No. 544] BOTANICAL SOCIETY OF AMERICA 



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sequently found extending through Siberia to the eastern 

 coast of Asia and through Europe, Iceland, Greenland 

 and the Arctic regions to Alaska, and thence southward 

 to the home of the two remaining living species on the 

 western coast of North America. The phytogeographic 

 problem of the genus Sequoia, as we know it to-day, was 

 thus resolved into the geologic problem of the causes 

 which produced the climatic changes resulting in the ex- 

 tinction of the genus over vast areas where it formerly 

 existed, and the total extinction of all except two of the 

 numerous species by which it was formerly represented. 

 Modern areal limitation of the genus was thus shown by 

 paleobotany to be a result of former areal elimination. 



(Incidentally it may be remarked that this example 

 also involves a question of nomenclature which, however, 

 I trust our chairman may declare to be not germane to 

 the subject and hence ineligible for discussion. It is one 

 of the few instances in which a genus was known and 

 named as a fossil before it was discovered and named in 

 its living form.) 



The genus Taxodium, comprising two, or possibly three 

 living species, is confined to the southern United States 

 and Mexico, so far as its present distribution is con- 

 cerned. Up to the close of the Tertiary period, however, 

 it flourished throughout what are now the temperate and 

 arctic zones of North America and Eurasia— not only 

 the genus, but apparently the identical species yet living 

 and others now extinct. Paleobotany has adduced ample 

 proof of these facts, so that, as in the case of Sequoia, the 

 present distribution of Taxodium is explained as merely 

 the result of its elimination from other regions where it 

 formerly existed. 



The monotypic genus Ginkgo, which by many is also 

 regarded as representing a monotypic family and order, 

 is confined, so far as its natural distribution is concerned, 

 to eastern China and Japan. No known facts could ade- 

 quately account for its taxonomic and geographic isola- 

 tion until paleobotany revealed the multiplicity of its ex- 



