36 résultats pour "flowers"

• Flower - biology.

  insects. The sepals unfurl as the flower opens and often resemble small green leaves at the flower’s base. In some flowers, the sepals are colorful and work with thepetals to attract pollinators. E Variations in Structure Like virtually all forms in nature, flowers display many variations in their structure. Most flowers have all four whorls—pistil, stamens, petals, and sepals. Botanists callthese complete flowers. But some flowers are incomplete, meaning they lack one or more whorls. Incomplet...

• Pollination - biology.

  rapidly as in cross-pollination, because one plant with a beneficial gene can transmit it only to its own offspring and not to other plants. Self-pollination evolved laterthan cross-pollination, and may have developed as a survival mechanism in harsh environments where pollinators were scarce. IV POLLEN TRANSFER Unlike animals, plants are literally rooted to the spot, and so cannot move to combine sex cells from different plants; for this reason, species have evolved effectivestrategies for ac...

• Tree - biology.

  The major parts of a tree are its roots, trunk, leaves, flowers, and seeds. These components play vital roles in a tree’s growth, development, and reproduction. A Roots Trees are held in place by anchoring organs called roots. In addition to anchoring the tree, roots also absorb water and minerals through tiny structures called roothairs. From the roots the water and mineral nutrients are carried upward through the wood cells to the leaves. Although the internal structure of most kinds of roots...

• Colorado - geography.

  Although the rivers of Colorado are navigable only by small boats, they are important as a source of irrigation water for use in Colorado and adjoining states. However,the water level of the rivers fluctuates seasonally and from year to year. The level is generally low in winter and high in spring and summer, during the runoff of meltedsnow from the mountains. Colorado has no large lakes of natural origin, but there are numerous small lakes in the mountains. The largest bodies of water in Colora...

• Colorado - USA History.

  Although the rivers of Colorado are navigable only by small boats, they are important as a source of irrigation water for use in Colorado and adjoining states. However,the water level of the rivers fluctuates seasonally and from year to year. The level is generally low in winter and high in spring and summer, during the runoff of meltedsnow from the mountains. Colorado has no large lakes of natural origin, but there are numerous small lakes in the mountains. The largest bodies of water in Colora...

• Butterflies and Moths - biology.

  The smallest butterflies are certain blues that have wingspans of a mere 0.7 cm (0.25 in). The largest are the female giant birdwings of Papua New Guinea, whichmeasure up to 30 cm (12 in) across. Moths range in size from tiny Microlepidoptera, several groups of small moths with wings no more than 0.16 cm (0.06 in) across, togiant silk moths, such as the atlas moth, which may exceed 30 cm (12 in) in wingspan. IV REPRODUCTION AND LIFE CYCLE Butterflies locate potential mates by sight, identifyin...

• Grasses - biology.

  This, together with details of overall structure and less easily observed characteristics of anatomy, cytology, and chemistry, accounts for the tremendous number ofspecies of grasses. VI OTHER GRASSLIKE PLANTS Plants of two other groups, the sedges and the rushes, are superficially similar to grasses and are often confused with them. The three groups are easily distinguished,however, by examining their flowers, stems, and leaves. Rushes have flowers with six-part perianths (floral whorls) and...

• Fruit - biology.

  from a flower with several pistils. The ovary may have a single compartment, or carpel, which houses the ovule or ovules. Or the ovary may consist of two or morecarpels, each of which may contain one or more ovules. A drupe develops from an ovary with a single carpel and is characterized by an edible exocarp and mesocarp and an inedible, hard endocarp, or pit that encloses asingle seed. Cherries, peaches, apricots, and plums are examples of drupes. Almonds also are classified as drupes, but in a...

• From Bulfinch's Mythology: Proserpine - anthology.

  the furrow, the seed failed to come up; there was too much sun, there was too much rain; the birds stole the seeds—thistles and brambles were the only growth.Seeing this, the fountain Arethusa interceded for the land. 'Goddess,' said she, 'blame not the land; it opened unwillingly to yield a passage to your daughter. I can tellyou of her fate, for I have seen her. This is not my native country; I came hither from Elis. I was a woodland nymph, and delighted in the chase. They praised mybeauty, bu...

• Tennessee (state) - geography.

