Leather is a natural durable and flexible material created by tanning animal rawhides and skins. The most common raw material is cattle hide, it can be produced at manufacturing scales ranging from artisan to modern industrial scale. Leather is used to make a variety of articles, including footwear, automobile seats, bags, book bindings, fashion accessories, furniture, it is decorated by a wide range of techniques. The earliest record of leather artifacts dates back to 2200 BC; the leather manufacturing process is divided into three fundamental subprocesses: preparatory stages and crusting. A further subprocess, can be added into the leather process sequence, but not all leathers receive finishing; the preparatory stages are. Preparatory stages may include: soaking, liming, bating and pickling. Tanning is a process that stabilizes the proteins collagen, of the raw hide to increase the thermal and microbiological stability of the hides and skins, making it suitable for a wide variety of end applications.
The principal difference between raw and tanned hides is that raw hides dry out to form a hard, inflexible material that, when rewetted, will putrefy, while tanned material dries to a flexible form that does not become putrid when rewetted. Many tanning methods and materials exist; the typical process sees tanners load the hides into a drum and immerse them in a tank that contains the tanning "liquor". The hides soak while the drum rotates about its axis, the tanning liquor penetrates through the full thickness of the hide. Once the process achieves penetration, workers raise the liquor's pH in a process called basification, which fixes the tanning material to the leather; the more tanning material fixed, the higher the leather's hydrothermal stability and shrinkage temperature resistance. Crusting is a process that lubricates leather, it includes a coloring operation. Chemicals added during crusting must be fixed in place. Crusting culminates with a drying and softening operation, may include splitting, dyeing, whitening or other methods.
For some leathers, tanners apply a surface coating, called "finishing". Finishing operations can include oiling, buffing, polishing, glazing, or tumbling, among others. Leather can be oiled to improve its water resistance; this currying process after tanning supplements the natural oils remaining in the leather itself, which can be washed out through repeated exposure to water. Frequent oiling of leather, with mink oil, neatsfoot oil, or a similar material keeps it supple and improves its lifespan dramatically. Tanning processes differ in which chemicals are used in the tanning liquor; some common types include: Vegetable-tanned leather is tanned using tannins extracted from vegetable matter, such as tree bark prepared in bark mills. It is the oldest known method, it is supple and brown in color, with the exact shade depending on the mix of materials and the color of the skin. The color tan derives its name from the appearance of undyed vegetable-tanned leather. Vegetable-tanned leather is not stable in water.
This is a feature of oak-bark-tanned leather, exploited in traditional shoemaking. In hot water, it shrinks drastically and congeals, becoming rigid and brittle. Boiled leather is an example of this, where the leather has been hardened by being immersed in hot water, or in boiled wax or similar substances, it was used as armor after hardening, it has been used for book binding. Chrome-tanned leather, invented in 1858, is tanned using chromium other chromium salts, it is known as "wet blue" for the pale blue color of the undyed leather. The chrome tanning method takes one day to complete, making it best suited for large-scale industrial use; this is the most common method in modern use. It is more supple and pliable than vegetable-tanned leather and does not discolor or lose shape as drastically in water as vegetable-tanned. However, there are environmental concerns with this tanning method. Aldehyde-tanned leather is tanned using oxazolidine compounds, it is referred to as "wet white" due to its pale cream color.
It is the main type of "chrome-free" leather seen in shoes for infants and automobiles. Formaldehyde has been used for tanning in the past. Chamois leather is a form of aldehyde tanning that produces a porous and water-absorbent leather. Chamois leather is made using marine oils that oxidize to produce the aldehydes that tan the leather. Brain tanned leathers are made by a labor-intensive process that uses emulsified oils those of animal brains such as deer and buffalo, they are known for their exceptional washability. Alum leather is transformed using aluminium salts mixed with a variety of binders and protein sources, such as flour and egg yolk. Alum leather is not tanned. In general, leather is produced in the following grades: Top-grain leather includes the outer layer of the hide, known as the grain, which features finer, more densely packed fibers, resulting in strength and durability. Depending on thickness, it may contain some of the more fibrous under layer, known as the corium. Types of top-grain leather incl
A seed is an embryonic plant enclosed in a protective outer covering. The formation of the seed is part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiosperm plants. Seeds are the product of the ripened ovule, after fertilization by pollen and some growth within the mother plant; the embryo is developed from the seed coat from the integuments of the ovule. Seeds have been an important development in the reproduction and success of gymnosperm and angiosperm plants, relative to more primitive plants such as ferns and liverworts, which do not have seeds and use water-dependent means to propagate themselves. Seed plants now dominate biological niches on land, from forests to grasslands both in hot and cold climates; the term "seed" has a general meaning that antedates the above – anything that can be sown, e.g. "seed" potatoes, "seeds" of corn or sunflower "seeds". In the case of sunflower and corn "seeds", what is sown is the seed enclosed in a shell or husk, whereas the potato is a tuber.
