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117-443: The emblema is bordered by an intricate floral pattern, which itself is bordered by stylized depictions of waves . The mosaic is a pebble mosaic with stones collected from beaches and riverbanks which were set into cement . As was perhaps often the case, the mosaic does much to reflect styles of painting . The light figures against a darker background may allude to red figure painting. The mosaic also uses shading , known to

234-520: A diploid (two copies of each chromosome ) cell. Whereas in fertilization only plasmogamy, or the fusion of the whole sex cells, results, in Angiosperms (flowering plants) a process known as double fertilization, which involves both karyogamy and plasmogamy, occurs. In double fertilization the second sperm cell subsequently also enters the synergid and fuses with the two polar nuclei of the central cell. Since all three nuclei are haploid , they result in

351-411: A filament , or stalk. The anther contains microsporocytes which become pollen , the male gametophyte , after undergoing meiosis . Although they exhibit the widest variation among floral organs, the androecium is usually confined just to one whorl and to two whorls only in rare cases. Stamens range in number, size, shape, orientation, and in their point of connection to the flower. In general, there

468-764: A 54% increased chance of asthma attacks when exposed to pollen. The number of people in the United States affected by hay fever is between 20 and 40 million, including around 6.1 million children and such allergy has proven to be the most frequent allergic response in the nation. Hay fever affects about 20% of Canadians and the prevalence is increasing. There are certain evidential suggestions pointing out hay fever and similar allergies to be of hereditary origin . Individuals who suffer from eczema or are asthmatic tend to be more susceptible to developing long-term hay fever. Since 1990, pollen seasons have gotten longer and more pollen-filled, and climate change

585-411: A broad base, stomata and chlorophyll and may have stipules . Sepals are often waxy and tough, and grow quickly to protect the flower as it develops. They may be deciduous , but will more commonly grow on to assist in fruit dispersal. If the calyx is fused it is called gamosepalous. The petals , or corolla, are almost or completely fiberless leaf-like structures that form the innermost whorl of

702-409: A burglar who brushed against a Hypericum bush during a crime, and has even been proposed as an additive for bullets to enable tracking them. In some Native American religions , pollen was used in prayers and rituals to symbolize life and renewal by sanctifying objects, dancing grounds, trails, and sandpaintings . It may also be sprinkled over heads or in mouths. Many Navajo people believed

819-426: A continuum with intermediate forms, the type of microsporogenesis has systematic significance. The predominant form amongst the monocots is successive, but there are important exceptions. During microgametogenesis, the unicellular microspores undergo mitosis and develop into mature microgametophytes containing the gametes. In some flowering plants, germination of the pollen grain may begin even before it leaves

936-404: A different flower of the same plant, but others have mechanisms to prevent self-pollination and rely on cross-pollination , when pollen is transferred from the anther of one flower to the stigma of another flower on a different individual of the same species. Self-pollination happens in flowers where the stamen and carpel mature at the same time, and are positioned so that the pollen can land on

1053-418: A different plant of the same species. Because the genetic make-up of the sperm contained within the pollen from the other plant is different, their combination will result in a new, genetically distinct, plant, through the process of sexual reproduction . Since each new plant is genetically distinct, the different plants show variation in their physiological and structural adaptations and so the population as

1170-407: A generative (reproductive) cell. In flowering plants the vegetative tube cell produces the pollen tube , and the generative cell divides to form the two sperm nuclei. Pollen grains come in a wide variety of shapes, sizes, and surface markings characteristic of the species (see electron micrograph , right). Pollen grains of pines , firs , and spruces are winged. The smallest pollen grain, that of

1287-497: A hard coat made of sporopollenin that protects the gametophytes during the process of their movement from the stamens to the pistil of flowering plants, or from the male cone to the female cone of gymnosperms . If pollen lands on a compatible pistil or female cone, it germinates , producing a pollen tube that transfers the sperm to the ovule containing the female gametophyte. Individual pollen grains are small enough to require magnification to see detail. The study of pollen

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1404-432: A large endosperm nucleus which is triploid . Following the formation of zygote it begins to grow through nuclear and cellular divisions, called mitosis , eventually becoming a small group of cells. One section of it becomes the embryo , while the other becomes the suspensor; a structure which forces the embryo into the endosperm and is later undetectable. Two small primordia also form at this time, that later become

1521-399: A lumen (plural lumina). These reticulations may also be referred to as brochi. The pollen wall protects the sperm while the pollen grain is moving from the anther to the stigma; it protects the vital genetic material from drying out and solar radiation. The pollen grain surface is covered with waxes and proteins, which are held in place by structures called sculpture elements on the surface of

1638-1336: A mate). In pursuing this attractant from many flowers of the same species, the pollinator transfers pollen to the stigmas—arranged with equally pointed precision—of all of the flowers it visits. Many flowers rely on simple proximity between flower parts to ensure pollination, while others have elaborate designs to ensure pollination and prevent self-pollination . Flowers use animals including: insects ( entomophily ), birds ( ornithophily ), bats ( chiropterophily ), lizards, and even snails and slugs ( malacophilae ). Plants cannot move from one location to another, thus many flowers have evolved to attract animals to transfer pollen between individuals in dispersed populations. Most commonly, flowers are insect-pollinated, known as entomophilous ; literally "insect-loving" in Greek. To attract these insects flowers commonly have glands called nectaries on various parts that attract animals looking for nutritious nectar . Some flowers have glands called elaiophores , which produce oils rather than nectar. Birds and bees have color vision , enabling them to seek out colorful flowers. Some flowers have patterns, called nectar guides , that show pollinators where to look for nectar; they may be visible only under ultraviolet light, which

