86 ANCIENT PLANTS 



in numbers; yet the Gymnospermic and Angiospermic 

 woods which are found with petrified structure show 

 well-marked annual rings and seem to contradict this 

 view. 



Toward the end of the Tertiary times there were 

 practically no more tropical forms in the European flora, 

 though there still remained a number of plants which are 

 now found either only in America or only in Asia. 



The Glacial epoch at the close of the Tertiary appears 

 to have driven all the plants before it, and afterwards, 

 when its glaciers retreated, shrinking up to the North 

 and up the sides of the high mountains, the plant 

 species that returned to take possession of the land in 

 the Quaternary or present period were those which are 

 still inhabiting it, and the floras of the tropics, Asia, and 

 America were no longer mixed with that of Europe. 1 



CHAPTER IX 



PAST HISTORIES OF PLANT FAMILIES 

 II. Higher Gymnosperms 



The more recent history of the higher Gymnosperms, 

 in the Upper Cretaceous and Tertiary periods, much 

 resembles that of the flowering plants as sketched in the 

 previous chapter. Many of the genera appear to have 

 been those still living, and some of the species even may 

 have come very close to or have been identical with 

 those of to-day. The forms now characteristic of the 

 different continents were growing together, and appear 

 to have been widely distributed over the globe. For 

 example, Sequoia and Taxodium, two types now charac- 

 teristic of America, and Glyptostrobus, at present found 



1 A fuller account of the Angiospermic flora can be had in French, in M. Laurent's 

 paper in Progressns Rei Botanica. See Appendix for reference. 



