Fossils preserved in either of the modes, (_a_) or (_b_), usually show more or less of their minute structures under the microscope. These may be observed:--(1) By breaking off small splinters or flakes and examining them, either as opaque or as transparent objects. (2) By treating the material with acids, so as to dissolve out the mineral matters, or portions of them. This method is especially applicable to fossil woods mineralised with calcite or pyrite. (3) By grinding thin sections. These are first polished on one face on a coarse stone or emery hone, and then on a fine hone, then attached by the polished face to glass slips with a transparent cement or Canada balsam, and ground on the opposite face until they become so thin as to be translucent. In most cities there are lapidaries who prepare slices of this kind; but the amateur can readily acquire the art by a little practice, and the necessary appliances can be obtained through dealers in minerals or in microscopic materials. Very convenient cutting and polishing machines, some of them quite small and portable, are now made for the use of amateurs. In the case of exogenous woods, three sections are necessary to exhibit the whole of the structures. One of these should be transverse and two longitudinal, the latter in radial and tangential planes. IV.--GENERAL WORKS ON PALÆOBOTANY. In the text frequent reference has been made to special memoirs and reports on the fossil plants of particular regions or formations. There are, however, some general books, useful to students, which may be mentioned here. Perhaps the most important is Schimper's "Traité de Paléontologie Végétale." Very useful information is also contained in Renault's "Cours de Botanique Fossile," and in Balfour's "Introduction to Palæontological Botany," and Nicholson's "Palæontology." Unger's "Genera et Species," Brongniart's "Histoire des Végétaux Fossiles," and Lindley and Button's "Fossil Flora," are older though very valuable works. Williamson's "Memoirs," in the "Philosophical Transactions," have greatly advanced our knowledge of the structures of Palæozoic plants. Lastly, the "Palæophytology" of Schenk, now in course of publication in German and French, in connection with Zittel's "Palæontology," is an important addition to manuals of the subject. INDEX. Acer, 228. Acrogens, 6. Agassiz, Prof., 16. Alaska, Flora of, 245. Algæ, real and spurious, 26, 230. Amboy clays, Flora of, 203. America, Cretaceous of, 190. Angiosperms, 6. Annularia, 122. Anogens, 6. Antholithes, 132. Aporoxylon, 25. Araucarioxylon, 148. Araucarites, 134. Archæocalamites, 170. Archæopteris, 77, 85. Arctic origin of plants, 221, 238. Arthrophycus, 30. Arthrostigma, 67. Asterophyllites, 78, 122, 170. Asteropteris, 77, 85. Astropolithon, 30. Atané, Plants of, 242, 281. Atanekerdluk, Plants of, 283. Australia, Palæozoic flora of, 147. Tertiary flora of, 217.