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Welcome: September 2007

Saturday, September 29, 2007

Mendel :

Mendel, Gregor Johann (1822-1884), Austrian monk, whose experimental work became the basis of modern heredity theory.
Mendel was born on July 22, 1822, to a peasant family in Heinzendorf (now Hynèice, Czech Republic). In 1843 he entered the Augustinian monastery at Brünn (now Brno, Czech Republic), which was known as a centre of learning and scientific endeavour. He studied science as well as theology, and later attended the University of Vienna. On his return to Brünn he taught for a time at the local technical school and became actively engaged in investigating variation, heredity, and evolution in plants at the monastery’s experimental garden.
Between 1856 and 1863 Mendel cultivated and tested at least 28,000 pea plants, carefully analysing the inheritance patterns of seven pairs of seed and plant characteristics. He had an interest in hybridization, and was probably experimenting to determine whether new plant species could be obtained through hybridization. From an early stage in his work, he came to believe that characteristics are not inherited through a simple blending of paternal and maternal attributes. To account for the inheritance patterns observed between generations, he enunciated two generalizations that later became known as the laws of heredity. The first was that there were hereditary units (now known as genes) that often expressed dominant and recessive characteristics. When egg and sperm unite, forming a gene pair, the dominant gene masks the recessive gene. The second generalization was that hereditary units did not blend, but remained unchanged from one generation to another, and that the expression of a hereditary unit for any single characteristic is usually not influenced by the expression of another. See Mendel’s Laws and Genetics.

Mendel published his important work on heredity in 1866. Despite, or perhaps because of, its descriptions of large numbers of experimental crosses that allowed him to express his results numerically and subject them to statistical analysis, this work made virtually no impression for the next 34 years. Only in 1900 was his work recognized more or less independently by three investigators, one of whom was the Dutch botanist Hugo De Vries, and not until the late 1920s was its full significance realized, particularly in relation to evolutionary theory. As a result of years of research in population genetics, investigators were able to demonstrate that Darwinian evolution can be described in terms of the change in gene frequency of Mendelian pairs of characteristics in a population over successive generations.

Mendel himself published only one further scientific paper after 1866. This concerned his inconclusive hybridization experiments with the hawkweed Hieracium, although he continued an important correspondence with the botanist Carl von Naegeli. In 1868 Mendel was elected abbot of his monastery, and he spent the last years of his life carrying out his administrative duties.

Monday, September 24, 2007

Hellebore :

Hellebore, common name for any of a genus of plants of the buttercup family. Native to Eurasia, the flowers have five large, petal-like sepals, eight to ten inconspicuous tubular petals, many stamens, and three to ten pistils. Green hellebore produces greenish-yellow flowers in late winter or early spring. It is occasionally grown in gardens and has become naturalized. The commonly cultivated Christmas rose bears large white flowers from midwinter to early spring, and the Lenten rose has purplish flowers and usually blooms after the Christmas rose.
The false hellebores, or false helleborines, belong to a different genus and family. White false hellebore is a conspicuous perennialherb of damp mountain pastures throughout much of Europe. It has white flowers and numerous large leaves that are narrow at both ends and are accordion-pleated lengthwise. Black false hellebore, of high woods and meadows, is similar in appearance but has reddish-brown flowers. The rootstocks of these plants and of the related American species of false hellebore are known to contain a number of alkaloids. Recently, it has been discovered that the foliage of false hellebores can produce birth abnormalities in sheep and other animals if eaten by the female at a particular time in pregnancy. The susceptible period is less than one day. The common deformity produced, known as cyclopia, is malformation of the face resulting in a single median eye or two eyeballs in a single central socket.

Scientific classification: Hellebores make up the genus Helleborus of the family Ranunculaceae. Green hellebore is classified as Helleborus viridis, Christmas rose as Helleborus niger, and Lenten rose as Helleborus orientalis. False hellebores belong to the genus Veratrum of the family Liliaceae. White false hellebore is classified as Veratrum album, and black false hellebore as Veratrum nigrum.

