2019 Solved Old Paper (BOT-102)
Bryopsida (Mosses):-
> They are commonly called mosses.
(इन्हें आम तौर पर मौस कहा जाता है।)
> The gametophyte is divided into protonema and foliose gametophore.
(युग्मकोदभिद को प्रोटोनिमा और पर्णीय गैमेटोफोर में विभाजित किया गया है।)
> Foliose gametophore is formed of the stem as an axis and leaves without a midrib.
(पर्णीय गैमेटोफोर एक अक्ष के रूप में तने और मध्यशिरा रहित पत्तियों से बना होता है।)
> Rhizoids are multicellular with oblique septate.
(मूलाभास तिरछे पट्ट युक्त बहुकोशिकीय होते हैं।)
> Sex organs are borne apically on the stem.
(लैंगिक अंग शीर्षस्थ रूप से तने पर उत्पन्न होते हैं।)
> Elaters are absent.
(इलेटर अनुपस्थित होते हैं।)
> The sporophyte is differentiated into foot, seta and capsule.
(बीजाणुदभिद को फुट, सीटा और कैप्सूल में विभेदित किया जाता है।)
> Sporogenous tissues develop from endothecium.
(बीजाणुजनित ऊतक एन्डोथेसियम से विकसित होता है।)
> The columella is present.
(कोल्यूमेला उपस्थित होता है।)
> Separation of the lid is the result of the Dehiscence of the capsule.
(ढक्कन का अलग होना कैप्सूल के फूटने का परिणाम है।)
Sphaerocarpos:-
Classification (वर्गीकरण):-
Division (प्रभाग):- Bryophyta
Class (वर्ग):- Hepaticopsida
Order (गण):- Sphaerocarpales (It includes 2 families) (इसमें 2 कुल शामिल हैं)
Family (कुल):- Sphaerocarpaceae (It includes 2 genera) (इसमें 2 वंश शामिल हैं)
Genus (वंश):- Sphaerocarpos (It includes 8 species) (इसमें 8 जातियाँ शामिल हैं)
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ii. Position, structure and dehiscence of antheridium is like jungermanniales (e.g. Porella)
iii. Position origin and development of archegonium is similar to that of acrogynous Jungermanniales.
These resemblances between the liverworts and Sphagnum point to the its intermediate position between the liverworts and mosses.
Resemblance with Anthocerotopsida:-
i. Absence of apical growth in the young sporogonium.
ii. Development of archesporium from the amphithecium which overarch the columella.
iii. Development of entire endothecium into columella.
iv. Capsule wall possess chloroplast and rudimentary stomata.
v. Sporogonium is differentiated into bulbous foot, and constriction like seta.
Resemblance with Mosses:-
i. Presence of erect, leafy gametophore.
ii. Multicellular, branched rhizoids with oblique septa.
iii. Apical growth of stem, leaves and antheridia.
iv. Archegonium having massive stalk and venter.
v. Absence of elaters.
vi. Dehiscence of capsule by operculum.
Special Features of Sphagnum:-
i. Absence of rhizoids in adult leafy gametophore.
ii. Branches arise in tufts from the axil of every fourth leaf.
iii. Absence of mid rib in the leaves.
iv. Stem and leaves show unique structures. Cortex in the old stem is spongy and sometimes develops spiral thicknings. Single layered leaf consists two types of cells: large hyaline cells and small green photosynthetic cells.
v. Presence of hyaline retort cells.
vi. The water in which it grows is highly acidic. It is due to the presence of some organic substance of a colloidal nature in the cell walls.
Above resemblance of Sphagnum with Hepaticopsida, Anthocerotopsida and Bryopsida suggest that Sphagnidae may be synthetic group.
Economic importance of Bryophytes:-
1. Uses of Bryophytes
2. Ecological Role of Bryophytes
3. Bryophytes as Indicators
4. Bryophytes as Preserver of the Past
5. Bryophytes and Research Work
1. Uses of Bryophytes:-
a. As Medicine
b. As Construction Material
c. As Decorative Material
d. As Packing Material
e. House Hold Uses
f. Treatment of Waste Water
g. Mosses as Animal Food and Shelter
h. Uses of Bryophytes in Horticulture
a. As Medicine:-
> In ancient times bryophytes have been used as herbal medicines in various parts of the world.
