i«4 W. S. Cooper 



the sea. Much o£ the arctic archipelago was unglaciated, but here 

 conditions must have been almost prohibitive in their severity. 

 In Siberia, Kamchatka and the Taimyr Peninsula were glaciated 

 (Woldstedt, 1929), but the arctic coast as a whole was probably 

 free of glacial ice. The extended and fairly continuous ranges of 

 today strongly suggest a wide preglacial distribution and re- 

 advance from several centers. As the ice sheets receded, these 

 species probably moved forward almost as fast as the shores 

 became open to colonization. In Glacier Bay, Alaska, at the 

 present time, Elymus and Mertensia are following less than half 

 a century behind the disappearance of the ice. Honckenya and 

 Lathyrus invade somewhat more slowly (Cooper, 1931). On the 

 Pacific coast of North America there was advance southward 

 from arctic Alaska and northward from Washington. For Mer- 

 tensia it seems almost necessary to assume an arctic center, for 

 its present range ends at the Queen Charlotte Islands. On the 

 Atlantic coast of North America, invasion was probably from 

 the south, and it was doubdess from here that Elymus and Lathy- 

 rus reached the region of the Great Lakes. The arctic coast of 

 Canada may well have been invaded both from the Adantic and 

 from Alaska. In Europe the southern Adantic coast must have 

 been the starting point, although for Elymus and Honc\enya 

 arctic Siberia also may have been a center. For all species except 

 Honc\enya, the present ranges on both sides of the Adantic 

 lie entirely within the glaciated regions, so that these ranges 

 must have shifted bodily northward. This is a perfectly reason- 

 able assumption; the range of Glehnia actually underwent such 

 a movement. Distribution of the species of the group on the Pa- 

 cific coast of Asia may not have been seriously disturbed during 

 the Pleistocene. Elymus and Honc\enya have most nearly re- 

 gained their assumed preglacial territory. There is an apparent 



