Retting is a process employing the action of micro-organisms and moisture on plants to dissolve or rot away much of the cellular tissues and pectins surrounding bast-fibre bundles, so facilitating separation of the fibre from the stem. It is used in the production of fibre from plant materials such as flax and hemp stalks and coir from coconut husks; the most practised method of retting, water retting, is performed by submerging bundles of stalks in water. The water, penetrating to the central stalk portion, swells the inner cells, bursting the outermost layer, thus increasing absorption of both moisture and decay-producing bacteria. Retting time must be judged. In double retting, a gentle process producing excellent fibre, the stalks are removed from the water before retting is completed, dried for several months retted again. Natural water retting employs stagnant or slow-moving waters, such as ponds and slow streams and rivers; the stalk bundles are weighted down with stones or wood, for about 8 to 14 days, depending upon water temperature and mineral content.
Tank retting, by contrast, employs vats made of concrete, requires about four to six days, is feasible in any season. In the first six to eight hours, called the leaching period, much of the dirt and colouring matter is removed by the water, changed to assure clean fibre. Waste retting water, which requires treatment to reduce harmful toxic elements before its release, is rich in plant minerals, such as nitrates, can be used as liquid fertilizer; this is a common method in areas with limited water resources. It is most effective in climates with warm daytime temperatures; the harvested plant stalks are spread evenly in grassy fields, where the combined action of bacteria, sun and dew produces fermentation, dissolving much of the stem material surrounding the fibre bundles. Within two to three weeks, depending upon climatic conditions, the fibre can be separated. Dew-retted fibre is darker in color and of poorer quality than water-retted fibre; the retted stalks, called straw, are dried in open air or by mechanical means, are stored for a short period to allow "curing" to occur, facilitating fibre removal.
Final separation of the fibre is accomplished by a breaking process in which the brittle woody portion of the straw is broken, either by hand or by passing through rollers, followed by the scutching operation, which removes the broken woody pieces by beating or scraping. Some machines combine scutching operations. Waste material from the first scutching, consisting of shives and short fibres, is treated a second time; the short fibre thus obtained is used in paper manufacture, the shives may serve as fuel to heat the retting water or may be made into wallboard. Textile manufacture during the Industrial Revolution Timeline of clothing and textiles technology Video footage of the Low House retting pond
A slough is a wetland a swamp or shallow lake a backwater to a larger body of water. Water tends to be stagnant or may flow on a seasonal basis. In North America, "slough" may refer to a side-channel from or feeding a river, or an inlet or natural channel only sporadically filled with water. An example of this is Finn Slough on the Fraser River, whose lower reaches have dozens of notable sloughs; some sloughs, like Elkhorn Slough, used to be mouths of rivers, but have become stagnant because tectonic activity cut off the river's source. In the Sacramento River, Steamboat Slough was an alternate branch of the river, a preferred shortcut route for steamboats passing between Sacramento and San Francisco. Georgiana Slough was a steamboat route through the Sacramento–San Joaquin River Delta, from the Sacramento River to the San Joaquin River and Stockton. A slough called a tidal channel, is a channel in a wetland, it is either stagnant or slow flowing on a seasonal basis. Vegetation patterns in a slough are determined by depth and duration of in the environment.
Moreover, these same variables influence the distribution, abundance and seasonal movements of aquatic and terrestrial life within the sloughs. Sloughs support a wide variety of plant life, adapted to changing physical conditions such as salinity, oxygen levels and depth. In general, sloughs are microhabitats high in species diversity. Open water sloughs are characterized by submerged and floating vegetation which includes periphyton mats dominated by sawgrass typically; the topographical and vegetation heterogeneity of ridge and slough landscape influences the productivity and diversity of birds and fish adapted to that wetland. Fish that inhabit sloughs include tidewater goby, California killifish and topsmelt. Food habits of fish within sloughs consist of preying upon invertebrates. Fish can feed on plant material. Research on prey species for fish in sloughs found that in a study done on Elkhorn Slough in California the mean prey richness for fish was greatest near the ocean and lowest inshore.
