Thursday, 27 May 2021

Morphologically distinct sporophytic and gametophytic generations

 Morphologically distinct sporophytic and gametophytic generations



Pole forms foot and roots, whereas the apical pole BIves rise to shoot apex. In some species the basal pole forms suspensor. The embryo of pteridophytes may be classified into two forms on the basis of polarity : (i) exoscopiC embryo - where the apical pole is directed outward, towards the neck of the archegonium (e.g., Psilotum, Equisetum, Ophioglossum); and (ii) endoscopic embryo directed towards the base of the archegonium (e.g., Lycopodium, Selaginella, Isoetes). where the apical pole is In exoscopic as well as endoscopic type of embryo development the first division of the zygote is transverse.

 Pteridophytes show a typical heteromorphic alternation of generations. Morphologically distinct sporophytic and gametophytic generations alternate with each other in regular succession. The (antheridia) and female (archegonia) reproductive structures develop on the gametophytic prothallus. 

They between the Bryophyta and Spermatophyta (seed plants). Classification of Pteridophytes: are between the Bryophyta and Spermatophyta (seed plants Marsilea, Azolla, Dryopteris, Salvinia are the men common examples of pteridophytes Called archegonium. It produces an egg. sporophyte called embryo. The embryo grows into ster-1).

The life cycle shows heteromorphic alternation of The male sex organ is called antheridium. It is a The female sex organ is a flask-shaped structure The diploid zygote gives rise to an young male gametes called spermatozoids. globular structure that produces motile flagellate Fertilization takes place in the presence of water. a sporophytic plant. generations. Classification Based on the recommendations of ICBN, G. M. Smith (1955) has classified all Pteridophytes into four divisions.

 They are - (1) Psilophyta (3) Calamophyta (2) Lepidophyta (4) Pterophyta Division Psilophyta : It includes fossils and living members. The sporophytic plant consists of underground rhizome, and erect dichotomously branched aerial shoots. True leaves are absent, if present they are small. Leaf, gaps are absent. True roots are absent and rhizoids are present.

Fertilization and form a mucilagenous antherozoids towards

 Fertilization and form a mucilagenous antherozoids towards




A The zygote divides to form embryo. The first antheridium is sessile or shortly stalked. The basal and egg fuse to form a diploid zygote, which antheridial jacket. The jacket is always single The antheridium is surrounded by a sterile spirally coiled with two apical flagella. But they are antheridium or separation of the terminal cell. 

The antherozoids are unicellular, uninucleate and layered in species with projected antheridia. The r-1) multi-flagellate in the order Psilotales, Equisetales The antherozoids are liberated by bursting of the functions as the mother cell of the sporophytic and Pteropsida. known as opercular cell or cover celI.

 The archogonium is differentiated into neck and venter; the neck is projected and the venter is embedded in the prothallus. The neck is made up of four vertical rows of neck cells and it has usually two neck canal cells, but more than two (e.g., some species have Lycopodium) - or only one (e.g., Pteridium). 

Neck canal cells degenerate before fertilization and form a mucilagenous antherozoids towards archegonium. which attracts substance Water is essential for fertilization; The antherozoid generation.

Are commonly .called 'Vascular cryptogams'. Pteridophyta Marsilea, Azolla, Dryopteris, Salvinia are the most Bryophytes. They form an intermediate group of plants but also a great many fossil Pteridophytes. Pteridophytes includes not only a large number of present day genera, more advanced than the Thallophyets and The Pteridophytes are lower vascular plants. 

Wednesday, 26 May 2021

Sporangial development is seen in Salvinia

 Sporangial development is seen in Salvinia



Actinopteris radiata. Presence of sieve tubes have also been reported in the phloem of Equisetum anense and E. giganteum.or forms the stalk of the sporangium; this type of sporangial development is seen in Salvinia, whereas the inner cell either remains inactive Marsilea sporangia are present within specialized Lycopodium, Pteris) or heterosporous.

 In aquatic forms like Azolla, Isoetes, Salvinia. Plants are either homosporous (e.g., Equisetum, Pteridophyte structures, called sporocarps, Selaginella, Marsilea, Salvinia). initials and an inner layer of primary sporogenous cells; the jacket initials eventually form the multi-layered wall of the sporangium.

Whereas the primary sporogenous cells, by repeated divisions, give rise to spores: this type of sporangial development is found in Psilotum, Lycopodium, Selaginella and Equisetum or Leptosporangiate from a single initial cell which divides transversely into an outer and an inner cell.

