176 W. S. Cooper 



trjbution: Carex macrocephala and Glehnia littoralis. Their 

 ranges on the American and Asiatic coasts correspond rather 

 closely; both are absent from the Alaska Peninsula and the 

 Aleutian Islands. On the American coast both are abundant 

 south of the glacial boundary and occur on Vancouver Island. 

 North of there, they have been found in only a few scattered 

 localities, partly because exploration has been incomplete, but 

 principally because suitable habitats along this coast are few 

 and widely separated. Both species require accumulating sand. 

 Northward invasion of the glaciated region has thus been diffi- 

 cult and slow. The fossil record of Glehnia 400 miles south of its 

 most southerly station of today, in connection with its invasion 

 of the glaciated area, proves that the range of this species has 

 shifted bodily northward in postglacial time. It is reasonable to 

 assume that the same thing has happened to other plants, for 

 example: Carex, Tanacetum, Elymus, Honc\enya, Lathyrus. 

 The ultimate origin of Carex macrocephala, with no near rela- 

 tive in its very cosmopolitan genus, is veiled in mystery; Glehnia 

 seems quite certainly to be descended from American stock. 

 Another parallel between the two is that both have developed, 

 under isolation, into pairs of forms, Asiatic and American, that 

 may be specifically distinct. 



4. Species occurring also in South America. 



Juncus lescurii Fragaria chiloensis 



Carpobrotus chilensis 



(also Lathyrus japonicus) 



Though similar in present range, these species have had quite 

 diverse histories. Juncus is an almost cosmopolitan genus, but 

 /. balticus, probably the closest relative of /. lescurii, is mainly of 

 the northern hemisphere. Fragaria chiloensis also belongs to a 



