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Fern

A fern is a member of a group of vascular plants that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e. having specialized tissues that conduct water and nutrients and in having life cycles in which the sporophyte is the dominant phase. Ferns have complex leaves called megaphylls, that are more complex than the microphylls of clubmosses. Most ferns are leptosporangiate ferns, sometimes referred to as true ferns, they produce coiled fiddleheads that expand into fronds. The group includes about 10,560 known extant species. Ferns are defined here in the broad sense, being all of the Polypodiopsida, comprising both the leptosporangiate and eusporangiate ferns, the latter itself comprising ferns other than those denominated true ferns, including horsetails or scouring rushes, whisk ferns, marattioid ferns, ophioglossoid ferns. Ferns first appear in the fossil record about 360 million years ago in the middle Devonian period, but many of the current families and species did not appear until 145 million years ago in the early Cretaceous, after flowering plants came to dominate many environments.

The fern Osmunda claytoniana is a paramount example of evolutionary stasis. Ferns are not of major economic importance, but some are used for food, medicine, as biofertilizer, as ornamental plants and for remediating contaminated soil, they have been the subject of research for their ability to remove some chemical pollutants from the atmosphere. Some fern species, such as bracken and water fern are significant weeds worldwide; some fern genera, such as Azolla can fix nitrogen and make a significant input to the nitrogen nutrition of rice paddies. They play certain roles in folklore. Like the sporophytes of seed plants, those of ferns consist of stems and roots. Ferns differ from seed plants in reproducing by spores and from bryophytes in that, like seed plants, they are Polysporangiophytes, their sporophytes branching and producing many sporangia. Unlike bryophytes, fern sporophytes are free-living and only dependent on the maternal gametophyte. Stems: Fern stems are referred to as rhizomes though they grow underground only in some of the species.

Epiphytic species and many of the terrestrial ones have above-ground creeping stolons, many groups have above-ground erect semi-woody trunks. These can reach up to 20 meters tall in a few species. Leaf: The green, photosynthetic part of the plant is technically a megaphyll and in ferns, it is referred to as a frond. New leaves expand by the unrolling of a tight spiral called a crozier or fiddlehead into fronds; this uncurling of the leaf is termed circinate vernation. Leaves are divided into a sporophyll. A trophophyll frond is a vegetative leaf analogous to the typical green leaves of seed plants that does not produce spores, instead only producing sugars by photosynthesis. A sporophyll frond is a fertile leaf that produces spores borne in sporangia that are clustered to form sori. In most ferns, fertile leaves are morphologically similar to the sterile ones, they photosynthesize in the same way. In some groups, the fertile leaves are much narrower than the sterile leaves, may have no green tissue at all.

The anatomy of fern leaves can either be simple or divided. In tree ferns, the main stalk that connects the leaf to the stem has multiple leaflets; the leafy structures that grow from the stipe are known as pinnae and are again divided into smaller pinnules. Roots: The underground non-photosynthetic structures that take up water and nutrients from soil, they are always fibrous and structurally are similar to the roots of seed plants. Like all other vascular plants, the diploid sporophyte is the dominant phase or generation in the life cycle; the gametophytes of ferns, are different from those of seed plants. They are free-living and resemble liverworts, whereas those of seed plants develop within the spore wall and are dependent on the parent sporophyte for their nutrition. A fern gametophyte consists of: Prothallus: A green, photosynthetic structure, one cell thick heart or kidney shaped, 3–10 mm long and 2–8 mm broad; the prothallus produces gametes by means of: Antheridia: Small spherical structures that produce flagellate sperm.

Archegonia: A flask-shaped structure that produces a single egg at the bottom, reached by the sperm by swimming down the neck. Rhizoids: root-like structures that consist of single elongated cells, that absorb water and mineral salts over the whole structure. Rhizoids anchor the prothallus to the soil. Carl Linnaeus recognized 15 genera of ferns and fern allies, classifying them in class Cryptogamia in two groups and Musci. By 1806 this had increased to 38 genera, has progressively increased since. Ferns were traditionally classified in the class Filices, in a Division of the Plant Kingdom named Pteridophyta or Filicophyta. Pteridophyta is no longer recognised as a valid taxon; the ferns are referred to as Polypodiophyta or, when treated as a subdivision of Tracheophyta, although this name sometimes only refers to leptosporangiate fe

Kosmos 1793

Kosmos 1793 is a Soviet US-K missile early warning satellite, launched in 1986 as part of the Soviet military's Oko programme. The satellite is designed to identify missile launches using optical telescopes and infrared sensors. Kosmos 1793 was launched from Site 16/2 at Plesetsk Cosmodrome in the Russian SSR. A Molniya-M carrier rocket with a 2BL upper stage was used to perform the launch, which took place at 12:09 UTC on 20 November 1986; the launch placed the satellite into a molniya orbit. It subsequently received its Kosmos designation, the international designator 1986-091A; the United States Space Command assigned it the Satellite Catalog Number 17134. It re-entered the Earth's atmosphere on 15 May 2011. List of Kosmos satellites List of R-7 launches 1986 in spaceflight List of Oko satellites

Flag of Scarborough, Ontario

The Flag of the City of Scarborough, Ontario consisted of a stylized abstract impression of the Scarborough Bluffs and Lake Ontario are in blue on the left and bottom of the flag. The background is white, with the red Maple Leaf of the Flag of Canada near the centre of the otherwise void area; the flag was dedicated on August 19, 1969, by then-Mayor Albert Campbell at a special ceremony in Thomson Memorial Park. It was designed by local painter Doris McCarthy in the spring of 1968, presented with the idea by her friend Albert Campbell. McCarthy based the design on ideas presented by Campbell and from her influence in living by the Bluffs; the need for the flag was proposed by Campbell to give the new borough an identity at civic events. The flag was used at the Scarborough Civic Centre, municipal buildings and schools of the Scarborough Board of Education. Scarborough was one of three municipalities within Metropolitan Toronto to introduce a civic flag: Toronto - Flag of Toronto was adopted in 1974 Etobicoke - Flag of Etobicoke, was adopted in 1975 and amended in 1995The City of York, City of North York and Borough of East York used corporate slogan civic logo or motto as a banner instead of an official flag.

After the 1998 amalgamation of Toronto, the official use of civic symbols from the former municipalities was no longer valid and the Scarborough flag was no longer flown on municipal buildings. In early January 2004, Toronto City councilors Brian Ashton and Glenn De Baeremaeker argued at the newly established Scarborough Community Council for the re-establishment of the Scarborough flag as a symbol of the borough. On January 27, 2004, Toronto City Council granted a Scarborough Community Council request to be allowed to fly the former City of Scarborough flag. In early January 2008, De Baermaeker spoke up about a lack of funding for civic symbols, saying it would only cost "$5,000 to buy 100 Scarborough flags to put in front of our civic buildings." On January 29 and 30, 2008, Toronto City Council authorized the allocation of $20,000 to order Scarborough flags to be used for municipal and civic purposes by the City and local City Councillors. Flag of Toronto