560 LICHENS matter of the nature of mannite. One of the most useful nutritious species is Cetraria islandica, " Iceland moss," which, after being deprived of its bitterness by boiling in water, is reduced to a powder and made into cakes, or is boiled and eaten with milk by the poor Icelander, whose sole food it often constitutes. Similarly Cladina rangi- ferina and Cl. sylvatica, the familiar " reindeer moss," are frequently eaten by man in times of scarcity, after being powdered and mixed with flour. Their chief importance, however, is that in Lapland and other northern countries they supply the winter food of the reindeer and other animals, who scrape away the snow and eagerly feed upon them. Another nutritious lichen is the " Tripe de Roche " of the Arctic regions, consisting of several species of the Gyrophorei, which when boiled is often eaten by the Canadian hunters and Red Indians when pressed by hunger. But the most singular esculent lichen of all is the " manna lichen," which in times of drought and famine has served as food for large numbers of men and cattle in the arid steppes of various countries stretching from Algiers to Tartary. This is derived chiefly from Lecanora esculenta, which grows unattached on the ground in layers from 3 to 6 inches thick over large tracts of country in the form of small irregular lumps of a greyish or white colour. Speaking of the distribution of these nutritive lichens, whose qualities depend on the presence of amylaceous matter, Dr Lindsay (in Pop. Hist. Brit. Lich., p. 82) very appropriately remarks that, "by a beautiful provision of nature, they occur precisely under the circumstances where they are most wanted in northern or arctic countries, or on arid steppes, where grain stuffs are unknown, and food of a better kind is often scarce or deficient." In connexion with their use as food we may observe that of recent years in Scandinavia arid Russia an alcoholic spirit has been distilled from Cladina rangiferina and extensively con sumed, especially in seasons when potatoes were scarce and dear. Formerly also Sticta pidmonaria was much employed in brewing instead of hops, and it is said that a Siberian monastery was much celebrated for its beer which was flavoured with the bitter principle of this species. 3. Medicinal Lichens. During the Middle Ages, and even in some quarters to a much later period, lichens were extensively used in medicine in various European countries. Many species had a great repute as demulcents, febrifuges, astringents, tonics, purgatives, and anthelmintics. The chief of those employed for one or other, and in some cases for several, of these purposes were Cladonia pyxidata,. Usnea barbata, Ramalina farinacea, Evernia prunastri, Cetraria islandica, Sticta pulmonaria, Parmelia saxatilis, Phi/scia parietina, and Pertusaria amara. Others again were believed to be endowed with specific virtues, e.g., Peltigera canina, which formed the basis of the celebrated " pulvis antilyssus" of Dr Mead, long regarded as a sovereign cure for hydrophobia ; Platysma juniperinum, lauded as a specific in jaundice, no doubt on the similia similibus principle from a resemblance between its yellow colour and that of the jaundiced skin ; Peltidea apkthosa, which on the same principle was regarded by the Swedes, when boiled in milk, as an effectual remedy for the aphthae, or rash on their children. Almost all of these virtues, general or specific, were imaginary ; and at the present day, except perhaps in some remoter districts of northern Europe, only one of them is employed as a remedial agent. This is the "Iceland moss" of the druggists shops, which is undoubtedly an excellent demulcent in various dyspeptic and chest complaints. Probably also Pertusaria amara, from the intensely bitter principle which it contains, might still with propriety be employed as a febrifuge. No lichen is known to be possessed of any poisonous properties, although Cklorea vulpina is believed by the Swedes to be destructive to wolves when powdered and " mixed with pounded glass." Nor are lichens, as has sometimes been alleged, injurious to the trees upon which they grow, except to a very limited extent. Not being parasites properly so called, the only injury they can inflict upon them is by slightly interfering with the functions of respiration, or, when growing very crowdedly upon the branches of orchard trees, by checking the development of buds. Classification of Lichens. From the time of Acharius, the father of lichenological science, different authors have proposed different classifica tions of lichens, according to the degree of importance attached by them to one or other of their vegetative and reproductive organs. Most of these classifications, however, whether proposed by microscopical or pre-microscopical Hellenists, have been too artificial and arbitrary, and indeed less natural in various ways than that originally propounded by Acharius. Of recent years they have been entirely super seded by other two systems, viz., that of the Massalongo- Koerberian and that of the Nylanderian school. With respect to the former of these, its characteristic feature is the prominence which it assigns to the form and structure of the spores not only in the differentiation of species but also in the foundation of genera. Though it has been adopted, with various modifications, by many Continental lichenists, yet essentially it also proceeds on an artificial principle, and necessitates the adoption of far too many genera, distinguished from each other merely by slight differences in the spores. The other system that of Nylander, which was first proposed by him in his JEssai d une Nouvelle Classification des Lichens (1854-55), has since then commended itself more and more to the accept ation of lichenists, so that even the disciples of the opposite school (the sporologists) have in many respects gradually approximated towards it in their most recent writings. Not only is it the only complete system of classification yet wrought out ; it is also the most natural and philosophical of any hitherto propounded. In its main outline it proceeds upon the principle of showing the near relation of certain lichens to some genera of algae on the one hand, and of certain other lichens to some genera of fungi on the other hand, and connects these three great classes of cryptogams together by a sort of twofold chain, commencing with those genera of lichens nearest allied to the algte, working up to those genera best de veloped (Stictei), and thence retrograding and terminating with those nearest allied to the fungi. His genera also are principally founded, not upon a single special character, but upon the combined anatomical characters presented by the thallus, the apothecia, and the spermo- gones. It may here be further observed that we are indebted to the same accomplished Hellenist for the succinct but comprehensive diagnoses, generic and specific, of the different parts of a lichen, which have tended so much to facilitate their systematic study. The following is a conspectus of the Nylanderian classification of lichens, with the leading characters of the different families and tribes, and an enumeration of all the principal genera of which these are composed. Family I. Ephebacci, Nyl. Thallus but little turgid when moist, gonidial stratum consisting of gonimia which are tunicated ; medullary filaments none. Tribe 1. Sirosiphei, Nyl. Thallus filamentoso-fruticulose, gonimia variously connate. Apothecia biatorine or lecideine. Sper- mogones with sterigmata or arthrosterigmata. Genera : Sirosiphon, Ktz. ; Gonionema, Nyl. ; Spilonema, Born. Tribe 2. Pyrcnopsei, Nyl. Thallus thinly granulose, rubricose within, gonimia simple or connate. Apothecia lecanorine or pyrenocarpous. Spennogones with simplish sterigmata.