> Dioscorides ascribed medicinal properties to Marchantia polymorpha.
> During the middle ages, the large thallose liverworts Mere interpreted according to the Doctrine of
Signatures.
> The decoction of liverworts was supposed to be effective in the treatment of disorders of liver, and that of the "hairy-cap moss" to beautify ladiks hairs.
> In Northem Montana (USA) Polytrichum juniperinum is still used for preparing various medicines.
> In Kumaon region (North-Westem Himalayas) liverworts Marchantia polymorpha and M. palmata are used as medicine for boils and abscesses, whereas mosses are used in the preparation of an ointment for cuts, bums and wounds.
> In China, more than 30 species of bryophytes have been recognised as curative agents.
> Clinical researches are also being carried out to confinn the effectiveness of these medicines and it has been observed that the extract of moss Rhodobryum giganteum, which is used to cure angina (an attack of intense constricting pain), increased the rate of flow in aorta of white mice by over 30% causing a reduction in the amount of oxygen resistance.
> Modem phytochemists and biochemists have isolated a vast number of biologically active organic compounds from bryophytes which are of potential use in pharmaceutical industry.
> It has been demonstrated that certain products of bryophytes inhibit the growth of microorganisms. Three prenylbibenzyls from Radula spp. inhibit the growth of Staphylococcus aurens.
> Many species of bryophytes have been shown to possess antitumor activity. The first antitumor active compound, diplophylline, was obtained from liverworts. This compound shows significant activity against human carcinoma. Antitumor sesqueterpenoids have also been isolated from many liverworts:
The following antitumor.sesqueterpenoidsh ave been isolated from various bryophytes.
i. Diplophyllin:- Diplophyllum albicans, D. taxifolium -
ii. Marchantin A:- Marchantia polymorpha, M. tosana, M. palacea
iii. Riccardin:- Riccardia mulrijida
iv. Perrottetin E:- Radula perrottetii
v. Pagiochiline A:- Plagiochila sp.
vi. Pinguinsane:- Trocholejeunea sandvicensis
> Sphagnum has been used as absorbent dressing for centuries. Sphagnum dressings were first used on a large scale during the Russo-Japanese war, 1904- 1905. The following were the advantages of Sphagnum dressings over cotton.
i. They absorbed 16-20 times their own dry weight of liquid, whereas cotton dressings could only absorb 4-6 times.
ii. They were cool and soothing because the moss is porous (recall its anatomical fedtures); a dressing was found to be comparatively dry for 24 hours after an operation in cases where the wound had bled quite freely.
iii The dressing could be left on for up to 2-3 days which is much longer than cotton dressings.
iv. Sphagnum itself has mild antiseptic properties no possessed by cotton.
> Effective Against Plant Pathogens:- Bryophytes also show activity against some plant pathogens. Extract of the liverwort - Herbertus aduncus inhibits the growth of some plant pathogenic fungi. Many species of mosses (e.g. Dicranum scoparium and D. japonicum) contain some rare fatty acids which completely inhibit the growth of the fungus causing rice blast, Pyricularia oryzae.
Medicinal Uses of Bryophytes
b. As Construction Material:-
> In areas where woody plants are scarce, the tiny bryophytes have commonly been utilized in number of ways. They are also used in the construction of houses and for their furnishings.
> The aquatic moss Fontinalis antipyretics is used by Nordic people for filling spaces between the chimney and walls to prevent fires. Several mosses are used as chinking (chink-a crack or narrow fissure) materials.
> Similarly, in Alaska, chinking of wooden and log cabins is done using bryophytes.
> The shepherds in the Himalayan highlands also use bryophytes for chinking.
> In northern Europe Sphagnum is stuffed between timber used in houses to deaden the sound.
> Mosses have also been used in making huts by herdsman in Alps.
> Neckera complanata and other mosses are used for plugging the seams and cracks of boats.
> In the Scottish highlands Sphagnum mixed in tar is used for plugging the seams.
> In Russia, pressed and heated raw peat is used for making slabs which are used for insulation of domestic housing and refrigeration.
