2023 Solved Old Paper (BOT

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Ans. Polyembryonic Development.

Types of Polyembryony:- According to Webber, polyembryony is classified into three different types :

i. Cleavage Polyembryony:- In the case of this type, a single fertilized egg gives rise to a number of embryos.

ii. Simple polyembryony:- In this type, a number of embryos develop as a result of the fertilization of several archegonia.

ii. Rosette polyembryony:- Additional embryos develop from the rosette cells in certain gymnosperms, this type of polyembryony is termed rosette polyembryony.

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Manoxylic versus Pycnoxylic Wood:-

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Ginkgo biloba:-

Classification:-

Division - Coniferophyta

Class - Coniferopsida

Order - Ginkgoales

Family - Ginkgoaceae

Genus - Ginkgo

Species - biloba

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Seed of Cycas versus Pinus:-

Ans. Bitegmic ovules are found in plants of Order Gnetales.

Gnetales:-

> Gnetales is an order of the gymnospermic seed plants.

> The members of the order Gnetales are characterized by the presence of compound staminate strobili, opposite or whorled leaves.

> The vessels are present in the secondary wood and absence of resin canals.

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Ans. Welwitschia Mirabilis, a plant known as desert octopus, only exists in the Namib desert and they are able to live for more than 1000 years.

Systematic Position:-

Division:- Gnetophyta

Class:- Gnetopsida

Order:- Welwitschiales

Family:- Welwitschiaceae

Genus:- Welwitschia

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Paleontology:- It is the scientific study of life of the geologic past that involves the analysis of plant and animal fossils, including those of microscopic size, preserved in rocks.

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Kaspar Maria Von Sternberg:-

- He is the “Father of Paleobotany” (1761– 1838) was born in Europe.

- He established the Bohemian National Museum in Prague and is deemed to be the founder of Modern Paleobotany.

> Birbal Sahani:-

- He is the “Father of Indian Paleobotany” (1891–1949).

- He presented his research on two different areas of Paleobotany

i. The anatomy and morphology of Paleozoic Ferns.

ii. The fossil plants of the Indian Gondwana Formations.

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Origin of Gymnosperms:-

Fossil records indicate the first gymnosperms (progymnosperms) most likely originated in the Paleozoic era, during the middle Devonian period about 390 million years ago. Following the wet Mississippian and Pennsylvanian periods, which were dominated by giant fern trees, the Permian period was dry.

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Tri-Phyletic Origin of Gymnosperms:-

> Greguss (1972), in the latest edition of his book entitled “Identification of Living Gymnosperms on the Basis of Xylotomy”, pleaded for a tri-phyletic origin of gymnosperms. He opined that on the basis of Xylotomy (wood-anatomy) three well-defined evolutionary series may be traced among the existing

gymnospermous taxa.

> All these three series among existing gymnosperms have definite correlations with three types of

pteridophytes, another tri-phyletic group:

i. Cycadales (Cycas), Ginkgoales (Ginkgo), Araucariaceae, Podocarpaceae and probably Taxales showing correlations with Pteropsida of Pteridophytes.

ii. Cupressaceae showing correlations with Sphenopsida of Pteridophytes.

iii. Pinaceae and Taxodiaceae showing correlations with Lycopsida of Pteridophytes.

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Polyembryony:- When two or more than two embryos develop from a single fertilized egg, then this phenomenon is known as Polyembryony. In the case of humans, it results in forming two identical twins. This phenomenon is found both in plants and animals.

Polyembryony in Plants:- The production of two or more than two embryos from a single seed or fertilized egg is termed as Polyembryony. In plants, this phenomenon is caused either due to the fertilization of one or more than one embryonic sac or due to the origination of embryos outside of the embryonic sac. This natural phenomenon was first discovered in the year 1719 by Antonie van Leeuwenhoek in Citrus plant seeds.

Types of Polyembryony:- According to Webber, polyembryony is classified into three different types :

i. Cleavage Polyembryony:- In the case of this type, a single fertilized egg gives rise to a number of embryos.

ii. Simple polyembryony:- In this type, a number of embryos develop as a result of the fertilization of several archegonia.

ii. Rosette polyembryony:- Additional embryos develop from the rosette cells in certain gymnosperms, this type of polyembryony is termed rosette polyembryony.

Polyembryony in Different Groups of Gymnosperms:-

1. Polyembryony in Cycadales:- In Cycadales, polyembryony is not a usual phenomenon. But in 1964, Rao reported the occurrence of simple polyembryony in Cycas Circinalis. In this species, two adjacent archegonia of the same ovule sometimes grow independently into two embryos and also rarely into two seedlings.

2. Polyembryony in Coniferales:- In Case of Coniferales, simple polyembryony occurs in the majority of its members and here the number of embryos varies from 2 to many. It has been reported that cleavage polyembryony occurs in several groups of Pinaceae, Taxodiaceae, Cupressaceae, and Podocarpaceae. In Cupressus, both simple and cleavage polyembryony are common.

3. Polyembryony in Taxales:- Various archegonia are present in the female gametophyte of Taxus. Simple polyembryony occurs due to the fertilization of many of the archegonia eggs. But, out of many, only a single embryo attains maturity. Cleavage of suspensor cells occurs. The suspensors separate from each other, and each of them may carry one or more embryonal units. Sometimes, groups of meristematic cells are observed at the base of the suspensor cells These groups of cells are called the rosette embryos. Further development, however, does not take place in these embryos.

4. Polyembryony in Gnetales:- All Gnetales exhibit polyembryony. Polyembryony is found to be of very high order in Gnetum. In this group, there are not only several prothalli and zygotes in each seed, but there is a multiplication of embryos from each zygote by the branching of the primary suspensors.

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Bennettitales:-

> This group of fossil plants flourished well during the Triassic to Lower Cretaceous periods of Mesozoic era. As the Carboniferous period is called the “Ages of Ferns “, the Mesozoic era is called the ‘Ages of Cycads’. It is due to the fact that Cycadeoideales co-existed with Cycadales during Mesozoic era from Jurassic up to Cretaceous period, and hence this period is called Age of Cycads.