1755-508: A multitude of viruses and eukaryotic parasites are present in the pollen. It is currently unclear if the parasites are introduced by the bee that collected the pollen or if it is from the flower. Though this is not likely to pose a risk to humans, it is a major issue for the bumblebee rearing industry that relies on thousands of tonnes of honey bee collected pollen per year. Several sterilization methods have been employed, though no method has been 100% effective at sterilisation without reducing

1872-458: A noticeable scent. Because of this, plants typically have many thousands of tiny flowers which have comparatively large, feathery stigmas; to increase the chance of pollen being received. Whereas the pollen of entomophilous flowers is usually large, sticky, and rich in protein (to act as a "reward" for pollinators), anemophilous flower pollen is typically small-grained, very light, smooth, and of little nutritional value to insects . In order for

1989-470: A plant can interpret important endogenous and environmental cues such as changes in levels of plant hormones and seasonable temperature and photoperiod changes. Many perennial and most biennial plants require vernalization to flower. The molecular interpretation of these signals is through the transmission of a complex signal known as florigen , which involves a variety of genes , including Constans, Flowering Locus C, and Flowering Locus T. Florigen

2106-505: A pollen allergy is by preventing contact with the material. Individuals carrying the ailment may at first believe that they have a simple summer cold, but hay fever becomes more evident when the apparent cold does not disappear. The confirmation of hay fever can be obtained after examination by a general physician . Antihistamines are effective at treating mild cases of pollinosis; this type of non-prescribed drugs includes loratadine , cetirizine and chlorpheniramine . They do not prevent

2223-528: A small number feed on pollen as larvae (including some ant larvae). Spiders are normally considered carnivores but pollen is an important source of food for several species, particularly for spiderlings , which catch pollen on their webs . It is not clear how spiderlings manage to eat pollen however, since their mouths are not large enough to consume pollen grains. Some predatory mites also feed on pollen, with some species being able to subsist solely on pollen, such as Euseius tularensis , which feeds on

2340-404: A sonar-reflecting petal above its flowers, which helps the bat find them, and one species, the cactus Espostoa frutescens , has flowers that are surrounded by an area of sound-absorbent and woolly hairs called the cephalium, which absorbs the bat's ultrasound instead. Flowers are also specialized in shape and have an arrangement of the stamens that ensures that pollen grains are transferred to

2457-407: A third in 1944. Knuth named his two groups 'Hyphydrogamy' and the more common 'Ephydrogamy'. In hyphydrogamy pollination occurs below the surface of the water and so the pollen grains are typically negatively buoyant . For marine plants that exhibit this method, the stigmas are usually stiff, while freshwater species have small and feathery stigmas. In ephydrogamy pollination occurs on the surface of

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2574-435: A whole is better prepared for an adverse occurrence in the environment. Cross-pollination, therefore, increases the survival of the species and is usually preferred by flowers for this reason. The principal adaptive function of flowers is the promotion of cross-pollination or outcrossing, a process that allows the masking of deleterious mutations in the genome of progeny. The masking effect of outcrossing sexual reproduction

2691-797: A widespread anemophilous plant. Arizona was once regarded as a haven for people with pollen allergies, although several ragweed species grow in the desert. However, as suburbs grew and people began establishing irrigated lawns and gardens , more irritating species of ragweed gained a foothold and Arizona lost its claim of freedom from hay fever. Anemophilous spring blooming plants such as oak , birch , hickory , pecan , and early summer grasses may also induce pollen allergies. Most cultivated plants with showy flowers are entomophilous and do not cause pollen allergies. Symptoms of pollen allergy include sneezing , itchy, or runny nose, nasal congestion , red, itchy, and watery eyes. Substances, including pollen, that cause allergies can trigger asthma. A study found

2808-416: Is a loss of B gene function, mutant flowers are produced with sepals in the first whorl as usual, but also in the second whorl instead of the normal petal formation. In the third whorl, the lack of the B function but the presence of the C function mimics the fourth whorl, leading to the formation of carpels also in the third whorl. The principal purpose of a flower is the reproduction of the individual and

2925-422: Is a much rarer method, occurring in only around 2% of abiotically pollinated flowers. Common examples of this include Calitriche autumnalis , Vallisneria spiralis and some sea-grasses . One characteristic which most species in this group share is a lack of an exine , or protective layer, around the pollen grain. Paul Knuth identified two types of hydrophilous pollination in 1906 and Ernst Schwarzenbach added

3042-417: Is a way to represent the structure of a flower using specific letters, numbers, and symbols, presenting substantial information about the flower in a compact form. It can represent a taxon , usually giving ranges of the numbers of different organs, or particular species. Floral formulae have been developed in the early 19th century and their use has declined since. Prenner et al. (2010) devised an extension of

3159-458: Is also associated with asthma exacerbations in some people, a phenomenon termed thunderstorm asthma . In the US, people often mistakenly blame the conspicuous goldenrod flower for allergies. Since this plant is entomophilous (its pollen is dispersed by animals), its heavy, sticky pollen does not become independently airborne. Most late summer and fall pollen allergies are probably caused by ragweed ,

3276-630: Is also present in a wide variety of plants and plant-derived food products. The U.S. Food and Drug Administration (FDA) has not found any harmful effects of bee pollen consumption, except for the usual allergies. However, FDA does not allow bee pollen marketers in the United States to make health claims about their produce, as no scientific basis for these has ever been proven. Furthermore, there are possible dangers not only from allergic reactions but also from contaminants such as pesticides and from fungi and bacteria growth related to poor storage procedures. A manufacturers's claim that pollen collecting helps

