Chapter 13 Plant Kingdom Part 4 by Teaching Care online coaching classes
- Apogamy : The terms apogamy was coined by de Bary (1878). It is defined as formation of sporophyte from a gametophytic cell other than egg without fertilization. It was first observed by Farlow (1874) in Pteris cretica. Thereafter it was observed in several other plants g., Lycopodium, Selaginella, Nephrodium, Lastrea, Marsilea etc. The apogamy is of two types, obligate and facultative. If either both of the sex organs are nonfunctional or absent, the apogamy occurring on account of this is said to be obligate. But if a gametophytic cell is induced to form the sporophyte without fertilization, the apogamy is called as facultative or induced.
- Apospory : The formation of gametophyte from a sporophytic cell without meiosis is called as apospory. This phenomenon was first observed by Druery (1884) in Athyrium filix-femina. Thereafter it has been established in several pteridophytes. g., Pteridium aquilinum, Asplenium, Trichomanes etc. Induced apospory was seen in Pteris species.
- Parthenogenesis : Formation of sporophyte from egg without fertilization is called as parthenogenesis. Farmer and Digby (1907) observed that in homosporous, leptosporangiate ferns, apospory was always followed by parthenogenesis. This phenomenon has been observed in several species of Selaginella and Marsilea.
- Affinities of pteridophytes : The pteridophytes occupy an intermediate place between bryophytes and They represent affinities with both the groups.
(i) Similarities with bryophytes
- Both have terrestrial mode of
- Water is indispensable for the process of
- Male gametes are
- The structure and ontogeny of sex organs e. antheridium and archegonium is based on similar pattern.
- Both the groups have definite alternation of sporophytic and gametophytic
- Sexual reproduction is of oogamous Zygote is retained within the venter of archegonium to form embryo.
- Sex organs are surrounded by sterile jacket.
- The young sporophyte is partially or wholly dependent on the gametophyte for
(ii) Similarities with spermatophytes
- In both the cases, sporophytic plant body is large, independently existing and dominant phase of life
- The plant body is differentiated into true stem, leaves and
- Vascular tissue is
- Spores are produced inside the sporangia.
- Presence of distinct alternation of
- Process of photosynthesis is mainly confined to Stomata are present on the leaves.
- Fossil history of pteridophytes : The pteridophyta have a long fossil history. Their first traces were identified in the silurian period of paleozoic age (about 400 million years age). Pteridophytes flourished well during devonian, mississipian and pensylvanian periods of late paleozoic This period can be well recognised as “age of pteridophyta“.
- Classification : Eichler (1883) classified the plant kingdom into Cryptogamia and Phanerogamia. The Cryptogamia was further divided into Thallophyta, Bryophytes and Pteridophyta. Engler (1909) included Bryophyta and Pteridophyta under Embryophyta. Sinnott (1935) introduced the term Tracheophyta. A years later Eames (1936) classified Tracheophyta into four groups namely, Psilopsida Lycopsida, Sphenopsida and Pteropsida, and Pteropsida into Filicinae, Gymnospermae and Angiospermae. Smith (1938) classified pteridophytes into four classes namely Psilophytineae, Lycopodineae, Equisetineae and Filicineae. Oswald and Tippo (1942) classified pteridophytes in to four sub-phyla.
(19) Salient features of sub-phyla
- Sub-phylum : Psilopsida
- These are the oldest known vascular plants, most of them (except Psilotum and Tmesipteris) are
- Plant body is relatively less
- Roots are absent, instead dichotomously branched rhizome is
- Aerial axis is either naked or have small spirally arranged
- Sporangia are cauline (e., directly borne on the axis or stem); they are lateral or terminal in position. e.g., Psilotum, Tmesipteris.
(ii) Sub-Phylum : Lycopsida
- Plant body is differentiated into root, stem and
- Leaves small (e., microphyllous) with a single unbranched vein.
- Sporangia develop in the axil of the
- Sporophylls generally form compact e.g., Lycopodium, Selaginella, etc.