> Bennettitales are found either in the form of compressions or petrifactions. Due to Cycad-like form of their fronds and the presence of short stems covered with an armour of presistent leaf bases Bennettitales (Cycadeoideales) have been treated under Cycadophyta by some workers. However, the two groups are quite distinct from each other and maintain their independent identity.

General Characters:-

1. These extinct Mesozoic plants were present were present on the earth from Triassic to Cretaceous.

2. Bennettitales were so abundant during Mesozoic era that this period is known as ‘Age of Cycads’.

3. The members of this group are found either as compressions or petrifactions.

4. The stems were stout or slender and had a wide pith.

5. The stem grew very slowly and had manoxylic wood.

6. Resembling living Cycads, the Bennettitalean leaves were mostly pinnately compound, and only occasionally simple.

7. Venation was open, and only rarely closed.

8. Syndetocheilic type of stomata were present.

9. The wall of the epidermal cells was sinuous.

10. The reproductive organs were organised in the form of hermaphrodite (e.g. Cycadeoidea) or unisexual (e.g. Wielandiella) “flowers”, which in turn were protected by many bracts.

11. The ‘flowers’ developed in the axil of leaves.

12. Male reproductive organs were borne in a whorl. They were free or fused, entire or pinnately compound.

13. Microsporangia were present abaxially in the form of synangia.

14. Microsporophyll’s sometimes surrounded megasporophylls forming hermaphrodite “flowers”.

15. Ovules were numerous and stalked and borne on a conical, cylindrical or dome-shaped receptacle.

16. Many inter-seminal bracts were present on the ovule containing receptacle.

17. The scales or bracts were united at end to form shield through which micropyle protrudes.

18. Seeds were dicotyledonous.

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Coralloid roots of Cycas:-

- Cycas produces coralloid roots.

- Coralloid roots are short tufts and dichotomously branched roots.

- These roots contain an endophytic algae in the inner part of their cortex.

- Sometimes, bacteria are also present in the cortex. Bacteria fix nitrogen.

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Ovule of Taxus:-

- The ovule is somewhat rounded or oval in shape and orthotropous. A single thick integument is present. Integument is free from the nucellus right up to its base forming a long micropyle. The integument is differentiated into outer fleshy, middle stony and inner fleshy layers. Two vascular strands enter the integument from the base of the ovule and reach up to its top.

- A ring-like outgrowth develops from the base of the integument. It surrounds the entire ovule. It is called ‘aril’ or ‘cupule’ . Aril is green and saucer-shaped when young but at maturity it is red and cup-shaped.

- The aril also receives two vascular bundles but they are very minute and rudimentary. Pollen chamber and nucellar beak are absent in Taxus. The apex of the female gametophyte changes into a flask-shaped structure called tent-pole. The tent-pole disappears in the later stages.

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Ovule or Female Flower of Gnetum:-

> Each ovule consists of a nucellus surrounded of three envelopes. The nucellus consists of central mass of cells. The inner envelope elongates beyond the middle envelope to form the micropylar tube or style. The nucellus contains the female gametophyte. There is no nucellar beak in the ovule of Gnetum.

Stomata, sclereids and laticiferous cells are present in the two outer envelopes.

> Madhulata (1960) observed the formation of a circular rim from the outer epidermis of the inner integument in G. gnemon. Thoday (1921), however, observed the formation of a second such rim at a higher level. The ovules in G. ula are stalked.

Morphological Nature of Three Envelopes:- Several different views have been given by many different workers regarding the morphological nature of the three envelopes surrounding the nucellus. A few of them are under mentioned:

i. According to Strasburger (1872) three envelopes of nucellus are integuments developing from the differentiation of single integument.

ii. Baccari (1877) opined that the outer envelope is a perianth while the inner two envelopes are integuments.

iii. Van Tieghem (1869) considered the two inner envelopes as the integuments while the outer envelope as an ovary or analogous to it.

iv. According to Lignier and Tison (1912), however, the outer two envelopes form a perianth while the inner envelope is equivalent to an angiospermic ovary. Vasil (1959) also supported the view of Lignier and Tison (1912) in case of Gnetum ula.

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Structure of Seed of Ephedra:-

- Longitudinal section of the seed shows that it consists of a dicotyledonous embryo in the centre. This embryo is situated at the tip of the elongated suspensor and remains embedded in the endosperm. The nucellus is consumed during the development of embryo and persists as a nucellar cap at the micropylar end of the seed.

- The seed is enclosed by the seed coat which consists of two separate layers derived from the two envelopes. At the time of maturity, the subtending bracts of the megasporangiate strobilus become thick and fleshy and form an additional covering around the seed e.g.,E. foliata.

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Applied Aspect of Studying Fossil Plants:- To provide useful information in the exploration of fossil fuel like coal and oil.

> The plant inhabitants of Palaeozoic- Mesozoic swamps served as a source of coal and formed coal seams. Accumulation of plant materials with a variety of minerals coupled with mud, silt and other organic materials constitute a coal bed. Many plant parts get beautifully preserved as fossils in the stratified sedimentary layers which are closely adjacent to coal layers.

> A stratified scale based on fossils can be made to establish the age of coal deposits and their position in the succession of rocks. Palaeobotanical studies have served as a tool to ascertain age of coal layers, their lateral extent and quality of coal deposits. Such information are required to specify the suitability of a particular coal for energy production. In India, the palaeobotanical study has helped to demarcate the nature and quality of Raniganj coal (Permian Age) from that of Rajmahal coal (Jurassic Age).

> The assemblage of fossil pollen grains and spores has contributed significantly in the field of oil exploration. The problem of oil exploration begins with search of oil reservoirs.

> Exploration of oil is done by:

i. Determining the Thermal Alteration Index:-

- The sporopollenin present in the walls of pollen and spores undergo post depositional thermal changes in course of the geological ages. These thermal changes brought about carbonisation resulting in changes in exine colour of fossil pollen and spores in transmitted light.

