THE LEWIS BROOKS MUSEUM. 45 



ancient flora on the Atlantic side of the United States, and in 

 China and Japan we find many of the plants of these 

 widely separated countries to be almost identical. The fol- 

 lowing are some of the most noteworthy forms of this Cre- 

 taceous flora which still survive: 



The genus poplar, represented by the aspen and cotton- 

 woods of the present day, has, as was stated above, the dis- 

 tinction of being the oldest known angiosperm, for it made 

 its appearance in the lower Cretaceous of Greenland. It 

 still persists with many species, and shows no signs of de- 

 cadence. 



The genus liquidambar, or sweet gum, made its first 

 appearance in the middle Cretaceous of the Dakota group. 

 It is now found on the Atlantic slope, represented by only 

 one species, our common sweet gum., or liquidambar styra- 

 ciflua, and in eastern Asia by one almost identical species, 

 L. orientalis. Both surviving species differ in nothing 

 essential from their Cretaceous ancestry. The poverty in 

 species and strict limitation in habitat of the genus, show 

 plainly that it has long since passed its culminating point. 



The genus platanus, the sycamore or button-wood, 

 began in the middle Cretaceous. It is represented now in 

 eastern North America by only one species, the P. occiden- 

 talis, ano in eastern Asia by one P. orientalis. This genus 

 too is evidently declining. Our species, the noble syca- 

 more, is strictly limited in area and locality ^ while the old 

 trees soon become seriously diseased. 



The genus sassafras began in the middle Cretaceous, 

 and now survives in only one species, which is confined to 

 eastern North America. It is peculiarly an American plant, 

 and has not changed in any important point since its first 

 appearance. It ranges over a wide extent of country, and 

 is remarkable for its vigor of growth and prolific character. 

 r In Virginia certainly it does not seem to be in process of 

 extinction. 



