Lichens

Although usually green, lichens also show up as a yellow or orange "moss" that grows on naked rocks and logs. The oldest fossils of plants contain fossils of fungi: the joining together of members of separate living kingdoms, fungi and algae or monera (bacteria) to make lichens, is part of an ancient tendency for life to settle land by a combination of partners. (Similarly, if human beings were to settle space, we could not with present technology do it alone, but would require food plants to eat, and microbes such as bacteria and fungi to recycle air and turn our wastes into drinking water and soil.)

Perhaps the most famous example of symbiosis, or living together, lichens are syner-gistic associations between fungi and either algae (a protoctist) or cyanobacteria (a bacterium). In reproductive sex the two sexes come together briefly, contribute part of their genomes, and an offspring arises. In lichens, by contrast, the two components—fungus (mycobiont or fungal life form) and phyco-biont (photosynthetic life form)—have per

Lichen-covered rocks, Qlacier National Park, Montana (David Muench/Corbis)

manently merged. The fungus is usually an ascomycete. whose name derives from a saclike reproductive organ, the ascus. Yeasts, morels, and familiar molds are ascomycotes. The spores of ascomycotes can remain viable for years while dry, and some ascomycotes are responsible for tree diseases such as blight and Dutch elm disease. Of the approximately 50,000 ascomycote species, 20,000 are found only in association with photosynthetic green organisms—that is, as the fungal part of a lichen partnership. More rarely, the fungal partner in lichens will be classified as a basid-iomycotes, the other great phylum in the Kingdom Fungi.

Worm Farming

Worm Farming

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