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120 120 BIBLIOGRAPHY. constituting (the author considers), with great probability, the male organs of the Lichens. 5, the pycnidia, which Tulasne considers to be supplementary sporiferous organs, which resemble the sper- mogonia in form, in their eoncepiaclcs, and in the mode of insertion of the organs called slylospores, which they produce, but which latter are less numerous than the spermatia, of a much larger size, and capable of germination. The seventh chapter contains a recapitulation of the anatomical elements of Lichens ; the eighth chapter treats of their chemical properties and uses; the ninth, of their specific characters; and the tenth, of their classification. M. Nylander divides the Lichens into three families : the Col- lemacei, the Myriangiacei, and the Lichenacei. The Collemacei are distinguished by their heavy, dark colour, and by the structure of their thallus, which is rarely cellular, and is usually gelatinous, contain- ing gonimic granules, scattered or in rows. The Myriangiacei com- prise only two species of the genus Myriangium. They resemble the Collemacei in their external form and colour, but in their thalline tissue and thalamial tissue are nearer the Lichenacei: Their spheroidal thecse are always arranged irregularly, and are sometimes superposed in two or three rows. The Lichenacei are divided into six series : 1. theEpiconiodei, in which the spores, when they have escaped from the thecaB, accumulate like powder on the surface of thehymenium ; 2, the Cladoiiiodei, or Lichens with a stipitiform thallus, usually fruticulose, and furnished with squamules or folioles, with lecideine and convex apothecia (apothecia cephaloidea) ; 3, the Ramalodei, or Lichens with a fruticulose thallus, compressed or cylindrical, without squamules, and with fruit generally lecanorine and flat ; 4, the Phyllodei, or Lichens with a foliaceous thallus, and usually lecanorine apothecia, with jointed sterigmata ; 5, the Placodei, or Lichens with a crustaceous thallus and lecanorine lecideine, or lirelliform apothecia ; 6, the Pyrenodece, or Lichens with a peltate thallus or a crustaceous thallus, sometimes without any thallus, with pyrenocarpous apothecia, either immersed in the thallus, or more or less naked. A table of the families, series, tribes, and genera, is added. The eleventh chapter treats of the geographical distribution of Lichens. After this follows the systematic portion of the work, written in Latin, containing descriptions and synonyms of species, with indications of their geographical distribution. The two fascicles already published include the Collemacei and the Myriangiacei, and the first four series of the Lichenacei, with the exception of the tribes Gyrophorei and Pyxinei, which, with the series Placodei, which includes the tribes Lecanorei, Lecidinei, Xylographidei, and Graphidei, are to be dealt with in the forthcoming concluding parts. There are eight plates accompanying the two fascicles already published, giving illustrations of the genera, and of a certain number of species.