This allows for a higher availability of food to enhance the function of inshore habitats and emphasizes the importance of invertebrate prey populations and how they influence plant production. Birds inhabit sloughs. Sloughs are hotspots for bird watching. For example, the Elkhorn Slough in the western United States is one of the premier bird watching sites in the western United States. Over 340 species are seen visiting including several rare and endangered species. Species of birds seen in sloughs such as the Elkhorn slough include Acorn Woodpecker, Brown Pelican, Caspian Tern, Great BlueHeron, Great Egret, Great Horned Owl, Snowy Plover, White-tailed Kite. Sloughs are influenced by human development such as urban and agricultural expansion and agricultural practices, water management practices, humans influence on species composition. Uses of identifying these aspects of human involvement can help to better predict restoration efforts to be made in managing sloughs. Examples of attributes that are affected by human stress upon the environment include periphyton, marsh plant communities, tree islands, wading birds, marsh fishes and herpetofauna.
A slough can form when a meander gets cut off from the main river channel creating an oxbow lake that accumulates with fine overbank sediment and organic material such as peat. This creates a swamp environment. One end of the oxbow configuration continues to receive flow from the main channel, creating a slough. Sloughs are associated with the ridge formations found in their presence; such a landscape consists of mosaic linear ridges of some sort of grass such as sawgrass ridges in the Florida Everglades, that are separated by deeper water sloughs. Edges of sloughs are layers of sediment; the development of this landscape is thought to occur by the preferential formation of peat in bedrock depressions. Multiple of these deposits mounted on top of the surrounding bedrock can become elongated alongside the slough and create flow diversions within the system. Different rates of this peat accumulation could be triggered by variations in microtopography that alter plant production and vegetation type.
Water flow might be the key to preventing an accumulation of organic sediment in sloughs due to the fact that accumulation leads to lowering water depths and instead allows for the growth of vegetation. Overall little quantitative data on the degradation of slough landscape exists. Slough and ridge landscape has been degraded in terms of both topographic and vegetation changes over time. Topographical changes create an increase in the relief between ridge crests and slough bottoms. Vegetation changes consist of an increase in the amount of dense grass and decrease in the area of open water, creating a blurring of the directional ridge and slough pattern. Historical everglade and slough landscape has been affected and degraded by human activity. Open water sloughs support important ecological functions that have been seen to be sensitive to hydrologic and water quality problems stemmed from human activities. Sloughs are ecologically important, they act as a buffer from land to sea and act as an active part of the estuary system where freshwater flows from creeks and runoff from the land mix with salty ocean water transported by tides.
Restoration is a big effort in California wetlands to restore ridge landscapes. Examples of restoration projects on slough
Mosquitoes are a group of about 3500 species of small insects that are a type of fly. Within that order they constitute the family Culicidae; the word "mosquito" is Spanish for "little fly". Mosquitoes have a slender segmented body, a pair of wings, three pairs of long hair-like legs, feathery antennae, elongated mouthparts. Mosquitoes diverged from other insects about 226 million years ago. Fossils of primitive mosquitoes have been found; the life cycle consists of the egg, larva and adult. Eggs are laid on the water surface. Females of most species have tube-like mouthparts which can pierce the skin of the host in order to extract blood, which contains protein and iron needed to produce eggs. Thousands of mosquito species feed on the blood of various hosts — vertebrates, including mammals, reptiles and some fish; this loss of blood is of any importance to the host. The saliva of the mosquito transmitted to the host with the bite can cause a rash. In addition, many species of mosquitoes inject or ingest disease-causing organisms with the bite and are thus a vector for the transmission of diseases such as malaria, yellow fever, West Nile virus, dengue fever, Zika virus and other arboviruses.
Mosquitoes kill more people than any other animal: over 700,000 each year. The oldest known mosquito with an anatomy similar to modern species was found in 79-million-year-old Canadian amber from the Cretaceous. An older sister species with more primitive features was found in Burmese amber, 90 to 100 million years old. Two mosquito fossils have been found that show little morphological change in modern mosquitoes against their counterpart from 46 million years ago; these fossils are the oldest found to have blood preserved within their abdomens. Despite no fossils being found earlier than the Cretaceous, recent studies suggest that the earliest divergence of mosquitoes between the lineages leading to Anophelinae and Culicinae occurred 226 million years ago; the mosquito Anopheles gambiae is undergoing speciation into the M and S molecular forms. Some pesticides that work on the M form no longer work on the S form. Over 3,500 species of the Culicidae have been described, they are divided into two subfamilies which in turn comprise some 43 genera.
