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
Gynoecium is most used as a collective term for the parts of a flower that produce ovules and develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; the gynoecium is referred to as the "female" portion of the flower, although rather than directly producing female gametes, the gynoecium produces megaspores, each of which develops into a female gametophyte which produces egg cells. The term gynoecium is used by botanists to refer to a cluster of archegonia and any associated modified leaves or stems present on a gametophyte shoot in mosses and hornworts; the corresponding terms for the male parts of those plants are clusters of antheridia within the androecium. Flowers that bear a gynoecium but no stamens are called carpellate. Flowers lacking a gynoecium are called staminate; the gynoecium is referred to as female because it gives rise to female gametophytes. Gynoecium development and arrangement is important in systematic research and identification of angiosperms, but can be the most challenging of the floral parts to interpret.
The gynoecium may consist of one or more separate pistils. A pistil consists of an expanded basal portion called the ovary, an elongated section called a style and an apical structure that receives pollen called a stigma; the ovary, is the enlarged basal portion which contains placentas, ridges of tissue bearing one or more ovules. The placentas and/or ovule may be born on the gynoecial appendages or less on the floral apex; the chamber in which the ovules develop is called a locule. The style, is a pillar-like stalk; some flowers such as Tulipa do not have a distinct style, the stigma sits directly on the ovary. The style is a hollow tube in some plants such as lilies, or has transmitting tissue through which the pollen tubes grow; the stigma, is found at the tip of the style, the portion of the carpel that receives pollen. It is sticky or feathery to capture pollen; the word "pistil" comes from Latin pistillum meaning pestle. A sterile pistil in a male flower is referred to as a pistillode; the pistils of a flower are considered to be composed of carpels.
A carpel is the female reproductive part of the flower, interpreted as modified leaves bearing structures called ovules, inside which the egg cells form. A pistil may consist of one carpel, with its ovary and stigma, or several carpels may be joined together with a single ovary, the whole unit called a pistil; the gynoecium may consist of one multi-carpellate pistil. The number of carpels is described by terms such as tricarpellate. Carpels are thought to be phylogenetically derived from ovule-bearing leaves or leaf homologues, which evolved to form a closed structure containing the ovules; this structure is rolled and fused along the margin. Although many flowers satisfy the above definition of a carpel, there are flowers that do not have carpels according to this definition because in these flowers the ovule, although enclosed, are borne directly on the shoot apex, only become enclosed by the carpel. Different remedies have been suggested for this problem. An easy remedy that applies to most cases is to redefine the carpel as an appendage that encloses ovule and may or may not bear them.
If a gynoecium has a single carpel, it is called monocarpous. If a gynoecium has multiple, distinct carpels, it is apocarpous. If a gynoecium has multiple carpels "fused" into a single structure, it is syncarpous. A syncarpous gynoecium can sometimes appear much like a monocarpous gynoecium; the degree of connation in a syncarpous gynoecium can vary. The carpels retain separate styles and stigmas; the carpels may be "fused" except for retaining separate stigmas. Sometimes carpels possess distinct ovaries. In a syncarpous gynoecium, the "fused" ovaries of the constituent carpels may be referred to collectively as a single compound ovary, it can be a challenge to determine. If the styles and stigmas are distinct, they can be counted to determine the number of carpels. Within the compound ovary, the carpels may have distinct locules divided by walls called septa. If a syncarpous gynoecium has a single style and stigma and a single locule in the ovary, it may be necessary to examine how the ovules are attached.
Each carpel will have a distinct line of placentation where the ovules are attached. Pistils begin as small primordia on a floral apical meristem, forming than, closer to the apex than sepal and stamen primordia. Morphological and molecular studies of pistil ontogeny reveal that carpels are most homologous to leaves. A carpel has a similar function to a megasporophyll, but includes a stigma, is fused, with ovules enclosed in the enlarged lower portion, the ovary. In some basal angiosperm lineages and Winteraceae, a carpel begins as a shallow cup where the ovules de
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
North America is a continent within the Northern Hemisphere and all within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the west and south by the Pacific Ocean, to the southeast by South America and the Caribbean Sea. North America covers an area of about 24,709,000 square kilometers, about 16.5% of the earth's land area and about 4.8% of its total surface. North America is the third largest continent by area, following Asia and Africa, the fourth by population after Asia and Europe. In 2013, its population was estimated at nearly 579 million people in 23 independent states, or about 7.5% of the world's population, if nearby islands are included. North America was reached by its first human populations during the last glacial period, via crossing the Bering land bridge 40,000 to 17,000 years ago; the so-called Paleo-Indian period is taken to have lasted until about 10,000 years ago. The Classic stage spans the 6th to 13th centuries.