Many structures referred to as "seeds" are dry fruits. Plants producing berries are called baccate. Sunflower seeds are sometimes sold commercially while still enclosed within the hard wall of the fruit, which must be split open to reach the seed. Different groups of plants have other modifications, the so-called stone fruits have a hardened fruit layer fused to and surrounding the actual seed. Nuts are the one-seeded, hard-shelled fruit of some plants with an indehiscent seed, such as an acorn or hazelnut. Seeds are produced in several related groups of plants, their manner of production distinguishes the angiosperms from the gymnosperms. Angiosperm seeds are produced in a hard or fleshy structure called a fruit that encloses the seeds for protection in order to secure healthy growth; some fruits have layers of both fleshy material. In gymnosperms, no special structure develops to enclose the seeds, which begin their development "naked" on the bracts of cones. However, the seeds do become covered by the cone scales.
Seed production in natural plant populations varies from year to year in response to weather variables and diseases, internal cycles within the plants themselves. Over a 20-year period, for example, forests composed of loblolly pine and shortleaf pine produced from 0 to nearly 5 million sound pine seeds per hectare. Over this period, there were six bumper, five poor, nine good seed crops, when evaluated for production of adequate seedlings for natural forest reproduction. Angiosperm seeds consist of three genetically distinct constituents: the embryo formed from the zygote, the endosperm, triploid, the seed coat from tissue derived from the maternal tissue of the ovule. In angiosperms, the process of seed development begins with double fertilization, which involves the fusion of two male gametes with the egg cell and the central cell to form the primary endosperm and the zygote. Right after fertilization, the zygote is inactive, but the primary endosperm divides to form the endosperm tissue.
This tissue becomes the food the young plant will consume until the roots have developed after germination. After fertilization the ovules develop into the seeds; the ovule consists of a number of components: The funicle or seed stalk which attaches the ovule to the placenta and hence ovary or fruit wall, at the pericarp. The nucellus, the remnant of the megasporangium and main region of the ovule where the megagametophyte develops; the micropyle, a small pore or opening in the apex of the integument of the ovule where the pollen tube enters during the process of fertilization. The chalaza, the base of the ovule opposite the micropyle, where integument and nucellus are joined together; the shape of the ovules as they develop affects the final shape of the seeds. Plants produce ovules of four shapes: the most common shape is called anatropous, with a curved shape. Orthotropous ovules are straight with all the parts of the ovule lined up in a long row producing an uncurved seed. Campylotropous ovules have a curved megagametophyte giving the seed a tight "C" shape.
The last ovule shape is called amphitropous, where the ovule is inverted and turned back 90 degrees on its stalk. In the majority of flowering plants, the zygote's first division is transversely oriented in regards to the long axis, this establishes the polarity of the embryo; the upper or chalazal pole becomes the main area of growth of the embryo, while the lower or micropylar pole produces the stalk-like suspensor that attaches to the micropyle. The suspensor absorbs and manufactures nutrients from the endosperm that are used during the embryo's growth; the main components of the embryo are: The cotyledons, the seed leaves, attached to the embryonic axis. There may be two; the cotyledons are the source of nutrients in the non-endospermic dicotyledons, in which case they replace the endosperm, are thick and leathery. In endospermic seeds the cotyledons are papery. Dicotyledons have the point of attachment opposite one another on the axis; the epicotyl, the embryonic axis above the point of attachment of the cotyledon.
