A catkin or ament is a slim, cylindrical flower cluster, with inconspicuous or no petals wind-pollinated but sometimes insect-pollinated. They contain many unisexual flowers, arranged along a central stem, drooping, they are found in many plant families, including Betulaceae, Fagaceae and Salicaceae. For some time, they were believed to be a key synapomorphy among the proposed Hamamelididae known as Amentiferae. Based on molecular phylogeny work, it is now believed; this suggests that the catkin flower arrangement has arisen at least twice independently by convergent evolution, in Fagales and in Salicaceae. Such a convergent evolution raises questions about what the ancestral inflorescence characters might be and how catkins did evolve in these two lineages. In many of these plants, only the male flowers form catkins, the female flowers are single, a cone or other types. In other plants both male and female flowers are borne in catkins. Catkin-bearing plants include many other trees or shrubs such as birch, hickory, sweet chestnut and sweetfern.
The word catkin is a loanword from the old Dutch katteken, meaning "kitten", on account of the resemblance to a kitten's tail. Ament is from the Latin amentum, meaning "thong" or "strap". In Britain, they can be seen in February, when many trees are bare for winter, they can occur in December. Catkins in Fagales Catkins in Salicaceae
The Cretaceous is a geologic period and system that spans 79 million years from the end of the Jurassic Period 145 million years ago to the beginning of the Paleogene Period 66 mya. It is the last period of the Mesozoic Era, the longest period of the Phanerozoic Eon; the Cretaceous Period is abbreviated K, for its German translation Kreide. The Cretaceous was a period with a warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas; these oceans and seas were populated with now-extinct marine reptiles and rudists, while dinosaurs continued to dominate on land. During this time, new groups of mammals and birds, as well as flowering plants, appeared; the Cretaceous ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs and large marine reptiles died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary, a geologic signature associated with the mass extinction which lies between the Mesozoic and Cenozoic eras.
The Cretaceous as a separate period was first defined by Belgian geologist Jean d'Omalius d'Halloy in 1822, using strata in the Paris Basin and named for the extensive beds of chalk, found in the upper Cretaceous of Western Europe. The name Cretaceous was derived from Latin creta; the Cretaceous is divided into Early and Late Cretaceous epochs, or Lower and Upper Cretaceous series. In older literature the Cretaceous is sometimes divided into three series: Neocomian and Senonian. A subdivision in eleven stages, all originating from European stratigraphy, is now used worldwide. In many parts of the world, alternative local subdivisions are still in use; as with other older geologic periods, the rock beds of the Cretaceous are well identified but the exact age of the system's base is uncertain by a few million years. No great extinction or burst of diversity separates the Cretaceous from the Jurassic. However, the top of the system is defined, being placed at an iridium-rich layer found worldwide, believed to be associated with the Chicxulub impact crater, with its boundaries circumscribing parts of the Yucatán Peninsula and into the Gulf of Mexico.
This layer has been dated at 66.043 Ma. A 140 Ma age for the Jurassic-Cretaceous boundary instead of the accepted 145 Ma was proposed in 2014 based on a stratigraphic study of Vaca Muerta Formation in Neuquén Basin, Argentina. Víctor Ramos, one of the authors of the study proposing the 140 Ma boundary age sees the study as a "first step" toward formally changing the age in the International Union of Geological Sciences. From youngest to oldest, the subdivisions of the Cretaceous period are: Late Cretaceous Maastrichtian – Campanian – Santonian – Coniacian – Turonian – Cenomanian – Early Cretaceous Albian – Aptian – Barremian – Hauterivian – Valanginian – Berriasian – The high sea level and warm climate of the Cretaceous meant large areas of the continents were covered by warm, shallow seas, providing habitat for many marine organisms; the Cretaceous was named for the extensive chalk deposits of this age in Europe, but in many parts of the world, the deposits from the Cretaceous are of marine limestone, a rock type, formed under warm, shallow marine circumstances.