- The basic idea involved is the usage of the variation in the exine colour as an indicator of the degree of carbonisation in the rocks to predict their changes of bearing reservoir. Pearson’s colour chart directly relates exine colour to a numerical index called Thermal Alteration Index (TAI) which is a measure of the degree of carbonisation. TAI having a range of 2+-3+ and exinite flourescence colour white-yellow, dark yellow-brown indicates the possibility of exinite containing rock to possess liquid petroleum and even natural gas.

ii. Palynostratigraphy:- To avoid unnecessary and costly drilling the determination of oil zone is made by comparing the biostratigraphic data of one to those of the others.

iii. Defining of Ancient Shorelines:- The sediments parallel to sea shore are rich in oil. The density of pollen and spores decreases in the seaward direction. Sedimentary environment with pollen assemblages are limited to near shore marine or lacustrine waters. Thus by the study of microfossils along with marine microfossils if presents, one can determine the distance and direction of ancient shore lines, possibly bearing oil deposits.

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Process of fossilization:- The process of formation of fossil in the rocks is called fossilization.

Common methods of fossilization includes petrifaction, molds and cast, carbonization, preservation, compression and infiltration.

i. Petrifaction:- Minerals like silica slowly penetrate in and replace the original organic tissue and forms a rock like fossil. This method of fossilization can preserve hard and soft parts. Most bones and wood fossils are petrified.

ii. Mold and Cast:- A replica of a plant or animal is preserved in sedimentary rocks. When the organism gets buried in sediment it is dissolved by underground water leaving a hollow depression called a mold. It shows the original shape but does not reveal the internal structure. Minerals or sediment fill the hollow depression and forms a cast.

iii. Preservation:- Original remains can be preserved in ice or amber (tree sap). They protect the organisms from decay. The entire plant or animal is preserved.

iv. Compression:- When an organism dies, the hard parts of their bodies settle at the bottom of the sea bed and are covered by sediment. The process of sedimentation goes on continuously and fossils are formed.

v. Infiltration or Replacement:- The precipitation of minerals takes place which later on infiltrate the cell wall. The process is brought about by several mineral elements such as silica, calcium carbonate and magnesium carbonate. Hard parts are dissolved and replaced by these minerals.

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Evolutionary Trends of Gymnosperms:- On the basis of the available studies of several fossil groups, although it appears that the gymnosperms constitute a heterogenous group, yet it is possible to delineate several over-all trends in the evolution in this group.

1. Vascular System:-

> The primary vascular system exhibits a narrow range among gymnosperms. Majority of the

gymnosperms are monostelic, and only some exhibits polystelic condition. Some of the members also possess co-axial evolutionary cylinders of secondary wood which develops from the anomalous activity of cambium.

> A change from the cauline to foliar nature has been the main evolutionary trend in the stem anatomy of different members of gymnosperms. The primary wood is suppressed in this change from cauline to foliar nature.

> During this suppression the primary wood passes through various stages such as:

i. Solid protostele

ii. Pith surrounded by mesarch strands

iii. Development of endarch strands adjacent to the secondary wood

iv. Mixed xylem

v. Parenchyma

> During the entire process of these changes a gradual transference of function from primary to

secondary wood takes place. The leaf trace system, which was associated with the primary wood in the

earliest types, now becomes “more and more closely associated with the secondary wood”.

> In members of Cordaitales, Ginkgoales and Coniferales there is a definite increase in the secondary

wood. In Gnetales, however, vessels replace tracheids, though not completely but only partly.

2. Leaves:-

> The microphylls and megaphylls are the two different kinds of leaves found in gymnosperms. The

microphylls are small and usually possess one or two parallel veins. The megaphylls are quite large, frond-like leaves and possess well-branched veins.

> The gymnosperms of Coniferophyta-line possess microphylls while the members of Coniferophytaline bear megaphylls. Ginkgoales, however, possess neither microphylls nor megaphylls but wedge-shaped or fan-shaped leaves of almost normal size.

> Majority of the recently reported fossil members of gymnosperms indicate their affinities more with

the microphylls than with the megaphylls. Several botanists consider Cycadophytes as more primitive than Coniferophytes. This indicates that megaphyllous leaves are more primitive than microphyllous leaves.

> Much evolutionary significance has not been attached with the leaf anatomy of gymnosperms. A little

consideration has, however, been given to the xeric conditions of these members. It is supposed that

inappropriate condition of water by the tracheids has been the major reason for the xeric condition among gymnosperms.

3. Reproductive Organs:- Some important events of the evolution of reproductive organs among gymnosperms may be listed as under:

> Probably, all reproductive organs in the beginning were stachyspermous (i.e. reproductive organs

borne on stem). Some gymnospermous genera have managed to stay as stachyspermous even today.

> During the course of the evolution, the structures bearing reproductive organs progressively became

more leaf-like, i.e. phyllospermous. The sporophylls were thus originated.

> In Ptendosperms, the sporophylls were leaf-like.

> A From the compact sporophylls developed the cone. The Cordaitales were the first to produce monosporangiate cones. The tendency of bearing mono-sporangiate cones is also retained in Ginkgoales and Coniferales.

> The mono-sporangiate cones or strobili evolved into bisporangiate cones or strobili during course of

evolution. Gnetales (e.g. Welwitschia) possess bisporangiate strobili.

> In Cordaitales, Ginkgoales and Coniferales, the sporophylls are distinctly attached to the axis, and,

therefore, the strobili, in these groups are simple. On the other hand, compound strobili are produced

in some more advanced groups such as Gnetales.

4. Microsporophylls:-

> In Cycadophytes, the microsporophyll’s are pinnate and peltate. They bear sori only on their lower

surface. Due to these characters the microsporophyll’s of Cycads are very primitive. In different members of different groups of gymnosperms, a reduction of long sporophyll to a short discoid structure and then also to a filament is observed, and these all are the features of evolutionary significance.