  The climate of Tennessee is characterized by hot summers, mild winters, and abundant rainfall. C1 Temperature Average July temperatures range from less than 21° C (70° F) in the Blue Ridge region to 27° C (80° F) at Nashville and Memphis. Maximum daytime temperatures insummer often rise above 35° C (95° F) in central and western Tennessee. Daytime temperatures in the mountains rarely rise above 32° C (90° F). Summer nights tendto be warm and muggy in central and western Tennessee, but temperatu...

• Tennessee (state) - USA History.

  The climate of Tennessee is characterized by hot summers, mild winters, and abundant rainfall. C1 Temperature Average July temperatures range from less than 21° C (70° F) in the Blue Ridge region to 27° C (80° F) at Nashville and Memphis. Maximum daytime temperatures insummer often rise above 35° C (95° F) in central and western Tennessee. Daytime temperatures in the mountains rarely rise above 32° C (90° F). Summer nights tendto be warm and muggy in central and western Tennessee, but temperatu...

• From Bulfinch's Mythology: The Golden Fleece - anthology.

  It remained to lull to sleep the dragon that guarded the fleece, and this was done by scattering over him a few drops of a preparation which Medea had supplied. Atthe smell he relaxed his rage, stood for a moment motionless, then shut those great round eyes, that had never been known to shut before, and turned over on his side,fast asleep. Jason seized the fleece and with his friends and Medea accompanying, hastened to their vessel before Æetes the king could arrest their departure, andmade the...

• Plant - biology.

  B1 Vacuoles Vacuoles are membrane-bound cavities filled with cell sap, which is made up mostly of water containing various dissolved sugars, salts, and other chemicals. B2 Plastids Plastids are types of organelles, structures that carry out specialized functions in the cell. Three kinds of plastids are important here. Chloroplasts contain chlorophyllsand carotenoid pigments; they are the site of photosynthesis, the process in which light energy from the sun is fixed as chemical energy in the b...

• Insect - biology.

  they almost always have six legs. In some insects, such as beetles, the legs are practically identical, but in other insects each pair is a slightly different shape. Still otherinsects have specialized leg structures. Examples are praying mantises, which have grasping and stabbing forelegs armed with lethal spines, and grasshoppers andfleas, which have large, muscular hind legs that catapult them into the air. Mole crickets’ front legs are modified for digging, and backswimmers have hind legs de...

• Beetle - biology.

  cut, or crush prey. Beetles that consume nectar from flowers use tubelike mouthparts to suck up nectar like a primitive straw. C Thorax The thorax, the body region behind the head, consists of three segments that provide attachments for the legs and wings. Each segment of the thorax carries a pair oflegs. The middle segment also bears the stiff wing sheaths called elytra, and the hind segment holds the membranous hind wings. D Legs Beetles have six jointed legs, each leg with five parts. The f...

• Butterflies.

  When the change is complete, the adult butterfly splits the chrysalis. The insect unfolds its wings andpumps blood and air into them. It spreads out the wings until they dry and harden. The beautifulbutterfly then flies off to slurp nectar from flowers. Most butterflies live only one or two weeks. BUTTERFLY RELATIVES Butterflies are closely related to moths, another type of insect. One difference between butterflies andmoths is how their antennae look. Butterflies have knobs called clubs on the...

• Evolution - biology.

  genetic diversity to extinction. Sexual reproduction ensures that the genes in a population are rearranged in each generation, a process termed recombination. Although the combinations of genes inindividuals change with each new generation, the gene frequency, or ratio of different alleles in the entire population, remains relatively constant if no evolutionaryforces act on the population. One such force is the introduction of new genes into the genetic material of the population, or gene pool...

• Honey Bee - biology.

  B Reproduction and Development The queen controls the sex of her offspring. When an egg passes from her ovary to her oviduct, the queen determines whether the egg is fertilized with sperm from thespermatheca. A fertilized egg develops into a female honey bee, either worker or queen, and an unfertilized egg becomes a male honey bee, or drone. The queen lays the eggs that will develop into more queens in specially constructed downward-pointing, peanut-shaped cells, in which the egg adheres to the...

• Delaware - geography.

