Pteridophytes
Cryptogams can be classified into non vascular cryptogams and vascular cryptogams. Since vascular system is absent in Algae, Fungi and bryophytes, they called as non-vascular cryptogams.
The term pteridophyta was first introduced by Haeckel in 1866. Pteridophytes
(pteron-feather)possess vascular tissues and reproduce by spores they are called as vascular cryptogams. The reproduction by spores is the basis for placing pteridophytes under cryptograms.
Bryophytes and pteridophytes and gymnosperms are together called as archegoniates because of presence of archegonium in all of this group of plants.
Sinnott in 1935 proposed a group of Tracheophyta to include the vascular plants i.e., pteridophytes and spermatophytes.
The pteridophytes appeared in early Silurion period. They formed a dominant Flora on the earth in the late devonian and carboniferous periods, about 35 million years ago.tree like massive arborescent forms flourished in the devonian and carboniferous periods but the present forms are small and herbaceous except the tree ferns. There are about 400 general and 10500 species of Living pteridophytes
Distribution and habitat
They grow in tropical and temperate regions of the globe. The plants grows luxuriantly in cool damp shady places. Some species flourish well in open,dry situations like Selaginella letridophylla, Equisetum arvers. A few pteridophytes are aquatic like Azolla and Salvinia. Some are epiphytic L.phegmaria, c.squarrosum, S.aregana.
All living pteridophytes are herbaceous except a few woody ferns like Cyathea.
The plant body:
The most characteristic feature of pteridophytes is the presence of independent sporophyte and gametophyte. The diploid sporophyte generation is dominant in pteridophyte in contrast to bryophyte. It attends a high degree of complexity with reference to external and internal organisation.
The sporophyte plant body is differentiated into root, stem and leaves for the first time in pteridophyte. Sporophyte shows such differentiation for the first time in plant Kingdom.
The primary root is short lived and it is replaced by permanent adventitious roots arising from the base of the stem from the nodes of aerial stem. The branching of roots is either monopodial or dichotomous. Roots shows diarch and exarch arrangement of xylem in the Stele.
The stem may be horizontal or erect. The creeping horizontal stem maybe subterranean or aerial or ephiphytic. The stem looks like a corm(Isoetes) or tuber(Equisetem).
The stem may be smooth or covered with hairs or scales. Branching maybe dichotomous as in Lycopodium or lateral as in Polypodium.
The vascular system in stem varies in different species. Stele ranges from protostele to polycyclic condition. Xylem consists of tracheids only. Phloem is made up of sieve tubes but lack companion cells. Vessels are reported in some members for example Selaginella and Equisetum.
Secondary growth is absent in majority of the living species, Isoetes being an exception.
In erect stem leaves are arranged around the stem in spirals or in pairs or in whorls. In rhizomatous stems the leaves arise from the upper side.
On basis of their size the leaves may be microphyllous or megaphyllous. In microphyllous leaves there is only midrib which is unbranched running from base to apex example Selaginella, Lycopodium. The megaphyllous leaves have a stout petiole and lamina with dichotomous venation. The leaves may be simple or compound. Young leaves of plants exhibit circinate vernation.
Internally the mesophyll may be un -differentiated as in microphyllous leaves (primitive character) or may be differentiated into palisade and spongy parenchyma as in megaphyllous leaves (advanced character).
Reproduction:
Vegetative reproduction takes place due to death and decay of the rhizome, tuber, Gemma and adventitious buds etc.
The plants reproduce asexually by means of spores. The sporophyte produces spores which may be homosporous that is produce only one type of spores, (example Rhynia, Lycopodium, Equisetum) or heterosporous that is produces two types of spores the small microspore and larger megaspore, (example Selaginella, Marsilea).
The spores are produced in sac like structure called sporangia. Sporangia are usually born on leaf like structure called sporophylls on axils of the leaves. The sporophylls along with the sporangia are scattered throughout the vegetative part of the plant or may be restricted to terminal parts.
In Equisetum and Selaginella the sporangia form distinct compact structures called strobilus or cone. In some forms the sporangia bearing special stalked structure called sporangiophore
are arranged in whorls on the axis of the strobilus, e.g., Equisetum. The sporangia in some cases maybe produced within the bivalved specialised structures called the sporocarps example Marsilea, Salvinia, Azolla.