> Recently, new construction materials like "peat crete", "peat wood", and "peat foam" have been developed from Sphagnum using certain binders for solidification and strengthening.
c. As Decorative Material:-
> In decorative industry ahd floral trade mosses play significant role.
> In countries like Japan, England, France, Finland and America mosses are used for decoration of ladies hats.
> In the floral trade mosses are marketed as "sheet moss" or "blanket moss" and are used commonly
in this industry the year-round.
> The moss sheets form blanket material for Christmas tree yards and nativity scenes.
> The decorative uses of mosses are as follow:
i. Dicranum scoparium:- for forming banks of green,in shop window displays.
ii. Rhytidiadelphus loreus, R. triquettus and Hylocomium splendens:- as green carpets for floral exhibitions
iii. Climacium americanum:- fashioned into wreaths and crosses
iv. Hylocomium splendens:- for making moss roses
v. Climacium hndroides:- (dyed) for decorating women's hats
> Some aquatic bryophytes are used in aquaria. These bryophytes are also useful to fishes because they provide oxygen and egg-laying substrata.
d. As Packing Material:-
> Mosses are suitable for packing purposes because they have soft elastic texture and are not easily attacked by micro-organisms.
> In the western United States mosses are used for packing vegetables.
> In tropics, leafy liverworts are used for packing, largely because of their abundance.
> In the Himalayas, apples and plums in particular are wrapped in mosses.
> Nurserymen in India use wet Sphagnum for sending or supplying live plants and also for shipment of vegetables, cacti, ferns and other delicate plants.
> Moist Sphagnum is used for packing live frogs, snakes, lizards, worms and some insects for shipment.
e. House Hold Uses:-
i. As Absorbent:-
> A layer of Sphagnum is used in hiking boots for cushioning the foot and absorbing moisture and odour.
> Dry Sphagnum is used as diapers and in cradles to keep babies clean and warm.
> In Azores, mosses are used in making moss beds and pillows. Laplanders use Polytrichum commune for this purpose.
> In alpine regions of the North Western Himalayas Indians make beddings, mattresses, cushions and pillows by stuffing mosses into coarse linen sacks or by spreading them on muddy floor of huts.
> Mosses are preferred due to their soft texture, insect-repellent property and resistance to rotting.
ii. Insect Repellents:-
> It is generally known that bryophytes, even as herbarium specimens, are hardly ever attacked by microorganisms and insects.
> Many bryophyte species have their own peculiar odour and taste.
> In many villages of Naini Tal and Pithoragarh, mosses in particular are used as insect repellents.
> The locally available mosses and liverworts are dried and coarsely powdered.
> The moss powder is sprinkled over the grains and pulses that are to be stored in containers.
iii. Smoke Filters and Pads:-
> Bryophytes are used as smoke filters in the hubble-bubble or "hookah" in the Kumaon Himalayas.
> Women who have to fetch water from long distances in the villages of Kumaon, make a round base of moss mats called "sirona" which is kept on the head to hold the pitcher.
f. Treatment of Waste Water:-
> Sphagnum has been used as an effective filtering and absorptive agent for the treatment of waste water and effluents of hries with acidic and toxic dischanrge containing heavy metaIs, and many organic substances.
> Peat can also be used as an absorbent for oil spills and as filtering agent for oily waste water in vegetable oil factories.
g. Mosses as Animal Food and Shelter:-
i. Food:-
> The biomass of mosses in many vegetational zones of the world is considerable. However, it is in tundra that they are most abundant.
> The caloric content of mosses from the Canadian tundra is about 4.5-5.0 kcal/g. This is comparable 'to higher plants growing in the same habitat.
> Other than proteins and fats mosses contain a large amount of lignin-like compounds.
> It is reported that they are rich in vitamins, especially B2.
> Mosses are consumed by many animals like bison, reindeer, rodents insects and birds.
> Another interesting use is feeding of mosses to baby pigs. If pigs are born anemic, the Sphagnum feed is ideal for binding the iron and vitamins fed to baby pigs. It has ability to absorb and hold nutrients.
ii. Shelter:-
> Some insects and birds use mosses for building shelter. A wide range of birds use green leafy gametophores of mosses to construct nests which provide protection to their eggs and young ones.
