The spermatophytes known as phanerogams or phaenogams, comprise those plants that produce seeds, hence the alternative name seed plants. They are a subset of the embryophytes or land plants; the term phanerogams or phanerogamae is derived from the Greek φανερός, phanerós meaning "visible", in contrast to the cryptogamae from Greek κρυπτός kryptós = "hidden" together with the suffix γαμέω, gameein, "to marry". These terms distinguished those plants with hidden sexual organs from those with visible sexual organs; the extant spermatophytes form five divisions, the first four of which are traditionally grouped as gymnosperms, plants that have unenclosed, "naked seeds": Cycadophyta, the cycads, a subtropical and tropical group of plants, which includes a single living species of tree in the genus Ginkgo, the conifers, which are cone-bearing trees and shrubs, Gnetophyta, the gnetophytes, various woody plants in the relict genera Ephedra and Welwitschia. The fifth extant division is the flowering plants known as angiosperms or magnoliophytes, the largest and most diverse group of spermatophytes.
Angiosperms possess seeds enclosed unlike gymnosperms. In addition to the taxa listed above, the fossil record contains evidence of many extinct taxa of seed plants; the so-called "seed ferns" were one of the earliest successful groups of land plants, forests dominated by seed ferns were prevalent in the late Paleozoic. Glossopteris was the most prominent tree genus in the ancient southern supercontinent of Gondwana during the Permian period. By the Triassic period, seed ferns had declined in ecological importance, representatives of modern gymnosperm groups were abundant and dominant through the end of the Cretaceous, when angiosperms radiated. A whole genome duplication event in the ancestor of seed plants occurred about 319 million years ago; this gave rise to a series of evolutionary changes. A middle Devonian precursor to seed plants from Belgium has been identified predating the earliest seed plants by about 20 million years. Runcaria and radially symmetrical, is an integumented megasporangium surrounded by a cupule.
The megasporangium bears an unopened distal extension protruding above the mutlilobed integument. It is suspected. Runcaria sheds new light on the sequence of character acquisition leading to the seed. Runcaria has all of the qualities of seed plants except for a solid seed coat and a system to guide the pollen to the seed. Seed-bearing plants were traditionally divided into angiosperms, or flowering plants, gymnosperms, which includes the gnetophytes, cycads and conifers. Older morphological studies believed in a close relationship between the gnetophytes and the angiosperms, in particular based on vessel elements. However, molecular studies have shown a clade of gymnosperms, with the gnetophytes in or near the conifers. For example, one common proposed set of relationships is known as the gne-pine hypothesis and looks like: However, the relationships between these groups should not be considered settled. Other classifications group all the seed plants in a single division, with classes for the five groups: Division Spermatophyta Cycadopsida, the cycads Ginkgoopsida, the ginkgo Pinopsida, the conifers, the gnetophytes Magnoliopsida, the flowering plants, or AngiospermopsidaA more modern classification ranks these groups as separate divisions: Cycadophyta, the cycads Ginkgophyta, the ginkgo Pinophyta, the conifers Gnetophyta, the gnetophytes Magnoliophyta, the flowering plantsAn alternative phylogeny of spermatophytes based on the work by Novíkov & Barabaš-Krasni 2015 with plant taxon authors from Anderson, Anderson & Cleal 2007 showing the relationship of extinct clades.
Unassigned spermatophytes: †Avatiaceae Anderson & Anderson 2003 †Axelrodiopsida Anderson & Anderson †Alexiales Anderson & Anderson 2003 †Hamshawviales Anderson & Anderson 2003 †Hexapterospermales Doweld 2001 †Hlatimbiales Anderson & Anderson 2003 †Matatiellales Anderson & Anderson 2003 †Petriellales Taylor et al. 1994 †Arberiopsida Doweld 2001 †Czekanowskiales Taylor et al. 2008 †Iraniales E. Taylor et al. 2008 †Vojnovskyales E. Taylor et al. 2008 †Hermanophytales E. Taylor et al. 2008 †Dirhopalostachyaceae E. Taylor et al. 2008
Alternation of generations
Alternation of generations is the type of life cycle that occurs in those plants and algae in the Archaeplastida and the Heterokontophyta that have distinct sexual haploid and asexual diploid stages. In these groups, a multicellular gametophyte, haploid with n chromosomes, alternates with a multicellular sporophyte, diploid with 2n chromosomes, made up of n pairs. A mature sporophyte produces spores by meiosis, a process which reduces the number of chromosomes to half, from 2n to n; the haploid spores grow into a haploid gametophyte. At maturity, the gametophyte produces gametes by mitosis, which does not alter the number of chromosomes. Two gametes fuse to produce a zygote; this cycle, from gametophyte to gametophyte, is the way in which all land plants and many algae undergo sexual reproduction. The relationship between the sporophyte and gametophyte varies among different groups of plants. In those algae which have alternation of generations, the sporophyte and gametophyte are separate independent organisms, which may or may not have a similar appearance.
