=Group 2.= Substances which also form red products with CaCl, but do not break up into orsellinic acid. Among the most noteworthy are olivetoric acid (C₂₁H₂₆O₇), a constituent of _Evernia furfuracea_, perlatic acid (C₂₈H₃₀O₁₀) and glabratic acid (C₂₄H₂₆O₁₁), which are obtained from species of _Parmelia_. =Group 3.= Contains three acids of somewhat restricted occurrence. They do not form red products with CaCl, and they yield on splitting everninic acid. They are: evernic acid (C₁₇H₁₆O₇), found in _Evernia prunastri_ var. _vulgaris_, ramalic acid (C₁₇H₁₆O₇) in _Ramalina pollinaria_, and umbilicaric acid (C₂₅H₂₂O₁₁) in species of _Gyrophora_. =Group 4.= The numerous acids of this group are not easily soluble and have a very bitter taste. They are not coloured by CaCl; when extracted with concentrated sulphuric acid, the solution obtained is reddish-yellow or deep red. Among the most frequent are fumarprotocetraric acid (C₆₂H₅₀O₃₅), the bitter principle of _Cetraria islandica_, _Cladonia rangiferina_, etc., psoromic acid (C₂₀H₁₄O₉), obtained from _Alectoria implexa_, _Lecanora varia_, _Cladonia pyxidata_ and many other lichens, and salazinic acid (C₁₉H₁₄O₁₀), recorded by Zopf as occurring in _Stereocaulon salazinum_ and in several _Parmeliae_, but now found by Lettau[829] to be very wide-spread. He used micro-chemical methods and detected its presence in 72 species from twelve different families. The distribution of the acid in the thallus varies considerably. =Group 5.= This is called the atranorin group from one of the most important members. They are colourless substances and, like the preceding group, are not affected by CaCl, but when split they form bodies that colour a more or less deep red with that reagent. Atranorin (C₁₉H₁₈O₈) is one of the most widely spread of all lichen-acids; it occurs in Lecanoraceae, Parmeliaceae, Physciaceae and Lecideaceae. Barbatinic acid (C₁₉H₂₀O₇), another member, is found in _Usnea ceratina_, _Alectoria ochroleuca_ and in a variety of _Rhizocarpon geographicum_. A very large number of acids more or less fully studied belong to this group. SUBSERIES II. ANTHRACENE DERIVATIVES The constituents of this subseries are derived from the carbohydrate anthracene, and are characterized by their brilliant colours, yellow, red, brown, red-brown or violet-brown. So far, only ten different kinds have been isolated and studied. Parietin[830] (C₁₆H₁₂O₅), one of the best known, has been extracted from _Xanthoria parietina_, _Placodium murorum_ and several other bright-yellow lichens; solorinic acid (C₁₅H₁₄O₅) occurs in orange-red crystals on the hyphae of the pith and under surface of _Solorina crocea_; nephromin (C₁₆H₁₂O₆) is found in the yellow medulla of _Nephromium lusitanicum_; rhodocladonic acid (C₁₂H₈O₆ or C₁₄H₁₀O₇) is the red substance in the apothecia of the red-fruited _Cladoniae_.