  D Climate Delaware has generally hot and humid summers and mild winters. D1 Temperature In July, average daytime temperatures are usually in the upper 20°s to lower 30°sC (80°sF) or even higher. But because summer nights tend to be cooler than thedays, July averages are about 24°C (about 75°F). In addition, onshore sea breezes can reduce daytime temperatures along the coast by 3 to 6 Celsius degrees (5 to 10Fahrenheit degrees). January averages range from -1°C (31°F) at Newark, in the north, t...

• Delaware - USA History.

  D Climate Delaware has generally hot and humid summers and mild winters. D1 Temperature In July, average daytime temperatures are usually in the upper 20°s to lower 30°sC (80°sF) or even higher. But because summer nights tend to be cooler than thedays, July averages are about 24°C (about 75°F). In addition, onshore sea breezes can reduce daytime temperatures along the coast by 3 to 6 Celsius degrees (5 to 10Fahrenheit degrees). January averages range from -1°C (31°F) at Newark, in the north, t...

• Washington (state) - geography.

  The crest of the Cascade Range divides Washington into two distinct climatic regions. The area west of the Cascades, which is exposed throughout the year to rain-bearing winds from the Pacific Ocean, has a temperate marine type of climate that is characterized by mild wet winters and cool summers. The Cascades prevent themoist air blowing in from the Pacific from reaching eastern Washington. The Rocky Mountains on the eastern border also represent a climatic barrier. As a result, thesevere winte...

• Washington (state) - USA History.

  The crest of the Cascade Range divides Washington into two distinct climatic regions. The area west of the Cascades, which is exposed throughout the year to rain-bearing winds from the Pacific Ocean, has a temperate marine type of climate that is characterized by mild wet winters and cool summers. The Cascades prevent themoist air blowing in from the Pacific from reaching eastern Washington. The Rocky Mountains on the eastern border also represent a climatic barrier. As a result, thesevere winte...

• Louisiana - geography.

  lakes are on the Red River and its tributaries. In addition, small oxbow lakes are numerous in the Mississippi Alluvial Plain. Oxbow lakes are formed when a river cutsthrough the neck of one of its loops, or meanders, thus establishing a shorter course and leaving the former loop as a lake separate from the river. Louisiana also hassome artificially created reservoirs. C Coastline Louisiana’s long and irregular coastline extends along the Gulf of Mexico from the Pearl River on the east to the S...

• Louisiana - USA History.

  lakes are on the Red River and its tributaries. In addition, small oxbow lakes are numerous in the Mississippi Alluvial Plain. Oxbow lakes are formed when a river cutsthrough the neck of one of its loops, or meanders, thus establishing a shorter course and leaving the former loop as a lake separate from the river. Louisiana also hassome artificially created reservoirs. C Coastline Louisiana’s long and irregular coastline extends along the Gulf of Mexico from the Pearl River on the east to the S...

• India - country.

  delta in the north, are intensely farmed. B Rivers and Lakes The rivers of India can be divided into three groups: the great Himalayan rivers of the north, the westward-flowing rivers of central India, and the eastward-flowingrivers of the Deccan Plateau and the rest of peninsular India. Only small portions of India’s rivers are navigable because of silting and the wide seasonal variation inwater flow (due to the monsoon climate). Water transport is thus of little importance in India. Barrages,...

• Gardening - biology.

  of synthetic and organic fertilizers, see Organic Farming.) Fertilizers usually are sold in packages, on which the percentage by weight of the macronutrients nitrogen (N), phosphorus (P), and potassium (K) are listed on thelabel—always in the order N-P-K. For example, a fertilizer that is labeled 10-5-3 is 10 percent nitrogen, 5 percent phosphorus, and 3 percent potassium. V PLANTING AND TRANSPLANTING Before planting seeds, gardeners prepare, or till, the soil using a variety of methods. Some...

• Mao ZedongIINTRODUCTIONMao Zedong (1893-1976), foremost Chinese Communist leader of the 20th century and the principal founder of the People's Republic of China.

  outside the government was also muted because the educated elite remembered the turmoil of the “Hundred Flowers” and “Antirightist” campaigns of 1957. Mao’srelationship with intellectuals was an uneasy one, and he was critical of the gap between the lives of the urban educated elite and the rural masses. These tensions wereamong the underlying causes of the Cultural Revolution, a period of social unrest and political persecution launched by Mao in 1966. Mao mobilized youth into the RedGuards to...