3393-404: Is an example of coevolution , as the flower and pollinator have developed together over a long period to match each other's needs. This close relationship compounds the negative effects of extinction , however, since the extinction of either member in such a relationship would almost certainly mean the extinction of the other member as well. Flowers that use abiotic, or non-living, vectors use

3510-468: Is an extensive fossil record of pollen grains, often disassociated from their parent plant. The discipline of palynology is devoted to the study of pollen, which can be used both for biostratigraphy and to gain information about the abundance and variety of plants alive — which can itself yield important information about paleoclimates. Also, pollen analysis has been widely used for reconstructing past changes in vegetation and their associated drivers. Pollen

3627-440: Is an important aspect of the pollination process. Bee pollen for human consumption is marketed as a food ingredient and as a dietary supplement . The largest constituent is carbohydrates , with protein content ranging from 7 to 35 percent depending on the plant species collected by bees. Honey produced by bees from natural sources contains pollen derived p-coumaric acid , an antioxidant and natural bactericide that

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3744-427: Is because it is directly connected to the method of seed dispersal; that being the purpose of fruit - to encourage or enable the seed's dispersal and protect the seed while doing so. Following the pollination of a flower, fertilization, and finally the development of a seed and fruit, a mechanism is typically used to disperse the fruit away from the plant. In Angiosperms (flowering plants) seeds are dispersed away from

3861-519: Is broken down by an enzyme called callase and the freed pollen grains grow in size and develop their characteristic shape and form a resistant outer wall called the exine and an inner wall called the intine. The exine is what is preserved in the fossil record. Two basic types of microsporogenesis are recognised, simultaneous and successive. In simultaneous microsporogenesis meiotic steps I and II are completed before cytokinesis , whereas in successive microsporogenesis cytokinesis follows. While there may be

3978-402: Is called palynology and is highly useful in paleoecology , paleontology , archaeology , and forensics . Pollen in plants is used for transferring haploid male genetic material from the anther of a single flower to the stigma of another in cross-pollination. In a case of self-pollination, this process takes place from the anther of a flower to the stigma of the same flower. Pollen

4095-706: Is described as monosulcate , has two sulci, as bisulcate , or more, as polysulcate . Colpate pollen has furrows other than across the middle of the outer faces, and similarly may be described as polycolpate if more than two. Syncolpate pollen grains have two or more colpi that are fused at the ends. Eudicots have pollen with three colpi ( tricolpate ) or with shapes that are evolutionarily derived from tricolpate pollen. The evolutionary trend in plants has been from monosulcate to polycolpate or polyporate pollen. Additionally, gymnosperm pollen grains often have air bladders, or vesicles, called sacci. The sacci are not actually balloons, but are sponge-like, and increase

4212-485: Is first found in the fossil record in the late Devonian period, but at that time it is indistinguishable from spores. It increases in abundance until the present day. Nasal allergy to pollen is called pollinosis , and allergy specifically to grass pollen is called hay fever . Generally, pollens that cause allergies are those of anemophilous plants (pollen is dispersed by air currents.) Such plants produce large quantities of lightweight pollen (because wind dispersal

4329-602: Is frequently portrayed as a sequential process that begins with placement on the vector, moves through travel, and ends with deposition. This transfer can be mediated by the wind, in which case the plant is described as anemophilous (literally wind-loving). Anemophilous plants typically produce great quantities of very lightweight pollen grains, sometimes with air-sacs. Non-flowering seed plants (e.g., pine trees) are characteristically anemophilous. Anemophilous flowering plants generally have inconspicuous flowers. Entomophilous (literally insect-loving) plants produce pollen that

4446-656: Is from the Middle English flour , which referred to both the ground grain and the reproductive structure in plants, before splitting off in the 17th century. It comes originally from the Latin name of the Italian goddess of flowers, Flora . The early word for flower in English was blossom , though it now refers to flowers only of fruit trees . The morphology of a flower, or its form and structure, can be considered in two parts:

4563-541: Is highly reduced or absent). The stem or stalk subtending a flower, or an inflorescence of flowers, is called a peduncle . If a peduncle supports more than one flower, the stems connecting each flower to the main axis are called pedicels . The apex of a flowering stem forms a terminal swelling which is called the torus or receptacle. In the majority of species, individual flowers have both carpels and stamens. These flowers are described by botanists as being perfect, bisexual, or hermaphrodite . In some species of plants,

4680-442: Is infrequently used as food and food supplement . Because of agricultural practices, it is often contaminated by agricultural pesticides. Pollen itself is not the male gamete. It is a gametophyte , something that could be considered an entire organism, which then produces the male gamete. Each pollen grain contains vegetative (non-reproductive) cells (only a single cell in most flowering plants but several in other seed plants) and

4797-494: Is known as "genetic complementation". This beneficial effect of outcrossing on progeny is also recognized as hybrid vigour or heterosis. Once outcrossing is established due to the benefits of genetic complementation, subsequent switching to inbreeding becomes disadvantageous because it allows the expression of the previously masked deleterious recessive mutations, usually referred to as inbreeding depression. Charles Darwin in his 1889 book The Effects of Cross and Self-Fertilization in

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4914-408: Is only one type of stamen, but there are plant species where the flowers have two types; a "normal" one and one with anthers that produce sterile pollen meant to attract pollinators. The gynoecium , or the carpels , is the female part of the flower found on the innermost whorl. Each carpel consists of a stigma , which receives pollen, a style , which acts as a stalk, and an ovary , which contains

5031-443: Is preferred because it allows for genetic variation , which contributes to the survival of the species. Many flowers depend on external factors for pollination, such as the wind, water, animals, and especially insects . Larger animals such as birds, bats, and even some pygmy possums , however, can also be employed. To accomplish this, flowers have specific designs which encourage the transfer of pollen from one plant to another of

