GEOLOGICAL HISTORY OP GYMNOSPERMS 39 



question but that the Taxaceae were more differentiated and 

 more abundant during the Mesozoic than at the present time, 

 or that in those early days genera were cosmopohtan that have 

 since become isolated, of which Tumion affords an excellent 

 illustration. 



Of the three subfamilies into which the Pinaceae are commonly 

 segregated both the Taxiodieae and Cupressineae appear to pre- 

 cede the Abietineae in the geologic record and to be much more 

 common during the Mesozoic. Sequoia, which survives in such 

 grandeur in California, is represented continuously from the late 

 Jurassic onward. 



The Actinostrobinae, easily recognized, are represented by 

 Widdringtonia and Frenela at a majority of the Mesozoic out- 

 crops. The subfamily Abietineae as compared with the other 

 two subfamilies is relatively modern. There can be no question 

 of the evidence of the geologic record on this point, for while the 

 Abietineae are well represented toward the close of the JVIesozoic 

 they are greatly outnumbered and completely overshadowed in 

 differentiation by the Taxaceae and Araucariaceae and by the 

 subfamilies Taxodieae and Cupressineae. The record is com- 

 pleteh" in accord with the older views that the Abietineae are 

 the most specialized and most modern conifers, and although 

 this relationship is questioned by Jeffrey, his theory of the origin 

 of the Coniferales from a primitive Abietinean stock cannot be 

 said to have convinced many students who have a first hand 

 knowledge of paleobotany. 



CENOZOIC HISTORY 



The Cenozoic era was a time during which the floral types were 

 essentially modern in character. Their most marked features 

 were their arborescent richness as compared with existing condi- 

 tions and the very general cosmopolitanism of the different 

 types. The development of arid conditions over large areas in 

 North America, Asia, Africa and South America, and the marked 

 effect of the subsequent Pleistocene glaciation, were the main 

 factors in the gradual segregation of these Cenozoic floras into 

 more or less detached regions. No traces of Cycadeoidales or 