> Some birds like Pink Robin of Australia make very complex nests. They use mosses for making the main body of nest and line it with tree fern.
h. Uses of Bryophytes in Horticulture:-
> Bryophytes are usehl in horticulture because of their high water holding capacity.
> You may have observed money plant or other climbers growing in pots around sticks. They are used
for providing moisture to the plant.
> Gardners use moss wrapped hanging baskets and pots for cultivating Begonias, Fuchsia and Orchids.
> It is observed that when plants are grown in a pot with a layer of moss sandwiched between the humus-rich top and bottom soil, they grow well and produce buds and flowers more prohsely in comparison to the ones grown without it.
> Mosses are used as soil additives. Moss carpet serves to stabilize the soil and retain its moisture.
> When Sphagnum is mixed with soil or spread over the ground it lightens soil mixture, discourages weed growth and prevents excessive drying of the upper soil layers.
> Mosses are used as ground cover for making Bonsai.
> In Japan mosses have long been used as precious attributes of gardens. They are useful as an evergreen ground cover in much the same way as lawn grasses.
> In some countries mosses are used as seed beds. It has been reported that pioneer white spruce in Nova Scotia (Canada) germinates most prolifically in carpets of Polytrrchum.
> Similarly, the mosses, especially Hypnum imponens provide the seedling bed for Tsuqga and Betula.
> Extract of Sphagnum promote germination of Jack Pine seeds.
> Mosses such as Pleurozium schreberi has been found to act as good seed beds for the germination of seeds of pines.
2. Ecological Role of Bryophytes:-
a. Bryophytes as Pioneer of Vegetation
b. Role of Bryophytes in Soil Erosion
a. Bryophytes as Pioneer of Vegetation:-
> Many bryophytes are the first ones to appear on open and often nutrient-poor sites where no other plant is able to grow. For instance, they grow on bare rocks and on recently deposited volcanic ash.
> Gradually, the bryophytes build up an organic layer that is invaded by microorganisms, resulting in changes in the mineral substratum beneath. This increases in nutrient availability makes the site suitable for invasion by vascular plants.
> In this way, bryophytes help in succession of plants on bare rocks by becoming pioneer plant community (pioneers-first to appear).
> Several bryophytes like Andreaea are restricted mainly to bare rock surfaces. Most of these bryophytes are highly tolerant to extended period of desiccation.
> The mosses are also pioneer species on burnt sites. Every year large areas of grassland, and temperate and tropical forests catch fire. The resulting tracts of land provide habitats for the succession of mosses like Funaria and Polytrichum.
> Mosses are pioneers in dune systems as well. They help in retaining moisture and stabilizing dunes that otherwise are at the mercy of the wind. Eg. Ceratodon and Tortula.
b. Role of Bryophytes in Soil Erosion:-
> You have learnt that bryophytes grow as cdmpact cushions forming a carpet on the forest floor.
> Actually, their rhizoids bind soil particles together and also interweave with the rhizoids of adjacent plants keeping the whole cushion compact and difficult to detach from the soil. The soil particles thus trapped do not flow alongwith water during floods.
> The colonization of bryophytes on the roadside is important in stabilizing these sites.
> Species of Barbula, Weissia, and Bryum are pioneers on new road banks.
> Extensive sand dune systems occur along many sea coasts of the world.
> Mosses play a very important role in helping to retain moisture and stabilize dunes. Such mosses can survive even if they get covered by sand. An example of such a moss is Cerafodonpurpureus.
> Mosses have a potential role as inhibitors of soil erosion due to their trample-resistant structure and their high regenerative ability.
> In present times, certain mosses like Polytrichum, Atrichum and Ceratodon are grown to prevent soil erosion around fruit trees such as apples and pears.
3. Bryophytes as Indicators:-
a. Indicators of Mineral Deposits
b. Indicators of pH
c. Indicators of Seed Plant Community
d. Indicators of Air Pollution
e. Indicators of Water Pollution
a. Indicators of Mineral Deposits:-
> Some mosses are restricted to the soil rich in a particular metals.
> The metals often gets accumulated in the plant.