> Some other such features include:

i. Formation of individual sporangia instead of synangia

ii. Fast elimination of annulus from the fern-like appearance.

5. Ovules:-

> Two evolutionary trends are visible in the ovules of the gymnosperms. These are:

i. Degeneration of the outer fleshy layer

ii. Appearance of two integuments

> In most primitive type of gymnospermous ovules, the integument is single and it is also free from the

nucellus. Three distinct layers are discernible in the integument, viz. outer fleshy layer, middle stony layer and inner fleshy layer. Two vascular strands supply the ovule, of which the outer strand enters the outer fleshy layer and the inner strand enters the peripheral region of the nucellus.

> In majority of the gymnosperms the integument remains fused with the nucellus in most of its part,

except the micropylar region, where the nucellar beak is formed and the trilayered integument is not reduced at all.

> The outer fleshy layer develops quite conspicuously in the ovules of Cycadophyta-line. In the ovules

of the Pinaceae-line, the outer fleshy layer is represented by a young ovule. Instead of one, two integuments are present in the ovules of Gnetales, and, therefore, it exhibits an example of a second evolutionary trend in the gymnospermous ovules.

6. Male Gametophyte:-

> The pollen grains of most of the fossil gymnosperms, except of Coniferales and Taxales, are almost

uniform in possessing a layer of parietal cells surrounding the centrally located spermatogenous region. The layer of parietal cells probably represents an antheridial jacket.

> In the early stages of the evolution of gymnosperms, the vegetative prothallial cells have been in such

a low number that the male gametophyte might be treated as a reduced form of an antheridium. A reduction in the antheridial jacket and the simultaneous formation of a pollen tube have been observed between the fossil gymnosperms and the extant forms (i.e. members still in existence).

> A homology, probably exists between the tube cell of the modern gymnosperms and the antheridial

jacket of Palaeozoic gymnosperms The male gametophyte development appears to be quite uniform within a family.

> In Pinaceae, two senescent primary prothallial cells are produced from the embryonal cell of the

microspore. This embryonal cell functions as an antheridial initial and results in the formation of a peripheral tube cell and a generative cell. A periclinal division in the generative cell gives rise to an outer spermatogenous cell and an inner sterile cell. Two male gametes are produced by the division of the spermatogenous cell.

> In Taxaceae, Taxodiaceae, Cupressaceae and Cephalotaxaceae there is no prothallial cell, and the

function of the antheridial initial is performed directly by the embryonal cell.

> In Araucariaceae and Podocarpaceae, the prothallial cells show secondary proliferation. The ontogeny of male gametophyte in Araucariaceae resembles greatly with Pinaceae. In Araucariaceae and Podocarpaceae. however, the generative cell divides anticlinally and not penclinally. Very little proliferation of primary prothallial cells is observed in Podocarpaceae in comparison with that of Araucariaceae.

> In Gnetales (e.g. Gnetum and Welwitschia), the prothallial cells are generally absent The function of

the antheridial initial is performed by the embryonal cell. A tube cell and a generative cell are formed.

> Division of the generative cell results in the formation of a spermatogenous cell and sterile cell. The

spermatogenous cell divides and form two male gametes.

> The male gametes or sperms are ciliated and motile in Cycas. Probably the same condition existed in

Ptendospermales, Cycadeoideales and Cordaitales. In Coniferales and Gnetales, however, naked nuclei are present in place of motile and ciliated ones. Pollen chamber also disappears simultaneously. The sperms are carried away by the pollen tubes.

> In Ephedra, however, a deeply situated pollen chamber is present. This is, however, an indicative of a

secondary origin. A well- developed archegonial neck is also present in Ephedra.

7. Female Gametophyte:-

> In gymnosperms, the female gametophyte is a massive, multicellular body. It serves the dual purpose

of bearing the archegonia and providing nourishment to the young embryo.

> Major evolutionary steps in the female gametophyte include:

i. Free-nuclear divisions,

ii. Vacuolation,

iii. Process of wall-formation resulting into the formation parietal tissues, and

iv. Process of wall-formation extending towards the central region and resulting into the development of endosperm.

> In majority of Cycadales, Ginkgoales, Coniferales and some Gnetales (e.g. Ephedra), the early

development of female gametophyte involves a fairly uniform plan. Alveoli also appear in members of almost all these groups but the pattern of alveoli vanes. The archegonia develop in the female gametophyte.

> In both pteridophytes and gymnosperms, the general structure of the archegonium is almost similar.

An egg cell, a ventral canal cell, a few neck cells and a venter are present in an archegonium of both the

groups.

> The gametophyte is, however, parasitic on sporophyte in gymnosperms while it is free-living and

green in pteridophytes. Neck canal cells are absent in gymnosperms while they are present in the archegonia of ptendophytes.

> These differences indicate some evolutionary trends showing a reducing capacity of gametophyte for

its independent existence. On the other hand, several simulates show homologies in the structure of the female gametophyte of both ptendophytes and gymnosperms.

Q. From Which Type of Earliest Gymnosperms Developed the Modern Gymnosperms?

Ans. The earliest gymnosperms, responsible for the evolution of this entire modern group, probably had the following characteristic features, according to Sporne (1965):

i. Stems with primary solid wood, also perhaps possessing some amount of secondary wood.

ii. Plants perhaps had little distinction between leaf and stem.

iii. Pollen-bearing organs were borne fully exposed at the tips of green photosynthetic branch- lets.

iv. Seeds were also fully exposed.

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Distribution of living and fossil Gymnosperm in India:-

1. Cycadales:-

> Indian Cycadales are represented by only 5 species of Cycas and occur mainly in South India. These are Cycas beddomei (Madras and dry hills of Cudapah in Andhra Pradesh), C. circinalis (Andaman and Nicobar Islands and some dry deciduous forests of South India), C. rumphii (Andaman and Nicobar Islands), C griffithi (Manipur and Nega Hills) and C. pectinata (Assam, Bihar, Sikkim and several parts or Eastern India).