In liverworts and hornworts, the sporophyte is less well developed than the gametophyte and is dependent on it. Although moss and hornwort sporophytes can photosynthesise, they require additional photosynthate from the gametophyte to sustain growth and spore development and depend on it for supply of water, mineral nutrients and nitrogen. By contrast, in all modern vascular plants the gametophyte is less well developed than the sporophyte, although their Devonian ancestors had gametophytes and sporophytes of equivalent complexity. In ferns the gametophyte is a small flattened autotrophic prothallus on which the young sporophyte is dependent for its nutrition. In flowering plants, the reduction of the gametophyte is much more extreme. Animals develop differently, they directly produce haploid gametes. No haploid spores capable of dividing are produced, so they do not have a haploid gametophyte alternating with a diploid sporophyte. Life cycles of plants and algae with alternating haploid and diploid multicellular stages are referred to as diplohaplontic.
Life cycles, such as those of animals, in which there is only a diploid multicellular stage are referred to as diplontic. Life cycles in which there is only a haploid multicellular stage are referred to as haplontic. Alternation of generations is defined as the alternation of multicellular diploid and haploid forms in the organism's life cycle, regardless of whether or not these forms are free-living. In some species, such as the alga Ulva lactuca, the diploid and haploid forms are indeed both free-living independent organisms identical in appearance and therefore said to be isomorphic; the free-swimming, haploid gametes form a diploid zygote which germinates into a multicellular diploid sporophyte. The sporophyte produces free-swimming haploid spores by meiosis that germinate into haploid gametophytes. However, in some other groups, either the sporophyte or the gametophyte is much reduced and is incapable of free living. For example, in all bryophytes the gametophyte generation is dominant and the sporophyte is dependent on it.
By contrast, in all modern vascular land plants the gametophytes are reduced, although the fossil evidence indicates that they were derived from isomorphic ancestors. In seed plants, the female gametophyte develops within the sporophyte which protects and nurtures it and the embryo sporophyte that it produces; the pollen grains, which are the male gametophytes, are reduced to only a few cells. Here the notion of two generations is less obvious; the alternative term'alternation of phases' may be more appropriate. Debates about alternation of generations in the early twentieth century can be confusing because various ways of classifying "generations" co-exist. Chamisso and Steenstrup described the succession of differently organized generations in animals as "alternation of generations", while studying the development of tunicates and trematode animals; this phenomenon is known as heterogamy. Presently, the term "alternation of generations" is exclusively associated with the life cycles of plants with the alternation of haploid gametophytes and diploid sporophytes.
Wilhelm Hofmeister demonstrated the morphological alternation of generations in plants, between a spore-bearing generation and a gamete-bearing generation. By that time, a debate emerged focusing on the origin of the asexual generation of land plants and is conventionally characterized as a conflict between theories of antithetic and homologous alternation of generations. Čelakovský coined the words gametophyte. Eduard Strasburger discovered the alternation between diploid and haploid nuclear phases called cytological alternation of nuclear phases. Although most coinciding, morphological alternation and nuclear phases alternation are sometimes independent of one another, e.g. in many red algae, the same nuclear
Loam is soil composed of sand, a smaller amount of clay. By weight, its mineral composition is about 40–40–20% concentration of sand-silt-clay, respectively; these proportions can vary to a degree and result in different types of loam soils: sandy loam, silty loam, clay loam, sandy clay loam, silty clay loam, loam. In the USDA textural classification triangle, the only soil, not predominantly sand, silt, or clay is called "loam". Loam soils contain more nutrients and humus than sandy soils, have better drainage and infiltration of water and air than silt and clay-rich soils, are easier to till than clay soils; the different types of loam soils each have different characteristics, with some draining liquids more efficiently than others. The soil's texture its ability to retain nutrients and water are crucial. Loam soil is suitable for growing most plant varieties. Bricks made of loam, mud and water, with an added binding material such as rice husks or straw, have been used in construction since ancient times.