Due to the high sea level, there was extensive space for such sedimentation. Because of the young age and great thickness of the system, Cretaceous rocks are evident in many areas worldwide. Chalk is a rock type characteristic for the Cretaceous, it consists of coccoliths, microscopically small calcite skeletons of coccolithophores, a type of algae that prospered in the Cretaceous seas. In northwestern Europe, chalk deposits from the Upper Cretaceous are characteristic for the Chalk Group, which forms the white cliffs of Dover on the south coast of England and similar cliffs on the French Normandian coast; the group is found in England, northern France, the low countries, northern Germany, Denmark and in the subsurface of the southern part of the North Sea. Chalk is not consolidated and the Chalk Group still consists of loose sediments in many places; the group has other limestones and arenites. Among the fossils it contains are sea urchins, belemnites and sea reptiles such as Mosasaurus. In southern Europe, the Cretaceous is a marine system consisting of competent limestone beds or incompetent marls.
Because the Alpine mountain chains did not yet exist in the Cretaceous, these deposits formed on the southern edge of the European continental shelf, at the margin of the Tethys Ocean. Stagnation of deep sea currents in middle Cretaceous times caused anoxic conditions in the sea water leaving the deposited organic matter undecomposed. Half the worlds petroleum reserves were laid down at this time in the anoxic conditions of what would become the Persian Gulf and the Gulf of Mexico. In many places around the world, dark anoxic shales were formed during this interval; these shales are an important source rock for oil and gas, for example in the subsurface of the North Sea. During th
The gymnosperms known as Acrogymnospermae, are a group of seed-producing plants that includes conifers, cycads and gnetophytes. The term "gymnosperm" comes from the Greek composite word γυμνόσπερμος, meaning "naked seeds"; the name is based on the unenclosed condition of their seeds. The non-encased condition of their seeds stands in contrast to the seeds and ovules of flowering plants, which are enclosed within an ovary. Gymnosperm seeds develop either on the surface of scales or leaves, which are modified to form cones, or solitary as in Yew, Ginkgo; the gymnosperms and angiosperms together compose the spermatophytes or seed plants. The gymnosperms are divided into six phyla. Organisms that belong to the Cycadophyta, Ginkgophyta and Pinophyta phyla are still in existence while those in the Pteridospermales and Cordaitales phyla are now extinct. By far the largest group of living gymnosperms are the conifers, followed by cycads and Ginkgo biloba. Roots in some genera have fungal association with roots in the form of mycorrhiza, while in some others small specialised roots called coralloid roots are associated with nitrogen-fixing cyanobacteria.
The current formal classification of the living gymnosperms is the "Acrogymnospermae", which form a monophyletic group within the spermatophytes. The wider "Gymnospermae" group is thought to be paraphyletic; the fossil record of gymnosperms includes many distinctive taxa that do not belong to the four modern groups, including seed-bearing trees that have a somewhat fern-like vegetative morphology. When fossil gymnosperms such as these and the Bennettitales and Caytonia are considered, it is clear that angiosperms are nested within a larger gymnospermae clade, although which group of gymnosperms is their closest relative remains unclear; the extant gymnosperms include 12 main families and 83 genera which contain more than 1000 known species. Subclass Cycadidae Order Cycadales Family Cycadaceae: Cycas Family Zamiaceae: Dioon, Macrozamia, Encephalartos, Ceratozamia, Zamia. Subclass Ginkgoidae Order Ginkgoales Family Ginkgoaceae: GinkgoSubclass Gnetidae Order Welwitschiales Family Welwitschiaceae: Welwitschia Order Gnetales Family Gnetaceae: Gnetum Order Ephedrales Family Ephedraceae: EphedraSubclass Pinidae Order Pinales Family Pinaceae: Cedrus, Cathaya, Pseudotsuga, Pseudolarix, Nothotsuga, Abies Order Araucariales Family Araucariaceae: Araucaria, Agathis Family Podocarpaceae: Phyllocladus, Prumnopitys, Halocarpus, Lagarostrobos, Saxegothaea, Pherosphaera, Dacrycarpus, Falcatifolium, Nageia, Podocarpus Order Cupressales Family Sciadopityaceae: Sciadopitys Family Cupressaceae: Cunninghamia, Athrotaxis, Sequoia, Cryptomeria, Taxodium, Austrocedrus, Pilgerodendron, Diselma, Callitris, Thuja, Chamaecyparis, Cupressus, Xanthocyparis, Tetraclinis, Microbiota Family Taxaceae: Austrotaxus, Taxus, Amentotaxus, Torreya There are over 1000 living species of gymnosperm.