5148-429: Is produced in the leaves in reproductively favorable conditions and acts in buds and growing tips to induce several different physiological and morphological changes. The first step of the transition is the transformation of the vegetative stem primordia into floral primordia. This occurs as biochemical changes take place to change the cellular differentiation of leaf, bud and stem tissues into tissue that will grow into

5265-563: Is random and the likelihood of one pollen grain landing on another flower is small), which can be carried for great distances and are easily inhaled, bringing it into contact with the sensitive nasal passages. Pollen allergies are common in polar and temperate climate zones, where production of pollen is seasonal. In the tropics pollen production varies less by the season, and allergic reactions less. In northern Europe, common pollens for allergies are those of birch and alder , and in late summer wormwood and different forms of hay . Grass pollen

5382-444: Is reflected morphologically in the presence of more pulp , an aril , and sometimes an elaiosome (primarily for ants), which are other fleshy structures. Pollen grains Pollen is a powdery substance produced by most types of flowers of seed plants for the purpose of sexual reproduction. It consists of pollen grains (highly reduced microgametophytes ), which produce male gametes (sperm cells). Pollen grains have

5499-403: Is relatively heavy, sticky and protein -rich, for dispersal by insect pollinators attracted to their flowers. Many insects and some mites are specialized to feed on pollen, and are called palynivores . In non-flowering seed plants, pollen germinates in the pollen chamber, located beneath the micropyle , underneath the integuments of the ovule. A pollen tube is produced, which grows into

5616-409: Is responsible, according to a new study. The researchers attributed roughly half of the lengthening pollen seasons and 8% of the trend in pollen concentrations to climate changes driven by human activity. In Denmark , decades of rising temperatures cause pollen to appear earlier and in greater amounts, exacerbated by the introduction of new species such as ragweed. The most efficient way to handle

5733-571: Is thought that Actaeon tried to rape Artemis. In this image we see the same concept of a stag being torn apart by a dog just as in the myth as well as by Alexander the Great on the right. It is speculated who is on the left. The theme here is the "hunter being hunted". It is a quite fitting mosaic for The House of The Abduction Of Helen, who was raped. The stag also represents the Persians that Alexander would later conquer. He had stated his motives for battling

5850-580: Is thought to be a severe underestimate as the feeding habits are only known for 1,000 species). Similarly, Ladybird beetles mainly eat insects, but many species also eat pollen, as either part or all of their diet. Hemiptera are mostly herbivores or omnivores but pollen feeding is known (and has only been well studied in the Anthocoridae ). Many adult flies, especially Syrphidae , feed on pollen, and three UK syrphid species feed strictly on pollen (syrphids, like all flies , cannot eat pollen directly due to

5967-418: Is typically another part. In some families, such as the grasses , the petals are greatly reduced; in many species, the sepals are colorful and petal-like. Other flowers have modified petal-like stamens; the double flowers of peonies and roses are mostly petaloid stamens. Many flowers have symmetry. When the perianth is bisected through the central axis from any point and symmetrical halves are produced,

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6084-479: Is variously sculptured, and the character of the markings is often of value for identifying genus, species, or even cultivar or individual. The spines may be less than a micron in length (spinulus, plural spinuli) referred to as spinulose (scabrate), or longer than a micron (echina, echinae) referred to as echinate . Various terms also describe the sculpturing such as reticulate , a net like appearance consisting of elements (murus, muri) separated from each other by

6201-574: Is visible to bees and some other insects. Flowers also attract pollinators by scent , though not all flower scents are appealing to humans; several flowers are pollinated by insects that are attracted to rotten flesh and have flowers that smell like dead animals. These are often called carrion flowers , including plants in the genus Rafflesia , and the titan arum . Flowers pollinated by night visitors, including bats and moths, are likely to concentrate on scent to attract pollinators and so most such flowers are white. Some plants pollinated by bats have

6318-477: The Greeks as skiagraphia , in its depictions of the musculature and cloaks of the figures. This along with its use of overlapping figures to create depth renders the image three dimensional . It is often wondered if Gnosis, whose signature ("Gnosis epoesen", i.e. Gnosis created) is the first known signature of a mosaicist , could have been the painter of an earlier picture which the mosaic reproduces, rather than

6435-421: The buoyancy of the pollen grain and help keep it aloft in the wind, as most gymnosperms are anemophilous . Pollen can be monosaccate , (containing one saccus) or bisaccate (containing two sacci). Modern pine , spruce , and yellowwood trees all produce saccate pollen. The transfer of pollen grains to the female reproductive structure ( pistil in angiosperms) is called pollination . Pollen transfer

6552-414: The calyx , corolla , androecium , and gynoecium . Together the calyx and corolla make up the non-reproductive part of the flower called the perianth , and in some cases may not be differentiated. If this is the case, then they are described as tepals . The sepals , collectively called the calyx, are modified leaves that occur on the outermost whorl of the flower. They are leaf-like, in that they have

6669-494: The cotyledon , which is used as an energy store. Plants which grow out one of these primordia are called monocotyledons , while those that grow out two are dicotyledons . The next stage is called the Torpedo stage and involves the growth of several key structures, including: the radicle (embryotic root), the epicotyl (embryotic stem), and the hypocotyl , (the root/shoot junction). In the final step vascular tissue develops around

6786-449: The forget-me-not ( Myosotis spp.), is 2.5–5  μm (0.005 mm) in diameter. Corn pollen grains are large, about 90–100 μm. Most grass pollen is around 20–25 μm. Some pollen grains are based on geodesic polyhedra like a soccer ball . Pollen is produced in the microsporangia in the male cone of a conifer or other gymnosperm or in the anthers of an angiosperm flower . In angiosperms, during flower development

