Strand and Dune Flora of the Pacific Coast 183 



species of strand and shifting dunes to which local origin has 

 been assigned. Cardionema ramosissima alone, like Carpobrotiis 

 chilensis, seems to have originated in South America. 



SUMMARY 



The flora of strand and dunes on the Pacific coast of North 

 America comprises two groups distinguished by environmental 

 preferences: (a) species of strand and shifting dunes; {b) species 

 of stabilized dunes. The latter constitute a distinct community 

 only on the southern portion of the coast; the corresponding 

 vegetation in the north is not of a strictly maritime type. 



A province such as the one here treated, linear in form, fre- 

 quendy interrupted, unstable in the extreme, cannot be expected 

 to be a center of evolution, to give rise to a distinctive flora, to 

 become a focus for centrifugal migration. Instead, the population 

 of such a province is made up in part of species differentiated 

 from neighboring inland stock in response to the special condi- 

 tions of the shore, and in part of species that have migrated, 

 mainly along the shore, from other maritime provinces where 

 they have been differentiated from inland stock. 



Thus, on the Pacific coast of North America we find first, a 

 group of 26 species definitely derived from stock of the local 

 hinterland, representing either genera confined to the region or 

 local sections within widespread genera. This group includes 

 one-third of the species of strand and moving dunes and prac- 

 tically all those of stabilized dunes. The genera represented are 

 mainly characteristic of arid and semiarid habitats. Of the re- 

 maining 17 species, 14 (all of strand and moving dunes) are of 

 subarctic or north temperate origin. Most of the genera which 

 these species represent occur in the neighboring regions inland, 

 but are widespread, and their local representatives are not closely 