> C. revoluta, a Japanese species, is cultivated commonly in Indian gardens. It does not occur in wild state.

2. Gnetales:-

> Indian Gnetales include species of Gnetum and Ephedra. Welwitschia, the third genus of the order, has not been reported from India. Five species of Gnetum (viz. G. ula, G. contractum, G. gnemon, G. montanum and G. latifolium) occur in various parts of the country.

> According to Bhardwaj (1957) various Indian species of Gnetum along with their places of distribution in parenthesis include G. ula (Western Ghats near Khandala, forests of Kerala, Nilgiris, Andhra Pradesh and Orissa), G. contractum (Nilgiri Hills, Conoor and hills of Kerala), G. gnemon (eastern parts of the country, particularly Assam), G. montanum (Assam, Sikkim and parts of Orissa) and G. latifolium (Andaman and Nicobar Islands).

> Ephedra, in India, is represented by only 6 species. These are Ephedra foliata, E. gerardiana, E. intermedia, E. nebrodensis, E. regeliana and E. saxatilis. These are distributed widely in dry parts of Haryana, Punjab, Rajasthan, and parts of Sikkim, Kashmir, and also at high altitudes in Himalayas.

3. Coniferales:-

> Coniferales are the dominant forest-makers of the world. Out of 54 living genera of Coniferales in the world, ten have been reported from different parts of India. These are Abies, Cedrus, Cephalotaxus, Cupressus, Juniperus, Larix, Picea, Pinus, Podocarpus and Tsuga. The distribution of the majority of these members is restricted mainly in the Himalayas, and governed chiefly by altitudes.

Brief description of their distribution:-

- Abies is represented in the country by only 4 species, of which A. delavayi and A. densa grow in eastern Himalayas, whereas A. pindrow and A. spectabilis are restricted to western Himalayas. A. pindrow grows luxuriantly at about 2500 metres above sea level, whereas A. delavayi occurs commonly at an altitude of about 2750-3350 metres above sea level. A. densa grows luxuriantly in Darjeeling and adjacent hills.

- Cedrus, in India, is represented by only one species i.e. Cedrus deodara (vern. Deodar). This beautiful tree is famous for its wood, and grows in western Himalayas between 1200-3300 metres. Cephalotaxus grows in eastern Himalayas, and is represented by only two species (C. griffithi and C. mannii).

- Cupressus tortulosa grows throughout in the outer and middle ranges of Himalayas from Chamba hills in Himachal Pradesh to Aka Hills in Assam at an altitudes from 1800 to 2800 metres C. funiberus and C. sempervirens are cultivated as ornamental plants in Indian gardens.

- Six species of Juniperus have been reported from higher altitudes of eastern as well as western Himalayan regions of India and Bhutan. J. communis occurs between 2900-4250 metres in Garhwal Himalayas, whereas J. coxii grows both in eastern as well as Western Himalayas.

- J. macropoda grows between 2500-4300 metres in Laddakh, Kanawar and Alaknanda valley, whereas J. recurva and J. squamalata grow between 3000-5000 metres in the eastern Himalayas. J. wallichiana grows at an altitude between 3000 to 4200 metres in the Himalayan ranges.

- Larix griffithiana occurs generally mixed with Abies, Pinus and Tsuga in Sikkim, Chumbi valley of Tibet, Bhutan and Mishmi Hills in Assam. Picea smithiana grows in western Himalayas and attains a height of about 60 metres. It grows from Afghanistan to Kumaon.

- Pinus is represented by 6 species in India. These are P. roxburghii, P. wallichiana, P. insular is, P. gerardiana, P.armandi and P.merkusii. They are distributed throughout in Himalayas. Pinus roxburghii (vern. Chir) grows at lower altitudes between 2000-5000 feet, whereas P. wallichiana grows in north-west Himalayas ranging from an elevation of 5000-12000 feet.

- Pinus gerardiana (vern. Chilgoza) occurs on the Himalayan flanks extending from Punjab to Afghanistan and Baluchistan ranging within the altitudes of 5000 to 12000 feet. Pinus insularis grows in Khasia and Chittagong hills.

- Two species of Podocarpus (P.neerifolia and P. wallichianus) occur in India. The former grows in Andaman Islands and eastern Himalayas, whereas latter grows in Nilgiri hills and Assam. Tsuga dumosa grows luxuriently in Darjeeling and adjacent regions, along with Abies densa, above an altitude of 2700 metres.

- Besides the above-mentioned 10 genera, which grow naturally in different parts of India, some Coniferales are cultivated as ornamentals in Indian gardens.

- There include Araucaria cooki and A. cunninghamii of Araucariaceae, Thuja occidentalis and Cupressus cashmeriana of Cupressaceae. Callitris cupressi of Cupressaceae is grown as a hedge plant in Nilgiris, whereas Cryptomeria japonica of Taxodiaceae is grown in Darjeeling and other areas.

Ans.

Similarities of Gymnosperms with Pteridophytes:-

i. Sporophytic, independent plant body is present in both the groups. It is differentiated into root, stem

and leaves.

ii. Sporophyte possess a well-developed vascular tissue.

iii. Xylem lacks vessels and phloem companion cells.

iv. Young leaves show circinate vernation.

v. Presence of megaphyllous leaves.

vi. Gymnosperm and few pteridophytes e.g. Selaginella are heterosporous i.e. form micro- and

megaspores in micro- and megosperangia, borne on the micro and megasporophylls respectively.

vii. In Cycas, sporangia are grouped in sori like pteridophytes.

viii. The female sex organ is archegonium in both the groups.

ix. The male gametes of Cycas and Ginkgo are motile like the pteridophytes.

x. Permanent retention of megaspore within the megasporangium.

xi. Gametophytes are endosporic and highly reduced.

xii. Female prothallus develops before fertilization and there is free nuclear division.

xiii. Germination of spores is precocious in gymnosperms and hetrosporous pteridophytes.

xiv. Development of distinct embryo after fertilization.

xv. Like the pteridophytes, gymnosperms show marked alternation of generation between

gametophytic and sporophytic phase. Sporophytic generation or sporphytic phase is dominant,

independent and large at maturity while the gemetophtic generation exhibits progressive reduction and

dependence.