> By studying the distribution of such plants or analysing their metal contents, it is possible to discover new mineral deposits. This technique is known as geobotanical prospecting.
> In Almora, Naini Tal and Pithoragarh districts in the Kumaon region of North Western Himalayas various mineral-rich substrates have been recognised.
> Each mineralized area has a characteristic bryoflora of its own. The distinction is so pronounced that the bryoflora provides an idea of the precise nature of the underlying substrate. Some of the examples are as follows:
i. Granite and Mica:-
- Bryophytes belonging to order Grimmiales are the invaders and sole colonizers of smooth, polished surfaces of mica rocks, granites and other rocks.
- Hard granite surfaces are always colonized by Grimmia spp. and Rhacomitrium of Bryophytes
himalayanum.
- The colonization is so sharply delimited that one can predict the substrate by merely studying the moss.
ii. Dolomitemcks:-
- These rocks are a characteristic feature of the Himalayan geology.
- The substrates are calcium-rich.
- The mosses growing on these substrates have a remarkable capacity to absorb and accumulate different amounts of calcium from the substrate.
- The mosses which are always present on such sites are - Hyophila involuta and Tortella tortuosa.
iii. The magnesite (MgCO3):-
- One of the largest deposits of this mineral in India is at Kumaon.
- At all sites, the large magnesite deposits present a strikingly barren appearance.
- The only species of moss growing on these sites is Hymenostylium recurviroshum.
iv. Copper:-
- Some species of mosses serve as indicators of high copper concentrations in the substrate and are known as "copper mosses".
- It is suggested that the copper concentration tolerated by the "copper mosses" is lethal to other plants and thus bryophytes have no competition on such sites.
- The important copper mosses are - Mielichhoferia elongata and Scopelophila cataractae which can serve as indicator of copper.
b. Indicators of pH:-
> Some bryophytes grow only on the soil that is at particular pH. So, the presence of a particular species indicates the acidic or alkaline condition of the soil.
i. The mosses also grow on haematite (ore of iron) with alkaline pH (7.3 - 7.6). It is a well known fact that in an alkaline medium. iron remains unavailable to most of the plants.
ii. Some bryophytes grow only on strongly acidic, highly soluble, iron enriched limonitic substrates. Iron is readily available on such substrates. These substrates have pH 2.9 - 4.1. Polyrrichum is a reliable indicator of acidic conditions.
iii. Gypsum containing areas are alkaline to varying degrees and even contain acidic pockets. The moss Campylopus gracilis serves as an example of a species that is tolerant to both acidic and basic conditions over a pH range of 4.9-7.8.
Bryophytes that can Illustrate Typical pH Condition
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c. Indicators of Seed Plant Community:-
> Some bryophyte species are consistent inhabitant at the sites where a particular seed plant community is growing, so these species can be used as indicator species.
> While some other persist at localized sites though the original vascular plant vegetation gets destroyed due to some reason.
> Consequently,they become useful remnants to indicate the past existance of a forest or non-forest vegetation and can be used as indicators as to which vegetation could be effectively regenerated on that site.
d. Indicators of Air Pollution:-
> We all know that lichens are bioindicators of pollution.
> Similarly, bryophytes can also be used as bioindicators of pollution as they are sensitive to SO2, fluorides and heavy metals.
> They show symptoms of injury when exposed to minute quantities of pollutants.
> Exposure to SO2 results in loss of green colour.
> The leafy liverwort Radula complanata changes its colour within ten minutes and its chloroplasts are destroyed at concentration of 120 ppm.
> Bryophytes are also very sensitive to hydrogen fluoride and show symptoms of injury at concentrations as low as 0.001 to 0.1 ppm.
> The colour of leaves of moss Pylaisiellapolyantha changes to brown at low concentration and appears burnt at higher concentration.
> Some bryophytes have the capacity to absorb and retain pollutant in quantities much higher than those absorbed by other plants growing in the same habitats. These can be used to lower the concentration of certain pollutants in the environment.
> Analysis of such bryophytes can also provide the idea of the degree of pollutant present in that area.
> Heavy metals constitute a very important class of pollutants. The most significant among these are
lead, cadmium, arsenic and chromium.