Loam is considered ideal for gardening and agricultural uses because it retains nutrients well and retains water while still allowing excess water to drain away. A soil dominated by one or two of the three particle size groups can behave like loam if it has a strong granular structure, promoted by a high content of organic matter. However, a soil that meets the textural definition of loam can lose its characteristic desirable qualities when it is compacted, depleted of organic matter, or has clay dispersed throughout its fine-earth fraction. Loam is found in a majority of successful farms in regions around the world known for their fertile land. Loam soil is easy to work over a wide range of moisture conditions. Loam may be used for example in loam post and beam construction. Building crews can build a layer of loam on the inside of walls, which can help to control air humidity. Loam, combined with straw, can be used as a rough construction material to build walls; this is one of the oldest technologies for house construction in the world.
Within this there are two broad methods: unfired bricks. Loess – A predominantly silt-sized clastic sediment of accumulated wind-blown dust Grain size Soil texture
Plants are multicellular, predominantly photosynthetic eukaryotes of the kingdom Plantae. Plants were treated as one of two kingdoms including all living things that were not animals, all algae and fungi were treated as plants. However, all current definitions of Plantae exclude the fungi and some algae, as well as the prokaryotes. By one definition, plants form the clade Viridiplantae, a group that includes the flowering plants and other gymnosperms and their allies, liverworts and the green algae, but excludes the red and brown algae. Green plants obtain most of their energy from sunlight via photosynthesis by primary chloroplasts that are derived from endosymbiosis with cyanobacteria, their chloroplasts contain b, which gives them their green color. Some plants are parasitic or mycotrophic and have lost the ability to produce normal amounts of chlorophyll or to photosynthesize. Plants are characterized by sexual reproduction and alternation of generations, although asexual reproduction is common.
There are about 320 thousand species of plants, of which the great majority, some 260–290 thousand, are seed plants. Green plants provide a substantial proportion of the world's molecular oxygen and are the basis of most of Earth's ecosystems on land. Plants that produce grain and vegetables form humankind's basic foods, have been domesticated for millennia. Plants have many cultural and other uses, as ornaments, building materials, writing material and, in great variety, they have been the source of medicines and psychoactive drugs; the scientific study of plants is known as a branch of biology. All living things were traditionally placed into one of two groups and animals; this classification may date from Aristotle, who made the distincton between plants, which do not move, animals, which are mobile to catch their food. Much when Linnaeus created the basis of the modern system of scientific classification, these two groups became the kingdoms Vegetabilia and Animalia. Since it has become clear that the plant kingdom as defined included several unrelated groups, the fungi and several groups of algae were removed to new kingdoms.
However, these organisms are still considered plants in popular contexts. The term "plant" implies the possession of the following traits multicellularity, possession of cell walls containing cellulose and the ability to carry out photosynthesis with primary chloroplasts; when the name Plantae or plant is applied to a specific group of organisms or taxon, it refers to one of four concepts. From least to most inclusive, these four groupings are: Another way of looking at the relationships between the different groups that have been called "plants" is through a cladogram, which shows their evolutionary relationships; these are not yet settled, but one accepted relationship between the three groups described above is shown below. Those which have been called "plants" are in bold; the way in which the groups of green algae are combined and named varies between authors. Algae comprise several different groups of organisms which produce food by photosynthesis and thus have traditionally been included in the plant kingdom.
