178 W. S. Cooper 



extraterritorial extensions of range, are of subarctic or north 



temperate origin : 



Poa confinis Honckenya peploides 



Poa douglasii Fragaria chiloensis 



Poa macrantha Lathy rus japonicus 



Carex macrocephala Lathyrus UttoraUs 



Elymus arenarius Mertensia maritima 



Juncus lescurii Tanacetum camphoratum 



Polygonum paronychia Tanacetum douglasii 



Nine species of six genera, all (except Glehnia) endemics, are 

 derived from the neighboring arid and semiarid hinterland : 



Atriplex leucophylla Oenothera cheiranthif olia 



Abronia latif olia Glehnia littoralis 



Abronia maritima Franseria bipinnatifida 



Abronia umbellata Franseria chamissonis 

 Lupinus littoralis 



The remaining two species have entered from South America 

 or the subtropics: 

 Carpobrotus chilensis Convolvulus soldanella 



FEATURES OF LOCAL DISTRIBUTION 



Species density. — Maximum species density occurs from mid- 

 dle Oregon to Mendocino County, California. Within this 

 stretch 22 of the 25 species occur, with a maximum number of 19 

 at any one point. The only species not present within this strip 

 are Carex macrocephala, Abronia maritima, and Mertensia 

 maritima. Northward we find a species density of 18 as far as 

 Cape Flattery, beyond which there is a sharp decline to 8 at the 

 center of Vancouver Island. Farther north there is a very gradual 

 decrease to a minimum of 5 in southern Alaska. South from 

 Mendocino County, decrease is fairly regular. The only excep- 

 tion is in the vicinity of Monterey Bay, where there is a sudden 