The entire sporangium develops from the outer cetr the sporangium develops Marsilea, Pteris, etc. (i) Simple sorus : In this type of sorus all sporangia appear, grow and mature at the same time (e.g., Botrychium, Ophioglossum.)

  The spore wall is differentiated into an outer exine and an inner intine. The exine consists of an outer layer or ectin, composed of radially placed columnar rods, called columellae and inner relatively thin and uniform endine. The free and fused ends of columellae form various patterns on the spore wall which may be of taxonomic utility. 

The spore, germination, gives rise on to gametophytic generation. The germination of spore may be bipolar (e.g., Lycopodium, Equisetum), tripolar (e.g., Hymenophyllum) or amorphous or irregular (e.g., Angiopteris).

The root and stem have well developed vascular system

 The root and stem have well developed vascular system



Anthocerotales. According to them, both bryophytes and hypothetical aichegoniate land plants along different lines. pteridophytes have evolved from a common group of Pteridophyte Characteristic Features of Pteridophyta :

 The plant body is sporophytic, differentiated into root, stem and leaves. They range from annuals (e.g., Azolla, Salvinia) to large tree-like perennials (e.g., Angiopteris, Osmunda).

 Members (e.g., Azolla, Isoetes, Marsilea, Salvinia, Fig. IB, F) are aquatic, usually occurring in permanent ponds. Primary roots are ephemeral and are soon replaced by adventitious roots. The root has a permanent growing apex.

 Except for some woody ferns (e.g.. Angiopteris, Marattia, most pteridophytes have herbaceous stem. small and sessile (e.g. Lycopodium, Selaginella, or large, petiolate and compound (e.g. ferns). On the basis of eat structure, pteridophytes are classified into.

The root and stem have well developed vascular system, composed of xylem and phloem. But stems of few living pteridophytes (e.g., Botrychium, Isoetes) do show secondary growth regularly. Te.g., Lycopodium, Selginella), The stělě is a siphonostele (e.g., Equisetum, Ophioglossum pendulum, Botrychium).

In homosporous species, the development of gametophyte is exosporic (i.e., the gametophyte develops outside the spore wall), whereas in heterosporous species it is endosporic (i.e., the gametophyte develops within the spore wall).dictyostele (e.g., Pteris, Nephrolepis, Polystichum) or polycyclic (e.g., Angiopteris, Marattia). dictyostele (e.g., Pteris, Nephrolepis, Polystichum) or polycyclic (e.g., Angiopteris, Marattia). 

Tuesday, 25 May 2021

Biochemical and ultra structural studies also suggest

Biochemical and ultra structural studies also suggest



  It is a period of Palaeozoic era. This period started years back. It lasted 35 million years. This period was from 460 million years ago and ended by 425 million (ii) Ordovician period (i) Cambrian period (iii) Silurian period (M) Mississipan period (vi) Pennsylvanian period (iv) Devonian period (vii) Permian period Cambrian Period : (i) It is a period of Palaeozoic era. This period is named tter the Roman city Wales meaning Cambrian. The rocks of this period was first discovered in that city.

 This period was between 600 million years and 525 million years ago. The climate was very cool. The fossils of cryophycean algae were recorded. Ordovician Period : (ii) It is a period of palaeozoic era. This period is named after the ancient tribe Ordovices inhabited in Wales city. This period lasted for 65 million years. The fossils of Chara and Red algae were reported from sediments of this period. 

(iii) Silurian Period : It is a period of Palaeozoic era. This period is also named after the ancient tribe of Wales city. It last for 35 million years. The fossils of diatoms, brown-algae, club mosses (Lycopsida of Pteridophytes) and herbaceous marshes were discovered from rock deposits of this period. 

(iv) Devonian Period :Only Chiorophyceae (monophyletic origin) or Chtorophyceae and Phrdeophyceae (polyphyletic origin) have been considered as the progenitor of this group by these workers. Biochemical and ultra structural studies also suggest a strong affinity between algae and archegoniate plants (Stebbins and Hill, 1980: Whatley, 1982; Graham, 1982).


