E. V. Wulfif — 194— Historical Plant Geography 



Irmscher's final conclusions may be summarized as follows: (i) In 

 order to understand the geographical distribution of plants, it is neces- 

 sary to assume a shifting of the poles, and, as a corollary to this proposi- 

 tion, a shifting of the climatic zones; (2) of all the hypotheses advanced 

 regarding the origin of our continents Wegener's theory is most closely 

 in accord with data on the distribution of angiosperms, and, hence, 

 these data serve as a proof of the theory. 



Wegener's theory is likewise substantiated by the data presented 

 by Lam in two papers (1932, 1934) devoted, respectively, to the floras 

 of the Malay Archipelago and New Guinea. In the former, which 

 constitutes a detailed, monographic study of the Burseraceae and of the 

 phylogenetic relationships between its component species, Lam (1932, 

 p. 300) comes to the conclusion that the primitive Burseraceae must 

 have originated in South America, in Brazil, whence, thanks to a con- 

 nection with West Africa and Eurasia that existed as late as the 

 Upper Cretaceous or even as the Lower Eocene stage, species of this 

 family reached eastern Asia and became established there, particularly 

 on the islands of the Malay Archipelago. From the point of view of 

 this investigator, the history of the Burseraceae and of their distribution 

 agree quite closely with Wegener's theory. 



Of very great significance in this connection is Shaparenko's paper 

 (1937) devoted to the past and present distribution of the tulip tree, 

 Liriodendron. This investigator had as his special aim to test We- 

 gener's theory on the basis of data on angiosperm distribution. His 

 work is of all the more value, since it is based not only on published 

 data but on a first-hand study of a number of collections of the fossil 

 remains of this plant. Liriodendron is represented at the present time 

 by only two species: the first, L. Tulipifera, is distributed throughout 

 the Atlantic section of the United States, from Florida to Michigan 

 (between the 30th and 45th parallels) ; the second, L. chinense, has^ a 

 more restricted area at about the same latitude but in eastern Asia, 

 not far from the Pacific Coast, in the Kiang-si Province of China. 



The first fossil leaves of the tulip tree are found in Cretaceous de- 

 posits in North America. The Cretaceous area of Liriodendron was 

 located in the southeastern part of North America, the center of the 

 area being at about the 30th parallel, according to the climatic zonation 

 given for this period by Koppen and Wegener. The eastern end of 

 the area lies a little south of this parallel and the western end a little 

 north of it. This is in accord with the present lack of full coincidence 

 between the isotherm and this parallel. 



By the beginning of the Upper Cretaceous Liriodendron attains its 

 greatest development in North America, but by the end of the Cre- 

 taceous period it has already become much poorer in number of species, 

 and from the Tertiary period no fossil remains at all have been found. 

 We have no data for judging as to whether this genus died out com- 

 pletely in America or whether, in connection with the onset of a much 

 warmer climate, which attained its maximum in America during the 

 Eocene stage, its area was shifted considerably farther north. The 

 latter supposition seems to us the more probable, despite the fact that 

 fossil remains of the tulip tree have not yet been found in Tertiary 

 deposits in America. 