6903-439: The gizzard of animals or even to germinate better after passing through them. They can be eaten by birds ( ornithochory) , bats ( chiropterochory) , rodents , primates, ants ( myrmecochory ), non-bird sauropsids ( saurochory) , mammals in general (mammaliochory) , and even fish . Typically their fruit are fleshy, have a high nutritional value, and may have chemical attractants as an additional "reward" for dispersers. This

7020-408: The nucellus to provide nutrients for the developing sperm cells. Sperm cells of Pinophyta and Gnetophyta are without flagella , and are carried by the pollen tube, while those of Cycadophyta and Ginkgophyta have many flagella. When placed on the stigma of a flowering plant, under favorable circumstances, a pollen grain puts forth a pollen tube , which grows down the tissue of the style to

7137-511: The ovary , and makes its way along the placenta , guided by projections or hairs, to the micropyle of an ovule . The nucleus of the tube cell has meanwhile passed into the tube, as does also the generative nucleus, which divides (if it has not already) to form two sperm cells. The sperm cells are carried to their destination in the tip of the pollen tube. Double-strand breaks in DNA that arise during pollen tube growth appear to be efficiently repaired in

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7254-518: The wind or, much less commonly, water , to move pollen from one flower to the next. In wind-dispersed ( anemophilous ) species, the tiny pollen grains are carried, sometimes many thousands of kilometers, by the wind to other flowers. Common examples include the grasses , birch trees , along with many other species in the order Fagales , ragweeds , and many sedges . They do not need to attract pollinators and therefore tend not to grow large, showy, or colorful flowers, and do not have nectaries, nor

7371-490: The Persians as to get vengeance for them sacking Athens and destroying temples there such as the Parthenon . This would again represent the idea of the hunter being hunted. Floral A flower , also known as a bloom or blossom , is the reproductive structure found in flowering plants (plants of the division Angiospermae ). Flowers consist of a combination of vegetative organs – sepals that enclose and protect

7488-401: The Persians had tried to subdue Hellas - an effort earlier Macedonian kings had participated in - resulting ultimately in the empire's destruction by Alexander. In Greek mythology , the stag is associated with Artemis who was the virginal huntress. The myth goes when Actaeon saw Artemis naked, out of anger she turned him into a stag and he was torn to pieces by his own. In other accounts it

7605-462: The Vegetable Kingdom at the beginning of chapter XII noted, "The first and most important of the conclusions which may be drawn from the observations given in this volume, is that generally cross-fertilisation is beneficial and self-fertilisation often injurious, at least with the plants on which I experimented." Self-pollination is the pollination of the carpel of a flower by pollen from either

7722-438: The anther is composed of a mass of cells that appear undifferentiated, except for a partially differentiated dermis. As the flower develops, fertile sporogenous cells, the archespore , form within the anther. The sporogenous cells are surrounded by layers of sterile cells that grow into the wall of the pollen sac. Some of the cells grow into nutritive cells that supply nutrition for the microspores that form by meiotic division from

7839-484: The apical meristem, which becomes a whorl of sepals. In the second whorl, both A and B genes are expressed, leading to the formation of petals. In the third whorl, B and C genes interact to form stamens and in the center of the flower C genes alone give rise to carpels. The model is based upon studies of aberrant flowers and mutations in Arabidopsis thaliana and the snapdragon, Antirrhinum majus . For example, when there

7956-464: The bee colonies is also controversial. Pine pollen ( 송화가루 ; Songhwa Garu ) is traditionally consumed in Korea as an ingredient in sweets and beverages. The growing industries in pollen harvesting for human and bee consumption rely on harvesting pollen baskets from honey bees as they return to their hives using a pollen trap . When this pollen has been tested for parasites, it has been found that

8073-582: The bodies of the pollinator when it lands in search of its attractant. Other flowers use mimicry or pseudocopulation to attract pollinators. Many orchids, for example, produce flowers resembling female bees or wasps in color, shape, and scent. Males move from one flower to the next in search of a mate, pollinating the flowers. Many flowers have close relationships with one or a few specific pollinating organisms. Many flowers, for example, attract only one specific species of insect and therefore rely on that insect for successful reproduction. This close relationship

8190-474: The body became holy when it traveled over a trail sprinkled with pollen. For agricultural research purposes, assessing the viability of pollen grains can be necessary and illuminating. A very common, efficient method to do so is known as Alexander's stain. This differential stain consists of ethanol , malachite green , distilled water , glycerol , phenol , chloral hydrate , acid fuchsin , orange G , and glacial acetic acid . (A less-toxic variation omits

8307-517: The collective cluster of flowers is called an inflorescence . Some inflorescences are composed of many small flowers arranged in a formation that resembles a single flower. A common example of this is most members of the very large composite ( Asteraceae ) group. A single daisy or sunflower , for example, is not a flower but a flower head —an inflorescence composed of numerous flowers (or florets). An inflorescence may include specialized stems and modified leaves known as bracts . A floral formula

8424-619: The developing flower. These petals attract pollinators, and reproductive organs that produce gametophytes , which in flowering plants produce gametes . The male gametophytes, which produce sperm, are enclosed within pollen grains produced in the anthers . The female gametophytes are contained within the ovules produced in the ovary . Most flowering plants depend on animals, such as bees, moths, and butterflies, to transfer their pollen between different flowers, and have evolved to attract these pollinators by various strategies, including brightly colored, conspicuous petals, attractive scents, and