Similarities of Gymnosperms with Angiosperms:-

i. Main plant body is sporophytic and is differentiated into root, stem and leaves.

ii. Plants are trees or shrubs and may be erect or climbing.

iii. Root system is well developed and the roots may be diarch, triarch, tetrach or polyarch.

iv. The xylem is exarch in the roots.

v. Stem is eusteltic. Vascular bundles are conjoint, collateral, open and endarch.

vi. Secondary growth takes place.

vii. Wood may be monoxylic or polyxylic.

viii. Vessels and companion cells also occur in some gymnosperms (Gnetales) like angiosperms.

ix. Heterosporous and have reduced gametophytes.

x. Nucellus is surrounded by integument to form a structure called ovule.

xi. Like gymnosperms many angiosperms are wind pollinated.

xii. Megaspore permanently remains inside the megasporangium and develops into female

gametophyte.

xiii. Pollen grains grow into pollen tube.

xiv. Male gametes are non-motile in majority of gymnosperms and angiosperms.

xv. Fertilization is siphonogamous.

xvi. Suspensor is formed during development of embryo.

xvii. Formation of endosperm.

zviii. Formation of seeds from ovules.

xix. As in gymnosperms, polyembryony is found in several angiosperms.

xx. Embryogeny is endoscopic.

xxi. Life cycle is similar in both groups.

Ans.

Gametophytes in Ginkgo:-

Male gametophyte:-

> Male gametophyte starts developing in situ, i.e. within the sporangium. Microspore is the first cell of the male gametophyte.

> Each microspore is a rounded structure having thin intine and thick exine layers.

> A centrally located nucleus contains one or two nucleoli and remains surrounded by dense cytoplasm. > An un-thickened portion, called pore, is also present in each microspore. It is a region where exine is not covering the intine.

> Two unequal cells are formed by the first mitotic division in the microspore.

> These are called 1st prothallial cell and inner cell. The 1st prothallial cell is smaller than that of inner cell.

> The inner cell again divides forming a 2nd prothallial cell and an antheridial initial. By this time the 1st prothallial cell starts to degenerate.

> The antheridial initial then divides forming a generative cell near the 2nd prothallial cell and a tube cell.

> The tube cell does not divide any further. This is the 4-celled stage of the male gametophyte and the microspores are dispersed by wind at this stage.

> Pollination in Ginkgo biloba takes place sometime in April. At the time of pollination the ovule secretes a mucilaginous substance.

> Further development of the male gametophyte takes place in the pollen chamber. In pollen chamber the generative cell of the 4-celled young male gametophyte divides into a stalk cell, which is close to the 2nd prothallial cell, and a body cell.

> Now the intine protrudes out near the pore and functions as a pollen tube. The pollen rube swells up and advances towards the archegonia by protruding into the nucellus. Just before fertilization the body cells divides into two. Two cells which function as sperms or male gametes.

Female gametophyte:-

> Out of the four megaspores formed from the megaspore mother cell, only the lowermost remains functional and the remaining three degenerate.

> The nucleus of the functional megaspore migrates towards the micropylar end and divides into two followed by a number of free- nuclear divisions forming hundreds of free nuclei.

> First the anticlinal walls are formed followed by the vertical walls.

> Each cell generally contains one nucleus but in some cells 2-3 nuclei are also seen. Due to more rapid cell divisions on the micropylar end a pole-like structure develops.

> The female gametophyte possesses abundant chlorophyll.

> The development of archegonium starts from the cells towards the micropylar end of the female gametophyte.

> Each archegonium possesses a short neck made up of only four cells and a small venter having a central cell. The central cell later on forms a ventral canal cell and an egg cell.

> Two cells are present in the archegonial neck.

> The pollen tube reaches up to the neck of the archegonium just after its (archegonium) differentiation.

> The tube ruptures releasing the sperms and the other contents in the archegonial chamber.

> A sperm passes through the neck of the archegonium, comes in contact and fuses with the egg nucleus.

Ans.

Reproduction in Welwitschia:-

> Welwitschia is strictly dioecious, i.e., two sexes are present in separate individuals. The inflorescences develop from a series of several transverse ridges arising parallel to the leaf bases. The branching in inflorescences is dichasial, and each branch ends in an attractive cone.

> Several bracts or cone scales, arranged in opposite decussate manner, are present in each cone. Because of crimson or scarlet colour, the mature cones of Welwitschia provide a beautiful look. Martens (1961 1963, 1974, 1975, 1977) and his pupil Waterkeyn have done extensive work on the embryology of Welwitschia.

a. Male Strobilus and Male Flower:-

- A male or microsporangiate strobilus or male cone is a compound structure bearing a quadrangular cone axis. It contains several bracts or cone scales arranged in opposite decussate manner. In the axil of each subtending bract is present a male flower.

- Two lateral bracts and a perianth are also present in each male flower. The perianth is formed from two bract-like anterior-posteriorly placed structures.

- Inner to the perianth is present a whorl of six micro-sporangiophores which remain fused at the base to form a cup-like structure. A sterile ovule with a single integument is present in the centre of each male flower.

- At the top of each micro-sporangiophore is present a synangium. Each synangium is formed by the fusion of three microsporangia. Each microsporangium contains many pollen grains which are shed through a vertical slit. Pollination is effected either by wind or by insects.

Male Gametophyte:-

- Pollen grain matures into a three-celled male gametophyte (Sterling, 1963) but much is not known about the actual process of the male gametophyte development. The 3-celled stage includes a tube nucleus, a sterile cell and a spermatogenous cell. The sterile cell usually aborts even before the pollination.

- The spermatogenous cell gives rise to two male nuclei or sperm nuclei. Since the general process of the male gametophyte development resembles with that of Gnetum, it is assumed that the prothallial cells are absent in Welwitschia.

