190 BROOKLYN BOTANIC GARDEN MEMOIRS 



continent, extending in an east and west direction, formed barriers 

 which prevented their migration southward and there they became 

 extinct. In North America, however, with its mountain systems 

 extending in a north and south direction, migration to more congenial 

 regions was possible and here they continued to exist. Their present 

 isolated geographic distribution was, therefore, determined long ago, 

 by a combination of climatic changes and topographic features, and is 

 not a modern phenomenon that can be satisfactorily explained by 

 present conditions alone. 



Incidentally it may also be pertinent to recall that the genus 

 Sequoia enjoys the unique distinction of having been found in the 

 fossil form previous to its discovery as an element in our existing 

 flora. Cones and leaf-bearing twigs, representing what we now know 

 as the genus Sequoia, were found in Europe and were described and 

 figured (but not, of course, under the modern generic name) before 

 the living trees on our western coast were discovered. This fact, 

 however, can hardly be cited as an instance in which paleobotany has 

 been of assistance to botany, inasmuch as it involves the question in 

 nomenclature whether or not the generic name first applied to the 

 fossil remains should have precedence over that subsequently given to 

 the living trees. 



I shall not attempt, in this paper, to discuss the debt which botany 

 owes to those paleobotanical students who have made special studies 

 of. the internal structure of fossil plants, and thus determined exact 

 botanical relationships along lines of modern morphological investi- 

 gations. This is a relatively recent phase in the development of 

 paleobotany and the results attained are familiar to us all. The dis- 

 covery of the extinct class or order of plants, the Pteridosperms or 

 Cycadofilicales, and its taxonomic relations to the Pteridophytes and 

 Gymnosperms, is due to their labors, as is also the determination of 

 the exact afifinities of many extinct families and genera with those now 

 living. They have filled in the details of the broad phylogenetic 

 sequence outlined by the earlier paleobotanists and they represent 

 the field of work in which botany and paleobotany are most closely 

 and intimately related today and in which it is impossible to dissociate 

 them. 