8541-557: The discharge of histamine , but it has been proven that they do prevent a part of the chain reaction activated by this biogenic amine , which considerably lowers hay fever symptoms. Decongestants can be administered in different ways such as tablets and nasal sprays . Allergy immunotherapy (AIT) treatment involves administering doses of allergens to accustom the body to pollen, thereby inducing specific long-term tolerance. Allergy immunotherapy can be administered orally (as sublingual tablets or sublingual drops), or by injections under

8658-484: The existing model to broaden the descriptive capability of the formula. The format of floral formulae differs in different parts of the world, yet they convey the same information. The structure of a flower can also be expressed by the means of floral diagrams . The use of schematic diagrams can replace long descriptions or complicated drawings as a tool for understanding both floral structure and evolution. Such diagrams may show important features of flowers, including

8775-413: The flower is said to be actinomorphic or regular. This is an example of radial symmetry . When flowers are bisected and produce only one line that produces symmetrical halves, the flower is said to be irregular or zygomorphic . If, in rare cases, they have no symmetry at all they are called asymmetric. Flowers may be directly attached to the plant at their base ( sessile —the supporting stalk or stem

8892-497: The flower's stigma. This pollination does not require an investment from the plant to provide nectar and pollen as food for pollinators. Some flowers produce diaspores without fertilization ( parthenocarpy ). After fertilization, the ovary of the flower develops into fruit containing seeds . Flowers have long been appreciated for their beauty and pleasant scents, and also hold cultural significance as religious, ritual, or symbolic objects, or sources of medicine and food. Flower

9009-511: The flowers are imperfect or unisexual: having only either male (stamen) or female (carpel) parts. If unisexual male and female flowers appear on the same plant, the species is called monoecious . However, if an individual plant is either female or male, the species is called dioecious . Many flowers have nectaries , which are glands that produce a sugary fluid used to attract pollinators. They are not considered as an organ on their own. In those species that have more than one flower on an axis,

9126-424: The following two broad groups of pollination methods: Flowers that use biotic vectors attract and use insects , bats , birds , or other animals to transfer pollen from one flower to the next. Often they are specialized in shape and have an arrangement of the stamens that ensures that pollen grains are transferred to the bodies of the pollinator when it lands in search of its attractant (such as nectar, pollen, or

9243-451: The gametophytes also develop inside the spores, i.e., they are endosporic. Since the flowers are the reproductive organs of the plant, they mediate the joining of the sperm, contained within pollen, to the ovules — contained in the ovary. Pollination is the movement of pollen from the anthers to the stigma. Normally pollen is moved from one plant to another, known as cross-pollination , but many plants can self-pollinate. Cross-pollination

9360-427: The generative cell that carries the male genomic information to be passed on to the next plant generation. However, the vegetative cell that is responsible for tube elongation appears to lack this DNA repair capability. The sporopollenin outer sheath of pollen grains affords them some resistance to the rigours of the fossilisation process that destroy weaker objects; it is also produced in huge quantities. There

9477-475: The grain. The outer pollen wall, which prevents the pollen grain from shrinking and crushing the genetic material during desiccation, is composed of two layers. These two layers are the tectum and the foot layer, which is just above the intine. The tectum and foot layer are separated by a region called the columella, which is composed of strengthening rods. The outer wall is constructed with a resistant biopolymer called sporopollenin. Pollen apertures are regions of

9594-544: The identification of classes of pollen. Pollen may be referred to as inaperturate (apertures absent) or aperturate (apertures present). The aperture may have a lid ( operculum ), hence is described as operculate . However the term inaperturate covers a wide range of morphological types, such as functionally inaperturate (cryptoaperturate) and omniaperturate. Inaperaturate pollen grains often have thin walls, which facilitates pollen tube germination at any position. Terms such as uniaperturate and triaperturate refer to

9711-467: The microsporangium, with the generative cell forming the two sperm cells. Except in the case of some submerged aquatic plants, the mature pollen grain has a double wall. The vegetative and generative cells are surrounded by a thin delicate wall of unaltered cellulose called the endospore or intine , and a tough resistant outer cuticularized wall composed largely of sporopollenin called the exospore or exine . The exine often bears spines or warts, or

9828-438: The mosaic-setter. In the case of pottery , 'epoesen' referred to a maker of the pot while 'egraphsen' was the verb used to designate the painter. Therefore, if an analogy to pottery is warranted, it seems likely for Gnosis to have been a mosaicist. Since gnosis ( Greek : γνῶσις) is also the Greek word for knowledge , others have said the inscription does not refer to an author at all; but to an abstract noun. The figure on

9945-516: The myth wherein Artemis transforms the huntsman Actaeon into a stag when he tries to rape her. Once he is turned into a stag his own hounds turn on him and he is torn apart. The theme of abduction may relate the mosaic not only to the Rape of Helen by Theseus , depicted in another mosaic in the same house, but also to Alexander's conquest of Persia. As Actaeon had hunted Artemis but was destroyed by his dogs, so

10062-416: The number of apertures present (one and three respectively). Spiraperturate refers to one or more apertures being spirally shaped. The orientation of furrows (relative to the original tetrad of microspores) classifies the pollen as sulcate or colpate . Sulcate pollen has a furrow across the middle of what was the outer face when the pollen grain was in its tetrad. If the pollen has only a single sulcus, it

10179-491: The nutritional value of the pollen In forensic biology , pollen can tell a lot about where a person or object has been, because regions of the world, or even more particular locations such a certain set of bushes, will have a distinctive collection of pollen species. Pollen evidence can also reveal the season in which a particular object picked up the pollen. Pollen has been used to trace activity at mass graves in Bosnia , catch