> Lead is most toxic metal. You may know that it is used as anti-knock compound and is released in the automobile exhaust.
> It is found that lead content of mosses growing at a distance of 2 metre away from anti-knock manufacturing factory was found to be 320 ppm.
> Similarly, Zinc was accumulated 13 15 ppm in moss (Hypnum cupressiforme) growing at a distance of three miles away from the manufacturing factory.
> Herbarium specimens of three mosses which were collected at intervals during 1860 to 1968 were tested for lead contents. , The results are given below:
Lead Content in Herbarium Specimens of Bryophytes
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e. Indicators of Water Pollution:-
> Bryophytes can also act as indicator of water pollution. For example. Amblystegium riparium was found to be absent in the upper part of the river with clean water.
> However, it appeared at a place where the quality of river water deteriorated due to joining of a polluted tributary coming from a village. This Species seems to be an indicator of more or less
polluted water.
> Aquatic bryophytes can be used for monitering heavy metal pollution as they accumulate them in high concentration. Jungermania spp. and Scapania spp. accumulate mercury and thus can be used for monitoring its concentrations.
4. Bryophytes as Preserver of the Past:-
> You may have heard about peat bogs. These were formed as a result of accumulation and compression of the plant remains including mosses, sedges, grasses and shrubs.
> Among mosses Sphagnum is the key plant responsible for rapidly accumulated deep deposits.
> The area of earth covered by peat bogs, more properly called mires is vast, especially in the temperate and sub-arctic regions.
> Peat bogs are of great interest to biologists because a number of well preserved fossils of organisms or their parts have been found in them.
> In peat deposits the microbial degradation of buried organisms is extremely slow because of acidic and anaerobic environment.
> The organisms trapped in peat bogs when excavated are found beautifully preserved.
> Pollen grains of several plants have been obtained from peat bogs. These have helped scientists in
characterising flowering plants and in establishing the flora and fauna of a particular, geological period.
> You will be surprised to know that about 100 human corpses of Iron and Bronze age were recovered from Scandinavian peat bogs. Their skin and cloths are still preserved even their stomach contents can be analysed to determine the nature of their last meal. Some of the preserved human bodies still show their caps on the head.
5. Bryophytes and Research Work:-
> Bryophytes-are excellent material for investigating physiological and biochemical aspects of plant development, as they are simple in organisation, multiply at fast rate and are easy to handle.
> They are small in size and their life cycle is of short period.
> Several plants can be grown together in a small test tube by tissue culture technique.
> Research on bryophytes has contributed to the knowledge of plants in the following way:
a. Discovery of chromosomes
b. Alternation of generations
c. Cytological Basis of Alternation of generations
d. Artificial Production of Polyploids
e. Discovery of Heterochromatin
f. Hormones
a. Discovery of chromosomes:-
- Sex chromosomes were first identified in plants by C.E. Allen in 1917 in the liverwort Sphaerocarpos donnellii.
- He showed that a dimorphic chromosome pair was correlated with sex difference.
- The female plant always has a very large x chromosome in addition to seven smaller autosomes and the male plant has very small x chromosome and a y chromosome in addition to seven autosomes and the dimorphic chromosomes are brought together during fertilization.
b. Alternation of generations:-
- Wilhelm Hofmeister in 1851, while working on Sphagnum, observed alternation of generations for the first time.
- The conspicuous green leafy plant which bore at its apex gamete producing organs was termed gametophyte.
- The fertilized egg i.e. zygote produced sporophyte which is differentiated into spore-containing capsule, foot and seta.
c. Cytological Basis of Alternation of generations:-
- In 1895 Strasburger discovered that gametophytic generation was haploid (n).
- It included spore, gametophore and sex organs i.e., gametangia.
- The sporophytic generation initiated from fertilised egg upto the formation of diploid (2n) spore mother cells.
d. Artificial Production of Polyploids:-
- In 191 1 E. Marchal and E. Marchal demonstrated the artificial production of polyploids in plants by culturing diploid tissue of mosses.
- The tissue differentiated to form protonema and ultimately gametophores.
- Since the egg and sperm were diploids they produced tetraploid embryo which developed into sporophyte.
