OCR Text |
Show 416 ISLAND LIFE. (PAR'L' II. and Bourbon, where, originally, dense forest covered the en~ire surface, and perennial moisture, with its ever-accompanymg luxuriance of vegetation, prevailed. Flora of .Jfadagascar allied to that of Sm~th Africa.-In my Geographical Distribution of .Animals I have remarked on the relation between the insects of :Madagascar and those of south temperate Africa, and have speculated on a great southern extension of the continent at tho time when Madagascar was united with it. As supporting this view I now quote Mr. Bentham's remarks on the Compositre. He says : "The connections of the 1\-Iascarene endemic Compositre, especially those of Madagascar itself, are eminently with the southern and sub-tropical African races; the more tropical races, Pluch0inere, &c., may be rather more of an Asiatic type." He further says that the Composite flora is almost as strictly endemic as that of the Sandwich Islands, and that it is much diversified, with evidences of great antiquity, while it shows insular characteristics in the tendency to tall shrubby or aborescent forms in several of the endemic or prevailing genera. Preponderance of Ferns in the Mascarene Flora.-A striking character of the flora of these smaller Mascarene islands i8 the great preponderance of ferns, and next to them of orchidere. The following figures are taken from Mr. Baker's Plo?'a for· Mauritius and the Seychelles, and from an estimate by M. Frappier of the flora of Bourbon given in Maillard's volume already quoted:- .Mauritius, &c. Ferns ........................ .'.. 168 Orchidere....................... 79 Graminere..................... 69 Cyperacero... .. .. .. . . . . . .. . .. .. 62 Hubiacere...................... 57 Euphorbiacere................ 45 Compositro..................... 43 Leguminosre.................. 41 .l)ou1·bon. Ferns ..................... 240 Orchidere ................ 120 Graminere........... .... 60 Compositro............... 60 Leguminosm............ 36 Rubiacero................ 24 Cyperacero............... 24 Euphorbiaceoo.......... 18 The cause of the great preponderance of ferns in oceanic islands has already been discussed in my book on Tropical Nat,ure; and we have seen that Mauritius, Bourbon, and Rodriguez must be classed as such, though from their proximity to Madagascar they have to be cousidered as satellites to that great island. CHAP. XIX.] THE MADAGASCAH GLWUP. 4J7 The abundance of orchids may be in part due to analogous causes. Their usually minute and abundant seeds would be as easily carried by the wind as the spores of ferns, and their frequent epiphytic habit affords them an endless variety of stations on which to vegetate, and at the same time removes them in a great measure from the competition of other plants. When, therefore, the climate is sufficiently moist and equable, and there is a luxuriant forest vegetation, we may expect to find orchids abundant on such tropical islands as are not too far removed from other lands or continents from which their seeds might be conveyed. Concl~~din,q remaTlcs on Madagascar and the Masca1·ene Islands. -There is probably no portion of the globe that contains within itself so many and such varied features of interest connected with geographical distribution, or which so well illustrates the mode of solving the problems it presents, as the comparatively small insular region which comprises the great island of Madagascar and the .smaller islands and island-groups which immediately surround it. In Madagasca.r we have a continental island of the first rank, and undoubtedly of immense antiquity; we have detached fragments of this island in the Comoros and Alctabra ; in the Seychelles we have the fragments of another very ancient island, which may perhaps never have been continental ; in Mauritius, Bourbon, and Rodriguez we have three undoubtedly oceanic islands; w bile in the extensive banks and coral reefs of Cargados, Saya de Malha, the Chagos, and the Maldive Isles, we have indications of the submergence of many large islands which may have aided in the transmission of organisms from the Indian Peninsula. But between and around all these islands we have depths of 2,500 fathoms and upwa.rds, which renders it very improbable that there has ever been here a continuous laud surface, at all events during the Tertiary or Secondary periods of geology. It is most interesting and satisfactory to find that this conclusion, arrived at solely by a study of the form of the sea-bottom and the general principle of oceanic permanence, is fully supported by the evidence of the organic productions of the several islands; because it gives us confidence in those principles, and E E |