Antarctic Plants in Polynesia 307 



riers; it is endemic, but close to two Magellanic species, and may 

 be only an isolated part of one collective species. If this be right 

 — and the behavior of another species, A. adscendens, strength- 

 ens the opinion — we conclude that oversea dispersal is a rare 

 phenomenon; otherwise we should not find one uniform sub- 

 species in South Georgia, another in Kerguelen, etc. We cannot 

 very well believe that the seeds of a species A give rise to A only 

 as long as they germinate in the island which it inhabits and that, 

 if they are carried to other islands, they yield B or C or D instead 

 of A; but we may believe that special types from a large and 

 polymorphous population may become isolated in islands or on 

 mountains where they are recognized as endemic varieties. Of 

 course, the profoundly endemic species of Astelia, Gunnera, Co- 

 prosma, etc., require further explanation. Returning to Acaena, 

 it is one thing to presume that A. adscendens obtained its pres- 

 ent area in postglacial time with the aid of migrating birds, and 

 another to conclude that the genus Acaena has conquered the 

 southern hemisphere in the same manner, leaving relict endemic 

 sections and species to bear witness to a traffic long suspended. 

 Not rapid transportation across oceans, but slow migration over 

 land of an already differentiated genus, with isolation and dying- 

 out processes, accounts for this kind of endemism. 



Uncinia resembles Acaena. The hooked rhachilla is an effec- 

 tive dispersal organ, and there is nothing supernatural in the 

 way some species have traveled. However, the jump of U. ru- 

 pestris from New Zealand to the Philippine Islands is quite 

 astonishing and almost without parallel, matched only by the 

 occurrence of U. uncinata in Hawaii. 



Lagenophora has small adhesive achenes without any pappus, 

 which suggests epizoic dispersal of such wide-ranging species 

 as L. Billardieri and one or two subantarctic ones. Other species 