The plumule, the tip of the epicotyl, has a feathery appearance due to the presence of young leaf primordia at the apex, will become the shoot upon germination. The hypocotyl, the embryonic axis below the point of attachment of the cotyledon, connecting the epicotyl and the radicle, being the stem-root transition zone; the radicle, the basal tip of the hy
United States Government Publishing Office
The United States Government Publishing Office is an agency of the legislative branch of the United States federal government. The office produces and distributes information products and services for all three branches of the Federal Government, including U. S. passports for the Department of State as well as the official publications of the Supreme Court, the Congress, the Executive Office of the President, executive departments, independent agencies. An act of Congress changed the office's name to its current form in 2014; the Government Printing Office was created by congressional joint resolution on June 23, 1860. It began operations March 4, 1861, with 350 employees and reached a peak employment of 8,500 in 1972; the agency began transformation to computer technology in the 1980s. For its entire history, GPO has occupied the corner of North Capitol Street NW and H Street NW in the District of Columbia; the large red brick building that houses the GPO was erected in 1903 and is unusual in being one of the few large, red brick government structures in a city where most government buildings are marble and granite.
An additional structure was attached to its north in years. The activities of GPO are defined in the public printing and documents chapters of Title 44 of the United States Code; the Director, who serves as the head of GPO, is appointed by the President with the advice and consent of the Senate. The Director selects a Superintendent of Documents; the Superintendent of Documents is in charge of the dissemination of information at the GPO. This is accomplished through the Federal Depository Library Program, the Cataloging and Indexing Program and the Publication Sales Program, as well as operation of the Federal Citizen Information Center in Pueblo, Colorado. Adelaide Hasse was the founder of the Superintendent of Documents classification system. GPO first used 100 percent recycled paper for the Congressional Record and Federal Register from 1991-1997, under Public Printers Robert Houk and Michael DiMario. GPO resumed using recycled paper in 2009. In March 2011, GPO issued a new illustrated official history covering the agency's 150 years of Keeping America Informed.
With demand for print publications falling and a move underway to digital document production and preservation, the name of the GPO was changed to "Government Publishing Office" in a provision of an omnibus government funding bill passed by Congress in December 2014. Following signature of this legislation by President Barack Obama, the name change took place on December 17, 2014. By law, the Public Printer heads the GPO; the position of Public Printer traces its roots back to Benjamin Franklin and the period before the American Revolution, when he served as "publick printer", whose job was to produce official government documents for Pennsylvania and other colonies. When the agency was renamed in December 2014 the title "Public Printer" was changed to "Director". Davita Vance-Cooks was therefore the first "Director" of GPO. Public Printers: Almon M. Clapp John D. Defrees Sterling P. Rounds Thomas E. Benedict Frank W. Palmer Thomas E. Benedict Frank W. Palmer, O. J. Ricketts Charles A. Stillings, William S. Rossiter, Capt. Henry T. Brian John S. Leech Samuel B. Donnelly Cornelius Ford George H. Carter Augustus E. Giegengack, John J. Deviny John J. Deviny, Phillip L. Cole Raymond Blattenberger, John M. Wilson, Felix E. Cristofane James L. Harrison Adolphus N. Spence, Harry J. Humphrey, L.
T. Golden Thomas F. McCormick John J. Boyle, Samuel Saylor Danford L. Sawyer, Jr. William J. Barrett Ralph E. Kennickell, Jr. Joseph E. Jenifer Robert Houk, Michael F. DiMario Michael F. DiMario Bruce James, William H. Turri Robert C. Tapella William J. Boarman Davita Vance-Cooks GPO contracts out much of the federal government's printing but prints the official journals of government in-house, including: Code of Federal Regulations Public and Private Laws The Congressional Record The Federal Register, the official daily publication for rules, proposed rules, notices of Federal agencies and organizations. United States Code United States Statutes at Large House Journal and Senate Journal GPO has been producing U. S. passports since the 1920s. The United States Department of State began issuing e-passports in 2006; the e-Passport includes an electronic chip embedded in the cover that contains the same information, printed in the passport: name and place of birth, dates of passport issuance and expiration, passport number, photo of the bearer.
GPO produces the blank e-Passport, while the Department of State receives and processes applications and issues individual passports. GPO ceased production of legacy passports in May 2007, shifting production to e-passports. In March 2008, the Washington Times published a three-part story about the outsourcing of electronic passports to overseas
A leaf is an organ of a vascular plant and is the principal lateral appendage of the stem. The leaves and stem together form the shoot. Leaves are collectively referred to as foliage, as in "autumn foliage". A leaf is a thin, dorsiventrally flattened organ borne above ground and specialized for photosynthesis. In most leaves, the primary photosynthetic tissue, the palisade mesophyll, is located on the upper side of the blade or lamina of the leaf but in some species, including the mature foliage of Eucalyptus, palisade mesophyll is present on both sides and the leaves are said to be isobilateral. Most leaves have distinct upper surface and lower surface that differ in colour, the number of stomata, the amount and structure of epicuticular wax and other features. Leaves can have many different shapes and textures; the broad, flat leaves with complex venation of flowering plants are known as megaphylls and the species that bear them, the majority, as broad-leaved or megaphyllous plants. In the clubmosses, with different evolutionary origins, the leaves are simple and are known as microphylls.
