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pteridophyta
Значение термина pteridophyta в knolik
pteridophyta - pteridophyta
pteridophyta - Division of plant kingdom comprising ferns, horsetails, clubmosses, etc. A prominent group of the Carboniferous era, when tree-like forms were common; living representatives forming a small, widely distributed group attaining its greatest development in the tropics. Largely terrestrial; characterized by possession of true stems, leaves, and roots; a well-developed vascular system (but no cambium); sporangia borne on leaves (sporophylls) and by separate, small, inconspicuous sexual plants (prothalli), bearing antheridia and archegonia. Sporophylls resembling ordinary foliage leaves, e.g. bracken, or much modified, arranged in a cone, e.g. horsetail. The sporangia liberate spores which germinate to give rise to prothalli. Fertilization of egg in archegonium is effected by male gametes motile by flagella. Zygote develops into a new plant. Alternation of generations is well marked. The fern plant, the sporophyte, is the dominant generation; the prothallus is the gametophyte. Contrasted with lower plants the outstanding feature of the pteridophytes is the development of an independent sporophyte, with roots, stems, leaves, and well-developed vascular system. In most ferns the sporophyte gives rise to only one kind of spore and one kind of gametophyte (prothallus) bearing both antheridia and archegonia; they are homosporous. In other, heterosporous members, e.g. Selaginella, the sporophyte produces small microspores and larger megaspores. The microspores give rise to extremely reduced male prothalli, each bearing an an-theridium containing a small number of spermatozoids. The megaspores, which may be reduced to one per sporangium, produce slightly larger female prothalli, each bearing a few archegonia. During their development these gametophytes are retained within the spores. In some species with a single, large megaspore per sporangium, development of gametophyte, fertilization of egg and embryo formation takes place while the megaspore is enclosed within the sporangium which maintains its physiological connection with the sporophyte. This condition foreshadows that in seed plants where the megaspore is permanently retained within the megasporangium, on the sporophyte. Living representatives are in four orders, Filicales (ferns), Equisetales (horsetails), Lyco-podiales (clubmosses), Psilotales. Fossil forms include orders Psilo-phytales and Sphenophyllales. These groups are now frequently classified in Subdivisions of Division Tracheophyta : Psilotales and Psilophytales in Psilopsida, Lycopodiales in Lycopsida, Equisetales and Sphenophyllales in Sphenopsida, and Filicales in Pteropsida (with seed plants).
Рядом со словом pteridophyta в knolik
| psychrophilic | В начало буква "" буквосочетание "" | pteridospermae |
Статья про pteridophyta была прочитана 257 раз
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