These figures are subject to continual change, as more species are discovered, as DNA studies compel rearrangement of the taxonomy of the family. The two main subfamilies are the Anophelinae and Culicinae, with their genera as shown in the subsection below; the distinction is of great practical importance because the two subfamilies tend to differ in their significance as vectors of different classes of diseases. Speaking, arboviral diseases such as yellow fever and dengue fever tend to be transmitted by Culicine species, not in the genus Culex; some transmit various species of avian malaria, but it is not clear that they transmit any form of human malaria. Some species do however transmit various forms of filariasis, much as many Simuliidae do. Mosquitoes are members of a family of nematocerid flies: the Culicidae. Superficially, mosquitoes resemble. Anophelinae Culicinae Over 3,500 species of mosquitoes have thus far been described in the scientific literature. Like all flies, mosquitoes go through four stages in their lifecycles: egg, larva and adult or imago.
The first three stages—egg and pupa—are aquatic. These stages last 5 to 14 days, depending on the species and the ambient temperature, but there are important exceptions. Mosquitoes living in regions where some seasons are freezing or waterless spend part of the year in diapause. For instance, Wyeomyia larvae get frozen into solid lumps of ice during winter and only complete their development in spring; the eggs of some species of Aedes remain unharmed in diapause if they dry out, hatch when they are covered by water. Eggs hatch to become larvae; the adult mosquito emerges from the mature pupa. Bloodsucking mosquitoes, depending on species and weather conditions, have potential adult lifespans ranging from as short as a week to as long as several months; some species can overwinter as adults in diapause. In most species, adult females lay their eggs in stagnant water: some lay near the water's edge while others attach their eggs to aquatic plants; each species selects the situation of the water into which it lays its eggs and does so according to its own ecological adaptations.
Some are generalists and are not fussy. Some breed in some in temporary puddles; some breed in some in salt-marshes. Among those that breed in salt water, some are at home in fresh and salt water up to about one-third the concentration of seawater, whereas others must acclimatize themselves to the salinity; such differences are important because certain ecological pre
A desert is a barren area of landscape where little precipitation occurs and living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to the processes of denudation. About one-third of the land surface of the world is semi-arid; this includes much of the polar regions where little precipitation occurs and which are sometimes called polar deserts or "cold deserts". Deserts can be classified by the amount of precipitation that falls, by the temperature that prevails, by the causes of desertification or by their geographical location. Deserts are formed by weathering processes as large variations in temperature between day and night put strains on the rocks which break in pieces. Although rain occurs in deserts, there are occasional downpours that can result in flash floods. Rain falling on hot rocks can cause them to shatter and the resulting fragments and rubble strewn over the desert floor are further eroded by the wind; this wafts them aloft in sand or dust storms.
Wind-blown sand grains striking any solid object in their path can abrade the surface. Rocks are smoothed down, the wind sorts sand into uniform deposits; the grains are piled high in billowing sand dunes. Other deserts are flat, stony plains where all the fine material has been blown away and the surface consists of a mosaic of smooth stones; these areas are known as desert pavements and little further erosion takes place. Other desert features include rock outcrops, exposed bedrock and clays once deposited by flowing water. Temporary lakes may form and salt pans may be left when waters evaporate. There may be underground sources of water in the form of seepages from aquifers. Where these are found, oases can occur. Plants and animals living in the desert need special adaptations to survive in the harsh environment. Plants tend to be tough and wiry with small or no leaves, water-resistant cuticles and spines to deter herbivory; some annual plants germinate and die in the course of a few weeks after rainfall while other long-lived plants survive for years and have deep root systems able to tap underground moisture.
Animals need to find enough food and water to survive. Many stay in the shade or underground during the heat of the day, they tend to be efficient at conserving water, extracting most of their needs from their food and concentrating their urine. Some animals remain in a state of dormancy for long periods, ready to become active again during the rare rainfall, they reproduce while conditions are favorable before returning to dormancy. People have struggled to live in the surrounding semi-arid lands for millennia. Nomads have moved their flocks and herds to wherever grazing is available and oases have provided opportunities for a more settled way of life; the cultivation of semi-arid regions encourages erosion of soil and is one of the causes of increased desertification. Desert farming is possible with the aid of irrigation, the Imperial Valley in California provides an example of how barren land can be made productive by the import of water from an outside source. Many trade routes have been forged across deserts across the Sahara Desert, traditionally were used by caravans of camels carrying salt, gold and other goods.
