64 A SUMMER IN GREENLAND 



Grinnell Land to eastern Canada and the United 

 States and Japan, two species of the widely spread 

 American and Siberian genus, Cassiope, the com- 

 monest of which, Cassiope tetragona, has small 

 crowded leaves like green overlapping scales 

 grasping the slender stems in four regular geo- 

 metrical rows with here and there a yellowish white 

 bell pendulous on a delicate stalk. 



The geographical distribution of many of the 

 Greenland flowering plants presents interesting 

 problems in relation not only to the efficiency of 

 the plants as travellers, but to the position of the 

 places from which they originally spread. Two 

 examples may be briefly considered in this con- 

 nexion. 



Phyllodoce coerulea has a wide distribution: it 

 occurs on both coasts of Greenland, in Iceland, 

 from northern to southern Scandinavia and the 

 mountains of Scotland, in eastern Asia, where it 

 extends, in Japan, south of lat. 40 N.; it flourishes 

 from Labrador to the White Mountains on the 

 eastern side of the United States; it is found also 

 in Alaska and in the north-west district of the 

 Pacific coast of North America. Phyllodoce may 

 have begun its existence in the northern Pacific 

 region, probably in the latter part of the Tertiary 

 epoch, long before the Glacial period. As the 

 climatic conditions in the north became more 

 severe it gradually migrated to the south, where it 

 is still represented in the central Pyrenees and in 

 Japan. As conditions ameliorated, the species re- 

 turned to the north or ascended to the higher 