- According to Bomman (1972) Welwitschia is wind-pollinated. However, van Jaarsveld (1990) opined that it is insect-pollinated.

b. Female Strobilus and Female Flower:-

- The female strobilus, also called ovulate or megasporangiate strobilus or ovuliferous cone is also a compound structure like male cone. The axis of the female strobilus bears many broad decussate bracts or cone scales, in the axil of each of which is present a female flower.

- Inside the subtending bract of each female flower are present two small lateral bracts, two envelopes and a single nucellus. Out of the two envelopes the inner one functions as a true integument, and prolongs in the form of a long tubular micropyle.

- The outer envelope develops from two posterior-anterior primordia which fuse with each other in the early stages of the development. Some prefer to call this fusion product as perianth The perianth expands into a broad wing-like structure in the mature seed.

Female Gametophyte:-

- A single megaspore mother cell develops quite deep in the nucellus tissue. Its diploid nucleus divides meiotically but there is no cross-wall formation. Linear tetrad of spores is not formed, and a tetrasporic female pro-thallus develops directly. Haploid nuclei of young female gametophyte divide and redivide several times mitotically but there is no cross-wall formation. Thousands of free-nuclei are thus formed.

- At this stage the cell wall formation starts irregularly, and each cell contains varying number of nuclei. In several of these cells the nuclei fuse to form polyploids. Formation of archegonia has not been observed in Welwitschia.

c. Fertilization and Post-Fertilization Changes:-

- The fertilization process is quite unique in Welwitschia. At the time of fertilization, the pollen tubes elongate and grow downwards through the nucellus. Simultaneously the apical cells of the female pro-thallus elongate and form prothallial tubes which grow upwards.

- The pollen tubes and the prothallial tubes thus grow in opposite directions and come in contact with each other, somewhere in the nucellar cap.

- The contact walls between the two tubes dissolve and it is said that female nuclei pass into the pollen tubes and thus the male and female nuclei fuse with each other to form a fusion nucleus. The act of fertilization thus takes place in the pollen tube rather than in an archegonium or embryo-sac.

- The diploid zygotic nucleus divides and forms a 2-celled pro-embryo. The upper cell of this pro-embryo develops into a primary suspensor while the lower cell divides and re-divides to form a large number of secondary suspensor cells and a multicellular embryo. A cap of about eight cap cells protects the young multicellular embryo which is pushed down into the pro-thallus by the elongating suspensor.

- Welwitschia exhibits a high degree of polyembryony because many zygotes and young embryos are produced. However, only one embryo finally matures into a seed. A lateral finger-like process, called feeder, is present in the mature embryo.

- The winged outer envelope of the ovule matures into a papery structure. The seed germination is epigeal and both the permanent leaves appear soon after the germination. The cotyledons grow for about six months and finally die.

Ans.

Fossils and their types:-

> A plant fossil is any preserved part of a plant that has died long back. Fossils may be a prehistoric impression that may be hundred to millions of years old. Majority of the plant fossils are disarticulated parts of plants, it is rare to find plants to be preserved as whole.

> Importance of fossils:-

i. They throw light on phylogeny and evolution of plants.

ii. Fossil plants give a historical approach to plant kingdom.

iii. Fossils are useful in classification of plants.

iv. Fossil plants can be used in the field of descriptive and comparative anatomy.

> 8 Types:-

i. Petrified Fossils:-

- The word petrifaction means turning into stones. The fossils form when minerals replace all or the parts of the organisms. Water is full of dissolved minerals. It seeps through the layer of sediments to reach the dead organism. When water evaporates only the hardened, materials are left behind.

- There is molecule by molecule replacement of plant parts by minerals such as iron, pyrites, silicates, carbonates, sulphates etc. These minerals get deposited and impregnated inside the cells and the tissues of the plant. This type of fossil can be studied by preparing the sections and are most suitable for the study of structural details. Petrified plant organs roughly spherical in shape are known as coal balls.

ii. Molds and Casts:-

- A mold forms when hard parts of an organism are buried in the sediment such as sand, silt or clay. The hard part completely dissolves overtime, leaving behind a hollow area of organism shape.

- A cast forms as a result of the mold. Water with dissolved minerals and sediments fills the mold’s empty space or cavity. The cavity is known as incrustation and the mineral sediments that are left in the mold make a cast. A cast is opposite to its mold. These fossils are suitable for the study of the morphology of fossil plants.

iii. Carbon Films:- All living things contain an element carbon. When an organism dies and is buried in sediment, the materials that make the organism break down and eventually only the carbon remains. The thin layer of carbon left behind can show an organism’s delicate parts like leaves or plant e.g. fern fossil 300 million years old.

iv. Trace Fossils:- These fossils show the activities of the organisms. An animal makes a foot print when it steps in sand. Overtime the foot print is buried in layers of sediment. Then the sediment becomes solid rock.

v. Preserved Remains:- Some organisms are preserved in or close to their original states. These fossils are called preserved remains e.g., an organism such as an insect is trapped in a tree’s sticky resin and dies. More resin covers it sealing the insect inside. It hardens into amber. Some organisms such as a wooly mammoth dies in a very cold region. Its body is frozen in ice which preserves organism even its hair.

vi. Compression:-

- This type of fossil is common in the sedimentary deposits of rocks. It is a sort of impression where most of the organic remains of the plant remain in the fossil state. The plant or plant part gets buried and the sediments go on accumulating over the plant.

- The growing pressure of the sedimentary rocks removes the air and the watery contents of the fragment out and causes the plant tissue to compress. The compression shows the original outline of the plant or plant parts but the original thickness of the plant material cannot be determined. The buried part becomes flat due to compression or overlying pressure of the sediments.

vii. Impression:- These fossils are just impression of plants or plant parts on sediments. These fossils are useful in studying the external features of various plant parts and venation pattern of leaves.

viii. Pseudofossils:- Sometimes watery solutions of various minerals speed through the sediments and it takes the shape of some plant part or animal. Their study shows that they are neither plants nor animals. Such fossils are called pseudofossils.