It is accepted that the gymnosperms originated in the late Carboniferous period, replacing the lycopsid rainforests of the tropical region. This appears to have been the result of a whole genome duplication event around 319 million years ago. Early characteristics of seed plants were evident in fossil progymnosperms of the late Devonian period around 383 million years ago, it has been suggested that during the mid-Mesozoic era, pollination of some extinct groups of gymnosperms was by extinct species of scorpionflies that had specialized proboscis for feeding on pollination drops. The scorpionflies engaged in pollination mutualisms with gymnosperms, long before the similar and independent coevolution of nectar-feeding insects on angiosperms. Evidence has been found that mid-Mesozoic gymnosperms were pollinated by Kalligrammatid lacewings, a now-extinct genus with members which resembled the modern butterflies that arose far later. Conifers are by far the most abundant extant group of gymnosperms with six to eight families, with a total of 65-70 genera and 600-630 species.
Conifers most are evergreens. The leaves of many conifers are long and needle-like, other species, including most Cupressaceae and some Podocarpaceae, have flat, triangular scale-like leaves. Agathis in Araucariaceae and Nageia in Podocarpaceae have flat strap-shaped leaves. Cycads are the next most abundant group of gymnosperms, with two or three families, 11 genera, 338 species. A majority of cycads are native to tropical climates and are most abundantly found in regions near the equator; the other extant groups are one species of Ginkgo. Gymnosperms have major economic uses. Pine, fir and cedar are all examples of conifers that are used for lumber, paper production, resin; some other common uses for gymnosperms are soap, nail polish, food and perfumes. Gymnosperms, like all vascular plants, have a sporophyte-dominant life cycle, which means they spend most of their life cycle with diploid cells, while
The Eocene Epoch, lasting from 56 to 33.9 million years ago, is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Paleocene Epoch to the beginning of the Oligocene Epoch; the start of the Eocene is marked by a brief period in which the concentration of the carbon isotope 13C in the atmosphere was exceptionally low in comparison with the more common isotope 12C. The end is set at a major extinction event called the Grande Coupure or the Eocene–Oligocene extinction event, which may be related to the impact of one or more large bolides in Siberia and in what is now Chesapeake Bay; as with other geologic periods, the strata that define the start and end of the epoch are well identified, though their exact dates are uncertain. The name Eocene comes from the Ancient Greek ἠώς and καινός and refers to the "dawn" of modern fauna that appeared during the epoch; the Eocene epoch is conventionally divided into early and late subdivisions.
The corresponding rocks are referred to as lower and upper Eocene. The Ypresian stage constitutes the lower, the Priabonian stage the upper; the Eocene Epoch contained a wide variety of different climate conditions that includes the warmest climate in the Cenozoic Era and ends in an icehouse climate. The evolution of the Eocene climate began with warming after the end of the Palaeocene–Eocene Thermal Maximum at 56 million years ago to a maximum during the Eocene Optimum at around 49 million years ago. During this period of time, little to no ice was present on Earth with a smaller difference in temperature from the equator to the poles. Following the maximum was a descent into an icehouse climate from the Eocene Optimum to the Eocene-Oligocene transition at 34 million years ago. During this decrease ice began to reappear at the poles, the Eocene-Oligocene transition is the period of time where the Antarctic ice sheet began to expand. Greenhouse gases, in particular carbon dioxide and methane, played a significant role during the Eocene in controlling the surface temperature.