Some leaves, such as bulb scales, are not above ground. In many aquatic species the leaves are submerged in water. Succulent plants have thick juicy leaves, but some leaves are without major photosynthetic function and may be dead at maturity, as in some cataphylls and spines. Furthermore, several kinds of leaf-like structures found in vascular plants are not homologous with them. Examples include flattened plant stems called phylloclades and cladodes, flattened leaf stems called phyllodes which differ from leaves both in their structure and origin; some structures of non-vascular plants function much like leaves. Examples include the phyllids of liverworts. Leaves are the most important organs of most vascular plants. Green plants are autotrophic, meaning that they do not obtain food from other living things but instead create their own food by photosynthesis, they capture the energy in sunlight and use it to make simple sugars, such as glucose and sucrose, from carbon dioxide and water. The sugars are stored as starch, further processed by chemical synthesis into more complex organic molecules such as proteins or cellulose, the basic structural material in plant cell walls, or metabolised by cellular respiration to provide chemical energy to run cellular processes.
The leaves draw water from the ground in the transpiration stream through a vascular conducting system known as xylem and obtain carbon dioxide from the atmosphere by diffusion through openings called stomata in the outer covering layer of the leaf, while leaves are orientated to maximise their exposure to sunlight. Once sugar has been synthesized, it needs to be transported to areas of active growth such as the plant shoots and roots. Vascular plants transport sucrose in a special tissue called the phloem; the phloem and xylem are parallel to each other but the transport of materials is in opposite directions. Within the leaf these vascular systems branch to form veins which supply as much of the leaf as possible, ensuring that cells carrying out photosynthesis are close to the transportation system. Leaves are broad and thin, thereby maximising the surface area directly exposed to light and enabling the light to penetrate the tissues and reach the chloroplasts, thus promoting photosynthesis.
They are arranged on the plant so as to expose their surfaces to light as efficiently as possible without shading each other, but there are many exceptions and complications. For instance plants adapted to windy conditions may have pendent leaves, such as in many willows and eucalyptss; the flat, or laminar, shape maximises thermal contact with the surrounding air, promoting cooling. Functionally, in addition to carrying out photosynthesis, the leaf is the principal site of transpiration, providing the energy required to draw the transpiration stream up from the roots, guttation. Many gymnosperms have thin needle-like or scale-like leaves that can be advantageous in cold climates with frequent snow and frost; these are interpreted as reduced from megaphyllous leaves of their Devonian ancestors. Some leaf forms are adapted to modulate the amount of light they absorb to avoid or mitigate excessive heat, ultraviolet damage, or desiccation, or to sacrifice light-absorption efficiency in favour of protection from herbivory.
For xerophytes the major constraint drought. Some window plants such as Fenestraria species and some Haworthia species such as Haworthia tesselata and Haworthia truncata are examples of xerophytes. and Bulbine mesembryanthemoides. Leaves function to store chemical energy and water and may become specialised organs serving other functions, such as tendrils of peas and other legumes, the protective spines of cacti and the insect traps in carnivorous plants such as Nepenthes and Sarracenia. Leaves are the fundamental structural units from which cones are constructed in gymnosperms and from which flowers are constructed in flowering plants; the internal organisation of most kinds of leaves has evolved to maximise exposure of the photosynthetic organelles, the chloroplasts, to light and to increase the absorption of carbon dioxide while at the same time controlling water loss. Their surfaces are waterproofed by the plant cuticle and gas exchange between the mesophyll cells and the atmosphere is controlled by minute openings called stomata which open or close to regulate the rate exchange of carbon dioxide and water vapour into
Lithocarpus is a genus in the beech family, differing from Quercus in the erect spikes of insect-pollinated male flowers and the short styles with punctate stigmas on the female flowers. The World Checklist accepts 334 species. About 100 Asian species of the genus were treated in the genus Pasania. All are native to southeast Asia; these Asian species do not have a well-known English vernacular name, though the generic term stone oak has been proposed. The North American tanoak or tanbark oak was included in the genus Lithocarpus but recent evidence, both genetic and morphological, suggests that the North American species is only distantly related to Asian stone oaks therefore tanbark-oak has been moved into a new genus, based on multiple lines of evidence. Lithocarpus trees are evergreen trees with leathery, alternate leaves, which may be either entire or toothed; the seed is a nut similar to an oak acorn, but with a hard, woody nut shell. The nut kernel is edible in some species, but inedible, bitter, in others.