In true ferns (Filicales) the sporangia are usually born on group called sori. The sori are found on the margins or under abaxial surface of the leaves. The shape of sori maybe circular, linear or reniform. The sori are of three types based on the mode of development of sporangia in a sorus (Bower 1935).
1. The simple sorus:
All the sporangium in a sorus develop simultaneously and all of them mature together example Ophioglossum, Osmunda.
2.The gradate or basipetal sorus:
The sporangia develop in a basipetal manner that is the oldest sporangia is at the top
of the receptacle and the younger sporangium at the base example Dicksoria, Cyathea.
3.The mixed sorus:
The sporangium of different ages are intermixed in the same sorus and show no regular arrangement. The sporangia usually have long stalks and vertical annulus, example Pteris, Adiantum.
The development of sporangium may be eusporangiate or leptosporangiate
Eusporangiate type :
The sporangium originates from a group of superficial initials known as sporangial initials this initials divide periclinally into outer primary cell walls and inner sporogenous cells
The primary wall cells develop into several layered wall of sporangium. The innermost wall layer functions of tapetum which forms a nourishing plasmodial fluid.
The wall of the mature sporangium maybe single layer due to degeneration of remaining layers, example Lycopodium, Selaginella, Equisetum.
But in Psilotum and Tmesipteris the mature sporangial wall remains multilayered. The sporogenous cells divide meiotically and give rise to haploid spores. The spore output is high that is 1000 to 25000 spores. Eusporangium is primitive.
Leptosporangiate type:
The leptosporangiate develops from a single superficial initial. The initial divides transversely into an outer and inner cell. The entire sporangium develops from the outer cells. The inner cell is responsible for the formation of stalk of the sporangium.
The mature sporangium is small and the sporogial wall is single layer. The spore output is less that is 4-256 spores. The leptosporangiate is more advanced and found in Filicales (example Pteridium, Pteris, Marsilea).
Within the sporangium, the diploid spore mother cell undergo meiosis to form spores. The spores maybe homosporus (example Lycopodium, Equisetum) or heterosporous (example Selaginella, Marsilea). In heterosporous type the smaller spores are termed as microspores and larger spores are termed as megaspores.
Spores are haploid and form after reduction division in the sporogenous cells of the sporangium.
Spore germination to multicellular gametophytic body called prothallus.
The gametophytes are of two types:
Gametophytes that develop from homospores grow up on the soil surface and form independent plants. Such gametophytes are known as exosporic gametophytes example Lycopodium, Equisetum.
Gametophytes that develop from microspores and megaspores are for the most part retained within the spore wall. Such gametophytes are known as endosporic gametophytes example Selaginella, Marsilea. They live on food deposited in the spores.
Generally the prothallus are green, simple somewhat branched and aerial structures but in some genera such as lycopodium they are subterranean, well branched, tuberous, colourless.
The gametophyte or prothallus bears the sex-organs, the antheridia and archegonia.
They are similar in structure to those of bryophyta
Generally the prothalli of homosporous pteridophytes are monoecious and protandrous. Where as the prothallus of heterosporous pteridophytes are dioecious.
The antheridium
The antheridia may be embedded either wholly or in part in the tissue of the gametophyte. The farmer are the embedded type example lycopodium selaginella acquisitive and the later are the projecting type example Pteris.
The antheridium is a spherical structure. It has a sterile jacket that encloses a group of androcytes. Each androcyte gives rise to a single motile antherozoid. The antheridia are unicellular, uninucleate and biflagellate structures in Lcopodium, Selaginella but they are multiflagellate in Psilotum, Equisetum and ferns.
The archegonia
Each archegonium is a flask shaped structure consisting of a basal, swollen, embedded part, the venter and a short projecting neck. The venter encloses the egg and venter canal cell. Inside the neck are found 1-6 neck canal cells.
Fertilization
Fertilization takes place with the help of water and results in the formation of a diploid zygote antherozoids are attracted chemotactically towards the archegonium.
Zygote
zygote is the first cell of sporophyte and it is diploid.
Zygote develops into the embryo embryo maybe endoscopy where the effects of the embryo is directed inwards towards the gametophytic tissue ( Lycopodium, Selaginella) or exoscopic in which the apex of the embryo is directed towards the neck of archegonium (Psilotum). It develops into a well developed sporophyte bearing roots, stem and leaves.
Pteridophytes show alternation of generations.