- Similarly culture of a tetraploid material formed tetraploid gametophores and octaploid sporophyte.
e. Discovery of Heterochromatin:-
- Heterochromatin was discovered in the nucleus of plants by E. Heitz.
- It was demonstrated using mosses.
- The discovery of heterochromatin is of considerable importance in cytological research, since heterochromatic bands of chromosomes have served as valuable markers to distinguish the different chromosomes within sets.
f. Hormones:-
- It has been observed that just like higher plants bryophyfes also contain hormones such as auxin, cytokinins, ethylene and abscisic acid.
- Experimental studies have shown that interaction of these regulates the normal development of plants.
Apomixis:- When embryo and seed are produced from the parent plant without fertilization, it is called asexual reproduction. Any vegetative cell of the ovule acts as a zygote. The resulting seedlings are clones of their parents. It is of four types -
1. Vegetative Apomixis
2. Adventive Embryony
3. Apospory
4. Diplospory
1. Vegetative Apomixis:- In this apomixis type, vegetative bulbils or buds are produced in the inflorescence instead of flowers. They are easily reproducible and are seen in certain plants like Fragaria, Agave, Poa bulbosa, etc.
2. Adventive Embryony:- When the embryo develops from a vegetative cell of ovule (integument or nucellus or challaza) without the formation of embryo sac, it is called adventive embryony. Examples:- Lemon, mango etc.
3. Apospory:- When the development of the embryo sac occurs without meiosis from any vegetative cell of ovule (integument or nucellus or challaza), it is called as apospory. It means megaspore is not produced here. Each cell of the embryo sac is diploid. An embryo is developed from any one cell of the embryo sac. Example:- Crepis
4. Diplospory:- When the embryo sac develops from a diploid megaspore, it is called as diplospory. Megaspore is diploid because it is formed by mitosis instead of meiosis. Therefore, each cell in the embryo sac is also diploid.
Embryo development occurs without fertilization. Depending upon the embryo develops from which cell of the embryo sac, there are 2 types of diplospory -
a. Parthenogenesis
b. Apogamy
a. Parthenogenesis:- When the embryo develops from the egg cell, it is called parthenogenesis. As shown in the diagram below. Example:- Taraxacum (grass)
b. Apogamy:- When the embryo develops from the antipodal cell or the synergid, it is called apogamy. As shown in the diagram below. Example:- Onion
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Cones of Sphenophyllum:-
> Reproductive organs of the Sphenophyllales consist of aggregations of sporangiophores and bracts that form cones or strobili.
> Fructification:- Terminal cones, describe under the genus Bowmanites. There are various species formed based upon cone size:
i. S. trifurcatus (6cm X 1cm) = Homosporous
ii. S. speciosum (12cm X 2cm) = Homosporous
iii. S. dawsonii (30cm X 2cm) = Homosporous
iv. S. delectus (Length is not determined) = Heterosporous (Rare)
> The axis, which in structure resembles the vegetative stem in its primary condition, bears numerous verticals of bracts, those of each verticil being coherent in their lower part, so as to form a disc or cup, from the margin of which the free limbs of the bracts arise.
> 1 or 2 sporangiophores develop from one bract.
> The sporangia, which are about twice as numerous as the bracts.
> 1 or 2 sporangia were hanging down, it means pendulous type.
> The sporangium is attached to the enlarged distal end of its pedicel, from which it hangs down, so as to suggest an anatropous ovule on its funiculus.
> Dehiscence appears to have taken place at the free end of the sporangium; the spores are numerous, and, so far as observed, of one kind only.
>Each sporangiophore is traversed throughout its length by a vascular bundle connected with that which supplies the subtending bract.
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Stele:- The central cylinder or core of vascular tissue, consisting of xylem, phloem, pericycle and sometimes medullary rays and pith, is technically called stele.
Stelar theory:-
> Van Tieghem and Douliot (1886) developed this theory.
> They used the term stele in collective sense and mentioned that the stele is not only made up of xylem and phloem, but the tissue like pericycle, vascular rays and pith are also associated with it.
> According to them the cortex and the stele are the fundamental parts of a shoot and both these parts are separated from each other by the endodermis.