A few sections of the genus have evolved a novel type of fruit where the seed is embedded in the receptacle material of the fruit which becomes lignified and hard, lending greater mechanical protection to the seed. Several of the species are attractive ornamental trees, used in parks and large gardens in warm temperate and subtropical areas. Lithocarpus burkillii Lithocarpus cleistocarpus Lithocarpus crassinervius Lithocarpus curtisii Lithocarpus dodonaeifolius Lithocarpus edulis - Japanese Stone Oak Lithocarpus erythrocarpus Lithocarpus formosanus Lithocarpus glaber Lithocarpus hancei - Hance's Tanbark Lithocarpus hendersonianus Lithocarpus henryi - Henry's Stone Oak Lithocarpus indutus Lithocarpus kingianus Lithocarpus kingii Lithocarpus kostermansii Lithocarpus kunstleri Lithocarpus maingayi Lithocarpus neorobinsonii Lithocarpus orbicarpus Lithocarpus ovalis Lithocarpus pachylepis Lithocarpus pachyphyllus Lithocarpus platycarpus Lithocarpus qinzhouicus C. C. Huang & Y. T. Chang Lithocarpus quangnamensis A.
Camus Lithocarpus quercifolius C. C. Huang & Y. T. Chang Lithocarpus rassa Rehder Lithocarpus recurvatus Barnett Lithocarpus reinwardtii A. Camus Lithocarpus revolutus Hatus. Ex Soepadmo Lithocarpus rhabdostachyus A. Camus Lithocarpus rigidus Soepadmo Lithocarpus robinsonii Rehder Lithocarpus rosthornii Barnett Lithocarpus rotundatus A. Camus Lithocarpus rouletii A. Camus Lithocarpus rufescens Barnett Lithocarpus rufovillosus Rehder Lithocarpus rufus A. Camus Lithocarpus ruminatus Soepadmo Lithocarpus sandakanensis Julia & Soupadmo Lithocarpus scortechinii A. Camus Lithocarpus scyphiger A. Camus Lithocarpus seishoi Barnett Lithocarpus sericobalanos E. F. Warb. Lithocarpus shinsuiensis Kaneh. Lithocarpus shunningensis Hu Lithocarpus siamensis A. Camus Lithocarpus silvicolarum Chun Lithocarpus skanianus. Ex A. Camus Lithocarpus solerianus Rehder Lithocarpus songkoensis A. Camus Lithocarpus sootepensis A. Camus Lithocarpus sphaerocarpus A. Camus Lithocarpus stenopus A. Camus Lithocarpus stonei Julia & Soupadmo Lithocarpus submonticolus Rehder Lithocarpus suffruticosus Soepadmo Lithocarpus sulitii Soepadmo Lithocarpus sundaicus Rehder Lithocarpus syncarpus A.
Camus Lithocarpus tabularis Y. C. Hsu & H. Wei Jen Lithocarpus taitoensis Hayata Lithocarpus talangensis C. C. Huang & Y. T. Chang Lithocarpus tawaiensis Julia & Soupadmo Lithocarpus tenuilimbus H. T. Chang Lithocarpus tenuinervis A. Camus Lithocarpus tephrocarpus A. Camus Lithocarpus thomsonii Rehder Lithocarpus toumorangensis A. Camus Lithocarpus touranensis A. Camus Lithocarpus trachycarpus A. Camus Lithocarpus triqueter A. Camus Lithocarpus truncatus Rehder Lithocarpus tubulosus A. Camus Lithocarpus turbinatus. Lithocarpus uvariifolius Rehder Lithocarpus variolosus Chun Lithocarpus vestitus A. Camus Lithocarpus vidalianus A. Camus Lithocarpus vidalii Rehder Lithocarpus vinhensis A. Camus Lithocarpus vinkii Soepadmo Lithocarpus wallichianus Rehder Lithocarpus wenxianensis Y. J. Zhang, Z. X. Peng & K. L. Zhang Lithocarpus woodii A. Camus Lithocarpus wrayi A. Camus Lithocarpus xizangensis C. C. Huang & Y. T. Chang Lithocarpus xylocarpus Markgr. Lithocarpus yangchunensis H. G. Ye & F. G. Wang Lithocarpus yersinii A. Camus Lithocarpus yongfuensis Q.