(iii) Sub-Phylum : Sphenopsida
- Stem differentiated into nodes and internodes.
- Leaves microphyllous, present in whorls at each
- Sporangia are borne on the sporangiophores which form compact cones at the apex of the fertile
(iv) Sub-Phylum : Pteropsida
- Plant body well differentiated into root, stem and
- Leaves megaphyllous, pinnately
- Sporangia develop on the ventral surface of the sporophylls, usually aggregated into e.g., Dryopteris, Pteris, Pteridium, Polypodium, etc.
(20) Economic importance
- Ornamental value : Many ferns are grown as ornamental plants in gardens for their large, Show and graceful e.g., species of Lycopodium, Nephrolepis, Selaginella, Lygodium, Anemia, Cyathea etc.
- Medicines : An anthelmintic drug is obtained from the rhizomes and petioles of the fern Lycopodium clavatum is used in skin diseases. Equisetum arvense has diuretic properties.
- Food : The sporocarps of Marsilea are rich source of starch and used by tribals for their nutritive
- Soil conservation : Plants like Selaginella are useful in soil
- The term Pteridophyta was first introduced by Haeckel in
- The term Cryptogams was coined by Linnaeus (1737) which means plants without
- Tracheophytes : Sinnott (1935) coined the term to include vascular plants (pteridophytes and seed plants).
- The chloroplasts of Selaginella contain pyrenoids.
- Stem of Selaginella kraussiana shows distelic
- Smallest pteridophyte is Azolla whereas the largest is Cyathea/Alsophila (Tree ferns).
- Adiantum is commonly called ‘Maiden hair fern’.
- Elaters : Elongated structures which help in spore They have spiral bands of thickening for xerochasy. Elaters are epispore appendages in horsetail Equisetum. Anthoceros has pseudoelaters.
- Cormophytes : Plants with distinction of stem, leaves and
- Selaginella lepidophylla and pilifera are xerophytes and sold in the market as novelties.
- Salvinia is root less
- Adiantum is commonly known as walking fern because it propagates vegetatively by its leaf tips. Some species of Adiantum are
- Meristeles are found in fern
- Selaginella oregana, Lycopodium squarrosum and Asplenium nidus are epiphytes.
- Rudimentry seed habit occurs in selaginella.
- Acrostichum aureum is a halophyte.
- Marsilea occurs as terrestrial, amphibious as well as aquatic
- Azolla is an aquatic water fern used as biofertiliser. The alga – Anabaena fixes atmospheric nitrogen in symbiotic association with Azolla.
- Salvinia is an aquatic pteridophyte weed.
- Equietum is commonly known as Horsetails or Scouring rushes. A few species of Equisetum contain
- Lycopodium is commonly known as club
- In ferns, young leaves are protected by Ramenta.
- Vernation is arrangement of leaves in bud
- Unbranched erect axis is called caudex.
- Brown scale are called ramenta.
- Selaginella is also Rnown as ‘resurrection plants‘.
- Stomium is the area on sporangial wall from which spores
- Psilophytes (Cooksonia, Rhynia ) primitive pteridophytes of Silurian and Devonian period.
- Ophioglossum (Adder’s tongue fern) has maximum number of chromosomes (2n = 1242) in plant
- The vascular supply given for a leaf from the main stele is called ‘leaf trace‘.
- The parenchymatous region left behind in the main stele after the departure of the leaf trace is called ‘leaf gap‘.
- The vascular supply given out for a branch from main stele is called ‘branch trace’.
- The parenchymatous region left out in the main vascular sylender due to departure of branch trace is called ‘branch gap’.
- Introduction : Gymnosperm (Gk. Gymnos = naked ; sperma = seed) are the plants with exposed or naked seeds or ovules. These plants represent the most ancient group of seed They have been generally placed in the division spermatophyta (seed bearing plants) along with angiosperms. They were not grouped separately as gymnosperms. But Robert Brown (1827) separated them from angiosperms and placed under a distinct group due to presence of unprotected ovules in them. The gymnosperm originated much earlier then angiosperms. However, most of the members of this group have now become extinct and only few living forms are known today. The living gymnosperm are generally grouped under four orders (Cycadales, Ginkgoales, Coniferales and Gnetales).