Cryptogams can be classified into non vascular cryptogams and vascular cryptogams. Since vascular system is absent in Algae, Fungi and bryophytes, they called as non-vascular cryptogams.
The term pteridophyta was first introduced by Haeckel in 1866. Pteridophytes
(pteron-feather)possess vascular tissues and reproduce by spores they are called as vascular cryptogams. The reproduction by spores is the basis for placing pteridophytes under cryptograms.
Bryophytes and pteridophytes and gymnosperms are together called as archegoniates because of presence of archegonium in all of this group of plants.
Sinnott in 1935 proposed a group of Tracheophyta to include the vascular plants i.e., pteridophytes and spermatophytes.
The pteridophytes appeared in early Silurion period. They formed a dominant Flora on the earth in the late devonian and carboniferous periods, about 35 million years ago.tree like massive arborescent forms flourished in the devonian and carboniferous periods but the present forms are small and herbaceous except the tree ferns. There are about 400 general and 10500 species of Living pteridophytes
Distribution and habitat
They grow in tropical and temperate regions of the globe. The plants grows luxuriantly in cool damp shady places. Some species flourish well in open,dry situations like Selaginella letridophylla, Equisetum arvers. A few pteridophytes are aquatic like Azolla and Salvinia. Some are epiphytic L.phegmaria, c.squarrosum, S.aregana.
All living pteridophytes are herbaceous except a few woody ferns like Cyathea.
The plant body:
The most characteristic feature of pteridophytes is the presence of independent sporophyte and gametophyte. The diploid sporophyte generation is dominant in pteridophyte in contrast to bryophyte. It attends a high degree of complexity with reference to external and internal organisation.
The sporophyte plant body is differentiated into root, stem and leaves for the first time in pteridophyte. Sporophyte shows such differentiation for the first time in plant Kingdom.
The primary root is short lived and it is replaced by permanent adventitious roots arising from the base of the stem from the nodes of aerial stem. The branching of roots is either monopodial or dichotomous. Roots shows diarch and exarch arrangement of xylem in the Stele.
The stem may be horizontal or erect. The creeping horizontal stem maybe subterranean or aerial or ephiphytic. The stem looks like a corm(Isoetes) or tuber(Equisetem).
The stem may be smooth or covered with hairs or scales. Branching maybe dichotomous as in Lycopodium or lateral as in Polypodium.
The vascular system in stem varies in different species. Stele ranges from protostele to polycyclic condition. Xylem consists of tracheids only. Phloem is made up of sieve tubes but lack companion cells. Vessels are reported in some members for example Selaginella and Equisetum.
Secondary growth is absent in majority of the living species, Isoetes being an exception.
In erect stem leaves are arranged around the stem in spirals or in pairs or in whorls. In rhizomatous stems the leaves arise from the upper side.
On basis of their size the leaves may be microphyllous or megaphyllous. In microphyllous leaves there is only midrib which is unbranched running from base to apex example Selaginella, Lycopodium. The megaphyllous leaves have a stout petiole and lamina with dichotomous venation. The leaves may be simple or compound. Young leaves of plants exhibit circinate vernation.
Internally the mesophyll may be un -differentiated as in microphyllous leaves (primitive character) or may be differentiated into palisade and spongy parenchyma as in megaphyllous leaves (advanced character).
Reproduction:
Vegetative reproduction takes place due to death and decay of the rhizome, tuber, Gemma and adventitious buds etc.
The plants reproduce asexually by means of spores. The sporophyte produces spores which may be homosporous that is produce only one type of spores, (example Rhynia, Lycopodium, Equisetum) or heterosporous that is produces two types of spores the small microspore and larger megaspore, (example Selaginella, Marsilea).
The spores are produced in sac like structure called sporangia. Sporangia are usually born on leaf like structure called sporophylls on axils of the leaves. The sporophylls along with the sporangia are scattered throughout the vegetative part of the plant or may be restricted to terminal parts.
In Equisetum and Selaginella the sporangia form distinct compact structures called strobilus or cone. In some forms the sporangia bearing special stalked structure called sporangiophore
are arranged in whorls on the axis of the strobilus, e.g., Equisetum. The sporangia in some cases maybe produced within the bivalved specialised structures called the sporocarps example Marsilea, Salvinia, Azolla.