F. Zheng A full list of the species and their synonyms can be seen by entering Lithocarpus in the search box in the World Checklist Flora of China Online includes descriptions of the 123 Chinese species
Native Americans in the United States
Native Americans known as American Indians, Indigenous Americans and other terms, are the indigenous peoples of the United States, except Hawaii. There are over 500 federally recognized tribes within the US, about half of which are associated with Indian reservations; the term "American Indian" excludes Native Hawaiians and some Alaska Natives, while Native Americans are American Indians, plus Alaska Natives of all ethnicities. Native Hawaiians are not counted as Native Americans by the US Census, instead being included in the Census grouping of "Native Hawaiian and other Pacific Islander"; the ancestors of modern Native Americans arrived in what is now the United States at least 15,000 years ago much earlier, from Asia via Beringia. A vast variety of peoples and cultures subsequently developed. Native Americans were affected by the European colonization of the Americas, which began in 1492, their population declined precipitously due to introduced diseases as well as warfare, territorial confiscation and slavery.
After the founding of the United States, many Native American peoples were subjected to warfare and one-sided treaties, they continued to suffer from discriminatory government policies into the 20th century. Since the 1960s, Native American self-determination movements have resulted in changes to the lives of Native Americans, though there are still many contemporary issues faced by Native Americans. Today, there are over five million Native Americans in the United States, 78% of whom live outside reservations; when the United States was created, established Native American tribes were considered semi-independent nations, as they lived in communities separate from British settlers. The federal government signed treaties at a government-to-government level until the Indian Appropriations Act of 1871 ended recognition of independent native nations, started treating them as "domestic dependent nations" subject to federal law; this law did preserve the rights and privileges agreed to under the treaties, including a large degree of tribal sovereignty.
For this reason, many Native American reservations are still independent of state law and actions of tribal citizens on these reservations are subject only to tribal courts and federal law. The Indian Citizenship Act of 1924 granted U. S. citizenship to all Native Americans born in the United States. This emptied the "Indians not taxed" category established by the United States Constitution, allowed natives to vote in state and federal elections, extended the Fourteenth Amendment protections granted to people "subject to the jurisdiction" of the United States. However, some states continued to deny Native Americans voting rights for several decades. Bill of Rights protections do not apply to tribal governments, except for those mandated by the Indian Civil Rights Act of 1968. Since the end of the 15th century, the migration of Europeans to the Americas has led to centuries of population and agricultural transfer and adjustment between Old and New World societies, a process known as the Columbian exchange.
As most Native American groups had preserved their histories by oral traditions and artwork, the first written sources of the conflict were written by Europeans. Ethnographers classify the indigenous peoples of North America into ten geographical regions with shared cultural traits, called cultural areas; some scholars combine the Plateau and Great Basin regions into the Intermontane West, some separate Prairie peoples from Great Plains peoples, while some separate Great Lakes tribes from the Northeastern Woodlands. The ten cultural areas are as follows: Arctic, including Aleut and Yupik peoples Subarctic Northeastern Woodlands Southeastern Woodlands Great Plains Great Basin Northwest Plateau Northwest Coast California Southwest At the time of the first contact, the indigenous cultures were quite different from those of the proto-industrial and Christian immigrants; some Northeastern and Southwestern cultures, in particular, were matrilineal and operated on a more collective basis than that with which Europeans were familiar.
The majority of Indigenous American tribes maintained their hunting grounds and agricultural lands for use of the entire tribe. Europeans at that time had patriarchal cultures and had developed concepts of individual property rights with respect to land that were different; the differences in cultures between the established Native Americans and immigrant Europeans, as well as shifting alliances among different nations in times of war, caused extensive political tension, ethnic violence, social disruption. Before the European settlement of what is now the United States, Native Americans suffered high fatalities from contact with new European diseases, to which they had not yet acquired immunity. Smallpox epidemics are thought to have caused the greatest loss of life for indigenous populations. William M Denevan, noted author and Professor Emeritus of Geography at the University of Wisconsin-Madison, said on this subject in his essay "The Pristine Myth: The Landscape of the Americas in 1492".