- Distribution : Plants of Gymnosperms occur throughout the world. The group is presently represented by only 900 living Of these, about 500 species belong to ‘Conifers’ or cone bearing plants. Several species of conifer occur in north-west America and eastern and central China. In India several members are found in Himalayas, Podocarpus and Cupressus in the central and Larix, Tsuga, Cephalotaxus in the eastern. The Indian species of Ephedra are commonly found in Punjab, Rajasthan, Haryana and from Sikkim to Laddak. Gnetum sp. occur in Kerala, Assam, Naga hills, Orissa, Sikkim, Burma, Thailand and China. Welwitschia is endemic to south- west Africa. Ginkgo is native of South China.
- Habit : Living gymnosperms are mostly perennials, xerophytic, evergreen, arboreal and woody plants. They grow as wood trees, bushy shrubs or rarely as climbers (g., Gnetales). None of them are herbs or annuals.
(4) External features
- The plant body is sporophyte and differentiated into root, stem and
- The plant possess well developed tap root system. In some cases the roots are symbiotically associated with algae (g., Coralloid roots of Cycas) or with fungi (e.g., Mycorrhizal roots of Pinus).
- The stem is erect, aerial, solid, woody and branched (unbranched in Cycadales) but almost tuberous in
- The leaves may be microphyllous or
(5) Gymnospermous wood
- Manoxylic wood : Cambial activity is short lived, cortex and pith are broad, parenchymatous rays are broad, wood is soft and commercially e.g., Cycas.
- Pycnoxylic wood : Cambial activity is long lived, cortex and pith are reduced, parenchymatous rays are few, wood is hard and compact, wood is commercially most important and used as good quality e.g., Pinus.
- Reproduction : Gymnosperms are heterosporous, e., produce two different kinds of spores – the male microspores and the female megaspores. The spores are borne inside the sporangia. The two types of sporangia are borne on special leaf-like structures, called sporophylls. The microsporangia (pollen sacs) are born on microsporophylls (= stamens) and the megasporangia (ovules) are borne on megasporophylls (= carpels).
The sporophylls are usually aggregated in the form of compact structures called cones or strobili. The cones are generally unisexual, i.e., the male cones are microsporangiate (pollen cones) and the female cones are megasporangiate (seed cones). The male cones are short lived whereas the female cones are long lived. The female cones remain attached on the plants for several years till the maturity or ripening of the seeds.
- Pollination : The microsporangium (Pollen sac) produces numerous light pollen grain. Pollination is anemophilous (wind pollination). The ovules are orthotropous and remain exposed on the Each ovule surrounded by integuments. It incloses the nucellus and a female gametophyte formed from the haploid megaspore. The female gametophyte contains archegonia. The pollen grains are captured by the pollination drop secreted by the micropyle of the ovule. When it dries, the grains are sucked in the pollen chamber. The pollen grains now germinate. A pollen tube is formed due to elongation of the tube cell. In Cycas and Ginkgo the pollen tube is haustorial in nature. The lower end of the tube bursts and releases the male gametes which fuse with the egg to form the zygote.
- Fertilization : Fertilization occurs by siphonogamy, e. the male gametes are carried to the archegonia through pollen tube (except in Cycas where pollen tube functions as haustorium and fertilization occurs by zoodiogamy). Fertilization thus takes place in the absence of external water.
- Embryogeny : The zygote undergoes free-nuclear divisions in Cycas followed by wall formation. There are no free-nuclear divisions in Sequoia and Gnetum. The embryo is soon differentiated into an upper haustorial, middle suspensor and lower embryonal In Pinus, on the other hand, the zygote gets differentiated into four tiers of four cells each, designated as open tier, rosette tier, suspensor tier and embryonal tier. Cleavage polyembryony is seen in Pinus. The embryonal part shows differentiation of radicle, hypocotyl, cotyledons and plumule.