In true ferns (Filicales) the sporangia are usually born on group called sori. The sori are found on the margins or under abaxial surface of the leaves. The shape of sori maybe circular, linear or reniform. The sori are of three types based on the mode of development of sporangia in a sorus (Bower 1935).
1. The simple sorus:
All the sporangium in a sorus develop simultaneously and all of them mature together example Ophioglossum, Osmunda.
2.The gradate or basipetal sorus:
The sporangia develop in a basipetal manner that is the oldest sporangia is at the top
of the receptacle and the younger sporangium at the base example Dicksoria, Cyathea.
3.The mixed sorus:
The sporangium of different ages are intermixed in the same sorus and show no regular arrangement. The sporangia usually have long stalks and vertical annulus, example Pteris, Adiantum.
The development of sporangium may be eusporangiate or leptosporangiate
Eusporangiate type :
The sporangium originates from a group of superficial initials known as sporangial initials this initials divide periclinally into outer primary cell walls and inner sporogenous cells
The primary wall cells develop into several layered wall of sporangium. The innermost wall layer functions of tapetum which forms a nourishing plasmodial fluid.
The wall of the mature sporangium maybe single layer due to degeneration of remaining layers, example Lycopodium, Selaginella, Equisetum.
But in Psilotum and Tmesipteris the mature sporangial wall remains multilayered. The sporogenous cells divide meiotically and give rise to haploid spores. The spore output is high that is 1000 to 25000 spores. Eusporangium is primitive.
Leptosporangiate type:
The leptosporangiate develops from a single superficial initial. The initial divides transversely into an outer and inner cell. The entire sporangium develops from the outer cells. The inner cell is responsible for the formation of stalk of the sporangium.
The mature sporangium is small and the sporogial wall is single layer. The spore output is less that is 4-256 spores. The leptosporangiate is more advanced and found in Filicales (example Pteridium, Pteris, Marsilea).
Within the sporangium, the diploid spore mother cell undergo meiosis to form spores. The spores maybe homosporus (example Lycopodium, Equisetum) or heterosporous (example Selaginella, Marsilea). In heterosporous type the smaller spores are termed as microspores and larger spores are termed as megaspores.
Spores are haploid and form after reduction division in the sporogenous cells of the sporangium.
Spore germination to multicellular gametophytic body called prothallus.
The gametophytes are of two types:
Gametophytes that develop from homospores grow up on the soil surface and form independent plants. Such gametophytes are known as exosporic gametophytes example Lycopodium, Equisetum.
Gametophytes that develop from microspores and megaspores are for the most part retained within the spore wall. Such gametophytes are known as endosporic gametophytes example Selaginella, Marsilea. They live on food deposited in the spores.
Generally the prothallus are green, simple somewhat branched and aerial structures but in some genera such as lycopodium they are subterranean, well branched, tuberous, colourless.
The gametophyte or prothallus bears the sex-organs, the antheridia and archegonia.
They are similar in structure to those of bryophyta
Generally the prothalli of homosporous pteridophytes are monoecious and protandrous. Where as the prothallus of heterosporous pteridophytes are dioecious.
The antheridium
The antheridia may be embedded either wholly or in part in the tissue of the gametophyte. The farmer are the embedded type example lycopodium selaginella acquisitive and the later are the projecting type example Pteris.
The antheridium is a spherical structure. It has a sterile jacket that encloses a group of androcytes. Each androcyte gives rise to a single motile antherozoid. The antheridia are unicellular, uninucleate and biflagellate structures in Lcopodium, Selaginella but they are multiflagellate in Psilotum, Equisetum and ferns.
The archegonia
Each archegonium is a flask shaped structure consisting of a basal, swollen, embedded part, the venter and a short projecting neck. The venter encloses the egg and venter canal cell. Inside the neck are found 1-6 neck canal cells.
Fertilization
Fertilization takes place with the help of water and results in the formation of a diploid zygote antherozoids are attracted chemotactically towards the archegonium.
Zygote
zygote is the first cell of sporophyte and it is diploid.
Zygote develops into the embryo embryo maybe endoscopy where the effects of the embryo is directed inwards towards the gametophytic tissue ( Lycopodium, Selaginella) or exoscopic in which the apex of the embryo is directed towards the neck of archegonium (Psilotum). It develops into a well developed sporophyte bearing roots, stem and leaves.
Pteridophytes show alternation of generations.
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