Old World diseases were the primary killer. In many regions the tropical lowlands, populations fell by 90 percent or more in the first century after the contact. "Estimates of the pre-Columbian population of what today constitutes the U. S. vary ranging from William M Denevan's 3.8 million in his 1992 w
The flowering plants known as angiosperms, Angiospermae or Magnoliophyta, are the most diverse group of land plants, with 64 orders, 416 families 13,164 known genera and c. 369,000 known species. Like gymnosperms, angiosperms are seed-producing plants. However, they are distinguished from gymnosperms by characteristics including flowers, endosperm within the seeds, the production of fruits that contain the seeds. Etymologically, angiosperm means a plant; the term comes from the Greek words sperma. The ancestors of flowering plants diverged from gymnosperms in the Triassic Period, 245 to 202 million years ago, the first flowering plants are known from 160 mya, they diversified extensively during the Early Cretaceous, became widespread by 120 mya, replaced conifers as the dominant trees from 100 to 60 mya. Angiosperms differ from other seed plants in several ways, described in the table below; these distinguishing characteristics taken together have made the angiosperms the most diverse and numerous land plants and the most commercially important group to humans.
Angiosperm stems are made up of seven layers. The amount and complexity of tissue-formation in flowering plants exceeds that of gymnosperms; the vascular bundles of the stem are arranged such that the phloem form concentric rings. In the dicotyledons, the bundles in the young stem are arranged in an open ring, separating a central pith from an outer cortex. In each bundle, separating the xylem and phloem, is a layer of meristem or active formative tissue known as cambium. By the formation of a layer of cambium between the bundles, a complete ring is formed, a regular periodical increase in thickness results from the development of xylem on the inside and phloem on the outside; the soft phloem becomes crushed, but the hard wood persists and forms the bulk of the stem and branches of the woody perennial. Owing to differences in the character of the elements produced at the beginning and end of the season, the wood is marked out in transverse section into concentric rings, one for each season of growth, called annual rings.
Among the monocotyledons, the bundles are more numerous in the young stem and are scattered through the ground tissue. They once formed the stem increases in diameter only in exceptional cases; the characteristic feature of angiosperms is the flower. Flowers show remarkable variation in form and elaboration, provide the most trustworthy external characteristics for establishing relationships among angiosperm species; the function of the flower is to ensure fertilization of the ovule and development of fruit containing seeds. The floral apparatus may arise terminally from the axil of a leaf; as in violets, a flower arises singly in the axil of an ordinary foliage-leaf. More the flower-bearing portion of the plant is distinguished from the foliage-bearing or vegetative portion, forms a more or less elaborate branch-system called an inflorescence. There are two kinds of reproductive cells produced by flowers. Microspores, which will divide to become pollen grains, are the "male" cells and are borne in the stamens.
The "female" cells called megaspores, which will divide to become the egg cell, are contained in the ovule and enclosed in the carpel. The flower may consist only of these parts, as in willow, where each flower comprises only a few stamens or two carpels. Other structures are present and serve to protect the sporophylls and to form an envelope attractive to pollinators; the individual members of these surrounding structures are known as petals. The outer series is green and leaf-like, functions to protect the rest of the flower the bud; the inner series is, in general, white or brightly colored, is more delicate in structure. It functions to attract bird pollinators. Attraction is effected by color and nectar, which may be secreted in some part of the flower; the characteristics that attract pollinators account for the popularity of flowers and flowering plants among humans. While the majority of flowers are perfect or hermaphrodite, flowering plants have developed numerous morphological and physiological mechanisms to reduce or prevent self-fertilization.
Heteromorphic flowers have short carpels and long stamens, or vice versa, so animal pollinators cannot transfer pollen to the pistil. Homomorphic flowers may employ a biochemical mechanism called self-incompatibility to discriminate between self and non-self pollen grains. In other species, the male and female parts are morphologically separated, developing on different flowers; the botanical term "Angiosperm", from the Ancient Greek αγγείον, angeíon and σπέρμα, was coined in the form Angiospermae by Paul Hermann in 1690, as the name of one of his primary divisions of the plant kingdom. This included flowering plants possessing seeds enclosed in capsules, distinguished from his Gymnospermae, or flowering plants with achenial or schizo-carpic fruits, the whole fruit or each of its pieces being here regarded as a seed and naked; the term and its antonym were maintained by Carl Linnaeus with the same sense, but with restricted application, in the names of the orders of his class Didynamia. Its use with any