Techniques of study of fossils:-

1. Ground Thin Section Technique:-

> The specimen to be studied is cut into small-sized sections. Its surfaces are smoothed with 400-carborundum. The smooth surface of the section of the specimen is mounted on a glass slide. It is warmed and coated with melted resin.

> The latter hardens upon cooling. The fastened specimens are cut to form very thin slices which are ground on revolving 100-carborundum lap. Liquid resin-mounting medium is used for mounting the sections.

2. Peel Technique:-

> The first step of this technique involves the etching of the fossil surface with the help of some mineral acids (e.g., hydrofluoric acid) and the final step involves transfer of the exact fossil structure.

> Another mixture usually used for etching is prepared by mixing butyl acetate (1000ml), nitrocellulose (115gm), toluol (10ml), amyl alcohol (200ml) and dehydrated castor oil (5ml). Before using for etching purposes, this mixture is aged for at least two weeks.

> After etching the specimen surface is washed with water, dried and covered with nitrocellulose. Wait for a few hours. The so formed film will dry during this period. It is peeled off from the specimen and studied.

3. Transfer Technique:- Delicate fossil materials are studied by this technique. Several methods are used in the form of transfer technique In the Ash by cellulose film transfer method, peel solution is coated on the delicate fossil material adjoining the rock surface. When the solution dries, the portion of the rock having fossil material is removed. 25% hydrofluoric acid is then used for dissolving the rock material.

4. Maceration Technique:- In the usual method of maceration technique, the fossil material is immersed in a mixture of 5% KOH and Cone. HNO3 for one week. The material is then washed thoroughly with water so that the acid is completely removed. It is then incubated with the solution of NaOH. Hydrofluoric acid is used for cleaning the thus separated cuticularized parts of the fossil material.

5. X-ray Technique:- Highly sensitive celluloid films are used to obtain X-ray photographs of the fossil specimens.

6. Microtomy Technique:- Fossil specimens, specially their macerated tissues, are embedded in celloidin or wax before microtomy. Sectioning of the embedded material is done by usual process of microtomy. The sectioned materials are stained and studied.

Ans.

Economic importance of Gymnosperms:-

1. Food:-

> In some parts of India, Malaya, Philippines and Indonesia, young succulent leaves of various species of Cycas are cooked and eaten as vegetable.

> The famous “Sago” starch is obtained from the stem / seeds of Cycas and used as food. This stem starch obtained from Macrozamia spiratis is an important source of food for poultry, dairy animals and pigs.

> The seeds of Cycas are used as paste and eaten as cakes in Nicobar Island.

2. Green Manure:- Leaves of Cycas are rich in nitrogen and used as green manure for rice, sweet potato and sugarcane.

3. Medicine:- Leaf extract of Ginkgo biloba is useful in the treatment of cerebral insufficiency and vertigo.

4. Ornamental:-

> Ginkgo biloba and Cycas species are grown as an avenue tree and in gardens also for beautification.

> These trees are preferred especially due to their slow growth, evergreen nature and beautiful symmetry.

5. Timber:-

> Conifers and Taxales are most important genera of gymnosperms significantly important to produce high quality, straight grained, light colored, high weight and strong wood in comparison to their weight.

> They are suitable for making cabinets and furniture due to their strength and durability.

> The wood of Abies is light and termite free. It also has pleasant scent smell and used for packing cases, match wood, wood wool, aircraft work, plywood, light camp furniture and also used as household materials.

> Juniperus wood is fragrant, reddish brown and rarely damaged by insects.

> Cedrus wood is also durable, oily, fragrant, insect repellant and rot resistant.

> The wood of Taxus is strong, oily, elastic, close- grained, fragrant and very durable with smooth glossy surface.

> Beside this, wood of Araucaria canninghana used for plywood manufacture.

6. Resin:-

> Conifers exudated resins, this help the wood resistant to decay.

> Conifers are the major resin yielders of the world. These resins evaporate their oil and became harder which makes them invaluable in paints, varnishes, paper sizing, medicines and liquors industries.

7. Canada Balsam:- A resin obtained from Abies balsamea which has a very high refractory index approximately that of glass. Due to this property it is extremely suitable as amounting medium for microscopic objects and as cements for uses in optical work.

8. Essential Oils:-

> All conifers young branches and adherent leaves provide essential oils.

> Himalayan Cedar oil (Cedrus deodara) and Red Cedar Wood (Juniperus virginiana) are used cleaning tissues in histological work and also use with the oil immersion lens of the microscope.

> The oil obtained from Cedrus atlantica possess medicinal properties and used against bronchitis, tuberculosis, skin diseases and gonorrhea.

> The essential oils are used extensively in preparation of deodorants, room sprays, disinfectants, perfumery and medicine etc.

9. Fatty Oils:-

> Many conifer seeds are rich in fatty oils.

> The oil from the seeds of Pinus cembra and Torreya nucifera is edible and also used for paints.

> The Tail Oil obtained as a by product from sulphate process of cooking conifer wood for making Kraft paper is used in paints, soaps, linoleum, emulsifiers etc.

10. Pharmaceuticals:-

> The leaves of Taxus baccata are used in asthma, bronchitis, hiccough, epilepsy and for indigestion.

> Taxol (from Taxus brevifolia) is found effective against ovarian cancer, breast cancer, and melanoma and colon cancer.

> Ephedra is the source of a valuable drug Ephedrine obtained from E. equisetina, E. gerardiana, E. major, E. sinica, E. intermedia and E. nebrodensis. It is used against cold, respiratory disorder and hay fever.

> An aromatic beverage, known as Mormon tea is also brewed from the species of Ephedra in south western United State.

11. Amber:-

> It is a fossil, water insoluble tree resin which was secreted by the now extinct pine, (P. succinifera).

> It is yellow, brown to black, hard and brittle with an aromatic odor.