184 W. S. Cooper 



related to the maritime species. Three species (2 of shifting, i 

 of stabiHzed dunes) are derived from the subtropics and South 

 America. 



Considering the strand and shifting dune flora alone, species 

 density is greatest in southern Oregon and northern CaUfornia. 

 This center does not correspond with the region where the great- 

 est number of individuals occurs, which is in southern Cali- 

 fornia. In the unglaciated portion of the coast, physiographic 

 barriers to migration have been of slight importance. In the 

 glaciated region, fewness and wide separation of suitable habi- 

 tats, combined with shortness of available time, have greatly 

 hindered reinvasion. The strand floras of the Atlantic and Pa- 

 cific coasts of North America are strongly similar in the north 

 and entirely different in the south. 