- Seed : As a result of fertilization the ovule develops into a seed. The integument forms the seed coat. The outer fleshy layer of the integument forms the testa whereas the middle stony layer gives rise to tegmen. The nucellus persists as a cap like perisperm. In Taxus a fleshy aril is also present at the base as a cup like The seeds of gymnosperms comprise tissue of three generations namely parent sporophytic (integument and nucellus), gametophytic (endosperm) and second sporophytic (embryo).
- Living fossils : When a group of plants is represented by a single genus or species while rest of the other representatives of the group have become extinct and fossilized the long surviving individual is called a living fossil g., Ginkgo biloba. However, Cycas is also regarded as a living fossil because most of the cycad species are confined to tropical and subtropical region and the group is becoming endangered. Therefore, cycads have been referred as reptiles of plant kingdom or panda of vegetable kingdom.
- Classification : Robert Brown (1827) recognised the gymnosperms as a group distinct from However, Bentham and Hooker (1862-83) in their ‘Genera Plantarum’ placed them between Dicotyledonae and Monocotyledonae, Chamberlain (1934) divided gymnosperms into following two sub-classes.
- Sub-class I. Cycadophyta : These are characterised by the presence of unbranched stem and large foliage leaves. Internally, the stem has large pith and cortex but the wood is relatively It includes following 3 orders.
Order 1. Cycadofilicales : It is a group of fossil plants. These plants resembled with ferns, hence they were given the name Pteridospermae (i.e., seed bearing ferns). e.g., Lyginopteris, Medullosa.
Order 2. Bennettitales or Cycadeoidales : It is also a group of fossil forms. These plants resembled with modern cycads. e.g., Cycadeoidea, Williamsonia.
Order 3. Cycadales : It includes both living and fossil forms. e.g., Cycas, Nilssonia, Zamia.
- Sub-class II. Coniferophyta : These are characterised by long profusely branched stem and simple small leaves. In stem the amount of wood is much more than cortex and It includes following four orders.
Order 1. Cordaitales : All the members of this order are extinct. e.g. Cordiates, Dadoxylon.
Order 2. Ginkgoales : All the members of this order, except for Ginkgo biloba are extinct. Ginkgo biloba is a medium sized tree with branched stem and bilobed leaves. Because of the resemblance of the leaves of this plant with those of Adiantum (maiden hair fern), the name Maiden hair tree has been given.
Order 3. Coniferals : The order includes both fossils and present day forms. e.g., Pinus, Cedrus, Sequoia.
Order 4. Gnetales : Gnetales are modern group consisting of living forms. The order differs from other gymnosperms in the presence of vessels in the xylem. e.g., Ephedra, Gnetum, Welwitschia.
(13) Economic importance
- Ornamentals : Some of the gymnosperms are grown in the gardens in different parts of the world g., Cycas revoluta, Ginkgo biloba, Auraucaria cookii, A. bidwilli, Biota orientalis, Cupressus sp., Juniperus sp., Thuja sp., Taxus baccata, Cryptomeria japonica etc.
- Wood : Several plants of this group yield useful timber. The wood of Cedrus deodara is used for making railway It is also used as a structural timber and making bridges. The wood of Callitris verrucosa, Pinus roxburghii, P. wallichiana, P. pinaster, P. lambertiana etc. is used for making furniture. Juniperus virginiana wood is used for making pencils. The gymnosperm Agathis australis is perhaps the largest timber producing tree of the world. Soft wood of many gymnosperms is used for making toys.
- Resins : Several conifers yield resin which is obtained by tapping. By distilling the oleoresin obtained from pines. The resins are of three types namely hard resins, oleoresins and gum-resins. Several hard resins are obtained from living and fossil conifers which are as under :
- Copals : Kauri copal is obtained from Agathis australis and manila copal from Agathis alba.
