1899] ORIGIN OF AUSTRALIAN FLORA 20 



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flora necessarily have been peculiar and isolated ? If there is one 

 point on which students of biological geography are agreed it is this, 

 that the antarctic continent must formerly have extended considerably 

 farther north than it does now, an extension which permitted the 

 migration of certain animal forms from South America to New 

 Zealand, and must equally have allowed the southward migration of 

 South American and New Zealand plants. This stocking of the 

 antarctic continent may have occurred comparatively early in Tertiary 

 times, and so long as glaciation did not supervene, a large and by no 

 means peculiar or isolated flora may have flourished in the antarctic 

 continent. But now, communication with lands lying to the north 

 being cut off, if a glacial period occurred, the result in the southern 

 hemisphere would be very different from one in the northern, for 

 while in the latter there would be nothing to hinder the southward 

 migration of plants, their escape from the antarctic continent would 

 be cut off by the ocean, and since all antarctic lands must have been 

 covered with an ice-cap during a glacial period, all, or almost all, but 

 the lowliest organisms must necessarily have perished. Obviously the 

 nature of the flora of the antarctic continent previous to the last 

 glacial period must have depended upon the occurrence or no of a 

 glacial period or of glacial periods intercalated between the last of 

 such periods and the stocking of the continent when it was in connec- 

 tion or close relation with lands to the north. If no such period 

 intervened, then the flora must have consisted of a mixture of South 

 American, New Zealand, and possibly to some extent of Australian 

 types, or of descendants from such, together with endemic genera, of 

 which many, for all that we know, may have been identical with 

 genera characteristic of northern lands. But if a glacial period was 

 intercalated, and that after the connecting lands to the northward had 

 disappeared beneath the waves, then the flora of the antarctic con- 

 tinent during the subsequent warm period must have been closely 

 similar to that of other antarctic lands, since it would have been 

 derived from the same source or sources ; while if the connection with 

 lands to the north was still open at the commencement of the interca- 

 lated glacial period or periods, the antarctic flora would have migrated 

 northward, and, the connection being still maintained, would have 

 advanced southward on the return of warmer conditions, so that it 

 would have borne approximately the same fades after as before the 

 glaciation of the continent. If this reasoning be sound, therefore, in 

 no event does it seem likely that the antarctic flora could have been 

 in any special sense isolated and highly peculiar. 



As an instance of the way in which the brief — if the term may be 

 allowed without offence — for the predominance of the northern flora has 

 been handled, I shall cite the assumption that glaciation first affected the 

 northern hemisphere. Let us hear Mr. Darwin. After ' alluding to 

 the southward migration of species when glacial conditions obtained 