10296-400: The ovary. After penetrating the center-most part of the ovary it enters the egg apparatus and into one synergid . At this point the end of the pollen tube bursts and releases the two sperm cells, one of which makes its way to an egg, while also losing its cell membrane and much of its protoplasm . The sperm's nucleus then fuses with the egg's nucleus, resulting in the formation of a zygote ,

10413-504: The ovule is fertilized by pollen from the same flower or plant, occurs in flowers that always self-fertilize, such as many dandelions . Some flowers are self-pollinated and have flowers that never open or are self-pollinated before the flowers open; these flowers are called cleistogamous ; many species in the genus Viola exhibit this, for example. Conversely, many species of plants have ways of preventing self-pollination and hence, self-fertilization. Unisexual male and female flowers on

10530-524: The ovules. Carpels may occur in one to several whorls, and when fused are often described as a pistil . Inside the ovary, the ovules are attached to the placenta by structures called funiculi . Although this arrangement is considered "typical", plant species show a wide variation in floral structure. The four main parts of a flower are generally defined by their positions on the receptacle and not by their function. Many flowers lack some parts or parts may be modified into other functions or look like what

10647-534: The perianth. They are often delicate and thin and are usually colored, shaped, or scented to encourage pollination. Although similar to leaves in shape, they are more comparable to stamens in that they form almost simultaneously with one another, but their subsequent growth is delayed. If the corolla is fused together it is called sympetalous. The androecium , or stamens, is the whorl of pollen-producing male parts. Stamens consist typically of an anther , made up of four pollen sacs arranged in two thecae , connected to

10764-451: The plant so as to not force competition between the mother and the daughter plants, as well as to enable the colonization of new areas. They are often divided into two categories, though many plants fall in between or in one or more of these: In allochory, plants use an external vector , or carrier, to transport their seeds away from them. These can be either biotic (living), such as by birds and ants, or abiotic (non-living), such as by

10881-474: The pollen of dozens of plant species. Members of some beetle families such as Mordellidae and Melyridae feed almost exclusively on pollen as adults, while various lineages within larger families such as Curculionidae , Chrysomelidae , Cerambycidae , and Scarabaeidae are pollen specialists even though most members of their families are not (e.g., only 36 of 40,000 species of ground beetles , which are typically predatory, have been shown to eat pollen—but this

10998-455: The pollen wall that may involve exine thinning or a significant reduction in exine thickness. They allow shrinking and swelling of the grain caused by changes in moisture content. The process of shrinking the grain is called harmomegathy. Elongated apertures or furrows in the pollen grain are called colpi (singular: colpus) or sulci (singular: sulcus ). Apertures that are more circular are called pores. Colpi, sulci and pores are major features in

11115-400: The process of pollination. Fertilization , also called Synagmy, occurs following pollination, which is the movement of pollen from the stamen to the carpel. It encompasses both plasmogamy , the fusion of the protoplasts , and karyogamy , the fusion of the nuclei . When pollen lands on the stigma of the flower it begins creating a pollen tube which runs down through the style and into

11232-453: The production of nectar , a food source for pollinators. In this way, many flowering plants have co-evolved with pollinators to be mutually dependent on services they provide to one another—in the plant's case, a means of reproduction; in the pollinator's case, a source of food. When pollen from the anther of a flower is deposited on the stigma , this is called pollination. Some flowers may self-pollinate , producing seed using pollen from

11349-600: The relative positions of the various organs, including the presence of fusion and symmetry, as well as structural details. A flower develops on a modified shoot or axis from a determinate apical meristem ( determinate meaning the axis grows to a set size). It has compressed internodes, bearing structures that in classical plant morphology are interpreted as highly modified leaves . Detailed developmental studies, however, have shown that stamens are often initiated more or less like modified stems (caulomes) that in some cases may even resemble branchlets . Taking into account

11466-420: The reproductive organs. Growth of the central part of the stem tip stops or flattens out and the sides develop protuberances in a whorled or spiral fashion around the outside of the stem end. These protuberances develop into the sepals, petals, stamens, and carpels . Once this process begins, in most plants, it cannot be reversed and the stems develop flowers, even if the initial start of the flower formation event

11583-411: The right is possibly Alexander the Great due to the date of this mosaic along with the depicted upsweep of the hair. Pella is also the birthplace of Alexander. The figure to the left wields a double-headed axe, likely alluding to Hephaistos ; meaning the figure depicted could be the general Hephaestion . The dog depicted is possibly Peritas accompanying Alexander. The stag and hound may allude to

11700-490: The same flower or another flower on the same plant, leading to the creation of a genetic clone through asexual reproduction . This increases the reliability of producing seeds, the rate at which they can be produced, and lowers the amount energy needed. But, most importantly, it limits genetic variation . In addition, self-pollination causes inbreeding depression , due largely to the expression of recessive deleterious mutations . The extreme case of self-fertilization, when

11817-412: The same plant may not appear or mature at the same time, or pollen from the same plant may be incapable of fertilizing its ovules. The latter flower types, which have chemical barriers to their own pollen, are referred to as self-incompatible. In Clianthus puniceus , self-pollination is used strategically as an "insurance policy". When a pollinator, in this case a bird, visits C. puniceus , it rubs off

11934-769: The same species. The period during which this process can take place (when the flower is fully expanded and functional) is called anthesis , hence the study of pollination biology is called anthecology . Flowering plants usually face evolutionary pressure to optimize the transfer of their pollen , and this is typically reflected in the morphology of the flowers and the behavior of the plants. Pollen may be transferred between plants via several 'vectors,' or methods. Around 80% of flowering plants make use of biotic or living vectors. Others use abiotic, or non-living, vectors and some plants make use of multiple vectors, but most are highly specialized. Though some fit between or outside of these groups, most flowers can be divided between