The tertiary period started 63 million years ago

 The tertiary period started 63 million years ago 



 Gymnosperms predominant during : Coenozoic Era and Quarternary period.(1) Tertiary Period : This is the first period of coenozoic era. The tertiary period started 63 million years ago and ended just one million years back. The climate was warm earlier and later it was cooler. The tertiary period is divided into five epochs : 

(i) Palaeocene: It lasted for 17 million years. Angiosperms were modernised during this time. (ii) Eocene : It lasted for 22 million years. Woody ángiosperms developed during this epoch. (iii) Oligocene : It started 36 million years ago and ended 11 million years back. The woody angiosperms dispersed in broad areas.

 (iv) Miocene : It started 25 million years ago and. ended 13 million years back. The fossils of monocot plants were discovered from deposits of this age. Pliocene : This epoch started 13 million years (v) ago and ended one million years back. The monocots and herbaceous plants spreaded to large areas. 

(2) Quarternary Period: This is the latest period of coenozoic era. The quarternary period started just one million years ago and lasted till today. The climate has been varying so much. The quarternary period has an epoch, Pleistocene.

 The species development of herbaceous plants have been taking place during this period. On the basis of comparative morphology of living and fossil forms, two different views have been put forward regarding the origin of pteridophytes. Scott (1900), Bohin (1901), Church (1919), Fritsch (1916, 1945), Eames (1936), and Arnold (1947) believe 'in algal origin df pteridophytes.

Monday, 24 May 2021

The Mississipian and Pennsylvanian periods are together

 The Mississipian and Pennsylvanian periods are together



Named so after Devon city in England where rocks of that period was first discovered. The fossils of Psilopsids, Tycopsids, Sphenopsids, ferns, Liverworts, Horse tails, Pterospermales etc. were discovered from rock sediments of this period. (v) Mississipian Period : This is a period of Palaeozoic era. It is named after the city Mississipi. It lasted for 25 million years. Coal beds were discovered. The fossils of tree-like Lycopods were discovered from rock of that age.

 (vi) Pennsylvanian Period : It is a period of Palaeozoic era. This period was named after the city Pennsylvania. It lasted for 25 years. The Mississipian and Pennsylvanian periods are together called Carboniferous period. The fossils of mosses, cordaitals and Pteridospermales were predominant in the rocks of that age.

 (vii) Permian Period : It is a period of Palaeozoic era. This period lasted for 30 million years. The fossils of Ginkgoales and primitive coniferales were discovered from rock deposits of this period. 5. Mesozoic Era The mesozoic era is the period of 'middle life', It started 225 million years ago and ended 75 million years back.

 Cycads had flourished well in that era, so that it is called 'age of cycads'. The supporters of this view consider that the similarity in the sex organs and life-cycles of bryophytes and pteridophytes is due to their parallel evolution. Campbell (1895), Lignier (1903), Zimmermand (1930, 1938), and Bower (1935), on the other band nostulated that ancestors of pteridophytes were some.

Sunday, 23 May 2021

Smaller vascular bundles lie in the middle of mesophyll

Smaller vascular bundles lie in the middle of mesophyll




A leaf having stomata on both the surfaces is called amphistomatic. Each stoma possesses two dumb-bell shaped guard cells with or without subsidiary cells. Functions : (i) Epidermis provides protection to the leaf interior. (ii) Its thickened cells and cuticle reduce the rate of surface transpiration. (iii) Protection from entry of pathogens. 

(iv) Exchange of gases with the help of stomata. (vi) Folding and unfolding of leaves with help of bulliform cells in response to changes in atmospheric humidity and change availability of water.

 In Mesophyll : chymatous ground tissue of the leaves. Mesophyll of isobilateral monocot leaves is undifferentiated. All the cells are similar. They It constitutes the chloren- are, generally, oval or rounded in outlines.

The enclose small intercellular spaces. intercellular spaces with are connected substomatal cavities, Mesophyll cells contain abundant chloroplasts; therefore, they are the seat of photosynthesis. 3) Vascular Strand : It consists of a number of parallel vascular bundles. Smaller vascular bundles lie in the middle of mesophyll. The Targer vascular bundles and their extensions occupy the whole area between the two leaf surfaces.

 Bundle sheath extensions are sclerenchymatous. Each vascular bundle is covered by a sheath of parenchyma cells having chloroplasts. A single bundle sheath occurs in panicoid grasses while double sheath occurs in festucoid grasses. It has phloem towards abaxial side and xylem towards adaxial side.The Phloem does not show distinction.

Saturday, 22 May 2021

Metaxylem vessels have pitted thickenings while protoxylem

Metaxylem vessels have pitted thickenings while protoxylem



  In smaller vascular bundles xylem is compact and without distinction of protoxylem and metaxylem. In larger, vascular bundles, xylem is endarch. Protoxylem cavity is often formed. Both protoxylem and metaxylem have oval or rounded vessels arranged in the form of V or Y-shaped configuration.