The seaweeds range from large multicellular algae to single-celled organisms and are classified into three groups, the green algae, red algae and brown algae. There is good evidence that the brown algae evolved independently from the others, from non-photosynthetic ancestors that formed endosymbiotic relationships with red algae rather than from cyanobacteria, they are no longer classified as plants as defined here; the Viridiplantae, the green plants – green algae and land plants – form a clade, a group consisting of all the descendants of a common ancestor. With a few exceptions, the green plants have the following features in common, they undergo closed mitosis without centrioles, have mitochondria with flat cristae. The chloroplasts of green plants are surrounded by two membranes, suggesting they originated directly from endosymbiotic cyanobacteria. Two additional groups, the Rhodophyta and Glaucophyta have primary chloroplasts that appear to be derived directly from endosymbiotic cyanobacteria, although they differ from Viridiplantae in the pigments which are used in photosynthesis and so are different in colour.
These groups differ from green plants in that the storage polysaccharide is floridean starch and is stored in the cytoplasm rather than in the plastids. They appear to have had a common origin with Viridiplantae and the three groups form the clade Archaeplastida, whose name implies that their chloroplasts were derived from a single ancient endosymbiotic event; this is the broadest modern definition of the term'plant'. In contrast, most other algae not only have different pigments but have chloroplasts with three or four surrounding membranes, they are not close relatives of the Archaeplastida having acquired chloroplasts separately from ingested or symbiotic green and red algae. They are thus not included in the broadest modern definition of the plant kingdom, although they were in the past; the green plants or Viridiplantae were traditionally divided into the green algae (including
Protozoa is an informal term for single-celled eukaryotes, either free-living or parasitic, which feed on organic matter such as other microorganisms or organic tissues and debris. The protozoa were regarded as "one-celled animals", because they possess animal-like behaviors, such as motility and predation, lack a cell wall, as found in plants and many algae. Although the traditional practice of grouping protozoa with animals is no longer considered valid, the term continues to be used in a loose way to identify single-celled organisms that can move independently and feed by heterotrophy. In some systems of biological classification, Protozoa is a high-level taxonomic group; when first introduced in 1818, Protozoa was erected as a taxonomic class, but in classification schemes it was elevated to a variety of higher ranks, including phylum and kingdom. In a series of classifications proposed by Thomas Cavalier-Smith and his collaborators since 1981, Protozoa has been ranked as a kingdom; the seven-kingdom scheme presented by Ruggiero et al. in 2015, places eight phyla under Kingdom Protozoa: Euglenozoa, Metamonada, Choanozoa sensu Cavalier-Smith, Percolozoa and Sulcozoa.
Notably, this kingdom excludes several major groups of organisms traditionally placed among the protozoa, including the ciliates, dinoflagellates and the parasitic apicomplexans, all of which are classified under Kingdom Chromista. Kingdom Protozoa, as defined in this scheme, does not form a natural group or clade, but a paraphyletic group or evolutionary grade, within which the members of Fungi and Chromista are thought to have evolved; the word "protozoa" was coined in 1818 by zoologist Georg August Goldfuss, as the Greek equivalent of the German Urthiere, meaning "primitive, or original animals". Goldfuss created Protozoa as a class containing; the group included not only single-celled microorganisms but some "lower" multicellular animals, such as rotifers, sponges, jellyfish and polychaete worms. The term Protozoa is formed from the Greek words πρῶτος, meaning "first", ζῶα, plural of ζῶον, meaning "animal"; the use of Protozoa as a formal taxon has been discouraged by some researchers because the term implies kinship with animals and promotes an arbitrary separation of "animal-like" from "plant-like" organisms.
In 1848, as a result of advancements in cell theory pioneered by Theodor Schwann and Matthias Schleiden, the anatomist and zoologist C. T. von Siebold proposed that the bodies of protozoans such as ciliates and amoebae consisted of single cells, similar to those from which the multicellular tissues of plants and animals were constructed. Von Siebold redefined Protozoa to include only such unicellular forms, to the exclusion of all metazoa. At the same time, he raised the group to the level of a phylum containing two broad classes of microorganisms: Infusoria, Rhizopoda; the definition of Protozoa as a phylum or sub-kingdom composed of "unicellular animals" was adopted by the zoologist Otto Bütschli—celebrated at his centenary as the "architect of protozoology"—and the term came into wide use. As a phylum under Animalia, the Protozoa were rooted in the old "two-kingdom" classification of life, according to which all living beings were classified as either animals or plants; as long as this scheme remained dominant, the protozoa were understood to be animals and studied in departments of Zoology, while photosynthetic microorganisms and microscopic fungi—the so-called Protophyta—were assigned to the Plants, studied in departments of Botany.
