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258 G. Einar D'u Rietz>>Es werden a]so auch in der Zeit der stärksten Abkiihlung verhältnismässig nur wenigewirkliche Hochgebirgsarten imstande gewesen sein, vom N orden kommend die Senkungsgebieteim Zuge der mittelamerikanischen Kordillere zu iiberschreiten. Denn sonst miisstezwischen der nord- und mittelamerikanischen Hochgebirgsflora und der der Anden ein vielergiebigerer Austausch zustande gekommen sein. Material fiir solchen Austausch hätteder Norden sichedich geboten.>> (DIELS 1937, pp. 41-42.)For the bipolar species of South America, ALEOFF (1902) assumed a Pleistoceneimmigration from the north with the aid of alternating boreal and austral glaciations,a tbeory adopted by DARWIN in later editions of bis >>Origin of species>> andby V\T ALLACE, but rejccted by recent gladolagists (cf. 0ALDENIUS 1932). SKOTTSEERG(1916) critisized ALEOFF and v. IHERING (1893), sbowing tbat the latter had obviouslygone too far in denying the existence of any boreal element in the flora of the Andes.SKOTTSEERG's own views were summarized as follows: >>Dass der Sprung zwischenden mexikanischen Bergen und den närdliebsten Abscbnitten der Kordillera grossist, wissen wir alle; schwer wäre zu versteben, wie die barealen Gebirgspflanzenohne Hilfe von den Anden und von der Eiszeit nach dem Feuerlande wanderten>>(SKOTTSEERG 1916, p. 340).HULTEN (1937, p. 103) believed tbat some of bis >>arctic-montane plants>>, whichoccurred in Soutb America, >>were apparently enabled to pass the tropics duringone of the glacials>>, adding to this statement that >>the intermediate stations vanishedduring the interglacials>>. STEFFEN (1939) disenssed the bipolar species(sens. lat.) of South American vaseular plants from the epeirophoretic point ofview. He came to the conclusion that the species in question had migrated alongthe Cordillera during Pleistocene glaciations, though >>die Wanderung der betreffendenArten nicht ohne Schwierigkeiten vor sich ging>> (p. 558).The present author (Du RIE'l'Z 1926 b, 1929), in disenssing the bipolar elementof the N e w Zealand flora, pointed out t hat even if no attention is payed to borealgenera f o und in Tertiary d epasits of N e w Zealand, >>t here is no reason to as sign themigration of the bipolar units in question to a period as late as the glacial period,because there seems to be no reason to assume any considerably better connectionsbetween N e w Zealand and the northern hemispbere during that period, neither onthe direct northern route nor via the antarctic continent, which was then stillmore completely glaciated than now>> (translation from Du RrETZ 1926 b, p. 301).Opposing the current theory of an immigration of the South American bipolarelement during the Pleistocene glaciations, I added in my later paper (1929, p. 633):>>Already the occurrence of N othofagus in Antarctic ertiary deposits shows that thebipolar element must be much older. And to get an increased Antarctic connectionbetween South America and New Zealand we must certainly go back, not to aperiod colder, but to one warmer, than the present one, that is, at least to the 'l'ertiarytime. Not only the areas of the rainforest species at present common to SouthAmerica and N e w Zealand, b ut also those of moderately alpine lichen s like Cetrariaislandica cannot possibly have been connected during any period later than theTertiary.>> After summarizing the particularly instructive Chloronephrorna case