Wednesday, September 19, 2007

Soil Profile and Soil Types :

A number of soil types that cover extensive areas possess distinctive soil profiles. Podzols derive their name from the Russian words pod (“under”) and zola (“ash”), because of their strongly bleached E-horizon. This bleached horizon, the result of intense leaching, underlies a thick surface O-horizon, and overlies a brown B-horizon in which iron, aluminium, and, sometimes, humus have accumulated. Podzols are characteristic of cool environments with vegetation, such as conifers and heaths, that produces acid litter. Podzols are acidic with a low nutrient status, so cultivation is difficult. They are used mostly for forestry and grazing.

Chernozems (black earths) are characteristic of the great temperate grasslands of the world, with cold winters, hot summers, and an excess of evapotranspiration over precipitation. There is a rapid incorporation of organic matter into the soil accompanied by its humification, and by the leaching of soluble salts and carbonates. Some carbonates are redeposited in the middle of the soil. There is tremendous small-vertebrate and earthworm activity, which aerates and mixes the soil. Chernozems are extremely fertile because of their high nutrient status, good structure, and high water-holding capacity. They are used largely for the extensive cultivation of cereal crops. Brown Earths, typical of temperate deciduous woodland, possess a relatively thin surface O-horizon underlain by a light brown, weathered B-horizon. Other horizons are obliterated by the operation of soil organisms. A variety of red and reddish-brown soils occur in wet equatorial and tropical wet-dry climates, with rainforest and semi-deciduous tropical forests being the principal plant communities. Such soils are characterized by the intense weathering of bedrock into clays and contain a variety of oxides, including iron. On exposure such soils tend to harden and produce laterite. Because of their low nutrient status and low content of organic matter they are of low fertility. When the forest is cleared, what little fertility exists is soon lost.

Monday, September 17, 2007

Manatee :

manatee:common name for three species of large water mammals popularly called sea cows। The Amazonian manatee occurs in the Amazon river system, the West Indian manatee is found in central Florida and along the Gulf of Mexico and Caribbean coasts, and the West African manatee is found in rivers of tropical West Africa. A manatee usually stays within its small home range, where it grazes on water plants. Its greyish to black corpulent body tapers to a horizontally flattened, rounded tail. The forelimbs are flippers set close to the head; it has no external hind limbs. The head is small, with a straight snout and a cleft upper lip with bristly hairs. Adults are about 2.5 to 4.5 m (8 to 15 ft) long depending on the species, and weigh 200 to 600 kg (440 to 1,300 lb). They live in small family groups and sometimes in herds of 15 to 20; groups of 500 to 1,000 Amazonian manatees may be observed during the dry season. After a gestation of about a year, usually a single pinkish calf is born. The number of manatees has been reduced by heavy hunting for their hides, meat, and blubber oil, but some governments, including the United States, have placed them under protection. One practical reason for this is that they have proved useful in clearing irrigation and transport channels clogged with water plants. See also Dugong.

Scientific classification :
Manatees make up the family Trichechidae in the order Sirenia. The South American manatee is classified as Trichechus inunguis, the Caribbean manatee as Trichechus manatus, and the African manatee as Trichechus senegalensis.

Friday, September 07, 2007

Aardvark :

Aardvark (Afrikaans, “earth pig”), common name for a burrowing, ant-eating mammal. The aardvark is found throughout much of Africa, from the southern part of Egypt in the north to the Cape of Good Hope in the south. A primarily nocturnal animal, it lives in burrows and feeds on ants and termites, occasionally eating other insects and a species of wild ground cucumber.

The aardvark is up to 2.3 m (7y ft) long, including the fleshy, tapering tail, which it uses to throw earth backwards when it burrows. It has an arched back, a tubular snout, and large, upright ears. The aardvark uses its specialized, chisel-shaped claws to break open the hard clay of ant and termite nests; it then uses its sticky tongue to capture the insects. Unlike the animals known as anteaters, which are toothless, the aardvark has 20 cylindrical, rootless teeth that grow continually throughout its lifetime.

The female gives birth to one or occasionally two offspring, which can dig their own burrows at the age of six months. Although timid, the aardvark fights when it cannot flee or burrow to safety; it defends itself with its powerful claws or by striking with its tail or shoulders.

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