- Amber : It is obtained from the fossil conifer Pinites succinifera.
- Sondarac : This pale-yellow resin comes from Callitris quadrivalis and Tetraclinis articulata. The turpentines are oleoresin which are also contributed by conifers. An important source of turpentine is Pinus australis, P. ponderosa and caribeae. Besides, some of the following products of turpentine nature are also obtained from conifers :
- Canada balsam : It is obtained from Abies balsamaea.
- Spruce gum : It is obtained from Picea rubens.
- Bordeaux turpentine : It is obtained from Pinus pinaster.
- Venetian turpentine : It is obtained from Larix decidua.
- Essential oils : They are obtained from several plants. These oils are used mainly in perfumery, soap industry etc. The important oil yielding plants are Tsuga canadensis, Picea glauca, Abies siberica and Cedrus deodera. The oil obtained from Juniperus virginiana (cedar wood oil) is also used in microscopic
- Paper industry : The wood of several gymnosperms, particularly those of conifers is used in paper industry g., Abies pindrow, Picea smithiana, Cryptomeria japonica, Pinus roxburghii, Tsuga canadensis etc.
- Edible : The seeds of Pinus geradiana (chilgosa) and roxburghii are edible. Sago is obtained from
Cycas revoluta. The seeds of Cycas sp. are ground and used in the preparation of many edible products.
- Medicinal use : Species of Ephedra yield an alkaloid called ephedrine. It is used in the preparation of medicines for the treatment of cough, asthma and
- The term gymnosperm was introduced by
- Cycas ovules are sessile and orthotropous. The ovules of circinalis are about 6 cm wide whereas those of C. thouarsii are 7 cm wide. They are largest ovules in the plant kingdom.
- The egg of Cycas is largest among all living It is about 1/2 mm in diameter in Cycas circinalis.
- Sperms of Cycas revoluta are largest in the plant kingdom and measure about 200 to 300m They are top-shaped, multiciliate with spiral band of cilia. (First observed by lkeno, 1896).
- World’s tallest gymnospermous tree is Sequoia sempervirens, which measures about 5 ft. in height (found in Red wood park of California).
- The largest gymnospermous tree (in girth) is Sequodendron, which measure about 13-16 meters in However, Taxodium mucronatum (the big tree of Tule) is not too tall but sometimes measures about 24 meters in diameters.
- The longest (oldest) gymnospermous tree (in age) is Pinus longavaea, which is about 4900 years
- The smallest gymnosperms is Zamia pygmia, which has underground tuberous
- In gymnosperm xylem is generally made up of tracheids (Non-porous) but vessels have been observed in Gnetum, Ephedra and
- The primitive haplochelic type of stomata are found in Cycas, Pinus, Ginkgo, Ephedra
- The plants of Welwitschia are unique in
- The wood formed may be in one ring due to persistent Such a wood is called as monoxylic. e.g., Pinus.
- The wood is formed in more than one ring due to ephimeral nature of Such a wood is called as polyxylic. e.g., Cycas.
- The female cone of Pinus takes three years for complete
- The pollen grain of Cycas are shed at three celled stage while in Pinus pollen is shed at four celled
- Prothallial cell absent in pollen grains of
- Dwarfism is seen in many gymnosperms perphaps due to wind e.g., Picea engelmannaii (15 cm).
- In Pinus, pollen grains are winged.
- All gymnosperms bear unitegmic orthotropous
- Cycas wood is mano and monoxylic, where wood of Pinus is pycnoxylic.
- In gymnosperm endosperm is haploid and develops before
- About two hundred million years ago, the gymnosperms formed the dominant vegetation on the
- The only gymnosperm showing limited growth is Welwitschia (45 tall).
- The ramnent nucellar tissue present within the seed covering of embryo is called perisperm.
- Cycas revoluta is commonly called ‘sago palm‘.
- Pinus gerardiana is commonly called ‘chilgoza pine’.
- Embryo sac of gymnosperm is
- Monkey’s puzzle is a common name of Araucaria embricata.
