one climate to another, provided there is no sudden change of temperature to check their progress[1]; that is to say, if in each climate the difference between the extremes is the same, small, and that change slow; and that we may expect the range of individual species to increase with the uniformity of the temperature throughout the year.
The above observations have been drawn chiefly from a consideration of the antarctic American Flora, which is the only one sufficiently investigated hitherto for this purpose. The plants of the Middle Island of New Zealand are only known from the collections of Banks and Solander, Forster and Menzies, which were made in Queen Charlotte's Sound and Dusky Bay, chiefly in the latter; those of the Southern or Stewart's Island are entirely unknown; the Northern Island maybe considered as pretty well explored, but an aggregate of the whole shows the Flora of New Zealand to be in all probability the poorest of any country of its size situated in the same latitude. Though this group extends from lat. 34° to the 48th degree, the summers of the northern extremity are not scorching, nor the winters, in its southern, severe. It is true that its high mountains have been but partially explored; but botanists have ascended them, as Mr. Bidwill, Dr. Dieffenbach, and Mr. Colenso, in whose collections the amount of new forms from so considerable an altitude as that of 6-10,000 feet is very trifling, and the species brought by each person the same. In the immediate neighbourhood of Port Jackson, 400 species of flowering plants may be easily collected in four days' excursions; in the same time scarcely half that number would be detected in the Bay of Islands, very little to the southward of Sydney in latitude; and on extending the journeys further in each country to thirty or forty miles, the disproportion increases. A remarkable uniformity in the Flora pervades all the South Sea Islands, also accompanied with a singularly equable temperature. The change which an elevation of 10,000 feet produces in the Flora of Colombia is complete, and the number of species inhabiting the plains of Quito much exceeds that in the low forests of the west coast of America, in the same parallel; but though the volcanic islands of the Sandwich group attain a greater elevation than this, there is nosuch development of new species at the upper level.
Amongst the many branches of inquiry into which the science of Botanical Geography divides itself, that which concerns the comparative richness in species of countries similarly situated is a highly interesting one. An exuberant vegetation we find not to be necessarily the index of an extensive flora, nor is it in the most densely clothed spots that the greatest variety of forms is to be met with, but very often the contrary. Few lands we have seen are so deceptive in this respect as New Zealand and Tierra del Fuego; and on extending the inquiry, we further see that the sandy plains of Australia, the Cape of Good Hope, and the campos of central Brazil, are richer in species than the more luxuriant woods of those or most other countries.
Plate XLIV. & XLV. Fig. 1, a male flower; fig. 2, petal; fig. 3, stamen; fig. 4, pollen; fig. 5, imperfect ovarium of male flower; fig. 6, female flower with pedicel and bractea; fig. 7, ovarium from do.; fig. 8, ovule; fig.' 9, immature capsule; fig. 10, longitudinal, and fig. 11, transverse section of do.; fig. 12, ripe capsule, the valves burst open; fig. 13, side, and fig. 14, front view of a seed; fig. 15, transverse section of do., showing the outer membrane; fig. 16, albumen coated with the inner membrane removed from the outer; fig. 17, embryo:—all magnified.
- ↑ A familiar instance of the advantage of slow changes of temperature in enabling plants to endure transportation, is found in the application of Mr. Ward's glazed cases for transmitting plants to England through different climates. One of the main features of his philosophical contrivance is, that their construction induces a slow change of temperature in the atmosphere immediately surrounding the plants, and prevents their suffering from any sudden variations.