The end of the PETM was met with a large sequestration of carbon dioxide in the form of methane clathrate and crude oil at the bottom of the Arctic Ocean, that reduced the atmospheric carbon dioxide. This event was similar in magnitude to the massive release of greenhouse gasses at the beginning of the PETM, it is hypothesized that the sequestration was due to organic carbon burial and weathering of silicates. For the early Eocene there is much discussion; this is due to numerous proxies representing different atmospheric carbon dioxide content. For example, diverse geochemical and paleontological proxies indicate that at the maximum of global warmth the atmospheric carbon dioxide values were at 700–900 ppm while other proxies such as pedogenic carbonate and marine boron isotopes indicate large changes of carbon dioxide of over 2,000 ppm over periods of time of less than 1 million years. Sources for this large influx of carbon dioxide could be attributed to volcanic out-gassing due to North Atlantic rifting or oxidation of methane stored in large reservoirs deposited from the PETM event in the sea floor or wetland environments.
For contrast, today the carbon dioxide levels are at 400 ppm or 0.04%. At about the beginning of the Eocene Epoch the amount of oxygen in the earth's atmosphere more or less doubled. During the early Eocene, methane was another greenhouse gas that had a drastic effect on the climate. In comparison to carbon dioxide, methane has much greater effect on temperature as methane is around 34 times more effective per molecule than carbon dioxide on a 100-year scale. Most of the methane released to the atmosphere during this period of time would have been from wetlands and forests; the atmospheric methane concentration today is 0.000179% or 1.79 ppmv. Due to the warmer climate and sea level rise associated with the early Eocene, more wetlands, more forests, more coal deposits would be available for methane release. Comparing the early Eocene production of methane to current levels of atmospheric methane, the early Eocene would be able to produce triple the amount of current methane production; the warm temperatures during the early Eocene could have increased methane production rates, methane, released into the atmosphere would in turn warm the troposphere, cool the stratosphere, produce water vapor and carbon dioxide through oxidation.
Biogenic production of methane produces carbon dioxide and water vapor along with the methane, as well as yielding infrared radiation. The breakdown of methane in an oxygen atmosphere produces carbon monoxide, water vapor and infrared radiation; the carbon monoxide is not stable so it becomes carbon dioxide and in doing so releases yet more infrared radiation. Water vapor traps more infrared than does carbon dioxide; the middle to late Eocene marks not only the switch from warming to cooling, but the change in carbon dioxide from increasing to decreasing. At the end of the Eocene Optimum, carbon dioxide began decreasing due to increased siliceous plankton productivity and marine carbon burial. At the beginning of the middle Eocene an event that may have triggered or helped with the draw down of carbon dioxide was the Azolla event at around 49 million years ago. With the equable climate during the early Eocene, warm temperatures in the arctic allowed for the growth of azolla, a floating aquatic fern, on the Arctic Ocean.
Compared to current carb
In botany, a stoma called a stomate, is a pore, found in the epidermis of leaves and other organs, that facilitates gas exchange. The pore is bordered by a pair of specialized parenchyma cells known as guard cells that are responsible for regulating the size of the stomatal opening; the term is used collectively to refer to the entire stomatal complex, consisting of the paired guard cells and the pore itself, referred to as the stomatal aperture. Air enters the plant through these openings by gaseous diffusion, contains carbon dioxide and oxygen, which are used in photosynthesis and respiration, respectively. Oxygen produced as a by-product of photosynthesis diffuses out to the atmosphere through these same openings. Water vapor diffuses through the stomata into the atmosphere in a process called transpiration. Stomata are present in the sporophyte generation of all land plant groups except liverworts. In vascular plants the number and distribution of stomata varies widely. Dicotyledons have more stomata on the lower surface of the leaves than the upper surface.
Monocotyledons such as onion and maize may have about the same number of stomata on both leaf surfaces. In plants with floating leaves, stomata may be found only on the upper epidermis and submerged leaves may lack stomata entirely. Most tree species have stomata only on the lower leaf surface. Leaves with stomata on both the upper and lower leaf are called. Size varies across species, with end-to-end lengths ranging from 10 to 80 µm and width ranging from a few to 50 µm. Carbon dioxide, a key reactant in photosynthesis, is present in the atmosphere at a concentration of about 400 ppm. Most plants require the stomata to be open during daytime; the air spaces in the leaf are saturated with water vapour, which exits the leaf through the stomata. Therefore, plants cannot gain carbon dioxide without losing water vapour. Ordinarily, carbon dioxide is fixed to ribulose-1,5-bisphosphate by the enzyme RuBisCO in mesophyll cells exposed directly to the air spaces inside the leaf; this exacerbates the transpiration problem for two reasons: first, RuBisCo has a low affinity for carbon dioxide, second, it fixes oxygen to RuBP, wasting energy and carbon in a process called photorespiration.
