ยป logical Review

The sustainability of earth's ecosystems depends upon a balance between production of biomass by photosynthetic organisms and breakdown of that biomass and recycling of the nutrients it contains. In the process of recycling, the fungi play prominent roles in all major ecosystems. In addition, as food, as agents of disease, and as sources of antibiotics and other drugs long used by humans, the fungi have had important influences on the quality of the human environment and have even changed the course of history. Fungi are also a source of many plant diseases, such as the Dutch elm disease, chestnut blight, and the black stem rust of wheat, which have devastated plant populations across entire continents. Lichens, which can grow under some of the most extreme environmental conditions, are remarkably sensitive to air pollution and are useful indicators of air quality.

in Lapland absorbed radioactive elements and rendered the meat of reindeer that fed on the contaminated lichens unsafe to eat.

Lichens contribute to the degradation of historic ruins and other exposed rock or stone materials. Archaeological sites such as those of Troy (in modern Turkey) and Machu Picchu in Peru have suffered damage from the acids produced by lichens, and sometimes older gravestones slowly become covered by various lichen species.

Lichens provide food for many lower animals as well as large mammals. Reindeer and caribou can survive exclusively on fruticose lichens in Lapland when other food is unavailable, while North African sheep graze on a crustose lichen. By themselves, lichens do not make good food for human consumption, but they have been used as a food supplement (e.g., in soups) in parts of Europe. Most have acids that make them unpalatable, and some (e.g., rock tripe) have had harsh laxative effects on those who have tried them.

More than half of the lichens investigated have antibiotic properties. One lichen substance has been used in Europe in combination with another antibiotic in the treatment of tuberculosis. Europeans have also used lichen antibiotics to produce salves that have been effective in treating cuts and skin diseases.

Lichens were used for dyes by the Greeks and Romans, and a lichen dye industry persisted for many centuries in Europe. Native Americans and others also used lichens for dyes. Coal tar dyes now have largely replaced those of lichens, but lichens are still used in the manufacture of Scottish tweeds and East Indian cotton fabrics. Lichens are used in the preparation of the litmus paper used in elementary chemistry laboratories as an acid-alkaline indicator. The paper turns red under acid conditions and blue under alkaline ones.

Soaps are scented with extracts from lichens, and such extracts are still used in the manufacture of some European perfumes. Because of their resemblance to miniature trees and shrubs, some fruticose lichens are used by toy makers for the scenery of model railroads and car tracks. The importance of lichens in initiating soil formation is discussed in Chapter 25.

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