12051-482: The seed. The ovary, inside which the seed is forming from the ovule, grows into a fruit . All the other main floral parts die during this development, including: the style, stigma, sepals, stamens, and petals. The fruit contains three structures: the exocarp , or outer layer, the mesocarp , or the fleshy part, and the endocarp , or innermost layer, while the fruit wall is called the pericarp . The size, shape, toughness, and thickness varies among different fruit. This

12168-429: The skin (subcutaneous). Discovered by Leonard Noon and John Freeman in 1911, allergy immunotherapy represents the only causative treatment for respiratory allergies. Most major classes of predatory and parasitic arthropods contain species that eat pollen, despite the common perception that bees are the primary pollen-consuming arthropod group. Many Hymenoptera other than bees consume pollen as adults, though only

12285-439: The species. All flowering plants are heterosporous , that is, every individual plant produces two types of spores . Microspores are produced by meiosis inside anthers and megaspores are produced inside ovules that are within an ovary. Anthers typically consist of four microsporangia and an ovule is an integumented megasporangium. Both types of spores develop into gametophytes inside sporangia. As with all heterosporous plants,

12402-438: The sporogenous cells. The archespore cells divide by mitosis and differentiate to form pollen mother cells (microsporocyte, meiocyte ). In a process called microsporogenesis , four haploid microspores are produced from each diploid pollen mother cell, after meiotic division . After the formation of the four microspores, which are contained by callose walls, the development of the pollen grain walls begins. The callose wall

12519-428: The stigmatic covering and allows for pollen from the bird to enter the stigma. If no pollinators visit, however, then the stigmatic covering falls off naturally to allow for the flower's own anthers to pollinate the flower through self-pollination. Pollen is a large contributor to asthma and other respiratory allergies which combined affect between 10 and 50% of people worldwide. This number appears to be growing, as

12636-408: The structure of their mouthparts, but can consume pollen contents that are dissolved in a fluid). Some species of fungus, including Fomes fomentarius , are able to break down grains of pollen as a secondary nutrition source that is particularly high in nitrogen. Pollen may be valuable diet supplement for detritivores , providing them with nutrients needed for growth, development and maturation. It

12753-463: The temperature increases due to climate change mean that plants are producing more pollen , which is also more allergenic. Pollen is difficult to avoid, however, because of its small size and prevalence in the natural environment. Most of the pollen which causes allergies is that produced by wind-dispersed pollinators such as the grasses , birch trees , oak trees, and ragweeds ; the allergens in pollen are proteins which are thought to be necessary in

12870-428: The vegetative part, consisting of non-reproductive structures such as petals ; and the reproductive or sexual parts. A stereotypical flower is made up of four kinds of structures attached to the tip of a short stalk or axis, called a receptacle . Each of these parts or floral organs is arranged in a spiral called a whorl . The four main whorls (starting from the base of the flower or lowest node and working upwards) are

12987-619: The water and so the pollen has a low density to enable floating, though many also use rafts, and are hydrophobic . Marine flowers have floating thread-like stigmas and may have adaptations for the tide, while freshwater species create indentations in the water. The third category, set out by Schwarzenbach, is those flowers which transport pollen above the water through conveyance. This ranges from floating plants, ( Lemnoideae ), to staminate flowers ( Vallisneria ). Most species in this group have dry, spherical pollen which sometimes forms into larger masses, and female flowers which form depressions in

13104-401: The water; the method of transport varies. Flowers can be pollinated by two mechanisms; cross-pollination and self-pollination. No mechanism is indisputably better than the other as they each have their advantages and disadvantages. Plants use one or both of these mechanisms depending on their habitat and ecological niche . Cross-pollination is the pollination of the carpel by pollen from

13221-480: The whole diversity in the development of the androecium of flowering plants, we find a continuum between modified leaves (phyllomes), modified stems (caulomes), and modified branchlets (shoots). The transition to flowering is one of the major phase changes that a plant makes during its life cycle. The transition must take place at a time that is favorable for fertilization and the formation of seeds , hence ensuring maximal reproductive success. To meet these needs

13338-460: The wind or water. Many plants use biotic vectors to disperse their seeds away from them. This method falls under the umbrella term zoochory , while endozoochory , also known as fruigivory, refers specifically to plants adapted to grow fruit in order to attract animals to eat them. Once eaten they go through typically go through animal's digestive system and are dispersed away from the plant. Some seeds are specially adapted either to last in

13455-419: The wind to effectively pick up and transport the pollen, the flowers typically have anthers loosely attached to the end of long thin filaments, or pollen forms around a catkin which moves in the wind. Rarer forms of this involve individual flowers being moveable by the wind ( pendulous ), or even less commonly; the anthers exploding to release the pollen into the wind. Pollination through water ( hydrophily )

13572-416: Was dependent on some environmental cue. The ABC model is a simple model that describes the genes responsible for the development of flowers. Three gene activities interact in a combinatorial manner to determine the developmental identities of the primordia organ within the floral apical meristem . These gene functions are called A, B, and C. Genes are expressed in only the outer and lower most section of

13689-508: Was suggested that obtaining nutrients from pollen, deposited on the forest floor during periods of pollen rains, allows fungi to decompose nutritionally scarce litter. Some species of Heliconius butterflies consume pollen as adults, which appears to be a valuable nutrient source, and these species are more distasteful to predators than the non-pollen consuming species. Although bats , butterflies and hummingbirds are not pollen eaters per se , their consumption of nectar in flowers

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