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Problems of Bipolar Plant Distribution 243Fig. 12. Distribution of Azorella selaga Hook. f. Three main distribution areas: one in Tierradel Fuego and the Falkland Islands, one in the Kerguelen group, and one in Macquarie Island.Compiled from available literature by G. E. Du Rietz.of being traced back at some time in their history to the northern hemisphere. Itis easy on this supposition to account for their possession of common characterswhich, in their widely scattered southern distribution, is not readily explained onother grounds.>> (p. 441.) The hypothesis of TmSELTON-DYER was reviewed withfriendly neutrality (not accepted, as DRUDE believed) by HoOKER (1881, p. 737)and adopted by DRUDE (1887, pp. 195-201). In 1910, it was summarized by THI­SELTON-DYER (p. 311) in the following suggestive words: >>The extraordinary congestionin species of the peninsulas of the Old World points to the long-continuedaction of a migration southwards. Each is in fact a cul-de-sac into which they havepoured and from which there is no escape.>> According to this hypothesis, the affi-