> According to stellar theory, primarily there is no fundamental difference in the gross anatomy of stem and roots, because in both of them a stele is surrounded by the cortex is present.
> Foster and Gifford (1959) have mentioned that the most debated and controversial aspect of “stellar theory is the nature of the anatomical boundaries which separate the cortex from the stele”.
> According to Van Tieghem and Douliot (1886) the endodermis represents the inner boundary of the cortex. The cells of the endodermal layer have the characteristic casparian strip strips.
> But in the stems of many seed plants, the characteristic endodermal layer is not present. Some have mentioned that in such cases the pericycle serves as separating layer between the stele and the cortex.
Types of stele:- 7 types of steles are found in the whole plant kingdom -
1. Protostele
2. Siphonostele
3. Solenostele
4. Dictyostele
5. Polycyclic stele
6. Eustele
7. Atactostele
Note:- Out of these the first 5 types of steles are found only in the stem of pteridophytes. Eusteel is found in the stem of gymnosperms and dicots. Atactostele is found in the stem of monocots.
Note:- The development of stele has also happened in this sequence. Atactosteel is considered to be the most advanced type of stele.
1. Protostele:- This is the most primitive type of stele in which the pith is completely absent and the phloem surrounds the xylem. According to Jeffrey (1898), the protostele is primitive type of stele in vascular plants.
On the basis of the shape of the xylem in the cross section, it is of 4 types -
i. Haplostele:- The xylem appears circular in cross section. It has been observed in fossil genera like Rhynia, Horneophyton and living genera like Selaginella chrysocaulos, S. kraussiana, S. selaginoides, S. willdenowi, Gleichenia dichotoma, Lygodium and Cheiropleuria.
ii. Actinostele:- The xylem appears star shaped in cross section. Brebner (1902) named such a protostele as actinostele. Eg.- Asteroxylon, Psilotum, Lycopodium serratum and Sphenophyllum.
iii. Plectostele:- In cross section, the xylem appears as parallel plates. Eg.- Lycopodium clavatum and L. volubile.
iv. Mixed protostele:- In cross section, the xylem is seen scattered in the form of segments. Eg.- Lycopodium cernuum
2. Siphonostele:- In this, pith or pith cavity is found in the center around which vascular tissues are found.
Origin of siphonostele:- There are different views among scientists regarding the origin of siphonostele. But they all agreed that the siphonostele originated from protostele by the formation of a pith in the center. Here, the centrally placed xylem core is replaced with a parenchymatous pith.
Different stages of changing protostele to siphonostele can be observed in the T.S. at different levels in Gleichenia, Osmunda, and Anemia.
There are two views regarding the origin of pith in the siphonostele.
i. Jeffrey’s theory:-
- According to this theory, the pith is formed as a result of the invasion of cortical parenchymatous cells into the stele. The invasion of the pith occurs through the leaf gap or branch gap.
- Thus pith and cortex are homogeneous structures according to this theory.
- This theory is not accepted by most of the authors since in many pteridophytes there is a stele without leaf gaps but having siphonostele.
ii. Boodle’s theory:- According to the theory proposed by Boodle (1901), and Gwynne Vaughan, the siphonostele has evolved from the protostele by a transformation of the inner vascular tissue into the parenchyma.
On the basis of the location of phloem it is of two types –
i. Ectophloic siphonostele:- Phloem is found around the xylem. Eg.- Osmunda, Schizaea, etc.
ii. Amphiphloic siphonostele:- Phloem is found at both outside and inside the xylem. Eg. Rhizome of Marsilea, Adiantum, Dipteris.
3. Solenostele:- The vascular tissue in the ectophloic siphonostele forms a leaf gap when it enters the leaf as a leaf trace.
4. Dictyostele:- When the leaves are found densely, many leaf gaps come together causing the vascular tissue of the amphipholic siphonostele to break into many pieces. Each piece is called a meristele and each meristele is a haplostele. In this way many merysteles are found in the form of a circle.
5. Polycyclic stele:- When 2 or more cycles of meristeles are found.
6. Eustele:- When vascular bundles are found in a circle.
7. Atactostele:- When vascular bundles remain scattered throughout the ground tissue.
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