For both of these reasons, RuBisCo needs high carbon dioxide concentrations, which means wide stomatal apertures and, as a consequence, high water loss. Narrower stomatal apertures can be used in conjunction with an intermediary molecule with a high carbon dioxide affinity, PEPcase. Retrieving the products of carbon fixation from PEPCase is an energy-intensive process, however; as a result, the PEPCase alternative is preferable only where water is limiting but light is plentiful, or where high temperatures increase the solubility of oxygen relative to that of carbon dioxide, magnifying RuBisCo's oxygenation problem. A group of desert plants called "CAM" plants open their stomata at night, use PEPcarboxylase to fix carbon dioxide and store the products in large vacuoles; the following day, they close their stomata and release the carbon dioxide fixed the previous night into the presence of RuBisCO. This saturates RuBisCO with carbon dioxide; this approach, however, is limited by the capacity to store fixed carbon in the vacuoles, so it is preferable only when water is limited.
However, most plants do not have the aforementioned facility and must therefore open and close their stomata during the daytime, in response to changing conditions, such as light intensity and carbon dioxide concentration. It is not certain how these responses work. However, the basic mechanism involves regulation of osmotic pressure; when conditions are conducive to stomatal opening, a proton pump drives protons from the guard cells. This means that the cells' electrical potential becomes negative; the negative potential opens potassium voltage-gated channels and so an uptake of potassium ions occurs. To maintain this internal negative voltage so that entry of potassium ions does not stop, negative ions balance the influx of potassium. In some cases, chloride ions enter, while in other plants the organic ion malate is produced in guard cells; this increase in solute concentration lowers the water potential inside the cell, which results in the diffusion of water into the cell through osmosis.
This increases the cell's turgor pressure. Because of rings of cellulose microfibrils that prevent the width of the guard cells from swelling, thus only allow the extra turgor pressure to elongate the guard cells, whose ends are held in place by surrounding epidermal cells, the two guard cells lengthen by bowing apart from one another, creating an open pore through which gas can move; when the roots begin to sense a water shortage in the soil, abscisic acid is released. ABA binds to receptor proteins in the guard cells' plasma membrane and cytosol, which first raises the pH of the cytosol of the cells and cause the concentration of free Ca2+ to increase in the cytosol due to influx from outside the cell and release of Ca2+ from internal stores such as the endoplasmic reticulum and vacuoles; this caus
Leiden is a city and municipality in the province of South Holland, Netherlands. The municipality of Leiden had a population of 123,856 in August 2017, but the city forms one densely connected agglomeration with its suburbs Oegstgeest, Leiderdorp and Zoeterwoude with 206,647 inhabitants; the Netherlands Central Bureau of Statistics further includes Katwijk in the agglomeration which makes the total population of the Leiden urban agglomeration 270,879, in the larger Leiden urban area Teylingen and Noordwijkerhout are included with in total 348,868 inhabitants. Leiden is located on the Oude Rijn, at a distance of some 20 kilometres from The Hague to its south and some 40 km from Amsterdam to its north; the recreational area of the Kaag Lakes lies just to the northeast of Leiden. A university city since 1575, Leiden has been one of Europe's most prominent scientific centres for more than four centuries. Leiden is a typical university city, university buildings are scattered throughout the city and the many students from all over the world give the city a bustling and international atmosphere.
