E. V. Wulff —170— Historical Plant Geography 



(in Florida and North and South Carolina, in the Rocky Mountains, in 

 California, and in Mexico); the other group is found at a symmetri- 

 cally opposite point in eastern Asia (the Himalayas, Tibet, and the 

 Philippines). The area of one species, P. canariensis, growing in the 

 mountains of the Canary Islands, seems to be an outlying spur of 

 the former, more extensive range of this latter group. 



Of two relic species of pine found on the Balkan peninsula, Pinus 

 Pence and P. omorica, the former is related to the eastern white pine, 

 P. Strobus, of North America, and the latter to species of Manchuria 

 and Japan. We have here, therefore, a clear case of the breaking up 

 of a once-continuous area into two widely separated sections, one in the 

 east and one in the west. 



Analogous facts are likewise found in the distribution of angio- 

 sperms. For instance, the genus Magnolia has about 60 species, dis- 

 tributed in eastern Asia and in the Atlantic states of North America. 

 Liriodendron Tulipifera, another member of the magnolia family, also 

 grows both in China and in the Atlantic states of North America. The 

 genus Talauma, also of the Magnoliaceae, has 32 species in India, Java, 

 and the Philippines and 8 species in the New World (the West Indies, 

 Mexico, Central America, and the northern part of South America). 

 In a fossil state the Magnoliaceae are found in the outer arc of oscilla- 

 tion in deposits in Europe (beginning with the Cretaceous and ending 

 with the Pliocene stage) and as far north as Greenland and Spitsbergen. 



At first some biologists regarded the pendulum theory favorably, 

 since they hoped to find in it a solution to those inexpHcable features 

 of the distribution of organisms about which we have already spoken. 

 However, there are very serious objections to this theory which make 

 it impossible to adopt it even as a working hypothesis. The chief 

 objections are, first, that no cause can be found for such an oscillation, 

 and, second, that geological data are not in accord with this theory. 

 But even biologists advanced a number of serious objections, of which 

 we shall note the most important. The assumption made by Simroth 

 that Europe, as the region that has been most subjected to climatic 

 changes, has constituted the chief center of origin of new forms is 

 merely a h3^othesis without any foundation. It is more logical to 

 assume the exact contrary, since such great climatic changes as oc- 

 curred in Europe during the Ice Age resulted in the creation of nothing 

 essentially new. Europe, as compared with the other continents, is a 

 comparatively small territory, and during the Tertiary period it was 

 even smaller than now, so that it is difficult to believe that it con- 

 stituted the place of origin of most of the flora and fauna of the 

 world. Moreover, the existence of such centers of species-formation in 

 other continents, e.g., Asia, is beyond any doubt. Two other important 

 objections are that many of the facts in the distribution of organisms 

 cited by Simroth as caused by such oscillation of the earth may be 

 explained, without assuming such oscillation, on the basis of ecological 

 and edaphic data, and, lastly, that not all cases of discontinuous areas 

 can be explained by the horizontal or meridional migration of species. 



Nevertheless, the fact of symmetry in the discontinuous areas of 

 many species and the fact that the break in these areas occurs pre- 

 cisely in the Euro-African sector were quite correctly established by 



