magnesia, sparingly soluble in cold dilute acetic acid. This com bination takes place between 180° and 200° C., at which temperatures the magnesian carbonate tends to pass into the still less soluble state of magnesite, in which, as we have shown, it no longer shows any disposition to unite with carbonate of lime. Hence it happens that in all our experiments a portion of magnesite is mingled with the dolomite, and cannot be completely separated from it. Dilute acids slowly attack both, but unequally, so that we finally obtain a residue which contains carbonate of magnesia free from lime: but the solution having taken up a portion of magnesite, contains more magnesia than is required to form a dolomite with the carbonate of lime; so that we have from 53.0 to 600 p. c. of magnesian carbonate instead of 450 as in pure dolomite. In nature the combination of the two carbonates has doubtless taken place slowly, and necessarily at the lowest temperature, which is probably much below 130° C., so that we may suppose that it is only in the absence of a sufficient quantity of carbonate of lime that a portion of the magnesian carbonate has been converted into magnesite. (To be concluded in the next No.) ART. XX.-Extract from the concluding part of a Memoir on the Botany of Japan, in its Relations to that of North America, and of other parts of the Northern Temperate Zone; by ASA GRAY.* It is interesting to notice that, notwithstanding the comparative proximity of Japan to Western North America, fewer of its species are represented there than in far distant Europe. Also,showing that this difference is not owing to the separation by an' ocean, that far more Japanese plants are represented in Eastern North America than in either. It is, indeed, possible that my much better knowledge of American botany than of European may have somewhat exaggerated this result in favor of Atlantic North America as against Europe, but it could not as against Western North America. If we regard the identical species only, in the several floras, the preponderance is equally against Western as compared with Eastern North America, but is more in favor of Europe. For the number of species in the Japanese column which likewise occur in Western North America, is about 120: in Eastern North America, 134; in Europe, 157. Of the 580 Japanese entries, there are which have corresponding European representatives, a little above 8.48 per cent of identical species, 0.27 Western N. American representatives, about 0.37 Eastern 66 66 0.20 46 0.61 66 " a 0.23 * Extracted from the Memoirs of the American Academy of Arts and Sciences, new series, vol. vi. So geographical continuity favors the extension of identical species; but still Eastern North America has more in common with Japan than Western North America has. The relations of this kind between the floras of Japan and of Europe are obvious enough; and the identical species are mostly such as extend continuously-as they readily may-throughout Russian Asia, some few only to the eastern confines of Europe, but most of them to its western borders. To exhibit more distinctly the features of identity between the floras of Japan and of North America, and also the manner in which these are distributed between the eastern and the western portions of our continent, after excluding those species which range around the world in the northern hemisphere, or the greater part of it, or (which is nearly the same thing in the present view), which are unknown in Europe,-I will enumerate the remaining peculiar species which Japan possesses in common with America: The names enclosed in parentheses are of species which I have not seen from Japan; some of them inhabit the adjacent mainland; some are imperfectly identified. Those marked * are high northern species in America. Of those 56 extra-European species, 35 inhabit Western, and 41 Eastern North America. And 15 are Western, and not Eastern; 21 Eastern and not Western; and 20 common to both sides of the continent. Eight or ten of these 56 species extend eastward into the interior of Asia. On the other hand, the only species which I can mention as truly indigenous both to Japan and to Europe, but not recorded. as ranging through Asia, are Euonymus latifolius, Pyrola media, Fagus sylvatica, Blechnum Spicant, Streptopus amplexifolius, Athyrium fontanum. Two of these species extend across the northern part of the American continent, and on to the Asiatic; another occurs on the northwest coast of America; and another, the Fagus, is represented in Eastern America by a too closely related species. It is noteworthy, that not one of these seven plants is of a peculiarly European genus, or even a Europao-Siberian genus ;while of the fifty-six species of the Americo-Japanese region wanting in Europe, twenty are of extra-European genera; seven teen are of genera restricted to the North American, East Asian, and Himalayan regions (except that Brasenia has wandered to Australia); fourteen of the genera (most of them monotypic) are peculiar to America and Japan or the districts immediately adjacent; one is peculiar to our northwest coast and Japan; and eight are monotypic genera wholly peculiar (Brasenia excepted) to the Atlantic United States and Japan. Add to these the similar cases of other American species (nearly all of them peculiarly Atlantic-American) which have been detected in the Himalayas or in Northern Asia, such as Menispermum Canadense (Dauricum, DC.), Amphicarpaea monoica? Clitoria Mariana, Osmorrhiza brevistylis, Monotropa uniflora, Phryma leptostachya, Tipularia discolor? &c.,-and it will be almost impossible to avoid the conclusion, that there has been a peculiar intermingling of the Eastern American and Eastern Asian floras, which demands explanation. The case might be made yet stronger by reckoning some subgeneric types as equivalent to generic in the present view, and by distinguishing those species or genera which barely enter the eastern borders of Europe; e. g. Cimicifuga fætida, Mæhringia lateriflora, Geum strictum, Spiræa salicifolia, &c. It will be yet more strengthened, and the obvious conclusion will become irresistible, when we take the nearly allied, as well as the identical, species into account. And also when we consider that, after excluding the identical species, only 15 per cent of the entries in the European column of the detailed tabular view are in italic type (i. e. are closely representative of Japanese species); while there are 22 per cent of this character in the American column. For the latter, I need only advert to some instances of such close representation, as of and many others of the same sort,-several of which, when better known, may yet prove to be conspecific; while an equally large number could be indicated of species which, although more positively different, are yet no less striking counterparts. To demonstrate the former proposition, I have only to contrast the extra-American genera common to Europe and Japan with the extra-European genera common to North America and Japan. The principal European genera of this category are Adonis, Epimedium, Chelidonium, Malachium, Lotus, Anthriscus, Hedera, Asperula, Rubia, Carpesium, Ligularia, Lampsana, Picris, Pæderota, Ajuga, Thymus, Nepeta, Lamium, Ligustrum, Kochia? Daphne, Thesium, Buxus, Mercurialis, Cephalanthera, Paris, Asparagus,-to which may as well be added Paonia and Bupleurum, the former having a representative on the mountains, and the latter in the arctic regions, of Western America, but both absent from the rest of our continent. Excepting Pæderota and Buxus (the latter a rather doubtful native of Eastern Asia), none of these genera are peculiar to Europe, but all extend throughout Asia and elsewhere over large parts of the world. The following incomplete list of North American genera or peculiar subgeneric types represented in Japan and its vicinity, but unknown in Europe, presents a very different appearance. Those which are absent from the flora of Western North America are italicised. Trautvetteria Philadelphus Cimicifuga (barely reaches Penthorum Illicium Cocculus & Menispermum F Hammelis Diervilla Mitchella Stuartia (& Gordonia?) Oldenlandia Cissus Ampelopsis Berchemia Sophora Asarum & Heterotropa Benzoin & Sassafras? Saururus Pachysandra (Siegesbeckia, in Mexico) Chamaecyparis |