• Mao Zedong.

  outside the government was also muted because the educated elite remembered the turmoil of the “Hundred Flowers” and “Antirightist” campaigns of 1957. Mao’srelationship with intellectuals was an uneasy one, and he was critical of the gap between the lives of the urban educated elite and the rural masses. These tensions wereamong the underlying causes of the Cultural Revolution, a period of social unrest and political persecution launched by Mao in 1966. Mao mobilized youth into the RedGuards to...

• Mao Zedong - History.

  outside the government was also muted because the educated elite remembered the turmoil of the “Hundred Flowers” and “Antirightist” campaigns of 1957. Mao’srelationship with intellectuals was an uneasy one, and he was critical of the gap between the lives of the urban educated elite and the rural masses. These tensions wereamong the underlying causes of the Cultural Revolution, a period of social unrest and political persecution launched by Mao in 1966. Mao mobilized youth into the RedGuards to...

• Birding - biology.

  swallows, and rock doves nest on buildings in cities, towns, and farms. The chimney swift has abandoned hollow trees for chimneys as a nest site in urban areas.Mallards and Canada geese—once exclusively wild, migratory species—now live year-round in the open spaces found in city parks and golf courses. Nearly all purplemartins, a songbird species that once used the abandoned nests of woodpeckers or the natural cavities of cliffs or dead trees, now live primarily in structures specificallyconstru...

• Cell (biology) - biology.

  proteins, or other proteins required by the cell. While relatively simple in construction, prokaryotic cells display extremely complex activity. They have a greater range of biochemical reactions than those found in theirlarger relatives, the eukaryotic cells. The extraordinary biochemical diversity of prokaryotic cells is manifested in the wide-ranging lifestyles of the archaebacteria andthe bacteria, whose habitats include polar ice, deserts, and hydrothermal vents—deep regions of the ocean un...

• Guatemala - country.

  C Climate The climate of Guatemala varies according to elevation, from hot coastal plains to cold mountain heights. Most of the population lives between 900 and 2,400 m (3,000and 8,000 ft) above sea level, where there are warm days and cool nights with average annual temperatures of 20°C (68°F). The coastal regions are hot and humid,with average annual temperatures of 28°C (83°F). A rainy season, from May through October, is sometimes called “winter” because it brings cloudy afternoons andlower...

• Nevada - geography.

  The Truckee, Carson, and Walker rivers flow out of the Sierra Nevada, thread their way around several of the desert ranges, and also end in closed basins. The Walkerflows into Walker Lake, the Carson into Lahontan Reservoir. The major part of the Truckee’s flow is now diverted to Lahontan Reservoir, although as required by lawsome of it empties into Pyramid Lake. Because these three streams flow constantly, the lakes into which they empty never dry up. Winnemucca Lake formerly receivedoverflow w...

• Nevada - USA History.

  The Truckee, Carson, and Walker rivers flow out of the Sierra Nevada, thread their way around several of the desert ranges, and also end in closed basins. The Walkerflows into Walker Lake, the Carson into Lahontan Reservoir. The major part of the Truckee’s flow is now diverted to Lahontan Reservoir, although as required by lawsome of it empties into Pyramid Lake. Because these three streams flow constantly, the lakes into which they empty never dry up. Winnemucca Lake formerly receivedoverflow w...

• Texas - geography.

  D Climate Eastern Texas has a humid subtropical climate, while a semiarid low latitude climate prevails in central areas, and an arid low latitude climate in the extreme west. Alongthe coast the climate is much milder, with fewer extremes in temperatures. Hurricanes sometimes hit the coastal areas of Texas from late July through September, andtornadoes are common in north-central Texas in April and May. D1 Temperature Summers are hot throughout the state, and temperatures exceeding 35°C (95°F)...

• Texas - USA History.

  D Climate Eastern Texas has a humid subtropical climate, while a semiarid low latitude climate prevails in central areas, and an arid low latitude climate in the extreme west. Alongthe coast the climate is much milder, with fewer extremes in temperatures. Hurricanes sometimes hit the coastal areas of Texas from late July through September, andtornadoes are common in north-central Texas in April and May. D1 Temperature Summers are hot throughout the state, and temperatures exceeding 35°C (95°F)...