The Pre-Columbian era ended in 1492, the transatlantic migrations—the arrival of European settlers during the Age of Discovery and the Early Modern period. Present-day cultural and ethnic patterns reflect interactions between European colonists, indigenous peoples, African slaves and their descendants. Owing to the European colonization of the Americas, most North Americans speak English, Spanish or French, their culture reflects Western traditions; the Americas are accepted as having been named after the Italian explorer Amerigo Vespucci by the German cartographers Martin Waldseemüller and Matthias Ringmann. Vespucci, who explored South America between 1497 and 1502, was the first European to suggest that the Americas were not the East Indies, but a different landmass unknown by Europeans. In 1507, Waldseemüller produced a world map, in which he placed the word "America" on the continent of South America, in the middle of what is today Brazil, he explained the rationale for the name in the accompanying book Cosmographiae Introductio:... ab Americo inventore... quasi Americi terram sive Americam.
For Waldseemüller, no one should object to the naming of the land after its discoverer. He used the Latinized version of Vespucci's name, but in its feminine form "America", following the examples of "Europa", "Asia" and "Africa". Other mapmakers extended the name America to the northern continent, In 1538, Gerard Mercator used America on his map of the world for all the Western Hemisphere; some argue that because the convention is to use the surname for naming discoveries, the derivation from "Amerigo Vespucci" could be put in question. In 1874, Thomas Belt proposed a derivation from the Amerrique mountains of Central America. Marcou corresponded with Augustus Le Plongeon, who wrote: "The name AMERICA or AMERRIQUE in the Mayan language means, a country of perpetually strong wind, or the Land of the Wind, and... the can mean... a spirit that breathes, life itself." The United Nations formally recognizes "North America" as comprising three areas: Northern America, Central America, The Caribbean.
This has been formally defined by the UN Statistics Division. The term North America maintains various definitions in accordance with context. In Canadian English, North America refers to the land mass as a whole consisting of Mexico, the United States, Canada, although it is ambiguous which other countries are included, is defined by context. In the United States of America, usage of the term may refer only to Canada and the US, sometimes includes Greenland and Mexico, as well as offshore islands. In France, Portugal, Romania and the countries of Latin America, the cognates of North America designate a subcontinent of the Americas comprising Canada, the United States, Mexico, Greenland, Saint Pierre et Miquelon, Bermuda. North America has been referred to by other names. Spanish North America was referred to as Northern America, this was the first official name given to Mexico. Geographically the North American continent has many subregions; these include cultural and geographic regions. Economic regions included those formed by trade blocs, such as the North American Trade Agreement bloc and Central American Trade Agreement.
Linguistically and culturally, the continent could be divided into Latin America. Anglo-America includes most of Northern America and Caribbean islands with English-speaking populations; the southern North American continent is composed of two regions. These are the Caribbean; the north of the continent maintains recognized regions as well. In contrast to the common definition of "North America", which encompasses the whole continent, the term "North America" is sometimes used to refer only to Mexico, the United States, Greenland; the term Northern America refers to the northern-most countries and territories of North America: the United States, Bermuda, St. Pierre and Miquelon and Greenland. Although the term does not refer to a unifie
In botany, the trunk is the stem and main wooden axis of a tree, an important feature in tree identification, which differs markedly from the bottom of the trunk to the top, depending on the species. The trunk is the most important part of the tree for timber production. Trunks occur both in "true" woody plants as well as non-woody plants such as palms and other monocots, though the internal physiology is different in each case. In all plants, trunks thicken over time due to formation of secondary growth. Trunks can be vulnerable to damage, including sunburn. Trunks which are cut down in logging are called logs and if cut to a specific length bolts; the trunk consists of five main parts: the bark, inner bark, cambium and heartwood. From the outside of the tree working in, the first layer is the bark. Under this is the inner bark, made of the phloem; the phloem is. The next layer is the cambium, a thin layer of undifferentiated cells that divide to replenish the phloem cells on the outside and the xylem cells to the inside.
Directly to the inside of this is the living xylem cells. These cells transport the water through the tree. At the center of the tree is the heartwood; the heartwood is made up of old xylem cells that have been filled with resins and minerals to keep other organisms from growing and infecting the center of the tree. Bark Basal area Tree measurement Tree volume measurement Diameter at breast height Inside a tree trunk from the University of the Western Cape
Betulaceae, the birch family, includes six genera of deciduous nut-bearing trees and shrubs, including the birches, hazels, hazel-hornbeam, hop-hornbeams numbering a total of 167 species. They are natives of the temperate Northern Hemisphere, with a few species reaching the Southern Hemisphere in the Andes in South America, their typical flowers are catkins and appear before leaves. In the past, the family was divided into two families and Corylaceae. Recent treatments, including the Angiosperm Phylogeny Group, have described these two groups as subfamilies within an expanded Betulaceae: Betuloideae and Coryloideae. Diagnostically, Betulaceae is similar to Rosaceae and other rose motif families; the Betulaceae are believed to have originated at the end of the Cretaceous period in central China. This region at the time would have had a Mediterranean climate due to the proximity of the Tethys Sea, which covered parts of present-day Tibet and Xinjiang into the early Tertiary period; this point of origin is supported by the fact that all six genera and 52 species are native to this region, many of those being endemic.