 Metaxylem vessels have pitted thickenings while protoxylem vessels have annular or spiral thickenings. number of other grasses, mesophyll forms concentric layers around the vascular bundles that possess large sized centrifugally arranged chloroplasts in bundle sheath cells.

 This arrangement is called Kranz anatomy. The anatomy is tropical conditions. It is also found in some an evolutionary adaptation to dicot leaves. Midrib : It is the widest or thickest part of the leaf. Similar but less prominent thickenings occur in the region of other large veins.

 A shallow groove is present in the upper or adaxial surface while a broad ridge is present on the abaxial surface. Mesophyll is absent. The ground tissue is parenchymatous with sclerenchymatous patches towards both the sides. A number of conjoint, collateral and closed vascular bundles are embedded in the ground tissue. 

Reasons for Identification : (i) Presence of larger sized bulliform cells on upper surface. (ii) Flat structure. (iii) Undifferentiated mesophyll. (iv) Presence of bundle sheath with chloroplasts. (v) Vascular bundle with xylem towards upper side and phloem towards lower side, (vi) Xylem vessels rounded.It is formed of sieve tubes and companion cells.protophloem and metaphloem. 


The various components of a monocot leaf are epidermis

   The various components of a monocot leaf are epidermis




It is surrounded by parenchymatous ground tissue. Vascular bundles have conjoint, collateral but closed nature with xylem towards the upper side and phloem towards the lower side. Reasons for Identification : (i) Bifacial flattened structure with stomata nmostly on lower surface. (iii) Vascular bundles with colourless bundle sheath. 

Internall Structure of an Isobilateral Monocot Leaf : (Fig. 6) In monocot leaves the two surfaces are equally green and liable to face the sun. They are, therefore, called isobilateral leaves (Gk. isos equal, bis side).

 The various components of a monocot leaf are epidermis, mesophyll, vascular twice, latris strand and midrib. (1) Epidermis : It is the outer most covering of the lamina on both the surfaces. The cells are parenchymatous rectangular barrel shaped. They are devoid of chloroplasts and are, therefore, transparent.

 Free surface of the epidermal cells possesses cutin and silica thickenings. Separate layer of cuticle is also present. At places the adaxial epidermis of Maize and a number of grasses possess large sized thil.walled colourless protruding cells called bulliform or motor cells. They become flaccid when water is deficient. Consequently, the leaves curl inwardly to minimise exposed surface.

 The leaves become flát again when water is available and bulliform cells become turgid. Bulliform or motor cells, therefore, take part in folding and unfolding of leaves depending upon the moisture content of the atmosphere. Stomata occur on both the surfaces with almost equal frequency. 

Wednesday, 19 May 2021

The heterosporous species are always dioecious

The heterosporous species are always dioecious



 In the latter, development of gametophyte is independent. external environment, whereas in the former, it homosporous pteridophytes the prothallus is branches. In species of Lycopodium, the prothallus simple, green and heart-shaped or has aerial gametophyte in different genera. In most of the the microspore gives rise to the male gametophyte (e.g.. Lycopodium, Selaginella. Equisetum) and the megaspore to the female gametophyte.

 There is much variation in the shape. The heterosporous species are always dioecious. The sex organs are embedded in the prothallus Pteridop is vulnerable to environment. is of the following three types. (i) In L. cernum it is very small and inconspicuous but autotrophic. In species like L. clavatum, L.

 Obscurum and (ii) L. selago, the prothallus is tuberous, subterranean and sporophytic. (iii) In some epiphytic species (e.g., L. phlegmaria) the whole prothallus is heavily associated with endophytic fungal hyphae which show symbiotic association.

 Most of the homosporous species are monoecious, i.e., antheridia and archegonia are borne on the same prothallus. They are protandrous of protogynous. Some homosporous forms (e.g.. Pterb Pteridium) are also dioecious. or are projected (e.g., Psilotum, Pteridium).

(ii) Gradate sorus : in this type the central or distal part of the sorus has mature/older sporangia and the peripheral or proximal part has immature younger sporangia (e.g., Marsilea, Cyathea; Fig. 4B). (iii) Mixed sorus : Here mature and immature sporangia are arranged irregularly (e.g., Pteridium, Pteris, Adiantum, Polypodium).