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THE AMERICAN NATURALIST [Vol. XLVI 



tinct specific and allied generic forms, and its former 

 wide distribution throughout the Eurasian and North 

 American continents. 



Another monotypic living genus, Sassafras, limited in 

 its present distribution to eastern North America, repre- 

 sents an ancient type of angiosperm vegetation whose 

 fossil remains have been found not only throughout 

 North America, but also in many parts of the Old World. 



These are merely a few of the many examples of 

 generic isolation — geographic and taxonomic — the expla- 

 nations of which have been supplied by the study of 

 paleobotany. 



Other apparent peculiarities of distribution, such as are 

 represented in our living flora by Liriodendron and iVe- 

 lumbo, genera which are restricted to eastern Asia, east- 

 ern North America and the central American regions, are 

 exceedingly difficult to explain satisfactorily on any 

 theory of migration in recent times; and the theory of 

 origin de novo in each of the widely separated regions is 

 too thoroughly discredited to merit discussion. None of 

 the known facts of recent plant migration, or evolution, 

 or mutation, are adequate to explain the conditions as we 

 now find them. Paleobotany, however, has demonstrated 

 that such apparent peculiarities of generic distribution 

 are readily explained when the facts of former distribu- 

 tion are ascertained. Each of these genera was formerly 

 world-wide in its distribution and prolific in species ; but 

 changes in environment caused their extinction in all ex- 

 cept the widely separated regions which they now inhabit, 

 reducing the species of Nelumbo to two, and of Lirioden- 

 dron to one. What have been regarded as problems of 

 distribution, explainable by improbable theories of mi- 

 gration or evolution, have thus been shown by the facts 

 of paleobotany to be merely some of the many examples 

 of isolation due to elimination in intermediate regions. 



The peculiar endemic flora of Australia did not origi- 

 nate de novo by reason of its isolation. Paleobotany has 

 shown that the living endemic flora of Australia in many 