Large numbers of slaves were taken northwards across the Sahara. Some mineral extraction takes place in deserts, the uninterrupted sunlight gives potential for the capture of large quantities of solar energy. English desert and its Romance cognates all come from the ecclesiastical Latin dēsertum, a participle of dēserere, "to abandon"; the correlation between aridity and sparse population is complex and dynamic, varying by culture and technologies. In English before the 20th century, desert was used in the sense of "unpopulated area", without specific reference to aridity. Phrases such as "desert island" and "Great American Desert", or Shakespeare's "deserts of Bohemia" in previous centuries did not imply sand or aridity. A desert is a region of land, dry because it receives low amounts of precipitation has little coverage by plants, in which streams dry up unless they are supplied by water from outside the area. Deserts receive less than 250 mm of precipitation each year; the potential evapotranspiration may be large but the actual evapotranspiration may be close to zero.
Semideserts are regions which receive between 250 and 500 mm and when clad in grass, these are known as steppes. Deserts have been defined and classified in a number of ways combining total precipitation, number of days on which this falls and humidity, sometimes additional factors. For example, Arizona, receives less than 250 mm of precipitation per year, is recognized as being located in a desert because of its aridity-adapted plants; the North Slope of Alaska's Brooks Range receives less than 250 mm of precipitation per year and is classified as a cold desert. Other regions of the world have cold deserts, including areas of the Himalayas and other high-altitude areas in other parts of the world. Polar deserts cover much of the ice-free
Animals are multicellular eukaryotic organisms that form the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, grow from a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. Animals range in length from 8.5 millionths of a metre to 33.6 metres and have complex interactions with each other and their environments, forming intricate food webs. The category includes humans, but in colloquial use the term animal refers only to non-human animals; the study of non-human animals is known as zoology. Most living animal species are in the Bilateria, a clade whose members have a bilaterally symmetric body plan; the Bilateria include the protostomes—in which many groups of invertebrates are found, such as nematodes and molluscs—and the deuterostomes, containing the echinoderms and chordates.
Life forms interpreted. Many modern animal phyla became established in the fossil record as marine species during the Cambrian explosion which began around 542 million years ago. 6,331 groups of genes common to all living animals have been identified. Aristotle divided animals into those with those without. Carl Linnaeus created the first hierarchical biological classification for animals in 1758 with his Systema Naturae, which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa and the Protozoa, single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics, which are effective at demonstrating the evolutionary relationships between animal taxa. Humans make use of many other animal species for food, including meat and eggs. Dogs have been used in hunting, while many aquatic animals are hunted for sport.
Non-human animals have appeared in art from the earliest times and are featured in mythology and religion. The word "animal" comes from the Latin animalis, having soul or living being; the biological definition includes all members of the kingdom Animalia. In colloquial usage, as a consequence of anthropocentrism, the term animal is sometimes used nonscientifically to refer only to non-human animals. Animals have several characteristics. Animals are eukaryotic and multicellular, unlike bacteria, which are prokaryotic, unlike protists, which are eukaryotic but unicellular. Unlike plants and algae, which produce their own nutrients animals are heterotrophic, feeding on organic material and digesting it internally. With few exceptions, animals breathe oxygen and respire aerobically. All animals are motile during at least part of their life cycle, but some animals, such as sponges, corals and barnacles become sessile; the blastula is a stage in embryonic development, unique to most animals, allowing cells to be differentiated into specialised tissues and organs.
All animals are composed of cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. During development, the animal extracellular matrix forms a flexible framework upon which cells can move about and be reorganised, making the formation of complex structures possible; this may be calcified, forming structures such as shells and spicules. In contrast, the cells of other multicellular organisms are held in place by cell walls, so develop by progressive growth. Animal cells uniquely possess the cell junctions called tight junctions, gap junctions, desmosomes. With few exceptions—in particular, the sponges and placozoans—animal bodies are differentiated into tissues; these include muscles, which enable locomotion, nerve tissues, which transmit signals and coordinate the body. There is an internal digestive chamber with either one opening or two openings. Nearly all animals make use of some form of sexual reproduction, they produce haploid gametes by meiosis.