- In gymnosperm, the arrangement of megaspore tetrad is linear.
- Archegonia are not formed in Gnetum and
- Neck canal cell absent in
- Sulphur shower is due to pollen of Pinus/Cedrus.
- In gymnosperms phloem lacks companian
- Introduction : The angiosperms, or flowering plants, constitute the most dominant and ubiquitous vascular plants of present day flora which changed the green and yellow melancholy of the earth’s vegetation by the colourful brightness and fragrance of their flower. The term angiosperm means ‘enclosed seed’ because the ovules or potential seeds are enclosed within a hollow In this respect they are considered most highly evolved and advanced as compared with the naked seeded gymnosperms.
(2) Characteristic features
- Angiospermous plants grow in almost every kind of habitats. In the deserts, these plants grow, flower, shed seeds and complete their life cycle in a few weeks of rainy season. Some flowering plants like Zostera, occur in shallow seas. A small orchid even lives underground. It survives as a saprophyte on decaying organic matter because of the mycorrhizal association which helps to obtain nourishment. In rain forests, some plants grow on the branches of other plants but do not obtain water or food from They are called epiphytes (e.g., Vanda).
- The angiospermous leaves show reticulate or parallel venation forming areoles. The libriform fibres are present in the xylem and the companion cells are present in the The true vessels are present in the xylem of angiosperms.
- The angiosperms produce flowers which normally consist of 4 whorls of appandages – the two outer accessory and reproductive structure such as sepals and petals and the two inner essential parts – stamens and
- The stamens (microsporophylls) are bilaterally Each stamen consists of a filament and an anther.
- The anthers produce tectate pollen grains with exine differentiated into rod-like columellae covered by a
- In angiosperms, the insects and animals also act as pollinating For this purpose the flowers possess bright and showy petals, edible pollen and nectar.
- The carpels (= megasporophylls) are rolled and partly sterile so that they enclose the ovules within a hollow ovary that is connected with the stigma and
- The female gametophyte is highly reduced and consists of single egg cell, two synergids, three antipodals and two polar The archegonia are absent.
- The most characteristic feature of angiosperms is double fertilization.
- The male gamete fuses with the egg producing diploid zygote that develops into embryo or new
- Another male gamete fuses with the polar nuclei (triple fusion) resulting in the formation of triploid
- After fertilization, the ovules ripens into seeds and ovary ripens into
- The smallest angiosperm is Wolffia. The plant body of Wolffia consists of tiny flat oval green stem (phylloclade) having a few small The plants are about 1 mm in diameter and found free floating in aquatic habitats like ponds, etc.
- The tallest angiosperm is Eucalyptus. Their trees may attain a height upto 100 meters or
- Banyan (Ficus bengalensis) tree covers a large It’s slanting aerial branches spread in all directions. The tree spreads with the help of prop or pillar roots.
- Longevity : Based on the duration of life, the plants are divided into following 4 categories :
- Ephemerals : This category includes the plants which live only for a few weeks because of a very short growing season. Such plants are found near deserts or in very cold countries. For example, Arabidopsis species have a life span of 20–28
- Annuals : The plants of this category live and complete their life-cycle in a single favourable season. During this period, they grow in size, produce flowers, shed their seeds, undergo senescence and die. They pass the unfavourable period in the form of seeds. Many crop plants (g., wheat, rice, maize, etc.) are annuals. The smallest angiosperm – Wolffia is an aquatic annual.
- Biennials : The plants of this category complete their life-cycle in two favourable seasons (e., in two years). They grow vegetatively in the first season and produce flowers and set seeds in the next. Often they produce some storage organs, as in the sugar beet, where food is stored in their swollen roots.
- Perennials : Plants of this category live for more than two Generally they live for many years and bear the flowers and fruits during specific seasons. Some perennials continue their vegetative growth for several years and produce fruits and seeds only once in their life time, e.g., Agave, Bamboos, etc. They are called monocarpic. Others produce flowers and fruits every year after attaining a definite stage of maturity, e.g., Mango, Lemon, Apple, etc. Such plants are called polycarpic.
