- Includes all eukaryotic multicellular and chlorophyllous living organisms, which have cell wall made up of true cellulose.
- Majority of members are autotrophic but few are parasite e.g.: “Cuscuta”
- They have localized growth, regions of growth lying primarily at the extremities that is root and stem apices.
Kingdom planatae is divided into tow sub-kingdom on the basis of presence or absence of vascular tissue (xylem and phloem).
A – SUB-DIVISION – BRYOPHYTES (NON-VASCULAR)
- Class Hepatica (Liverworts)
- Class Musci (Mosses)
- Class Anthroccrota (Hornworts)
- Class Psilopsida (Psilopsids)
- Class Lycopsida (Club Mosses)
- Class Sphenopsida (Horse Tails)
- Class Pteropsida (Ferns)
- ClassSpermopsida (Seed Plants)
- Absence of lignin-fortified tissue to support tall plants on land.
- Members of this sub-division usually sprawl horizontally as mats over a large surface.
- Always have a low profile (1-2cm-20cm tall).
- Sporophyte stage of bryophytes is generally smaller and shorter lived, and it depends on gametophyte for water and nutrients.
- The diploid sporophyte produces haploid spores via meiosis in a structure called “sporangium”
- The tiny, spores, protected by sporopollenim, disperse and give rise to new gametophytes.
- All members of bryophytes need water to reproduce.
- Gametes produce within reproductive structures “Gametangia” (Male-Antheridia and Female-Archer-gonium)
- Antheridium produces flagellated sperm while female archegonium contains one egg (ovum).
- Fertilization occurs w/t in the archegonium
- Zygote develops into an embryo within the protective jacket of Archegonium.
- Windblown spores disperse the speies.
- All bryophytes belong to Silurian/Devonian period (345-395Million yrs. Ago.)
All Bryophytes show amphibious form of land plants. Following are main adaptations exhibited by them.
a. Rhizoid for water absorption
b. Conservation of water
c. Absorption of CO 2
e. Protection of reproductive cells
f. Formation of embryos
CLASSES OF BRYOPHYTES
- Plants grow in a tight pack, in the form of mat, in order to hold one another up.
- Mat of moss possess spongy quality and enables it to absorb and retain water.
- Rhizoids are elongated cells or cellular filaments of mats which grip the substratum.
- Photosynthesis occurs in upper part of the plant w/c has many small stem like and leaf like appendages. E.g Funaria.
- Usually present in tropical areas
- Plant body is divided into lobes somewhat of the lobed liver, of an animal.
- These plants are less fimiliar than Mosses.
3- ANTHROCERATAE:- (HORNWORTS)
- These plants resemble w/t liverworts, but are differentiated by their sporophytes plants.
- Sporophyte are elongated capsules that grow like horn from mat like gametophyte.
- Sporophyte has stomata and chloroplast, performs photosynthesis
- Sporophyte plant can survive even often the death of gametophyte due to presence of Meristem.
- Meristem is a specialized tissue, which keeps on adding new cells in sporophyte plant.
- Hornworts are the most advanced members of bryophytes.
SUB-DIVISION TRACHEOPHYTA (VASCULAR PLANTS)
Main characters are as follow,
- Conducting vessels Xylem and Phloem are present in plant body.
- A protective layer of sterile “Jacket” cells around reproductive organs are present.
- Multicellular embryos retained within the archegonia.
- On aerial parts protective covering “Cuticles” is present w/c prevents excessive loss of water during hot climate.
- In life cycle Sporophyte stage is dominant.
- These are the fossil representatives of the vascular plants, belonging to “Silurain period” and “Devonian Period”
- Sporophytes are simple dichotomously branching plants.
- True leaves and true roots absent.
- Underground stems that contain unicellular rhizoid similar to root hairs.
- The aerial stems are green and carry out photosynthesis.
- Lacking secondary growth due to absence of “Cambium”
- Reproductive structure “Sporangia” develop at the tips of some of the aerial branches.
- Meiosis produces haploid spores, within the sporangia.
A) RHYNIA (FIRST VASCULAR PLANT)
- One of the most primitive vascular plant
- It is an extinct genus, was named often the village “Rhynia of Scotland where the first fossils of Rhynia were discovered.
- It belongs to Devonian period, which started about 400 million years ago.
- The fossils of this plant are so well preserved that the stomata are still intact.
- The plant body (Sporophyte) was simple.
- It consisted of slender, dichotomously branched creeping rhizome, bearing erect, dichotomously branched aerial stem.
- Instead of roots, rhizoids were given out from rhizome.
- The aerial branches were leaf-less having terminal fusiform naked sporangia.
- The internal structure of branches show a solid central core of vascular tissues surrounded by Cortex.
- The outer most layer is Epidermis having stomata.