These fuse to form zygotes, which develop via mitosis into a hollow sphere, called a blastula. In sponges, blastula larvae swim to a new location, attach to the seabed, develop into a new sponge. In most other groups, the blastula undergoes more complicated rearrangement, it first invaginates to form a gastrula with a digestive chamber and two separate germ layers, an external ectoderm and an internal endoderm. In most cases, a third germ layer, the mesoderm develops between them; these germ layers differentiate to form tissues and organs. Repeated instances of mating with a close relative during sexual reproduction leads to inbreeding depression within a population due to the increased prevalence of harmful recessive traits. Animals have evolved numerous mechanisms for avoiding close inbreeding. In some species, such as the splendid fairywren, females benefit by mating with multiple males, thus producing more offspring of higher genetic quality; some animals are capable of asexual reproduction, which results
Flies are insects with a pair of functional wings for flight and a pair of vestigial hindwings called halteres for balance. They are classified as an order called Diptera, that name being derived from the Greek δι- di- "two", πτερόν pteron "wings"; the order Diptera is divided with about 110 families divided between them. The earliest fly fossils found so far are from the Triassic, about 240 million years ago. Many insects, such as the butterfly, contain the word are not Dipterans; the word "fly" is sometimes used colloquially and non-scientifically as a name for any small flying insect: the term "true fly" is sometimes invoked to make clear the insect being referenced is a Dipteran. Flies have a mobile head, with a pair of large compound eyes, mouthparts designed for piercing and sucking, or for lapping and sucking in the other groups; the suborder Nematocera have long antennae. Flies have only a single pair of wings to fly; the hindwings evolved into advanced mechanosensory organs, which act as high-speed sensors of rotational movement and allow them to perform advanced aerobatics.
Claws and pads on their feet enable them to cling to smooth surfaces. The life cycle of flies consists of the eggs, larva and the adult. Flies undergo complete metamorphosis; the pupa in higher dipterans is a tough capsule. Flies have short lives: for example, the adult housefly lives about a month; the source of nutrition for adult flies is liquified food, including nectar. Flies are of human importance, they are important pollinators, second only to their Hymenopteran relatives. They may have been responsible for the first plant pollination in the Triassic. Mosquitoes are vectors for malaria, West Nile fever, yellow fever and other infectious diseases. Flies can be annoyances in some parts of the world where they can occur in large numbers and settling on the skin or eyes to bite or seek fluids. Larger flies such as tsetse flies and screwworms cause significant economic harm to cattle. Blowfly larvae, known as gentles, other dipteran larvae, known more as maggots, are used as fishing bait, as food for carnivorous animals, in medicine for debridement to clean wounds.
Fruit flies are used as model organisms in research. In culture, the subject of flies appears in religion, literature and music. Dipterans are insects that undergo radical metamorphosis, they belong to the Mecopterida, alongside the Mecoptera, Siphonaptera and Trichoptera. The possession of a single pair of wings distinguishes most true flies from other insects with "fly" in their names. However, some true flies such as Hippoboscidae have become secondarily wingless; the cladogram represents the current consensus view. The first true dipterans known are from the Middle Triassic around 240 million years ago, they became widespread during the Middle and Late Triassic. Phylogenetic analysis of times of divergence suggests that dipterans originated in the Permian, some 260 million years ago. Modern flowering plants did not appear until the Cretaceous, so the original dipterans must have had a different source of nutrition other than nectar. Based on the attraction of many modern fly groups to shiny droplets, it has been suggested that they may have fed on honeydew produced by sap-sucking bugs which were abundant at the time, dipteran mouthparts are well-adapted to softening and lapping up the crusted residues.
The basal clades in the Diptera include the enigmatic Nymphomyiidae. Three episodes of evolutionary radiation are thought to have occurred based on the fossil record. Many new species of lower Diptera developed in the Triassic, about 220 million years ago. Many lower Brachycera appeared in the Jurassic, some 180 million years ago. A third radiation took place among the Schizophora at the start of the Paleogene, 66 million years ago; the phylogenetic position of Diptera has been controversial. The monophyly of holometabolous insects has long been accepted, with the main orders being established as Lepidoptera, Coleoptera and Diptera, it is the relationships between these groups which has caused difficulties. Diptera is thought to be a member of Mecopterida, along with Lepidoptera, Siphonaptera and Strepsiptera. Diptera has been grouped with Siphonaptera and Mecoptera in the Antliophora, but this has not been confirmed by molecular studies. Diptera were traditionally broken down into two suborders and Brachycera, distinguished by the differences in antennae.
The Nematocera are recognized by their elongated bodies and many-segmented feathery antennae as represented by mosquitoes and crane flies. The Brachycera have rounder bodies and much sh