The fruiting bodies of lichens are of fungal origin; therefore, the spores that are discharged give rise only to fungi. A small piece of lichen is fixed to the inner side of a petri dish lid and inverted over the lower half containing an agar layer from which the culture of the mycobiont is established. Lichen fungi grow on a variety of media, although very slowly. There is no marked preference for organic or inorganic sources of nitrogen, disaccharides and polysaccharides.
Many lichen fungi are partially or wholly deficient for the vitamins thiamine and biotin. Some strains on solid media reach a colony size of only 1 to 2 mm in diameter after 9 to 12 months. The temperature range for maximum growth of lichen fungi is 14 to 28°C, the optimum pH is 4.5 to 7.4 and light has no influence. Most isolated mycobionts do not produce spores and are, therefore, difficult to relate to free-living fungi. The synthesis of lichen established the controversy regarding the dual nature of the lichen thallus.
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