- The vascular tissue is differentiated into centrally placed xylem and surrounded phloem
B) PSILOTUM AND TEMESIPTERIS (LIVING SPECIES OF PSILOPSIDA)
- Sporophyte plant produce spores, which give rise to minute subterranean gametophytes.
- Each gametophyte bears both female reproductive organ Archegonia and male reproductive organ Antheridia w/c produce both egg and sperm respectively.
- As a result of fertilization a diploid zygote is formed which develops into sporophyte plant.
- Sporophyte stage of life cycle is dominant, but haploid gametoplyte stage is still relatively large.
The leaf is the most important organ of a green plant because of its photosynthetic activity. Leaves are of tow types
1. Single veined leaves- Contain only one vein
2. Poly veined leaves- Contain two or more veins
1- EVOLUTION OF SINGLE-VEINED LEAF
- It is assuming that a thorn like out growth emerged on the surface of the naked stem.
- With an increase in size of the leaf, the vascular tissues were also formed for the supply of water and support to the leaf.
- Another possibility is that a single veined leaf originated by a reduction in size of a part of the leafless branching system of the primitive vascular plants.
- These are the evolutionary modifications of the forked branching in the primitive plants.
- The first step in the evolution of this leaf was the restriction of forked branches to a single plane.
- The branching system become flat.
- The next step in the evolution was filling the space b/w the branching and the vascular tissues.
- The leaf so formed looked like the webfoot of a duck.
2-LYCOPSIDA(THE CLUB MOSSES)
- These plants belong to middle Devonian and carboniferous periods.
- They were very large trees that formed the earth’s first forests.
- Only five living genera of this group are present.
- Two members, selaginella and lycopodium are common in many areas of Pakistan
- These plants have true branched underground roots.
- True leaves also present w/c have arisen as simple scale like outgrowth (emergence) from the outer tissues of the stem.
- Specialized reproductive leaves bearing sporangia on their surfaces, are present, such type of leaves are known as “Sporophylls”.
- In some members, the sporophylls are collected on a short length of stem and form cone like structure “Strobilus”.
- The cone is rather club-shaped; hence name “Club-Mosses” for the lycopsids.
- Gametophytes plant may be homosporous or heterosporous .
- Spores produced by sporophyte plant are all alike, and each give rise to a gametophytes that bear both archegonia (female reproductive structure) and antheridia (male reproductive structure)
B) HETEROSPOROUS GAMETOPHYTES
- Sporophyte (2n) plant produces two types of sporangia, which produced different kinds of spores.
- One type of sporangium produces very large spores called “Megaspores,” which develop in female gametophytes bearing archegonia.
- Other type of sporangium produces small spores called “Microspores, which develop into male gametophytes bearing antheridia.
- That’s mean sexes are separate in the gametophytes generation (Heterosporous).
EVOLUTION OF SEED
Seeds are evolved from primitive spores.
STEPS OF EVOLUTION
1. PRIMITIVE SPORES
All spores of specie are nearly identical in size, structure and function.
- There are many vascular plants that form two kinds of spores, these plants are said to be “Heterosporous” and spores are called “Heterospores.”
- These spores on germination give rise to two different types of plants.
B) FEMALE SPORE: It grows into egg forming gametophyte.
3. PROTECTION OF HETEROSPORES
- The two different kinds of spores are formed in two different kinds of sporangia.
- Various enveloping structures develop in order to protect these spores.
- Certain fern like plants first developed seed like structures, each of their sporangia, containing one or more female spores, was surrounded by little branch like out growth structure forming “Integument.”
- Instead of being shed from the sporangium, the female spores are retained and protected inside the integument.
- The female spore develops into a tiny female gametophyte protected by the integuments.
- Seed is formed as the result of fertilization of male spore with this protected female spore.
- Immature seed is called “Ovule.”
- Ovule is protected by integuments and it contains great quantities of food.
- Ovule not only protects the female gametophyte from the environment but also provides food for the new off springs that is produced when the seed matures and germinate. The development of seed has given the vascular plants better adaptations to their environment.
- These plants belong to late Devonian and Carboniferous period.
- Only one living member “Equisetum” commonly called “Horse-tail” exists today.
- Ancient sphenopsids were large trees but now most of these are small (Less than one meter).
- Coal deposits of today was formed from the dead bodies of those plants.
- These plants possess true roots, stems and leaves.
- Stems are hollow and are jointed, whorls of leaves occur at each joint.
- Secondary growth absent, because modern species do not possess cambium.
- Spore are born in terminal cones (Strobili) and all are alike (i.e. plants are homosporous) and give rise to small gametophytes that bear both archegonia and antheridia (i.e. the sexes are not separate).
