human beings like aspergillosis (ear, lungs, disease), moniliasis (skin, mouth, gums disease). Most of the fungi that cause skin diseases in humans, including athlete’s foot and ringworm, are also fungi imperfecti.

• Plant Disease:
  Fungi destroy many agricultural crops, fruits, ornaments, and other kinds of plants. Some of the diseases are loose smut of wheat, downy, and powdery mildews, etc.

• Spoilage:
  Many fungi spoil leather goods, wool, books, timber, cotton, etc.

Economic Losses Due to Fungi:
Fungi are responsible for many serious plant diseases because they produce several enzymes that can break down cellulose, lignin, and even cutin. All plants are susceptible to them. Extensive damages due to rusts and smut diseases of wheat, corn, and rice prompted mass displacement and starvation to death of many people. Powdery mildews (on grapes, rose, wheat, etc.), ergot of rye, red rot of sugarcane, potato wilt, cotton root, apple scab, and brown rot of peaches, plums, apricots, and cherries are some other common plant diseases caused by fungi.

Fungi also cause certain animal diseases. Ringworm and athlete’s foot are superficial fungal infections caused by certain imperfect fungi. Candida albicans, a yeast, causes oral and vaginal thrush. Histoplasmolysis is a serious infection of the lungs caused by inhaling spores of a fungus.

which is common in soil contaminated with bird’s feces. If infection spreads into the bloodstream and then to other organs (which is very occasional), it can be serious and even fatal. Aspergillus fumigatus causes aspergillosis, but only in a person with a defective immune system, such as AIDS, and may cause death. Some strains of Aspergillus flavus produce one of the most carcinogenic (cancer-causing) mycotoxins (toxins produced by fungi), called aflatoxins. Aspergillus contaminates improperly stored grains, such as peanuts and corn, etc. Milk, eggs, and meat may also have small traces of aflatoxins. Any moldy human food or animal forage product should be discarded. Ergotism is caused by eating bread made from purple ergot-contaminated rye flour. The poisonous material in the ergot causes nervous spasms, convulsions, psychotic delusion, and even gangrene.

Saprobic fungi are not only useful recyclers but also cause incalculable damage to food, wood, fiber, and leather by decomposing them. 15-50% of the world’s food is lost each year due to fungal attack. Wood-rotting fungi destroy not only living trees but also structural timber. Bracket/shelf fungi cause lots of damage to stored cut timber as well as stands of timber of living trees. A pink yeast (Rhodotorula) grows on shower curtains and other moist surfaces.