E. V. Wulff —198— Historical Plant Geography 



possess a number of characters indicating that they are undoubtedly 

 closely related to the species of Australasia, a circumstance undoubtedly 

 attesting a former trans-Antarctic connection between these two an- 

 cestral centers. The two new species from the Philippines are very 

 close in their morphological characters to the Japanese species, partic- 

 ularly those from Formosa. The latter, in turn, are closely related to 

 E. horneensis (Mt. Kinabalu, Borneo), but the characters which they 

 have in common are not shared by the Philippine species. E. horneen- 

 sis, in its turn, shows close relationship with species growing in the 

 mountains of New Guinea, where the genus Euphrasia became con- 

 siderably more differentiated than in Borneo or the Philippines. 



"The tropical species of Euphrasia occurring on the high mountains of New Guinea, 

 Borneo, Luzon, and Formosa thus obviously form a natural connection and a gradual 

 transition between the austral and the boreal parts of the genus" (Du Rietz, 1931, p. 529). 



The data assembled by Du Rietz led him to the assumption that 

 "the tropical £w^/?ra5ia-population ... is not only the result of acci- 

 dental colonization of isolated tropical mountains by species from the 

 main distribution areas of the genus in the north and in the south, and 

 the subsequent transformation of these species into the present tropical 

 species, but that these tropical species are really remains of the old 

 bridge once forming a more continuous connection between the boreal 

 and the austral populations of the genus. In Euphrasia this trans- 

 Malayan bridge . . . has obviously been the only connection between 

 the boreal and the austral parts of the genus. The present distribution 

 of the genus Euphrasia, together with the entire lack of traces of a direct 

 relationship between the widely separated North American and South 

 American £M/'/zra5za-populations, clearly shows that the Andean 

 trans-tropical bridge, so important in many other bipolar genera . . . 

 has never been in use in this genus. On the other hand, there is a very 

 distinct relationship between the South American population and the 

 populations of Tasmania and New Zealand" {Ibid., pp. 531-532). This 

 last-mentioned circumstance clearly indicates that in the past there 

 existed a trans-Antarctic connection between South America and 

 Australasia. 



Of exceptional interest is the discovery by Skottsberg in the sub- 

 alpine belt of Juan Fernandez of a single species, E. formosissivia, en- 

 demic to this island. Most remarkable is the fact that this species shows 

 close af&nity not to the South American species but to the Australasian 

 species, particularly those of New Zealand. Analogous relationships 

 are found as regards the Juan Fernandez species of several other 

 genera, e.g., Halorrhagis, Ranunculus, Coprosma, and Santalum, which 

 indicates the former existence of a direct connection between this island 

 and the islands of the western part of the Pacific. Thus, we seem to 

 have here fragments of a former trans-Pacific land-bridge. 



Du Rietz {loc. cit., p. 538) considers that Wegener's theory with 

 "its absurd phytogeographical consequences" cannot provide an 

 explanation of the foregoing facts. Despite the interest and importance 

 of the data presented by Du Rietz, his conclusions are too categorical. 

 His data show the need of further research on the theory of continental 

 drift, but touching, as they do, only one of its propositions, they cannot 

 serve as grounds for discarding the theory as a whole. 