- These plants belong to Devonian and Carboneferous Period and then decline in Paleozoid Period.
- They are very well developed plants having vascular system with true roots, stem and leaves.
- Leaves are probably arisen from flattened web branched stems. They are large and provide much greater surface area for photosynthesis.
- Leaves of Ferns are sometimes simple, but more often they are compound, being divided into numerous leaflets.
- In most modern ferns of temperate regions, the stems are prostrate on or in the soil, and the large leaves are only part normally seen.
- The large leafy plant (fern) is diploid sporophytic phase.
- Spores are produced in sporangia (Reproductive structure) located in clusters on the underside of some modified leaves “Sporophyll.”
- Most modern ferns are homosporous i.e. all these spores are alike.
- Vascular sporophytes can live in drier places and grow bigger.
- After germination, the spores develop into gametophytes that bear both archegonia and antheridia.
- These gametophytes are tiny (less than one centimeter wide), thin and often more or less heart-shaped.
- Free-living, non-vascularized gametophytes can survive only in moist places, their sperms are flagellated and water is required for fertilization.Young sporophyte develops directly from the zygote without passing through any protected seed like stage.
ALTERNATION OF GENERATION
- In Kingdom Plantae, life cycle of many plants is completed in two stages or generations known as Gametophyte and Sporophyte.
- The two generations normally differ from each other in morphology, reproduction and number of chromosomes.
- The gametophyte is haploid and reproduces sexually by forming the gametes, while the sporophyte is diploid and reproduces a-sexually by forming the spores.
- The two generations regularly alternate with each other and therefore, the phenomenon is called “Alternation of generation” (Heteromorphic).
- In Bryophytes, the main plant itself is the Gametophyte while the sporophyte is reduced.
- In Tracheophytes, the main plant is “Sporophyte” and the “Gametophyte” is reduced.
- First appeared in late Devonian and became dominant in Carboniferous Period.
- Gametophyte stage is even more reduced than in the ferns, and non-photosynthetic or free-living.
- The sperms of most modern species are not independent free-swimming flagellated cells.
- Young embryo, is enclosed within a seed coat and can remain dormant for long periods.
- Spermosida can be divided into two main sub-groups, which are as follows:
These plants have naked seed because ovules are not covered by ovary i.e. fruit is absent.
Sub-divisions of Gymnosperms are
- They have arisen from the seed ferns.
- These plants appeared in “Permian Period” and Mesozoic Period and declined in Cretaceous Period.
- They possessed large palm like leaves with short height stems.
- Living species commonly found in tropical regions and also known as “Sago Palms.”
- Nine living genera with over a hundred species exist today.
- Cycads and its relatives.
- Mostly contains extinct species, only one living specie, “the Ginkgo” which is also known as “Maiden Hair Tree.”
- Ginkgo often planted as lawn tree.
- Most familiar and best-known group of gymnosperms.
- Leaves are small evergreen needles or scales with an internal arrangement of tissues.
- Reproductive organs are cone like modified leaves.
This plant belongs to Gymnosperms. It includes about 90 species.
HABIT AND HABITAT
- It is distributed world-wide mostly in northern hemisphere. 30 species are found in the Himalayas. Some are reported in the planes of Punjab.
- The pinus plant belongs to the “Sporophytic Phase.”
- It is a tall tree, pyramidal in form and gives a conical appearance and therefore commonly grouped under “Conifers.”
- It is well differentiated into stem, root and leaves.
It is erect, cylindrical, solid and covered with thick, rough and brownish bark. The branches are dimorphic,
- Branches of unlimited growth or long shoot.
- Branches of limited growth or dwarf shoot.
Underground root system is formed by “Tap Roots” which disappear early and only lateral roots persist later on.
It bears two types of leaves (dimorphic condition)
a) Scale leaves
b) Foliage leaves
A) SCALE LEAVES
- Thin, membranous small scale like structures.
- Provide protection and do not help in photosynthesis.
- Only develop on dwarf shoots.
- Number of foliage leaves is fixed for particular specie.
- Each leave is needle shaped, simple green therefore also known as “Needles.”
- They have smooth surface and are evergreen and persistent.
The adult plant of Pinus represents the “Sporophytic Phase” of life cycle.
The sporophytic plant body of pinus reproduces asexually by means of spores and after passing through “Gametophytic Phase” of the life cycle again produce Sporophytic plant, showing distinct Alternation of Generation.
1. SPOROPHYTIC PHASE
- The sporophytic plants of Pinus are mostly monoecious i.e. male and female cones are found on same plant.
- Special reproductive organs called “Cones,” developed on it.
- The male cones occur in clusters near the end of long branches at the place of dwarf shoot. (Dwarf shoots are replaced by male cone).
- Each male cone is simple ovoid structure 3-4 cm in length.
