332 



C. SKOTTSBERG 



Selbst bei Inseln, die erst in relativ junger Zeit vom Festlande abgetrennt worden 

 sind, ist ein weiterer Austausch der Florenelemente zum mindesten wesentlich erschwert 

 und eine weitere Zuwanderung von Elementen der Festlandsflora wenig wahrscheinlich. 



If this be true, liow was immigration over thousands of miles ever possible? 



Several writers who have paid special attention to Pacific problems occupy, 

 more or less dogmatically, the same standpoint as Hayek. Setchell, with whom 

 I had the privilege to discuss this subject on various occasions, was already quoted 

 p. 271 ; I shall add here what he says, in the same paper, about migration {2ig. 300). 

 He found that I was "too narrow" in my allowances for migration possibilities; 

 he believed in "migration over very considerable breadth of barrier, whether of 

 sea or land", and absence was not a result of failure to migrate successfully, but 

 could be explained by obstacles to establishment. He regarded the oceanic islands 

 as Tertiary, but in his summary pp. 307-309 admitted the possibility of their 

 being considerably older, late Mesozoic or early to middle Tertiary, which would 

 give time for extensive progressive evolution of endemic taxa and for the dying- 

 out of their continental ancestors; or they had developed in other directions, 

 making the relationships difficult or impossible to recognize. Geologists, however, 

 refuse to give even the Hawaiian Islands a greater age than late Tertiary or even 

 Pleistocene. It goes without saying that travel facilities are difterent in different 

 cases; spore-plants are supposed to spread more freely than seed-plants, but even 

 these are supposed to be quite capable. Thus Stebbins C?/^. 537): 



The seeds of plants may occasionally be transported over many hundreds of miles 

 of ocean and may establish themselves on Oceanic islands like Hawaii, Juan Fernandez, 

 St. Helena and the Canary Islands. 



Florin has, he writes, shown that conifers of the south hemisphere have migrated 

 freely from Australasia to South America and vice versa, whereas mammals are 

 unable to pass and are absent from oceanic islands — but is it not customary to 

 place them on a par.? Stebhins' Antarctic connection does not include land-bridges, 

 for "it existed for plants, but not for vertebrates" (but what about birds.-). He 

 looks for assistance in lost islands between Antarctica and New Zealand; on the 

 opposite side the width of open water is not so great, and seeds can still be carried 

 from South America to Antarctica without much difficulty. 



As mentioned before, no botanist has greater confidence in long-distance dis- 

 persal than FOSBERG: 



. . . transoceanic migration across at least 2500 miles without stepping-stones is not 

 only a possibility but a relatively common occurrence (99.867). 



FoSBERG's subject was the American element in the Hawaiian flora, but in order 

 to explain the presence of the dominant Australasian element we must count with 

 still greater distances. Axelrod [14) quoting FoSBERG takes a modified position. 

 In case of distances not exceeding some 200 or 300 miles there are no difficulties, 

 a complete flora can transgress such a barrier without the loss of any significant 

 floristic units". A greater distance results in "waif assemblages", but many will 

 find it impossible to regard e.g. the Hawaiian flora as a haphazard accumulation 



