Lichens Are Symbiotic Associations Of A Fungus

Lichens are symbiotic associations of a fungus with a photosynthetic partner that can produce food for the lichen from sunlight. The photobiont is usually either green alga or cyanobacterium. A few lichens are known to contain yellow-green algae or, in one case, a brown algae. The body of most lichens is quite different from that of either the fungus or alga growing separately, and may strikingly resemble simple plants in form and growth (Sanders 2001). The fungus surrounds the algal cells, often enclosing them within complex fungal tissues unique to lichen associations; however, in almost all kinds, the algal cells are never enclosed inside the fungal cells themselves. It has been suggested that the fungus is sometimes penetrated by haustoria by the mycobiont, but with the development of electron microscopy there is little solid evidence of this, and if true, is an isolated occurrence and in any event is entirely unecessesary. Thus lichens are poikilohydric, that is, capable of surviving extremely low levels of water content. However, the re-configuration of membranes following a period of dehydration requires several minutes at least. During this period a "soup" of metabolites from both the mycobiont and phycobiont leaks into the extracellar spaces. This is readily available to both bionts to uptake essential metabolic products ensuring a perfect level of mutualism Definitive data derived from poikilohydric canopy mosses is provided by Coxson (1990)showing leaching from the canopy mosses in Guadaloupe of numerous matabolites immediately following rehydration. Not only do the two bionts profit, but also the all the other epiphytic organisms from the nutrient rich leachate. This fundamental phenomenon also points to a possible explanation of lichen evolution from its original phycobiont and mycobiont components with its subsequent migration from an aquatic environment to dry land. In the natural environment, lichen "provides" the alga with water and minerals that the fungus absorbs from whatever the lichen is growing on, its substrate. As for the alga, it uses the minerals and water to make food for the fungus and itself. Algal and fungal components of some lichens have been cultured separately under laboratory conditions, but in the natural environment of a lichen, neither can grow and reproduce without a symbiotic partner. Indeed, although strains of cyanobacteria found in various cyanolichens are often closely related to one another, they differ from the most closely related free-living strains. The lichen association is a close symbiosis: It extends the ecological range of both partners and is obligatory for their growth and reproduction in natural environoments. Propagules typically contain cells from both partners, although the fungal components of so-called "fringe species" rely instead on algal cells dispersed by the "core species". Lichens must compete with plants for access to sunlight, but because of their small size and slow growth, they thrive in places where higher plants have difficulty growing.

Lichens do not have roots and do not need to tap continuous reservoirs of water like most higher plants, thus they can grow in locations impossible for most plants, such as bare rock, sterile soil or sand, and various artificial structures such as walls, roofs and monuments. Many lichens also grow as epiphytes on other plants, particularly on the trunks and branches of trees. When growing on other plants, lichens are not parasites; they do not consume any part of the plant nor poison it. Some ground-dwelling lichens, such as members of the subgenus Cladina, however, produce chemicals which leach into the soil and inhibit the germination of plant seeds and growth of young plants. Stability (that is, longevity) of their substrate is a major factor of lichen habitats. Most lichens grow on stable rock surfaces or the bark of old trees, but many others grow on soil and sand. In these latter cases, lichens are often an important part of soil stabilization; indeed, in some desert ecosystems, vascular (higher) plant seeds cannot become established except in places where lichen crusts stabilize the sand and help retain water. The Taj Mahal is entirely made of white marble and its pure white walls are decorated with exquisite pietra dura (stone inlay) work. It is said that different types of precious and semiprecious stones were used in the intricate inlay work done on Taj Mahal. The Taj Mahal is considered the finest example of Mughal architecture, a style that combines elements from Persian, Turkish, Indian, and Islamic architectural styles. In 1983, the Taj Mahal became a UNESCO World Heritage Site and was cited as "the jewel of Muslim art in India and one of the universally admired masterpieces of the world's heritage." Qutub Minar is the highest stone tower in India. Qutub Minar was built in red and buff sandstone and covered with intricate carvings and verses from the holy Quran. All the five storeys of Qutub Minar are surrounded by a projected balcony and supported by stone brackets, which are decorated with honeycomb designs. Qutub Minar, also spelled is the tallest brick minaret in the world, and an important example of Indo-Islamic Architecture. Jama Masjid of Delhi is the largest mosque in India. The first three storeys of the Jama Masjid tower are made of red sandstone and the fourth one is made of marble, while the fifth is made of sandstone. The Jama Masjid is covered with intricate carvings and has verses inscribed from the holy Koran. Jama Masjid is the largest mosque in India and stands across the road from the Red Fort, built in 1656 by Shahjahan. About 25,000 people can pray here at a time. Jaipur is synonymous with Hawa Mahal. It has five stories and is constructed of red and pink sandstone, highlighted with white quakeee quick lime .The structure comprises of 953 beautiful windows made out of pink sandstone. These windows are known as "Jharokhas" and are built in a way that it resembles a honeycomb.Its original intention was to allow royal ladies to observe everyday life in the street below without being seen. Delhi's famous Red Fort is known by that name because of the red stone with which it is built and it is one of the most magnificent palaces in the world. India's history is also closely linked with this fort. Built by Emperor Shah Jahan, the construction of this massive Red fort in Delhi ended in 1648 and has been since then a place of tremendous historical importance.