- Habit : Depending upon the habit of plants, the angiosperms belong to following categories –
- Herb : These are small, soft, non-woody plants without persistent parts aboveground. The height of plants usually reaches upto 1 m. The plants may be annual (Brassica), biennial (Sugar beet) or perennial (Canna). The perennial herbs usually possess underground rhizomes which form the new aerial shoots every year. The plants of banana are perennial
- Shrubs : These are woody plants of relatively low height (1-4 m). They typically branch at or near the base and do not have a main trunk, g., Rose. They are mostly perennial.
- Trees : These are perennial woody plants with one main The trunk may or may not be branched. These are of the following types :
- Caudex : The stem is unbranched and usually bears a crown of leaves at the e.g., Date-palm.
- Excurrent : The lower part of stem is thicker which gradually tapers Branches arise from the main stem in acropetal succession and plant appears conical e.g., Pinus.
- Deliquescent : The apical bud of the main stem dies after some time and branches and sub-branches spread in different e.g., Tamarindus, Ficus.
- Culms : In these plants, nodes and internodes are extremely Internodes of such plants are usually hollow. These plants are grasses but cannot be considered as herb or shrub or tree. e.g., Bambusa (Bans).
- Habitat : Warming (1895) divided the plants, on the basis of their adaptation to water, into four major groups – hydrophytes, mesophytes, xerophytes and A fifth group epiphytes can also be included.
- Hydrophytes : The plants which grow in aquatic habitats are called They are further grouped as –
- Submerged (g., Hydrilla)
- Attached floating (g., Nymphaea)
- Free-floating (g., Eichhornia, Wolffa)
- Amphibious or partly emerged hydrophytes (g., Sagittaria).
- Mesophytes : These are the plants which grow under moderate moisture and temperature conditions. They have no special adaptations to grow either in very dry or in very wet conditions (g., Sun flower, Brassica). These plants do not possess special adaptations to reduce transpiration.
- Xerophytes : The plants which grow in dry or xeric habitats (e., under deficient supply to available water) are called xerophytes. These plants face acute shortage of water and therefore, develop morphological,
structural and physiological adaptations in order to survive under such habitats. The adaptations in plants are mainly to check the transpiration and survive under acute shortage of water. e.g., Cynodon (Doob grass), Casuarina, Euphorbia tirucalli, Asparagus, etc.
- Halophytes : Halophytes are those plants which grow in saline habitats, e., in salt marshes, alkaline soils, river estuaries, saline ponds near seashore or sandy and heavy soils having excess of salts. In such habitats, the water is present in sufficient amount but due to high osmotic concentrations it is physiologically not available to normal plants. Such conditions are said to be physiologically dry. e.g., Spartina, Atriplex, Portulaca etc.
- Epiphytes : These are the plants which grow on other plants for space The plants are autotrophic and occur both in aquatic and terrestrial habitats. e.g., Vanda (an orchid).
- Modes of nutrition : On the basis of modes of nutrition plants are classified as follows –
- Autotrophs : These plants manufacture their organic matter from inorganic
- Photoutotrophs : These are green coloured due to the presence of In the presence of light they are capable of synthesizing their food from CO2 and H2O. e.g., Mango, Mustard etc.
- Chemoautotrophs : Those plants which synthesize their food from CO2 and H2O by using energy product in the chemical e.g., Many bacteria.
- Heterotrophs : They are either unable to photosynthesize their food or are unable to take their water and minerals directly from the soil or unable to synthesize They are classified as follows :
- Insectivorous plants
- Modes of nutrition : On the basis of modes of nutrition plants are classified as follows –
A detailed discussion of these group is given in chapter “Plant nutrition”.
- Reproduction : (See in embryology).
