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Show 68 BOTANICAL GEOGRAPt-IY· [Ch. V. d P pro uccs lants of different species; and it is . not by the diversity of climates that we can attempt to explam why equi. noctial Africa has no laurinire, and the New World no heaths; why the calceolarire are found only in t~e southe:n hemisphere; why the birds of the continent of India glow With .colours less splendid than the birds of the hot parts of Amenca ; finally, why the tiger is peculiar to Asia, and the ornithorhynchus to New Holland *'. "We can conceive, he adds, that a small number of the families of plants, for instance the musacere and the palms, cannot belong to very cold regions, on account of their internal structure and the importance of certain organs; but we cannot explain why no one of the family of melastomas vegetates north of the parallel of thirty degrees; or why no rose-tree belongs to the southern hemisphere. Analogy of climates is often found in the two continents without identity of productions t ." L'l- The luminous essay of Decandolle on " Botanical Geography" presents us with the fruits of his own researches and those of Humboldt, Brown, and other eminent botanists, so arranged, that the principal phenomena of the distribution of plants are exhibited in connexion with the causes to which they are chiefly referrible +· " It might not, perhaps, be difficult," observes this writer, '' to find two points, in the United. States and in Europe, or in equinoctial America and Africa, which present all the same circumstances: as for ex· ample, the same temperature, the same height above the sea, a similar soil, an equal dose of humidity, yet nearly all, perhaps all, the plants in these two similar localities shall be distinct. A certain degree of analogy, indeed, of aspect, and even of structure, might vet·y possibly be discoverable between the plants of the two localities in question, but the species would in general be different. Circumstances, therefore, difl'erent from those which now determine the stations, have had an influence on the habitations of plants." * Pers. Narr., vol. v. p. 180. t Ibicl. t Essai Elementaire de Geographie Botanique, E~trait du 18e vol. du Diet, des Sci. N ~t. Ch. V.J STATIONS AND IIABITATIONS OF PLANTS. 69 As we shall frequently have occasion to speak of the stations and habitations of plants in the technical sense in which the terms are used in the above passage, we may remind the geological reader that station indicates the peculiar nature of the locality where each species is accustomed to grow, and has reference to climate, soil, humidity, light, elevation above the sea, and other analogous circumstances; whereas by habitation is meant a general indication of the country where a plant grows wild. 'l'hus the station of n plant may be a salt-marsh, in a temperate climate, a hill-side, the bed of the sea, or a stagnant pool. Its habitation may be Europe, North America, or New Holland between the tropics. The study of stations has been styled the topography, that of habitations the geography of botany. The terms thus defined, express each a distinct class of ideas, which have been often confounded together, and which are equally applicable in zoology. In further illustration of the principle above alluded to, that difference of longitude, independently of any influence of temp~ rat~re, ~s accompanied by a great, and sometimes a complete diversity lll the species of plants, Decandolle observes, that out of two thousand eight hundred and ninety-one species of phanerogamic plants described by Pursh, in the United States, there are only three hundred and eighty-five which are found in northern or temperate Europe. MM. Humboldt and Bonpland, in all their travels through equinoctial America, found only twenty-four species (these being all cyperacea and graminea) common to America and any part of the Old 'Vorld. On comparing New Holland with Europe, Mr, Brown ascertained that out of four thousand one hundred species, disc~ vered in Australia, there were only one hundred and sixtysix common to Europe, and of this small number there were some which may have been transported thither by man. Most of the others belong to those classes which are provided with the most ample means of dispersion to vast distances. But it is still more remarkable, that in the more widely separated parts of the ancient continent, notwithstanding the |