Criticism of this system began in the latter half of the 19th century, with the realization that many organisms met the criteria for inclusion among both plants and animals. For example, the algae Euglena and Dinobryon have chloroplasts for photosynthesis, but can feed on organic matter and are motile. In 1860, John Hogg argued against the use of "protozoa", on the grounds that "naturalists are divided in opinion—and some will continue so—whether many of these organisms, or living beings, are animals or plants." As an alternative, he proposed a new kingdom called Primigenum, consisting of both the protozoa and unicellular algae, which he combined together under the name "Protoctista". In Hoggs's conception, the animal and plant kingdoms were likened to two great "pyramids" blending at their bases in the Kingdom Primigenum. Six years Ernst Haeckel proposed a third kingdom of life, which he named Protista. At first, Haeckel included a few multicellular organisms in this kingdom, but in work he restricted the Protista to single-celled organisms, or simple colonies whose individual cells are not differentiated into different kinds of tissues.
Despite these proposals, Protozoa emerged as the preferred taxonomic placement for heterotrophic microorganisms such as amoebae and ciliates, remained so for more than a century. In the course of the 20th century, the old "two kingdom" system began to weaken, with the growing awareness that fungi did not belong among the plants, that most of the unicellular protozoa were no more related to the animals than they were to the plants. By mid-century, some biologists, such as Herbert Copeland, Robert H. Whittaker and Lynn Margulis, advocated the revival of Haeckel's Protista or Hogg's Protoctista as a kingdom-level eukaryotic group, alongside Plants and Fungi. A variety of multi-kingdom systems were proposed, Kingdoms Protista and Protoctista became well est
The Ancient Greek language includes the forms of Greek used in Ancient Greece and the ancient world from around the 9th century BCE to the 6th century CE. It is roughly divided into the Archaic period, Classical period, Hellenistic period, it is succeeded by medieval Greek. Koine is regarded as a separate historical stage of its own, although in its earliest form it resembled Attic Greek and in its latest form it approaches Medieval Greek. Prior to the Koine period, Greek of the classic and earlier periods included several regional dialects. Ancient Greek was the language of Homer and of fifth-century Athenian historians and philosophers, it has contributed many words to English vocabulary and has been a standard subject of study in educational institutions of the Western world since the Renaissance. This article contains information about the Epic and Classical periods of the language. Ancient Greek was a pluricentric language, divided into many dialects; the main dialect groups are Attic and Ionic, Aeolic and Doric, many of them with several subdivisions.
Some dialects are found in standardized literary forms used in literature, while others are attested only in inscriptions. There are several historical forms. Homeric Greek is a literary form of Archaic Greek used in the epic poems, the "Iliad" and "Odyssey", in poems by other authors. Homeric Greek had significant differences in grammar and pronunciation from Classical Attic and other Classical-era dialects; the origins, early form and development of the Hellenic language family are not well understood because of a lack of contemporaneous evidence. Several theories exist about what Hellenic dialect groups may have existed between the divergence of early Greek-like speech from the common Proto-Indo-European language and the Classical period, they differ in some of the detail. The only attested dialect from this period is Mycenaean Greek, but its relationship to the historical dialects and the historical circumstances of the times imply that the overall groups existed in some form. Scholars assume that major Ancient Greek period dialect groups developed not than 1120 BCE, at the time of the Dorian invasion—and that their first appearances as precise alphabetic writing began in the 8th century BCE.