- It has got single centrally located cone axis around which are arranged spirally, many scaly microsporophylls (60-135).
- Each microsporophyll has an expanded triangular central part and a stalk like base.
- Each microsporangium, which is born on the lower side bears numerous “Pollen grain mother cells.”
- When the microsporangium matures, on its lower side a horizontal slit is formed through which numerous Pollen grains are liberated and dispersed by wind.
- Each pollen grain is winged structure and yellow in colour.
- The female cones are developed laterally in the axis of scale leaves.
- The female cones are much bigger, woody, dry and hard structure.
- The young female cone is reddish green structure. Each female cone consists of a central axis to which are attached the “Megasporophyll.”
- Each megasporophyll on its surface has two ovules.
- Each ovule is orthosporous and consists of a central mass of tissue, surrounded by a single integument, made up of 3 layers.
- The integument bears a wide gap, the microphyle.
- Within the megasporangium, megaspore mother cells are present, which undergoes reduction division to produce a “Megaspore.”
- Only one megaspore is functional, however the other three degenerate.
- The spores are the units of gametophytic phase of life cycle.
- In case of Pinus the spores are of two types, microspores and megaspores.
- Microspore is a unit of male gametophyte.
- Each microspore or pollen grain is a unicellular body, covered with an outer layer, “Exine,” thick and heavily culticularized, while the inner layer, the “Intine” is very thin.
- The Exine forms the balloon shaped wings on either side, which help in pollination.
- The microspore is at this, four celled stage (consisting of one generative cell and two prothalial cells and a tube cell).
- The Megaspore is the first cell of female gametophyte.
- The functional megaspore increases in size and forms a complete cellular female gametophyte, also known as “Endosperm.”
- The “Archegonia” are formed towards micropylar side.
- The cells of the endosperm or Archegonia initial cell divides and forms the central cell.
- The central cell forms the venter canal cell and a large egg cell.
In case of Pinus, Pollination is effected by wind (Anemophyllous).
1. The pollen grains reach the apex of the Archegonium.
2. The pollen tube carrying the two male gametes and the tube nuclei comes in contact with the archegonium.
3. The tip ruptures, discharging its contents into the egg.
4. One of the male gamete fuses with the egg nucleus and unites forming the oospore or zygote.
5. The second male gamete along with the tube and tube nuclei disintegrate.
- Fertilized ovules get transformed into seeds.
- Seeds are small elongated and winged.
The seed undergoes into a condition of dormancy when the conditions are favourable, the seed absorbs moisture and the embryo resume growth.
STRUCTURE OF OVULE
- Ovules are female part of flower, form seed after fertilization.
- Microscopic study of an ovule reveals following structural features of an ovule.
It is slender stalk of ovule through which it attaches to the placenta.
It is the point of attachment of the body of the ovule to its funicle.
In the inverted ovule, the funicle continues beyond the hilum along side of the body of the ovule forming a sort of ridge, which is called the “Raphe.”
The distal end of the raphe, which is the junction of integuments and the nucellus is called the “Chalaza.”
It is the main body of ovule.
Nucellus is surrounded by two coats called the “Integuments.”
It is the small opening at the apex of integuments.
It is a large, oval cell lying embedded in the nucellus towards the micropyle end. It is the most important part of the ovule as it bears the embryo. It is further developed, and in the mature embryo sac following cells can be seen:
A) EGG APPARATUS
- It is the group of three cells lying towads the micropyle.
- One cell of the group is the female gamete, the ovum/egg, and the other two are called “Synergids.”
- The ovum or egg-cell on fertilization gives the embryo, synergids get disorganized soon after fertilization.
This is the group of three cells lying at the opposite end of egg apparatus. These have no definite function.
C) DEFINITIVE NUCLEUS
In the middle of the embryo-sac there is a distinct nucleus known as a definitive nucleus, which is the fused product of the two polar nuclei.
STRUCTURE OF POLLEN GRAIN
- Pollen grains are male part of flowers, and are contained in the “Pollen-Sac.”
- They are very small in size, usually varying from 10 to 200 μm.
- Microscopic study of a pollen grain shows following features:
- It is the outer coat of the pollen grain.
- It is tough, cutinized layer, which is often provided with spinous out growths or markings of different patterns, sometimes smooth.
- It has one or more weak slits or pores called “Germopores.”
- It is the inner coat of the pollen grain.
- It is thin, delicate, cellulose layer lying internal to the exine.
- During fertilization in time grows to form pollen-tube.
- Each pollen grain contains a bit of cytoplasm on a nucleus.
- During germination of pollen grain nucleus further divides to form a “Tube Nucleus,” and a smaller one the “Generative Nucleus.”
- The generative nucleus soon divides into two male gametes.