All six modern genera are believed to have diverged by the Oligocene, with all genera in the family having a fossil record stretching back at least 20 million years from the present. According to molecular phylogeny, the closest relatives of the Betulaceae are the Casuarinaceae, or the she-oaks; the common hazel and the filbert are important orchard plants, grown for their edible nuts. The other genera include a number of popular ornamental trees planted in parks and large gardens; the wood is hard and heavy, hornbeams so. In most of these uses, wood has now been replaced by metal or other man-made materials. Betuloideae Alnus Mill. 1754 – alder Betula L. 1753 – birch Coryloideae Carpinus L. 1753 – hornbeam Corylus L. 1753 – hazel Ostrya Scop. 1760 – hop-hornbeam Ostryopsis Decne. 1873 – hazel-hornbeam †Asterocarpinus †Coryloides †Cranea †Kardiasperma †Palaeocarpinus Modern molecular phylogenetics suggest the following relationships
A lenticel is a porous tissue consisting of cells with large intercellular spaces in the periderm of the secondarily thickened organs and the bark of woody stems and roots of dicotyledonous flowering plants. It functions as a pore, providing a pathway for the direct exchange of gases between the internal tissues and atmosphere through the bark, otherwise impermeable to gases; the name lenticel, pronounced with an, derives from its lenticular shape. The shape of lenticels is one of the characteristics used for tree identification. Before there was much evidence for the existence and functionality of lenticels, the fossil record has shown the first primary mechanism of aeration in early vascular plants to be the stomata. However, if there are internal stresses present, stomatal tissue expansion or damage can result. Woody plants, with cork cambia activity, are prime candidates for the latter; this necessity of aeration structures that combated stomatal damage in the presence of the secondary tissues of these woody plants is where lenticels are believed to have evolved.
The extinct arboreal plants of the genera Lepidodendron and Sigillaria were the first to have distinct aeration structures that rendered these modifications. "Parichnoi" are canal-like structures that, in association with foliar traces of the stem, connected the stem's outer and middle cortex to the mesophyll of the leaf. Parichnoi were thought to give rise to lenticels as they helped solve the issue of long-range oxygen transport in these woody plants during the Carboniferous period, they evolved to acquire secondary connections as they evolved to become transversely elongated to efficiently aerate the maximum number of vertical rays as well as the central core tissue of the stem. The evolutionary significance of these parichnoi was their functionality in the absence of cauline stomata, where they can be affected and destroyed by pressure similar to what can damage to stomatal tissue. Evidently, in both conifers and Lepidodendroids, the parichnoi, as the primary lenticular structure, appear as paired structures on either side of leaf scars.
The development and increase in the number of these primitive lenticels were key to providing a system, open for aeration and gas exchange in these plants. In plant bodies that produce secondary growth, lenticels promote gas exchange of oxygen, carbon dioxide, water vapor. Lenticel formation begins beneath stomatal complexes during primary growth preceding the development of the first periderm; the formation of lenticels seem to be directly related to the growth and strength of the shoot and on the hydrose of the tissue, which refers to the internal moisture. As stems and roots mature lenticel development continues in the new periderm. Lenticels are found as raised circular, elongated areas on stems and roots. In woody plants, lenticels appear as rough, cork-like structures on young branches. Underneath them, porous tissue creates a number of large intercellular spaces between cells; this tissue fills the lenticel and arises from cell division in the phellogen or substomatal ground tissue. Discoloration of lenticels may occur, such as in mangoes, that may be due to the amount of lignin in cell walls.
In oxygen deprived conditions, making respiration a daily challenge, different species may possess specialized structures where lenticels can be found. For example, in a common mangrove species, lenticels appear on pneumatophores, where the parenchyma cells that connect to the aerenchyma structure increase in size and go through cell division. In contrast, lenticels in grapes are located on act as a function of temperature. If they are blocked and successive ethanol accumulation may result and lead to cell death. Lenticels are present on many fruits, quite noticeably on many apples and pears. On European pears, they can serve as an indicator of when to pick the fruit, as light lenticels on the immature fruit darken and become brown and shallow from the formation of cork cells Certain bacterial and fungal infections can penetrate fruits through their lenticels, with susceptibility sometimes increasing with its age; as mentioned the term lenticel is associated with the breakage of periderm tissue, associated with gas exchange.
"Lenticel" seems to be the most appropriate term to describe both structures mentioned in light of their similar function in gas exchange. Pome lenticels can be derived from no longer functioning stomata, epidermal breaks from the removal of trichomes, other epidermal breaks that occur in the early development of young pome fruits; the closing of pome lenticels can arise when the cuticle over the stomata opening or the substomatal layer seals. Closing can begin if the substomatal cells become suberized, like cork; the number of lenticels varies between the species of apples, where the range may be from 450 to 800 or from 1500 to 2500 in Winesap and Spitzenburg apples, respectively. This wide range may be due to the water availability during the early stages of development of each apple type.“Lenticel breakdown” is a global skin disorder of apples in which lenticels develop dark 1–8 mm diameter pits shortly after processing and packing. It is most common on the ‘Gala’ variety the ‘Royal Gala’, occurs in ‘Fuji’, ‘Granny Smith’, ‘Golden Delicious’, ‘Delicious’ varieties.
It is more common in arid regions, is thought to be related to relative humidity and temperature. The effect can be mitigated by spraying the fruit with lipo