What is lichen?



The lichens are usually regarded as difficult forms. In younger stages they occasion no trouble, but an old apothecium or a leathery thallus often fails to cut well. Satisfactory sections could be obtained from thalli and mature apothecia of Physcia, Usnea, Sticta, Parmelia, and Peltigera. Collema and other lichens of such gelatinous consistency, while they cut readily, show a strong tendency to wrinkle.

Cyanin and erythrosin is a very good stain for lichens. The algae stain blue and the filaments of the fungus take the red. Where the association of the alga and the fungus is rather loose, as in Dichonema, more satisfactory mounts can be made by staining in eosin, or haem-alum and eosin, and then teasing slightly with needles and mounting in glycerin.





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