E. V. Wulff — 180 — Historical Plant Geography 



All the foregoing forces us to assume that the continents in past 

 ages must have been differently situated with respect to the poles. A 

 way out of all these diificulties in the geography of plants of former 

 geological periods is provided, as we stated above, by Wegener's 

 theory of continental drift, in the light of which the climates of former 

 geological periods receive an entirely different explanation. A detailed 

 exposition of this viewpoint is given by Koppen and Wegener (1924) 

 in a special work devoted to this problem. According to these in- 

 vestigators, in the Carboniferous period the equator passed through 

 North America (from the southwest to the northeast), central Europe, 

 the Caspian Sea, Asia, and the Sunda Isles. Central Europe was, 

 therefore, included in the zone of equatorial rains, and it was, over 

 much of its extent, submerged beneath the sea. Consequently, the 

 Carboniferous deposits of central Europe must be of tropical origin; 

 this is confirmed by the finding in such deposits of plants of the type 

 of Pecopleris. Thus, the riddle of the finding in the Carboniferous de- 

 posits of central Europe of tropical flora lacking periodicity of growth 

 is solved, and the assumption that the continents were formerly united 

 explains the uniformity of climatic conditions over a considerable part 

 of their territory. The theory of continental drift makes possible a new 

 way of explaining problems involved in the paleogeography of plants, 

 just as it aids in clearing up many formerly inexplicable facts in zoo- 

 geography. 



The location of climatic zones in past geological periods was, ac- 

 cording to Wegener's theory, not at all the same as now; only 

 gradually, beginning with the second half of the Tertiary period, did 

 these zones begin to assume their present location. The shiftings of the 

 climatic zones were accompanied by shiftings of floras, particularly on 

 both sides of the Atlantic, in North America and Euro-Africa. Asia, 

 on the other hand, suffered climatic changes to a considerably less 

 degree, due to the fact that here the shiftings of the zones took place 

 not symmetrically and in a circumpolar direction but asymmetrically. 

 There are numerous facts both of a paleontological and of a floristic 

 and faunistic character, long since noted by many investigators, that 

 attest the relative constancy of the floras and faunas in the eastern part 

 of the tropics of the Old Worid and, in particular, in the region of the 

 Sunda Isles and eastern Asia. Thus, numerous Tertiary coal deposits 

 have been found on the East-Asiatic coast and also on adjacent islands, 

 e.g., in the Soviet Far East (northern Sakhalin, Amur and Ussurian 

 Regions), Manchuria, southern China, the Philippines, Java, Sumatra, 

 and Borneo. According to data of Dutch geologists, there have been 

 found on the Sunda Isles coal deposits from all stages of the Tertiary- 

 period. These facts, as well as the finding of species of palms in a fossil 

 state, led Koppen and Wegener to the conclusion that throughout 

 this region there has been a humid, tropical climate at least since the 

 beginning of the Tertiary period. 



Irmscher (1922, 1929), on the basis of Ettingshausen's data, draws 

 attention to the presence in the composition of the flora of this region 

 not only of families but also of genera likewise found there in a fossil 

 state. This has been confirmed by data of other paleobotanists, such 

 as KuBART (1929) and Krausel (1929). Merrill (1923), on the basis 



