332 C. SKOTTSBERG 



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

 sind, ist ein weitcrer Aiistaiisch der Florenelemente zum mindesten wesentlich erschwert 

 iind eine weitere /uwandcriing von Elementcn der Festlandsflora wenig wahrscheinlich. 



If tliis be true, lunv was immigration over tbousands of miles ever possible? 



Several writers who have {)aid special attention to Pacific problems occupy, 

 more or less do^^matically, the same standpoint as Havek. Setciiell, with whom 

 I had the j)ri\ile<;e to discuss this subject on various occasions, was already quoted 

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

 He found that 1 was "too narrow" in my allowances for migration possibilities; 

 he belie\ed 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 Tertiar)', but in his summary pp. 307-309 admitted the possibility of their 

 being considerabl}' 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 difi'erent 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 (ji'p. 537): 



'{"he seeds of j)lants 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. 



r'l.oKiN has, he writes, shown that conifers of the south hemisphere have migrated 

 freely from Australasia to South Ainerica and vice versa, w-hereas mammals are 

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

 place them on a j)ar.' S'lEHl^.lxs' 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 

 o{)|)osite side the width of oj)en 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 h'()Siii;K(; : 



. . . transo(eani<; migration across at least 2500 miles without stej^ping-stones is not 

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



Im)SI!I:i<(.s subject was the American element in the Hawaiian flora, but in order 

 to exj)lain the j)resence f)f the dominant Australasian element we must count with 

 still gieater distances. AxKl.RoD (7^) quoting F'o.SBERG takes a modified position. 

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

 "a coni|)]ete 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 



