INTRODUCTION TO THE REPORTS ON INSULAR FLORAS. 51 



the whole zone are associated in different parts of it. From our tabular views of the 

 distribution of the plants inhabiting the various groups of islands in the South Indian 

 Ocean, and the sketch of the flora of Macquarie Island a few pages forward, it is quite clear 

 that in the southern, as in the northern hemispere, the only admissible demarcation of the 

 coldest floral region is a zonal one. Proceeding northward in the three Great land areas, 

 the differences in the vegetation soon become so pronounced, that it is convenient to treat 

 them as distinct floral regions ; yet, apart from the Antarctic types, the relationships of 

 the distribution of other peculiarly southern types is highly interesting, and seems to point 

 to a migration northward, and a former greater land connection in the southern hemisphere. 

 Wallace, while discarding Hutton's theory of a great southern continent uniting New 

 Zealand and Australia with South America, and probably also with South Africa, suggests 

 the probability of a former less interrupted communication between Cape Horn and New 

 Zealand by way of the South Shetland Islands, Graham's Land, " whence the Antarctic 

 continent or a group of large islands probably extends across or around the south polar 

 area to Victoria Land, and thence to Adelie Land." And he assumes that there have been 

 alternations of climate within the Antarctic Circle, as within the Arctic, " during which 

 some portions of the now ice-clad lands became able to support a considerable amount of 

 vegetation." Assuming this to be a correct deduction, the greater difficulties encountered 

 in accounting for the present distribution of plants in the southern hemisphere disappear ; 

 for drifting ice and oceanic currents might well have conveyed seeds of the few plants 

 found in the islands of the South Indian Ocean, when they were less isolated from each 

 other than now. And, if we accept Dyer's theory of an original southward migration of 

 the forms of vegetable life from which all the southern ones have been derived, this 

 explanation is sufficient. But the evidence seems to point to a former greater land con- 

 nection than Wallace admits, and to a northward migration of southern forms which has 

 hardly ceased. Until more conclusive testimony is forthcoming of the former existence 

 of Proteacese, Eucalypti, &c, in Europe, we cannot avoid the conviction that they 

 originated in the south. 



Sir Joseph Hooker, discussing 1 the probable origin of the vegetation of Kerguelen 

 Island, says : " Turning to the natural agents, winds are no doubt the most powerful and 

 sufficient to account for the transport of the cryptogamic spores ; these, almost through- 

 out the year, blow from Fuegia to Kerguelen Island, and in the opposite direction only for 

 very short periods, but appear quite insufficient to transport seeds over 4000 miles. 

 Oceanic currents have, doubtless, brought the marine algse ; but the transport of the seeds 

 of the fresh-water plants, of the grasses, and of the two plants with hooked and barbed 

 appendages to the fruit, is not apparent in the -case of a country that has no land-birds 

 but an endemic one (Chionis), and of which the water-birds come to land only, or 

 chiefly, at the breeding season, and this after long periods of oceanic life in a most 

 1 Philosophical Transactions of the Royal Society of London, clxviii. p. 13. 