The invasion would not be "Dorian" unless the invaders had some cultural relationship to the historical Dorians. The invasion is known to have displaced population to the Attic-Ionic regions, who regarded themselves as descendants of the population displaced by or contending with the Dorians; the Greeks of this period believed there were three major divisions of all Greek people—Dorians and Ionians, each with their own defining and distinctive dialects. Allowing for their oversight of Arcadian, an obscure mountain dialect, Cypriot, far from the center of Greek scholarship, this division of people and language is quite similar to the results of modern archaeological-linguistic investigation. One standard formulation for the dialects is: West vs. non-west Greek is the strongest marked and earliest division, with non-west in subsets of Ionic-Attic and Aeolic vs. Arcadocypriot, or Aeolic and Arcado-Cypriot vs. Ionic-Attic. Non-west is called East Greek. Arcadocypriot descended more from the Mycenaean Greek of the Bronze Age.
Boeotian had come under a strong Northwest Greek influence, can in some respects be considered a transitional dialect. Thessalian had come under Northwest Greek influence, though to a lesser degree. Pamphylian Greek, spoken in a small area on the southwestern coast of Anatolia and little preserved in inscriptions, may be either a fifth major dialect group, or it is Mycenaean Greek overlaid by Doric, with a non-Greek native influence. Most of the dialect sub-groups listed above had further subdivisions equivalent to a city-state and its surrounding territory, or to an island. Doric notably had several intermediate divisions as well, into Island Doric, Southern Peloponnesus Doric, Northern Peloponnesus Doric; the Lesbian dialect was Aeolic Greek. All the groups were represented by colonies beyond Greece proper as well, these colonies developed local characteristics under the influence of settlers or neighbors speaking different Greek dialects; the dialects outside the Ionic group are known from inscriptions, notable exceptions being: fragments of the works of the poet Sappho from the island of Lesbos, in Aeolian, the poems of the Boeotian poet Pindar and other lyric poets in Doric.
After the conquests of Alexander the Great in the late 4th century BCE, a new international dialect known as Koine or Common Greek developed based on Attic Greek, but with influence from other dialects. This dialect replaced most of the older dialects, although Doric dialect has survived in the Tsakonian language, spoken in the region of modern Sparta. Doric has passed down its aorist terminations into most verbs of Demotic Greek. By about the 6th century CE, the Koine had metamorphosized into Medieval Greek. Ancient Macedonian was an Indo-European language at least related to Greek, but its exact relationship is unclear because of insufficient data: a dialect of Greek; the Macedonian dialect (or l
An ascospore is a spore contained in an ascus or, produced inside an ascus. This kind of spore is specific to fungi classified as ascomycetes. Ascospores are formed in ascus under optimal conditions.. A single ascus will contain eight ascospores; the eight spores are produced by meiosis followed by a mitotic division. Two meiotic divisions turn the original diploid zygote nucleus into four haploid ones; that is, the single original diploid cell from which the whole process begins contains two complete sets of chromosomes. In preparation for meiosis, all the DNA of both sets is duplicated; the nucleus that contains the four sets divides twice, separating into four new nuclei – each of which has one complete set of chromosomes. Following this process, each of the four new nuclei duplicates its DNA and undergoes a division by mitosis; as a result, the ascus will contain four pairs of spores. The ascospores are released from ascus; the ascospores of Blumeria graminis are released under the humid conditions.
After landing onto a suitable surface, unlike conidia, ascospores of Blumeria graminis showed a more variable developmental patterns. The fungi Saccharomyces produces ascospores when grown on V-8 medium, acetate ascospore agar, or Gorodkowa medium; these ascospores are globose and located in asci. Each ascus contains one to four ascospores; the asci do not rupture at maturity. Ascospores are stained with ascospore stain; when stained with Gram stain, ascospores are gram-negative. The fission yeast Schizosaccharomyces pombe is a single-celled haploid organism that reproduces asexually by mitosis and fission. However, exposure to the DNA damaging agent hydrogen peroxide induces pair-wise mating of haploid cells of opposite mating type to form transient diploid cells that undergo meiosis to form asci, each with four ascospores; the production of viable ascospores depends on successful recombinational repair during meiosis. When this repair is defective a quality control mechanism prevents germination of damaged ascospores.
These findings suggest that mating followed by meiosis is an adaptation for repairing DNA damage in the parental haploid cells in order to allow production of viable progeny ascospores. Ascomycota Ascus Meiosis Neurospora crassa Saccharomyces cerevisiae Tetrad