Many important scientific discoveries have been made here, giving rise to Leiden's motto: ‘City of Discoveries’. The city houses Leiden University, the oldest university of the Netherlands, Leiden University Medical Center. Leiden University is one of Europe's top universities, with thirteen Nobel Prize winners, it is a member of the League of European Research Universities and positioned in all international academic rankings. It is twinned with the location of the United Kingdom's oldest university. Leiden University and Leiden University of Applied Sciences together have around 35,000 students. Modern scientific medical research and teaching started in the early 18th century in Leiden with Boerhaave. Leiden is a city with a rich cultural heritage, not only in science, but in the arts. One of the world's most famous painters, was born and educated in Leiden. Other famous Leiden painters include Jan van Goyen and Jan Steen. Leiden was formed on an artificial hill at the confluence of the rivers Nieuwe Rijn.
In the oldest reference to this, from circa 860, the settlement was called Leithon. The name is said to be from Germanic *leitha- "canal" in dative pluralis, thus meaning "at the canals". "Canal" is not the proper word. A leitha was a human-modified natural river natural artificial. Leiden has in the past erroneously been associated with the Roman outpost Lugdunum Batavorum; this particular castellum was thought to be located at the Burcht of Leiden, the city's name was thought to be derived from the Latin name Lugdunum. However the castellum was in fact closer to the town of Katwijk, whereas the Roman settlement near modern-day Leiden was called Matilo; the landlord of Leiden, situated in a stronghold on the hill, was subject to the Bishop of Utrecht but around 1100 the burgraves became subject to the county of Holland. This county got its name in 1101 from a domain near the stronghold: Holland. Leiden was sacked in 1047 by Emperor Henry III. Early 13th century, Countess of Holland took refuge here when she was fighting in a civil war against her uncle, William I, Count of Holland.
He captured Ada. Leiden received city rights in 1266. In 1389, its population had grown to about 4,000 persons. In 1420, during the Hook and Cod wars, Duke John III of Bavaria along with his army marched from Gouda in the direction of Leiden in order to conquer the city since Leiden did not pay the new Count of Holland Jacqueline, Countess of Hainaut, his niece and only daughter of Count William VI of Holland. Burgrave Filips of Wassenaar and the other local noblemen of the Hook faction assumed that the duke would besiege Leiden first and send small units out to conquer the surrounding citadels, but John of Bavaria chose to attack the citadels first. He rolled the cannons along with his army but one, too heavy went by ship. By firing at the walls and gates with iron balls the citadels fell one by one. Within a week John of Bavaria conquered the castles of Poelgeest, Ter Does, Hoichmade, de Zijl, ter Waerd, Warmond and de Paddenpoel. On 24 June the army appeared before the walls of Leiden. On 17 August 1420, after a two-month siege the city surrendered to John of Bavaria.
The burgrave Filips of Wassenaar was stripped of his offices and rights and lived out his last years in captivity. Leiden flourished in the 17th century. At the close of the 15th century the weaving establishments of Leiden were important, after the expulsion of the Spaniards Leiden cloth, Leiden baize and Leiden camlet were familiar terms. In the same period, Leiden developed an important publishing industry; the influential printer Christoffel Plantijn lived there at one time. One of his pupils was Lodewijk Elzevir, who established the largest bookshop and printing works in Leiden, a business continued by his descendants through 1712 and the name subsequently adopted by contemporary publisher Elsevier. In 1572, the city sided with the Dutch revolt against Spanish rule and played an important role in the Eighty Years' War. Besieged from May until October 1574 by the Spanish, Leiden was relieved by the cutting of the dikes, thus enabling ships to carry provisions to the inhabitants of the flooded town.
As a reward for the heroic defence of the previous year, the University of Leiden was founded by William I of Orange in 1575. Yearly on 3 Oc
The Ginkgoaceae is a family of gymnosperms which appeared during the Mesozoic Era, of which the only extant representative is Ginkgo biloba, for this reason sometimes regarded as a living fossil. However, there were several other genera, forests of ginkgo existed; because leaves can take such diverse forms within a single species, these are a poor measure of diversity, although differing structures of wood point to the existence of diverse ginkgo forests in ancient times. "Ginkgoopsida". Integrated Taxonomic Information System. "Ginkgopsida". Integrated Taxonomic Information System. "Ginkgoales". Integrated Taxonomic Information System. "Ginkgoaceae". Integrated Taxonomic Information System