- Classification : The plants of Angiosperms divided into two major groups as – Dicotyledons and
- Dicotyledons : They are show following distinguished
- Tap roots found in the members of this
- The leaves in members of these class exihibit reticulate (net like)
- The flowers are tetramerous or pentamerous having four or five members in the various floral whorls,
- The vascular bundles arranged in a ring, numbering 2–6, open and with
- The seeds of dicotyledons are with two cotyledons as the name
- Monocotyledons : They are show following distinguished characteristics :
- Adventitious roots found in the members of this
- The leaves are simple with parallel
- The flowers are trimerous having three members in each floral
- The vascular bundles scattered in the ground tissue, many in number, closed and without
- The seeds of monocotyledons are with one cotyledons as the name indicate. g., Cereals, bamboos, sugarcane, palms, banana, lilies and orchids.
(10) Economic importance
- Food : Flowering plants are the major sources of food. They produce cereals such as wheat (Triticum aestivum), rice (Oryza sativa), maize (Zea mays), barley (Hordeum vulgare), oat (Avena sativa), etc. pulses such as pigeon pea or Arhar (Cajanus cajan), gram (Cicer arietinum), pea (Pisum sativum), Soyabean (Glycine max), green gram (Vigna radiata, mung), black gram (Vigna mungo, vern. urd), etc ; Vegetables such as potato (Solanum tuberosum), tomato, carrot, cabbage, cauliflower, etc ; Fruits such as apple ; mango, grapes, banana, guava, pears, melons, etc. and nuts such as cashewnut, walnut, almond, etc.
- Edible oils : Flowering plants are the main source of edible oils used for These are obtained from ground nut (Arachis hypogea), mustard (Brassica campestris), sunflower (Helianthus annus), coconut (Cocos nucifera), etc.
- Spices : Common spices are obtained from various parts of flowering plants such as coriander (Coriandrum sativum dhania), chillies (Capsicum frutescens), cinnamon (Cinnamomum zeylanicum, vern. dalchini), cloves (Syzygium aromatica, vern. laung), cara way (Carum carvi, vern. jeera), fennel (Foeniculum vulgare, vern. saunf), black pepper (Piper nigrum, vern. Kali mirch), etc.
- Timber : Many angiospermous tree, particularly dicotyledons, yield valuable hard wood which is used as The important timber producing plants are – teak (Tectona grandis), sal (Shorea robusta), oak (Quercus alba), sisso or sisham (Dalbergia sisso), sandal wood (Santalum album), etc.
- Fibres : Fibres of different qualities are obtained from various species of flowering plants for g. :
- Textile fibres are obtained from cotton (Gossypium barbadense, Gossypium herbaceum, )
- Rough fibres are obtained from flax (Linum usitatissimum), hemp (Cannabis sativa), sunn hemp (Crotolaria juncea), These fibres are used for making ropes and gunny bags.
- Jute is obtained from Corchorus
- Husk of unripe coconut (Cocos nucifera) is used to obtain
- Beverages : Tea (Camellia sinensis = Thea sinensis), coffee (Coffea arabica) and cocoa (Theobroma cacao) are the common beverages obtained from the flowering
- Medicines : Our Indian system of medicine (Ayurveda) utilises many flowering plants for the cure of various Even today a large number of advanced medicines are prepared from these plants. Some of the important medicinal plants are – Aconitum napellus (aconite), Atropa belladona (belladona), Cinchona sp. (quinine), Withania somniferum (asvgandha), etc.
- Others : There is a long list of useful articles such as paper, rubber, volatile oils, tobacco, etc., which we get from flowering plants. sugar is obtained from sugarcane (Saccharum officinarum) and sugarbeet (Beta vulgaris). A large number of plants are grown in the gardens as
- Bamboo or Agave are monocarpic perennial
- A small archid grows underground as a
- Vessels are major water conducting cell in
- Double fertilization is a unique character of
- It is believed that Bodhi tree at Gaya is about 2000 years
- Anthophytes : Plants with flower/ flowering
- Marine angiosperm : Zostera,
- National tree : Ficus bengalensis (Banyan).